Beachable 1-2prsn. design using minimal materials?

[lewisboats]

Sounds reasonable to me! I ran the #'s too and it looks like you'll float...even with a passenger. I would foam the hulls to be sure...the extra weight would be worth it. If you are handy with a needle you could make a mesh of 2" webbing and cover with Polytarp for your tramp. This would be light and sturdy made of 4" squares....or at least lighter than a ply tramp.

Steve

edited to add...8x18 or 6x18??? 8x18 doesn't work out right for 4'x8' ply.

[lewisboats]

have you given thought to your control surfaces and sail size and balancing the whole thing?

Steve

[VBAjedi]

Steve,

8x18 is correct. It was 8x16, but at the end I somewhat arbitrarily decided against trying to get a whole pontoon out of a sheet and a half and gave myself an extra two inches of height/strength/flotation, figuring I could use the scraps from the second sheet for miscellaneous stuff. Not trying to win any "efficient design" contests here.

Control surfaces: As I said, I'm hoping daggerboards will not be necessary. The twin kickup rudders will each be laminated from two layers of 1/4" ply. I haven't finalized dimensions yet, but I was going to shamelessly copy the rudder shape/size of a bigger cat like a Prindle (figured that would give me a bit more size than I need).

Haven't settled on the rig for sure yet (leaning towards the claw) or calculated the sail area I need. Figured it would be a little south of 100 sq. ft. using the cat pointed out by Seafarer as a reference point:

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

[messabout]

Lewisboats suggests a fat little dory. He is right on for your application.Your cat hulls are too skinny and too short. You'll have the lee hull stuffed so far beneath the surface that any attempt at crossing beach breakers will cause grat pain and possible injury. You are going to use hard chines and they need to be near the surface to be manageable in turbulent water ways.

Your pictures show a hull that I am going to use the famous SWAG system to evaluate. Swag says the prismatic coefficient will be somewhere around 0.65 If the center section is 12 inches wide and a trial immersion of 6 inches is selected then.....12" x 6" =72 square inches. Apply the PC and you get 72 x 0.65 = 46.8 inches square. Take a guess at the length of the load water line...say 100 inches. 100 x 46.8 =4680 cubic inches of volume. That is good for 173 pounds of flotation. That ain't gonna get it. Lets try 9 inch immersion. Now the WL will be a little longer. Say 115 inches. 12" x 9" x 0.65 x 115" = 8073 cubic inches. (An easy conversion to pounds is volume multiplied by 0.03703.) In this case displacement is 299 pounds. That wont get it either.

If you insist on a catamaran, keep in mind that a single hull MUST be capable of supporting the entire load with room to spare. You must either make the hulls much wider or much longer. Preferably longer. Abandon what you have done, start over and build a sensible boat. With what you have, the boat will be a misery to try to tack. The word "try" is the operative word. It will be too heavy for as small a boat as it is to be, If you ever get this one going in even moderate air it will bury the lee bow and proceed to gleefully pitch your poor ass into the ocean.

Design a boat like Lewisboats has pictured. Turn the ends up a whole lot so that you can deal with the surf. A design like that is dead simple. Two sides and a bottom. You can have it built and sailing before you can get half the cat done.

All that said, I respect your commitment to actually doing something. We want you to have a good outcome so trash the cat idea. For what it's worth I have considerable experience with cats. They can be tons of fun but little ones do not fare well. Hobie once built a cat called the 3.5. ( 3.5 Meters long)It was a scaled down version of the H14 and H16. It would work reasonably well with a 60 pound skipper. With a 170 pound adult it was miserable. I put a horizontal foil between the hulls at the bow so that my 145 pound son would not pitchpole the thing. Little boats are weight sensitive in the extreme. Wide little sailboats boats will work fine but skinny little ones rarely do what was hoped for.

[VBAjedi]

messabout,

Yikes! You appear to have missed the part where I said I hadn't built a boat before. . . it took me half an hour of Googling to feel like I somewhat understood what you were saying with your SWAG (not that I'm complaining - it was an educational half hour). If I understand you correctly, all of your numbers were for one hull. Now, I agree that each hull should be able to support the entire displacement weight of boat/crew for safety purposes. At over 600 pounds of flotation per hull, and with a combined boat/crew weight less than 400 pounds, my design does that just fine. (The hull would be 9" or 10" immersed and wouldn't be interested in going anywhere in a hurry, of course).

However, my intention (which I stated) was that unlike most small cats, this design would keep both hulls on the water when underway - I'm not racing anybody and I intended to underpower the rig. Given that, is it not fair to think along the lines of a 60/40 weight distribution across the hulls? That puts my underway load on the downwind hull at around 250 pounds. My own WAG put that at around 7" or 8" immersion, leaving 10" or 11" freeboard on the downwind pontoon (upwind pontoon obviously riding higher).

You sound like you know what you're talking about (with experience to back it up), and I'm not trying to argue per se. . . it's just that your conclusions were so different from mine that it didn't make sense to me. The apparent success of the 12' Kitty Cat design mentioned earlier in this thread makes me think that a 11'6" cat is doable if high performance isn't the primary goal. If I'm gonna scrap my pet idea I want the reasons for doing so to be crystal clear!

[frosh]

Well done, on not procrastinating indefinitely like some previous posters and getting into the workshop so fast!
The 11'6" cat should work OK. I have sailed the 12' Kitty Kat years ago two crewed, and it was pretty quick. Your problems would start if you were to use a tall bermudan rig, but since you will probably end up with a crab claw the rig loads will be quite low. Therefore your cross beams are less critical, except if you use solid mahogany it is a lot of weight. Are you going for a beam of about 5'6"? Solid timber is OK for this project but ideally you want light timber so you can use a fairly large cross section. Maybe around 3" square for softwood, slightly less for hardwood, assuming crab claw sail.

Another problem you probably will have is sailing much higher than a beam reach. Both the lack of dagger/lee boards and crab claw sail will work against you. If this is not very important to you then don't bother, as creating dagger boards, or using a modern rig will add a major obstacle to you in Liberia. If you can source bamboo in sufficient diameter for mast and spars, then go with that. Polytarp also is satisfactory for a crab claw and this type of sail needs no seam shaping and should be a flat surface.

By the way, dont forget to make a well shaped sharp bow block for each hull as they will be fairly submerged a lot of the time.
Best of Luck.

[messabout]

VBAjedi;
I apoligize for the outburst posted previously. It was not my intent to be a naysayer. Those of us who are watching this thread admire you for persevering. You are going to build a boat in spite of your less than ideal circumstances. That makes you a certified, and revered, member of the boat nut brotherhood.

I have been digging, without success just yet, in search of and old magazine of 60s vintage. It is titled; How to Build 20 Boats. A US publisher named Fawcett used to put out a new 20 boats magazine every year. My magazine has a set of plans for a small Catamaran of the most simple kind. It was about eleven feet long, slab sided, bipod mast, lateen sail, and I think its' given name was Kit-Kat. The age of the plan set places it before the advent of epoxy and other exotic materials. Surely there must have been a number of them built. As far as I know there were no liability suits lodged against the publisher of the plans, so maybe those little cats did not drown too many people. The Kit-Kat looked pretty much like what you have done so far.

Please keep us posted about your progress. Hopefully you will get your boat in the water before long and report to us about the fun.

[VBAjedi]

messabout,

No need to apologize! If all I wanted was a blind stamp of approval for my plans, I wouldn't have posted my question here. Your post caused me to think carefully about whether I really wanted to go through with building my design. As I see it, unless I seriously overcanvass the boat, it will be a fairly safe design. So the main question is whether it will be a FUN design that meets my expectations in the performance area. My expectations aren't terribly high there, and I've decided that I'm ok with discovering that I couldn't even meet those. So at this point I intend to finish building my little "pet project" cat and just see how it goes.

To be honest, I very much expect that I'll be back in here in six months or so, asking questions about building a second boat. And I suspect that boat will be a monohull along the lines of the designs suggested in this thread. . . (unless my requirements change - always a possibility!). Let the boat-building addiction begin!

[VBAjedi]

Oh, and if you or anybody else find that issue of "How To Build 20 Boats" with the plans for the Kit-Kat, I would very much like to see a scan. . . I Googled around looking for it but didn't turn up anything online.

[sigurd]

wow, you're quick! That hull looks like an excellent ama for the multisection proa.. Good luck with the cat! Somebody here would surely know, whether it makes sense to move the rig a bit more aft then usual, to take lateral load off the hull(s) and onto the rudder?
PS my old Europe dinghy (11' olymic onedesign skiff, a copy of an ancient moth boat) uses plywood rudder and daggerboard. they are is just a bit rounded in the front and sharpened in the rear. works fine. probably 1/2" thick?

[messabout]

VBAjedi:
I have become intrigued by your project. There are philosophical grounds. I rooted around some more to find the magazine p[reviously mentioned. The copyright date is 1960. The magazine used to be a staple item for the nautically obsessed. It was edited by Boris Leonardi, who was the editor of Rudder Magazine. Rudder was a well regarded monthly publication that was popular before the advent of slick, commercial, trash magazines like Sail and others, became the norm. Leonardi was a responsible and respected journalist and knowledgeable boatman.

The plans for the little cat were not the Kit-Kat but close in name. The name of this one is King-Kat It is so much like your pictures that it could have come from the same drawing board.

The boat is eleven feet ten inches long. (we used to be able to get 12, 14, and 16 foot lengths of ply) The hulls are separated 48 inches center to center. The builder used a piece of 3/4" plywood to serve as a deck and hull joiner. Thus 48" c/c. He used a centerboard with the trunk on the centerline of the deck. Dual rudders were conected by a bar at the tiller ends as in current practice. The blades were merely whacked out of 3/4 ply. The board was 11" x 36".

The hulls had slight flare. The center section measures 12" wwide at the bottom and 14" wide at the sheer. The height of the main section is 15" The forward end of the bottom is turned up 6.25" and the aft end is up 3" In plan view the hull has flat sides in six mid sections spaced 16" apart. Twenty three inches of each end was turned in to meet the stems.

The legs of the bipod mast were cut from 3/4 ply, the length 8 feet. Width was tapered and the two legs held together at the top with a barn door hinge. The lateen sail was 70 square feet and loose footed. Luff 15"- 0", Foot 10' -0" leach 14'-10" There were numerous pictures that accompanied the plans. Obviously, the boat was built and sailed. The whole deal is a model of simplicity. It is basicly two long pointy boxes tied together with a piece of plywood. A minimalist boat indeed.

King-Kat is not going to tack well because its' end are immersed too far. One time, way back, I built and sailed an Australis. One of the early A-Cats. That thing was scary fast. Huge full battened monorig, trapeze, etc. Australis had a pointed stern that was slightly immersed. It would go straight ahead but did not like to tack. At various regattas I was often the fastest boat on the water but one of the slower ones around the course. Frustrating it was. If there is any moral to that story it is to get the ends of the boat up out of the water.

Hey, dont stop posting. I am hooked on this project and I need to know about the final outcome. So continue building and tell us more about it.

[lewisboats]

King Kat available at : http://www.dngoodchild.com/5165.htm

BooYaa!

[messabout]

Lewisboats has dredged up a valuable resource for those who like boats from outdated designs. They list a bunch of boats with familiar names and some not familiar. In additin to King-Kat they have, judging from the construction picture, a most creditable design called Kitty Kat. That one will work. It will tack, it will negotiate small surf, it will self compensate for varying loads including righting moments. and it is not hard to build. Whether the designer says so or not it is not a design for flying a hull. It has lines reminiscent of Arthur Piver designs of many years past.

Best of all the reprints of the various designs are all cheap.
The listed plans are quite old and will not likely be subject to copyright royalties. Old does not necessarily mean obsolete.

VBAjedi dont even think of putting "just south of 100 sq. ft." on that thing. Never mind what you found on the RClandsailor site. Land yachts have a very wide stance and they accelerate, in gusts, so quickly that the overturning moment is manageable. Start small at 50 or so and go up from there in cautious increments. If you use a bipod mast pair, a lug sail will work quite well while keeping the CE low and also giving some capacity for adjusting the balance.

[frosh]

Hi Messabout; I think your sail recommendation of around 50 sq ft. is really conservative keeping in mind it is going to be a fairly low aspect ratio sail probably set on bendy spars.
The King Kat photo shows a lateen sail of approx 70 sq. ft. and depending on the usual wind strengths this should be fine plus or minus 10 sq. ft.

[VBAjedi]

Thanks everyone for your help so far (nice find on that site, Lewisboats - wish I was in the US so I could order the plans! Not even the mail works here.).

Thought I'd post a pic of the first hull, which is now skinned, faired (with Bondo - looks decent but we'll see how it holds out), and has the false stem attached (nice and pointy just for you, Frosh! Hope I don't run into any other boats or surfers cause I'll cut 'em in half! ).



Of course, AFTER I started building this hull they ran out of the 1/4" plywood I'm using to skin it (they've had it in stock for a year, figures they'd run out now). So I have to wait a bit to start the second hull.

I'll keep updating as I progress. The sail plan is still very much up in the air (sorry, bad pun), as is the tramp construction, so I'm sure I'll have questions there.