The Melatelia: light wind dinghy

Yeah, my mistake. 40kg for normal strings. Although I had played with extra hard tension strings, which bring tension close to 60.

Bracing, of course, is very important. But I've seen guitars with same internal construction, but different choice whenever to make decks cambered or flat. I've yet to seen flat decked guitars that survived at least several years of active use, including expensive ones.

I asked them. They said they don't have regular customers in Lithuania, they export their stuff abroad. So, it seems I have little choice here.

Today, I called Birch plywood guys and asked if the highest grade oversized plywood sheets are still available. They said no. No high grade ply is available, in any size. The best they can give is 3rd grade plywood (still boil resistant, with branches cut out and patched). Well, if it's patched, then it shouldn't be much different in strength from the highest grade - I guess it's the looks that suffer.
And they said they can only give me 2500x1250 sheets, which are just a little over US 4x8 ft standard. I quickly re-done my nesting and determined that I can make do with 4 sheets, but I'll need to scarf 5 parts.
On the bright side, this plywood costs almost two times less. I can get all the ply I need for only 85$.

It seems this is the best I can get in my country. Sometimes I hate living in such a remote place. You can't get anything decent here.

Thank you for making time to draw this sketch. I can see what you mean. But I don't understand, what is the point of extending side tanks past the beam/bulkhead. They don't serve any purpose there - you can't sit on them, and they don't add buoyancy, if I understood you correctly. They would add weight, though. Why would you do that?

Well, some time ago that was just what I designed. But then someone said that if I were to extend daggerboard case timbers up to the side decks, it would help re-directing loads from bottom panel to side decks. And the timbers that run up the side tanks is to help side panels stay in correct angle during building and afterwards, when crew sits on them.

I mean, they don't add much to weight, and they do serve a very useful task. So why not?

Too much buoyancy, well, that's something I haven't thought about. But then the Duo of Richard Woods design comes to mind. You saw the capsize test video he posted in this thread some time earlier? His boat is even narrower, lighter, and has much more buoyancy than mine. When it capsizes, it takes almost no water. And still he manages to climb inside the boat without much trouble.


Again, I don't mean to complain, just asking why this and why that

And my latest update, would it work or wouldn't it, were I build it this way? Weight is pretty much okay, but I want to know if it structurally sound. You have proposed how you would do it, but didn't say if my way is wrong.

That's interesting. I noticed this guy put a lot of beams to support side deck plywood. Should I do the same? It seems like a lot of work, since I'd have to carefully and accurately bevel each beam due to the fact that my tank sides are angled. Very complex task. Would decks be strong enough without such bracing?

 

I went ahead and replaced side tank bulkheads with framing, 5 frames (2x1cm) per side. They are spaced around 40cm apart.

Weight is 25.2kg. Acceptable.

Although these braces will take some time to make, they should allow much easier side tank installation, and add some structural support to the tank tops.



Opinions? SukiSolo, you in particular, because you gave me the link that gave me this idea

 

two suggestions:

1.) double the thickness of the timber at the tank end/bulkhead joint, and
2.) put your inspection ports on to of the tanks, in an area where you will probably not be sitting.

 

On your fairly narrow side decks, the supports you show should not be hard to fit at all. They can be easily notched into the inwhale and carlin which should be large enough to accept them. So effectively square notched and dropped into place. the load is almoat 100% from above ie people sitting on the deck - they won't come out after glueing in. You only need 2 or 3mm of notch depth to create a pretty solid support - that is into the inwhale and carlin and say 10-12mm deep. Not too hard for a sharp chisel.

I'd probably substitute one of the supports with the internal brace (in tank) in edge plywood you had before (but different shape). If that was to coincide with the aft edge of the daggerboard case it would be useful for holding the entire hull athwartships.

Also you won't need the stern one IF the transom framing is internal. If you get super obsessive about weight saving the cross braces can be a double tapered parabolic arch. you need depth more than width, I'd guess 20-22mm in spruce would be good if the deck is only 4mm.

 

Okay, no problem. Thanks.

Good advice. I'll see what I can do about it.




All right, this thread is getting really big again, and I feel I'm becoming sort of an impolite guest who hasn't realized he stayed for too long. I hoped that my original design will only need several tweaks, and look where it all went.

But after all, it's the thing I have to do myself, and I don't want to be tiresome with my questions and requests to evaluate my work. I probably already asked too much. I thank you all for your patience and support. Some of you have stayed with me from the very beginning. I couldn't begin to describe what that means to me...

I'll try to move on my own from here on. I'll share the final plans once they are done, and photos of the scale model. Afterwards, of course - photos from building.

I take a big bow to you all for your genuine and sincere helpfulness, especially messabout, Skyak, Sharpii2, John Perry, SukiSolo, Richard Woods, WindRaf, rwatson, Petros, tdem, NoEyeDeer, Phil Sweet, Nick Sinev, and tom28751. I'm sorry I refer to some of you by your nicknames, as I do not know your names (and I'm not sure if some of you would like them disclosed here). I would like to, though. With your permission, when this project is finished, I'd like to publicly name you all as a valuable contributors. I couldn't have done it without you, guys.

I won't take any more of your time. I'll return with results.

 

time to stop thinking about and get out in the shed and start cutting some lumber! You will actually learn more by building it and sailing it than reading words written by someone else.

So get on with it! Have fun, and good luck.

 

I drew this sketch before I found out you were shutting this thread down.

I drew it to show what I meant by "running the side tanks under the fore deck".

As you can see, I meant only about 8 to 15 cm under.

This way, the water tight bulkheads at the front of the tanks also serve as rather large gussets, in way of the mast partner beam.

Hopefully, this is all the structure you will need there.

By running the tank ends under the fore deck, the tank end bulkheads are readily accessible, in case there are any leaks there.

Good luck with your build.

 

I preferred the 12ft version. As to weight, your car can take more than you think on the roof. Roof racks for my hatchback are rated at 70kg. A car roof is made strong enough to support the car in a roll over, thus they can support around 1.3 tonnes. A 50kg boat is no problem.

To get a 50kg boat on a roof-rack is not as hard as you think.

Best system I have seen is you take and aluminium ladder, bolt on a pair on pneumatic 8 inch wheels from a 30 dollar removalist trolley. You slide the ladder on and off the roof racks, the boat goes on the ladder

For some photos,, see hannu vartalia and his cartopping a 20ft rowboat on a small car. See Miss Cindy catamaran (extreme).

My point is that if you want to car top a 12ft boat that weighs 45kg you can. I car-top my 52kg boat easily. Takes 1 minute to get it on and off. (I put wheels on the boat transom). The ladder method (not mine) is better though

 

Thank you for that sketch, sharpii2. I'll probably modify the design per your suggestion, have to think a little on it. I'm not closing down this thread, just trying not to overstay my welcome with all the questions

Yeah, I know, that is reasonable, but the problem is twofold: one is that if the boat is heavy enough, it requires ladder or cradle or something to get it on and off the roof single handed, just like you said, and that adds to the complication. The other problem is that the legal limit for roof cargo is 35kg, and if police have any reason to think I have exceeded that weight, I'm in for a lot of trouble. I personally know several guys who got excessive fines for carrying overweight (NOT oversized) items on roof.

 

At risk of excessivly prolonging this discussion, I think Sharpii is right about overlaping the ply of the fordeck and the side deck. The reason, as I think Sharpii already explained in previous messages, is that when the hull comes under torsion, as it will do with the wind blowing the mast sideways and the crew sitting out to counter that, each side deck, as seen from above, will tend to rotate relative to the foredeck. Think of a cardboard shoe box without a lid. If you give it a twist the angles between the top edges of the sides and the ends are no longer right angles - you dont want that to happen to your boat. Without doing FEA I would not care to guess whether this is a real problem or just an imagined problem for your structure, but overlapping the plywood and perhaps placing a wooden block in between at the inboard edge of the overlapped region should make it stronger in torsion without adding much weight. The alternative of course would be to make the foredeck and side deck one continuous sheet of plywood and have the side deck sloped to match the slope of the foredeck (i.e. the inboard edge of the side deck higher than the gunnel. Lots of boats are like that. But then again, some boats have the side deck sloping the opposite way! Horizontal side decks are perhaps a good compromise.

 

I said I should be ending with this, but I just can't figure it out, sharpii2. Your sketch makes sense, and I'm trying to make something like it, but the problem is that because side decks are at sheer line height, it isn't possible to connect the timber parts on which mast partner would attach to the gunwales, because the side tanks are in the way.

Here's a screenshot, you can see the interference. Of course, I could just cut away part of this curved beam where it intersects with side tanks, but then all the loads from the mast would go directly to these tanks instead of gunwales, which is very bad.



I can't make it out of your sketch, how exactly did you mean to solve this? It would be great if this curved beam would run directly to the gunwale without any tapering, it would be strongest. But it seems impossible with the side tanks, unless I make slots in them so that this beam goes inside the side tanks. Which is very bad for watertightness.

If you could just help me out with this last one, all the problems would be solved.

 

I am not sure whether this is addressed to me or Sharpii, but I would say just cut away that curved beam where it interferes with the side tank. The side ways load from the bracket holding the mast will be transferred into the curved beam and from there distributed into the fordeck and so to the side tank, the gunnel and the rest of the structure. Also cut a little piece of wood to fill the wedge shaped space between the side deck and the foredeck in the overlap region. Is this what you had in mind Sharpii?

 

Sorry, I meant to address you both. I didn't add that wedge you're talking about yet (I'm aware of it and I will do that).

But I really don't like to cut away part of the curved beam, because it won't reach the gunwales. This is 4mm plywood, after all. I don't want to risk having all the mast forces being transferred through bow deck and side tanks. It would be best if this curved beam would reach gunwales somehow. Then I wouldn't have to worry about mast forces violating watertightness of these side tanks, as Sharpii warned about this potential problem.

 

I don't know, been thinking all day and found no solution.

So maybe it's better to go with what sharpii suggested earlier, having side tanks offset away from bow structure in the other direction, leaving a gap? Like this (2cm gap here):




Instinctively, I want to remove that gap, joining the curved beam with the side tank bulkheads. But if that's going to cause problems with water-tightness, then I can live with the gap.

 

I think this has been mentioned before, early on, but I will again suggest enclosing the bow and adding a hatch on top.
It would be faster to do than the side tanks, that is for certain.
Also enclose a small area in the stern with a hatch or two.
Then if you are still worried about flotation, you could strap down some buoyant items in the cockpit, like a cooler.
I have found that with two to three people in my 16 foot boat, every bit of extra cockpit space is appreciated.
That would solve a lot of your issues.
Of course I would go with a leeboard to free up even more space, but thats just me.