Is plywood suitable material for centerboard?

Thank you for your kind words, Skyak.

The budget remains pretty much the same, I have practically no limitations on this project now except for 2 meter folding parts.

I have no problem with reducing sail area. But talking of higher winds, isn't it an option to go with reef points? I always wanted to make a reef-able sail.

By the way, just for a reference, how much usually 4 meter sailboat weight, built from traditional materials, like plywood or fiberglass? My initial estimations place my boat weight about 70kg, maybe less. I guess that's pretty light, right?

And I'm in no hurry to cut anything yet - this is for the next summer, right now I can't afford any kind of sailboat. I'm trying to make full project now, and then input it into VPP program to balance everything. Speaking of which, (sorry, a bit off-topic), I can't find any free VPP. Maybe you know one, Skyak?

 

Even such tanks didn’t survive bending and torsion from 10-13 sq.m rig and hiking crew. They gave place to catamarans like in the picture. Certainly, this boat is over your budget, but pay attention to its dimensions – appx. 6.5x3 m. Still these boats capsize\pitchpole from time to time, so reefing will be a very useful addition to your sails.

 

Nnnnnnnn, this is such a beautiful catamaran - almost made me wish to consider multihull again. Out of pure interest, how much would such a catamaran cost to build, excluding sails? I see it's inflatable, so I guess it's completely folding.

 

I’m not builder, so can only estimate prices. IMHO, around 1500-2000 Euro in retail prices for materials. Ready to sail boat – around 5000-6000 Euro, AFAIK. But this is “cream of the cream” in its class and size.
In Russia and Ukraine you have a lot of alternatives from mass production ex-USSR boats to home-built cruisers, from 12 to 35 feet length and from 400-500 to 20 000 (may be more?) Euro prices.
Photos just to show the scale of problem

Yes. Usual max length for parts - 220 cm due to public trasport limit.

 

2M folding helps greatly and your 4M length fits your budget. For reference, the weight of my 14ft laser is about 140 to 150lbs and that is a solid but light Olympic single hand race dingy. One more question, do you expect to sail with a crew member? A 4M double ender would typically have a max load of 350lbs. The good news is I have been planning on building a packable sailboat of similar dimensions -did I tell you that before?

I don't know of any useful free VPP but here is my VPP result prediction equation;

inexperience+VPP+time=frustration+disappointment

VPP is a tool for someone who has experience and data from many similar boats to predict the performance of a boat that does nothing new. I have never seen a good VPP for dingies and I suspect it is because the crew is too big relative to the boat.

What I have that is useful is tools to relate geometry to forces. Then I take that data and do my own calculations in a spreadsheet. For hull design and properties I use kayak foundry

http://www.blueheronkayaks.com/kayak/software/software.htm

That gets you the displacement mode drag, then I use different tools to estimate sail forces. Note -there is no good transitional drag prediction that doesn't require test data.

http://www.wb-sails.fi/Portals/209338/news/SailPowerCalc/SailPowerCalc.htm

This will give you an idea of sloop sail forces.

Reefing is good, but I have never seen a reefable Tyvec sail. Most single hand dingies don't bother with reefing because the boats are not stable enough to do the reefing on the water -if the crew is at the sail, what's keeping the boat upright? Keep in mind, if you are going to have that much sail on that little boat ALL the controls must be operable from the rail where your weight needs to be to keep the boat upright.

 

Check this link about folding sailboats
http://iv70.narod.ru/IV4/SH_B/Reestr.html
especially this one:
http://parusa.narod.ru/bib/katy/1991/247.htm
And some pictures

 

Thank you both for such an extensive information.

Nnnnnnnn, I checked these links - this boat that you suggested to look at, has very interesting solutions, sadly, description doesn't go in detail at them. For example, it has non-flat bottom, which makes skinning extremely difficult, at least that's what Yost said at his site, and he made clear that this is to be avoided at all costs. Would be interesting to see how these russians solved this problem.
Also, using bent tubes for ribs - I didn't think that would be sturdy enough for a sailboat. We have our canoe built like this, but it doesn't have to withstand sailing forces... Also, I thought that bending tubes to such high angles would simply break them, and that such ribs can be made only at factory.
Also, they say that full displacement is achieved with 4 persons. And that boat is only 5 meters - that doesn't link with what you said about typical similar size boat displacement - how do they achieve this?
Very useful links, thank you.

Skyak, thank you also for these links to these online calculators, they will help a lot. You see, about VPP, as I'm now in a middle of "Principles of yacht design" book, I saw that there are much more factors that affect sailboat balance and performance than I thought - starting from centerboard shape, ending with with shroud air drag - and they all are related, affecting each other, and calculating them all to make balanced and safe sailboat manually is nearly an impossible task. Of course, I could go with averages, and ignore some not-as-important factors, but then again, if there is a chance to make a better boat just by adjusting some minor things to gain significant advantage, why not...

You didn't tell me of your planned similar folding boat. Could you, please?

As for crew members, I thought I would sail alone in light winds, and in heavier I would take a friend to help with hiking and with sail management. Seeing now that these russians made similar boat (a bit larger) that can sail with 4 persons, I dare to hope that 2 persons won't overload my boat...

As for reefing, well, I thought that reefing could be done before sailing, and if the worst should come - increase in windspeed while far from shore - just put boat in irons to reduce heel, lower the jib to move center of effort back, loosen the mainsheet, and boat should stay with nose pointing into the wind while I reef. Wouldn't that work?
I think that all principle controls - both jib sheets, mainsheet and tiller - can be brought to the rail using pulleys. It shouldn't be too hard to put halyard clamps in reach of the hand, should the worse come to happen.

 

those folding sailboats are pretty nice. I want to build something similar but with a wood frame. I wish I knew more Russian. Aluminum would work as well as anything else, it is just a matter of distributing the rigging loads.

The aluminum can be bent by hand, depending on the alloy and heat treat condition, or they can be done in the "O" (zero) condition (fully annealed), and than heat treated in an oven to get some strength back. I have done both before. wood is easier to work and cost less, but not as light as an all aluminum frame. In salt water the aluminum could get corrosion if allowed to set too long and make separating the aluminum parts a pain. I made a folding kayak with an aluminum frame, I do not think I would use aluminum again for a boat going in salt water.

You would make a skin fit by either cutting it to shape, with more seams, or relying on fabric stretch. The more seams the more work, and the higher the risk of leaks, and a weaker hull skin, that is why it should be avoided, not because it can not be done.

Usually in a small boat you will not be so far from shore or shelter than you would need to reef. so you choose your sails when you start, if things unexpectedly get heavy, I would drop the jib and sail on the main alone until I got back to sheltered water. I suppose if you had to reef it could be done with the boat in irons, helps to have assistance to keep it pointed into the wind while you mess with the sails. I do not recall ever feeling like I need to reef in any dingy I have owned or been on board, it is pretty rare you would be so far out that making a run back was a problem. It cold happen, but I just do not remember it ever being an issue. Dropping the jib makes handling it much more simple.

 

The Klepper Passat(German design) shown in the Russian link is also available for view in German links: http://www.faltbootbasteln.de/fbb-klepper_passat.html http://www.youtube.com/watch?v=E4rPHrozoG4 .

 

laukejas,
I wanted to know about crew to figure what displacement and sail handling you need. So you have a crew weight from ~160lbs to say 350lbs? And you need single hand capable controls. Light, fast single hand dingys typically only have one sail because you can only control one continuously. You don't cleat the sheet, you hang off the side and 'fly'.

I am not sure what you read about "flat bottoms" at yost's but I didn't see it. Maybe I missed something or maybe it's your english -could you point out the statement? Working with manufactured PVC impregnated poyester canvas it is easy to make "conic" shapes and difficult to deviate from them by a significant amount without big folds adding drag. A conic is a shape that has ellipses at opposite ends and linear section between. To avoid this conic limitation you can canvas and then apply waterproof seal after sewing.

The russian SOF boats above are not so far off conic that they could not be built. There is allot done right on it. The only things I don't like are the small number of frames and the transom. A double end SOF is naturally easier to tension the skin because the ends are cones. With a transom the boat needs some means of evenly tensioning the skin. I suspect there is something complex going on in the frames that makes them expand to tension the skin and that is why there are so few frames.

I have a concept for a racing dingy one design class that can be broken down for storage and transport. LOA ~13ft breaks down to 6ft to avoid premium shipping. It's part of my effort to expand sailing by lowering the cost and difficulty.

About reefing; when you aim a light dingy into a strong wind it stops and in seconds begins to go backward and naturally turns. The only way to stop this might be a drogue off the bow. It takes minutes to reef a main unless single line reefing is installed. Roller reefing is a good way to address this on the jib and the boom. On the other hand, if you just have cheap tyvek sails, why not just carry a set of smaller sails?

 

If multihulls are possible, then something like catamaran Ducky-13: 4 m, 35 kg, 2 packs №1 - 1,8 х 0,25 х 0,25 m with tubes and sail №2 - 0,8 х 0,4 х 0,3 m with the rest/
If single hull is necessary then, IMHO, combination of SOF and inflatable elements or inflatable with frame can create more rigid construction.

 

Hi all again, sorry for late reply, I was away on a travel, and could not connect to the internet.

Again, thank you for such an extensive information.

Well, I plan to sail only in closed fresh waters with this boat, so I guess corrosion isn't a factor... Then again, if aluminum gets corroded in salt water, what about marine plywood cross sections coated with water-resistant (not waterproof) varnish (my primary option right now) - how does it react with salt water, better than aluminum?

Probably I wasn't very clear on this. With "flat bottom" I meant not in traditional sense (flat bottom versus round or V-shape hull), but that the keel line is straight, without "belly" when looking from the side. Take a look at Yost kayaks - I think all of them are have completely flat side profile, because if skin-on-frame hull would have this "belly", the skin would have to bend in two directions - to U shape (forward view), and ͜ shape (side view), creating wrinkles that can be solved only by cutting them out and sewing or glueing fabric in several places. Yost wrote this somewhere, I can't find right now, but it seems reasonable.

Well, "cheap" depends... Of course they are cheaper than Dacron sails, but they still cost some. Last sails I made from Tyvek cost me about 70 dollars. These were two sails, 30° gaff mainsail (8.2m^2), and genoa (3m^2). It could cost a lot more, but I planned them so compact on Tyvek rolls, that only about 0.5m^2 was unused of about 15.7m^2 of Tyvek (I know numbers don't add, because much of Tyvek was used for intersections, second layers, reinforcements, etc). And then there's 4 rolls of sticky tape, about 30 meters of reinforcing rope, 27 rings for tying sail to the mast and boom... Also, they stole some 30 hours of my life and a whole lot of nerves.

With that in mind, I guess that making reefing lines will be much easier than to make completely new sail... Of course, jib can't be reefed (I considered low-budget roller-furling, but I guess that will be too complex and expensive anyway for such a small boat), so I guess I'll just drop it in heavy winds.



Thank you for your answers. I will continue on this project, and, since this topic deviated far from original question, I'll create a new thread with all drawings, schemes and solutions before I start building.

Thank you again, you've all been very helpful!