Sandwich or not?

[Rainer]

Hi!

there is a discussion in the german IOM-Forum about the legality of a sandwich-constructed hull. I used 3mm balsa for the planking. Now i want to use a layer of fiberglass for the outside and the inside of the hull.

They say: this is a sandwich-construction and it is forbidden!

But i didn´t find a such a statement in class rules. There ist only a hint that it is forbidden to construct the hull "honeycombed".

I think that "honeycombed" ist not the same as planks of balsawood.

What do you think about this?

yours
Rainer

[ole_peder]

andd therefore permitted material.

[ROY SCOTT]

Yes, I understand it to be OK/permitted. But, do keep you inner layering of glass fiber clear so that it can be seen that no forbidden materials are lurking hidden away inside.

[Rob Davis]

Yes, I understand it to be OK/permitted. But, do keep you inner layering of glass fiber clear so that it can be seen that no forbidden materials are lurking hidden away inside.

I've always understood that ANY inner layer of glass be unpigmented. Others have raised a very good point that the external layer could be carbon and have a painted exterior and it would be hard to detect.

[Roy Thompson]

This links up with the current discusion in this forum (class rules) about inspection of materials etc of built hulls. It is a good example of how it would be very difficult to non-destructively test the hull in question - even scraping a small layer of paint off the outer hull in one area would not guarantee that the rest of the outer layer of fibre was not carbon. The best bet here would be to have the hull measured and certified before painting the outside since class rules allow (re)painting etc without the need to re-certify. The measurer would be able to specifically state on the measurements form that he has inspected the outer layer of fibre and it was found to be legal. If you haven't already built and painted the hull, this is what I would recomend without looking further into it - specifically ask the measurer to mention it on the measurements form!

[Steve Landeau]

I think this rule works. It doesn't make much sense to build a boat out of carbon, try to hide it (and the only way to do that would be to pigment the inside, easily detectable), and then have to add corrector weight. You'll save maybe 70 to 100 grams at best in the complete layup, and not really gain any performance. Ther'es already a 250 gram difference between hulls that I've seen, and performance is not inhibited due to weight in either design. S-glass is without question as good as carbon in all aspects of this application, save the slight weight difference. There is a bigger gain between polyester and epoxy than you'll ever get between carbon and S-glass.
If anyone were to try to cheat with a carbon hull, they would be grossly disappointed.