Beachable 1-2prsn. design using minimal materials?

[VBAjedi]

Ok, this is a question for the boatbuilder minimalists here. I know there's a million small boat designs out there, so I'm going to be specific about what I'm looking for in hopes of getting some targeted answers (thus the long post).

I'm looking for design suggestions for a 10' - 12' beachable/ dry sailing boat (monohull or catamaran) that I can single-hand or take a second person on. Needs to be able to survive passing through a 3'-4' beach break and the rigors of fair-weather coastal day-sailing, but still have decent sailing performance in 4-15 knot winds. The length requirement simply stems from wanting the boat to be light enough for one person to lift and short enough to load onto my truck.

The big catch is that I'm in Liberia, West Africa, and boatbuilding materials are extremely limited here. I have access to good quality 1/4", 1/2", & 3/4" 5-ply plywood (NOT marine grade, but a sample of it has survived a three month total immersion test with no delamination). I also have access to mahogany dimensional lumber (one of the perks of being in Africa!) which is heavy but good quality.

In terms of fasteners I have screws and waterproof glue (Titebond II and Gorilla Glue). Sails will probably be polytarp, and other hardware for rigging will be improvised from wood, PVC pipe, eyebolts, etc.

Notably absent from my list of available materials is epoxy or polyester resin/fiberglass seam reinforcement material (thus eliminating stitch-n-tape designs). Also absent from my list is aluminum tubing for spar material (thus my mast has to be built up out of 1x2 mahogany or possibly bamboo - anybody have any info on whether 2" or 3" diameter bamboo is a legitimate option for a small boat mast?). In short, this is gonna be an old-fashioned, Popular Mechanics-style backyard boat.

I'm not trying to build a racing skiff here, just want to scratch the sailing itch in a manner that is relatively safe and lots of fun. I was crazy to think that I could stuff that urge for the four or five years I will be here. Back in the US, all my sailing experience was on a Cal 20 and San Juan 24 (no dinghy or catamaran experience).

I've been scouring this forum and the rest of the net looking at all the designs, but I don't have the luxury of building four or five of them to see which one works for what I need. I'd be very grateful for any suggestions you can make to help me get back on the water!

[marshmat]

Sounds like fun!
You can definitely build something without any fibreglass, epoxy or aluminum. After all, we did sail for some 3 millennia without these! With that in mind, I'd look at doing something in carvel/clinker planking, like they did in the 1700s only using plywood planks cut to shape. Mahogany is a great boatbuilding wood.
Meeting the requirements you've set out will be a bit tricky in a 10-footer, I think. Probably doable in a 12' although beaching will still be a bit hairy. This will definitely be a LOT of fun to build!
I might check back later with more ideas.....

[Seafarer24]

www.simplicityboats.com

[gggGuest]

Bamboo was used in the 1920s on boats as powerful as 14footers. Unfortunately I can't find any dimensions, but the spars for a 120sq ft gunter sloop rig including a spinnaker pole weighed 30lbs which might give you a guide.

Hull shape wise I'd look for a Jon Spencer style hard chine boat like his Cherubs in the early 60s. They were strong and sensibly light. Lightness is always a virtue, even in a shorebreak, because a light boats lands more softly. 1/4 inch ply is going to be plenty strong enough. I'd have a hog, a chine and two light intermediate stringers on the floor with plywood that heavy. If you can get 3/16 plywood that would be better for interior and frames. I'd then support the frames with a bulkhead under the mast, a skeleton one half way to the bow, and a more substantial one at the back of the daggerboard case andf possibly a skeleton one mid way between that and the floor. Built in side tanks add enrormous strength for the weight, flat decks and then the sides joining the floor at the outermost of the two floor stringers.

Be very wary of "traditional style" boats, too many designers just don't understand how best to use plywood and throw in any amount of weight for no great benefit. Weight is always your enemy because that's what smashes the boat on the ground. Only caveat with quarter inch ply on the floor is if you are going to be boumcing it off pointy rocks...

[VBAjedi]

Thanks for the link, Seafarer24. I had spent some time on that site reading all of his "thoughts" about various topics like polytarp sails. But his designs mostly stipulate that they are for use in calm sheltered waters, so I hadn't looked at them too closely. I'll look again.

gggGuest: thanks for the good info. Your general design thoughts make sense to me. I intend to stay far away from the few "pointy rocks" here, so that should be ok. I'll look into Jon Spencer's Cherub design to get an idea of his approach.

I'm curious - nobody has mentioned small catamaran designs as a possibility yet. Given the success of Hobiecats as beach-sailers, I have been more than a little interested in trying a little cat. Obviously this would involve more building work than a skiff - what other issues would I face? I used CAD to sketch up a rectangular cross-section pontoon design (allowing internal chinelog backing behind all seams). Pontoons 8" wide, 18" high, and 11'6" long provide quite a bit of flotation. Even if I couldn't put together a rig powerful enough to fly a hull, I'd think it would scoot along pretty good. Thoughts?

[Seafarer24]

I posted that link due to his information on using wood-glues in boat building. His designs are for sheltered water and not much use to you.

A catamaran can only be so small, and 10-12' is really pushing it. However- there is the Kitty Kat- a 12' spin/jib/main catamaran with dagger boards designed in New Zealand:

At the Kurnell Catamaran Club:


Modern day shot on Port Phillip Bay:


Also, catamaran construction is probably more than I would expect without fiberglass an epoxy. Unless, of course, you hollow out and shape a pair of logs... It would also be much more complicated to set up and rig.

[frosh]

In the 10-12ft. size range, I would prefer the dinghy option to the catamaran.
Also will be easier to build and rig. I think that the early Cherub shape would be almost perfect for an all round performance/ cruising purposes. The plywood that you tested likely has waterproof glue between veneers pretty much the same as on marine ply. I would definitely use that. Marine ply specifically has both outer veneers of very high quality, which is a different requirement to exterior ply. Can you source any softwood lumber?

[sharpii2]

Dear VB:

A pram or scow type might work surprisingly well in these conditions, if its transoms are high enough. The Brazilians designed an interesting board boat type scow with a slight 'V' bottom to replace the balsa rafts they used to use when the big balsa logs ran out. They take it out through the surf each day and come back through it each evening after fishing dozens of miles off shore.

Their boat is about 20ft long and about 7ft wide.

The big problem with a surf boat is that its ends have to be very bouyant and somewhat blunt so they don't dig in when riding a wave in or submarine when blasting through a surf. Sharp, pointed ends had better be much higher for that reason. Here is a web sight that offers two plans that might be of use to you. Just replace the aluminum spars with bamboo and you should be alright. Here's the sight:

http://www.stevproj.com/SailDingh.html

A good multihull option might be a single outrigger. You and your passenger could sit in the main hull, or sit up on a platform between the crossbeams depending on the wind strength. The float could be made of bamboo, solid timber, or be a simple box beam with tapered ends.

Due to its short length requirement and the load it will likely have to carry, it won't be much faster than a mono of the same size. But it would be easier to get its main hull between the wheel wells of a pickup. And though it will be heavier than a mono, the individual pieces will all be lighter.

A catamaran that size is likely to be somewhat faster because it will carry more sail area but it might be much wetter as well.

Bob

[sigurd]

There are some proas that have a vaka that can be broken down in several pieces. The ama could be a plastic tube, ply or canvas over wood frame? As per the indonesians you could use a log but it seems most westerners found a more bouyant ama useful.
I believe also that given the limited spar materials available the proa rig could be built slightly sturdyer than other configurations because of the wide and long staying platform. Beams could also be lighter than in a cat since, because of the one-way rig stays and short ama, they would mostly take compression loads and not much bending.

a three part vaka:
http://groups.yahoo.com/group/proa_f...alSail%20Proa/
another:
http://f4.grp.yahoofs.com/v1/4Ed1RCd...crw/KiaKia.pdf

As to how to build a ply/plank boat without glue, I have never seen a carvell boat with that thin skin. Seems difficult to get the planks to support each other without bead and cove, but you could have a stringer at each seam. Clinker boats can be very thin skinned though, probably even more so with xply since it is resistant to splitting. The timber clinkers I have used have leaked a bit until they had been on the water for a few days.
With a narrow hull and xply however, you would only have the keel to skin joins to waterproof (or if you want, the chines), or if it were a sectioned hull, the bulkhead to skin joins as well. Screws seem better than nails when there is good backing. Do you have access to a water resistant goo, such as tar or pitch? Tar impregnated hemp has successfully been used as a gasket.
Maybe paint will suffice if there is little movement?

There are lots of minimalist boats shown in the email group
http://groups.yahoo.com/group/proa_file/
and more pictures etc in their associated proa_file2 and 3 file sections.

[Seafarer24]

Maybe check into the "Crab Claw" style sail. Especially if you set it up on a bi-pod mast with the gaff and boom suspended between them. That could EASILY be made from Bamboo and is a real performer on some points of sail.

Here is a website of a home-built catamaran with this type of sail:
http://www.rclandsailing.com/catamaran/

[lewisboats]

Sounds like a perfect Instant Boat type build. I would think that a modified dory shape would cover just about all your requirements. The mods would include shifting the beam aft, widening the bottom a tad, not so much rocker or flare. Something like below. Using a chine log and butt blocks you would not need any goop other than glue and paint. Add a bit of a skeg, a dagger board or leeboard, rudder and sail and away you go.

Steve

PS: Waterline is at .4 ft (about 5 inches) for 485 lbs displacement. Hull wt...about 90 lbs with 3/8 for the bottom and 1/4 for the sides. Sailing kit would add another 30 lbs or so.

[VBAjedi]

Thanks to everyone for your input so far – it’s really been helpful! The consensus seems to be that the sensible design type is a pram or scow, with the Cherub being a good model to take as a starting point. However, if boaters always did the sensible thing. . . well, most of us wouldn't own boats, now would we?

At the risk of incurring the wrath of frosh , I decided to harness my interest/vision in little catamarans and actually DO something with it (I've been THINKING about building a boat for two years!). Seafarer24's link detailing the claw-rigged plywood cat pushed me over the edge. So I'm going to build a small cat of my own design as my first boat ever (I know, not a recommended or easy introduction to boat-building), and use the lessons learned in the construction and sailing to help me pick or design the best dinghy for my situation (which I will hopefully build next unless I'm just thrilled with the little cat).

Not being one to waste time when I've settled on a course of action, I made a materials run and waded right into building a pontoon. As described earlier, it's a rectangular cross-section (low marks for comfort in a chop, but high marks for ease of building and low wetted surface area, and I'm hoping the bow design reduces the risk of pitchpoling), 1"x1" chine logs in all four corners, and mechanical butt-joints for the 1/4" ply skins (backed by 1/2" plywood plates that are eight inches wide – that’s called a butt-block, right?). Gorilla glue and screws on 4" centers attach the structural skin, and good old silicone caulk will provide some extra insurance on internal seams (might also be able to find some Bondo to fair the exterior). I used 3/4" ply to make three watertight bulkheads (creating four waterproof chambers in the pontoon) that extend through the top of the pontoon and double as attachment points for three crossbeams (no tramp material here, so the tramp will actually be hard. . . still trying to decide on the lightest weight approach to that. . .). I'll add daggerboards if necessary, but hopefully the hard chines will be enough. I like the idea of a bipedal mast and crab claw sail - sounds feasible with what I have to work with. Not settled on that though if anybody has other rig suggestions for a polytarp/wood spar rig on a cat.

Here's a couple of pictures: with the chine logs, bulkheads, and sides done, this 11'6" pontoon weighs in at 40 pounds. The top/bottom pieces are another five pounds, and then paint. I'll be at about 100 pounds for two pontoons, which I thought was not bad given the total absence of composites here. Obviously the hard tramp and the spars will weigh a lot, but I'm hoping to come in around 175 pounds overall. . .

Hull from rear quarter (hard to see here, but the bottom slopes up at the bow like it does at the stern):

Detail of bulkhead, chine logs, and butt block:

Details of the probably-excessive bracing in the bow (false stem not attached yet):


Thoughts? I’m only into this about $40 and ten hours of work, so I could conceivably start over (though I don’t really want to). I just wanted to avoid being one of those that always TALKS about building a boat but never actually starts, so I started! “It’s a lot easier to steer a moving boat” and all that. . .

[lewisboats]

You could save yourself some weight in the butt block. 1/4" ply usually uses a 1/4" ply buttblock about 3-4" wide. How wide and how tall are the pontoons? They look pretty thin for their weight and the weight they are supposed to carry. You need to calculate the cubic footage of each pontoon and multiply it by 64. This will give you how much buoyancy you have gross. You will need to figure out how much of the pontoon you want submerged and multiply this fraction by your total buoyancy...eg 1/3 x 1000 lbs =333.3 lbs. THEN you need to subtract the weight of the boat from the result. This is the load that the boat can carry. I'm thinkin....You don't have enough buoyancy in those pontoons...but that is just eyeballin the pictures.


Steve

[VBAjedi]

Hey Steve,

Thanks for the dory plan, that posted just before my last post so I didn't see it to comment. Looks simple enough though.

The dimensions of this critter were heavily influenced by the dimensions of a sheet of ply. So the pontoons are one and a half sheets long, and I started with a 12" by 12" cross section so I could cut a sheet into four strips, no waste. Since the skin provides my primary strength, I modified the cross-section to improve the resistance to vertical flexing/breakage from interaction of the pounding surf and my weight and the load of the rig. So I ended up with pontoons that are 8" wide and 18" high. I ran the flotation calcs and it put me at over 600 pounds of buyancy per pontoon. With a boat weight of less than 200 pounds, plus my weight, my displacement will be less than 400 pounds. If I was flying a hull I'd have the pontoon 2/3 buried, but I'm not really thinking I'll be able to put together a powerful enough rig to worry about that.

Does that sound ok or did I make an error somewhere?

[VBAjedi]

Oh, and my thinking on the butt block size was that I needed backing for my screws (yes, the block is Gorilla-glued too, but the mechanical fasteners give me a little redundancy since I'm not using any epoxy). I also wanted the block to provide as much strength as possible since the skin is load-bearing. (The other thing I did was to stagger the seams on the inboard and outboard sides to provide at least one unbroken side skin at any point on the length of the boat.)

I'd hate to snap a pontoon at the seam! The heavier butt blocks only cost me two or three pounds, which I can live with for the peace of mind (real or imagined) it provided me.