Post your design ideas

Slider with a flat bottom

Ray,

I finally have come around to your idea of a flat bottomed cat. Doug Lord probably suggested you use the flat bottom to have a place for lifting foils that protrude thru the bottom like a daggerboard. That way when they are retracted you still have a perfectly flat bottom. When flying, the recess for the foil won't matter because it is above the water. The only problem I see is that the foil will be so small you will need to be at 20+ knots to fly, so you need another Nacra rig!!

(I hope everyone understands this is a little joke on my previous round bottom comments)

Marc

 

Slider

Ray, just out of curiosity ,why do you have the boards angled outboard at the bottom?

 

10m LOA Catamaran - continuation of design work

I carried on doodling my proposed 10m LOA catamaran design at odd moments over the last few months. Progress on this will have to stop for a while since we plan to go cruising in our present (monohull) boat for much of the rest of this summer. Below are a few views of the design as it stands at the moment. It probably does not look a whole lot different to the pics I posted here before, but there is now more internal detail - the previous drawings were just a shell with the main structural bulkheads inside. If I decide to continue with the catamaran design when we get back from sailing this summer there will be plenty still to do. Although there is now quite a lot of internal detail for the hulls, there is little for the bridgedeck structure between the hulls and almost no detail at all for the rig, sail handling arrangements, mooring and anchoring arrangements, electrical system etc. Also at some stage I would want to re-visit the finite element analysis of the structure. The initial simplified analysis indicated high stresses around the access openings into the hulls and also to some extent around the big windows. The wood work in these areas is now strengthened but another round of analysis would be needed to see if it is strengthened enough. Initially, the only load case considered was the 'close to diagonal capsize' situation. I might now look at a few more load cases, perhaps including situations like a heavy crew person jumping down onto the deck from a quayside - that kind of event can cause higher local stresses than sailing situations! Towards the end of the design process I would need to work out how to cut some hundreds of odd shaped pieces of plywood from standard sized sheets. The method I had in mind was to print out the silhouettes of all the pieces to scale on stiff paper, cut them out with scissors then jiggle them around on cardboard rectangles representing the blank sheets of ply, then finally re-draw them with 2D CAD to obtain those vital DXF files - it sounds like quite a job, does anyone know a better way?

A few points regarding the design for anyone who might be interested:

As before, the structure is basically wood and epoxy. I like the idea of foam core and resin infusion with glass or carbon fibre, but I am pretty sure that would be more work to build despite the claims made. My choice of wood and epoxy is primarily for easy building, although it is also true that the materials are cheaper, even allowing for getting all the plywood CNC cut, which would be nice. Nearly all the shell is plywood, in a range of thicknesses from 9mm down, but there would be small sections of strip planking at the turn of the bilge. The curved front of the bridgedeck structure might also be strip planked. Each hull has a knuckle a few inches above the waterline. The idea is that the lower hull below the knuckle would be built first, using female formers so that internal sheathing and structure could be fitted while the skin is still supported in the formers. I would hope that this lower hull would then be a sufficiently rigid unit to act as a base on which to assemble the rest of the hull structure. Glass epoxy sheathing above the knuckle would be thin, external only, and mainly for surface abrasion resistance. Sheathing below the knuckle would be inside and out and would be a bit thicker, with the glass fibers accross the grain of the strip planks.

I am keeping the structure demountable, so that it can be transported on a large lorry, preferably one of those lorries with a hydraulic crane for loading. The two main cross beams fit into 'trunkings' in the hulls and are fixed with an arrangement of wedges. Certainly I could use bolts, but I quite like the wedge scheme since it avoids some of the problems that can occur when loads are transfered between a low modulus material such as wood and a small load bearing section of a higher strength and higher modulus metalic material.

I have retained the moveable wheelhouse shelter, I think this is a nice feature allowing one to sit in shelter near the wheel, idly watching the autopilot at work, or alternatively to slide the shelter forward to stand at the wheel for better visibility, or to fold the shelter right out of the way in nice weather. I could make it a ridgid shelter but then sooner or later someone would try to walk on it, so it would have to be quite strong and heavy. Most people will not try to walk on a canvas shelter, hence that can be much lighter. Also a folding canvas shelter allows the mast to be lowered in a tabernacle arrangement. I agree with a previous post here that the mast will not often need to be lowered for navigation, but I am not keen on climbing up masts so I like the idea of a mast that can be fairly easily folded down to allow all parts to be inspected/maintaned.

My present boat, which I built in 1978, has a pivoting lead ballasted centreboard and over the years I have got into a bad habit of using the centreboard as a depth finder. I suspect that I may not be able to instantly drop that habit, so I have designed this catamaran with pivoting centreboards and dinghy style pivoting rudder blades, although of course no ballast is needed in the centreboards. There is a pivoted part in each centreboard case to closes the centreboard slot flush with the hull skin when the centreboard is fully lowered, giving little more water resistance than with a typical dagger board arrangement. I am not sure if it is worth also considering some kind of dingy type centerboard flaps for when the boards are only partly down. The centreboard cases are set inboard of the hull centrelines and there are also beaching 'skegs' that I have drawn on the hull centrelines. I wonder if these should be a bit outboard of the centrelines to keep them further from the centreboards?

The transom hung rudders are controlled from a steering wheel. The general arangement of this boat makes it difficult to include tiller steering and the proposed wheel steering system is really quite simple and should have little friction. I realise that the steering will be heavy if one ever needs to steer with the rudder blades part up, perhaps steering with the throttles of the two engines would be a better option for manouvering in really shallow water. Both rudders can be fully raised and turned 90 degs inwards to lie flat against the transoms for harbour stowage. Transom hung pivoting rudders are said to be prone to ventilation of the rudder blades, although I dont think that has been much of a problem with my present boat. To help avoid such ventilation, the lower rudder mounts are designed so that they form a 'fence' just below the nominal water plane and extending round the foreward part of the fully lowered rudder blades. The wedge under the transom might even recover a minute amount of energy from the sternwave - well who knows!

The design has sprouted a curved beam, or mainsheet horse, above the aft main cross beam. This would house an integral mainsheet track, I am thinking of a home made traveller with rollers that run under rails made from lengths of aluminium rod. This structure also provides bracing for a pair of dinghy davits and it acts as a robust fence that would make it hard to fall off the back of the boat, the downside is that it would also make it more awkward to climb down from the cockpit into the tender.

I have sketched a small gas powered fridge in the galley, but if necessary this could easily be changed to electric before the design is completed. I would think that refrigeration could be the main electrical load on this vessel, so gas refrigeration might significantly reduce the requirement for battery charging and allow lighter batteries to be fitted. I just dont know how practical a gas fridge would be on a boat, although I think that there is one type of American catamaran that has them fitted. I have the installation manual for a Dometic gas fridge and this indicates that it is OK to run it with the normal motion of a vehicle on the road, but what about a catamaran, does anyone have any thoughts, or ideally experience?. Since this is a catmaran it is possible to install the fridge in an enclosure which ventilates straight downwards to the open air, I imagine that should mitigate some of the safety issues, sorry if am sounding like an engineer at work!

I have sketched in two outboard engines, 8 to 10 HP each. I wonder if the luxury of power tilt on the engines is worth the extra weight? I have shown the engines fitted aft of the aft cross beam which allows a good spacing between the props for manouvering using the engine throttles. I have also considered locating the engines further forward within the bridge deck structure, which has some advantages, but it would mean that the distance between the props would need to be reduced to something like 2.5m. Would that be enough to turn the boat through the wind in a stiff breeze I wonder?

If I actually build this design I would be thinking of normally sailing it with just two persons on board, so the accomodation has one double berth in the starboard hull and this could be supplemented by using the 'L' shape settee in the port hull as an occasional single berth. The spaces forward of the main bulkheads would probably be left empty, or used for storage of a few light items, but if more berths become wanted there is a possibility to use one or both of these spaces as a single berth cabin, the tops of the forward bouyancy tanks are more than long enough for berths. These 'cabins' would offer excellent privacy, but not wonderful elbow room. Also, as drawn, there is no second escape route from these spaces, which might be considered unacceptable. It might just be possible to provide such an escape route, but for the likely use of the boat, this doesent seem worth the trouble at this stage. There is full standing headroom at the entrance to each hull and in the galley and shower/toilet areas, but only sitting head room elsewhere. Being used to cruising in a much smaller boat we are happy with these compromises. Generally, I am trying to keep down weight and windage whilst avoiding a purely racing inspired design and accomodation that feels like living in a pair of pipes.

 

Hi John,
Appears as though you are giving a lot of thought to various design aspects of your proposed catamaran. I've not had time to read thru them in any detail at all, but the little bit I did I took notice of was some of your construction desires. I would suggest you have a look thru this kit-boat construction technique utilizing poly-core panels that are computer cut.

http://www.australiancompositepanels.com.au/

http://www.australiancompositepanels.com.au/Templates/drawings_and_photos.pdf

http://www.australiancompositepanels.com.au/Construction%20Pics.htm

I was seriously considering becoming a representative for Solidary Catamarans here in the USA. I had a gentleman who was very interested in building one of these vesselsupon my suggestion,...one that I had made a few modifications on,...and including a rig similar to my mastaft rig. That has fallen through at the moment as the client selected a Schioning design to have built in South America.

I was impressed with this sandwich material utilized on this kit boat to give it serious considerations for use in the deck and superstructures of a couple of monohull motorsailers I am working on.

 

Underway...

Currently being built....plug being faired....

 

Smart as & great looking too

Gooday 'Is' - just what does 'Smart-as' weigh? Length? Width? Are the hulls canted out? If not - why not? In-shore - off-shore? Sail area? Aprox cost?

Sure as all heck - looks the full goods. How much weight will it carry & stiff boogy?

Sure do wish you a lot of good fortune !!!!!!!!!!!! Great looking hull + + +

Caio, james

 

John Perry Said:-

.

Jim and Joanne Brown had a nice cruising trimaran in which they were sailing on a cruise. One day at dockside they left a pan of potatoes bubbling on the gas cooker while they popped ashore to buy some item.
The pan boiled over and put out the flame. The gas, being heavier than air started filling the bilge. The gas fridge stood on the floor immediately above the bilge. When the gas level rose above the floor and reached the fridge pilot light------------------------------ Thats how they lost the boat.

 

Re Gas Fridge

I guess you have to be careful about using any gas fired equipment in a confined space. I know someone who stored a gas picnic stove in a locker on a 14 foot open sailing dinghy. One day the locker blew up - I assume the gas leaked, but I don't know what the source of ignition was, might have been a cigarette.

I have the instructions for installing the RM123E gas fridge and it is clear from this that there is a system to cut off the gas supply should a thermocouple detect that the flame has gone out. I can only assume that Jim and Joannes fridge was one that did not have this feature, or that it was faulty. Also, it would seem from what you say that the fridge was not ventilated as it should be. The instructions I have indicate that there should be a 40mm bore vent pipe from the bottom of the enclosure where the fridge is installed, this pipe sloping continuously downwards to the open air. This requirement would be difficult on most monhull boats but it would be no problem on a catamaran with the fridge above the level of the bridge deck.

I also note that the RM123E instructions state that the fridge 'should operate satisfactorily in ambient temperatures up to 90F, with some measure of cooling up to about 95F' (35C). Realistically, we dont often get summer temperatures that high in the UK, but it is the temperature inside the boat that counts, and this could well be a bit warmer than outside, so that ambient temperature could be exceeded in tropical areas. In fairness, the effectiveness of an electric fridge will also decline as ambient temperature increases, perhaps to the same extent as for a gas fridge.

 

Quote.
I have the instructions for installing the RM123E gas fridge and it is clear from this that there is a system to cut off the gas supply should a thermocouple detect that the flame has gone out. I can only assume that Jim and Joannes fridge was one that did not have this feature, or that it was faulty. Quote.

It wasn't the light in the fridge that went out.
The fridge pilot light triggered the fire.
It was the the flame of the cooker which went out leaving the gas flowing.

 

Nice boat. Google nesting programs to fins how to get your shapes onto your ply.
Make sure your mainsheet traveller is wide enough that crew's hands are not over the track when they grab it. Makes a big mess when you gybe and the car jams the hand.
We are currently building 6 unstayed masts for biplane catamarans. They are all hinged just above the boom. Not for maintenance, as there is none on unstayed rigs, but for getting under bridges.

 

Very neat, good looker and well thought out design, John Perry. By the way, you're a Kiwi from way back, aren't you mate? I remember reading long ago about one of your catamarans, (Perry, Perry? or was it John, John), in a Round Britain, did very well until something broke?

 

Gooday Gary & John Perry - oh & others also.

Gary - think '306' could build it in SE Asia for under $100K USD - if he built it himself?

John - that's a seriously good looking - well thought-out - nice piece of flotsam, for sure.

Please tell us more about it - thanks. Caio, james Please - more information!!

 

Old Sailor, My applogies for not reading your post properly. There is so much reading matter around these days that some of us get into a habit of skimming over it rather than looking properly. So, on this occasion the gas fridge was not the initial cause of the fire, but it does seem that the fridge was installed close to the bilge where it could not have been ventilated in accordance with the instructions that I have seen for this kind of fridge. I think the message is that one has to be careful about using gas fuel on a boat, or petrol for that matter. A catamaran has the advantage that it is easy to arrange downwards ventilation for the storage of these fuels.

I suppose the basic difference between a gas fridge and a gas cooker from the point of view of safety on a boat is that the gas supply to a cooker can be shut off when you are not actually cooking, whereas a fridge really has to be left running, even if there is nobody on board. If you dont leave it on 24/7 the food will be wasted, (unless perhaps the insulation is exceptionally good) so then no point having the fridge in the first place.

Your post started me looking up gas detectors on Google. You can buy a system that senses LPG and/or CO gas and can automatically shut off your gas supply near the cylinder. Sounds like a good idea as long as it does not lead to false alarms or complacency. One problem is that a typical 'fail safe' shut off valve consumes about 1.0 amps at 12V, not an insignificant continous current drain on a small sailing yacht. There are 'low power' valves that consume only about a third of that current, but that is still quite a lot. There is also a system from Seath Haztec that only takes significant current if it actually senses gas and shuts the valve. They describe it as fail safe, but I would want further infomation about that since it is not so obviously fail safe as a valve that is closed by a spring and held open by an energised solenoid. In any case 'Fail safe' often means no more than that a system will operate safely in the event of an external electric power failure, possibly ignoring other possible reasons for failure such as moving parts corroded solid.

Rob/Gary/SR, thanks for your favourable comments, I realise that I have some way to go to finish my design, let alone the building. IS at least has a large hull shaped object - is that really only a plug? There is no roof over it, but it looks like it might be in the kind of desert where you might see no rain in five years.

Rob, it had not really occured to me that people might instinctively grab that beam containing the mainsheet traveller to use as a hand hold, but it is a point to consider. As drawn, that beam is indeed of a width that you probably would not tend to place your hand across the top of it and you certainly could not get your hand around it, so it's better that way than the mainsheet tracks on some boats. The idea was to have a slot in the top of the beam and all that would protrude through the slot would be a lug, say 10 gauge stainless steel, to which the mainsheet would be attached. I had better be sure that the slot is not wide enough that fingers could get inside. Another thought is a proper hand rail along the front of the beam so that people hold that and not get hands too near the moving parts - but perhaps that only makes it worse.

An unstayed mast that can fold down from the base sounds pretty good. There were some types of commercial sailing boats in the UK and possibly elsewhere that had such a feature, for example Norfolk wherries, but I guess you have something more modern and lighter.

Gary - No you must be thinking of someone else, I am in the UK. I am not really a boat designer but I have done a variety of engineering design work over the years, e.g. air conditioning systems/theodolytes/vending machines/orthopaedic implants/printing machines/bits of warships and for a short time bits of yachts - I designed some of the deck equipment for a smart sloop nearly 50m LOA and for a time I worked for a firm that made yacht masts but that was not really design work, mainly laying up carbon fibre prepreg. One thing I did, as a hobby, was possibly the first sailing hydrofoil to 'fly' on two hydrofoils one ahead of the other. That was some years before the Moth people got the idea. I made two prototypes and by chance they were quite similar to a Moth dinghy in size and the rig, but rather crude construction. I used a surface piercing Vee foil at the front and a tee shaped foil aft, not the clever 'wand' arrangement that the Moth people developed. That's not really my interest in sailing though, I like to go somewhere in a sailing boat, hence the idea of a cruising catamaran.

 

Rob,
Could you give more details about your hinged free-standing masts.
How tall are the masts, and what do they weigh?
How is the tabernacle made?
What is the minimum bury required?
How is the hinge made?
How is the mast raised and lowered?
Is that a delicate operation done only on flat water, or could it be done "anytime"?
What do they cost?

 

Solitary Island 12M

Regretably I was just recently informed that these guys decided to throw in the towel for now due to the current boat economy around the world,...or at least there in Australia. They have taken these web-links down.

If anyone would be interested in going forward with this project I am in touch with Mark.

They put a lot of effort into this project, and I think they have a marketable project.

Here is a PFD of an article that appeared in Multihulls mag. I'll post some other photos when I get a chance.