The Melatelia: light wind dinghy

I understand that. So you're saying there is no way to meet those requirements with materials I have available? I can sacrifice a lot, but 30kg weight and comfortable seating for 2 persons is a non-movable requirements. If I don't meet them, then the whole project is pointless.

That Baltic Birch is imported from Latvia, actually, they don't make it in Lithuania. We only make indoor stuff. As for Finland, I'm sure they have good ply, but we certainly don't ship from them. I checked.

Yeah, I'd really like to stop. But it seems that my current design is doomed to fail. I'll try to shorted the boat to 3m, and add side tanks/seats. Still, I doubt I can do it under 30kg. MAYBE if I sacrifice all of timber framing except at the mast. Do you think it's worth trying, or should I go in another direction?

If I make this hull of 2 pieces, what does it change? Both pieces still have to go on car's roof. It's a small sedan, Mazda 323, so I can't fit the boat in the trunk if that's what you meant.

 

12 feet is good for your car;
changes that each piece enters in the weight limit you want

 

I'm not sure you understand. It's not the individual weights of pieces that matter. EVERYTHING that goes on roof cannot exceed 35kg in TOTAL. I reserve 5kg for oars and spars. The rest 30kg is for the hull. No matter how many pieces it is, one or two, it must still weight under 30kg in total.

 

????? ... two suitcases weigh more ... means that your car can not hold two suitcases on the roof?

 

I think it can hold more, but I guess it makes center of gravity too high up to drive safely. I don't know. Most cars have this kind of limit. Some have 40kg. I know people who were fined heavily for carrying overweight (not oversized!) items on roof.

Anyways, it would be difficult for a single person to put more than 30kg on roof at once.

 

Anyways, it would be difficult for a single person to put more than 30kg on roof at once.[/QUOTE]



is this the only reason, but with 2 pieces the problem does not exist

 

is this the only reason, but with 2 pieces the problem does not exist[/QUOTE]

This is secondary issue. 2 pieces would solve that. But such construction adds even more weight.

Primary issue is weight. There is no way around it. Boat has to weight under 30kg, period.

 

ok, good luck laukejas

 

Thank you for your attempts to help, WindRaf. I know these requirements are very steep.


Messabout, are you still reading this? What's your take on the problem? You gave great advice about the hull shape itself, but what about structure? If I go with side tanks/seats, do you see any way I can stay under my weight limit?

 

Okay, I re-worked the hull. Shortened to 3m, left the beam at 1.4m. Added side seats/buoyancy tanks that are separated from aft seat and bow compartment.

Linespan:



Attaching hydrostatics file if someone wants to look at.

The structure arrangement looks like this:





Everything is 4mm plywood, except transom and bow cross-section, which are 6.5mm. All compartments are isolated from each other.

The weight reads 23.8kg. That is only what you see in these screenshots. No gunwales, no thwart, no mast step and partner, no daggerboard box yet. I don't think I can fit them in 1.2kg, because last 5kg are reserved for hardware, epoxy and paint.

I'm out of my depth here. I don't know what else to do to have this boat in my weight limit. I can make bow cross-section 4mm too, but then I'd have to make some other support for it so it has enough strength to counter mast forces. Maybe this structure is strong enough no to need spaced gunwales, and I can do with a single 3x1cm timber strip on each side.

But still, that doesn't fit in 30kg total. Can anybody please advise?

 

Do you have a 2 or 4 door car? can you get a suitcase on the back seat? In which case you could maybe get the bow section of your boat in there

I assume 2 piece oars will fit in the car. My Duo has a 3 piece mast

RW

 

4 door car. But there is very little space back there. Only a very small suitcase. No way boat, or even part of it would fit there... Daggerboard at best. Very best.

I though of transporting oars on roof too.

 

There are a lot of kayaks out there that use 4mm okumee. That works well for kayaks but the flat panels are never more than about 15 inches (38cm) in unsupported width. a 12 footer can weigh in the 14kg range. The point I am trying to make, is that 4mm panels need to be kept to a modest width if they are to be serviceable. Alas, a kayak does not have to endure the torsional loads that a sailboat hull does. It does not need to be a robustly built as a sailboat, especially a sailboat with a free standing mast.

So what can we do to the boat design to keep those panels to a smaller width? Well we could make the boat a 7 or 9 panel deal, maybe glued lapstrake. That makes the build more challenging and is likely to use a little more material because of the curvatures in the flat panels before assembly, resulting in some waste.

Weight, material availability, cost, build time, absence of equipment such as a table saw or band saw, and a few other constraints make this a real tough nut to crack. Weight and cost obstacles could be avoided by using skin on frame. Petros would argue in that direction, almost surely, since he is our resident SOF guru.

Glass over foam would work but Laukejas can not get that sort of material. He could build a stripper that could be light and strong but ripping and routing all those strips are not within his equipment capability. Besides, he has said that he can not get glass fabric.

All this has been kicked around previously of course. What with the collective experience, wisdom, and cleverness of our members there must be a solution. No one believed that we could get a human on the moon 50 years ago did they?

I was all set to attack the OPs preference for the Lug rig with some salient engineering tid bits. Never mind, we have to build the boat before I quarrel about the rig.

 

Thank you for your support, and for trying to raise some attention for this topic. But I'm not yet giving up with stitch&glue approach. I've made some tweaks, and I think I'm closing up on the goal.

Here are two designs I've worked on now. Hull is the same 3 x 1.4m as in my previous post.



I took liberty to copy this kind of thwart from Eastwood Pram (more or less). Thwart supports daggerboard case, and gives something to sit on while rowing. On the downside, it would get in the way of the crew when trimming the boat, also when tacking. This thwart utilizes 4mm ply, so it might be too weak to be trusted not to break. Anyway, this weights 26.4kg in total.



Now this is what I like better - no thwart, but some timber pieces to support daggerboard case. Case is lower too (it's top is still 6cm above waterline at max load), and crew can move freely around. Weight is 25.7kg. Just a little above limit.

Here is another view with crew onboard:



The way crew is sitting now places CG over the LCB, so the boat should be trimmed properly.

What do you guys think of this design? I still need to trim off some weight, but this is very close. Please note that everything is 4mm ply except for transom, DB case sides and bow cross-section, which are 6.5mm. Do you think those side seats need some internal bulkheads, or will they'll be strong enough on their own (they are about 25cm wide where crew sits)?
Also note that I've sacrificed spaced gunwales. Now it's a simple 3x1cm piece.

I could do that. But yet it feels wrong somehow, eliminating aft seat at all. Can't point my finger to why, though.

Please let me know if I'm moving in the right direction. You're all being very helpful so far. I hope I'm not becoming tiresome.