Screw and Glue questions

My impression is the same as PAR's.

But I'd like to see if your scaled planking will take the bend to vertical. I'd be real concerned about the full size 1/2" ply taking that bend over 4' width. Are you planning the typical Tornado style banana shape to get the keel line glued, then pull the gunwales together?

How did you come up with the flat panel shape that will get you a shear line you want?

I really hope you know a lot more than you are telling us.

I'll be really impressed if you can bend the 1/2" in a simple cylinder even without compounding.

 

Me too.......

Unless you make the 12mm.1/2" out of 1.5 or 2mm ply lamination.....

 

Then it is not the classic "tortured plywood".
But I'm being narrow minded.
I just can't imagine getting 6 layers of 2mm ply 30 ft long bonded together well, unless you actually do it as cold molding with the 2mm cut into much smaller pieces. Not generally regarded as an easy method.

But enough speculating, I'm sure the OP will tell us his plan.

 

It would be helpful to see a set of lines so we can see how bad the shapes might be for this method. All else is speculation on the technique and application practicality.

 

Hi Par,
if you'll spare the time - here is my logic - a triangular cross section spruce centerline piece cut to a chosen angle (or even a varying angle) should hold the side panels at the correct angle prior to stressing and would be lighter and stronger than an epoxy-with-filler fillet. (In my understanding the fillet provides radius, not strength.) Then epoxy and tape over joins exterior and interior.

 

The fillet increases the thickness or depth of the corner, so it contributes to its strength. A triangular section wood piece will do that too.

 

No, not 'traditonal' tortured plywood.

"But enough speculating, I'm sure the OP will tell us his plan."

its not a traditional boat ( my take on the altantic proa) and its not a 'traditional ' building method. I'm working from the ground up here, its quite experimental, though not silly, I hope. So bear with me.

"I just can't imagine getting 6 layers of 2mm ply 30 ft long bonded together well, "

where did the 2mm come from. I"m working in US with old school measurements - so scarfing 4 sheets of 4x8 to make 30 ft. (good long scarfs).
Probably 1/2" or slightly thinner. I do not want to laminate ply. I thought about two layers of 1/4" but the difficulty laying the second layer without voids scared me off. So - use the ply for what its good for - strength and rigidity when flexed in two planes, and fair curves for free.

 

Exactly...but to clarify: The wood will provide some longitudinal fiber strength but very little athwartship. You would still be well advised to apply fiber in that direction.
Also you do understand you are making a lot more work for yourself. I presume you are cutting rabets for the ply? Otherwise I can't see where you would get the meat to sink these screws in?
Lastly you should try to work as much bend into your project as you can, without exploding your stitching method, before you apply the glass. Otherwise you may get a lesson in the strength of composites before you have formed your shape.
Build a model and do a full size test with some cheap ply building a 10 foot section. You may save yourself some real cash.

 

DGreenwood - thanks for your comments.

>You would still be well advised to apply fiber in that direction.

right

> Also you do understand you are making a lot more work for yourself. I presume you are cutting rabets for the ply?

sure, very simply with a table saw.

> you should try to work as much bend into your project as you can, without exploding your stitching method, before you apply the glass.

yuh, that's obvious

> Build a model and do a full size test with some cheap ply building a 10 foot section.

starting an 8ft model tomorrow

 

Unlike so many that come here, you are testing your independent ideas with experiments and listening to experienced advice. This is a good omen. It is ok to try out new stuff after you have hammered through the pain of learning the tried and established methods. I have personally trashed many thousands of dollars in materials with big ideas about a better way. Boat building really is a craft and an art form that is very developed despite the lack of easy to find documentation. Yacht design is a science that is far more developed than is readily apparent. The results are: many disappointed amateurs having squandered a lot of money to find out they weren't born with the intuitive ability to design and build a functional boat without some real guidance. This a rant I have worn out but I am repeating it again.

 

D Greenwood
thank you for your kind words. As previously noted, I am no stranger to experimental design/making projects, from (real) robotics to alternative technologies. And I am deeply respectful of the crafts of shipbuilding and of the design traditions. What intrigues me about my current project - an atlantic proa - is developing well considered - and even tested - answers to the question : how much of traditional naval design wisdom - both monomaran and multi - is relevant to a bilaterally asymmetrical shunting boat?

 

The answer? If you mean presynthetic materials and are talking about construction methods only---not much. Design was solely based on trial and error so there wasn't much science involved, or at least, nothing like is involved now.
To put it in perspective, Plank on frame construction is fun and I still love building boats that way, but it really doesn't qualify as a reasonable method structurally.

 

>If you mean presynthetic materials and are talking about construction methods only---not much.

Here is a great video - last canoe of mokil - very traditional methods and materials. https://vimeo.com/38971749

No, I'm thinking more about how the dynamics of a shunting boat effect design. ie -

1. If you don't have to tack through the eye of the wind, steering capability under sail does not require the capability of a quick 90 deg turn. In which case the maneuverabliity of skeg keel ad rudder are not advantageous. Tracking like it was on rails may be a good thing. ie justifying a deep V.

2. balancing sailplan. Uniquely, a proa has to have a reversible but balanced sailplan.

3. helm balance - Is the taboo of lee helm a taboo on an (atlantic) proa - it seems that weather helm would be a liability.

 

All three if those questions are topics well investigated by multihull designers, many of them visit this website regularly. Once again...there is much money to be saved in talking to them or having them design a boat for you or in cooperation with your ideas. The same can be said of the building process.

 

I'm all ears is anyone has input.
Maybe I should start another thread?