Proa design [Archive] - Boat Design Forums

Tcubed

09-13-2008, 11:47 PM

Yeah i'm under no illusions about the effort required to maneuver the thing.
And yes, the sponson's upper edge is a section of circle centered on the mast step. Along that edge, is a track for the mainsheet which gives good twist control. The whole sponson offers a excellent base for sheeting the jib too. It ends up being like Russ Brown's method. The mainsheet (or really the traveller control) is freed, the jib dumped, the up board lowered, the down board raised, the main sheeted in and finally up with the other jib (by this stage the boat is already well on it's way on the new board. Short tacks would be done without the jib of course, and the central daggerboard would be partially raised to balance. I toyed with a number of different ideas, before eventually deciding Russ's system was probably as good as it's going to get.

I'm not worried about this for a couple reasons. One is i will mostly be doing longer passages where shunting is not very frequent. Another reason is that i was brought up on an engineless fifty foot gaffer, with no electricity. So believe me, i'm used to flexing a couple of muscles when it comes to sailing! In fact, most of the time, we had two jibs and running backstays so that would be six things to deal with the same as above. Well sort of...

From experience, the hardest thing is raising and lowering the endboards. To make it at least possible, i plan on making them hollow with generous (but carefully faired) holes for the water to flood them and fall out of them. Also there will be some sort of rollers that they press against. Otherwise, i know that as soon as they are under pressure they are basically impossible to move. The rest is piece of cake.

rwatson

09-14-2008, 06:06 AM

I could say good luck, but its the silliest idea I have seen.

Thats what I meant by most Proas are designed with egos - not good design principles.

Oh well - keep the proa flag flying Rob.

Tcubed

09-14-2008, 08:11 AM

Please define "silly". Are you saying Russ's design's are "silly" too? He uses a very similar rig configuration.
I don't see the ego connection either. I just think that the advantages of a proa outweigh the disadvantages for my particular needs. You see, as i've already explained, i don't mind a boat that is a bit more work to sail than other's if it gives me other advantages.
Ever heard of the dipping lug? For centuries this was one of the most favored rigs by the Scots, Irish, and Bretons. Ever tacked a sixty ton dipping lug schooner? Yet those old boys did it every day in every season of the year. I don't think they were silly, they obviously had their reasons. After all they could just use the gaff sail and tacking is a whole lot easier. But the dipping lug is one of the most efficient sails (and still is) and they knew it. So like me they were prepared to put in a bit more effort to get a bit more speed. To shunt a proa is child's play in comparison.

rwatson

09-14-2008, 09:23 AM

Purely in the spirit of stretching some design ideas here, and not trying to rubbish you, I'll do the right thing and explain my terse comments.

1) As soon as you mention "heavy, hard, tricky" in the operation of a proa you lose me. I dont think this needs to be the case, and the fact that your rig will be hard to shunt makes it much less attractive for you and others to use. No matter how tough you are, after 3 weeks at sea, I am sure you will agree.

2) In high winds optimum sail performance in a Proa is not a big concern. Your biggest problem is keeping the boat upright - the sail will can produce more power than you will need. Dipping Lugs will produce a lot of power in a decent wind - they were designed to drive heavy, cargo laden monhulls at under 12 knots. In light winds, they are bad performers. You need to generate lots of lift with well shaped sails. When the apparent wind goes forward, and the hull gets into the low teens of speed, the lug sail plan is super innefficient. I havn't seen a lug sail on a cat since the first experimental cats appeared on the Thames in the late 1800's.(No, I wasnt there, just saw the pictures :-) )
I feel you need to consider a much more aerodynamic sail plan.

3) The hull layout - without detailed plans, it appears the ama is way too close to the main hull. Since it doesnt put accomodation or control out where the weight is needed, it will either need artificial and unneeded ballast, and/or putting all your stores in hard to get at locations.

4) Your daggerboard and rudder configuation appears excessive. Rob Denney controls 33 foot of proa with two rudders, and doesnt need to think about shifting 3 or 4 boards. (by the way, I cant see any rudders on your plans, but lets take them as read)

5) It looks like the boards in the main hull will impede the sails when raised.

6) There is little all accomodation on a boat that will be "doing long trips with few tacks". What accomodation you can put there will get mixed up with sail controls. Even if you stick to the tropics, shelter from the elements is a big thing.

I would strongly disagree with your intial comments "most production boats nowadays have grave performance and seaworthiness issues". I think you are starting from an incorrect premise.

Consider, there are more production boats scooting around the world, wasting money and stuffing up the environment than at any time in history. The few wrecks and crashes that make it to the news are few and far between.
Modern designs on the whole are very seaworthy and great performers.
If you ever try to insure that proa design - you will find that Insurance companies are very sensitive about this sort of thing.

It would be great to get you into a really good Proa, and start the revolution to civilised sailing machines, because they really are the most sensible design as you very rightly pointed out.

I hope some of these comments make sense, but hey, feel free to debate any and all points. Whats a forum for eh? :-) Viva La Debate!

rob denney

09-14-2008, 10:51 AM

i have looked at harryproa and actually was pleasantly surprised that he has arrived at a lot of the same conclusion as i have.

G'day.

RWatson, Thanks for your support. Everything you say is on the money except all my boats use only two rudder/leeway preventers. More than this just adds complexity, cost and drag, You can see an old version of the 2 rudder set up in the video at http://www.youtube.com/watch?v=8chR6DAFjGA. This 50'ter/15m weighs 3,500 kgs/3.5 tons ready to cruise. It is almost twice the weight of the standard version, one of which regularly takes sight impaired people sailing in Holland http://www.harryproa.com/BlindDate/Jan_9.htm. Both boats have 2 big double bunks, covered cockpits for 8 people and all amenities.

Tcubed,
You may have reached the same conclusions as me, but your implementation of them is very different to mine. Your boat looks like a copy of Russ Brown's work.

I have regularly debated the Russ Brown vs harry style of proa on the Yahoo proa-file list for the last 5 years or so. I suggest you look through those archives if you are interested in improving your design. You should also contact Russ and get his opinions on the boats.

Couple of opther points:
Shunting a harry is easier than tacking an overlapping headsail boat and easier and safer than gybing any boat.

Headsails (apart from those on ballestron rigs) are hard work on proas. See the shunting video at http://www.wingo.com/proa/brown/video.html#video. This is the one at the bottom of the page, the other one shows how much these hull shapes hobbyhorse.

Accommodation in the lee hull is wet and in the wrong place on a boat with limited righting moment.

Leeward pods are weight in the wrong place, involve large hull cut outs in highly stressed areas, excess drag and unless they are set high will have the same affect on stability in extreme conditions as small lee hulls on old trimarans.

Proa resale value is poor for 2 reasons:
1) there are so few of them sailing. This will not change until more boats are out there sailing. This may not be so far away. The third 15m/50' harry has just been launched and the first has just been sold (first owner died just after the launch). I have just sold the 38th set of plans, the largest of which is 66'/20m. Almost half of these have been started in the last 12 months, and there is now some interest from a cruising version production builder, so maybe things are picking up.

2) Russ' boats have had some diabolical press from people who have sailed on them.

I am happy to advise you on your boat regardless of what design you finally settle on. But the best advice you will receive is to build a smaller one first so you can find out all the things that are wrong before it costs you a lot of time and money to fix them. I have built half a dozen prototypes. The first had a lot in common with yours. It was rapidly superceded.

regards,

rob

Tcubed

09-14-2008, 12:33 PM

Alright, that's more like it!

First i regret not having started out a little more precise with my topic objective. The design in this case is purely for me (selfish bastard, heh?) and my top design priorities are performance in as wide a range of conditions and seaworthiness. Seaworthiness, by the way, i think is best defined, as retaining full control of the craft in all weather conditions.. The rest is low on the list of priorities apart from relative ease of construction.

1* If i could think of an easier way to arrange things for shunting i would. Harry's system is a marvel of ease of operation, but i have certain reservations about the aero rig. Firstly unstayed masts on a multi has never made engineering sense to me (on a mono, yes, unstayed is great) as the the multi's are so stiff, and why throw away that huge staying base? With a couple of lightwieight wires the mast can be suddenly much lighter. Of course the aero rig can be stayed. So maybe i should consider it. It would eliminate the dump one jib, raise the other, portion of the events, a considerable savings in effort.

2*I'm sorry to have confused the issue with my analogy with the luggers. It was only meant as an illustrative example. My proa will not have a lug rig. What you're seeing is a fully battened gunter rig, which as far as handling is concerned is pretty similar to a marconi sail. I must however disagree with your statements on the lug rig. It is a superb airfoil at all angles, and works very well in light airs, but that is definitely a topic for a different thread.
I must say i don't understand why you say rig performance is not so important in high winds. I would say that that is when it is the most important, as the hull windage cannot be reefed, its contribution to the total aerodynamic forces becomes ever greater as the winds increase and one reduces sail correspondingly, eventually making the boat unable to make good to windward. This ceiling on +ive VMG i feel is very important to have as high as possible for seaworthiness.

3*Here i need to explain the drawing better. The way i see it, the only way a proa will have superior performance to a cat is if the windward hull is the heaviest, therefore i have all the stores in the ama-Drinking water, food, clothes, tools, gas for cooking, batteries and solar panels, spare sails, books, bicycles, the tender, as well as water ballast tanks for trim. The main hull must be buoyant so it makes sense to use that one as accomodation. The ama does not have to be buoyant so it can be reduced as much as possible to reduce windage. It still has enough reserve of buoyancy to not get pushed under if caught aback. In the main hull, there would be a minimalist kitchen at one end with enough food for three days or so and a simple desk at the other. Sleeping is in the wing, or sponson. People are light, cargo isn't. Every few days one would go across to the ama and open the apropriate watertight hatches and get more supplies, exchange books, whatever. The water, gas and electricity gets piped across. Harry has both accommodation and cargo in the windward hull which is even more optimized. Although the cargo removes some of the living space but one's stuff is conveniently at hand. Pros & cons.
The leeward hull should have plenty of flare so it resists immersion strongly and plenty of volume in the bows, so its volume really lends itself to living in, i think. Excess volume in the windward hull is pointless-might as well just go back to having a catamaran-and possibly dangerous. A high windage ama can flip you over if you allow it to fly too high and could turn you the wrong way if lying a-hull. With my design, i can leave it drifting and with all the windage on the leeward hull, i'm confident it will stay where it needs to be; to leeward.

Having said all that I take your point about hull separation. Right now it's 6M and lenth WL ama 15M and about the same for the main hull. I want to have a pretty high factor of safety against pitchpoling but no doubt i could as you say make it wider. Just how wide is optimum?

4*There are three boards, one amidships in the ama, and one at each end of the main hull which contain the rudders. The midships board is used for balancing and beating: upwind down (clr forward) then progressively raised as the wind frees (clr moves aft). The bow board does nothing till it's needed again. The aft board is all the way down whenever it is used, with its rudder, which can be hooked to a windvane. (the windvane would be set out in clean air on the ama).

5*No they don't, they're to windward of the jibs.

6*I don't quite understand what you mean. In my sixty thousand miles bluewater experience, i found that the vast majority of my time was spent belowdecks. Why be outside, where the sun beats down ferociously, the tireless breeze buffets one around and just when you're starting to dry another blast of spray crawls under one's oilies, when inside it's all calm and peace? I would pop my head out every little while, check the horizon's clear and get back to my book or radio show. If the wind changes, i adjust everything and get back inside. The only other time i'm outside is to take the sextant sight.
I plan on also having a number of hatches where i can steer and trim sails from but have half my body inside. For shunting and reefing or sail changes i must go out completely, of course, that's what oilies where made for.
I'm also hoping the flare on the main hull will make that hull pretty dry, although no doubt when the ama's bow catches a wave that will send serious spray blowing across to the main hull. This then is where Harry's proa really shines!

Now to the other point of production boats..
Have you seen those black and white photographs of ports in the middle of the 19th century? They were crammed full of engineless workboats which actually got used every day even when it was blowing blue murder. They had families to feed and a boat sitting in a harbour is a liability, not an asset. So those boats HAD to work.
Nowadays sailboats are almost all for pleasure use and do not leave the harbour in anything less than optimum conditions and even then the stats show the average modern yacht spends more than 95% of its time in the harbour.
Considering that it is not surprising there are less sailing accidents now tan then.
I do agree that most modern production boats are very well designed for what they are meant to do. Cheap to mass produce, very comfortable in the harbour with all the luxuries of life on land and lively performance in good conditions, and meant to be motored in and out of harbors or when the wind is light. They are very poor performers in light airs and in heavy conditions, because they are not designed to do that stuff. In light winds the designer expects the engine to be used, hence the typically very small sail area to displacement ratios of modern boats. In heavy conditions, the heavily asymmetrical hull with the extremely tall rig creates serious handling problems. I also find most modern production boats to be pathetically weak. None of this is surprising though, because they are not designed for punishing conditions. You're supposed to listen to the forecasts and be in the harbour when its like that. I knew this would be a controversial point when i made it, but really if people want to follow this thread we should make a new one!!
And just to be absolutely clear i am not misunderstood i want to say there are a lot of astounding designs out there which are a pride to humanity.. I'm just referring to the majority of mass produced modern boats ( almost all of which are inspired by the obsolete race boats of the IOR era ).

Tcubed

09-14-2008, 12:35 PM

Hello Rob, good to hear from you! Our messages crossed. I'll be right back with you...

Tcubed

09-14-2008, 01:43 PM

Rob , Thanks for those very nice links. The construction is A1!
Good to hear the 3500 kg for 50 foot figures almost the same as mine. Very reassuring. This gives about 32 as disp/LWL ratio. I had seen that the IDEC tri has 10.5 disp/LWL ratio, which also reassured me, but not as much because it's really quite different.

<<You may have reached the same conclusions as me, but your implementation of them is very different to mine. Your boat looks like a copy of Russ Brown's work.>>
That's exactly right, and yes i draw heavy inspiration from Russ. But it is not a copy as there are two main points in which we differ: My ama is heavier than the main hull whereas his was quite a bit lighter, and my ama is as long as the main hull and semi surface piercing, his were shorter with a lot of sheer.
I have started looking at the yahoo forum, very interesting, although the format is not quite as user friendly as this forum, or maybe it's just me...

Accomodation in the lee hull i think is preferable for the reasons of windage and volume distribution i've already mentioned, although the rig on the lee hull is probably enough to keep the machine always the right way round anyways. The biggest advantage is staying dry and having one's stuff at hand, although on the other hand i quite like the idea of all one's junk completely out of the way. I'm kind of a minimalist freak..

I very much liked to see how you set up the rudders. Very nice. I was toying with the idea of a rotating cylinder that goes right through the boat with the daggerboards going through these, but it means cutting a huge hole through the hull and is a real pain to build. I've heard people say your system looks weak but i don't agree. I think it can be engineered with the supports far apart vertically and be plenty strong. Also they are easy to inspect, maintain and repair. Further, catastrophic impact to these boards cannot rip the bottom of the hull out.

The leeward pod or sponson is nescessary in my case to be able to sheet the sails. From all my research they do seem to give a little buffer between flying the ama and whoops over she goes.. It of course makes a fabulous place for sleeping, but that is a secondary consideration. The engineering of it is tricky due to the sheetloads, especially the mainsheet. However the mast is stepped on the windward edge of the main hull so does not affect the sponson. It is also so placed that it is essentially sitting on the leeward gunwale so no hull gets reduced really. There i don't think there is any problem, just the mainsheet, which i expect will pull in the order of 15000N to 20000N as a rough guess so yes it would have to be very strong. With a balestrone rig i get rid of all that but then i need to make an even more rigid boom.

As for prototyping, i was already planning on doing a ten to one scale radio control model just to make sure it all works as anticipated. It is my standard procedure whenever i feel it is outside of already tried things.

Thanks for your input and offer, Rob.
I will have some specific questions i want to ask you in the next post.

Tcubed

RHough

09-14-2008, 03:03 PM

I could say good luck, but its the silliest idea I have seen.

Thats what I meant by most Proas are designed with egos - not good design principles.

Oh well - keep the proa flag flying Rob.

Puuuuurfect! ;)

I've been following the proa threads with mild interest. I decided that life is too short to sail slowly. :)

At first glance the proa idea looks very attractive. I admit I have not looked real hard, but I have never seen anyone address sailing dynamics and crew motion comfort in any detail.

All motion acts through the CG. The greater the distance is between the CG and the CB the greater the RM is ... so wider is better (in general). It is the distribution of weight around the CG that concerns me. As mass is moved father from the CG, every excursion from steady state requires greater stability in that axis to resist and damp the motion.

Again very generally, most people are more comfortable when subject to lower accelerations than greater. That means put the people close to the CG.

I've never seen anyone show how the drive and drag forces interact on a proa. For a proa to have equal performance on both tacks, the longitudinal CG and CB must be at 50% of LOA, correct? The sail plan will have the CE aft of the CB correct? The rudder moves the CLR aft, does it move the CLR aft far enough so a single dagger board can be used? How efficient is a dagger board foil that must have equal lift slopes when the flow direction is reversed?

Lots of unanswered questions.

terhohalme

09-14-2008, 05:14 PM

You should read these too until final decision.

Terho

Tcubed

09-14-2008, 07:36 PM

Rhough ,
<<<All motion acts through the CG. The greater the distance is between the CG and the CB the greater the RM is ... so wider is better (in general). It is the distribution of weight around the CG that concerns me. As mass is moved father from the CG, every excursion from steady state requires greater stability in that axis to resist and damp the motion.>>>

Just a quick summary. Proas just like any multihull have very high initial stability and tend to conform to the local water surface very quickly. This can indeed produce quite high accelerations, but in practice it's not nearly as jerky as one might expect. No, the axis of rotation of motions does not necessarily pass through the CG, although it tends to pass in the vicinity. The analysis of a boats motion in a seaway is actually possibly one of the most complex facets of boat design and highly worthwhile to pursue but in another thread...
Mass should always be concentrated as close to midships as possible in all boats so as to reduce the boats' rotational moment of inertia about the transversal axis to allow the boat to follow the surface of the water as closely as possible. This is important and yet rarely followed with horrendous pitching the result.

<<<I've never seen anyone show how the drive and drag forces interact on a proa. For a proa to have equal performance on both tacks, the longitudinal CG and CB must be at 50% of LOA, correct? The sail plan will have the CE aft of the CB correct? The rudder moves the CLR aft, does it move the CLR aft far enough so a single dagger board can be used? How efficient is a dagger board foil that must have equal lift slopes when the flow direction is reversed?>>>
I suggest you just make some vector sketches. As for cambered foils that have interchangeable leading and trailing edges, i don't have data on these unusual foils, but i'd guess the L/D ratio becomes about 5% worse than a similar non reversible foil.
Any one out there with graphs of this type of foil?

Tcubed

09-14-2008, 08:01 PM

Thanks Terho . Those attachments sum up the fundamentals perfectly.

RHough

09-14-2008, 08:21 PM

rwatson

09-14-2008, 08:42 PM

That was a good link to the clips in shunting the KB proa.

It was enough work with someone balancing out on the skinny end of a hull with a handfull of jib in their hands, in great conditions.

Imagine doing it in 2 metre waves or more with severe winds!!! It doesnt bear thinking about. You would be crazy to do a long distance voyage short handed. As captain of that boat, the fact that the crew wasnt wearing a safety harness would worry me. Sure, the conditions were great, but look at the scenario of the poor guy bumping his head on the way under the boat, and he could be wrapped up in the jib. Now the boat doesnt have a jib to maneuver, and it stated these were strong tidal areas.

Proas have to be able to shunt quickly and often in some situations, and as most disasters occur near land, the ability to handle uncomfortable and rapidly changing situations is paramount to survival.

The performance analysis is very interesting. It boiled down to "put the most weight out to windward for the safest configuration". I could say duuuuuh!!

When there is a racing fleet of heavily sponsored Proas on the water, all the finesse of performance calculations will be required. For the average world cruiser, being able to comfortably and safely average 15-20 knots is plenty of performance. Until then, easy and safe to control, comfortable to pilot in all conditions is the big challenge. Thats why traditional monohulls "rule the waves". It doesnt matter that you are ten knots faster as you rapidly succumb to hypothermia after 6 hours in an open cockpit. And Catamaran and Tri owners, dont even have the speed differential to be envious of.

Now, consider just weekend sailing. How hard is it to get experienced and enthusiastic crew for an average day sail, let alone getting crew fit and able enough to walk out the slippery end of a hull every say, 30 minutes to and hour, and change the foresail ?

The idea of spending much less money on a high performing, safe and comfortable world cruising machine is the end goal here. Take away "safe and comfortable " and all you are left with is another experimental sailing machine that will end up sitting on the moorings year in and year out, as another "priced to sell" object amongst all the other design dogs.

Thats why I said initially that most of the Proas are designed by "egos". The talk of whether you are two percent faster on a broad reach with a dipping-lugsail, northern hi-aspect cantilevered folderall is all pure ego - and crap!!

When a designer puts safety, comfort and sheer usability first, *then* I will start looking at the comparative performance.

Lets get some good quality safe Proa stock out there on the oceans, and prove the concepts. Go Proa Go :-)

Tcubed

09-14-2008, 09:10 PM

Rob,
If you feel you'd be compromising your designs by answering feel free to not answer some or any of these questions. I will use the term ama for the windward hull and vaka for the leeward hull, irrespective of their size or weight.

1* I notice you use a surface piercing bow on the vaka, how does this not concern you in the sense that it has very little extra buoyancy to prevent submerging?
2*I notice you like a "hump" in the middle of the vaka, why the extra volume in the middle?
3*What sort of weight distribution do you favor between the two hulls?
I have 39% vaka, 61% ama.
4*What prismatic coeff. do you recommend for the ama & vaka respectively?
I have a prismatic of just under 0.6 for both hulls and the vaka's prismatic remains almost constant throughout the range of possible heeling moments. The vaka submerges about 17.5 cM by the time the ama is just out of the water.
5*What sail area/displacement would you recommend?
I have it at about 70 and have calculated that the ama starts coming out at about 15 knt wind. Keep in mind i don't plan on any engine so i want to make sure it has plenty enough sail for light winds. This is one of the reasons i drew it with a gunter mainsail, as it allows me to put more sail but without a dangerously tall mast. Excessively tall masts can be very bad news when winds get to the shrieking stage, i find. Much rather have spars i can lash down on deck and just be left with a compact and strong mast that is not so much windage or so vulnerable whipping around where the wind is even fiercer..
6*What are your thoughts on a best compromise CLbeam/length for a 61/39 mass distribution considering the need for speed and the avoidance of overpowering (pitchpoling)?
7*Have you any stories on your proas or any proas, in big storms?

Tcubed

rob denney

09-15-2008, 10:31 PM

G’day,

Tcubed,
Russ’s boats are light(ish) compared to same length cats, but still heavy compared to harry’s. I suspect you will have the same experience. Stayed rigs, big headsails, lee pods, rudders, daggerboards, cockpits and accommodation in stressed hulls are not light, nor is the structure they require to support them.

Pumping water ballast while sheltering in the lee hull when you could be sitting comfortably under cover in a windward cockpit with righting moment to spare does not make sense to me. You should also read Steve Callaghan’s account in Cruising World of the effects of an over ballasted, under buoyant windward hull in a seaway.

The rc model is a good idea and will show you a lot about the boat’s sailing characteristics, particularly when you have to ballast the windward hull, lift and lower rudders and change the jib to shunt. It will not model the hard work of living in the lee hull for extended periods, nor the slapping of the water on the underside of the pod when you are trying to sleep. Where abouts are you? There are some rc model (and full size) harrys around the place which may be of interest.

R Hough,
There are some unanswered proa questions, but not these. Harry crew (and everything else) is located in the middle 50% of the boat. The motion is far less than on a cat. The Multihull World journalist and his sea sick prone wife who did a boat test wrote that the motion in a harry is far less than in any cat they had been on. My very seasick prone wife agrees as do the sight impaired people who sail on the 50’ter in Holland. The harry format was specifically chosen so these people could move around confidently, yet still experience high speed sailing.

I use a single daggerboard/rudder combo mounted on the beam and it works very well. Use both of them (one on each beam) if you are too lazy to lift the front one or want steering that is superior to any sailing boat, plus the ability to crab sideways off a jetty or to pinch to a windward mark. The boats are balanced on all points of sail. I suspect this is a function of the rockerless hulls as well as the location of rig and rudders. Beam mounted rudders mean no holes in the boat and as they kick up in a collision, no damage from hitting things.

Shunting is safer and easier than tacking an overlapping headsail, and far easier and safer than gybing. The harry structure is less complex than, and about half the weight of, any other multi type. There is a video of a 25’ ter shunting in light air at http://www.harryproa.com/ShuntingVideo/ShuntingLg_st.wmv The technique and ease are the same for the bigger boats. The maneuver is even easier with a una rig and easier again with a ballestron.

Terho’s numbers are excellent, but do not allow for the fact that harrys are considerably lighter than Pacific proas of similar accommodation. I suspect that making the windward hull big enough for all the extras, but still having the crew and galley in the lee hull will exacerbate the poor numbers of the Pacific proa without achieving the good ones of the harry and equalL configurtaions. I see no benefit in equal length hulls if one of them is just for storage.

R Watson,
I agree again. For “safety, comfort and sheer usability” it is hard to beat the harry set up. There are few if any cruising boats capable of wind speed in 10-15 knots with as little fuss or crew discomfort as the boat in the harry video.

T cubed,
Happy to share what I have learnt, as I am sure you are honest enough to pay me for any ideas of mine you ask for and use. However, I would be very careful about too much mixing of Russ’ and my ideas in the same boat.

1) Harry bows are not surface piercing. They have more buoyancy further forward than modern tris with the same size rig. This is due to the high prismatic, long lee hull, low weight and small rig possible with the harry format. Flared bows, imo, are asking to be tripped over and cause hobby horsing.
2) The leeward hull (Polynesian terminology is great for Polynesian craft, but a bit pretentious for western craft with little or nothing in common with them) hump is to support the unstayed mast. Stayed masts are absurd in any cruising boat, but especially so in proas.
3) I have used many balance variations, depending on the boat use. 60/40 will be fine, but suspect you will need water ballast to achieve it with the crew and galley in the leeward hull.
4) Harry’s have prismatics over 0.8. See the Russ video on hobbyhorsing for why Cp of 0.6, high cog rigs, V hulls and weight in the ends of the lee hull is a bad idea.
5) I use Bruce number as a performance indicator for proas, but it does not tell the full story as harrys tend to outperform cats with similar numbers due to lower windage rigs, easier driven hulls and less draggy water foils. The 15m/50’ harry has 50 sqm/537 sq' of sail and weighs 2.5 tonnes/tons. The one in the video weighs 3.5t as it has a bunch of add ons.
6) I prefer to look at the righting moment rather than the beam to length ratio. 15 knots is dangerously low hull flying wind for a cruising boat. Harry’s are in excess of 25. Gunters are good for dinghies, but draggy when reefed and dangerous when swinging around. I prefer a telescoping unstayed wing mast.
7) No proas in storms stories apart from Russ in his first boat, which fell apart. This was in Wooden Boat magazine. Harrys have been sailing in 30 knots in the Tasman Sea and gone in and out of some pretty gnarly river mouth bars and behaved exactly as predicted (ie no problems).

Sorry for dumping on your ideas. Even if you go ahead with what you have drawn, you may still have a more suitable boat than many of the standard production and stock plans cats currently available. Just won’t be as good as it could be. IMO.

Regards,

rob

Tcubed

09-16-2008, 12:54 AM

Many thanks for that valuable info Rob.

0.8 prismatic! I would never have guessed so high.

I am in Vieques, Puerto Rico. Right by the Virgin islands.

Vaka .. i'm not being pretentious just lazy typing.

I must say i am amazed you feel so strongly about unstayed masts on multis. Like i said i love the simplicity of unstayed masts on monos, whenever there is no jib of course. But the maximum righting moment of multis mean the unstayed mast needs to be impressively strong and the engineer in me starts screaming 'hang the ama off the mast' and akas and mast are now in almost pure compression don't have to be made so strong and hence can be lighter..Especially with that huge staying base, there's not even much compression on the mast. Obviously you've thought about this enough and still think that stays are not worth it..But why?
Telescoping mast sounds very smart but i think i would worry about jams. Same reason i worry about in mast halyards or anything in the rig that is not as simple as possible. I would say the gunter is not draggy when reefed as it is a kind of telescoping mast, definitely better than the usual marconi where none of it comes down at all. The other thing i very much like about yards is that they make the sail come down, you never have to pull it down. Remember i've done the bulk of my sailing on gaffers, so sticks "swinging" around wildly is not something i'm worried about. In fact they don't swing around, the wind always blows it out to leeward unless there's a big swell and no wind, in which case i wait for it to be in the middle of a swing and drop it on the deck quickly. if you stay by the mast there's no way it can hit you.

I include a sketch of the heavy weather sails; trysail and staysail (set on a different wire further inboard from the stay used for the jib. I think this is very efficient geometry for sailing to windward in strong wind with no, or not so much (when reefed) unused mast.

You might well be right about the weight being too much in the hull, although it's really going to be not much more than an empty shell. There are no cockpits, just those hatches i can reach out of to steer and sailtrim. I am not a big fan of cockpits, personally, only time i've sailed in a cockpit has been on other people's boats and i must say i am of the opinion that in a lot of cases they waste a lot of space and can catch dangerous amounts of water. Although i must say multis allow for the whole cockpit concept to be completely retought... As the drawing is not yet finalized i haven't done the weight calcs. yet, but what i have in my mind for accomodation will probably weigh less than 150 Kg total. No, i'm not dreaming, when i say simple and basic it really is. Call me a masochist or whatever i don't mind

I'll no doubt trim my sail area down a bit after comparing your numbers to mine. I LOVE lots and lots of sail (you can always reef) as there is nothing more frustrating than not moving for no other reason than lack of sail area. However 163 M^2 is probably a bit more than necessary even for a nutter like me.

The reasoning behind the ama as long as the main hull is purely to get a very skinny shape that will have as small a drag torque effect as possible. If i make it shorter then it must be wider and deeper. I'm concerned about it affecting the steering as it slices through wavetops and in the air in between. Additionally, i've drawn in some curve to it so when it is in the water it tends to turn to leeward, ideally compensating perfectly for it's drag torque. Obviously this will be something that i'll experiment with on the model to fine tune and see how (and how well or not) it works. The neat thing with a scale model is i can see exactly how it will perform in different wind and wave conditions. You just have to scale the wind too by the correct factor, in this case 10:1 scale works out to be sqroot10 approx pi. So a five knot wind for the model simulates about 16 knt for the full size boat.

Any idea where i might find Steve Callahan's article, which issue? This intrigues me especially. I often wonder what the steering might be like on the worst point of sail broad reach to run. At least i can bring the CLR right back.

Your link gave me a blank page unfortunately.
That wooden boat magazine article by russ i read when i was fourteen so it made a indelible impression. A few months later i had bought a 22' sailing scow with money i had saved, and moved out of my father's boat.

What is imo?

boat fan

09-16-2008, 02:12 AM

I M O ( in my opinion...)

rob denney

09-16-2008, 10:14 AM

G'day,
Nothing in Puerto Rico. Sorry.

I originally used stayed masts for the same reasons you quote. But without a stay to leeward the hounds are not fixed and the mast gets some peculiar bends in it. Plus, there are dramas if (when) you are caught aback. Russ has found this to be the case as well. Main reason for unstayed though is simplicity. Nothing to break, nothing to check morning and evening, nothing to replace or maintain and the ability to raise, reef and lower sails on any point of sail in any wind strength. Add in automatic depowering in gusts and you can see why I think they are the answer.

Richard Woods, who has sailed both, reckons an unstayed ballestron rig is 25% more efficient than a conventional rig for typical 'set it and forget it' sailors. I don't rate it this highly, but it is certainly better. An unstayed wing mast rig is better again.

The 18m.60' mast in the sailing at windspeed video weighs 120 kgs, the rm is 18 ton metres. I suspect this will be lighter than your gunter rig plus wires. I am certain it will be lighter than your rig plus the beefing up required to support it. It will also have a much lower cog.

You have to design your stayed mast for the worst possible case. This is caught aback under full sail in wind strong enough to fly the windward hull. With only the bow and stern stays to support it, the compression loads on the mast and the loads on the ends of the boat are huge. With an unstayed rig, the boom weathercocks, the boat slows and stops, you steer back onto course, let the boom go forwards and around the mast and you are sailing again.

Jamming (and many other things!) worry me with the telescoping. Pretty sure I have got it figured out, won't know for sure until we build one. The gunter has the mast in front of it when reefed. Very draggy. Maybe not as dangerous as I thought, if the crew know what they are doing and you evidently do.

It is not the weight of the fitout, but the need to make a larger than necessary lee hull strong enough for the loads it will see, plus the befing up around the cut outs that adds the weight. Does the 150 kgs for the accommodation include the pod and it's beefing up, you, maybe a crew, yours and their gear, navigation, galley and safety gear, floor, toilet, doors, internal finish, somewhere to sit, two hatches and ladders, etc etc? I can't see this being less than 350 kgs, which is 10% of your proposed gross weight, all in the wrong place.

And for what? So that you can sit inside a cramped hull with a fire hose on you every time you go outside to enjoy some fast sailing or look around because the jib blocks your forwards vision, nowhere sheltered or comfortable to sit outside and the prospect of climbing up and down 6' of ladder to get in and out of the boat. There is masochism and there is stubborn. If you put as much effort into making accommodation to windward work as you have into accommodation to leeward, you will be surprised at how much sense it makes. Same applies to unstayed masts.

A long skinny windward hull is draggy at slow speeds when minimum drag is most required. At high speed the rudders work well and the ww hull is being lifted so drag is reduced. It will be interesting to see how assymetry on one hull works, but forget the daggerboard and try it symmetric first and you may save yourself a lot of unnecessary effort. In my experience with scaling nothing is simple enough to warrant the word "just".

Cruising World would not send Steve's article to me, but you can try them if you like. Otherwise, try the address from his posts on the Yahoo proa-file chat group. I strongly suggest you read all his changes of story, apologies, refutations and confessions about untruths and exagerations before you waste your time reading the article, although there are some good photos of the boat in it. If he won't send you a copy, please let me know.

I have no trouble steering harrys, with one beam mounted rudder, no daggerboard or keel, on any point of sail. The exception is sailing at speeds less than 2-3 knots in congested areas when both rudders are required.

Sorry about the link. Go to http://www.harryproa.com/ShuntingVideo/Shunting.htm and click on either of the Elementarry shunting videos.

regards,

Rob

Tcubed

09-16-2008, 10:09 PM

Rob ,

I know i'm stubborn but not so much so that i can't put other people's informed input into consideration and i must say you present a pretty convincing argument for both points.

Getting caught aback with the main pressing against the stay is not a pretty picture. And these stays can't be put very far to leeward or they get in the way of the boom close hauled, unless a runner is added which is yet more complication...
So you've given me some good points to ponder.

The weight of the accomodation may well be a bit more than i said, (i wasn't thinking about the pod) although i would be surprised if it gets anywhere near your number. As i said i have not yet done any precise final structural weight analysis. The sponson would be the single heaviest item since it needs to resist serious upload from the mainsheet and because it makes for a piece of very wide deck which will have support in the middle but still is much more engineering than merely decking a hull. The galley is all 6 mM ply, two burner stove, no fridge or any frills, just pot and pan and a few days food. The head is a couple of holes in the sponson with screw lid. There are no doors. There are steps up the side of the hull to reach the hatches. Very light and basic but none of this detracts from your points about accomodation in the ww hull being very sensible and certainly much drier!

This does remind me though of another question. How do you feel about flare in the leeward hull?

You see to me flare here makes a lot of sense to make this hull not get very depressed when at top performance. That was the thought that then made me consider the lifting hull with all that reserve of buoyancy the logical living (living not lifting) volume. I can't think of any performance or seaworthiness gain that can be had from reserve buoyancy in the ww hull above the bare minimum required...

Another question. Would you consider the lee sponson worthwhile for someone who might be pushing the boat very hard on a consistent basis? I.e. might benefit from another little bump on the righting moment curve?

Last question. I am pretty well convinced that allowing the hulls independance in pitching is the way to go as the stresses are vastly reduced and the hulls conform naturally to their particular piece of water much reducing resistance, despite the fact that most multis nowadays are as rigid as can be. Do you have any engineering preferences for the akas to do this and what do you think of this in general?

My solution so far to make a beam which is strong but which will flex easily vertically and only vertically, is this. Picture an I beam with the top and bottom horizontal flanges quite wide, so the hulls cannot surge relative to one another (horizontally stiff). Now the vertical web which would run athwartships and which would give it vertical stiffness gets removed and replaced instead with a number of vertical webs running fore and aft. This ties the upper and lower 'boards' together so it is strong but allows for a considerable amount of vertical flexing. It also has the important bonus of being aerodynamic and 'spray-dynamic' due to all those holes. (low frontal area in other words)

I'm still getting blank pages on all the video options apart from the first where i get a still image only, no play button or anything, but i'll try again.

Tcubed

Bruce Woods

09-16-2008, 11:41 PM

Tcubed, be warned, Denny has very little if any offshore proa experience in his designs. This has repeatedly been admitted to by Denny on other forums . His steering systems have been a disaster to date with owners having to rebuild numerous times. The man who I understand is responsible for the looks and drawings of the 50 footers Rob refers to, Mark Stevens, claimed no complete working plans are actually in existence. Try reading some of the unsubstantiated claims being uncovered at http://www.wingo.com/proa/links.html. see Reply to Denney's critiques of Brown et al by Steven Callahan and
Moderating the Proa List by Joseph Oster.

rwatson

09-17-2008, 08:38 AM

What fun! I never realised that Proa designers got so hot under the collar.

It appears that there will have to be a cross Pacific race between Robs design and Russels design.

At this stage I want to go in the HarryProa - because I saw the Russel Video (in fine weather), and read this response to one of Robs criticisms,

"Personally, I don't see what all the fuss is about getting wet. If
you like the water, you shouldn't mind getting some of it on you now
and then. Some of the best watches of my life have been while sitting
in exposed cockpits in rain and/or spray. I've often left the comfy
confines of a pilot house or dodger to roam the boat as it careens
over large waves. That's why God invented foul weather gear. And
maybe it should be up to the individual to decide whether to go the
conceptual route of the Inuit who insulates and protects his/her body
with efficient clothing, or the more wasteful Euor-American who
prefers to burn up way more resources heating a large space so he/she
can roam about in winter in his/her undies."

"Had Jzerro really been designed as an
offshore craft, perhaps it would have been prudent to build a dodger
on her. But short of building it with unobtanium, any such shelter is
going to involve cost, complication, and weight. And that does not
suit Jzerro's particular purpose. "

This puts us "cold weather" sailors out of a Russel Proa. 8 hours on deck in a cool day at the lower lattitudes is Hypothermia territory, as any number of cruising articles confirm. I consider all the "no shelter" malarcky to be the very worst kind of justification. Sure, I enjoy the romance of randrops in my hair, but not at the risk of dying of cold due to a week of inclement weather.

Now as far as the harryproa's ocean going abilities V the Russel Proa - I have an open mind. Thats why I want to see a race organised.

The proof of the pudding is in the eating. Any ocean going HarryProas out there ?

RHough

09-17-2008, 11:56 AM

What fun! I never realised that Proa designers got so hot under the collar.

Now as far as the harryproa's ocean going abilities V the Russel Proa - I have an open mind. Thats why I want to see a race organised.

The proof of the pudding is in the eating. Any ocean going HarryProas out there ?

There needs to be a qualifying series. Open to all boats of a certain weight. The designer/skipper of each takes supermodels out daysailing in SF bay, until each boat has a volunteer crew.

The boats that can't get a supermodel to crew, are eliminated. The others get to race to Hawaii. ;)

rob denney

09-18-2008, 08:44 AM

G'day,

Tcubed,
It is a pleasure explaining things to people who are prepared to consider them.

My rigs (ballestron and una) do not have any down force on the mainsheet, the boom is rigidly attached to bearings on the mast. This is easy enough with an unstayed rig as it is so solid in this area. The sheet leads directly to the windward hull so as well as no vertical loads, it can be caught aback without putting any loads on the rig.

No more from me about your weight until I see the detailed analysis. But no matter how light it is, it is still in the wrong place, particularly if you intend to overcanvas the boat and/or pump ballast.

Flare is drag. And it is drag when you least want it. I much prefer to have a longer hull and get the additional buoyancy this way. The 50’ proas have less sail than most 40’ cats. The additional length makes them much less prone to pitching and nose diving and increases top speed. It is very cheap (except for marina fees) and adds very little weight. The same cannot be said for flared bows with forestays attached which add considerable weight. Wide flat decks are also scary when you go through a wave or nosedive as they make it slower to surface.

I agree about buoyancy in the ww hull, but while it does not do any good, it does not do much harm either. And any harm is far outweighed by having the low drag lee hull.

Lee sponsons do give you a little more safety when sailing beyond the limit, but the limit is much higher when they are to windward. They are also increased drag in waves and a large hole in the side of a highly loaded hull. However, my main complaint about them is that they behave like the small hulls on old trimarans, and in extreme sea conditions, they may dig in while the boat is sliding down a wave and cause it to capsize. I would also worry that if the boat does capsize past the sponson, it will be impossible to right.

If self righting is important to you, you can cant the buoyant mast to leeward about 10 degrees (depends on the weight and it’s distribution in the windward hull) and the boat will have positive righting moment at 90 degrees of heel. The canted mast also helps a lot in light air.

Re independent pitch. I designed and built a 40’ cat in NZ a few years ago. It had a single beam in bearings so the hulls could pitch independently. Worked well and was very fast, but it was also very light (600 kgs/1,320 lbs) so we never really found out how much speed was because of what. It certainly had a very nice motion. I tried the same idea on U, an early 7.5m/25’ prototype proa. Did not make much speed difference, except if you inadvertently moved forward, the bow would pitch down, which was slow. I have since found that with the short ww hull, the motion is very pleasant, partly because upwind the bows hit the waves at the same time, so there is none of the corkscrewing you get in cats. Consequently, I would not bother on a harry. If you do go with free to pitch, let me know, there are plenty of pitfalls.

Our beams are all box section with large radius corners as they are so easy to build, light and cheap. They are also relatively low drag. I would be very wary about relying on the section shape to give you pitch freedom as the engineering on twisted I beams is pretty tricky. Much safer to mount the ends in bearings or slots. Yet another advantage of an unstayed rig is that the boat does not have to be rigid. This is another weight and money saver.

Sorry about the video. Have you downloaded the player?

Rwatson,
Weird about the proa designers, although it is not Russ and I so much as the fans of Russ who got upset because I used quotes from the articles in Wooden Boat and Cruising World to compare the two types. None of the fans have ever seen or sailed a harry, but consider they know all about them. In the early days some of the criticism was worthwhile and made me think about solutions. Now that harrys are out there doing what the prototypes suggested they would, the criticism is mostly personal and tedious. This is why it is great when someone like tcubed comes along with an open mind.

No ocean going harrys yet. First ocean capable one launched, the owner died, second one has been up and down the East Australian coast and seen breaking waves big enough to fill the open box boom (3m/10' off the water) with no problems, 3rd one has been too busy taking blind people sailing in Holland, 4th one still has not got a rig.

Not sure what a tradewind slide to Hawaii will prove (a race back, up the trades would be more interesting), but would love to do it.

When Steve was giving me (not harry's, he showed very early in his tirade that he knew nothing about them) a hard time on the proa list, he made a $2,000 wager that Russ' boat would beat mine in an ocean race. Half a dozen people who knew about harry's immediately jumped on the offer and put up $5,000. Steve and a few other previously vocal people dropped off the list and have not been heard from since. No one offered to match the increased bet, and most of the sniping stopped. There are still a few people following me around the forums, but i ignore them except on the very rare occasions they have something new or interesting to say.

RHough,
The race idea sounds good to me. My 50' entry for the Single Handed Transpac (hulls, rudders and beams are built, "just" the rig to go) weighs less than a tonne/2,200 lbs. Russ' 38' boat weighs about twice as much. They have similar accommodation, mine is much cheaper.

There is no reason to put any limits on who can compete. If I ever get organised enough to campaign my ocean racer, I will gladly race anyone.

Regards,

Rob

terhohalme

09-18-2008, 09:36 AM

Nicely put.

Terho

keith66

09-18-2008, 02:34 PM

Back in 1984 i and a group of 5 friends built a 36ft flying proa to compete in a sailing class of the Southend raft race. he was built from 3 ex USAF grp drop tanks cut & shut together. We put in 3" of rocker and a gracefull clipper bow each end. His hull was 2' in diameter and the Ama was made from a written of unicorn cat with both bow sections glued back to back. The whole contraption was 16' wide and then we stuck a 170sq ft standing lug on him from an admiralty whaler, roller furling jibs were fitted each end and served mainly to balance the ferocious weather helm.
"Voodoo child" was built in three weeks with a total outlay of £200 between us all. I would never have taken him far out to sea but in the estuary he was fine and sailed like the clappers. To this day i have never had so much fun with my clothes on!

Tcubed

09-18-2008, 08:52 PM

Flare is resistance,.. How so?
It's not really appropriate to say making it longer is a better way to add buoyancy, as it then ceases to be comparable. Longer is automatically faster unless you keep the same sail area and you look at ghosting conditions. Longer also means you can increase beam whilst keeping the decided Max Longitudinal Righting Moment/Max Transversal Righting Moment the same, which implies more sail to take advantage of the extra righting moment (even if weight is kept the same) i.e. faster and faster . It's not for nothing these racing tris, when not limited by a length rule become longer and longer.
In practice length is a constraint that one decides upon when creating a design (more so even than when designing a mono) which reflects the available budget, the variety of harbours one might visit (maneuverability) and space available for the build. In my personal case i've decided 16 M is about as long as i want to go, and it still gives plenty of speed potential and a reasonable amount of internal volume to move around in.

You're certainly right about wider flat end decks being slow to rise if submerged, compared to the semi-wave piercing bow. On the other hand, a tall bow with flare has enough volume, or reserve buoyancy to be very difficult to submerge in the first place. Question of preference i think.. Apart from running in high young waves where the faces typically exhibit a maximum of concavity. In this situation, i think i would prefer a shape with enough sheer to keep the ens out of the water, no matter what, over the hogged sheerline style where both ends would be submerging at once which if it does not cause a pitchpole, at least creates a very strong yaw moment, which could easily lead to a broach. Remember that water particles are compressing on the wave face, which in wave lengths around twice to four times the boatlength means the bow is experiencing considerably higher water speed than the stern when on the wave face.

Which brings me back to flare, given a certain leeward hull length.
If there is no flare and one designs for underwater semicircular sections, then at low rig pressure conditions the lee hull is on a section of circle which is no longer minimal wetted surface shape, when it matters most. If on the other hand, one designs for semicircle at low pressure conditions then at max heeling moment the underwater sections of the lee hull look like a 'U', which is not so optimal either......Also the lee hull will experience greater variations in immersion if it does not have flare.
That is the thinking that made me opt for a parabolic cross section which immerses relatively little as the rig loads up to maximum allowable force and which is a fairly close to achieving minimum underwater girth, whilst retaining a pretty similar underwater geometry irrespectve of where in the power range one is operating. It is a compromise as well, i acknowledge, but in my opinion so far, somewhat preferable to not having flare.

On lee sponsons. It is certainly true they could trip a capsize in a big breaking cross sea. But i'm inclined to think that if it is high enough and the lee hull has generous reserve buoyancy it would be quite difficult to get the wing deck underwater such that it could trip. I think by the time waves were breaking that monstrously, one would be avoiding beam on seas already and no doubt be under not much more than bare poles. All of which makes me think it is probably a worthwhile safety feature, although it probably comes down to personal judgment as to the pros and cons in one's own particular requirements.

On volume in the windward hull. I applaud the innovative design solutions you've created for the proa. They will certainly make the proa type more appealing to a large majority of sailors who have been hesitant of the proa for the obvious reasons..However i do think that the harryproa, as is so far, does not represent an oceangoing performance optimization solution. I think you underplay the role of windage. This is not a problem for coastal cruising, but in my particular case where my main objective is fast transoceanic passage making, it might well be.
I have always been very concerned with windage in all my designs because apart from it lowering pointing angles to windward (by lowering the total L/D ratio of the entire above water structure) it is the single most important factor determining just how much wind is needed to prevent being able to make good to windward, a very important safety issue, i feel.

So, it seems that we will have to organize an ocean crossing race to determine once and for all the merits of the different proa options. I take it yours have not done ocean crossings yet ( due to lack of storm stories)..? It would certainly be a lot of fun. Proas barred from multihull races? No problem, we'll just organize our own! Hey Russ! you listening to any of this? Or anybody?

As for the funny idea of the ladies for qualifiers, i'm all for it. So far , in all the races i've competed in i only allow female crew. They're easier to train, and they're much easier on the eyeballs. Besides i might be prequalified: My wife is quite a looker, i'de post a picture of her but i don't want to upset admin.

Tcubed

P.S. The race should be the sum of the times of a round trip so there is unavoidable upwind work to insure testing is for all points of sail.

RHough

09-19-2008, 12:30 PM

P.S. The race should be the sum of the times of a round trip so there is unavoidable upwind work to insure testing is for all points of sail.

Oh my ... dear chap, gentlemen don't sail to weather. That is why yachts have engines, for upwind work and to run the ice maker. ;)

Tcubed

09-19-2008, 12:51 PM

Are you taking the piss, mate?

RHough

09-19-2008, 03:20 PM

Are you taking the piss, mate?

Just having fun. :)

Of course windward ability in heavy air is a primary seaworthiness consideration. Once you have a vessel that is capable of boat speed > wind speed you are always 'sailing upwind'.

MAINSTAY

09-20-2008, 07:37 PM

Tcubed

Your Proa is a great project. Congratulations. With such a large sail area and single handling. the choics of rigging is so extrordonarily important.

Might I suggest a rig that can be handled entirely from the hatchway?

The primary feature is that the mainsail is not set on the mast, but on a vertical stay. The mast for a proa is stepped near the third point of the forward cross arm and canted so the head is over the centerline of the hull and raked so the head is at the head of the mainsail. It is supported by one shroud to the end of the crossarm, the stay for the mainsail, and the forestay. For a boat of this size another stay between the main and fore stays is suggested to divide the sail area into smaller pieces, and to help keep balance when reefed. All sails, including the main, are on stays and can be roller-reefed with ease. The mast is not in bending or torsion since no sail is set on it. The mast is primarily in compression.

With the mast out of the cabin you would have more room below. But adaption at this late date depends on the stage of construction.
Larry Modes

The attached .xls sketchs may hwlp visualization.

RHough

09-20-2008, 08:01 PM

rwatson

09-21-2008, 02:15 AM

Yes, especially with the hull not being symetric fore and aft in the XLS diagram - are you sure you are "up to speed" with the Proa concept Mainstay?

You gotta be able to sail backwards and forwards.

Rob has a couple of shunting videos on his site for clarification if you want to check it out ( links just a few Posts ago)

re the balestrom,unstayed mast option - I guess a comparison of costs would be in order here. It might be worth a less handy rig if there were substantial cost saving to be made. I know the average carbon fibre mast isnt cheap.

Any sample costs available Rob?

rob denney

09-21-2008, 10:02 AM

G'day,

Tcubed
Immerse the flare, the boat slows down. Immerse the long skinny tube, nothing noticable happens. Hence my comment that flare is drag.

You are quite correct, it is neither appropriate nor fair to contemplate extending the length of a lee hull which is "high enough to keep the ends out of the water, no matter what", strong enough to take the forestay loads and wide enough to stand on. If, on the other (harry) hand, a 10% length increase adds less than 5% to the cost and weight of the hull it makes perfect sense to make it as long as possible.

Extending the shed, or building the small lee hull in pieces is no big deal (my 50 footer has 5' removable at each end for easy containerisation), nor is maneuvering with two harry size rudders. Extra sail is not a requirement, just be content with the higher speed, nicer motion and increased safety.

It seems you are justifying your design based on what it is rather than what it could be. The same could be said about the location of your accommodation and rig type.

There is no evidence or reason that I know of that a hogged sheer causes nosediving or broaching. Harry's track as if they are on rails, and need to be driven very hard to immerse the bows, and even then, they are in no danger of pitchpoling until the bows are very immersed.

The slight variations in immersion and wetted surface caused by U, semi circular or parabolic hull sectional shape are secondary concerns if your hull is twice as heavy as it could be.

"Quite difficult to trip" is nowhere near safe enough, at least for me. If you can avoid beam seas under bare poles for a couple of days in a storm, you are doing well. And the max righting moment is still less than having the accommodation in the ww hull, so it is a pretty nebulous safety feature. Add in the drag from waves hitting it and it is slow as well.

The relevant windage is at 30 degrees off the windward bow, which is where the wind blows from while sailing to windward. The harry with a similar comfort level as your boat has 18.5 sq m of area including rigging, beam mounted rudders and both beams. All are aerodynamic shapes.

If we include your "lee bows high enough not to submerge", standing rigging (over 1 sq m of very unaerodynamic shape) and full length windward hull with enough freeboard for it to support the entire boat when caught aback then my bet is the harry will have less.

Happy to compete in a race, yunder whatever terms you want. The harry with the same fit out level and payload as your boat will have a comfortable covered cockpit, easy access to the rig and deck, and be dry to sail. Based on Russ' boats and the harrys sailing, it will be about 50% lighter and cheaper in sailing configuration. These attributes are directly attributable to it being a harry configuration and not a Russ one. Look forward to seeing detailed plans and weight analysis of your boat.

Mainstay,
I cannot open your rig drawing, but any design with as many parts to fail as a stayed mast has, has no place on a sensible cruising boat.

Rwatson,
The mast on the boat in the video (http://www.youtube.com/watch?v=8chR6DAFjGA) was the first one we built and there was a fair bit of stuffing around involved. It cost $12,000 and is for a righting moment of 18 tonne/metres. Painting and the lightweight carbon track added another couple of grand. The boom is an open topped design which was more complex than it needed to be, a box boom would cost about $8,000. Fittings for the jib and the bearings for the mast maybe another $2,000, depending on what was required. Say $Aus25,000 all up, to build it in Australia where the charge out rate was $65/hour. 75% of the cost is labour. In Panama, where we might be building masts next year, it is about $20/hour and in China, where we might be building masts later this year, it is about $5 per hour. If I was to do it again, I would make it a wing mast, with in boom roller reefing. Cost would be a little more, efficiency a lot more.

This is not a "less handy rig". This is a very simple rig with almost nothing to go wrong, replace or maintain. It can be easily handled by one person with very little effort. It is also highly efficient, about the same as a conventional rig upwind and superior reaching and running according to tests done by the Woolfson unit.

regards,

Rob

Tcubed

09-21-2008, 11:18 AM

Although i'm always interested in new rig ideas, attaching sails to stays instead of spars makes for poor engineering, because of the colossal tension required to keep the stay straight(ish), which implies more compression stress, meaning a more robust and heavier mast. This is the downside of any jib and why i favor small jibs/large mains-and this is a more aerodynamically efficient solution as well. Unfortunately, single masted proas must have the mast in the middle of the boat (unless movable mast step, which i don't think anyone will say is practical for this size!) so the jib ends up somewhat larger than what i would consider ideal.

The compression force on the mast of a sloop rigged proa as drawn above is

C = Wa + 2(T*I)/(sqrt(I^2+J^2))

where C is the compression on the mast, Wa is the weight of the windward hull, T is the tension in the forestay, I is the height of the foretriangle, and J is the base of the foretriangle. I made a couple of simplifications for this formula but that's the bulk of it.

I tried to figure forestay tension based on aerodynamic force of jib and % sag in the stay but did not get very far.
Q*If someone has the formula for this i would very much appreciate it.

In the balestrone rig there is compression too but only due to jib, which is also quite small, and this compression is not transmitted to the mast step, but rather to the gooseneck.

As for roller reefing, i wouldn't consider it. Period.
These are the reasons:
1*They are complex pieces of equipment that i have personally seen break, jam or otherwwise malfunction too many times to count. (I do rigging work)
2*They create a ton of windage when fully furled-comparable to having another mast.
3*They don't actually save much effort. To reduce sail you have to WINCH in the drum rope..On a normal jib you just let the halyard go, and if the wind is blowing it partly back up the stay, you can yank on a downhaul (if you've decided to have one). It's true to raise a jib is more work than letting out a roller furler, but what's important is how quickly can you dump sail, not how quickly can you set it. Seaworthiness is important.
4*I have yet to see a roller furling sail that has a nice shape when reefed.
5*There always exists a wind strength which will break open the wraps-just look at what happens to people's roller furling jibs after a hurricane, if they neglect to remove the sail completely beforehand.
6*To remove the sail completely, it must first be completely unfurled. By the time it's blowing so hard you decide it might have been better to bring it in completely, you cannot unfurl it anymore!
7*They are expensive.

To give one juicy example of point #1 i'll relate how a modern french schooner with all roller furling sails got caught in ever increasing winds. They got a jam in the foresail and tried everything they could to free it, but couldn't, leaving that sail permanently one third reefed. Meanwhile, they reduced the other sails appropriately. Eventually it was blowing so hard the foresail burst into horizontal banners, which after a while of thunderous shaking, brought down the foremast. To make things worse yet, the foremast wildly swinging around on the end of the triatic eventually brought down the mainmast too...From one little glitch to complete de-rigging.
Sails must come down with 100% reliability-not 99.999%

I have the mast deck stepped as it's a fully rotating wing mast. It is stepped on the windward side of the leeward hull with some clever WEST system laminates underneath to spread out the load using a minimum of material and taking up little space inside. The mast is strip planked spruce built up on 6 mM plywood forms every meter or so all epoxied together. No glass anywhere, i feel it adds more weight than strength. A glass sheath also has different modulus of elasticity to wood and can, through stress, develop invisible cracks which let water in and rots the mast. Water does not rot wood, trapped water rots it. Chord is about 65 cM , thickness about 20 cM. One set of very light diamonds keep it rigid across the thin axis. An extremely rigid setup- so wall thickness can be quite small. Just how small i don't know yet.
Q*Maybe someone can relate some examples of wall thicknesses in comparable wooden masts.?

BTW adaptation is quite possible as so far it is only on paper. I hope to be able to start building within a couple of years.

Tcubed

09-21-2008, 11:26 AM

<<<<<It seems you are justifying your design based on what it is rather than what it could be. The same could be said about the location of your accommodation and rig type.>>>>>

Good point.

Tcubed

09-21-2008, 11:29 AM

<<<You are quite correct, it is neither appropriate nor fair to contemplate extending the length of a lee hull which is "high enough to keep the ends out of the water, no matter what", strong enough to take the forestay loads and wide enough to stand on. If, on the other (harry) hand, a 10% length increase adds less than 5% to the cost and weight of the hull it makes perfect sense to make it as long as possible.>>>>

Ok, but suppose you ARE length constrained.

RHough

09-21-2008, 02:48 PM

rob denney

09-22-2008, 01:17 AM

Ok, but suppose you ARE length constrained.[/QUOTE]

Story of my life! ;-)

My design spiral starts with the expected payload of the boat, including accommodation. I then design a windward hull around this. Next is the Bruce number and /or the required wind to lift a hull. This then goes on the longest, lowest, narrowest lee hull possible, within engineering restrictions. For cruisers I work on the lee bow being 50% immersed with the ww hull flying, so I guess the answer to your question is I would make the bows higher, although not wider. However, I would keep the same section shape.

The boat in the video was much heavier than the original design as the owner decided he wanted a bunch of add ons after the lee hull was built. This has lead to it being, effectively, length limited. It still performs well, and if you can get your boat down to this weight, then I see no reason for high flared bows, except to give you somewhere to change the jib, if you choose this rig option. As I said, mixing Russ and harry is fraught, so changing the bow leads to changing the rig, which leads to eliminating the pod (big hole in highly stressed area, plus internal space limits), which leads to moving everything to the windward hull and allows you to build a much smaller lee hull. But not doing all of these will lead to problems.

I should also admit that to make them easier to build from flat panels, I am now putting flat decks on my boats. However, the decks at the bows are very narrow, so I do not expect there to be any nose diving ramifications.

All going well, there will be a stripped out 15m/50' harry in Panama early next year. I would be happy to take you for a sail if you can get there.

I completely agree with you about roller reefing headsails. A heavy waste of money. However, I would not be that happy about a lowered jib sitting on the aft deck, and even less happy about having to unhank it and rehank it on the other end every shunt.

I completely disagree with you about no glass on strip planked wooden masts. It may not rot but there are twisting loads, Euler buckling and "bursting" of lengthwise fibres under compression to consider. You must restrain the fibres with some off axis material and glass is good for this. The different moduli are not a problem as the wood is lengthwise and the glass is at +/-45. A wing mast with a gunter will be an interesting beast, particularly when reefed.

Wood is a great building material, but is heavy compared to carbon, and for a wing mast, foam. An 18m/60' length of your mast will weigh about 90 kgs/200 lbs, without any off axis material (minimum 25 kgs if you use 6 ounce/200 gsm inside and out), fittings (track, hounds, head, ball joint, gooseneck, wires and spreaders) or local beefing up at the hounds, diamonds, top and bottom (probably near enough solid at each of these). I would be surprised if it ended up any lighter than 150 kgs, compared to 120 kgs for the unstayed carbon/glass mast in the video. I would be further surprised if 6mm spruce is sufficient to take the loads from the tight staying angle if the rig is caught aback.

With the price of mast quality spruce in most of the world, it will also be more expensive than a carbon mast.

regards,

Rob

boat fan

09-22-2008, 01:38 AM

Hello Rob ,

Question : Is it at all possible to build a Harryproa (for example a Visionarry Sport) out of plywood, maybe Hoop Pine /stringers on frame , or would it just be too heavy ?

rob denney

09-22-2008, 08:21 AM

Hello Rob ,

Question : Is it at all possible to build a Harryproa (for example a Visionarry Sport) out of plywood, maybe Hoop Pine /stringers on frame , or would it just be too heavy ?

G'day,

Certainly could, although it would take longer and may not be much cheaper. The added weight would need to be trimmed from the payload, or you accept a heavier/slower boat. Maybe make it a little longer to compensate. The Vis is 12mm kiri with 600 gsm glass each side. Similar stiffness and puncture resistance (strength is not an issue) would use 12mm ply with 200 glass on the outside, 3 coats of epoxy on the inside. The kiri weighs 5.9 kgs, the hoop about 8.5 kgs. Surface area is 200 sq m, so you are adding half a ton. I am not sure of the price difference. You could use thinner hoop and put in more frames and stringers, but I doubt the savings would be huge.

You are also shape constrained, but not enough to worry about.

The quickest build is undoubtedly to use partially glassed flat panels for everything. Depending on resin and core selection, this is also the cheapest, I think.

Any questions, let me know.

regards,

Rob

boat fan

09-22-2008, 07:09 PM

Thank you Rob , great reply.

I like plywood I`m afraid.I know how to use it and therefore I am confident to build that way.

As to weight , I do believe it could be done in 9 mm ply .I looked at the Peter Snell Easy 37.Similar accommodations to a Harryproa. Those boats are light .

I enquired about the Easy payloads and Anne Snell was kind enough to reply with the following :

The 10.5ss displaces 3700kg and the 37 displaces 4000kg when on their designed wl. At the risk of stating the obvious, payload is the difference between the built weight and this figure. If you build a heavy boat you eat into your payload. Ply can range from 13kg a sheet to 20kg a sheet. Many builders feel more is better and they try to “improve” their boats by adding extra bits while reality is far more simple-if you don’t need it get it off. A well built fitted out shell will come in at around 2500kg for both boats. You can only spend the difference once so spend it well. As an indication, on our boats(which are always on their lines!! ) we would carry 350l water, 100l fuel, 400amp hour battery bank, 50 m chain anchor winch, dinghy and outboard less that 70kg, and stuff for 2 people. Easys float on their wl chine so have a visual reference for overloading. But please remember, these boats are light displacement for their length, hence sail very well, but take care comparing with other cats of the same length which could displace 50% more. If you are thinking of a nice heavy timber fitout and all the fruit, this is not the boat for you. Our 12m Sarah displaces 4800kg- many 10m cats will come in at this weight or more. Hope this helps

Take it Easy
Anne

http://easycatamarans.com.au/

It made me think that the Harryproa could be built to similar specs (scantlings ) .

I think a very attractive boat could be built in multi chine.

rob denney

09-22-2008, 10:19 PM

Tcubed

09-22-2008, 10:33 PM

Interesting to see your design process and approach, Rob. I think we're pretty much agreed on most points, and on the points that we're not, we're pretty much agreed that we are disagreed. Thank Jah it is like this, otherwise there would only be one designer in the world and all boats would look identical!!

Re the mast. I'm getting basic figures for the 14.3 M mast of 45 kg for all the wood + ~25 kg for all the hardware (track, three blocks, the little diamond spreaders and some straps) + ~1 kg = 75 kg , say. All the standing rigging comes out at ~30.5 kg. And let's not leave out the sprit at around 18 kg for a grand total of 123.5 kg approx...

Now that is with no glass, and yes you're right about the glass not cracking if it's not in line. However, I still prefer all wood. I can substitute the glass fibers for lightweight woodfibers at +/- 30 degrees in a layer of veneer cold molded over the strip planks to achieve the same thing and spare myself the hassle of making the mast in two halves to subsequently join. But each to his favorite method i guess.
However your cost comment on carbon fiber is really surprising. I don't know about Aus. prices, but here wood is still cheaper than carbon fiber, even sitka spruce.

I, like you B. fan, am very enthusiastic about plywood construction, and in fact, had originally designed this boat to be made out of 6 mM marine ply with a fairly extensive array of edge set stringers and frames skeleton, with a five panel shape. One day, i met a fellow called John Patterson on a very professionally self built trimaran. He had used strip planking, with a unidirectional glass layer oriented athwartships inside and out. The result was strong, light, no shape limitations, completely frameless interior, but what really impressed me was how fast it was to build. The more i thought about it the more convinced i became, so i will basically use his method to create the hulls. Scroll near the bottom of:
http://www.nemasail.org/pdf/Spring2005.pdf
to read more about this great home made tri.

But, don't think i'm saying don't build it in ply, quite the contrary. I would say, however that with 12 mM ply and at least five panels to make up a hull (so the flats are not too wide) you would barely need any frames if the shape is nice to cut, and not slam and for these kinds of ultra low displacements. 9 mM is better, but with more skeleton (more work but better strength/materials ratio). Scantlings are decided by boat weight more than anything else. I was designing for 6 mM ply but then the skeleton becomes quite complex. I sailed on a 42 foot newick style tri and it was 6 mM ply and i could not detect any flexing. The skeleton wasn't even all that elaborate either. He did have a layer of glass on the outside.

Q*Another topic for discussion is pros and cons of rocker. Rocker allows to design for emmersed length in light conditions and full length in heavier winds, allows for improved maneuverability, but it is difficult to get high prismatic into it and some opine that it leads to strange or excessive pitching . I wonder though whether prismatic doesn't sometimes get confused with longitudinal distribution of reserve buoyancy...and why would a blunter curve of areas be less drag at higher froude numbers anyways? If i remember right, Uffa Fox had this full prismatic coefficient analysis in one of his famous books. Anyone care to give us a refresher?

boat fan

09-22-2008, 11:15 PM

G'day,

A nice reply from Anne. They are more in tune with low cost building than most of the other main stream aussie designers. 2,500 kgs/2.5 tons is pretty good for a 10.5m/35' cat shell, but it compares with 2,000/2 tons for a 15m/50' Visionarry or under 1,000 kgs/1 ton for a 12m/40' harry, both ready to sail.

Still, no reason why you couldn't build in ply if that is what you are comfortable with. 9mm would probably need a bit more framework on the lee hull of the visionarry, but harry is 8mm kiri so 9mm would be ample. It would be easy enough to build a rockerless hull from ply and compared to strip planking, panel boats or foam one offs, it would be pretty quick. Could also build it from tortured ply, or as I did with the first harry, bending ply. Been a while since I have drawn anything in ply, but it would be fun seeing what can be done.

regards,

Rob

Thank you once again Rob , another great reply.

Anne was nice , and helpful.

I don`t know much about bending ply . I always have this fear of tortured plywood not turning out the same as the planned sectional shape.I did build a mosquito cat many years ago , which turned out pretty ok , so I`m probably just paranoid :D I have " Gougeon Brothers On Boat Construction and their experiments and results freaked me a little - seems a little " hit and miss" - :D

I`m more concerned about the mast step / bearing / bulkhead structure.
I have tried to find some photos of your boats showing what is involved with all that , but could not find much.Are we talking something like two strong bulheads at the mast step / bearings , or is there more structure ?I suppose it would end up the same as the stripped Kiri boats.Just worried about the weights of all that....Given that you don`t need the big truss type cross beam needed to carry the rig on a cat , you may well come out even there....Just pondering...I think I will will build a model in flat panel , make it look " pretty " as I can ;)

http://lh5.ggpht.com/terhohalme/SMLo5OgCbYI/AAAAAAAAANc/jH2osSyhcU4/catharsis%2027%20persp5.jpg

A double ended version of Terhalme`s Catharsis 27 or similar ?

As for the full size boat , I think it could be a quick build.

boat fan

09-22-2008, 11:58 PM

But, don't think i'm saying don't build it in ply, quite the contrary. I would say, however that with 12 mM ply and at least five panels to make up a hull (so the flats are not too wide) you would barely need any frames if the shape is nice to cut, and not slam and for these kinds of ultra low displacements. 9 mM is better, but with more skeleton (more work but better strength/materials ratio). Scantlings are decided by boat weight more than anything else. I was designing for 6 mM ply but then the skeleton becomes quite complex. I sailed on a 42 foot newick style tri and it was 6 mM ply and i could not detect any flexing. The skeleton wasn't even all that elaborate either. He did have a layer of glass on the outside.

http://lh5.ggpht.com/terhohalme/SMLo5OgCbYI/AAAAAAAAANc/jH2osSyhcU4/s640/catharsis%2027%20persp5.jpg
http://lh5.ggpht.com/terhohalme/SMQHBSzXWpI/AAAAAAAAAPg/shzs18EZ1_Q/s512/IMG_1070.JPG
http://lh3.ggpht.com/terhohalme/SMQGi63L70I/AAAAAAAAAPU/dMjL-a57HKs/s512/IMG_1072.JPG

I think 12 mm is too heavy.If I were to do this in ply , I think 9 mm is the way forward. I dont think the lw hull on Rob`s boat would take long to build that way.I would run a couple of 19 x 42 mm stringers along the side ( widest ) panels to stiffen them up a little.I think the mast bulkheads / bearing framing would have the most structure in the long hull.Given that the interior of that hull would not require much more than 2 or 3 coats of epoxy , there is fairing on the external chines then glass then paint .

The windward hull would require little in the way of framing on Rob`s boat I think.Rob`s galley stretches the best part of the outer windward hull face. Lots of additional stiffness there ! So...I would attempt mainly stitch and glue with filleted bulkheads I think.Those pics above are by terhohalme and his Catharsis 27.He used nidaplast , but also designed for 9 mm ply.Build would be very near the same he says.I see Rob`s windward hull looking similar to this boat , double ended of course.

rwatson

09-23-2008, 01:41 AM

Question : Is it at all possible to build a Harryproa (for example a Visionarry Sport) out of plywood, maybe Hoop Pine /stringers on frame , or would it just be too heavy ?

Just to throw my 2 cents in re the plywood V strip planking discussion, in my next project, I was all keen to do it from plywood. I had just finished a small strip plank boat, and the process was quite laborious and took me quite a while.

So I went out and bought a book, Sam Devlins "how to build any boat the stitch-and-glue way" Its an excellent read, and has some great tips in it re plywood building etc.

The big eye opener to me was that fact that even in plywood, the amount of finishing, (given that glass/epoxy was used on the outside and inside)- looked to be exactly the same as I had encountered in the strip planking. It seems as soon as you start adding epoxy/glass to something - you have to sand the stuff a lot.

The other jolt I got was something I have read a lot of - over the years, the importance of getting good, "well built" plywood. He spent quite a few pages on how to detect bad batches of ply. He even gave an example of how two new boats he just completed showed irregular condensation patches during cold weather, caused by voids in plywood. These had to be filled with epoxy.

That took me back to many years ago when I read a newspaper article about some people had to be rescued when their old plywood trailer/sailer opened up at the bow and sank. More recently, I was reading a story of an ocean going intrepid sailor in a Norwalk island Sharpie (all plywood) having visions of the plywood hull foot giving out during a fast 24 hour run in rough seas (it didnt, it was just normal paranoia).

I looked at the great little boat I built, and all the curves and elegant flowing hull (that could never be built out of ply), and then emailed my designer to forget about the multi-chine plywood plans, and just go with the curves that would need planking.

The point is that I really dont want the worry of wondering how good the ply is - and how it is holding up over the years. If I lay the planks of solid wood, and glass them, I know exactly what is going on. Paranoia is just not worth it.

The fact that the boats resale value will be higher, and the boat will be substantially lighter, are other big motivators.

Also, the "look" of a boat is a source of pleasure long after the pain of building is over. (especially when showing it to prospective buyers)

If a boat is lucky enough to have some developable surfaces, then frankly, laying planks is no harder than plywood. Certainly, long scarfed lengths of plywood take a quite a bit of manouvering compared to single planks. If the boat has some compound curves, its a bit more work, but I have decided to put up with that for the benefits.

The other building method that is on the horizon for me, is the kelsall flat bench vacuum bag technique. Its not something I would try without going to a workshop - so the complexity puts me off that for the moment.

My next boat is not a long slender multihull. If it were, I would seriously consider doing say, the bow and stern sections from fibreglass (on male sacrificial moulds) and plank over them ( glueing the planks to the hollow fibreglass shapes). This would do away with the really fiddly job of laying up glass and epoxy in narrow, hard to get at locations.

Rob uses a form of this technique for the bow and stern of the proa ama hull. He doesnt run the planks onto the bow sections, but there is no reason that they couldnt. I am seriously considering doing the hull foot (with its permanent flotation) as a module in my next sailboat, giving really good support to the planks, while taking away the need to do any finishing on the inside of the hull.

So - I vote for strip planking now after a lot of vacillating. Its really the epoxy sanding that is the horror in both methods, but I wouldnt go to sea without that protection.

boat fan

09-23-2008, 02:50 AM

I hear what your`e saying!

The other jolt I got was something I have read a lot of - over the years, the importance of getting good, "well built" plywood. He spent quite a few pages on how to detect bad batches of ply. He even gave an example of how two new boats he just completed showed irregular condensation patches during cold weather, caused by voids in plywood. These had to be filled with epoxy.

I have his ( Devlin`s ) book too , like you say it`s a good read.

A lot of Americans build with " Fir " plywood.I personally would not go near the stuff . It`s rubbish , and that`s being kind to it.As for the other ply available over there , I cannot comment.

I`m fairly fussy about the quality of plywood too.I would use Brunzeel if I could afford it , but the price of that stuff is absurd these days.

Plantation Hoop Pine made here in Oz however is another matter.That plywood is really nice , at least as far as voids go . There are very , very few voids that I have ever seen.If you put a 200 watt spotlight behind a 6mm sheet you can actually see if there are voids , they show .You will not find many , if any .

A couple of builders of cats up north have said that the Hoop Pine Ply can get mold spots , if you are building in the open , under tarps.Not a big deal they say because a little bleach is all that`s required to remove it.Besides I would not build out doors , ever.

The big eye opener to me was that fact that even in plywood, the amount of finishing, (given that glass/epoxy was used on the outside and inside)- looked to be exactly the same as I had encountered in the strip planking. It seems as soon as you start adding epoxy/glass to something - you have to sand the stuff a lot.

Yes you are right.

However , with strip planking you need to glass inside and out.Not with plywood.You do need to fair and sand all outside surfaces like the stripped hull .If you are careful , you can save considerable effort while you roll on epoxy on the inside of your plywood hull.You will not eliminate sanding , but with careful work you can actually minimize it on a plywood interior.

I looked at the great little boat I built, and all the curves and elegant flowing hull (that could never be built out of ply), and then emailed my designer to forget about the multi-chine plywood plans, and just go with the curves that would need planking.

Good for you ! Again , I hear you .I bet it looked good. :) The satisfaction of a job well done....I agree that there is nothing quite like lovely curves on a boat.well , ALMOST nothing ...;)

I used to loathe hard chines. I think it was a throwback of images of the clunky , boxy amateur built steel boats sitting in people`s back yards :D

I have now come to like them , especially on multihulls.I guess that`s a matter of taste .Terhohalme`s effort on that 26 ft cat is an example.I find those lines quite attractive .

All said and done , I do agree with you. I am not afraid to take a well built boat , built of quality plywood , offshore.

Thanks for your post rwatson , it`s appreciated.

rob denney

09-23-2008, 06:01 AM

boat fan

Bending (Flexi) ply is 3 veneers with the inner and outer ones running the same way and making up 95% of the total. 9mm dbends to something like a 50mm radius. Pacific Boatcraft used to supply it. It is also lighter than gaboon ply.

The Gougeon's technique looks scary, but they have built tornado cats to Olympic standard, so it is pretty repeatable.

Mast bearings are plastic, there is a ring frame, a short piece of keelson and tow around the deck bearing. It is not until you see how little materials is required to support an unstayed mast that you realise how complicated and heavy stayed masts are.

Ply is a quick way of building, probably quicker than most other methods, but slow compared to bending a partially glassed, full size panel into shape, dropping in the bulkheads and gluing on a deck with radiussed edges.

Looks are not my strong point, but if you like Terho's hull, it would be easy enough to make it double ended, I think.

Look forward to seeing what you come up with using flat panels.

Rwatson,
I stop the planks (or panels) before the ends, then glue on a polystyrene block, shape it and glass it. Much lighter than a stem, better impact resistance, positive buoyancy and much easier to get whatever shape you require.

Flat panels built on a table then shaped is so much easier than any other form of building, there is no comparison. With rockerless hulls, it is even easier, and quicker. I strongly recommend Derek's workshops.

Tcubed,
For someone who agrees with me on "most points", your design has very little in common with harrys, and almost all of the differences in the design are fundamental to what makes harrys so light, fast and easy to build and sail.

Veneers on the outside of the mast will help, but i would advise them on the inside as well (euler and bursting). Two halves allows for internal beefing up (a 600mm chord wing mast may need a sheer web and some bulkheads) and joining them before the external veneers go on is no work at all. I worry that thin veneers at 30 degrees will not resist the large torque wing masts and gunter yards exert. Applying 4 (or even 2) veneers, then epoxy coating them is very slow compared to a layer of glass, and unlike glass, they do not reinforce the join at the trailing edge, which may fail under peeling loads. I'd be happy to comment on your weights if you want to attach them.

How much do you pay for sitka spruce? I sell materials for carbon tube masts for about $aus25 per kg/$US44 per pound. This will be about 50% lighter than a wooden tube mast with the same properties. Wing masts are more complex to cost as a carbon one would include foam or Polycore core for the sides and sheer web, but I am pretty sure that this will make the spruce mast relatively even more expensive, as well as much heavier.

As for rocker, I agree it makes for a better very light air shape (less wetted surface) although if you are that concernedm, then moving crew or weight to one end of the boat will reduce the wetted area of the unrockered hull considerably. Yeah, I know this is a p[ain, bit much less so in light air than moving it to windward in a breeze. Like the section shapes, rocker is pretty irrelevant if the boat weighs twice as much as an unrockered one. Unrockered harry's with rudders on the beams turn quicker than cats and not much slower than fin keeled monos.

regards,

Rob

Tcubed

09-24-2008, 09:30 PM

Designers agreeing on fundamental concepts does not necessarily imply that they will come up with similar design solutions.

Right now, I'm tweaking the design, trying to create a shape that has higher prismatic the more it gets immersed, without creating too much of a strange shape for the waterflow. Light air performance is important to me, as i know light winds is very common on ocean passages, as is heavy conditions performance. So i'm always more interested in boats that will perform well in a very large range of conditions, than in peak performance.

No doubt i'll do some comparative tow tests with some models to make a final decision. There's nothing like empirical testing. Especially for things as complex as fluid flow past an object that is on a fluid interface.

MAINSTAY

09-24-2008, 09:57 PM

RHough

09-24-2008, 10:32 PM

Okay, so the .xls file didn't show shunting.
And I'm onboard with simplification.

You are not using roller furling. So how do you get the jib from one shunt to the other?

RHough
The main is on a stay that is better described as a vertical backstay rather than a shroud. A shroud connotes a lateral slope to the luff, whereas the luff is in the same vertical plane as the foresail. It is the mast, not the mainsail that cants.

That the weight of the rig is centered is a narrow view. The balance of a boat depends on all parts of the boat, not just the rig.

Right now I have 2 rigs for a Hobie16, but no hull. While moving to Lake Ponchartrain, the there was an accident that damaged the trailer and hull beyond repair.

Larry

Larry, you are hanging a sail on a wire that has different tension on each tack. That means the luff curve of the sail will be different on each tack. You are hanging a sail on a shroud. If you took the time to compute the lateral forces on the rig, you would see how unworkable the rig is. Any gain you might get from moving the sail from the mast will be lost in extra weight and the fact that a fabric sail cannot be cut to set properly form a sagged stay on one tack and a tight stay on the other. The stiffer the sail material is the worse the rig will perform.

If you size the stays so the sail loads are a small percentage of static tension, the size and weight of the wires required to handle that tension will be huge, the mast compression loads will be huge, and thus the entire rig will be orders of magnitude higher in weight. The hull structure to support that weight and those loads will need to be massive and heavy. I know you think you have a better mousetrap, but if you look beyond the fore and aft loads and calculate the lateral loads at maximum righting moment, you will see what I'm talking about.

Cheers,

Randy

Tcubed

09-25-2008, 08:36 AM

The jib is shunted by having two jibs. You dump one and raise the other.

I agree with Rhough. Any sail that hangs off a stay will impose much higher loads on the mast and therefore the boat. The mainstay rig reminds me of the mast aft rig. It could be argued that the mainstay rig won't put as much load on as the mast aft rig, but it is still much more than the loads from hanging the bulk of the sail on a spar. There was a production boat produced sometime early eighties with a mast aft rig. A few were made, until they realized they had under engineered for the monster loads and had to recall all the boats.
Consider this, in the twelve meters the compression loads on the mast are several times the weight of the whole boat. And this is fairly typical of modern rigs with big overlapping jibs and shrouds set inboard. Imagine how much greater the compression would be if all the sail surface where on stays. Another example are the masts made for in mast roller furling or behind mast roller furling. These masts are made heavier to handle the extra compression of keeping that extra stay taut.

MAINSTAY

09-27-2008, 03:18 PM

Guys, "huge tension," "mast compression loads will be huge," and "orders of magnitude higher in weight," "massive and heavy," "monster loads"? Very presumptive. Show me the numbers. "Those who fall out of love with practice inspite of math and science ..."

The quotes above are applicable to aft-mast rig. Not the Mainstay rig.

Attached are my numbers. Tell me about the numbers.

The longitudinal loads are based on identical sail load resulting in identical sag
Lateral loads for all three rigs are identical because the sail loads are identical.

The stresses in the rigs are very different. To keep the stresses within the capacity of current materials, practice requires more material, usually in the form of larger size elements, or thicker walls.

The stresses in the Mainstay are only larger if only compression is considered (as RHough points out). In the sloop rig the additional tortion and bending loads greatly increase the stress on the mast requiring a larger, heavier mast.
Or so the numbers show.

Larry

RHough

09-27-2008, 05:03 PM

Tcubed

09-29-2008, 10:36 PM

Now that is the correct way of leading a discussion, Mainstay, by, as you have done, posting your analysis. Although it is true that a new thread is required..

I redid the maths and i get slightly worse figures than you did but you are indeed correct in that the compression loads are not orders of magnitude greater. I'll even help you with the correct verbiage that i had myself overlooked and you should use if you don't already. Namely that you don't increase compression by having the mainsail on a stay, <because that stay (the backstay) is at that tension already>. You do however increase loads by reducing the longitudinal staying base especially when you take into account pitching forces- the sails forces do have a forward component, which in some extreme situations can challenge the boat's longitudinal righting moment which makes for asymmetry in the loads, just as in the shrouds. As for the offset mast, that invokes a whole other order of stress complexity that i won't go into right now, and less so in this thread...

What is also missing in the analysis and something that i am personally very interested in, (and is relevant to the proa) is the method for deriving the actual physical tension force in a stay with x per cent of sag and with S amount of sail with V wind speed and operating at Cl coefficient of lift. Someone must have already done this analysis, so i can be saved the tedium of working it out myself.

By the way, your using 600 lbs as an example loading can i think be taken to refer to a fairly light wind day!

MAINSTAY

10-02-2008, 01:01 AM

Tcubed

Yes, 600 is low. But the spreadsheet will handle any load.

I've never found a calc for the sail/stay sag/tension. If I started one, I'd divide the sail into slender triangles with the apex at the clew and equal bases along the luff. I can calc the wind pressure on a surface perpendicular to the wind. But don't know how to get the non-uniform pressure distrubution on a curved and angled surface. Any suggestions. anyone have any measurements of existing rigs to check the results against?

But to the real question. What do you mean by drop the jib? Do you have two permanent stays (Forestays(?), jibstays(?), ?) or do they come down, too? Do you need to go on deck or have some way to secure the sail? Details! Details!
Larry Modes

Tcubed

10-02-2008, 10:25 AM

Yes there are two stays. There are also two identical jibs. One is lowered and lashed down, the other is set. Yes, that's more work than other setups and i'm not saying it's perfect, but it has already been done that way. In my own case, where most of my sailing will be for the long stretch, shunting effort is a somewhat lesser consideration than if the design were intended for coastal sailing. In fact, for short tacks there is the option of dropping the mainsail and sailing with the jib only, shifting it across the mainhull on the tacks with an extra removable sheet. This would mean that the proa would then be tacking like a regular boat, but half the boards would be sailed with the wind blowing from the wrong side of the proa, which is not efficient but it's just another option for maneuvering in certain situations which might not allow for shunting.

In fact, i have drawn in another pair of stays inboard of the forestays for a staysail to have more options yet. You can compare looking at the regular rig and the heavy weather rig pictures that are posted earlier. So i guess some might call it a cutter.

The basic formula for aerodynamic lift force is

F = 0.5*rho*S*Cl*V^2

where rho is fluid density, S is surface area, Cl is coefficient of lift, V is fluid velocity past the foil. Use all S.I. units so F will be in Newtons.
Integrating triangles as you say is the way to go, i think, but one must keep in mind that the force the sail exerts on the stay is not the aerodynamic force per se , but rather the force required to keep the sail stretched in position with said aerodynamic force acting on it. Essentially it is something like a a continuous modified catenary acting in turn on a regular modified catenary.
It is essential here to identify possible mathematical simplifications for solveability.

MAINSTAY

10-04-2008, 05:53 PM

Tcubed
Thanks for the formula. Let me work with it for a while.

Your proa uses an unstayed mast, except for the jib stays. Are the stays a necessary part of the design? If not, there may be two other options for the jib.

First. Put the jib on a free-standing mast. Imagine a large wind surfing rig at each end, one acting as an overlapping jib and the other as a mizzen, and then on the other shunt the opposite. When you shunt, you only have to handle 3 sheets and no need to go on deck to secure a jib. The jib masts do not have to clear the boom, but can be close to the mast. Right? My understanding is that the boom is always alee the main hull.

Second. Put the non-overlapping jib tack to a forward extension of the boom. There’s only 1 sheet to handle. Or 2 sheets, if you have an overlapping jib. One form is AeroRig, but there are other forms in the public domain that are free to use.

Whether you use the jib-stay or wind-surfing or boom-extension, your CE shifts. I like your idea of a fixed fin on the windard hull, with a pair of centerboards in the lee hull to adjust the CLR.

There is a patent that uses a large circular bearing to pivot the rig. A familiar analogy is a 6’ or 8’ lazy-susan. In this way the mast shifts around the CE and there is one less thing to do when you shunt. Your widened deck in this area seems well suited to this type of base for the rig. The design is firmly in the public domain.
Larry

Tcubed

10-05-2008, 02:09 PM

So far in my design i have a deck stepped freely rotating wing mast stayed in all directions. The outer forestays are set to leeward so they would be the load carriers in the case of an accidental backwinding. The inner forestays are set on the leeward hull centerline, so less to leeward than the outer forestays. Then there is the shroud to the windward hull in an inverted Y arrangement, which allows the hulls free independant movement.

The unstayed mast is attractive, especially for not being able to be caught aback, but i have yet to be convinced that the unstayed mast can be engineered to be lighter for the same strength.

Your suggestion sounds similar to the arrangement used in 'Cheers', which had two unstayed masts, each with a regular bermudan sail. This arrangement is easy to shunt and does not move the CE around all that much.
Yes the boom is always to leeward.
I think that a stay hung rig is feasible on a proa but only with rig to windward configurations.

The foil in my windward hull is not fixed. It would be adjusted dependant on the heading relative to the apparent wind, with maximum immersion at the close hauled angle and progressively raised at freer angles. The end foils are fully assymetric so the bow foil is not used at all. CLR is adjusted with the windward foil. The stern foil in the present configuration is not adjustable, it is either being used- all the way down- or fully up.
My idea is that by adjusting the CLR the boat can be directionally stable at all headings. This follows experimentation i have done with non radio control model sailboats with adjustable foils which could be made to self steer at any desired relative wind angle. The only complication here is the extreme effect of apparent wind to the very high performance capacity of this type of boat. I'm pretty sure that i can get it to work with the working model though.

I include three images of the latest incarnation of the design, with wishbone boom, reduced leeward hull freeboard and volume and reduced sponson. The shroud is just visible. Two of the images are from the water surface and all represent the boat at design wind with the windward hull just out of the water.

MAINSTAY

11-02-2008, 12:19 AM

Tcubed

I imagine myself single-handing your proa in the South Atlantic at sunset with a rising wind with the coast of Nambia 20 leagues ahead. I imagine I need to shunt or reef.

What do I do to shunt? I imagine I would:
1. Loose the jib sheet and go on deck to the present bow to lower and secure the jib. I imagine the halyard is cleated near the tack so I may control the rate it drops and simultaneously keep it on deck. I imagine with the change in CE hull will head up, but to what degree I can’t imagine.
2. Go to the main sheet and reverse the sail. I imagine the proa will pick up speed on the new heading quickly.
3. Go on deck to the new bow to unsecure and raise the jib. I imagine the halyard is cleated near the tack so I may control the hoist and keep the sail from dipping into the sea.
4. Go below to sheet in the jib and adjust the main sheet and wing angle.
In heavy seas or cold weather I would be reluctant to walk to both ends of the proa and back.

What do I do to reef? I imagine I would:
1. Loose the main sheet and go on deck.
2. Loose the halyard, fasten the tack.
3. Adjust the outhaul, hopefully without having to go to the end of the boom.
4. Go below and readjust the main sheet and wing angle.
That’s not as bad in heavy seas or cold weather, or any time.

Your original idea was a gunter rig with a short mast. Let’s revisit the short mast idea.

Class C has experimented with wing sails that pivoted in the center on a short mast and on each tack the wing set at an abeam angle. This may work even better for shunting. A wingmast-like yard pivoted as its center on a short mast like a see-saw or teeter-totter. For the proa, the pivot may be raised and lowered.

To shunt , I imagine I would:
1. Loose the main sheet.
2. Keep tension in one brace(sheet to end of yard) while gathering other
3. Secure both braces and wing angle.
4. Adjust other main sheet. (Like a tacking jib, this shunting main has two sheets.)
Since it does not require going on deck, I can imagine doing this in any weather and single handed.

To reef, I imagine I would:
1. Lower the pivot, and secure the loose brace.
2. The main covers the cockpit or hatch, come up under the mainsail.
3. Loose the right outhaul, and gather the sail to the center of the yard,
4. Repeat for the left half, and stuff sail below.
5. Bring up new sail, “raise” right half, and then left half of sail.
6. Raise pivot with halyard (which unlike a sloop, is actually hauling the yard).
7. Adjust main sheet and wing angle.
8. Get a cup of hot java.
Since it does not require going on deck, I can imagine doing this in any weather and single handed.

Of course, this is only imagination. How are shunting and reefing going to be done on your proa?
Larry

PS Still working on sag.

keith66

11-02-2008, 04:27 AM

Tcubed

11-02-2008, 01:11 PM

I look forward to your numerical forestay sag analysis, mainstay.

In the argument of rigs for proas one must define what the priorities are. If avoiding going on deck is a priority, i would not recommend the rig i have drawn. Actually, if that were my priority i would be designing for myself a motorboat. No matter how you slice it, there will always be a lot of physical work and getting wet, etc, with sailing.

For me, i'm used to going on deck for all sail handling issues, so it is not a priority. And i would say that handling a jib set well inboard on a narrow hull (~1.2 M beam @ outer f'stay, ~1.9 M beam @ inner f'stay, ~2 M beam @ front of cabin ) is pretty cushy after years of going out twelve feet of bowsprit.

Shunting is pretty much like you describe it mainstay, except there is no going belowdecks at any point of this manoeuvre. And the halyards all go to base of the mast. This has worked for centuries. I have never had problems with raising and lowering jibs. I would put the sheets to the hatch, though, because trim adjustments are much more frequent than anything else, and also so they're within easy reach for quick action in the case of a sudden squall, etc.

The process for dropping a jib is like this;
The sheet is eased if it is too tight to allow the jib to go all the way down its stay.
The halyard is untied (the very tip is always secured) and the downhaul-if there is one- is pulled smartly.
Go forwards and get the lashings on.
If there was no downhaul this last step should read ;
Go forward, pull the jib the rest of the way down and get the lashings on.

If the jib does touch the water, so what? It's clipped on to the stay so it will not fill up. It just skims along the surface, waiting for you to tie it down.

My views on roller furlers can be seen at post #49.

For reefing it would be as you describe as well Mainstay, and of course there's no climbing out to the end of the boom. The clew lines come in to the mast, all very standard slab reefing. This can be done very quickly, contrary to what some people think.

The rig you describe does not convince me that it would be all that easy to reef, i'm afraid. These types of sails can be made to be very efficient, though.

Keith, you describe <<running up and down..>>. I imagine you don't mean that literally. I consider that when sailing you must be hanging onto something at all times, or at least wedged up against something, or life expectancy becomes very short. Ommited from my drawing are all the grab rails that run the full length of the boat. I almost never tie myself to the boat so lots and lots of sturdy handholds is very important to me.

Anyone know a simple method of drawing grab rails in in maxsurf or rhino? It's pretty much pointless for the design, but nice for the rendering. There are, i think, a lot of things for which good old pencil and paper is still the quickest and easiest tool for design and drafting....

rob denney

11-02-2008, 10:09 PM

I imagine that having to reef or shunt at sea by running up & down the length of a skinny proa to fist sails would be a quick way to get drowned!
Our 36 footer the Voodoo child had a jib at each end set on a wykeham martin furling gear, very simple & instant to use. When shunting we bore away & let the main go and she would sit stopped with the outrigger to windward it was just a matter of furling one jib, unfurling the other and then powering up the mainsail and away she would go. The standing lug main set on a midships mast generated the horsepower the jibs just balanced it out, i will try & find some photos of her it was a good few years ago now!

G'day Ken,

Would love to see all the pictures and details you have for Voodoo Child.

Absolutely agree about the folly of going out to the ends of the boat to shunt. Of course it can be done, and it may be less difficult than a bowsprit, but it is still wet and dangerous. I have found the jib is not required for balance, now just have a single main. Works well, saves a lot of money, weight and windage and shunting is very simple.

No matter how simple a stayed rig is to shunt, it is not as simple as an unstayed one, which bends in strong winds so automatically puts in the first reef for you. And shakes it out when the breeze eases. Further reefs are far simpler with a rig that weathercocks and a boat that stops to make it easy.

regards,

Rob

Taikaha

11-04-2008, 03:41 AM

http://www.dailymotion.com/register/3b07e126bbfd3b74c35d04c6f/6519333

This Proa has been doing a lot of hard ocean miles and seems to have got rig and rudders well sorted.

If you search Proa_file there is a lot of detail and links. The crew must be some of the skilled proa sailers out there.

Taikaha

11-04-2008, 03:49 AM

http://www.dailymotion.com/praoplip/video/x5b3mq_prao-voir-le-flotteur-se-soulever-a_sport

I think this was video being taken by the crewman carrying a camera in a large box.

MAINSTAY

12-14-2008, 03:45 PM

Tcubed
Hope for your contributions in an analysis aimed at determining stay sag I've started in the Boat Design Forum.
Larry

sigurd

01-28-2009, 10:39 AM

Tcubed,

Congratulations on very beautiful design. I hope it will not be as heavy as Rob says. Then it will be fast in light weather. But in heavy weather it would be faster if you turn it around, your lw hull is so wide, it meets any chop and slows... 20-30kt, meets wave, driven down hard by rig, stops quickly, but does the rig stop as well? I mean, there are several ways to attain longitudal authority, but a thinner boat does not need as much in the first place because it stops slower! If there is a need for more bouyancy in the bows, make them tall, not wide, is my opinion.

There is a big race tri with tall "canoe bows". Wish I could find a pic but I can't remember its name.

The point that you make on being suspended between two crests, and losing yaw authority, and broach, may be important. Me I have only broached in monos, which is not a problem unless the spinakker tears. Not so for your proa. So if you designed your rig to be so slow to release that you are trying to make a failsafe hull to compensate, then you should ditch it and find a better rig.
A free flying kite is one example.

Cutting away the fore and aft foot may give your rudders less to work against, but you already designed the rudders to have part of the chord non-pivoting (as far as I understand), and that you have to lift the fore one, so those parts doesn't add up. It will slow you down a bit. You get a blunter, shorter boat in waves. As with the flare, you get more hobbyhorsing. That old thing about reducing wetted surface in the light, by rocker, I have almost no faith in. How many % are we talking? And what is your aero, wave and friction drag at that speed?

The flare, overhang and tall ends of trad surf boats (proas, canoes, kajaks, viking ships) are bow-lifters, but remember that these boats are not tolerant of dipping the bows much, unlike closed boats with the crew to ww. Also they had less yaw authority than what is possible with two rudders.
I suggest getting beam- or side-hung rudders for crash worthiness, authority, quick and easy shunting and finally because you can put hydrofoils on them and still retract. I believe trimming a long skinny hull correctly in pitch will account for a lot of speed. I once picked up a huge, heavy log from the water and laid it across the bows. My all up weight increased maybe 20% but my speed increased. After that I put windsurfer fins on the 6hp, and gained a knot or more. But I have those silly transom thingys back there, getting them up and another half meter bow into the water, making the waterline longer and pointier, is probably what did it. A masted rig will trim you down (kite and motor pitches me up), but having control over it cannot hurt, and will help against digging into the surf.
To lift half the 3.5 ton boat, CL 1, at 15kt you need about 0.6 m2, 20kt 0.35m2, 25kt 0.22m2, 30kt 0.15m2. So there is a good amount of pitch control even for not so huge surfaces fore and aft. I would like to mention a model in the proafile yahoo group which steered by tilting the foils laterally, since you seem to be adamant about the WSA. That may also be less prone to ventilation than a rudder, on the other hand it could be complex to implement. Another way is ofcourse to invert them (from inverted T to T) in the light. For a normal rig the seakeeping of a proa like yours would probably be great, but you seem to want to push the area a bit (as do I), which can lead to pitch issues.

What rob said about the pod. It is like a short fractional bouyancy ama with no control surfaces, and a huge lateral area when immersed - except it will be slamming like hell when not capsizing you. And relying on it for safety... I'd rather not say my opinion. I could be wrong though. I'd rather have a water sensor to a rig trim line for dumping power, if I had a boat that could not tolerate inversion.

Another thing, whatever rig you choose, unless you fly a kite, see if you can close the gap completely to deck. This will reduce your induced drag. Tom Speer wrote about it somewhere here, and there was a spreadsheet even.

"I have always been very concerned with windage in all my designs[...]"

Then no doubt you are aware of that there is a very big difference between the drag of rounded corners and sharp ones, as in your sketches. I think there is something about it here, and the fellow writes a bit about the history of multi hull shapes and stuff. http://www.john-shuttleworth.com/Articles.html

I don't fathom why you think a ww cabin would have more windage than a lw one. rather the opposite, since harry ww hull is shorter. Your ama has less projected area than his lw hull though but hinging an argument on this doesn't add up when you concider the CD of your LW hull.

In short, I think your boat will be great to sail, and may be a great kiteboat, it even has a rig for when the wind is less than 8kt or so. As for the design decisions, you know best ofcourse, it is your boat.

"Anyone know a simple method of drawing grab rails in in maxsurf or rhino?"

Rhino: Make a curve and make a pipe/tube around it?

To MAINSTAY: "To reef, I imagine I would:
1. Lower the pivot, and secure the loose brace."

How can you lower the pivot with a leeward stayed mast? you'd have it sliding along the shrouds? Sounds sketchy. This is like a gibbons rig, am I right?

EDIT: your ama is too long. It is like putting a fourth wheel on a trike, and then having to make extra suspension to account for the extra loads and accelerations.

Tcubed

01-28-2009, 03:12 PM

Thanks . And thanks for a well thought out post .

The leeward hull ha en lwl/wlbeam of 12.33 at design wind and 13.7 at rest. I think those are pretty good slenderness ratios. It looks wide due to the flare. So i don't think it will have problems but maybe it would be better still to try and increase slenderness even more. I will experiment a bit with the flare and see how that can be optimized. The flare gives tremendous reserve of buoyancy which means it goes through less immersion changes due to the conditions. The total displacement is 3360 kg of 2180 kg is in the ama so the main hull is only 1180 kg. Compared to tris these are fairly low (but not crazy low) figures.

The rudder is now on struts sticking out of the ww side of the main hull. It is balanced and the whole thing can swing through 180 deg plus the normal range of angles for steering. I'm not sure what you mean about the rudders.

The rocker thing i am not sure about. I'm pretty final about the length, and the weight of each hull. The question remains on how to best optimize. Like you say the rocker may not be worthwhile for the saving in wetted area. I am not just trying to reduce wetted area in light airs (which is always a problem for any bi hull arrangement) but also have variable prismatic. It is quite interesting to play with.

I don't see why you say flare will create 'hobbyhorsing' as it is a powerful heave damper. Rocker does induce pitching though , that is true.

The gap between sail and deck . You are completely right and in fact that gap is not how it should be. However there are two problems with closing the gap; One is that it can only be closed for a portion of the foot due to the cabin that drops down . This could seemingly be solved by making a flush deck but that does not work either as the sail is at an angle so nescessarily it goes off the edge of the boat at some point. The pod helps here by creating a kind of endplate, but there are certainly limits to how big it can be made (and a lot of reasons to not make it so big either).
The other reason is that having the clew too low is dangerous. The reason is that when flying/almost flying a hull it must obey the same kind of 'rules' as a dinghy. If a gust suddenly hits and heels the boat to a large angle , when the sheet is released the boom hits the water and the rushing water prevents the sail from going out. Therefore the clew must be high or a boomless sail used but i cannot see how a boomless sail could be used here without sacrificing efficiency or going to a (too) narrow sail.

There certainly are two schools of thought on the sponson issue. The way i see it , it works a you say a kind of 'third' hull that creates a bump in the righting moment curves and a sort of 'buffer' against letting the sail capsize the boat. It is not meant to make it uncapsizable of course.
As for tripping , i know what you mean, but the shape of it is such as to minimize this effect (flare and immersed volume before the edge goes underwater. ) Also by the time tripping becomes an issue -survival conditions- i imagine that the conditions are already such that no sail can be carried and it would be lying to sea anchors. The exact shape of the sponson is not yet finalized, in fact nothing in this design is yet finalized. As for the pounding there is no reason why it should pound heavily if it is correctly designed.

Your point about the square corners and windage is a very good one. The reason i drew them square was because another factor of consideration in the design is ease of construction and i was intending to build the cabin and sponson of plywood on stringers type of thing but i might change that so i can round out some of those corners.

The reason i say it is less windage for the cabin in lw hull is because that hull needs to be buoyant anyways. Imagine you were to design a racing proa that did not need any accomodations at all. The windward hull becomes not much more than heavy 'log' and the leeward hull still needs enough buoyancy to hold its own weight plus the weight of the heavier ww hull and go over the waves easily, so it is naturally the more voluminous hull. So by adding just a little volume to lw hull it becomes livable, whereas to make ww hull livable means making it much more voluminous.

You say the ww hull is too long - when you see that it displaces almost twice as much as the leeward hull do you still think it is too long?

What does WSA mean? [...adamant about WSA..]

Unfortunately i'm without rhino till the weekend , or i would show the better pics in rhino.

I do expect a certain amount of trimming to happen of course and will be analyzing this further once i get to the detailed number crunching stage of the events. I will also make a 10 to 1 model to double check it does behave as anticipated. This is also one of the reasons i did not put a very high aspect rig on it.

A foil at the stern pulling down would cure bow down attitude but one has to calculate what its drag is (plus the comlications, weight and addition to apparent displacement etc) . In fact it is something i experimented with on my models. Models have enormous righting moments for their length so when the sheets are eased the bow goes down and a foil at the stern prevents this. In the models case it was so extreme (almost submarining from a reach to downwind) that a foil was very much worthwhile. In this case i'm not so sure , but it's worth thinking about.

Pictures

Profile to show sheer line and fairly high bows,
sections with sponson (so far) and static waterline and waterline at design wind,
Newicks' Greewich propane showing wing water clearance.

sigurd

01-29-2009, 12:04 AM

To be more clear, I feel that the traditional flare is probably appropriate for the leeward cabin boat (as is hard edges for plywood construction), but that it is going to slow down the boat when it gets immersed - the static waterline becomes more irrelevant since the wl is moving up and down. So I think that the unflared lw hull of harrys will be faster (and I argued that it was not neceserily more prone to pitchpole, due to less abrupt stop, and that reserve bouyancy can come from height), and that the eventual extra windage will not make up for it.

If I were to make a masted race boat, then I would first optimise the lw hull, and likely it would be much like a double ended race tri ama. Not much flare there. But also impossible to step a mast on (except with compression members to the akas), due to the low height and narrow beam. Modifying it for an unstayed mast would not require beam or flare, so that is what I'd do - ending up with a harry-like lw hull.

Then I would make the log voluminous enough to carry the cargo, and I think I would end up with a shorter and taller log than yours, based on intuition and experience from the twitchy movement of my cat. Basically with a short ama you don't get pitch torque input from the ama immersion - the vaka can do its thing. I would not make it flexible in pitch, risking resonant movement.
Same goes for the inertia, in the tall one the weight can be more centered.
I think it may get less WSA (wetted surface area) than the long one too, when there is some pressure in the rig - the long one is more all in or all out of the water, whereas the tall one is more gradually rising - a bit difficult to explain what I mean, but basically flying the ama is not stable, you will be trimming or steering to keep it there. When the long one dips, the whole ama surface will dip (I exaggerate), whereas the tall one's volume and WSA will more gradually change.

Then I would ask myself where to put the volume of people space. Clearly, there is already volume in the vaka, but how much must I compromise its first purpose (going fast) in order to live there? That is the most subjective question. If I had to add much flare close to the waterline, then effectively I had a wider boat in seas. The ama would ride much higher in inclement weather so flare there could be wider and deeper without seeing much water. What I would end up with, I am not sure - maybe like yours, maybe like harry lw hull but a tad wider high up between the beams, maybe with the living space to ww.

As for the hobbyhorsing of a flared vs. a piercing, taller hull. I may be wrong on that point. I base my belief more on dreaming than experience there, I think. But let me try to explain.
Exaggerated, the tall bow slices into the wave, continues to slice, gradually the up force increases, at the maximum upward acceleration the center of bouyancy of that bow is close to the center of gravity of that vaka. So the motion will be more heaving and less pitching than the flared one.
Flared hulls, in my imagination, tend to over-react - the maximum pitch upward speed occurs after you really need it - the bow rise too fast and just at the top of a wave where there is a trough behind. So the boat is not properly in phase with the sea.
I am pretty sure that even if this assumption is correct for some hullshapes, driving force vectors and weight distributions, it will be wrong or irrelevant for others.

As for the rudders. Ok you changed them to sit on axles sideways through the hull. That is what I would do as well.
Incidentally you then already have them pivoting in the right direction for AoA control of the eventual foils (but would require good bearings and more actuation power than flapped foils).

The pod: If you intend to fly the ama, then I think you are already just a heavy gust from immersing it, which would lift your rudders. How close is immersion of the roof then, I don't know. When immersed, the roof may be your only submerged lateral area. On the other hand there may not be much pressure in the sail at that point. The old fractional bouyancy tri amas were dangerous, according to Shuttleworth.

sigurd

01-29-2009, 01:07 AM

This is the one I mentioned, steering by tilting the foils.
http://f1.grp.yahoofs.com/v1/4EWBSX7c3Gs2DOgdQMUe8pAnWf9jldJybak6oHFGPUoyLoy09c4NBaK7ljwaVCzXUYcqW7S3L4vRb5Z_3_6eDvaXDzbJuyG_t64/Hydrofoil%20proa%20model/Foiledproa.jpg

Tcubed

01-30-2009, 08:07 PM

Dynamic response to the sea surface is one of the most complex aspects of boat design. And very interesting too.

There are essentially three factors at play ; the rotational moment of inertia, the curve of righting moments and the damping .

This in turn can be separately analyzed for each of the three rotational axes; pitch (transversal axis) , roll (longitudinal axis) and yaw (vertical axis).

Furthermore , there is also the linear responses in sway, surge and heave but we'll leave that to one side for now.

Ideally, for pitch response, one wants the boat to instantaneously adapt to the sea surface, without wasting energy creating unnecessary disturbances to the water.

The most important thing here is to reduce rotational moment of inertia about the transversal axis (rmoita). This reduces the amount of energy that goes into accelerating the ends of the boat up and down again with each wave.

Then there is the damping . Long , shallow shapes have a lot of pitch damping anyways due to the straightness of the buttock lines. Flare increases heave stiffness so i would associate it with greater pitch damping.

Length, or really the longitudinal righting moment, versus the rmoita will determine the pitching period , whilst damping determines the decay.

Making the ama longer will increase the period of its pitching. For each and every hull there is a wavelength that will coincide with its pitching period and thus induce resonance. At this point damping becomes all the more important as it is the only thing that keeps cyclic motion from growing uncontrolably. Fortunately it is actually impossible to design a boat with zero damping. However what is of concern here is how to maximize damping without compromising other aspects of the design.

Sigurd, your last post is missing the link i think.

sigurd

01-31-2009, 01:36 AM

http://f1.grp.yahoofs.com/v1/4OiDSX01LcaJq9FV2-6P1WKWE1CN2-f4lv-qYps5WBvRdB5o8RejLqmftezFj5PNeyr_PuN2pQC46U8AbxT7nYRj79bpYeB0oEk/Hydrofoil%20proa%20model/Foiledproa.jpg

here. Maybe you have to be a member of proafile to see it. I can send it to your email.

I like your rig, but even if your boom is prevented by water, you could let out the outhaul? Also, with the windsurf boom I don't know why you need the track on the pod.
How is the upper yard, what do you call it?, held to windward?

I think your rig could do with a little more complexity for the long trips with nothing to do but trim sails, so what about trying to incorporate topsails or wingtip feathers? variable camber double skin (http://www.boatdesign.net/forums/sailboats/variable-camber-double-skin-25808.html)? It would be a bastard to trim the tips in leeward angle, AoA and fore aft rake, but if you got it right you could possibly get rid of half the induced drag?

sigurd

01-31-2009, 01:53 AM

Edit: I see the Propane, its akas will ofcourse slam like mad, but fortunately nobody sleeps there!

These are the sort of pictures I am comparing your lw hull to, that is why I am saying it is wide: John Shuttleworth's Naia: http://www.john-shuttleworth.com/Images/Naia.JPG
http://www.john-shuttleworth.com/Images/Naia_2_front_view.jpg
http://www.john-shuttleworth.com/Images/30RacingTri.jpg

Tcubed

01-31-2009, 07:22 PM

I do not understand what you mean with pitch torque input.

What i have decided is to let the hulls conform to the water surface independently. I guess you mean if they are rigidly connected. I have yet to understand why white man's multihulls are almost all like this, as each hull is going through a different piece of water. To make them rigidly connected means they are perpetually fighting one another and the entire boat takes an average path , so neither hull is ever well aligned to the water surface. Plus the forces involved are large and so the akas have to be very strong, therefore heavier.

In the case of a proa i would think it is even more important than for a catamaran as the hulls are quite different. In this particular case they are both about the same waterline length but that is about the only similarity as the WH weighs almost twice as much as the LH and is much less voluminous. Initially the WH had a total volume specific density of 0.5 but then i expanded it a little bit so it' about 0.35 so it would be easier to pack in the cago. By contrast the LH is something like 0.09.

I expect the WH to not pitch very much at all and fly from wave crest to crest, sometimes going right through a wave and out the other side, whilst the LH will closely follow the water surface.

***

I imagine that in practice i will aim to sail with the ama displacing 10 or 15 % of its weight. If i'm sailing on my own i would lower this to about 50 or 60 % while i'm asleep. If asleep with my wife on watch i might increase this to 40 or 50%.

As far as complexity goes, no that is about as complex as i want to go even for long passages.

My goal for speed is to be able to get to Venezuela in a day (24 h) providing there is a reasonable wind like 15 knts or more.

Your link gives me 'document not found'.

sigurd

02-01-2009, 12:22 AM

Pitch torque input is probably a wrong term. What I mean is that if the buoyancy of the ww hull is hypothetically just a ball between the akas, the pitch of the ama will not be affected by waves, and it will not have any rotational inertia in the pitxh axis. Thus the whole boat's pitch will be ruled entirely by the vaka. I am thinking about my 6m cat, which has a sort of twitchy motion from the requirements of the two hulls to conform to the water. It is not entirely rigid - but I'm not sure if that helps, or makes it worse.
I drew a 2ton hull to see what you are talking about, I am used to thinking of lighter boats. I think 30cm beam is ok for 6-7m boats, 60cm by 10-12m gives 2 ton for a reasonable depth. Not as small as I thought, maybe 15m (your length, more or less?) is in the sweetest spot after all - it is sharp enough to go through waves without noticing much, as you say. Have you had a look at Leo Lazauskas' pages (http://www.cyberiad.net/hydro.htm) on slender hulls?
It will be fun to watch the long, flexibly connected ama. Is the pitch swinging of it damped also when flying?

Tcubed

02-02-2009, 01:30 PM

Right now i have the ama wbeam of 0.8 M and lwl of 15 M with semi circular underwater sections from end to end. This gives a slenderness ratio of 18.75.

As it comes out of the water it will be less and less affected by buoyancy forces so will tend to pitch less and less. By contrast, as the LH gets immersed under the transferred weight off the ama, it becomes more affected by buoyancy forces. However as it is almost empty of stuff and the weight of the ama acts upon the mast step it should have an excellent pitch response.

Yes i just got michlet a month ago but haven't yet had time to learn how to use it. Any hints on how to transfer a shape from rhino or maxsurf into Michlet? I obviously must learn to be fluent with this program.

sigurd

02-09-2009, 12:43 PM

About that flexing. Howcome is it that regatta cats are requesting stiff beams? Probably it is faster. I can't really see how flexy beams will reduce the design load requirement a lot - if the difference in pitch for the hulls are big, the torque will still be transferred between the hulls. You also have a potential of getting non parallell hulls in yaw. Also I am not sure you can build a flexy beam as strong as a rigid one?
Also, when the ama is in the air, I think it will go resonant or at least add a phase delayed pitch input to the main hull, since you apparently haven't thought out a method of damping the structure when unsupported by water?

Tcubed

02-09-2009, 08:55 PM

Some excellent points.

No i do not think resonance will be a problem as it would require resonant frequency that is close to values such as 1, 1.5, 2 etc. A final mass distribution calculation can determine whether or not there might be reason for concern. If it seems too close to a integer or integer fraction the weights (cargo) can be shifted slightly.

You are right of course that fluid dynamic damping reduces to almost nil when in the air. But at that point the only pitching input would be from whatever stiffness is in the crossbeams, which i hope to be able to make very flexible in that direction only. There is also a small amount of damping from the inverted Y shroud arrangement. I see that it could possibly be a problem when sailing over long waves ie slow cycles, and the small amount of input could create pitch resonance in the ama. In practice though i don't expect to ever be consistently flying the ama, but rather be at 90 % say ideally so there is a buffer zone and of course a bit of damping.

The yaw thing is not difficult to prevent as the cross beams , even if very flexible up and down will not stretch or shorten. The much greater engineering challenge is how to make the beams very flexible vertically but very stiff horizontally. So the hulls don't move for and aft relative to each other.

I have not had opportunity to speak to other designers about the preponderance of rigid multihulls but a simple observation is that with the usual staying arangements it is essential to have a minimum rigidity to counter rig forces. In a tri or cat the rig will try to lift the stern of the windward hull, so if they were made 'floppy' the rig would collapse forward pitchpoling the windward hull while the leeward hull keeps its normal trim. In the case of the proa the shroud points to the middle of the ama and so the rigs trimming moment is transferred directly to the only hull that needs to resist this moment , the leeward one.

Yes you can build a flexible beam just as strong as a rigid one . Those or two different things ; Young's Modulus of elasticity and breaking force.
And if you do not force the hulls to move just the same despite not being in the same piece of water it seems obvious to me that there will be much less forces transmitted along the beams.

sigurd

02-09-2009, 11:26 PM

"Yes you can build a flexible beam just as strong as a rigid one."

Yes sure, but it would be heavier, right? A stiff beam can make use of very tall shear webs, creating great strength with little flange material.
If you want the same advantage, you would have to find some very stretchy flange material, or have unsupported parts of the tension flange take "shortcuts" (increasing opportunity for it to buckle when compressed), or deform the shear web, which make the stiffness of the beam lesser the more it is bent, opposite to what one would want (the flanges come closer together). None of those are cunductive to using as little as possible of any high strength/weight material, as far as i know.
carbon tow is the shite for strong things, its not that expensive either. but unfortunately for you it is very stiff!

The most obvious way is to use a thin, large chord beam - it needs more material for the same strength as a tall one.
If you have fore aft wander, cross two ropes in the middle of the trampoline or lay the net diagonally.

"And if you do not force the hulls to move just the same despite not being in the same piece of water it seems obvious to me that there will be much less forces transmitted along the beams."
So what?
You still have to design it for the most load, which, i imagine, will not be less just because the hulls are skewed when it happens. When is that?
It's analog to the bridle on the mast. (It should be either bridle, OR mast, prefer the former.) The hung ama or wide staing base looks superb until you take into account the rig being broken from the wrong direction. Then you have a pissepoor staying base - worse than a mono, but your righting moment is big as a multi. And the bridle now does nothing to help your akas either.

The yaw thing. Did you try in your model to bend one of the beams and not the other? If I am not mistaken it is perfectly possible to ged yaw disalignment without shortening the beams. Unless your bridle can prevent this.

I'm confuddled with the ama movement, it will be very interesting to see how the boat behaves! When you find out that it sails better on the other tack, you can just make the Y bridle a V bridle!

sigurd

02-19-2009, 06:37 PM

I am curious how you are going to make a flexible beam. What do you think about something like this?

ThomD

03-10-2009, 09:30 PM

What about the Gougeon approach to a beam, suspension? The have used it several times with success, F-40 Adrenaline Tri and the C-cats trimaran. Hard to know whether it was really and truly the future since it kept getting banned.

keith66

03-11-2009, 10:39 AM

Saw a article in recent Yachting world magazine on L, Hydroptere the foil bourne tri, she utilizes suspension struts derived from Airbus landing gear on her main foils and this is reckoned to give her the flexibility not to break?
Apparently it is the one aspect of the boat that the crew won't talk about!

Tcubed

03-12-2009, 03:13 PM

Thanks for those tantalising tidbits, now where i might i find out more?..

My idea is something vaguely similar to Sigurd's drawing except the 'holes' are rectangular, not round.

Essentially, picture two planks, one above the other, spanning from main hull to windward hull. They are 'flat', such that their smallest dimension is vertical, and the second smallest dimension is longitudinal.
They are separated by approx the same as they are wide.

Then they are connected together in such a way that the planks' separation from one another cannot change, by struts every two widths or so. Imagine the struts are all individually pointing for and aft.

This would be one crossbeam. The whole thing is duplicated for the other one.

It seems to me that this setup would permit a considerable amount of bending and twisting yet have a decent breaking point.

Also it is very easy to build and presents a very small frontal area.

sigurd

03-12-2009, 04:47 PM

In my drawing, the black lines are flanges.
The red lines are hoops, they are connected to each other and to the flanges.
The green stuff is solid stuff, cored fiber laminate or whatever.
The idea is that the beam will be able to utilise a large separation between the flanges, for strength, but since the hoops can flex, it is also flexible.
Now the key to it is that, when it is flexed enough, the hoops are squeezed into full contact with the green stuff. Ergo, at the ends of the flex the beam is stiff - it behaves as a tall, prebent I-beam, and the hoops are supported all the way so they don't get broken by overstrain.
One would have to think some more on it or try it to see if it works as intended.

With your idea each flange must be reasonably stiff as not to kink at the strut points, or buckle inbetween. Also you cannot utilise a lot of height (I think) so you need more material for the same strength.

Tcubed

03-12-2009, 07:26 PM

I must say it is a pleasure to have intelligent input.

Now that you explain the diagram you posted i understand what you were meaning.

It has me thinking on methods of improving my conceptualization but without involving too much high tech materials and least of all complications or excessively elaborate construction methods.

If one were to use tension limiters instead of compression limiters, maybe it would be easier to engineer it in a reasonably low tech way.

Timothy

03-13-2009, 09:32 PM

Sorry to be off subject but Sigurd I couldn't help thinking that your idea would work well for flex limited battens.The battens would be free to assume thier intended shape in light winds and maintain that shape as the wind gains strength rather than let the sail become fuller as happens with conventional battens.

James Brett

03-14-2009, 02:10 AM

:) Hey All,

Just to let you know of my 5 metre proa design.

I am using a junk rig and ogive foil section rudders. The forward rudder is locked in a straight line to act as a centerboard while the aft rudder steers. The forward rudder can be lifted off the wind to reduce drag.

The junk rig is highly under rated IMO. On my boat it can point to 50 degrees from true wind, the same as most una rigged dinghys. Also it gives a great safety advantage over the sloop rig on your design, as it can be reefed to any point, and does not require people to go out to the ends of the hull, ever.

The junk rig can carry more sail area due to its easy reefing, this makes up for it's lack of efficiency in light wind. It can be shunted in about 20 seconds.

Your design to me looks like it will perform well but won't be much fun to handle. Will probalbly also be rather expensive.

Check out my website at: jbyachtdesigns.co.nz
and see some onboard videos here:http://www.youtube.com/watch?v=3sDfiajL9gk&feature=channel_page

sigurd

03-14-2009, 01:09 PM

James - nice boat!

Tcubed: tension limited? you could perhaps use a single transverse compression element, with struts sticking out perpendicular from it - holding rope for shear web and for tension "flanges".
edit: It could be perhaps be lighter than a stiff beam, because spectra is stronger to weight than carbon, and it does not need epoxy. Wood is good, carbon is usd18/lb (www.sollercomposites.com).

Timothy . Cool idea. did you think, with a single, or double sail? the hoops looks like they would fit around a mast. Double skin junk (http://www.boatdesign.net/forums/boat-design/shapeable-airfoil-wingmast-ice-boat-25193.html)

sigurd

03-14-2009, 01:53 PM

Here the center triangle is a backbone, the grey things are struts, and the blue stuff is rope

sigurd

03-14-2009, 02:24 PM

one set of vertical struts, plus one transverse compression element. add ropes to your heart is content

edit ofcourse, you must put longitudal battens over, and cloth over those, to decrease resistance.

sigurd

03-14-2009, 03:14 PM

Terminator^3 in gale

tspeer

03-14-2009, 11:03 PM

...Now the key to it is that, when it is flexed enough, the hoops are squeezed into full contact with the green stuff....

We used a technique like this to stiffen the axle of a landyacht (http://www.tspeer.com/landyachts/Lydia/LydiaPhoto.pdf). The axle was an aluminum teardrop extrusion, and it proved to be flexible enough to all the bottom of the landyacht to contact the ground when the rig was highly loaded and the yacht hit a bump. Once, it hit hard enough to put a small permanent set in the axle, so it had flexed to its yield point.

We took a piece of 2"x2" lumber and tapered it toward the ends, giving it a truncated spindle shape (but still rectangular in cross section). Unidirectional carbon fiber was then laminated on the top and bottom of the tapered wood. Then it was forced down the inside of the axle to the center to make the axle a nonlinear spring. The length of the insert was on the order of a quarter to a third of the length of the axle.

For small deflections, the axle only contacted the insert at the middle, and there was negligible influence on the flexibility of the axle. However, as the load increased, more and more of the insert contacted the inside of the axle, and the stiffness increased. Eventually, the entire insert was in contact with the axle, and it basically flexed outboard of the end of the insert.

This successfully stiffened the axle and we had no more problems with it contacting the ground.

Tcubed

03-17-2009, 01:30 PM

That's pretty funny (#106).

But in fact it wouldn't do that since there is a stay from the mast to the ama.

When it could be subjected to bending is if caught aback when essentially you have a monohull with lee buoyancy pod, and this is the situation that is difficult to engineer, as it should never happen (basically the frequency of it happening should be very low) yet it needs to be accounted for and with a minimum of cons for the 99.999% of the time.

Maybe it should have one under aka stay just for this purpose, and lift the akas up the side of the main hull as much as possible to improve the angle...?

sigurd

03-17-2009, 03:35 PM

yeah, either a completely depowering, feathering rig, or, as you suggest, flexing the beam ends upwards, to let the mast bend towards the ama, would also depower it when caught aback.

I have been pondering a bit more on the possibilities of flexible beams.
The following sketch is a bit far from the subject boat, but I thought I'd include it anyway.
If the ama can slide back and forth, and is fitted with a leeboard, and the rig is balanced, then rudders could possibly be omitted.
I read about a french "parallellogram" proa - it died when the skipper let go of the bridle line, the ama crashing into vaka.

Further, it would be possible to shape the leeboard like a J (or inverted T - kelp catcher), and adjust its pitch according to necessary downforce (or upforce). A sensor wand (or a hydraulic piston connected to a water port on the leeboard) could actuate this pitch change, possibly along with altering sail trim.
A further feature would be to use the leeboard's own force to power up the boat - since, when the leeboard is out of the water, it is time to effect generous depowering. In the sketch this "safety release" is done by letting the rig cant to lee, as well as letting out remaining tautness from the rig trim line. This could reset itself when the ama landed again.

Just some rough ideas, intended to show some variation on the "set and forget" rigging possible with proas.

sigurd

03-17-2009, 06:43 PM

I think the rig you have proposed looks good. But I like windsurf rigs, especially balanced ones. Here is a variation from the keel stepped, free standing sort.

If it is attached close to the boom/mast joint and to aka, the shroud could be able to take compression, so that no leeward shroud is needed. As shown, two S-shaped shrouds trades length between each other. This moves the rotation axis of the boom further back, making the balancing job easier on the tail.

Finally it should be possible to devise a way for the fore and aft stays, from the S shrouds or boom, to move away when caught aback, allowing +-180' boom rotation. For instance, a stay from leeward side of the rig would take over the job from a windward one, when the boom went past 90'.

Some things about such a rig. You can rake it fore aft and tilt it sideways, its flex is unimpeded for gust eating, no sheet loads, boom end can be tall, so can be depowered fully when heeling, meanwhile a batten can lock down the sail against the deck, closing the gap. Also, you can lock a sheet and use the tail for steering the boat. Works the same with canard but the windsurf boom end is already far aft, so an air rudder in that vicinity gets good leverage.

sigurd

03-20-2009, 10:29 AM

I would like to draw attention to this discussion, load paths in a catamaran (http://www.boatdesign.net/forums/multihulls/load-paths-catamaran-26229-6.html#post262647). My conclusion, a single beam is less stiff in torsion than two beams the same weight, but it would give more bending stiffness and strength. I thought, since your plans involve torsion flex, but not neceserily bending flex, that a single beam may be more favorable. In particular, I think that bending backwards, lifting the vaka off the water, is going to be the strongest load on your aka(s).

Reinforcing the vaka for beam/rigging loads may also be lighter when using a single beam?

edit: post #804 in the foiler design thread is about a shock damped foil for proas.

peterAustralia

04-11-2009, 10:52 PM

hi T cubed

First I would suggest moving your discussion/questions to the yahoo group proa_file. On this Yahoo group you will find many many people that have actually built proas. I know of three that have built very large pacific proas, and are on the yahoo group.

At least three people in this thread are on that group, Tehro, Gary and Rob. I think that in the yahoo group the quality of your replies and information will be higher. Secondly, do you have money? or is your proa sketch, just something you want to do one day.. when you get money?

In terms of dagger-boards, on a large boat the weight and mass of boards becomes an issue. If the sail plan could be balanced so as to only require small boards for steering, then you make shunting and raising and lowering of board much easier, as the boards will be smaller. If you notice Russ Brown's boats, they are very deep and appear to obtain lateral resistance from the hull as opposed to foils, this seems a rugged and simple approach, definitely less susceptible to damage. Downside may/may-not be does not point as high upwind (guess here, no hard data)

I see you have a board on the outrigger, I am personally not keen on that, but is not my decision to make. A little thing, a proa can allow for the outrigger to flex independently of the main hull so as to go over waves. This is not a bad thing and does not really have a downside. The equilibre proa, as best as I can tell, has the crossbeams going out a fair way and be rigid at that point, but later on they are allowed to flex. At this junction there is a torsion box, beams on main hull side are rigid, on outrigger side, can flex,

Rob does not like Russ Brown boats, that is OK. I humbly suggest taking his points with a grain of salt. Firstly he says that at 2 tonnes for Jzerro it is unnecessarily heavy. Well, I guess it is technically possible to build lighter, but is it really that that bad, I mean a 2 tonne 37ft boat, (is that overly heavy? In other places he has said that if the Jzerro Proa gets back-winded the mast falls down (I am going from memory and may possibly be mistaken) however this falling down claim has been disputed by some that have actually been on the boat.

I think if you want good advice, go to yahoo group,, and forget about boatdesign.net. Also some other russ brown boats, may be for sail, be that be Cimba or Kauri (there are 3 similar boats.. Jzerro, Cimba and Kauri)

regards
N Peter Evans