Twisting 8mm ply?

As for my first post, it’s time to introduce myself, I guess. I live in Bavaria, 50y.o. and have some little ocean/yachting experience, that is unfortunately 20 years past. My goal is to revive that big time in the next years. Obviously I’m not a native speaker/writer, so I apologize for eventually being cruel to you language beforehand and highly appreciate that you (hopefully) share your experience with i.e. mountain folks like me.
To start my remarinisation gently, I build a 12ft general purpose dinghy from plywood, stich & glue.

In order to make it ultimately bullet-proof I want to use 8mm for the hull panels instead of 6mm as specified. The bottom panel will be twisted some 170° from bow to stern.

1. Am I going to really hate me for that idea when trying to unfold, going 3D, due to the thicker ply?
…. or worse, could it proofe impossible?

2. How much worse will it become, when 25g/m² glas is glued to the inside before bending it, because it’s more convenient, flat on the bench?

 

Welcome
Do not worry about language. Translator program is awesome, most of time.

Great first project
In order to make it ultimately bullet-proof I want to use 8mm for the hull panels instead of 6mm as specified. The bottom panel will be twisted some 170° from bow to stern.
Is 170° error? That is a lot of rocker. Degree of turn is less problem than radius of turn. 4 M radius no problem; 1 M radius very difficult.

1. Am I going to really hate me for that idea when trying to unfold, going 3D, due to the thicker ply?
…. or worse, could it proofe impossible?

2. How much worse will it become, when 25g/m² glas is glued to the inside before bending it, because it’s more convenient, flat on the bench?
Bend and assemble first. The glass will be relaxed. If pre-glassed the glass will be stressed for a long time.

Good luck

 

No Sir, 170° is not an error, only a little exagerated perhaps. It's a single chine. The bottom panels start near vertical at the bow, beeing cork-screwed to a dead rise around 10° at the stern.

 

A drawing of the 12 foot dinghy in question, would be helpful.

 

That would be 80 degrees ?

 

This is the boat

 

Ooophs...yes you are right!
Still a lot of strain problably

 

Bending of ply depends on a few factors, timber species, ply orientation, number of plies, thickness, etc. I note one source gives 2 feet radius across the grain, and 6 feet along the grain, for 5/16 inch ( 8mm) ply. I would contact the provider of the plans, to get an opinion, the designer has created a shaped using developable surfaces, and the generating lines of the developed surface would be a good clue to the sharpest curvature. But that is usually not available to be seen.

 

^ This. You aren't building an ice breaker.

 

The architect, a wise man, retired and went off cruising.
Wood will be okoume, 7 plys problably.

I do not understand the term "radius" in this context?

 

Isn't ice breaking covered by "general purpose"?

 

It is half the diameter of the circle that it would require for your ply to bend 360 degrees, head to tail ! I think your best plan is, stick to the plans specification, and apply some epoxy and glass afterward, to the bottom, if you want more strength. That will save a lot of cursing trying to bend something that is resisting your efforts.

 

Not to mention imparting stresses that will cause your boat to fail.

 

It does go against the nature of stitch and glue. I think it would be silly to try 8mm, when the glass/epoxy option is available, which will add strength and water-tightness.

 

Radius and his sister refer to how big\small of barrel matches the curve you are making. While degrees measures how far around the barrel the plywood is forced. The smaller the barrel or tighter the bend, the harder it is to bend.