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  #1  
Old 08-23-2005, 08:00 PM
terabika terabika is offline
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planing catamaran hulls/sailboat

I am thinking (DANGER! DANGER!) of building a 40 ft cat about 8600lbs ready to sail. this works out to a box section of 1.33ft by 40 allowing for some taper in the nose. It is easy to build...and it is easy to build. Most cats are not planing hulls but go through their bow wave due to their beam to length ratio. 16/1 is high amongst cruisers. I can do 30/1 :1.33x40 so I should be able to get through the bow wave without planing. The flat section on the bottom should give me some lift and consequent reduction in wetted surface. Does anyone have any experience or ideas about this?? Am I missing something? I know it will not ride smoth but everything has its tradeoff! Life is evil like that it seems. Look forward to reading your thoughts! and i am not even phsychic!
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  #2  
Old 08-24-2005, 09:59 AM
nero nero is offline
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Can you post a drawing of your idea?
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  #3  
Old 08-24-2005, 04:42 PM
terabika terabika is offline
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I am driving 18 wheeler s about the USA trying to save bucks to build her...so it is not possible, sorry....but, it is VERY simple design to its sailing detriment....I want to go sailing, not build a boat! lol from the back, her underwater portion shal be a box 1.3 ft square going all the way up until 4 ft before the nose. Then, it shall taper to a point. above the waterline will be two flat surfaces ( I use playwoood) flairing out as they rise such that at 3ft above waterline, she shall be 4ft abeam. cross beams will lay on top of this and attatch between full and thick bulkheads. Beams are 3/4 inch playwood made into a 1.3ft box section beam wit 4x4 in each corner running across. In all of this, I tried to evenly divide sheets of playwod so that little is wasted and fewer cuts are needed. As a matter of fact, When driving down the road thinking of this, I did not think so much in feet and inches but in even fractions of a sheet of playwood. I also do not use ANY compound curves....it is SO much simpler to build! I know, It wont do this or that and she will ride rough but, given MY cercumstances, It is the best way for me to go sailing! There will be a cabin on each hull. Theses will be two sheets long (16ft) and 5 ft wide. Yes, it hangs over the hull 6 inches on each side but I do not care. These cabins will rise one sheet on side (4ft) and have a head and bed (5ft seemed right for a couple to sleep in. There will be stowage in each and one side shall have a propane rifrigerator built it and accessed from the trampoline. Cooking and such shall be on the tramp, 12 ft wide. the cabin tops shall be 3 ftt above tramp so some privacy is aforded. I use many means to save money and be able to go sailing..If I go for it,I will make a web site for folks to follow allong :-) Take care and God bless!
Terry
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  #4  
Old 08-24-2005, 09:22 PM
nero nero is offline
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Driving a big truck. kinda like running a motor cruiser on land. Did it 5 years ago for 2 years. Real experience and very educational.

If you run hard and live in the truck you should be able to buy all the materials for a nice sailing cat in a years time. With a months salary you could buy plans from Kirt Hughes. He has some rapid build, already built plans for sale at reasonable prices. I could have saved a few years of time, if I had gone this way.

If you're coming thru Effingham,IL drop me a private message. My boat building barn is 20 minutes from there.

Becareful of the IL bears.
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  #5  
Old 08-28-2005, 07:19 PM
terabika terabika is offline
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what are you building? any comments on my design?
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  #6  
Old 08-29-2005, 09:56 AM
nero nero is offline
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There are renderings of my project under multhull sailboats in the gallery. I'll take a photo today and post it this evening of where I am at.

From what I can visualize, your plan is square with a flat bottom until just before the bow where it will curve up. Perhaps this will be a very rough ride.

If you just want something to float on this should work. If you want to cruise or go off shore, tow a survival boat. smile

You really should look at compounded plywood hulls. The are even faster to make than your method, proven, and will sail well. Kurt Hughs catalog, if nothing else will help you with your design.
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  #7  
Old 08-29-2005, 12:21 PM
terabika terabika is offline
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The bottom does not curve up but the sides come in to a point at the bow. I really liked what you did....is the photo of a scale model in water? 14 meters? a person on it or near it would help se the scale . I am hoping that, even with the flat bottom, It will not be toooo rough a ride as its bottom is only 16inces wide. 8000 lbs loaded on this small of a bottom should mitigate the roughness somewhat but I dont expect a silky smoth ride either.....much less vibration than a cabover peterbuilt though! survavil boat?! HA! her bildges shall be completely fillled with a mix of empty pop bottles, milk jugs and foam! she will never sink! I would do just foam but expensive. she is the survival boat :-) If she rides toooo rough, I can easily pull her and ad a "V" to the bottom. SInce the bottom is flat, it would be easy. My lateral resistance shall be had from sideways keels in the center third of the boat, going to the outside of each hull, prohibiting water flow around the bottom. She will draw only 16inces with the boards up. I know she is not going to tack easily but thats OK. I will use a 15hp motor on a retractable sled for power and my ultra cool genset (see posting in electrical section) for charging bats. In moderate weather 8-15knots, she should fly (20plus knots?) as I will get lift and reduced wetted area at speed. I plan to sail to Key West, bahamas and BVI and the like...short hops with easy weather windows...I love sea anchors and have no problem with the thought of laying to one of these....if things go well, I will add a retractable,stayed poll of some 20 feet with 100 or 200 lbs at the end....4 stays, one to each corner. This will be the heavy weather mode with sea anchor out and a couple hundred pounds 20feett down, I do not not think she could capsize....so, as long as she does not break, I can wait out a storm...
if that goes well, circumnavigate! hey, being able to turn 350 mile days makes crossings much shorter and much safr....I plan on 1100 square foot of sail...with 4 reefs :-) I will post a VERY rudimantary graff paper drawing in a day or two or three.
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  #8  
Old 08-29-2005, 02:21 PM
nero nero is offline
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Looking forward to the sketch!

Thought about using weight suspended underwater for storm ballast. It would need to be a rigid connection.
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  #9  
Old 08-29-2005, 04:46 PM
terabika terabika is offline
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poll, would be rigid when stays are tightened but could be retracted when weather was good to get it out of the water. I will probably use lead. poll would go underneath mast which is at center of boat both fore/aft and port/starboard for max stability. even 100lbs on a 20 ft poll would provide much stability. I liked the swoopy lines of your boat! photo in water was a scale model or real boat? How long is it? other characteristics??
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  #10  
Old 08-29-2005, 04:50 PM
terabika terabika is offline
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plans for his 38ft cat are 3500$ way out of my price range....that is equivalent to all my wood and srews budget!
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  #11  
Old 08-29-2005, 07:33 PM
CT 249 CT 249 is offline
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I'm certainly no expert, but the planing cat concept has been tried time and time again, at various sizes up to 60'. I've sailed one or two small ones. They apparently have yet to show a performance edge, or even competitive all-round performance.

I'm not a designer but AIUI all the textbooks point to a basic physical problem and designers (from windsurfer legend Jim Drake, a real-life rocket scientist, to skiff and cat designers) agree. With a cat the water "sees" a long skinny hull, which is great for displacement performance. However, for effective planing you want the water to "see" a short, wide "planing patch". That's impossible on a long skinny cat hull.

Look at a diagram of the Savitsky tests and you'll see that almost all of the planing lift comes from the stagnation point, which is right forward where the hull hits the water. The rest of the planing surface provides comparativley little (or no) lift. The stagnation point does not get longer when the hull gets longer, but it does get narrower when the hull gets narrower - so with a 16" wide hull you'll have only a 16" wide stagnation point, just a few inches long.

Imagine trying to develop enough lift from water pressure on a patch of hull about 160 square inches to lift a big cat. On a long skinny hull like a cat's, the stagnation point is so small (compared to the overall hull) that it cannot provide sufficient lift to raise the bows, and therefore the boat never actually lifts onto a plane and reduces wetted surface effectively. Or, rather, if and when it does, the drag reduction is so small that the boat moves slower than a typical "displacement" style cat.

The guys who have been designing cats and ignoring planing hulls are not entirely stupid. There is a very good reason that they ignore planing hulls.

I'm not knocking the concept of a cheap, ply cat. It sounds cool. But there seems to be no performance breakthrough in going for a planing hull. Parlier's cat goes well in some conditions, but how do you separate the planing concept from the fact that it is (IIRC) the only cat in its class? And overall, AFAIK it is apparently slow - just like the other planing cats.
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  #12  
Old 08-29-2005, 07:52 PM
nero nero is offline
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photo of the model which is 1:10 scale making it 1.45 meters long. The post under wood boat building I just did has some up to date photos of the real build. Design displacement is somewhere around 6,584 kilos. Actually, it will come out heavy. I have a 2 ton margin of error and still have enough bridge deck clearance. Plans will be free once I float this one.
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  #13  
Old 06-02-2009, 11:16 AM
tugboat tugboat is offline
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planing trimaran

I have been thinking about using planing technology as well but for a tri not a cat...a famous sailor by the name of Yves Parlier has built a catamaran using gliding hulls which for the record- broke the single day sailing record of over 500 nautical miles!! he used aircraft floats and redesigned them for optimum performance. In fact i was researching the same idea for a planing trimaran using a plane float for a vaka. so he kind of beat me to the punch. Now- if you want to get really cheap plans for floats that ultralight aircraft use- you can go to Muktuk floats. the plans are 125.00 but you will need to rescale the drawings for cat sponsons since they are about 20 ft long. youll also need to increase the beam slightly and redesign the bow section to have a sharper entry, but its all there including rudders.

myself-I have never fully abondoned the idea. but keep in mind you will not be sailing fast in light airs. also Bernd Kohler has a small planing cat on his site but it is not designed by him and i dont know if he sells those plans(unfortunately)...

the idea that has evolved with my research is a slight v designed vaka- which is actually very wide (12 ft) shaped very much like the spirit of Canada.(wider means easier planing)which utilizes a planing hull..but instead of using a monohull and a ballasted swing keel i will be using two small floats to stabilize the large planing main hull so that ballasting is unnecesary in essence creating a trimaran/monohull withThe two small hulls (amas) to keep the heel and motion of the boat behaving like a trimaran. yet the hull is a planing hull much like an albacore(see uffa fox) or the tornado class. the second modification which I am currently exploring is the ideas of a parallel rig. this should lower the center of effort and enable the vessel to carry much more sail than usual(more sail area = more power to plane)..the entire boat is a composite using 1/2 inch ply all around stitch and glue- then reinforced, then covered inside and out(composite) in epoxy and glass(1 layer each side) the masts would rotate....hope this gives you some inspiration...on a side note- i think deisgners need to explore planing hulls more in depth as they have been proven. the gliding/planing hull idea could revolutionize the way we sail...
this thread is old..have you suceeded in building your cat?
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  #14  
Old 06-02-2009, 05:29 PM
Guest625101138 Guest625101138 is offline
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You are inevitably required to consider the forces involved when designing the tri. As described it would not work other than a howling gale directly downwind.

The linked images will give you an idea of what an optimum planing trimaran would look like:
http://www.macquarie.com.au/speedsailing/gallery.htm
It is all about managing the sail forces.

If you look at trimarans that travel fast the central hull is not in the water. All the displacement is carried in the ama. So it is the shape of the ama that counts. For realistic open sea conditions the long slender hull works best at speed. Planing OK for setting records in contrived conditions but not suitable for high speed in the open sea.

Rick W
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  #15  
Old 06-02-2009, 07:12 PM
tugboat tugboat is offline
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WOW thats some trimaran thanks for that site and photos!... i hear you Rick...the forces acting on the ama are intense especially when its a displacement tri.
most designers use heavily(not necessarily heavy)reinforced outriggers to compensate for the kinds of force acting on the hulls of a tri i.e. the whole vessel incuding the wind bearing down on one ama per se... but the design im talking about is really a scaled down very very light Volvo open class type of hull- but with a little more pronounced v shape. think almost a flat bottom sharpie with a slight v- those boats are very fast and do plane even in lighter winds. The only difference in my hull and a mono's is that I wouldnt need a weighted keel- the idea being that a bottle will float and goes over waves not through them as does a displacement boat. the volvo open class are very fast boats- occasionally exceeding 30 knots!! Now imagine doing that and not needing the complexity or the weight of a ballasted keel!?... these sailling characterstics would mean that the vessel would plane and not ride up on a ama. and probably plane in lighter airs(hopefully). The crossarms would need to be heavily built but not as much as in a tri- they dont have the same forces acting on them- the vessel would never heel one on ama... I AM thinking though of buying the Kohler designed p95 cat- the hulls dont come out of the water. 17 ft beam! assymetrical hulls..very fast.

btw i had a question - anyone know if the parellel rig would outperform a standard rig on a reach or a running? I understand they are good for windward performance in light vessels...but how do they perform off the wind?

Last edited by tugboat : 06-02-2009 at 07:16 PM. Reason: bad spelling
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