Foam stringers & engine mounts?

[larby]

Hi all,

When using foam for stringers, do I need to make the part of the stringers in the engine bay from ply or something to bolt the engine mounts through? Or do I just put more glass over those bits?

If you're wondering why I ask, the reasons are below...

I've been going nuts about what to use for the stringers in my revenger. I've spoken to a lot of people and been given a lot of advice, trouble is none of it was the same advice! I just don't know who to go with, so I did a list of pros and cons and came to an obvious conclusion.

Douglas fir or similar - Out 'cos I can't get it/price

Scaffold boards - Possible, but no different to any old length of pine, so not great. Knots, warping and allsorts.

Ply - Widely used, but hard to get good stuff over here. shipping cost would be astronomical. Also half of the wood faces the wrong way & there would have to be lots of joins. Lots of people said not to use it.

Foam - No major negs I'm aware of. Easily available locally, cheapish, easy to work with, light and flexible. 90% of people in the know have said to use this. Most people building boats use it too.

Then having spoken to a very trusted local guy who's built/rebuilt more than a few boats, his opinion was I'd be better off not using wood as it's very stiff. As my hull delaminated, I really want to keep it all a bit flexible. There were various other reasons I don't need to go into here too.
All in all, it looks like I'll be using foam. I've gotta make a decision some time soon, and apart from anything else, it's the only thing i can get locally!

James

[Hydrostream]

Foam is ok for stringers, will definitely need something solid where the engine mounts. Ply would be fine, even with only half the wood facing the right way, it still has more strength than the foam. It's not the stringer core that provides the strength in this case but the glass that encapsulates it!

The transition from the foam to the ply should be as gradual as possible to avoid any local stress on the hull. Long scarf or similar.

This is just my opinion not having built any boats with car motors in em Tony would be the one to answer this, I think!

BTW, are you a gluten for punishment???? Another project?

[larby]

Yep, definately glutton for punishment! Thanks for the answer, that's just as I thought. I've been told to do one complex over the stringers with 3" foam to keep it flexible, would that be enough?

Cheers, James

[boatnut]

Originally Posted by larby

Yep, definately glutton for punishment! Thanks for the answer, that's just as I thought. I've been told to do one complex over the stringers with 3" foam to keep it flexible, would that be enough?

Cheers, James

hi james, it seems your happiest building them than using them, good luck reece

[Tony Davis]

If your going to go the foam route, what type of foam are you planning to use?

This, or something like it is the correct stuff... http://www.diabgroup.com/europe/products/e_prods_2.html

but it makes marine ply seem cheap by comparison

[larby]

Something along those lines. All I know is that it's a closed cell foam designed and used for use as stringers etc. Price isn't too bad, they're using it for huge stuff so i practically just need some offcuts!

James

[larby]

One more question...

Most of the foam they have in stock over here is 3" wide. Is that too wide? The ply stringers I took out were 1 1/2" wide. I guess you use the extra width of foam to allow more glass on the top for strength?
My only concern is the weight of the ply in the engine mount part.

Cheers, James

[biffer]

foam's good, you can do your mounts in foam, we use to do foam, matt, mild steel plate approx 300mmx100mmx12mm and more matt, drill and tap plate for your mounts