Trying to design my own cat.

[Richard Atkin]

I don't want to bore all you pro boat designers....so I'll keep this short and sweet. When I get some better boat design software I will be able to refine my idea....without asking pesky questions...but for now, just 2 basic questions, if you have the time.

1. In extremely light winds and with a small sail area....which of these 2 hull types are better for speed (for a catamaran)....a double ended 'canoe' hull with rounded bottom, or the typical wider stern hull (with rounded bottom for minimal wetted sorface)? The boat will weigh 3500 pounds (including 8 passengers and camping gear). With the canoe hulls the draft comes to 11 inches at this weight.

2. If my hulls are too close together, will this create a problem with water flow between the hulls? (Please see my attachment to see the exact proportions of my boat....I have very good reasons for making the hulls this close together).

Again, thanks to anyone who is able to answer these 2 questions (crucial to my design).

- Richard

[Guest625101138]

Richard
I believe a cat made for light airs would be best with a canoe type hull. I have done some analysis of a cat with your constraints optimised for 8kts.

I have not considered any heal so there is an assumption that you have set crew weight to keep the hulls equally loaded and in perfect trim. The hull to your constraints could achieve 8kts with a 6HP outboard. A fractional rig with about a 30ft mast would achieve this in light winds, 15 to 18kph, on a reach.

I also looked at what would be possible if you allowed the beam of the hulls to be optimised. In this case the required power to do 8kts could be delivered with a 5HP outboard. So about 20% less. The hulls come down to 20" beam.

I then looked at a no compromise displacement cat designed for 8kts and 3500lb displacement. It ends up 13.4m long and an overall beam of 3.5m (only 11.5ft). It can do 8kts with a 3.5HP outboard. Just over half the power required to drive your 28ft hulls.

I have attached some basic lineplans for the three hulls and a chart comparing the drag.

Once you start to power up then you are no longer operating in displacement mode. In this case you start to get an advantage with a wide, flat aft section that gives lift rather than squatting. However 8kts is an impressive speed for a 28ft boat designed for light air performance.

The spacing of the hulls does have some bearing on performance but it is slight and the optimum changes depending on speed. Other factors like space and sail handling ability are more important considerations than reducing drag by spacing the hulls optimally.

Rick W.

[Richard Atkin]

What a great reply! Thanks for your time Rick. That was very generous of you. You've given me a few options to think about now.

Thanks again
- Richard.

[Richard Woods]

I think you may be a bit optimistic with the speed predictions.

But first, in very light winds, and, presumably, flat water, many people think a canoe stern is better - no transom drag.

Most performance predictions do not make enough allowance for air drag. It's obviously significant as anyone who has tried to motor an underpowered catamaran to windward knows.

Also most don't adequately allow for the wave interactions between the hulls. Many years, if not decades, ago, as a yacht design student at Southampton I ran some model tests in the big test tank there. I found that the total hull drag from a catamaran with a conventional hull spacing was about 20% more than that of two hulls at an infiite spacing.

Your design seems to be very narrow for a modern sailing catamaran.

I doubt if you will get more than 6 knots from an 8hp outboard, more likely 5.5, I'd also expect you to sail at about 1/2 wind speed unles you have a very big rig.

Hope this helps

Richard Woods

www.sailingcatamarans.com

[Guest625101138]

Richard
I agree with your comments that hull interactions on cats are important. I do not agree that the numbers are optimistic for calm conditions. In fact I made considerable allowance for the poor efficiency of an outboard propeller.

The designs offered came straight out of Michlet/Godzilla. It takes hull interaction into account and is very reliable for displacement mode. I have compared performance with numerous boats so have a lot of confidence in the results.

I am accutely aware of windage as I make human powered boats for my puny 120W engine and have a lot of performance comparisons under windy conditions. The windage in calm conditions would be small and is taken up in efficiency allowance.

This clip shows a younger test pilot doing 12kph at a relaxed cadence on a Godzilla generated monohull:
http://www.youtube.com/watch?v=jEadJFg2F9s
With my 120W I can hold 11kph all day on this boat. It was a product of Godzilla with minor variations for development using aluminium sheet. I am now doing a version true to Godzilla from carbon firbe - see attached.

All HP numbers on the cats were based on calm conditions and smooth hulls. So no waves and still air. It is worth noting though that the long slender hulls having little reserve buoyancy in the ends are not much affected by waves.

I also did not discuss the practicality of a long cat with a 11.5ft overall beam. It might not be as stable as you would like. But then it does not need much sail and was intended for good performance in light air. The idea was to show what compromises are made by choosing various options.

I have attached the the Michlet output file for the no compromise cat. You will see the power at the hull to do 4.35m/s (8kts) is only 1.8kW. So should be possible to deliver this using a 3.5HP motor.

Rick W.

[Richard Atkin]

A very late thank you to you Richard Woods! I appreciate all opinions from people with experience. I don't expect my boat to be quick. I just don't want to end up making a really stupid design. I have a lot of very strict requirements.

[Richard Atkin]

I have been doing a lot of internet research about catamaran design and have finally come up with the crude design of my boat.
It meets all my requirements and should be reasonably efficient.
The canoe hulls are now narrower than my original sketches, with rounded bottoms and shallow shoal keels which begin quite aft and join with deep kick-up rudders.
I am doing without the dagger boards.
The center of sail area is slightly more aft than what is typical.
The hulls are devoted only to storage, as all sleeping is done on deck with the use of a very low profile tent system.
I have come up with a radical bridgdeck construction and deck layout which I think is so unique for solving wave pounding issues and allowing extreme passenger comfort, that I have decided not to show any images yet because I am considering the possibility of commercialising my ideas. (won't be any time soon!)

I have reached the stage now where I really need to test the center of sail area / weather helm / lateral resistance. I also want to get some idea as to how it will handle a choppy sea.

So what's my point?

I just want to know what is a really good program to use for simulating the boat's performance. I imagine a 'perfect' wave simulator might be a bit optimistic. I assume Godzilla is good but does it deal with sails or just hulls? Any recommendations??

Cheers
- Richard

[marshmat]

Simulating a sailboat's performance is tricky.

The Michlet software mentioned by Rick W. is free, courtesy of Leo Lazauskas. Godzilla is a set of algorithms that uses Michlet to evaluate the fitness of a hull for a given set of criteria, then "breeds" new "offspring" from the best ones in the same way as animals that are well adapted to their environment will breed most successfully. Michlet calculates hull resistance in considerable detail but is not a VPP.

To predict a boat's performance by computer requires a Velocity Prediction Program (VPP). These algorithms account for the balance between the forces on hull, appendages and sails to estimate the boat's performance in given wind conditions. They are, in general, complex and require considerable experience to use, not to mention expensive.

[Richard Atkin]

Okay thanks Matt. It sounds like someone should make a 'dumbed down' program for people like me. Like....just enter all the data for my boat design kind of like filling out a large questionare form.....and then watch the computer spit out a beautiful rendering with all the perfomance predictions.
From there I could stretch and bend the rendered image using the simple drop and drag method and let the computer tidy up my alterations by calculating the best compromise between what I have drawn and how I want it to perform. You see....it should be that simple!! :) hahaha
Any computer programmers out there up to the challenge?

Anyway, I've had some fun with simple hull design programs and I think it will be well worth my while now to give my idea to a pro boat designer to refine it.

that'll be the next stage.

[Guest625101138]

I have a good VPP for propeller driven displacement boat in calm conditions. How is that for qualifiers?

I generate the Michlet data for the specific hull, load this into a spreadsheet and it provides a 3rd or 4th order regression of the michlet data to produce a simple drag formula. I generate the thrust data from a semi-analytical prop thrust integration and use a goal-seek in excel to ballance thrust and drag. It is very simple to use and not as complex as it sounds. Gives results within about 5% for powered displacement hulls.

It is much more complex for a sailing boat where things like heal, trim and sail performance has to be taken into account.

Rick W.

[Fanie]

Richard, you mention 8 persons and camping gear... have you taken this weight in consideration wrt the slim hulls... knowing this bunch of hooligans I fish with and the stuff they take with it mounts to quite a bit of junk I mean weight...

[Richard Atkin]

Hi Rick :)
I intend to build this cat (I mean get someone else to build it) in a couple of years from now, when I move to LA. I don't have the money right now to get it designed properly cos I have other commitments. I'm just letting the idea develop like a fine cheese....

My main concern is that the boat sails well in light air so that the motor is only the very last resort. I don't want to use the motor unless the boat is virtually stopped. As for windy conditions, I don't care at all about top speed.....so this is why I'm focusing on light air sailing.

My bridgedeck structural supports, mast, and bedding on deck are so integrated with each other that I can't actually move the rig forward or aft, unless I move EVERYTHING (to get the boat balanced). So I'm thinking the hulls would have to be altered while I am altering the rig and deck to find the best compromise....all of which I will do in the not too distant future.

For the record, if I knew anyone who wanted an efficient boat which is primarily motor driven, you would be the first person I'd recommend because I was impressed with the way you write and kept everything concise and relevant to my requirements. Maybe I'm just easily impressed :)
Hang on.....I'm asuming you are not fimiliar with designing sail rigs?? Have I got it all wrong?

Well whatever the case, I'll just put the boat on hold for now. That is, unless you want to design the whole thing for me for free....(kidding)

regards
- Richard

[Richard Atkin]

Fanie....yeah you're right, i've only allowed about 10kg of gear for each slim person...lol. But that's fine by me. If I overload it a little from time to time (in calm conditions) it should be alright cos the canoe shaped hulls can sink a bit without transom drag.
it's probably more of a 6 person boat.

[Guest625101138]

Richard
I guess over the years I have found sailing ocean worthy yachts to be too demanding on my time and money supply. It is hard to get value for money unless you live close to the boat or on it. My best period of ownership was when I had easement access to Lake Macquarie in NSW and my yacht on a sheltered swinging mooring a short wade/swim from shore.

My current objective is to build a seaworthy electric powered boat fueled from sun and wind. The aim will be to do extended coastal cruising hopping from point to point within the range of fully charged batteries topped up by sun and wind during the run. Cruising speed is just around 7.5kts with top speed of 10.5kts. However it has spartan accommodation. On the other hand I am aiming to make it trailerable. (I am an electrical engineer, boating is my hobby)

From a practical sense it is hard to order the perfect strength wind. If you want to get somewhere in a given time then you inevitably end up motoring. It can be very disappointing to lose a day of sailing drifting backwards with the current on a balmy night. It takes a lot of concentration to get a boat to ghost along at night particularly if there is a bit of slop around.

If you have not got FreeShip yet then it is a good tool to start to put ideas into concrete form. It will make it easier to talk to a designer when you get to that point. You can also elicit a bit of debate about the design from this forum.

Rick W.

[Fanie]

Rick, your electric / wind powered boat... you just gotta see 'Waterworld'. Since the poles are going to melt (must be real soon) you could probably adapt some of the techniques yourself. I especially liked the way you recycle water into drinking water again (wonder if the same bit of water doesn't become tired :rolleyes:) A trimaran though, but a motorised sailer just the same... even a wind power generator too. Are we behind or what...

[Guest625101138]

Fanie
I have the tape. I like that boat. I live 60m above water level so once the ice caps melt the best forecast make my property a water frontage. I figure the Solar-Wind boat will be the perfect way to do the grocery shopping across the bay. Unlike you I will be able to shop any time. The oil will be all gone so your big outboards will only be useful as anchors and you will have to wait for the wind before you can get to the shop. Hence the method in my madness.

Rick W.

[Fanie]

I like the idea of not being dependable on costly resources like fuel, so I'm with you on this one. Since I can fish, I won't be doing any shopping though. Don't have a bay in any case. There are quite a few places in SA where there should have been water, instead it's empty :o

[Richard Atkin]

Rick, my brother Andrew was talking to me some time ago about "why the hell don't we have electric powered multihulls".....batteries have come a long way now, as I'm sure you are aware. apparently there is a new battery called the carbon nano tube. It holds twice the charge of conventional lithium ion batteries.
My brother thinks the solar panels and windmill are good to have but most of the recharging could be done from home (particularly for a commercial model).
I personally find the idea of having a super quiet electric motor very appealing. When the wind dies down I can flick on the electrics and still feel like I am 'sailing'. Andrew thinks it's important to use a kind of double glazing to maximise the quietness because this is the elecctric motor's biggest advantage.
This is definitely something I'm thinking about for my design.

- Richard.

[Fanie]

Batteries may have come a long way but we're not there yet ! With electric motors you're still limited very much to smaller boats if you want to get anywhere. The distance you can travel is very limited as well. Sails are just as quiet (or can be) and fiddling with the ropes keeps you from smoking so much ;)

[Guest625101138]

Richard
My aim is to have a long distance, sea worthy coastal cruiser that I can operate single handed without fuss and park in my garage when I am finished for the season.

There is a whole lot of reasoning behind the design of my proposed boat. I have spent about 5 years working on hull and propulsion efficiency. The validity or otherwise will be in actual performance once built.

The batteries I have proposed provide ballast and will allow around 10 hours operation at 7kts. So battery range only 70nm at 7kts. It will go up quite a lot if I go slower but I think a capable cruiser needs to do at least 7kts.

I am hopeful that a bit of wind once the sun goes down will avoid regular deep cycle. Either solar or wind power would provide enough energy to cruise at 7kts but solar will only be useful for a limited period.

If your intention is to do day cruises within range of safe harbour then a battery powered cat would make a lot of sense. Much easier to handle and operate than a sailing boat. Batteries and motor probably cheaper than sails and rigging. Hull loads could be lower as well. These days it is likely to be cheaper to operate than petrol outboards and more planet friendly given NZ source of power. Sailing boats are extremely difficult to use for serious day sailing unless they have auxiliary power. So you need this as well as sails.


Rick W.

[Fanie]

Hi Rick and Richard,

I'm not trying to put your idea down, there are downs to it, I'm talking of years of experience using electric trolling motors on our boats. Keep in mind we charge the batteries from mains power every night if we are to go out the next day.

I suggest you do a couple of experiments with a small boat and a trolling motor... see how things hold up.

[Guest625101138]

Fanie
The sales pitch for trolling motors is based primarily on thrust. This is nonsense and has nothing to do with performance unless you want to have tug-of-wars with the motors. If you looked realistically at the energy that you put into the batteries in relation to the energy required to push the hull a given distance at a reasonable speed with a trolling motor, the efficiency would be under 25%. My aim is to get more like 70%. Applying that energy recovery to an easily driven hull equates to good range.

I have been doing some testing with batteries on one of my old boats and they seem better at present than their rating.

The tesing is on an old hull nowhere near my most efficient. The initial testing indicates I can get 15km from two tiny VRLA batteries at a cruise of around 6kph. The assembly of parts were simply what I had laying about and not in any way optimised. This is the data I posted last week:
http://www.boatdesign.net/forums/showthread.php?t=20445

I try to isolate and reduce all sources of loss so I can get the most efficient and still practical way to achieve the objective. Your experience with the trolling motors confirms my assessment that they are not designed for efficiency. You can buy more efficient electric outboards but they are more expensive. These are still less efficient than I am aiming for. Here is an example that has some interesting commentary and experiences:
http://www.rayeo.com/news.htm#1

So the combination of easily driven hull/hulls and efficient drive system will give very good range on batteries.

Any experience you have with trolling motors is not particularly applicable to what I am aiming for.

Rick W.

[Richard Atkin]

For me, the whole point is to have sails. I did a lot of sailing when I was a kid (mostly racing) and so I am used to focusing on trimming the sails and I enjoy doing it.....although I don't know what it's like to do it for 10 hours or so! I just like the feeling of being pushed along by wind and sail.
The battery and electric motor would be ample efficient enough for my purposes. I would use it only when the wind dies and would probably never need to use it for more than about 50km at a time. I like the idea of island hopping around places like catalina island.
But anyway, according to my brother, who is very involved with a few engineering projects (like you Rick), he reckons batteries are up to the play now. I have no idea what VRLA batteries are....so I'm going to do a bit of research on batteries now. bye for now

[Guest625101138]

Richard
If I am racing it is not too hard to work for well over 12 hours with a reasonable degree of concetration. An overnighter is my longest race. If you are cruising then you tend to have lots to do if you are short handed. I get tired of steering after about 2 hours so I prefer an autopilot. You then try to trim sails so you have good speed without being pressed. It is usually not as fast as it could be.

I think there will be a whole new dimension with a solar-wind boat. Initially I am thinking that I will not allow the turbine to weathervane. I will have a means of turning it so I can control power. I am aware this might cause some nasty loads on the blades but it is something I intend to experiment with. Also the load on the turbine needs to be mindful of the charging requirement anf thrust limit of the blades so this is something to work out.

The solar cells do best when they face the sun. I do not want to have them movable relative to the boat so am already thinking about how I can heal/trim the boat to partially track the sun.

Anyhow I think there will be a lot of thinking to get the best from it. Maybe a bit different if you were only using charged batteries but even then you have to decide how fast you can go in the conditions and conserve charge to get home. The range of a battery boat is bound to be less than a typical fuel powered boat.

Rick W.

[Richard Atkin]

Rick, I look forward to seeing your boat working in choppy sea conditions. If you can get it to be a good reliable boat in most conditions....then you will be truely advancing a whole new technology.
I did a bit of research on batteries and it turns out that Andrew was being a bit optimistic. Carbon nanotubes hardly exist at the moment. They are only being used on a small scale for power tools etc. because the cost is between a hundred and a thousand times more than conventional batteries! Some time to go yet.
Conventional lithium ion batteries have their problems too...they don't age well, are dangerous and can have unpredictable charging problems.
From what I can see at this point, maybe VRLA batteries are the way to go as long as they are well ventilated.
- Richard

[Guest625101138]

Richard
The thing about a sailing boat is that the whole power system that you have paid tens of thousands for is useless if there is no wind. You go nowhere on those beautiful balmy days unless you motor.

A solar boat will relish beautiful balmy days. Plenty of sun and calm water. I can see myself waking up at anchor; sun getting up, panels firing up and I head off on auto-pilot to the next island while having a leasurely breakfast. Arrive as the wind is picking up in the afternoon and anchor up. The sun and wind continue to charge the batteries while at anchor ready for the next day's run.

So my aim is to travel when the sea is calm and leave the sheets-in-the-teeth stuff to the more heroic types. Unless I really have to be somewhere by an appointed time I will stay at anchor until the weather suits me.

My reading suggests that gel VRLA has superior cycle life to AGM VRLA.

There is still a way to go with batteries. One of the big issues right now is the escalation in lead price. It has risen about 8X in the last 5 years so puts gold and oil in the shade. As the population of cars grow (China expects 10M/yr by 2010) and there is more use of alternate power then lead price will continue to skyrocket. No good having a $50,000 car you have to crank start. So the price of lead batteries will climb strongly.

The lithium nano batteries have such a high demand that they cannot be made fast enough right now and I am not certain that all the bugs have been ironed out for long-term use. I think they will be difficult to charge reliably. Anyhow main issue is the same as lead. There is simply not enough lithium to suport a large population of batteries. The biggest producer is Chilean based but is listed on the NYSE and their share price is strong - rightly so.

Rick W.

[Fanie]

Rick, there are brushless DC motors with effieciency that could be as high as 80%, maybe more.

[Guest625101138]

Fanie
I have priced one that achieves 92%. It weighs 5.5kg and is rated at 3.8kW. The air cooled version has an enclosure rating of IP54. I am having difficulty finding a gearbox that allows best use of the motor as it spins to 6000rpm.

I am yet to find a gearbox that allows me to get the best from this motor. To get overall efficiency around 70% you need all components - batteries, motor, gearbox, controller, prop to be getting efficiencies well into the 90s.

There are a few motors that get up around 90% that spin slower so they may end up a better overall compromise.

My aim for cruise speed is to spin something like a 500mm prop at 600rpm as this will give good prop efficiency. Finding a right angle gearbox that suits the application and will handle a high speed motor is not easy.

Rick W.

[Fanie]

Do you need a gearbox ? With a decent speed control you could maybe end up much better than with a gearbox. Any drive train stuff, prop shafts, gearboxes takes some energy away.

Have you considered looking at hydro fusion ? Some potential there.

[Richard Atkin]

Rick, you mentioned operating your boat single handed. Will it be large enough to take an extra person or more?
How would you expect it to perform during a sudden squall....when you say "long distance, sea worthy coastal cruiser" that suggests to me that it needs to be able to handle a bit of unexpected weather.

[Guest625101138]

Richard
The boat has small sectional area if you compare it with something like a sailing boat with all its rigging. The Cd is not too bad either so windage is not that high. Windage is similar to a small motor car.

If I use a big prop with suitable gearing I can get a bollard pull of around 1kN (220lbf) from a 3.8kW motor. See the attached JavaProp screen image.

I expect you would find small sail drives would not be able to produce this sort of thrust. One of the gearboxes I am considering has a 1" shaft so it is solid if you compare with most outboards.

Many people do not understand that thrust and power are not the same thing. If you use a big prop you can get huge thrust for little power. I worked out that I could get a bollard pull of around 1000lbf using pedal power with a suitable prop.

So I expect that in heavy weather I will have the ability to make way into a strong head wind. I agree that a competent coastal cruiser needs that ability.

Rick W.

[Fanie]

Fanie, I assume you're male?? Just wondering :)
Before I jump to the wrong conclusion here, why do you ask and why are you wondering about it ?

[Richard Atkin]

Sounds good to me Rick, I think your project is quite exciting. Hurry up and finish all development so I can see it on you-tube! And then you could make it commercially available. Maybe I'll add it to my boat collection when I am filthy rich. Still like sails though.

[Richard Atkin]

I have decidedto show my wonderful catamaran in it's full glory as soon I have some images to send. The entire deck is an array of waterproof cushions which rest on an aluminium grill. (think of 4 double bed mattresses lying on one wall of a shark cage). This allows bad waves to pass through the cage and the shock from pounding will be eliminated by the mattresses.
There are sofa-like back supports which attach to the outer edges of the deck. The hulls have no solid cabin structure above the deck line (excuse my terminology). Instead I use a well sealed mini dome tent which folds over each hatch, providing ample headroom for temporary tasks like making a coffee or checking the laptop during a storm. These mini tents fold away to nothing when the hatch needs to be robustly sealed. (think of the folding hood of a baby's pram, or a convertible car). The hulls will be used primarily for storage. Larger low, flat tents are used for sleeping on deck. (no room to sit inside the sleeping tents...so not good for the clostrophobic) These tents are robust and attach to the back supports (mentioned earlier).
This design is very light and provides a huge amount of deck space for 8 lazy sunbathers. hmmm...that sounds a bit creepy

[Richard Atkin]

These are just pretty pictures (incomplete) to give some idea of my proposed deck layout. The tiller will go in between the 2 aft back supports. The helmsman will rest his albow on the point at which the tiller pivots.....so the whole tiller actually supports his arm. The spade rudders will turn effortlessly but will have very little feel. I can accept that trade off.
I apologise for the incomplete drawings at this stage. (these were done with house architecture software, as I am more of an architect than a boat designer.)
No numbers to give you yet. In the coming weeks I'll be getting familiar with Freeship.

[Richard Atkin]

The attachment below is my attempt at using Freeship. The fairing above the waterline is crap but below is not too bad (I think), and that's all I'm really interested in. If anyone out there has the skill to make these hulls faster (Rick???? or even you JCD baby designer), then feel free to play with it and send it back!! (am I dreaming)


Data that must not be changed:

boat length = 22.5 feet (does not include rudder)
boat weight + payload = 2240 lbs
boa = 12 feet
no dagger boards ( I'll be beaching it all the time)
must be canoe shape (for light conditions)


I'm not really sure if the design I have done is ideal.

Even just some plain old advice would be awesome.

Cheers

- Richard

[JCD]

The attachment below is my attempt at using Freeship. The fairing above the waterline is crap but below is not too bad (I think), and that's all I'm really interested in. If anyone out there has the skill to make these hulls faster (Rick???? or even you JCD baby designer), then feel free to play with it and send it back!! (am I dreaming)


Data that must not be changed:

boat length = 22.5 feet (does not include rudder)
boat weight + payload = 2240 lbs
boa = 12 feet
no dagger boards ( I'll be beaching it all the time)
must be canoe shape (for light conditions)


I'm not really sure if the design I have done is ideal.

Even just some plain old advice would be awesome.

Cheers

- Richard

Hello Richard,

If this is your first attempt...you have done a pretty good job of it brother. Very nice. Unless you're like me that asks for everyone's opinion but doesn't let anyone make up my mind for me, Rick's optimized hull below the waterline will be the way to go for a hull at maximum design paramater. With that said, here is my 2 cents.

Excellent work...stated with a bit of envy because my first attempt was a total failure and took lots of work. You're LWL/BM ratio is 11.2. Those hulls will be easily driven. Your LWL (22.35ft) to LOA (22.5ft) ratio is low, so reserve end bouyancy is also low. This is good because it reduces hobbyhorsing, but its bad because the ends will not recover quickly upon submersion. Obviously, carrying capacity is reduced on the ends so most weight should be centered amidships.

For me, the mini keels in the design will probably add more wetted area than may be worth for pointing ability. Perhaps a shallower but longer keel will provide the pointing ability that may be lacking from the absence of boards without the addittional wetted surface. The longer the keel, the wider the turning radius, so a compromise will be required.

You may also want to consider high aspect lee boards pivoting on the outboard sheer and eliminate all un-necessary underwater wetted surface while introducing just enough required surface by dropping the board. I would try to think of a way to place them on horizontal tracks to move them forward or aft to balance the helm for different sail areas leeds.

The wetted area appears to be high and the draft is deep but, with that said, windage produces more drag than wetted area foot for foot and you have very little windage without a house on the hulls and getting the windward hull unstuck will require greater effort. Six humans on the tramps will however produce windage as will the tents, so staying low should be considered.

The LOA/BM ratio is a result of the width of the hulls and althought it is used often by many, I give it little thought unless the purpose is for trailering or slipping restrictions. The ratio I consider important is at the waterline. The ratio for your hull separation is 40% (9.1ft/22.35ft) which represents good maneuverability, but you will have to pay careful attention to the CE when designing the rig and I would make significant effort at the threat of lashing crew with a wet noodle, to keep crew or passengers on the windward side at all times. While anchored or not underway, make sure everyone doesn't decide to sit off on the same side or a titanic list is a possibility. This is ofcourse, my own paranoia and inate instinct to keep the boat right side up.

Take everything with a grain of salt since my intention is to provoke thinking. Well, except for the part that you did a good job. Keep it going, but be forewarned that this is addictive. :D

J:cool:

[Richard Atkin]

Great stuff J, thanks very much! You've definitely got me thinking. I never felt comfortable with those mini keels. Wetted surface is my main enemy. As you say, crew weight distribution will be important on my boat. I don't mind compromising a little on overall stability, but unnecessary wetted surface really bothers me.

quote "You may also want to consider high aspect lee boards pivoting on the outboard sheer and eliminate all un-necessary underwater wetted surface while introducing just enough required surface by dropping the board. I would try to think of a way to place them on horizontal tracks to move them forward or aft to balance the helm for different sail areas leeds."

I really like this idea. The boards would be very easy to access and could just kick up like the rudders? Is there any major performance compromise from using this type of system? I don't care less about visual appearance...I'm sure I could make them look tidy enough.

I'm going to take a look at your fbm files later tonight just for fun, now that I can view them.

- Richard

[Fanie]

On my previous boat I had a matress inside the cabin. It had a cushion you could remove to get to a hatch where stuff was put in for storage. It was a hassle to move things around to get in there. The more loose things the more irritating it gets to move a lot of things to get to another.

I like your tent idea. A stowable tent however has to have a support structure, and losing one piece... You could also think in the direction of an infatable tent. The advantages of an inflatable tent is you can blow it up and reverse the action to deflate it as well. Just an idea... deflated it may be served to sit or walk on ?

If you plan on having a boom and not sail at night you may use the boom for the tent support as well - just an idea.

[OldYachtie]

Why on the outboard side? If you put them on the inboard side you won't have to worry about bashing them while docking, and you won't have to look at them.
Multihulls are insensitive to lead, so just place them so that their center is under the CE of the rig. By the way, have you read any yacht design textbooks? Skene's Elements of Yacht Design, at least? If not, you should do so before continuing to try to design a boat. :o

[Guest625101138]

Richard
Have you any thought on the construction material for the hulls?

Also a 6% section is a poor choice for a rudder. I have attached the polar plot from JavaFoil for the rudder shown. It could be worse than this because it is surface piecing so will also ventilate. You have a lot of drag for not much steering force.

You could improve pitch damping with fuller sections above the waterline both bow and stern.

Rick W.

[JCD]

Richard
Have you any thought on the construction material for the hulls?

Also a 6% section is a poor choice for a rudder. I have attached the polar plot from JavaFoil for the rudder shown. It could be worse than this because it is surface piecing so will also ventilate. You have a lot of drag for not much steering force.

You could improve pitch damping with fuller sections above the waterline both bow and stern.

Rick W.

Agreed...

I think 15% would be best. That is the section I intend to use on mine. The boards at 12%.

J

[JCD]

Why on the outboard side? If you put them on the inboard side you won't have to worry about bashing them while docking, and you won't have to look at them.
Multihulls are insensitive to lead, so just place them so that their center is under the CE of the rig. By the way, have you read any yacht design textbooks? Skene's Elements of Yacht Design, at least? If not, you should do so before continuing to try to design a boat. :o

Hello Yachtie...

I suggested the outboard side because they're in clear water and not in the sideslip stream, and because if he needed to do a quick repair he wouldn't have to do it from under the deck. Bashing them is a matter of skipper error and easily avoidable with some caution.

Can you provide an authoritative reference that explains why multihulls are insensitive to leed? I would like to get my eyes into it since I have never found anything like that. The best range that I found for a multi is 12% to 15% of the LWL.

If the question about Skene was for me...yes. I agree 100% that it is at the very leats the book to read. But tell me this...how much help was it for multihulls instead of just yacht basic generalities? I tried to make connections with the material but fell short with my limited experience. I felt Principles of Yacht Design was better.

J

[JCD]

Great stuff J, thanks very much! You've definitely got me thinking. I never felt comfortable with those mini keels. Wetted surface is my main enemy. As you say, crew weight distribution will be important on my boat. I don't mind compromising a little on overall stability, but unnecessary wetted surface really bothers me.

quote "You may also want to consider high aspect lee boards pivoting on the outboard sheer and eliminate all un-necessary underwater wetted surface while introducing just enough required surface by dropping the board. I would try to think of a way to place them on horizontal tracks to move them forward or aft to balance the helm for different sail areas leeds."

I really like this idea. The boards would be very easy to access and could just kick up like the rudders? Is there any major performance compromise from using this type of system? I don't care less about visual appearance...I'm sure I could make them look tidy enough.

I'm going to take a look at your fbm files later tonight just for fun, now that I can view them.

- Richard

Hello Richard,

I think that you should reconsider compromising on stability even if just a little. Don't! Only million dollars thoroughbreds take the stability compromise to the edge to gain that extra 1/1000 of a knot. Wetted area is everyone's enemy but I will take that over instability anytime. Take your time and you will increase stability and reduce wetted area as the design evolves.

Tidy for the lees is nice. You may want to fair the trunk in. I'm not really sure of the performance reduction that may be encountered from having them above the waterline, but I would think that breaking the waterline plane could cause some cavitation or disruption of flow. I don't know how significant it can be. It may not be that serious for the design...unless it is a million dollar thoroughbred. Making them kick up is a must and really easy to set up.

Glad to hear the brain matter is firing up.:D

J

[masalai]

Thanks folks, I am thoroughly enjoying this thread and learning lots. Please consider yourselves all allocated brownie points.

Seasons salutations, safe sailing and fair winds

[Richard Atkin]

Wow, where do I start! This is all great advice. Thanks guys!!

Fanie, I like to sail with many passengers, so they will be doing most of the fiddling around...but most of the cushions are tied down and fit precisely to the deck. The 'cabin' tents have built in frames which fold open and closed, but never fully dismantle. I do want to sail at night occasionally. The sleeping tents are little more than tarpolines which are tied down firmly and touch each sleeping person's shoulder. I agree my boat is a bit 'fiddly', but that gives me something to do during the journey.

OldYachtie, after JCD mentioned the outboard boards, I started thinking about putting them on the inside, but I think it would be far more simple to put them on the outside. As far as reading a good book on yacht design....you got me. I've never read any books at all on boat design. And yes I know I should, especially for getting familiar with certain terminology. However, less than a year ago I didn't know anything at all about sailing catamarans other than the fact that they have 2 hulls and a sail. Since then the internet has provided me with a fun way to learn in my own way, rather than wading through a formiddable sea of text. I mean...hearing people's personal experiences and opinions is invaluable to me. I think it is time that I knuckled down into a good book though.

Rick (the ever-helpful), right from the start I have always wanted the boat to be all fibreglass and aluminium as much as possible. Maybe even a carbon fibre mast. Ofcourse I have a budget...so I will need to look into the cost of things. I want the boat to last a long time cos it's a lifestyle thing for me......probably the only expensive toy I will have.
As I will be getting professionals to build it, that shouldn't be a technical problem (I hope).
My rudder is crap.....great! I'll change it and learn a bit more about % aspect ratios etc. I wanted it to skim over rocks...but now I'm thinking to hell with the rocks....let it kick up.
Fuller sections at bow and stern....If you mean overhangs...I don't like the look of that. I like the simple rugged 'campercat' appearance of my boat. Am I being rediculous? How bad do you think the pitching/nose burying could be? Do you mean changing the curve of the hulls on the plan view so they are closer to eliptical?

J, I agree I shouldn't have an unstable boat, but because I am cramming a lot of people on to such a small boat, I think it will be a bit 'wobbly'. On the other hand, it does have a low centre of gravity and all those people can position themselves so the weight is used as an advantage (like you said). So the stability is not innate.....but I think it'll be safe enough. As you say, it's still evolving. You may ask..."why such a small boat for 6 to 8 people?" I did some outlines of my old 28 ft design on the lawn outside, and tried to imagine what it would feel like. It just felt too damn big. I have always liked the 'Huckleberry Finn' feeling that you get from smaller boats. And I will always want to be able to take friends without saying "maybe next time". Actually that sounds like the beginning of a disaster movie.....lol

Masalai, I'm glad you like this thread. Merry christmas


thanks to all
- Richard

[Fanie]

A mast under the mast (so to speak) could also be an option for your tent...

If you would consider longer hulls they would add to stability, you can still keep the deck area the same. Friend of a friend bought a deep V ski boat recently, first fishing trip already a disaster. They took along a heavy unexperienced guy who decided to join the others at the same side resulting in an almost tip over, people falling, breaking rods... no thanks. Stability is everything. Controlling people is like herding cats, you think everyone is going to stay put on one spot ? First time someone says 'look at this' the whole bunch is going to be on one place ;) Also, most articles hint the longer the hulls the better...

[Richard Atkin]

LOL!! :D (laughing out loud for real). Fanie, I was lying in bed last night thinking about the stability (hope I'm not becoming obsessed!) You're absolutely right. If I have to ask everyone onboard to do as they are told....it defeats the whole point of a holiday. I want the boat to be relaxing. People should be able to do what they like (within reason). You guys have convinced me that I'm being too stringent with my size restriction. A compromise on the Huckleberry Finn feeling is better than a drowning feeling.

I'm thinking about how I will enlarge the boat.

- Richard

[Guest625101138]

Richard
By fullness I meant more beam up high. As you put it the deckline becomes more eliptical. The waterline would be unchanged. This would increase bouyancy in the ends and increase damping of pitching forces.

Rick W.

[Fanie]

I'm thinking about how I will enlarge the boat.
Longer hulls and more beam. Rick has a good point there. You also have to think about when mother nature calls which is important if you take females along. They like to powder their noses in a bit of privacy. They also tend to take a lot of unusefull things along like clean clothes for every day, the hulls could provide for all of this. Whenever we go anywhere I tell the wife, don't bother to set the alarm, the thieves will think they were here already there's that little left.

[Richard Atkin]

Here's my old boat and the new one courtesy of Rick's optimised 28 foot hulls (see first page in this thread). If a fat woman needs to pee, she will only just be able to slide her hips into that 20 inch wide hatch....but she will be able to pee in privacy...so that's not a problem.

Overall I much prefer the new design. Lots of bonuses (speed being the most obvious), and not too much of a compromise....cos I want the hulls to be mainly for storage anyway. In fact, oddly.....when I walked about on deck (using my 3d architecture simulator), it didn't feel much bigger at all, because the hulls don't seem to be very dominant visually. The deck space is exactly the same size as the old boat. The new BOA is 15 feet.

Looks a bit meaner.....but that's okay :)

[masalai]

Looking good squire. If you're happy that is good

Seasons salutations and may your new year offer good sailing in fair weather and happy adventures.

[Richard Atkin]

Thanks Masalai.
It is looking like a wave piercer now. Maybe I should still make the hulls fuller at the ends. I don't think wave piercing is ideal on a cruiser. However its speed should be capped at about 8 knots, so maybe it won't pierce??? Or at that speed maybe piercing is good.....smoother ride?

Do I need to use a VPP to predict the bows tendency to dive and recover?

Note: the pics are done with software that does not draw accurate curves.

From bow to stern, the deckline is 30 inches from the waterline. I think thats a lot of reserve buoyancy, but after what JCD said about windage, I might need to lower that a little.

If anyone wants to comment on this new design...that would be great. I havent done a proper rendering in Freeship yet.
If anyone is getting annoyed because I'm asking instead of reading....I can understand that....but I am lazy....and you guys are very informative. Your comments are like turbo-chargers.


- Richard

[masalai]

Don't ask me I get others to do that if I can. non-compus-mentus in that area (freeship etc).

Just a little flare near the bows to allow some rounding to soften the "harsh" look. Then I suppose needs "balancing" look for stern. That is where I like pencil. it is easy to draw lines, step back (like an artist) to check the look/feel. All the technical stuff I presume is done so do not change that, I understand you are after a prettier look now.

The flare and rounding should look after reserve boyancy. From earlier posts a wet ride is not the objective.

Don't loose the current stage and redefine the area above waterline to let everyone express a view. So Far so Good. Well ahead of me.

[Richard Atkin]

Rick, I have read that 2 propellers is better than one, for catamarans: better steering and you have a reserve if one fails. But electric motors are so reliable that I think the rules could change? In my case, would just one motor and prop be more efficient on power? Mind you....2 would be nice for a tidy installation.

[Richard Atkin]

Masalai, I was asking everyone :)

[Guest625101138]

Richard
I think you could do a lot more with this boat that would make it more practical with just a little added cost.

The attached image has a few ideas. The colour is not one of the ideas. The hulls are based on the original hulls provided.

With some attention to detail you could get 4 bunks in the hulls and two in the bridge. The hulls have 5ft of height at the bridge so room to stoop about to climb into bunks.

There are other things I would do but it all takes work to think about.

The boat is very close in proportions to a model I made. My model was self-righting and was fun to sail. It was the best sailing model I have made. It is fun to sail a cat that has no limits at least with radio control.

Rick W.

[masalai]

Sorry about that Richard, I had to take mum out and a bit of a rush etc. Just banged out my thoughts without editing etc. If it was a solo thing I am sure I would have got a PM (to tell me off etc?)

[Guest625101138]

Rick, I have read that 2 propellers is better than one, for catamarans: better steering and you have a reserve if one fails. But electric motors are so reliable that I think the rules could change? In my case, would just one motor and prop be more efficient on power? Mind you....2 would be nice for a tidy installation.

Richard
The biggest cat I have actually sailed on is a 24 footer. They do not turn as well as a monohull. Some of the small ones will not tack without a jib.

Point is if you intend to work in tight spaces they are more difficult to postion under sail than a monohull. If you have propulsion in both hulls you can turn the boat in its own length.

Also a centrally mounted prop has to be deep to avoid ventilating. With your high clearance it would be a challenging installation for a mid-mounted motor.

You would get a slightly higher efficiency with a single prop but I think you would regret not having the better low speed steering of two motors.

Rick W.

[Richard Atkin]

No problem Masalai...what you say makes sense. The technical stuff is not all done, but because the cat is looking more typical in proportions, I don't think it will be rocket science to balance the rig to fit the hulls (when that time comes).

[Richard Atkin]

Rick, thanks for the pics. It's very clear to me now what you mean by 'fullness'. I'll do that to my boat (along with 2 motors).

I slept in a narrow bed once, in a Nolex 22, and hated every second of it. Bad air, and worst of all, no room to stretch my legs out. For me, the main goals have always been the following:

* great panaramic views for everyone on deck....no matter where they sit

* reasonable speed in light air (it's not windy most of the time where I'll be living).

* FULL size beds for everyone sleeping....with good ventilation

* a dry ride in choppy conditions

* good comfortable seating on deck

* most of all....the ability for everyone to socialise without disturbances (eg. people chatting with a hot drink, without healing or bending over to see someone's face.)


All other issues of practicality take a lower rank of importance for me. My friends are 'rough and ready' like me. Even the girls won't mind a tight squeeze for something so temporary as going to the toilet.

I'm sure there are heaps of things I haven't thought of, and I know you are full of good ideas Rick, and you can probably see lots of things that I can't....but at this stage I am definitely happy with where the design is at. :)

I've got another 2 years to think about it! (don't worry, I won't be hounding you for 2 years!)


Thanks for everyone's help so far

- Richard

[Richard Atkin]

Rick, you say it's just a hobby for you....do you have any commercial interest in boat design? Would you like to market your electric boat if it proves to be successful? Or does the business side of things bore you?

No reason for asking....just wondering

[Guest625101138]

Rick, you say it's just a hobby for you....do you have any commercial interest in boat design? Would you like to market your electric boat if it proves to be successful? Or does the business side of things bore you?

No reason for asking....just wondering

No commercial interest.

It will be an odd looking boat so I doubt that it will have wide appeal.

I did find this boat:
http://wolfeboats.com/
My concept is a stretched version of this so will be faster and more easily driven at speed. I am aiming to come in well under the price of this one but it is still early days. Sparky has the same motor and controller I am likely to use. I will have a more efficient prop. It still seems I will get 7.5kts with 1.5kW in calm weather.

Rick W.

[masalai]

Thanks Richard, would both you and Rick like to look at my similarly "in process stage" with my route to finals different to meet my needs (the software you guys use is not yet ported to Linux (except spreadsheets which I can use easy).

My efforts are in the member gallery. Comments are sought, PM please as I am shy. or comment on the image. I will make a thread when things move on a bit (I.E. I know where the design is going? - have a set of objectives and needs)

[Guest625101138]

Thanks Richard, would both you and Rick like to look at my similarly "in process stage" with my route to finals different to meet my needs (the software you guys use is not yet ported to Linux (except spreadsheets which I can use easy).

My efforts are in the member gallery. Comments are sought, PM please as I am shy. or comment on the image. I will make a thread when things move on a bit (I.E. I know where the design is going? - have a set of objectives and needs)
Brian
I am looking forward to a video of the model in operation. The underwater portion is almost identical to the RA_Opt that I posted earlier. Just a bit fuller in the ends because you have a higher target speed.

When do you do the first run?

Rick W.

[masalai]

Soon, possibly this Sunday.

[Richard Atkin]

Looks great to me Masalai. I don't know much about boats, I'm still learning heaps, so don't expect me to give you any educated comments! :) I'm still trying to understand what it is that I have designed lol.

Hmmm...do models behave like the bigger version? or do all the physics change with funny square laws (that question goes out to you and Rick in particular).

I know that models are made for testing Americas Cup boats in wind tunnels etc. I think my boat would be simple(r) to build as a model. (well....maybe not. I've never done it before). It looks like a lot of work.

- Richard

[masalai]

Modelling has its own issues, converting model performance to "full size" is still a mystery to me. but I am more comfortable with something to touch.

I may put my relevant PM's on the forum for those wishing to review my processes LATER. I paid for mine to be done. materials not cheap and still overweight (wanted 6.5kg came in at 10kg) for a tenth scale model.

Thanks for your interest.

[Guest625101138]

L......
Hmmm...do models behave like the bigger version? or do all the physics change with funny square laws (that question goes out to you and Rick in particular).

I know that models are made for testing Americas Cup boats in wind tunnels etc. I think my boat would be simple(r) to build as a model. (well....maybe not. I've never done it before). It looks like a lot of work.

- Richard

Richard
The model provides a good deal of information.

If you have a reliable performance prediction method then you can do comparitive analysis as long as the wave regime (Froude Number) is in the ballpark. You need to take into account all the scaling factors though. Basically what I am saying is that if you can accurately predict the performance of the model then you can also accurately predict the performance at full scale. There are some difficult to scale elements like breaking waves but these are not a serious issue with efficient hulls.

If the model does not perform as predicted then you need to narrow down the causes. Often this is appendage drag that gets forgotten about when you do the initial prediction and it typically needs to be allowed for. Could be surface roughness, etc.

Sailing balance can be directly scaled. If the model balances well then the full size will behave similarly. You can observe how stiff the boat will be. How well it points and so on.

The model also enables better appreciation of the 3D space. Layout of drives, steering, rig etc.

A model can help you work out how the full size boat can be built most efficiently.

So my personal view is that models are very useful and the bigger the better.

All my pedal boats have been models aimed at understanding hydrodynamics and I have learnt some things about hydrostatics I did not know before I started.

Rick W.

[Richard Atkin]

Okay, Masalai, I hope you do.

Cheers Rick...it sounds like a good excuse for having some fun. I imagine those little sails could be a headache though. Can you buy model spare parts, like complete mini sail rigs that just fit on to your home-made hulls?

Rick, would it take much time for you to send me the Godzilla optimised 28 ft hulls as a .fbm file so I can do a really good rendering of my design in Freeship? If it's not too much hassle, that would be awesome. I'll get Michlet soon.

- Richard

[Guest625101138]

Okay, Masalai, I hope you do.

Cheers Rick...it sounds like a good excuse for having some fun. I imagine those little sails could be a headache though. Can you buy model spare parts, like complete mini sail rigs that just fit on to your home-made hulls?

Rick, would it take much time for you to send me the Godzilla optimised 28 ft hulls as a .fbm file so I can do a really good rendering of my design in Freeship? If it's not too much hassle, that would be awesome. I'll get Michlet soon.

- Richard
Here is the original Michlet output and the Opt.fbm that I have done the deck on. So you can choose whether you start from scratch or just cut out the bits you do not want from the fbm.

[Richard Atkin]

Far out Rick, how helpful can a person be! This is GREAT! There's no need for me to start from scratch. As you say, it's similar to my design. Thank you VERY much for being such a big help, yet again.

:) Richard

[masalai]

Richard, check out the model racing clubs in your area, there is a special fabric/plastic used for sails.

Batons are applied rather than inserted in pockets and sheets are all adjusted by r/c but rigging and lots of other adjustments are made on land.

Easier that way. Enjoy the r/c model sailing!

I may join the club that is helping me. It is mainly social sailing/realistic models, power too. Also a group of younger members who race their electric powered speedsters.

[Richard Woods]

Richard Atkin wrote "I am an absolute amateur but I am designing my own catamaran as much as I can (admittedly I will get it checked over by people with more experience)."

Later he says "I don't want to do any building. I think this part of the process is best left to people with a lot of experience."

Now I will probably annoy a lot of people (but I find that is easy to do when I speak my mind) when I say that I find it strange that Richard is prepared to design his own boat but not build it. It always seems to me that visulising the shapes and strengths of boats is much easier when you are building them than when designing them.

Having said that, who does Richard plan to use to "check over" the design and give it the OK?

For that matter which professional boatbuilder will be prepared to build an amateur designed boat even if very full working drawings are provided. (So far all we have seen are some rough sketches. As a guide I would expect working drawings for a one off 28ft catamaran to take me 500 hours to draw, once I had decided on the final concept. I would assume that someone who hasn't spent 30 years designing catamarans will take much longer).

And who will be responsible if the resulting boat either doesn't have the performance, seakindliness or basic strength/seaworthiness that Richard expects? The builder?? The ones who gave the OK??

I have designed and sold more small catamarans than most, so might well be on a list of those suitably qualified to assess Richard's catamaran. But I wouldn't do it, if nothing else because of the potential liability problems. James Wharram would be another very experienced designer one might use to assess a design, but I am sure he would say the same as me.

Just something that needs thinking about soon.

Best wishes

Richard Woods of Woods Designs

www.sailingcatamarans.com

[masalai]

Richard Woods (to differentiate from other Richards - a popular name here?),
I am pursuing a similar path, essentially, my objective is to understand the lines for sailing comfort, accommodation, load carrying capacity for personal use and needs. I would like to use Kanga or Robin, as it was their efforts that inspired me to try and meet my particular needs/application, because I recognise there are engineering issues and build experience issues Professionals best understand and incorporate into the design for professional build. I guess Richard is following a similar track.

[Alan M.]

Pretty weird approach. You will save very little money by designing your own boat, and pay a bucketload to have a design that may or may not work, built by "professionals", possibly to very shoddy standards.

I can see that there would be some satisfaction in designing your own (providing it works) but I would sooner pay an experienced designer - even if I had to pay extra to have a "one off" design, and build the thing myself. The so called "professional" boat builders are notorious for trying to cut costs - at the expense of your boat. At least the guy building his own boat is interested in the final outcome - not just his pay packet, and how quickly he can get it down to the nearest pub.

[JCD]

Richard Atkin wrote "I am an absolute amateur but I am designing my own catamaran as much as I can (admittedly I will get it checked over by people with more experience)."

Later he says "I don't want to do any building. I think this part of the process is best left to people with a lot of experience."

Now I will probably annoy a lot of people (but I find that is easy to do when I speak my mind) when I say that I find it strange that Richard is prepared to design his own boat but not build it. It always seems to me that visulising the shapes and strengths of boats is much easier when you are building them than when designing them.

Having said that, who does Richard plan to use to "check over" the design and give it the OK?

For that matter which professional boatbuilder will be prepared to build an amateur designed boat even if very full working drawings are provided. (So far all we have seen are some rough sketches. As a guide I would expect working drawings for a one off 28ft catamaran to take me 500 hours to draw, once I had decided on the final concept. I would assume that someone who hasn't spent 30 years designing catamarans will take much longer).

And who will be responsible if the resulting boat either doesn't have the performance, seakindliness or basic strength/seaworthiness that Richard expects? The builder?? The ones who gave the OK??

I have designed and sold more small catamarans than most, so might well be on a list of those suitably qualified to assess Richard's catamaran. But I wouldn't do it, if nothing else because of the potential liability problems. James Wharram would be another very experienced designer one might use to assess a design, but I am sure he would say the same as me.

Just something that needs thinking about soon.

Best wishes

Richard Woods of Woods Designs

www.sailingcatamarans.com

Hello Mr. Woods...

You are definitely an authority and I can definitely say that confidently. Everything you have said is valid, but I would like to throw some things out to you in the hopes that you can straighten me out whereever possible... and no, I don't think that you are annoying for documenting your thoughts...I only wish many would do it more often.:)

I agree with Richard that if he does not consider himself confident to trust his design skills or trade skills that he should delegate those to competent individuals. I also agree that he should design his own even if he requires that a NA/NE or experienced builder complete the job. Why? Well, why do we get second opinions from Doctors even though we are not going to perform a proceedure? Why does an architect have an engineer check his calculations and why does he defer building to the contractor and not build himself? Why does the contractor build from plans he didn't design or approve himself?

My own answer would be that it is because there are those whom are more qualified and experienced than ourselves whom can do so with a fair amount of confidence that their experience and skills will produce a safe and reliable design or build. My other thought is that I would not throw out the baby with the dirty pan-water just because they are both in the pan.

I agree that visualizing strength is easier at the build than at the board but not everyone is capable, or able, or would want to acquire that experience, myself included, before designing, and we should. However, does every NA/NE wait until a similar design is built to witness the visualization before he puts pen to paper or does he rely on his experience and empirical existing data for similar designs? If this were not the case, then first engineering principles must always be the solution wouldn't it? How many designers utilize the ardous laws of first engineering principles even if empirical data exists?

Personally, I think Richard should use the other Richard, that would be you, to have his design assessed and, I believe that any builder will build his design and will contribute his own opinion on changes with justification for them being made AND, I don't think that there would be a builder that would not build a design from anyone that receives your stamp of approval. I also believe that the same is true for any other NA/NE of your calibur and track record.

Richard, the designer and owner is responsible. Not Richard, (you) or the other Richard (builder), would be responsible for a build that is not up to his standards because he designed it and probably did not take advise from others with more experience. But whom is responsible for a design that you drew and the builder built to spec and the owner is still not happy with the end result? The owner of course. So what that your design will only do 19 knots on a beam reach when he expects 20. So what if the design weighed 1# above design displacement because the glass/resin ration for a square foot by the builder was 59/41 instead of 60/40. You don't intend to refund fees and the builder will definitely not rebuild. So the line can only be crossed if the design is "grossly misrepresented by design or negligently built".

With all the disclaimers of warranty, express, implied or otherwise, etc., that our infamous litigators have authored, I'm still shocked anyone could be sued, let alone carry the expense of said litigation. With that said, I don't understand why you would not review a design or believe that any other qualified professional would not do so. Have you never been consulted by another colleague or by amateur in your 30 years? I do however agree, that this planet has become a litigous humanity and expect everyone would be worried.

God forbid I'm offshore and witness a knockdown and make any attempt to save the crew. Will I be sued because a spouse was saved and a life insurance could not be collected or will I be sued because the individual I saved was a NA/NE, whom lost a hand, and always believed he should not live if he couldn't sail? I think I would chance it even if either or were telling me "don't or I'll sue."

I have been working on my design for over two years (GOD knows it has got to stop soon) and was successful at acquiring the services to have the scantlings called out and the structural integrity assessed. Yes, it was with strict conditions like, "what I say goes" and "no changes without my review and approval" but it was still my design and only minor corrections were made to my initial callout because of "safety factors that were believed to be high".

A good example is a folding mechanism, scissor type if I remember correctly, that someone came up with and presented to a NA in the PNW. I'll be damned if the NA didn't only contribute to the design, but adopted it for his own portfolio. I don't remember. Two cats or two fold or something.

Wow...500 hours. Is that pen and manila or all these advanced programs available today? I should have kept track of my own, but I think it was definitely well above that, probably double, and I'm still going at it. The learning curve was at least 2 to 3 years.

I am not a PHD in making the written word express my attitude or thoughts exactly as they are, so please do not take my response as combative or callous or anything that may appear to seem negative, as it is not meant to be as such. If anything is perceived as such, it is not my intention.

One request...if not too much trouble...would you mind taking a looksie at my own design and perhaps comment on it...or not...it is ova there ----> at http://www.boatdesign.net/forums/showthread.php?t=20302.:D

Thanks
J:cool:

[Richard Atkin]

Yes Masalai, you are right. That is exactly my position.

Richard, my intention is to have a boat that is specifically tailored to suit my requirements. Whether I personally design most of it....or someone else designs most of it, is irrelevant to me. I just want a fun boat.

The reason why I am designing, is because it is fun and I am learning a lot and....after extensive searching, I haven't found a boat on the market that exactly matches my requirements. In fact, through my learning, I have discovered that a lot of professionally built cats have been designed poorly.

If you or James Wharram refuse to look at the final design, then you will never know whether it is good or bad. If you could see that it is good, then why would you be afraid to build it???

I would never hold anyone responsible for my own mistakes. But I would hold the builder respnsible if the workmanship is neglectful, and is obviously the cause of the wreckage.

I am not concerned about a lack of willing builders, because if all builders were unwilling to build a new design, there wouldn't be any new boats would there?

So who would I choose to check my design? People who can show me that they know what they are doing. I don't work on blind faith, and I wouldn't expect you or anyone else to do so.


Regards
- Richard

[masalai]

Richard Atkin, at the risk of borrowing your thread again, but relevant in current theme, I am sure a reasonable NA/NE would be delighted to receive a commission so well researched and defined. It almost becomes a technical matter with no need for redraws because the customers priorities were in another direction.

I bet the discount would not be noticable but still would be a valid service fee anyway.

[Fanie]

The Boxy Fisher cat I'm planning is also a self design because it has specific requirements with no easy way around some of them.

What I find disappointing is that the professional boat builders doesn't seem to care what is important to their potential customers. I for one would not be forced or bullied into buying anything that is not to my requirements.

I really expected that any pro boat builder would sit down with someone, evaluate the design and if nessesary make some apropriate suggestions to eliminate shortcomming or underdesign. I have had two boats built for myself in the past. In both cases the builder spent the time (patiently) and did exactly what I suggested, made some suggestions and he made a sale - twice.

It really bothers me if someone hasn't even seen something and already complains about liable issues.

All this as a whole, is why I often end up doing all the research, obtain the tools and do the job myself in the end. There are lots of very helpfull engineers that can assist in calculating all kinds of things without it costing a cent if you look for them. Material suppliers (gratefully) supply detailed information about their product. In most cases a bit of gained information brings two and two together.

Maybe one should then look for someone who is willing to take the time out and who wants to be the next generation boat builders. Always a new and upcomming guy who wants to set a new pace and make a reputation for himself.

Sorry..

[Guest625101138]

..........
I have designed and sold more small catamarans than most, so might well be on a list of those suitably qualified to assess Richard's catamaran. But I wouldn't do it, if nothing else because of the potential liability problems. James Wharram would be another very experienced designer one might use to assess a design, but I am sure he would say the same as me.

Just something that needs thinking about soon.

Best wishes

Richard Woods of Woods Designs

www.sailingcatamarans.com

Richard Woods
I am not sure of your motives in making the above statement. It is provoking and no doubt controversial. Something to think about:-

You have made a strong connection between the above statement and Woods Designs. Hence you are leaving yourself open to a claim of misrepresentation as the above statement directly contradicts paragraphs four and five on the Woods Designs consultancy page. If the above view is indeed your stance then you should reword you consultancy page.

Rick W.

[Trevlyns]

What a refreshingly different reply!

I speak as a well read but “unqualified” amateur designer with a leaning towards simplicity.

My interest is in the Polynesians (Wharram inspired) and I sometimes just can’t help thinking – what did those original fellas know about the technicalities of yacht design as we know it today? Not much, I submit.

I can only surmise they certainly had a good grasp of Archimedes Principle (although he came eons later.) They certainly knew that two hulls were better than one - Monohulls were only “invented” some 2000 years later.) For sure they had a grasp of the prismatic coefficient, hull spacing, rig efficiency…. Oh, and somewhere in between the computer was invented...

Professional people – I in no way undermine your years of study – I salute and admire you.

I just say – Let’s give amateurs a break! Provided you have basic knowledge of what will float, what will slide reasonably through the water, what will resist leeway, what sail area (compared with numerous other examples) will work in a blow…

Let the brothers have a go too!!!

[Richard Woods]

First, I don't use Freeship so cannot read the SR34 files. Furthermore the pdf files won't open on my computer (I have Adobe 8.1)

My consultancy page, paragraph 5, says:

"Many people would like help in choosing the right boat for their needs, while others who already have a catamaran want advice on suitable equipment or how to make their boat perform better. In either case it may well be that the boat in question is not a Woods Design. Don't let that stop you; this consultation service is open to all! "

In other words, what it says is that I offer advice to those choosing a design in the first place and also to those who want to improve an existing boat.

Nowhere does it say that I will modify or inspect someone else's design

However, maybe I am misunderstanding what you mean by "designing" a boat.

Perhaps you mean you are going to supply some sketches for a pontoon/party boat, but with sails instead of an engine, and then hand those sketches over to a qualified NA to turn into a real boat.

Or maybe you are going to draw the complete boat, including the detail metal work drawings, exact placement of deck gear etc as well as engine, plumbing and electrical installation drawings. And of course ensure that what is drawn can be built economically by your chosen builder.

In which case all you want is to have the drawings "inspected" by a NA.

Initially I thought it was option B you were planning, but now I think it maybe option A

A one off design costs a lot, especially for a small boat. Easily 10% of the build cost. 500 hours at even a hairdresser's rate is serious money.

That's why I prefer to design boats that I can sell many times at a low price. It also allows me time to go sailing instead of drawing, which is what I prefer to do.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[masalai]

Not only that they could navigate very effectively and their craft were sufficiently robust and seaworthe to make significant and long oceanic voyages reliably. The Pacific Islander voyaging culture is sadly being lost through lack of repeat efforts to pass on the skills at reading waves and stars through their maps.

[Richard Atkin]

Richard, would you be able to give me a very crude number to give me some idea of what sort of money I could be spending? I'm talking just a very wild guesstimate. Lets say it took you 100 hours to check it over and ammend any small problems, and then you built it.

Some info:
28 feet
fibreglass hulls with aluminium rigging and fittings.
light and heavy sails.
4 'awnings' and 2 fiddly little 'pram hood' tents.
unique aluminium 'shark cage' style bridgdeck.
4 waterproof bed mattresses.
watermaker.
a lot of batteries....2 electic motors to drive the boat.
no furniture in hulls.

Ofcourse it's a wild guess...but can you give me a ballpark figure?


Cheers

- Richard

[Richard Atkin]

I've budgeted for $150,000 USD.

[jamez]

Don't forget insurance and re-sale. Amateur designed boats are notoriously difficult to sell (unless they do something particularly well, like win a bunch of races) and can be impossible to insure at a reasonable cost.

I can understand a designer with an established range like Richard Woods not wanting to get involved in other peoples designs. There are other designers that like to specialise in one-offs or 'different' types of boat/concepts.

Richard Atken
You might like to try http://www.devilliersyachtdesign.co.nz/home.htm
I have no connection but judging by the breadth of stuff on their site they could be worth talking to. If not they may be able to steer you to someone who can.

[JCD]

I've budgeted for $150,000 USD.

I believe you are going to come in well under budget.:D

J:cool:

[Richard Woods]

I would agree that USD150,000 is excessive for a 28ft open deck non racing catamaran.

On my website you can see sketches of my 10m (33ft) Mustang design. You can buy one of those, delivered anywhere in the world, for USD100,000. And that is for a performance cruiser, so includes accommodation and good sails and deck gear in that price.

I charge USD50 an hour for consultancy work.

[masalai]

Give me the 150k then. I need some now, & recession, so the experts are saying is going to hit US in the new year, I can spend it before the R hits. Then on second thoughts, You keep it you may need it more than I.

Gee, in '80 my boss was hiring me out at $65/hr and he was a Pom called Christmas, I kid you not! (I didn't get that though. Pity?)

Seasons salutations.

[Richard Atkin]

Rick

If an optimised fully submerged foil, and an optimised surface piercing foil (for my cat) both have the same steering force/lift).....do you know their difference in drag as a rough percentage? I'm wondering how much drag I will have with 2 surface piercing rudders and 2 surface piercing dagger boards. I want to know if ventilation is a big problem, or insignifcant compared to the overall drag of my boat. I have been following your posts in J's forum....I was just hoping I could get some perspective without having to get more software just yet

Thanks

- Richard

[Guest625101138]

Rick, if a fully submerged foil and a surface piercing foil both have the same steering force/lift).....do you know their difference in drag as a rough percentage? I'm wondering how much drag I will have with 2 surface piercing rudders and 2 surface piercing dagger boards. I want to know if ventilation is a big problem, or insignifcant compared to the overall drag of my boat. I guess it's time I started doing more homework

- Richard

Answered on the other thread where you asked the question first.

You will see from Brian's video of his cat that these optimised hulls are a bit like trams on rails. They are not inclined to turn easily. Not the best for racing around buoys. A liitle rocker makes them easier to steer but increases hull drag.

I have a very strong preference for non-ventilating rudders. Dagger boards are not so critical as you want them to operate at a low angle of attack so the pressure is not as high. With the long deep hulls they may not be even warranted.

Like I recommended to JCD you should learn to operate JavaFoil. It helps you understand the physics of critical bits of a boat.

Rick W.

[Richard Atkin]

sorry Rick, I didnt think you would be that quick. I deleted the question on J's thread cos I posted it there by accident.

Thanks for your help

- Richard

[JCD]

First, I don't use Freeship so cannot read the SR34 files. Furthermore the pdf files won't open on my computer (I have Adobe 8.1)

Richard Woods of Woods Designs

www.sailingcatamarans.com

Hello Mr. Woods...

I apologize I missed your post.
Perhaps you would consider using Freeship just to view and critique, or give advise on some of the designs being generated here without using it for your more technical work. It's free.

I don't think I posted any PDF files but I'll go back and check and change them if it will allow you to read them.

A quick note to bring you up to speed without having to read my whole thread. The SR34 was one of 3 designs which was chosen to be optimized for a final design. That work on that design has already started and it is no longer the SR34. It is now The Green Lantern.

I'm not trying to polish my own shoes...but I believe the design has good merits and warrants further development. I would be dishonest if I didn't state that many in this forum contributed to the design in their own small way. Some unique ideas will be incorporated which I believe may be firsts but won't know until someone can point out otherwise.

I don't want to hijack this thread so I will not attach it here but I have attached the most recent work at my thread with some pictures if you would like to peruse it.

Thanks
J:cool:

[Richard Woods]

I am sure you have been following the IDEC trip. If you go to the website and view the video of IDEC crossing the equator you'll see the spray coming off the rudder as the main hull flies. Proves there is a LOT of aeration from a surface piercing rudder.

That is in part because a surface piercing rudder acts as a hull and creates its own wave train. Obviously it is going VERY fast, ie has a very high speed/length ratio.

A 1 1/2in (37mm) thick wall hollow stock rudder is fine up to say a 10m catamaran. A useful rule of thumb is that the rudder stock diameter in inches is 1/20 of the length in feet. So a 40ft cat has a 2in stock, a 30ft cat has a 11/2in stock etc.

If you look at my FAQs page you'll see my very simple, yet 100% reliable lifting semi balanced rudder system. Don't forget that the faster you go the more the C of E of the rudder moves aft and this can overbalance the rudder when at speed even though it is fine at lower speeds. Also that you won't actually turn a corner at 20 knots. So the rudder loads are lower than you might think.

I am sailing in Mexico for 4 weeks after Christmas so won't read this forum often. Also, unlike many others who design for a hobby, I have to make money from my design work. So although Freeship is free I'm not(LOL)

Happy holidays

Richard Woods of Woods Designs

www.sailingcatamarans.com

[Richard Atkin]

Thanks Jamez

....and

thanks Richard Woods

(this thread is LOADED with great advice!)


- Richard

[Richard Atkin]

Does anyone know the best way to make the bottom of my hulls more beach resistant? Like some kind of lamination?

[Fanie]

Plastics like PE offers very high wear and impact resistance. I've never thought of using them on a boat's hull but it may well be possible. They could be a pest since nothing glues to it either, so may have to be shaped and screwed in place

[Guest625101138]

Does anyone know the best way to make the bottom of my hulls more beach resistant? Like some kind of lamination?

Richard
It is not unusual to run a rib along the keel to give the hull the ability to ride up on hard ground. This is solid glass and eventually the gel coat will get worn off - just gets repainted when antifouled. Timber boats sometimes have a metal wear strip screwed to the keel timber.

Rick W.

[rasorinc]

Put and old chris craft cutwater over the stem and 10' down the keel. CC used bronze and cromed it. really looks nice. the easist way to do is wax up your stem and keel then put 2 layers of fiberglass over and fill with epoxy. make it at least 6" wide on each side of center. Once dry peel it off and you have a perfect mold for any sheetmetal shop to make you one 1/8" SS is more than enough and you can polish instead or crome. Stan

[DungBeetle]

i was going to try 1 mm lexan on the bottom because i intend to park on the beach everyday (heat formable lexan film is now available, about $10 per M2, run it along the hull before epoxying, use a heat gun and form it into shape, take it off and stick it on last. lexan when surface prepared has the same adhesion as wood)

also having small mini keels - ribs maybe 5cm tall, 5 m long, on a 35 ft cat.

some stick 300gm csm as the outer layer to protect the uni, for rocks, dings, and stuff, but lexan is incredibly stronger, (play with a test strip!) and i may well end up doing this.

cheers,
mal.

[Richard Atkin]

Well, here it is. Unless there is something seriously wrong (and someone please tell me if there is), I believe my cat is almost complete. The final testing of models and simulations etc. should not result in a fundamental change from this design. Just some balancing of the rig and rudders hopefully. It would be nice if there is enough lateral resistance to do without the dagger boards.

The diagonal bracing from stern to aft crossbeam prevents racking and allows the bridgdeck to have no annoying diagonal bracing. This allows me to have 4 double bed mattresses which are supported by trampolines (instead of my earlier 'shark cage' idea). Each bed is supported down the middle by a rope to prevent people from rolling together. The final result is similar to 8 hanging hammocks, except you can walk on them without a foot falling through.
It makes an excellent shock absorber during bridgdeck pounding in heavy seas. No stress on the hulls.....just a little stress perhaps on the 'sleeping' passengers.

The hulls will have internal struts/trusses which will make them incredibly strong. I can do this because I don't have to worry about passenger thoroughfare.....just many rubber sealed ports for luggage access. Even the mini folding dome tents will have rubber seals so the hulls are watertight during a bad storm. Not having to worry about sufficating in the hulls is a big bonus to me.

The sleeping tents will be brightly coloured and will let the light come through the fabric. When you combine this effect with soft squishy mattresses, it think it will create a really nice atmosphere. The walls of the tents can be folded completely open to let the air through and preserve the panoramic views.

The box in the middle can be stored behind the rear seats

I have spent far more time trying to imagine the social and atmospheric effects on various designs....than I have on structural efficiency. It is just lucky that my preferences made me end up with a more simple design.

Oh yes, and I have opted for a plain old single outboard motor on the back. The twin props dragging through the water doesn't appeal to me.


Any criticism or ideas would be great.

Cheers
- Richard

[Guest625101138]

Richard
If I was paying USD150K for a sailing cat I would be hoping to get some solid accommodation.

You seem confident that you will only be sailing in ligh air. I cannot see how this will be possible. I don't see your matresses standing up to any sort of weather.

There are some big trailerable cats around 30ft that have the hulls sliding on the bridge beams or easily assembled onto the beams They still have large trampoline area spanning the hulls and useful accommodation in the hulls. Here is an example:
http://www.reynoldssailing.com/en/pricing/rs33.asp
Bigger than you want and well within your budget.

The fact that these hulls are longer than your design will make them more easily driven at typical cruising speed. So if you do not like the big rig then just reduce the sails to the level of excitement you are prepared to accept.

Rick W.

[JCD]

Well, here it is. Unless there is something seriously wrong (and someone please tell me if there is), I believe my cat is almost complete. The final testing of models and simulations etc. should not result in a fundamental change from this design. Just some balancing of the rig and rudders hopefully. It would be nice if there is enough lateral resistance to do without the dagger boards.

The diagonal bracing from stern to aft crossbeam prevents racking and allows the bridgdeck to have no annoying diagonal bracing. This allows me to have 4 double bed mattresses which are supported by trampolines (instead of my earlier 'shark cage' idea). Each bed is supported down the middle by a rope to prevent people from rolling together. The final result is similar to 8 hanging hammocks, except you can walk on them without a foot falling through.
It makes an excellent shock absorber during bridgdeck pounding in heavy seas. No stress on the hulls.....just a little stress perhaps on the 'sleeping' passengers.

The hulls will have internal struts/trusses which will make them incredibly strong. I can do this because I don't have to worry about passenger thoroughfare.....just many rubber sealed ports for luggage access. Even the mini folding dome tents will have rubber seals so the hulls are watertight during a bad storm. Not having to worry about sufficating in the hulls is a big bonus to me.

The sleeping tents will be brightly coloured and will let the light come through the fabric. When you combine this effect with soft squishy mattresses, it think it will create a really nice atmosphere. The walls of the tents can be folded completely open to let the air through and preserve the panoramic views.

I have spent far more time trying to imagine the social and atmospheric effects on various designs....than I have on structural efficiency. It is just lucky that my preferences made me end up with a more simple design.

Oh yes, and I have opted for a plain old single outboard motor on the back. The twin props dragging through the water doesn't appeal to me.


Any criticism or ideas would be great.

Cheers
- Richard

Hello Richard,

I think it's great. I like the idea of the tramps fore and aft of the mast. I'm doing that. Mt aft tramps I'm going to make structural and the fore will just be regular tramps.

The pic shows that you may have room for Daggers, but if you don't want them, you can go to lee boards or put a keel guard of say 3 inches and you can get some pointing ability. Turns may be wider but you'll have grip.

I hope the caribbean accommodations is fully waterproofed from top to bottom and everywhere in between because exposure is significant. This is the best for daysailers or consecutive fair weather sails. I would recommend that you spare no expense when it comes to these and consider survival or storm ratings.

I would probably look at the cross bracing again and make sure you have good safety factors incorporated. My eyes could be deceiving, but it looks light...ppppfffff, my rudders are tiny!

Great job. Stuck to the design idea. Plan to put out any numbers to look at?
Material List?

Thanks
J:cool:

[Richard Atkin]

More great ideas pouring in....thanks people.
I like the idea of using something like lexan, as Mal suggests, and maybe screwing it in place as Fanie was saying. 'Replacable' sounds good.

[Richard Atkin]

Hi again Rick and J :)

Rick, I don't want to exceed 150k and if I can get well below that, and still have what I want, then cheaper is better.
I have gone all out to try to hold on to the 'small boat' feeling. This might sound a bit silly to some.....but when I see the reynolds design I see a boat that just doesn't have that 'huck fin' feeling.
What I have designed is really just an oversized (but not too oversized) hobie.
It just feels more fun to me.....(I'm saying all this without ever having been on a boat like the one you have pointed out.....but I have a pretty good imagination).

I disagree about the mattresses not being able to tolerate a storm. If the tramps and mattresses are designed right, they can be stronger than a cabin 'shell'. If you think of a fabric as many ropes spanning a given area, you will see that it is immensely strong. Also the elasticity means it does not suffer from peak loads.

J, to be honest, I just want to leave the final maths to someone else. I don't know how thick the beams will need to be etc. etc. Making the entire accomodations waterproof should be a no-brainer....just careful attention to overlaps and seals.

In a nutshell....I know this boat is not a 'solid' cruiser, but I will never be doing very long distance trips. Night sailing will be a rarity.....as will sailing in storms, cos I won't be on the water long enough to run into a storm by accident. If and when I do, I think the boat will handle it.....but not without a lot of study and practice on my part.

I don't wish to defend my design....I am just explaining my reasoning. If either of you (Rick and J) can show me a boat that already exists, that is very similar to mine.....I would probably buy it and just accept that the design process was fun and informative.


Thanks for your comments!
I'm sure you've got something to say, Rick....please do :)

- Richard

[Fanie]

Hi Richard,

I must say I like Rick's suggestion. I have now read a heck of a lot of stuff on cats (I'm now beginning to forget some already :D), and without fail it boils to the bigger the hulls the better every time.

The link he suggested with the 33' hulls, looks a lot like what you are after, it's within your budget with some spare for beer ;)

Another thing to keep in mind on such a caft, the setup is sorted out already. Doing this on a new rig is something else, usually ends up in a lot of chop and change and shuffeling things around.

I know you don't plan to hang around in stormy weather, but the wind can however pick up in a jiffy and again the larger hulls would contribute a lot to safety and comfort. You may not always have a choice, talking from experience.

Such a raft would be a better investment as well. We don't know what the future holds but you may well decide to get the larger 65er and you can then get your money back. Once you've got the boat you may realize you've got more friends than you thought... :rolleyes:

Personally, I would look at the full fledge catamaran with lounge and acess to the hulls. I was outside all of today, and I must say the sun was something else man, my wax is currently melted.

In my opinion it is going to be very nice to be able to retire to the lounge at the end of a day to a protected environment and just put your feet up and relax with whoever else is there. If th sun is a scorcher, you have protection.

If it rains it won't matter, if it's windy it won't matter, if I overnight it won't matter either, since you won't be wet from dew in the morning, but I can still sleep outside on the fore or aft deck if I want to. Need a bath at least once a week or so...

My first cat I drawed looked a lot like yours, same idea with a tent although I didn't have the matrasses and so on but solid decks instead. The more I read and enquired and gained info, the more it shifted to the full cat setup.

I may not be able to go out as often as you would, so for me it is important not to have to run every time the wind or weather plays up a bit, and it will happen.

And if you do change your mind and no-one wants to go with you to sail the cat home I may take you up on it. Count for my sailing experience ;)

[JCD]

Hello Richard,

I agree with Rick. Very nice design he pointed out and pretty close to what you're looking for...with hull comfort to boot. Not exactly as yours because none can be...but if you are really leaning to having it all engineered and then built within your budget...dammmm it's already done!:D

All you gotta do now to really make-up your mind is find one and pay the owner to take you on charter for a couple and days and that is when you will decide. To toot a different horn, you may want to do more research along the lines of your design and rule all other designs out if you plan to purchase anyway.

I wasn't talking about the mattresses...I was talking about the tents. Weather can get nasty fast and a boat full of friends can be miserable quick. Get the best and you will be able to enjoy it when it gets cooler too.

J:cool:

[Fanie]

Ok here's what I did when I first decided I was going to make me a motorized sailor -
I drawed the hulls on my driveway with white board chalk to scale. I then tried ti imagine what it would be like to be on the water on this thing.

First problems my hulls were too narrow and too shallow, I started over. I have then started reading articles and every time went back to drawing the hull and decks out on the paving. Gives one some perspective of the size, the spaces, restrictions, comfort and so on.

So it grew and every time I got a new idea somewhere or browsing through the 1 000 001 and a 1/2 pictures I have collected to date I live myself into them. Get a feel for things and you know if it will work for you or not.

[Richard Atkin]

J and Fanie, you both make very good points. And yes J, I agree I should keep looking at boats that are already available. I'll be doing this for another couple of years....so there's no hurry.

Many people talk about the 'boat' as if the boat is the final goal. Fanie says it is nice to relax in a sheltered lounge at the end of the day or if it's a bit chilly etc. I can appreciate that, but my idea of a 'sailing' trip is actually more about the trip and not the boat. The boat is a fun vehicle for getting to good camp sites. Camping has always been my priority (I love camping), and I want the boat to be a big part of that.....but it is just a vehicle. I would much rather relax on a nice island at the end of the day, after spending the day getting there by sea (or river).
My boat's sleeping facilities are there for those odd times when we want to sail on a clear night.
The fact that my boat doesn't feel like a proper cruiser, really appeals to me. I like the way a simple tent doesn't feel like a proper home, but you can still fill it up with goodies and have a great time surviving in the wild.
In the VERY beginning, I was actually going to buy a Hobie Getaway (don't laugh), but I soon realised it wasn't going to take the weight and would be totally dangerous for my purposes.
I have sailed small beach cats and really love the 'simple raft floating on the ocean' sort of feeling. I don't want to lose that.
It's not something to live on....but it is something to enjoy!

- Richard

[Richard Atkin]

Fanie, quote "And if you do change your mind and no-one wants to go with you to sail the cat home I may take you up on it. Count for my sailing experience"

Very nice of you to say that :) Who knows what'll happen 2 years from now.

- Richard

[Guest625101138]

Richard
My idea of a boat is a means of relaxed transport. I have seen the inside of enough airports to last me a lifetime. But unlike your view I aim to travel between hotel or resort style accommodation. The boat is just a means to get there. I don't like roughing it too much - a couple of nights is OK.

I lived in Brisbane and the Gold Coast for my childhood and my skin has already endured enough sunlight so when I travel I like to be sheltered from sun, wind and rain. Maybe it is simply that I am old.

Each to his own. Boy I like that Reynolds 33. If I was spending USD150k on a boat it would be on my shopping list. Think of something that can be towed - no marina fees. Will dash along easily at 10kts. Basic accommodation. Much less effort than actually getting one designed and built.

If I was building a basic 28ft boat I would be hoping to come in well under USD150k. A 33ft boat is nominally 60% bigger than a 28 footer.

Rick W.

[masalai]

Richard, I have been asleep all this time. A fellow NZ designer/builder produced a "Great Barrier Express" to day-trip to the coastal islands. 9m or so.

Until recently a version was built at shorncliffe in Brisbane by John Brown. Sadly his shop got burnt down by an idiot who set fire to an adjacent bldg. His website is still up at http://www.expressmultihulls.com.au/em/ and there are a few second hand on the market http://www.mynextboat.com.au/
reference # RBS491
GBE GREAT BARRIER EXPRESS 9M SPORTSDECK $28,500 AUD

[Richard Atkin]

thanks Masalai. I've heard that the GBE is a very good boat. I know it is very popular.

If my boat design can be finalised and built for say...under USD80k, then I think that it is unlikely that I will buy one of these great boats.....no matter how cheap they are. I would have to find one that can easily be converted to something that produces my kind of 'hippy' boat. (no I'm not a hippy). The conversion could prove to be a bigger hassle than doing a fresh design.

Rick, it's not a big effort for me to get a boat designed and built. If things become tedious....I will let someone (trustworthy) sort it out. It would be very satisfying to watch the design being finalised by someone else.
I don't have an expensive lifestyle, and don't like to waste money....but this boat is just a one-off treat for myself and my friends and I don't care about throwing a bit of money at it (without being rediculous). Even so, if it can be built cheaply then I would make sure it is.

Hey everyone.....no-one will get sunburnt or cold on my boat! :P It's amazing what you can do with a bit of fabric. You guys have got me thinking more though about better sunshade possibilities.

MERRY CHRISTMAS everyone

[Richard Atkin]

ps. I wasn't supposed to make that green face.....what the hell is that?

[JCD]

I can appreciate that, but my idea of a 'sailing' trip is actually more about the trip and not the boat. The boat is a fun vehicle for getting to good camp sites. - Richard

AMEN to that.

J:cool:

[Fanie]

Very nice of you to say that Who knows what'll happen 2 years from now.
I hope to have my skippers long done by then :D. It will be fun though.

Why don't you just build the thing yourself if you're going to wait two years ?

I've done enough camping to last another couple of lifetimes. I want to camp on the boat instead and since I fish I would prefer to sleep with the fishes like the Italian mafia would say, only up in the boat :D Now if you are going to wait another two years, you may well get to where you begin to dislike tents. The only discomfort I'm looking foreward to now is the big fish that would give me troubles to beat ;). At least it's a challenge.

[Richard Atkin]

I definitely won't be building it Fanie. I'm not much of a builder. I get too bogged down with the details. I'm not aggressive enough to grab the bull by the horns and just get the job done. I don't want it to take a million years, only to end up with something that I know will be worse than a pro build.

[Richard Atkin]

The boat has 3 types of tents:

the hatch tents,
the sun tents (for sleeping or sitting),
and the storm tents (for sleeping or screaming)

The storm tents are just bladders with a small entrance located towards the middle of the boat. The hole is the only part which can open and close. Keeping them ventilated won't be a problem in stormy conditions. These tents will be lined with heat reflective material and because they are so small, they will be very warm just from body heat. These tents, or 'bags' have no internal poles. They are just tied to rigid parts of the boat.

The sun tents will be light and airy with walls that fold open entirely, and can be raised or lowered on poles to create bimini shades

I have shown the hatch tent and the storm tent

[Richard Atkin]

Atcat 28

[Fanie]

Two YEARS from now ? Gee whiz. Wait a year and six months then post back here. In two years time your''e going to be too old to pitch a tent in any case. I like the projector idea (last pic previous post) You can show movies like 'Perfect Storm' while you sail your buddies around NZ.

T W O Y E A R S... bloody long wait...

[Richard Atkin]

LOL!!! You're a funny guy Fanie. People don't get much more than a chuckle out of me but you actually make me laugh. :)

I would love to hear the sound of power tools working on my boat right now....but I have other commitments right now. I am working overtime trying to finish an album I am recording, and in about 2 years I'll be moving to LA. There are financial reasons too. So all in all, I'm more comfortable to start the project when my situation is more concrete. There is the chance that I might have less money than I hope to have in 2 years time, so I don't want to do anyhting silly just yet.

Man.....it's not like I am putting my whole life on hold!!

Projector screen....

anyone who sails on my boat will see exactly why I have designed it like that :) Earlier you spoke about giving your imagination time to 'live' into the design to get a feel for what it would be like. I totally agree. That's what I've been doing for months and I love the design.


hope you enjoy your holidays....before you get to old :p

- Richard

[Richard Atkin]

As you can see, they look completely different

[terhohalme]

Richard,

Did you think to turn or tack your boat? No rocker at all is great for calculating resistance on (too) high speed but bad for turning ant tacking the boat.

Normal cruising speeds seldom exeed Fn = 0.6

Terho

[Richard Atkin]

Terho, how badly would it turn? Could you give me some perspective? I mean.....if I was running down a big wave would the steering be so unresponsive that it would actually be dangerous?
If safety is an issue, then I would use rudders with more steering force, instead of adding rocker to the hulls. Would that still give me less drag in a straight line? I am not at all concerned about tight turns, as long as the thing can actually tack, one way or another.
Good speed in a straight line in a light breeze is what I am interested in. I can always slow it down in strong winds, if necessary..

Regards,
Richard
(thanks for your input)

[terhohalme]

Downwind and big waves are propably not the problem but tacking. When you try to turn the sterns have to slide sideways. If the sterns are too deep they will increase resistance and speed lowers. Perhaps too much for a succesful tack turn. Ever thought why sailing catamarans usually have rocker aft midships?

Still, wharrams can tack...

[Richard Atkin]

Ok thanks Terho. Well....if tacking is the only big problem I'm likely to encounter....then I will start up the motor if necessary! Or probably do a gybe. I want lazy speed. I won't be picking the wind shifts constantly...so tacking will not be often.

I think I will need to be careful when sailing downwind in a big sea. My hulls are skinny no matter what way I look at them, and I will probably tell my crew to move aft. (not for steering reasons, but nose diving reasons)

[Richard Atkin]

I'm thinking of covering my deck with fake wood. Yeah I know, many people will want to throw up.....but I actually like fake wood. It looks good to me.....the fakeness doesn't bother me.

I found this website http://www.fibreglast.com/

Anyone had any experience with Chromaveil? Do you think it would fade away after one week in the sun and salt water? I like a worn out look, so maybe a bit of fading would be better!

[Richard Atkin]

Hello Rick? If you're not sailing in Mexico right now, I have a small question for you.
Quote "Running downwind in the conditions in the earlier photo would see a light, easily driven cat hitting 20kts under mast alone."
Even though the opt hulls are dislacement, do you think they can still achieve 20kts? I am aware that the rules for displacement hull speed change when the hulls are super slim, but do the rules change that much??
20 knots? Does the hull somehow create some lift even though it is not a planing hull?
Actually, some people argue that 'planing' cats don't actually plane. So that leaves me wondering if I have accidently created a monster.....a speed demon from hell.

Anyone else want to comment?

[Guest625101138]

All hulls have a "Hull Speed" by definition. It is the speed where the boat speed matches the phase velocity of a wave having the same wavelength as the hull waterline length. The phase velocity for deep water is:
v = (g * Wavelength / 2 / pi) ^ 0.5

Wide, heavy hulls require a huge amount of power to exceed their "hull speed". On the other hand light, narrow hulls need much less power to exceed their hull speed. In the limit, a thin plate does not create a wave; just skin friction.

So if your proposed cat is running with ocean waves that are doing 20kts then it will not need a lot of wind assistance to get up to that speed. You would need to add drag to slow it down.

Rick W.

[Richard Atkin]

Thanks Rick :)
So I have to add drag....
coooool
I'd like to see how it goes on a lake on a windy day.

Wow, J is doing study plans now. I'm just going to check that out....

Cheers
- Richard

[JCD]

All hulls have a "Hull Speed" by definition. It is the speed where the boat speed matches the phase velocity of a wave having the same wavelength as the hull waterline length. The phase velocity for deep water is:
v = (g * Wavelength / 2 / pi) ^ 0.5

Rick W.

Hello Rick...

Ooooohhhh... math. :eek:

Rick...where did you get that one? If I saw it, I forgot it. Is that the same as the "base speed" formula that I have in my final design figures sheet?

What is G? Is the wavelength measured by the usual manner when the bow wave reaches the same distance as the stern wave LWL^.5 * 1.34?

Thanks

J:cool:

[Guest625101138]

Hello Rick...

Ooooohhhh... math. :eek:

Rick...where did you get that one? If I saw it, I forgot it. Is that the same as the "base speed" formula that I have in my final design figures sheet?

What is G? Is the wavelength measured by the usual manner when the bow wave reaches the same distance as the stern wave LWL^.5 * 1.34?

Thanks

J:cool:

Your formula is the same as the one I have shown just that your version has a confusion of units but is most quoted. In the formala I have shown "g" is the gravitational constant - 9.8m/s/s MKS, or 31.8ft/s/s Imperial.

If you Google "ocean surface wave motion" you should find the derivation of the formula somewhere.

My understanding is that Froude was the first to make the connection between wave phase velocity (or celerity) and the rapidly increasing drag on a hull - hence "hull speed".

Rick W.

[Pericles]

Richard Atkin,

Enjoy this. No planing, just length X beam.

http://uncutvideo.aol.com/videos/cabce7fe77982ed5cbb7fcdf0dd91825

Pericles

[masalai]

That is why the mono's wont let us play in their races - when the cruising cats can "kik ass" in their racing divisions.... :D :D :D :P

[Pericles]

M.

I cannot get enough of the Gunboat video. I play it at least 4 times per day. Haven't you slept yet? It must be 11 AM there? :P

Pericles

[masalai]

9:25am, been up since 5 ish

Bloody drizzleing rain, no guts in the clouds as there is quite a solid wind-shear above the clouds stopping the formation of something useful, as the radar indicates it peeters out near our smallish (height) ranges

http://mirror.bom.gov.au/products/IDR082.loop.shtml?looping=1&reloaded=1&topography=true&locations=true&range=true&observations=true#skip

[JCD]

Richard Atkin,

Enjoy this. No planing, just length X beam.

http://uncutvideo.aol.com/videos/cabce7fe77982ed5cbb7fcdf0dd91825

Pericles

Tee Hee...I feel like crying.
Did you see what THE GREEN LANTERN did to them?:) :D :D :P :P

J:cool:

[Pericles]

JCD,

Nope, show us what Green Lantern did please,

Pericles

[Pericles]

M,

Thanks for the link. That's an amazing service you have there. AFAIK, a real time coastal radar weather watch is not available in the UK. I expect someone will put me right, as the facility would be mighty useful.

Pericles

[Pericles]

JCD,

Have found the pdf for Green Lantern on Catamaran Evolution thread. Very informative. I realise you might be joking about the superior performance of Green Lantern in comparison to Gunboat 62 video. :D

I like the Green Lantern, no mistake, but http://www.deltayachtsbrokerage.com/news/YWorld_gb62.pdf

It's just too much. http://www.deltayachtsbrokerage.com/news/boty.pdf

Pericles:D

[JCD]

JCD,

I realise you might be joking about the superior performance of Green Lantern in comparison to Gunboat 62 video. :D

Pericles:D

Hello Pericles...

Not joking...just dreaming.:D

J:cool:

[Richard Atkin]

To make the boat even more fun....I flared the hulls a little more to make room for 2 more hatches. (still the same below the waterline). The space between the hatches is a dining table for a couple....you know.....dinner by candle light. It's also much better for fishing. The hull deckline is exactly the same height as a dining table (measured from the false floor).....good for sitting while eating or standing while cooking. The opt hull shape provides ample width for a floor to stand on, while the small hatches support your body while you are standing.

Imagine watching your food being cooked by someone else while you lie back on a soft mattress.....watching the water wizzing by.

When your head is low, you feel closer to the water like on a small boat....holding on to that 'raft on the water' effect has always been important to me.

Can't think of how the boat could be any better....except brighter happier colours (shame Freeship doesn't have better lighting).

[Richard Atkin]

I liked the Gunboat video. Gotta say though....I was impressed by the speed of the monohull!! Also, the cat was taking it's wind....but don't worry....I will never defend a monohull LOL :D I didn't know there was an age old war between monos and multis....until I came onto this forum.

[masalai]

Richard, NZ is a unique place where that ******** is limited to non-existent, Where there are plenty of competitors, the mono boys seem to object loudly to being out paced. Even the Brisbane Gladstone has split (spat out the multi guys) & little media coverage too sadly - unless a disaster is caught on film.

I would love to visit but still too cold. . . Global warming is my only hope???

[Richard Atkin]

apparently NZ is supposed to be the last place that will be affected by global warming. Another reason why I'm off to LA.

[Pericles]

More very useful information about construction is available at http://www.mecat.com/indexpower.htm

The P-45 regular updates for 15th October 2006 reveal an unusual (to me) underwater hull form.

Pericles

[customerservice]

To: Richard Atkin
RE: Anyone had any experience with Chromaveil? Do you think it would fade away after one week in the sun and salt water? I like a worn out look, so maybe a bit ...

The Chromaveil product will not fade or be affected by salt water. Those issues would be a function of the resin and not the veil. If you have any questions regarding our products please don't hesitate to ask. My direct email is customerservice@fibreglast.com.

Have a Great Day!

[masalai]

Pericles, that is very similar to my hull-form, except the hulls are so close together it may as well be a mono!

There must have been something different or not using hull optimisation (I doubt that would have been missed).?????? and 22800jbs is 10.3 tons & mine is 7.5 metric tons? I dont understand - Pays to read the whole article - instead of going off half cocked.. :D :D

It still seems to have huge hp (2 x 160 hp volvos) Back to my numbers.... & some more model testing, just to be sure!

[Pericles]

M,

The P-45 is 42' 62 LWL and 18' beam, but it's value to you and me is the acquisition of knowledge, as always.:D

Take the matter of weight. She's built by vacuum infusion of Core-Cell with catalysed vinylester, which indicates to me how heavy that method seems in comparison with Epoxy/PVC foam. Gunboat 62 is carbon-Kevlar-epoxy. I am quite saddened that the OSSA diese lelectric trial was not satisfactory, but the 160 hp Volvo diesels do give 25 knot performance. if required. We live and learn.

Pericles

[masalai]

Yes weight does not necessarily come from the shell, as to bring the test platform to designed weight quite a bit of ballast was added...... I guess the clientèle must be demanding solid teak furniture & finish, every kitchen appliance built in and all that domestic consumerism that is un-necessary additional weight. 300 gal of fuel is less than half of my fuel tankage.
I am not keen on Kevlar because of the reputed claims on this net of it being a pain-in-the-arse to fix/repair after damage.

You & your love affair with gunboat - buy one!! and be happy, but 62 ft may be a little big for "empty nesters" so wait for the 42 or 38 to come into production?

[Pericles]

M,

Empty nesters! If only. House prices in UK are ***king stupid and the family house is to be sold and used to prime the pumps, so to speak. My sons are 25, 19 and 16. Actually, I don't mind so much as long as there are a few quid left for me to build a boat to live on. I've been divorced over 12 years, so no probs there.:D :D

Pericles

[Richard Atkin]

Hi Guys. Here's some more pics to help you visualise the effect I am after. It's a Hobie beachcat on steroids. No bulky floating hotel effect. It just feels more fun to me.
The boat has canvas sun shades. Remember the central storage box can be moved out of the way.
Run your hand through the water while you sip on a cold drink.....and chat to the person who is cooking the fish you caught today, while the sun is going down, but the boat is still scooting along nicely.
Yeah I know...corny...but you get the picture.

The yellow figure is at the helm.

[Richard Atkin]

Rick, I just threw on J's rudder in a similar place to where he put his. If I want to put it there, would the curve of the hull be a problem? If it is.....do you think it would be more efficient overall, to flatten out the aft part of the hull just enough to sit flush with the rudder (similar to what you did with the bows?) Or should I just stick a rudder off the stern like your pedal power cats?
The thing is....I want spade rudders, because my tiller needs to be easy to turn. The tiller is positioned like the arm of an armchair.

Just one other thing....Would that flatness at the bows (below waterline) do a lot to stop the bows burying? Do you think it would be unwise for me to just go with the unmodified optimised hull....for the sake of maximising light air performance?

If you are busy I don't expect you to be on call to answer all my questions. I feel like I have been leaning on you relentlessly....so if I am asking too many questions....don't bother to answer the boring ones!

Cheers Rick
- Richard

[Guest625101138]

Rick, I just threw on J's rudder in a similar place to where he put his. If I want to put it there, would the curve of the hull be a problem? If it is.....do you think it would be more efficient overall, to flatten out the aft part of the hull just enough to sit flush with the rudder (similar to what you did with the bows?) Or should I just stick a rudder off the stern like your pedal power cats?
The thing is....I want spade rudders, because my tiller needs to be easy to turn. The tiller is positioned like the arm of an armchair.

Just one other thing....Would that flatness at the bows (below waterline) do a lot to stop the bows burying? Do you think it would be unwise for me to just go with the unmodified optimised hull....for the sake of maximising light air performance?

If you are busy I don't expect you to be on call to answer all my questions. I feel like I have been leaning on you relentlessly....so if I am asking too many questions....don't bother to answer the boring ones!

Cheers Rick
- Richard

Richard
I would place the rudder further aft. You should trim the top of the rudder to match the line of the hull. You would not lose much in straight line performance by adding a little rocker aft. These hulls will track like they are on rails so it will be slow to tack. You will need to keep momentum up in a tack.

My most efficient pedal boat is 24ft long. It has a draft of 100mm with 40mm bow rocker and 30mm stern rocker. It is a product of Godzilla optimised for 12kph. The rudder is a NACA0020 section that is 120mm long and 150mm deep. I estimate the turning circle at 40m. The rudder is very effective but the boat likes to go straight. By contrast I have an OC1 that is 20ft long, draft of 80mm with bow and stern at waterline when trimmed. It has a 200mm deep by 70mm long rudder and has a turning circle of about 20m. This gives you some idea of the difference rocker makes. You can work out the resistance to turning - adding a rocker reduces the turning resistance.

The small angled plane on the front of the hull will provide some lift at speed. I have found the straight keel line without flare above the waterline will bury into a wave quite easily. You need some means of getting lift. A lifting surface will provide a lot more upward force at speed than the hull buoyancy. The flared bow certainly gives plenty of buoyancy but I am not sure it is enough to avoid pitchpole.

You do not need big waves to pitchpole. I have seen it occur in quite small waves 2 to 3 ft high where the cat has simply been overpowered (giving an exciting ride) and the lee bow has just dug into the back of a wave and the crew catapulted through about a 15ft high arc at the back of an 18ft cat. It is more likely when the boat is outpacing the waves and does not lift up the back of a wave. As soon as the bow buries the stern gets lifted by the following sea, the sail pressure increases as the boat slows down and over she goes. So these hulls need to have ability to lift out of a wave.

Rick W.

[Fanie]

Hi Richard,

I see 'people' lying all over the boat ! And one GREEN one too ! From outer space or just sea sick :D

Oh do provide for oars... you could always play some beaty music in case there's no wind. Otherwise you could get a nose bone, paint some white stripes all over yourself and hit the drum so they's row in tune.

Reading Rick's last post you better add some safety belts too unless it's going to be part of the fun getting throwed through the air every now and again.

[Frosty]

Thats a tiny mast. I would definately lengthen that a touch.

[Pericles]

"While the sun is going down, but the boat is still scooting along nicely."

Nice idea, but where are the navigation lights and usually the wind drops at sunset? :D Then the air gets chilly, the passengers start to panic and sharks begin to circle. :P :P

An outboard, an outboard, my kingdom for an outboard!

Pericles

[Richard Atkin]

Thanks again Rick. Yep, I'll give it a little bit of rocker and move the rudder aft. And I'll keep a lifting surface at the bows. If it's still a bit dodgy.....then I'll ask the crew to keep me company at the back of the boat. Hopefully they'll be scared enough to do as they are told.

Fanie, the way you write...you really make me laugh!
But hey....I DO want to use oars. I had that in mind when I was adding the extra hatches. There will be 4 rowing ring thingies attached for each hatch-slave. It's not as dumb as it sounds. The oars can be used for pushing off shallow ground, or pushing off a pier or other boats (when no-one's looking) and just for fun if someone feels like stretching their muscles a bit instead of listening to the drone of the outboard. Rowing to a beat.....sure thing!

Frosty, thanks for your insightful comment.....you're not supposed to be looking at the length of my mast

And Pericles.....there will always be the odd night to remember, warm with a little breeze.....it does happen. Or a nice sea breeze in the middle of a summer day....I guess you wouldn't know cos you live in grey old London....I don't know why you don't move to the sunshine

And besides....for the last time....MY BOAT IS NOT COLD!! It has TENTS.......WARM TENTS OK!? :D I can't be bothered drawing them up on Freeship. It took long enough doing the freakin aliens

[Pericles]

Richard,

I grew up in windy Wellington 1949 to 1953. My father was the MD of a Glaxo company that built a factory in Island Bay that is now a Marine Research Laboratory. I went to Marist Newtown from age 6 to 10. My teeth were drilled at the Dental Hospital by nurses being trained to work with treadle operated drills in the bush. We returned to UK on SS Strathaird.

I do NOT remember any sunshine in Wellington. :D :D :D

Pitching tents. Where do the tent pegs go and won't the rig get in the way?

Pericles

[Richard Atkin]

Wow, that's interesting Pericles. I grew up in Hawkes Bay. Lots of sunshine during the short summer....better than Wellington, which as you know is just crap for sailing.....can't even go to the beach without getting that nasty wind chill......and the water is ALWAYS cold. It's almost as bad as London.

I spent a year in Australia and hated coming back to NZ. I love the heat. I was tossing up between living in Queensland and Los Angeles. LA was my choice in the end because of work arrangements I have made over there.

Queensland is such a nice place though.

Oh the tents....you can read about that a few pages back in this thread. They will not be difficult to incorporate into the design.

[Richard Atkin]

Pericles, tents in post #119

[Richard Atkin]

Hello to any new viewers. Here is a quote from an earlier post in this thread: "When sailing at night, 6 passengers can sleep while 2 remain at the helm. The lid of the storage box is stored on the rear net and the flat part of the box is used to elevate the helmsman's cushion. This allows him to see over the 3 low profile tents (not shown) which cover the 3 sleeping couples."

As I am a graphic designer, it would only be fitting for me to do some proper and final illustrations of the boat, with full rig, people smiling, one of the four summer tents erected, a nice blue sky and calm sea.....etc.

Unfortunately I can't be bothered.

My brother looked at my boat design today. He said it looked scarey and creepy. Not the kind of place he would like to be. He also said "get rid of those f... aliens"

Well, it doesn't surprise me that cruising catamarans are sold at boat shows, after the customer simply strolls through the luxurious cabins and says "I love it....I'll buy it". People buy houses in the same way. And then regret it.

Just rambling......

Don't ever build or buy a boat or a house, while you are looking at it from a purely intellectual point of view. And don't ever think that a toy will bring you a revolutionary kind of happiness. It won't. Gotta place your priorities on the deeper feelings.

(sorry...I am tired and am just writing whatever comes to mind).

Goodnight

[JCD]

To: Richard Atkin
RE: Anyone had any experience with Chromaveil? Do you think it would fade away after one week in the sun and salt water? I like a worn out look, so maybe a bit ...

The Chromaveil product will not fade or be affected by salt water. Those issues would be a function of the resin and not the veil. If you have any questions regarding our products please don't hesitate to ask. My direct email is customerservice@fibreglast.com.

Have a Great Day!

This sounds like formica but in a cloth?

J:cool:

[Richard Atkin]

Hi J. I've been away on holiday. I don't know anything about Chromaveil. I have barely looked at the product. I don't care if it is made of pidgeon poo as long as it lasts. :D

[Richard Atkin]

Rick, my brother has informed me, after reading an article in Popular Science, that there is a new solar panel material that has not only been invented (secretly)....but is actually being manufactured now. It is thin enough to roll up like a sheet (OR SAIL), and provides a net power output one third the cost of coal (the capital expense of the solar material has been factored in to this number).
Just thought I should mention it in the unlikely event that you didn't already know :)

[Fanie]

We know about those solar panels, been waiting for them forever. I have my doubts about them wrt the amount of power they would supply, may not be much more than what the current ones do but we'll see.

All solar panels efficiency is very low, if one could double (or better) that it may well be really worth our whiles to begin thinking in the lines of electrical driven boats.

[Guest625101138]

Richard
There is a thread on this site about it.

It looks like it is less efficient than conventional panels. Not a problem if you have heaps of open countryside but somewhat precious on a narrow cabin top.

I was desperately trying to buy a Sanyo panel but they do not seem to be actually available. I have now changed to a Sunpower 220W panel in a side-by-side configuration. It fits well with the way the boat is evolving with a bit more beam. Preliminary canin top for 6 panels is shown in the attached.

I should be able to have a close look at one of these panels in Melbourne.

Rick W.

[Richard Atkin]

Rick, would you mind posting an fbm file?

[Guest625101138]

Rick, would you mind posting an fbm file?

Richard
This is a development from my full model that had the internal layout. I am still not happy with the looks of the cabin but this is the basis of the hull design and strength calculations. The canopy over the cockpit it just fiddling about. I will be able to extend the cockpit if I provide some guarding between the turbine blade and cockpit so I am yet to resolve this.

This hull is now 12m with overall beam of 1.8m. Displacement is 1100kg and this should be possible with composite panel construction. There is a long slender keel that will hold 8 off 12V batteries in series parallel configuration for 48V system.

You will see the KMt is good for such a narrow hull - thanks to Godzilla. Having the 250kg of batteries right at the bottom gets the CoG low so it has very powerful righting moment for its displacement without need for a deep keel.

Rick W.

[Richard Atkin]

Rick, I like it. I think it would have a fun feeling (spent a while trying to imagine what it would be like to actually be in it on the ocean). You would feel close to the water and I think this creates a fun feeling.

If you decide to keep the front shape of the hull and the upright windscreen, then I would give it a name relating to seahorses. (the shape reminds me of a seahorse).

Looks like pitching won't be a problem, but do you think it would roll around a bit? It looks to me like you have taken a monohull to the limit of slimming. I guess you would need to be careful if you have lots of people onboard.

[Guest625101138]

Richard
Our interests in boats are at either end of the social spectrum. I want a safe and secure means of transport for overnighting with a couple of people - four at a pinch for day sailing. You want a fun-parlour on water for the whole footy team that will be sailed in calm water and beached overnight.

I am not overly impressed with ocean-going boats that rely primarily on form stability unless they are getting up over the 40ft mark. These end up being big and expensive. More worry than my means affords me for casual use.

I like the motion of a ballasted boat as they do not need to follow the top of the water. They tend to ride up and down in a beam sea rather than roll. That said the Solar-Wind boat does have some form stability with only moderate ballast so the comfort index I worked out was toward the wrong end of the scale. I will rely on my ability to adapt to it - I hope. I usually have difficulty walking on land after a few days on a small boat so my body tends to adapt. I have not been seasick since I was in my early teens during my very first offshore fishing trips in outboard powered boats. Even then I just felt a little off-colour for the first couple of trips each year. I have never been sea sick when in control of the boat.

Rick W.

[Richard Atkin]

LOL!!! "fun-parlour on water for the whole footy team" For some reason I find that very funny. You are right, except definitely not a footy team.

The only time I feel seasick on small powerboats is when they stop moving forward. (for fishing or when the engine has conked out). I get used to it after about half an hour.....and yeah....I walk sideways when I get back on land.

If I had your boat I would turn the back half of the cabin into an awning. That would create a nice transition between inside and outside, and it would create a "happy" sort of feel. But I like the front half solid.

I know I know...I just can't drop my love affair with tents :D

[JCD]

These hulls will track like they are on rails so it will be slow to tack. You will need to keep momentum up in a tack.

Rick W.

Richard...

Maybe a couple of retractable bow thrusters can reduce the radius to turn and or keep you from getting caught in irons. Look at these here. I'm sure there may be others.

By the way... I really like the way the design is coming off. Gonna have to start calling you HuckaRichard FinnAtkin.:D

J:cool:

[JCD]

I was desperately trying to buy a Sanyo panel but they do not seem to be actually available.
Rick W.

Rick,

Did you check these out? I'm sure you looked around but...

http://www.solarelectricsupply.com/Solar_Panels/Sanyo/sanyo.html

J:cool:

[Guest625101138]

Rick,

Did you check these out? I'm sure you looked around but...

http://www.solarelectricsupply.com/Solar_Panels/Sanyo/sanyo.html

J:cool:

I have visited that site before but actually tried another firm in the US that posted prices. They were constrained by Sanyo not to supply to Australia. There was a complicated way around this but after getting that sorted out they did not have panels.

I also corresponded with and phoned Sanyo in Australia who made promises that their solar panel agent would make contact. The agent never has.

All this may have been in my favour as the Sunpower panels are currently available in Australia - albiet in high demand. They have the same conversion efficiency as the Sanyo, slightly better shape for my purposes and just a tad bigger and heavier.

The Australian Government has set up an AUD8000 solar power rebate scheme and it is stressing the supply chain here for panels. Sadly the scheme is not available for powering a boat.

Rick W.

[Richard Atkin]

Thanks for the compliment J. You might be the only person who likes my design. That will change when people go sailing with me!

I can't download the pdf. I am running Windows XP. Maybe there is something wrong with the file.

[JCD]

Thanks for the compliment J. You might be the only person who likes my design. That will change when people go sailing with me!

I can't download the pdf. I am running Windows XP. Maybe there is something wrong with the file.

Hawdy...

It appears to be working. Anyway, it's at www.sideshift.com

I like the design because it's within your design parameter as you set it out. If you told me it would be used for polar expeditions, I would hate it.:(

J:cool:

[Richard Atkin]

They use tents in polar expeditions :D :D

[Richard Atkin]

J, I had a look at the side thruster thingies (instead of working). I'm guessing they would probably slow me down more than just doing a gybe. Interesting though. Thanks for the link.
I can always get my slaves to use oars for helping me to dock. If I am sailing with just my girlfriend, then I will be weary of where I intend to birth. Patrol boats can drag us in at Catalina Island! More slaves.....

[Guest625101138]

J, I had a look at the side thruster thingies (instead of working). I'm guessing they would probably slow me down more than just doing a gybe. Interesting though. Thanks for the link.
I can always get my slaves to use oars for helping me to dock. If I am sailing with just my girlfriend, then I will be weary of where I intend to birth. Patrol boats can drag us in at Catalina Island! More slaves.....

Richard
Getting weary with your girlfriend usually happens about 9 motnths before the birth. On the other hand you should take care and be wary of hard projections when berthing the cat if you are in a rush to get your girlfriend to a hospital to give birth.

Rick W.

[Richard Atkin]

LOL!! :D Thanks for the spelling lesson Rick.

[JCD]

Richard
Getting weary with your girlfriend usually happens about 9 motnths before the birth. On the other hand you should take care and be wary of hard projections when berthing the cat if you are in a rush to get your girlfriend to a hospital to give birth.

Rick W.

ROFLMFAO!:D :D

I'm crying from the stitch. I knew there was some humor in there somewhere.
OMG... stop it...you're killing me. It's all true though.

J:cool:

[Richard Atkin]

I have come to the conclusion that I am just not man enough to be a true cruising sailor. I am more like a reptile. A lizard-like playboy. I want to lie in the sun, and do nothing....except eat and drink and talk to my friends and soak up the atmosphere of the ocean on a sunny day. Action time is when I hit land.

So.....I have decided to forget about storm tents. I don't even want the bimini shades. (they just create an enclosed feeling that I don't like. My architecture software is very good for simulating the feeling. It allows you to walk around the boat at any height or angle in true perspective (not zoom).

I will pick the weather and if we get caught out, we will all have to get into some good wet weather clothes (always stored onboard) and just stick it out until we reach land.

No brave journeys from one country to another. No sleeping provisions. I am a daysailor. So I will stop calling my boat a cruiser.

I guess it's time for me to shrivel up and fade away now.


- Richard

[JCD]

I have come to the conclusion...
...I will stop calling my boat a cruiser.
- Richard

You could cruise up and down the coast or rivers and tributaries in order to go camping. Oh yes, nearby islands also.:D

J:cool:

[Richard Atkin]

Exactly my intentions, J :)

Are you planning to do international trips? (or whatever the correct term is).
I think your boat is big enough....but only just. Any smaller and I would be worried. I've heard a few people say that they prefer boats over 40 ft for international voyages. Something to do with the boat length and the wave length.

oh...for that matter.....have you already done that sort of voyage?

[Richard Atkin]

Now that I have accepted my boat as a daysailer, everything becomes very tidy and even more simple.

No more mattresses. Just waterproof trampolines.

The central storage box is now a permanent fixture. No more mucking around with that. It will now be the water-maker and refridgerater.

The boat is tidy and beautifully balanced.....it's almost something that a child would draw....I love it.

[Fanie]

Taking the matresses off kinda take the romantic out of it. It was the only feature I liked :D

Simplifying things is always good. If the anchor doubles as a cork screw you can't open the whine bottle when you're at anchor.

Bringing the child in you out is good... you can always frame the pictures. They may become arts worth a lot of money in a few hundred years :D

[masalai]

Fanie, put good trampolines on your boat and make love thereon. You will be throwing out those old mattresses at home, & converting your bed to trampoline! In winter put a doona down first, in summer just sheets. Life is great!

New wines here are fitted with screw off tops - saves the cork trees in Spain & our beer bottles unscrew too!!!

Re last line see my first line??? :D

[Fanie]

If you sag the trampolines so they drag over the water surface... you have a waterbed ! Could make for some REAL fun.

I can see you tidied the boat up... at least the anchor is free :D

[Richard Atkin]

cheeky bastards!! :D

Here's another pretty picture that deserves to be framed

[masalai]

More cheek :D, - who is the white man? - at least ask/or get some women? - I like "milk coffee", my lovely lady is Indian!

Otherwise, an excellent product - now lets see a real one - when are you going to build such a pretty craft?

[Richard Atkin]

What the hell are you talking about masalai? lol.:D If you mean the yellow man...that's the helmsman. And yeah...Indian women are sexy. Computer can't draw those.
Won't be built for at least one and a half years. (discussed earlier in thread).

Oh....and I have decided to use mattresses after all. They would be much more comfortable than just tramps, even just for sitting. yeah sitting.....or lying.....but if anyone gets too comfortable they will be thrown overboard.

[Richard Atkin]

You know....some of you may feel the urge to fill this thread with wise cracks, and that's OK, and some of you may just yawn and hit the close button.....but all of you are overlooking the significance of this design.

Let me sober you up with some cold hard facts:

There is no other daysailing cat of similar weight, length, and sail area that is.....
faster than mine
safer than mine
stronger than mine.

I bet that sent a chill down your spine

(sail area 250 to 300 sq ft)

[Pericles]

Richard,

Use beanbags rather than mattresses. They float and they give support.

http://www.blob.co.nz/nz/home.html

Masalai,

The cork trees are being felled.

http://www.panda.org/news_facts/newsroom/features/index.cfm?uNewsID=22370

Pericles

[Richard Atkin]

Hmmm....small bean bags AND mattresses might be the trick. You could move the bean bags around to get the perfect angle for back and side support, and you can still stretch out on the mattresses.

[masalai]

Pericles, That is a very good idea, the versatility & flexibility of beanbags. The only need now is to figure how to stop them turning to dust so quickly.

Richard, better still throw out the mattress (keep the cover) and fill it with the foam beans - even better than mattresses & lighter & buoyant! Bean bags could be stuffed in small spaces in the hulls and also resist mould better than foam rubber et al.

I would give you a brownie point but I must spread myself around? ? Jeff, How much spreading to give just deserts where due?

[JCD]

Exactly my intentions, J :)

Are you planning to do international trips? (or whatever the correct term is).
I think your boat is big enough....but only just. Any smaller and I would be worried. I've heard a few people say that they prefer boats over 40 ft for international voyages. Something to do with the boat length and the wave length.

oh...for that matter.....have you already done that sort of voyage?

Top of the morning...or bottom of the night for some,

Yes I do intend to retire to the oceans where ever the wind blows and the Green Lantern floats.

You heard that? I know bigger is better out there, but I suspect that the 40 foot mark was made up by the brokers to overly enrich themselves.

I have about 20000 miles under the keel. All mono except about 1000 on a multi which is what made me go to the darkside. Something like 24 countries all together. I lost count on the inshore miles cruised. Worst trip was rounding the Cabo de Hornos, the imfamous Cape Horn, but I won't head to those higher lattitudes again although I have always wanted to make the Northern Passage.

I received an earing from the skipper after rounding the Horn as a right of passage but I still can't put my elbows on the table.:D

Thanks
J:cool: <---- J = earing which I always wear and, :cool: = glasses which I always wear too. In this case I got lucky with the "J".

[Richard Atkin]

I had no idea you are such a seasoned sailor! I sailed around buoys for a few years when I was a kid, but that's all.

[Richard Atkin]

Here's a crude representation of what the sail plan will look like. Just guessed it by eye.....measurements could be way off. It will be a little over 300 sq ft sail area.
It should probably have a true flat-top mainsail but I just think they look so ugly.

[Richard Atkin]

As you can see the sails will not obstruct the panaramic views. I don't want a huge tall mainsail because it would start to spoil the casual feel of the boat.
The dome tents can be half erected to provide some shelter when cooking while sailing. That would have a nice effect.

For me the mood comes first...performance comes second. But make no mistake....it will perform well. I'll probably fly a kite for more speed downwind in light air.

[Richard Atkin]

Rick or J
If I design my boat with a mainsail and jib which total 300 sq ft, plus additional area from a spinnaker.....
do you think it is unrealistic to expect my boat to do the same speed as the wind......
if the wind is 8 knots and I am sailing in my fully loaded boat (3500 lb displacement) on a flat lake?

[Guest625101138]

Rick or J
If I design my boat with a mainsail and jib which total 300 sq ft, plus additional area from a spinnaker.....
do you think it is unrealistic to expect my boat to do the same speed as the wind......
if the wind is 8 knots and I am sailing in my fully loaded boat (3500 lb displacement) on a flat lake?

Richard
It is not built yet so we are speculatiung or predicting. Whichever term you prefer.

With that area in the form of an EFFICIENT sail I determine you would need around 12kts of wind to do 8kts. This is on the basis of the boat sitting with level trim. It would not take much weight to do this. It might actually do a bit better if you move weight around to load the lee hull but then the analysis gets more complex.

The sail efficiency improves if the foot is closer to the deck but I do not have a means of calculating the benefit. I am sure there is someone else who has better knowledge of sails.

8kts is not much wind. This is the Beaufort description:
"Small wavelets, ripples formed but do not break: A glassy appearance maintained."
If you intend to only go out in these conditions you will not get much use out of the boat. In 8kts of wind you could expect about 6kts.

I would be interested to see what sailing prediction software produces for the hulls with 300sq.ft sails. I determine you would need around 450sq.ft to get 8kts in 8kts breeze.

Rick W.

[Fanie]

If you can get the same speed as the wind speed (or better for that matter) you would have invented perpetual motion and you could sail forever. You just have to stay in the wind. Please think of me when you're filthy stinking rich.

[Pericles]

Fanie,

Sailing faster than windspeed is common in multihulls and ice yachts etc., because of apparent wind.

http://en.wikipedia.org/wiki/Apparent_wind

Sadly, this kind of sailing is not http://en.wikipedia.org/wiki/Perpetual_motion

Sorry about that. :(

Pericles

[JCD]

I had no idea you are such a seasoned sailor! I sailed around buoys for a few years when I was a kid, but that's all.

Richard,
Cautious is a better word. Knowledge is gained if you survive the experience. I guess it could be said I survived a couple of "seasons" doing it so I may be "seasoned", but not like beef or chicken.:D

On a positive note, excluding the roaring forties, furious fifties and screaming sixties while rounding the horn, I have never been in any storm blowing greater than 57 mph.

That will take "caution" and planning. You need to say NO, HELL NO, when the weather window is iffy.

J:cool:

[JCD]

Rick or J
If I design my boat with a mainsail and jib which total 300 sq ft, plus additional area from a spinnaker.....
do you think it is unrealistic to expect my boat to do the same speed as the wind......
if the wind is 8 knots and I am sailing in my fully loaded boat (3500 lb displacement) on a flat lake?

Richard,

This is tough to say. I would expect that you can definitely exceed wind speed if apparant is large and drag and friction is low. I'm not sure however that you will do it if true wind is 8 knots.

Your SDR for your boat at that displacement and SA is 20.87 so it appears to be a lot of sail area at first look. You may want to consider running some of the stability formulas to see what kind of beast you may be trying to tame. The spread that I posted can help and if you have a hard time let me know and I'll run some numbers for you.

The obverse of the coin, at 8 knots, I don't think you will be in much danger of doing anything but maintaining way at 50 to 75% of true, unless everyone stands on the leeward hull to look at the fishies and a gust catches you unaware beam on while a wave converts to rolling motion.:eek:

J:cool:

[JCD]

If you can get the same speed as the wind speed (or better for that matter) you would have invented perpetual motion and you could sail forever. You just have to stay in the wind. Please think of me when you're filthy stinking rich.

Ahhhh...nope.

There are different laws concerning perpetual motion. Don't remember much about i but they have something to do with energy. Anyway, several vessels exceed wind speed.

J:cool:

[JCD]

Fanie,

Sailing faster than windspeed is common in multihulls and ice yachts etc., because of apparent wind.

http://en.wikipedia.org/wiki/Apparent_wind

Sadly, this kind of sailing is not http://en.wikipedia.org/wiki/Perpetual_motion

Sorry about that. :(

Pericles

Sorry...spoke too soon. There it is Fanie. Damnnn, I didn't know the wiki had so much info.

J:cool:

[Fanie]

I once saw this psychic woman and her glass ball with a German soldier waving a fist in the air saying 'Zer is vays to make you talk !'

Haven't tried that one yet, but seems we're stuck with Wikipedia for now.

[Richard Atkin]

Thanks for evryone's replies. I may take a look at VPP software in the near future if I have the time.....and without spending crazy money.

Rick,
I don't want to limit my sailing experience to just 8 knots on glassy water. I am just concerned about performance in light air cos I want to avoid the outboard motor as much as possible.
If the wind is stonger....like 15 to 25 knots....I will be very keen to go sailing! I don't ask about those conditions because if I have plenty of wind, then there is no problem.
If I can sail at 6 knots in 8 knots of wind, then I would be very happy. I can see myself increasing sail area though, if your estimates are right. California often has a lot of chop, even in light winds.
I keep wanting to bring the sails down closer to the deck....like you say....but I must resist the temptation because the views are more important to me. I don't want to be looking through a window in the sail.

J, if the boat is likely to be overpowered in stronger winds, I will use a second set of sails....the mast will be taller than the mainsail. As I say, if I have plwnty of wind....no problem! :)

Fanie, here's my way of explaining it. Imagine being in a baby's pram on a footpath. Think of the wind as mother pushing you. When you are on a reach, the wind is not just one mother pushing you along. It's many mothers all lined up down the footpath, and as you travel down the path, each mother waits for her turn to give you a quick push. Consequently, you end up going faster than any mother could run. :D

[Fanie]

Wow Richard. Don't avoid the outboard how ever small. Trust me on this. The main concern is firstly safety, and in my opinion if you leave the outboard you can leave the life jackets as well. If thing do go wrong (and they won't) then you need some kind of propusion. Oars don't work except to hit your buddy on the back with when he drinks your beer.

This is the second time prams and relevancy comes up on this thread... Are you pregnant or are you just worried :D I would think a set of rockets could get things moving along very well if it HAS to be a pram ;) but yes I understand. The high bar thus is to get your rig to exceed windspeed.

[Richard Atkin]

Fanie, quote: "Oars don't work except to hit your buddy on the back with when he drinks your beer."
:D:) LOL. You are funny.

I didn't say I wanted to unbolt the outboard and watch it sink to the bottom of the ocean. I just want to minimise this: hummmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm.........


As for prams, I like the ones with big wheels and suspension.

[Fanie]

It happens to be true ! Our fresh water rules states that a set of oars is compulsory to have aboard as a safety aid or secondary no third propulsion method. Now I challenge anyone to row my boat for 20 meters with an oar. They don't care how rediculous it is, as long as you have them.

You mean double the outboard as an anchor.... and a corkscrew was it :D

I like the mothers who could potentially be pushing the prams :D I know you refer to something else than prams per se, however you left the V8 out and prams nowadays do come with big wheels and suspension.

[Richard Atkin]

No...I actually do like prams. I like the tent part, and I really do like the big wheels and suspension. Some inventions are just so simple but they work so well. From an engineering point of view, I find prams satisfying to look at. Does this mean I am weird?

Don't answer that.

[JCD]

I keep wanting to bring the sails down closer to the deck....like you say....but I must resist the temptation because the views are more important to me. I don't want to be looking through a window in the sail.

Richard,

I think that your design and the above need to maintain panoramic visibility may be a very good reason for you to consider an upside down sail. The CRAB CLAW! Think about it.

J:cool:

[Richard Atkin]

J, this is very interesting. The crab claw rig only looks upside down to me when the boom is raised to spill the wind.
When the boom is pulled down to its lowest point, it looks to me like a conventional low aspect ratio rig, only the jib and mainsail have been fused together to create one continuous airfoil.
Like any low aspect ratio rig, it doesn't surprise me that it performs well on a reach and not so well to windward.
However, apparently it performs better to windward than a conventional low aspect ratio rig. Perhaps the cleaner airfoil shape is the reason for this???

The crab claw sites I have visited so far are not very specific. What is your knowledge on crab claws?

Thanks

[Pericles]

Richard,

Here are some sites I have found. Hope they are of use.

http://www.wharram.eu/cgi-bin/yabb2/YaBB.pl?num=1025071115

http://en.wikipedia.org/wiki/Crab_claw_sail

http://starbulletin.com/2007/03/06/news/story04.html

http://www.messingaboutinboats.com/archives/mbissuenovember98.html

http://www.rclandsailing.com/catamaran/design.html

http://www.dca.uk.com/articles/crabclw1.htm

You could also give some thought to Chinese sails.

http://www.friend.ly.net/~dadadata/junks.html

All the best.

Pericles

[Richard Atkin]

Thanks Pericles :)

[masalai]

Here we go - masalai drivelling where he shouldn't - If you like to see ahead think of the "Hitch Hiker" form with 2 forestays leading to each bow, use only leeward set.... :Dset both to sail directly into the wind:D then go no-where

For a laugh & think Fanie is misguided the oars he is thinking of are spelt with Wh & cost a lot more money...:P

[Fanie]

Filthy minded bugger.

Seems like both takes you somewhere. The ones I referred to is actually for use by masochists for rowing tiny canoes with (not boats), the ones you talk about takes you to heaven.

Richard, come up with some drawing to start on.

[Richard Atkin]

Thanks for more drivel Masalai :D

[Richard Atkin]

Fanie...you got in before me.....also with more drivel. You guys are the kings of drivel.....well not always

[Richard Atkin]

Back to crab claws:

I don't think we can break the basic rules. A sail that is pushed directly by the wind is best shaped like a circle, and a sail that uses lift to the limit, is best shaped like a tall narrow wing.
Because windward ability is important to me (especially in light winds), I will not use the crab claw. A standard fractional rig can always add a circle (spinnaker), when sailing downwind, so I am not so impressed by the crab claw. Also, I think the crab claw is a little ugly for my style of boat. It suits hulls that replicate the pointiness and curves of the crab claw.
I do need to consider the problems I will face with a large gap between my sails and deck. If the efficiency proves to be very poor, then I will reconsider my choice.

[Richard Atkin]

Back to the subject of drivel:
I do appreciate the drivel. I like it when helpful information is mixed with humour....so don't take it the wrong way.

[Richard Atkin]

As for oars, Fanie, I agree they are terrible when you are trying to get somewhere in windy wavey conditions. But in becalmed conditions, with super-duper efficient hulls, and FOUR oarsmen being whipped by my girlfriend (imaginary...I don't have a girlfriend right now), I would expect the boat to move quite well, at least for berthing.

[tcpbob]

On the subject of "crab claw" sails.. I published an edition with the warram cat "rapa nui" on the cover with crab claws. The cover photo of that boat is credited with making that edition the all time favourite for download, about 25 thousand so far not counting the 10,000 printed. Further more, the rig is incredably easy to construct and maintain. Short mast of native timber with bunbles of bamboo for spars. I asked the skipper and he was impressed with the rigs ability. And it is great lookin!! The pub is a pdf 1.86meg
www.thecoastalpassage.com/papers/tcp22.pdf
Also john hitch design is worth a look. His latest boat "X-it"uses headies only, no main. three furlers at the bows..

[Richard Atkin]

Cheers Bob I'll check it out.

Fanie, here is a view of the bottom of my hulls, to show you why I think rowing is an option. Think 4 guys could row that for a short while....even if it weighs 3500 pounds? I think so.

[JCD]

What is your knowledge on crab claws?

Thanks

Hello Richard...

My knowlege is limited to the study by Marchad and other published works. Nothing hands on. The form is 1.7x better than the standard marconi on any point of sail. Its weakness is pointing.

Conversely, all sails suffer pointing, but the CLAW performs like being in irons.
I like the sail and it has received a bad rap only because of one deficiency...albeit an important one.

I will however play devils advocate and attempt to present a defense on its behalf, based on my own experience which has been gained from some pretty knowlegable and radical "time management" skippers that play every puff on the water.

Marconi vs marconi, sister vessels to the line and pound racing to get from point a to point b with the wind on the nose. The vessel that sails closest to the wind or rhum, wins hands down everytime. That appears to be the accepted truth, but it isn't accurate.

If you deviate from rhum by x degrees and "zig-zag" more often you can beat the sistership which is sailing closer to the wind even if the distance is greater. It's true. How is it possible? Ahem, mathematics and, I have witnessed it. Here is the formula.

If the "percent" of gained speed is greater than the "percent" of increased distance, the sister ship falling off farther will get to point b from point a first. Guaranteed every single time. It's true and I challenge anyone to "prove" otherwise.

For example. Distance from a to b is 100 miles, b is directly on the nose as is the wind. Vessel 1 cuts a rhum +/- 10 degrees off, and runs at 10 knots. Her sister cuts a rhum +/- 20 degrees off, gains 9 extra miles to point b and runs at 11 knots. The gain in distance as a "percent" is 9% and the gain in speed as a percent is 10%. Since the percent of speed is greater than the percent of distance, the sister ship will get there first every time assuming conditions remain the same for both.

Now, on a catamaran where gains of speed can be large as a percent and the CRAB CLAW with 1.7x better efficiency than the marconi, I am prepared to bet it is a formidable sail. The problem? You are going to be tacking a hell of a lot more. The tracking will look like a zipper. That's my take on it.

Zippering may not be for you since you want to layabout, but now, you have another weapon in your arsenal in case if someone wants to race the ATCAT. :D

Also, I just wanted to demonstrate that the sail shouldn't be blamed for its failure to sail to windward as much as the skipper that fails to fall off just a bit to gain more speed because he is hell bent on sailing as close to the wind as possible.:mad:

Will the marconi take out the claw in a triangular course? Yes and maybe, depending on how busy the claw was kept up to the downwind leg. Will the marconi fare as well in all other conditions with a knowlegable and flexible skipper handling the claw? I don't think so.

That's my defense and contribution.

Thanks
J:cool:

[JCD]

Cheers Bob I'll check it out.

Fanie, here is a view of the bottom of my hulls, to show you why I think rowing is an option.

Richard,

Rowing is not an option. No skipper is considered proficient on any size ship, with any sail area, or amount of power until the oars have been mastered under all conditions. It is the most fundamental form of survival on the water.

No, no one can row a tanker, but everyone must be able to row the lifeboat before they get to navigate the tanker.

J:cool:

[masalai]

JCD, I concur... and no need to tack so often, unless in a tight channel, just make longer boards. :D

Can also be demonstrated by vessels equiped with a capacity to measure VMG to wind. The faster that speed the best angle to point.

Using a gps set a point 100 miles to windward at the start & measure velocity to mark! all too easy.....

In a bouys race, plot the leeward rounding mark & the windward mark, measure velocity to next mark. Done and be amazed......

[Richard Atkin]

Wow I'm really not sure now.

If I used a typical marconi rig to sail to windward for 6 hours to reach an island, would it be realistic to expect to do the same journey with a crab claw in no more than 7 hours?

The websites don't give that kind of perspective :confused:

[Richard Atkin]

Rick, do you have an opinion on the crab claw rig?

[JCD]

JCD, I concur... and no need to tack so often, unless in a tight channel, just make longer boards. :D

Can also be demonstrated by vessels equiped with a capacity to measure VMG to wind. The faster that speed the best angle to point.

Using a gps set a point 100 miles to windward at the start & measure velocity to mark! all too easy.....

In a bouys race, plot the leeward rounding mark & the windward mark, measure velocity to next mark. Done and be amazed......

Masalai,

Damn...I guess that would take the edge away from the handicapped.
It sounds right. Back then these skippers did it in their heads. The less learned like myself, had calculators and charts with little cards that gave you added distance per degree etc.:(

J:cool:

[masalai]

Hi JCD, Sorry to upset your apple-cart, those gauges have been around for ages, bit pricey then...... the math is quite simple trig stuff.

Need: heading (assuming no side slip - but if consistent not important), apparent wind direction, boat speed (thru water, as considering cross & other currents make the exercise more complex), wind speed.

From that is calculated true wind direction & speed. now knowing wind direction you have your distant point to head to, then compare actual speed against course offset to give heading velocity - ie velocity made to windward.

To a nearer marker, additional calculations need to be done, ensuring you do not pass optimum tacking point to make that mark...

A way to "race yourself" to see weather to point higher or ease off to get to windward quickest. - similar to or part of the "tuning" process.

That is much simplified, but with basic math can be figured out. Haven't done it for ages so probably a few redundant extras in there somewhere :D

Handicaps usually rate the hull (sometimes include in-experienced skippers et al...)

[Richard Atkin]

J, the crab claw is a fascinating rig. I'm glad you mentioned it. I've been reading more about it. Apparently the sail can cause steering problems....like extreme weather helm downwind. James Wharram found it difficult to handle in one of his experiments, and some others have said similar things.

There's no doubt it is a powerful sail. It's not an airfoil at all. It's more like an air-brake. Just a flat surface that creates a powerful vortex. Hence, it fails abruptly at 45 degrees to the wind.

Because of the handling problems, and the 'antique' appearance, I think I will watch the development of the crab claw from a distance, but use a marconi rig on my boat. Also it seems that the crab claw would create an annoying obstruction to the forward view.

A lot of people love the look of old boats. I think they look a bit depressing. I like the look of modern cats, especially ones with the mainsail rounded at the top (not so modern anymore). It just has a cheerful appearance to me. They don't necessarily look elegant or stylish...but they look 'sunshine-happy'. The crab claw looks like an ancient hang-glider that crashed into a boat, somewhere in asia on a lonely grey sort of day.

I'm sure there are sailors who will be appalled at my 'lack of taste'. :D

- Richard

[Richard Atkin]

I'm thinking a low aspect ratio rig could be the way to go. Here's why:

I would like to sail fast without daggers

I don't like the feeling of a skyscraper rig towering over me

bearing off makes a nicer ride than beating, and you'll still get there in good time

The power of the mainsail is easier to manage

Better for reefing (roller furling jib)

Low aspect sails are better for all round performance other than sailing directly to windward, which is rare when cruising.

Less strain on rigging and hulls

Less healing moment



If anyone would like to comment on this choice of rig, and tell me why it's a good or bad choice, I would appreciate that very much.
To make the rig perfect, I should be able to just keep reducing the size of the jib until the weather helm is correct. (assuming the centre of sail area is too far forward at this stage).


mainsail: 220 sq ft aspect ratio = 2.5
jib: 160 sq ft aspect ratio = 3.45
total sail area: 380 sq ft
mast height from waterline: 29 ft

[JCD]

J, the crab claw is a fascinating rig. I'm glad you mentioned it. I've been reading more about it. Apparently the sail can cause steering problems....like extreme weather helm downwind.- Richard

Hello Richard,

Just giving you the claw as food for thought even though it may not pan out for you. All sails, some more unbalanced than others, will cause lee or weather helm, ergo, the more difficult steering problems, some more pronounced than others. The variables causing these issues are many and can be overcome in many different ways.

How about a ketch or yawl form for powering, with or without the claw?Excellent balance of sail, lower CE, lower areas to handle and, if you use the claw and it develops steering issues, then the mizzen could be used to balance the helm. Shoot, the mizzen can balance the helm so well it can even be used as an auto pilot. The sloop is not the final form for all designs.

The old man taught us to maneuver without any mechanical power whatsoever. He would get in and out of a crowded marina, hook or unhook a mooring or come along side or leave any finger by just using his well reduced main for acceleration/decelaration or brakes. It was unbelievably amazing. I never attained that level of confidence nor did I ever get to that level of execution. I did however manage to do it all correctly in a dinghy although there may have been 1 or 2 spectacular tangos with fixed structures.

Just some more food for thought to keep you flexible.;)

J:cool:

[Richard Atkin]

Well J, I think you just might have me sold on the crab claw. I keep coming back to it and it really does have a lot of big advantages.

I don't like the appearance as shown in the attachment, but I can easily give it a 'fun' attitude by giving it coloured stripes on the sail that follow the lines of the spars. I would do it nicely....not too loud.

If I can get the appearance to my liking, then that's the only real hurdle, because I like everything else about it.

I love the way the spars can fold together in a few seconds, to lose all power. Great for pulling up onto a beach and just relaxing.

I haven't rendered the crab claw in my 'walk through' architecture simulator yet, but I think the forward view for passengers should be OK.

If what people say is true (by people I mean Marchaj, people in this forum, and various boat designers I have been reading about), I guesstimate that the crab claw I have shown will push my boat at 8 knots in an 8 knot breeze, on a reach, in a flat sea or lake.

Apparently if you can get the thing to provide upward lift, like a kite, it can even help to prevent pitch-poling in windy condtions.

Because my hulls don't turn easily, my boat may be more able to handle the weather helm when running in strong wind, and I'm sure there must be ways of pivoting the sail to minimise this.

After reading more about cruising, I accept your argument that windward ability is not so important....especially in the case of the crab claw.

The loads on the hulls and rigging are very small, not just because of the low centre of effort, but also because the rig is 'bendy'. With the right modern materials, the main rigging should last a life time (like a windsurfer). Ofcourse all the little fittings will need to be checked over.

When the time comes to replace the sail....cutting out a new one would be child's play, as it is best when it is sewn completely flat.



So in other words....WOW!!.....what a sail. I guess the polynesians, or micronesians, or whoever they were.....weren't mucking around all those thousands of years.

Thanks for taking the time to enlighten me on this subject, J :)

[JCD]

Well J, I think you just might have me sold on the crab claw...

Richard...

Whoa! That looks pretty nice on there! You're becoming pretty good at Freeship. If you set the tack higher so that it is above sitting headroom you will still lose the plate effect but at least you have the panoramic view again.

Go easy on purchasing what I'm selling. The claw is still very underdeveloped to make a significant contribution to "our" way of sailing. It may have served the poly's and micro's well because of their prevailing winds, maybe offshore and inshore winds, I'm not sure. They may not ever had to go up/down wind for all we know.

Pointing ability is not as important for some, but it is important nonetheless. I don't really think that too many prudent skippers find themselves trying to beat off from a lee shore and I don't think that you may find yourself in that situation based on your cruising model, but it is nice to know that you can if it does happen.

I was always told to head for open water if a storm is imminent and you cannot reach the shore 2 days before you get hit. Even then, I was told I have to be 100% certain I can get in safely and have her storm anchored before the storm hits. I'm sure they have all kinds of rules of thumb for a safe distance offshore, but I think I would attempt a minimum distance of 24(Hull speed)(Beaufort number of the storm).

For me, if worse came to worse, I would drop anchor the minute the depth allows me a scope of 12:1 and then drop 2 snubbing anchors at roughly +/- 30 degrees to the first so that shifting winds will drag the snubs and reset them but so that the main anchor bears all the loads without dragging. Then I would go to motors and make every effort to keep her headed up on the closest snub and reduce the loads on the secondary snub and primary anchor. Even if they lined up, there are 3 anchors holding her to the bottom. This whole explanation is oversimplified and much more is involved. I left out the part about enough radius room to swing and associated fear. You can forget about sleep being that close to shore.

Don't be in a hurry to make a decision...look at all the other sail forms and get enough data so you can make an informed decision. I chose to make a simple "argument" for the claw, but I can also make one against it just as easily. I won't.

J:cool:

[JCD]

Hi JCD, Sorry to upset your apple-cart, those gauges have been around for ages, bit pricey then...... the math is quite simple trig stuff.

Hello Masalai,

Yes they have been around and were prohibitively expensive back then. I am a dinosaur becoming extinct. Learned everything I needed without all the "tecky" gizmos. The mathematics was not as simple as you have indicated however. Lots of numbers to solve for sextant readings and the log deployed over the stern on a rope didn't make things any easier. Ever try a moon sight or sun sight? Different calculations for those you know.

I guess I will have to make time to "learn" the technology and trust that it will not fail when needed most. A better idea would be to have the tecky stuff to confirm my own calculations. After all, if my mind stops working while I'm out there then nothing else is of consequence, so accurate position won't mean diddly squat.

J:cool:

[masalai]

Definitely no sextant work needed. Inputs are wind direction, wind speed (masthead instrument), hull speed (paddle wheel thingie) and display usually gives speed & log data. That is all to do the maths, which can be done on a calculator - but B&G used to have it worked out to give VMG to wind as a continuous (live) feed. Still available from other suppliers for a reasonable amount.

[Richard Atkin]

Hi J. I think I have made a decision, and then I change my mind very easily, so I don't think there's any danger of me jumping in too quick. It's not just you selling me the idea, it's other people aswell. I haven't read of any naval architects who think the claw is a bad design, and many of them agree that it's performance is competitve with the bermudan rig.
I am close to being sold, but I still need to 'get a feel' for what it would be like onboard (using my architecture program). That is very very important to me.
If I can imagine it having the right atmosphere, then I will probably at least test the rig on my boat, because the rig is so cheap to build. If it doesn't work out, then I'll change the rig to something else.
I will leave all of the complicated testing and calculations to a naval architect. I am the 'test pilot'...not the engineer.



Just one question for you: do you know the basic correct positioning of the sail for each point of sailing? I see images of the claw almost 'upside down', with the leading spar near vertical....while other images show the claw with the lower spar parallel with the deck. After everything I have read, I still don't know what the sail is supposed to look like, when it is being sailed efficiently.

[Richard Atkin]

Hello everyone!

I am adding cabins to the hulls. By adding just 3 inches to the bridgdeck clearance, I can fit 2 people in each hull if they sit with their legs stretched out (facing each other toe to toe). So theoretically 4 very hardy people could sleep in the hulls, but they would be sleeping on mattresses less than 2 feet wide, so the idea is not really for sleeping. It will be comfortable for sitting.
Why am I being so stingy on space? Well....I can do all this without much compromise to the feeling on deck, which is my main priority. Cramped, but comfortable accomodation is better than none at all.

I'll send some pics that will make your heart pound, legs weak, and voice quiver.

The Atcat....coming soon. (probably change the name too)

[Guest625101138]

It is getting more like a real boat all the time. I cannot wait to see the brigedeck!

2ft wide bunks are just about perfect for average size people. Not too much room to be tossed about.

Rick W.

[JCD]

Just one question for you: do you know the basic correct positioning of the sail for each point of sailing? I see images of the claw almost 'upside down', with the leading spar near vertical....while other images show the claw with the lower spar parallel with the deck. After everything I have read, I still don't know what the sail is supposed to look like, when it is being sailed efficiently.

Hello Richard,

I don't know the correct position for different points of sail. I suspect that someone might, but everything else may be speculation. I will offer what little I remember and maybe surfing the net may give you more answers. It is a good idea to study the Sunfish or SSA Laser dinghy class as it appears that their racing sail is the claw. They definitely know how to handle that baby.

http://www.sunfishclass.org/
http://laser10.blogspot.com/2007/09/2007-laser-crab-claw-regatta.html

Since you intend to specify the sail to the designer, a good discussion around it may be a good idea.

If the sail is fully up and deployed it is at it's most efficient form. Up and deployed = flat as a plate and as vertical as possible. This will also mean a higher CE, therefore higher overturning moment and leeway. There are contradictions to "up" and "flat" really being horizontal and flat, having something to do with the aspect ratio or something but I'm not sure.

Anytime the sail is not fully up or fully deployed, (given more curvature), by any amount, then efficiency is reduced. Mind that this does not mean that the sail has been reduced in area. The ability to power he down by either reducing height or inducing a conical form is one of the best attributes of the sail because you are effectively depowering without any reduction in sail area whatsoever. I suspect this may be the reason that reef points are not needed or were ever used.

Knowing the above, all that needs to be established is how much you need to manipulate the sail in either axis so that she is most efficient for existing conditions for the required point of sail. This is the part I know little about.
Also, another attribute of claw is its ability to self steer.

Anything between fully deployed and stowed away is your pickle and I suspect that may only be learned by hands on.

J:cool:

[Richard Atkin]

That is very helpful....thanks J! Thanks for the links too. The crab claw is looking more and more ideal for me.

Here is the reshaped Atcat. I have increased the freeboard and significantly flared the hulls to allow for cabins with a little elbow room. Inside the cabins there will be back-supports and mattresses just like on the deck, but to sleep, the back-supports can be laid flat and the mattresses raised to take advantage of the flaring. This is more cramped than an old submarine....yikes!

I have removed the centre beam which was a real nuisance inside the cabins. If I use the crab claw, I don't need a centre beam at all.

To compensate for the tiny space, I would like to use plenty of large windows to let in the light and view. If the windows could open that would be even better.

My main concern is what effect the flaring will have in waves. Obviously the boat will be slower, but I hope I haven't really crippled it. If it can still do a respectable speed in light air with a moderately choppy sea, then I will be happy. Unless I get a VPP, it'll be a question for the final designer.

[Richard Atkin]

Rick,

quote "It is getting more like a real boat all the time."

bit of a double-sided compliment there :D

Thanks mate!!

[Richard Atkin]

I have also decided to raise the cabin house behind the forward back-supports. I checked it out on my house architecture software and it actually improves the feel onboard the deck. I thought it might start to get that big boat feeling....but it doesn't. It does however, when I raise the cabin house where the hatches are, so I won't do that.

[Fanie]

Hi Richard,

I'm beginning to like it more and more. The flanging of the upper hull's wouldn't slow it down, except if you run through waves where you would have to slow down in any case, but the extra buoyancy and comfort would be worth it. My boxy cat I have the fore and aft hull area flanged to the boa, add boyancy so the hull won't stick into a wave but also use the hull profile to plane upwards. Adds a lot of space in a small hull and if not for anything it would become buoyancy in the form of foam.

Keep at it, you're getting there.