"Terry Keeley" tkee(no wrote in message
...
Thanks again Ed, so high tensile strength is what I'm after.

Actually weight is a huge factor, these are for record attempt boats and
any weight on the right sponson has to be minimized to help counter
prop-walk. I'm running in a class that has a 120+ mph record and my buddy
I mentioned just broke the record in his class running 103+, here's pix if
you're interested:

http://gallery.intlwaters.com/thumbnails.php?album=1002

Here's the fin I'm talking about on my hull:

http://gallery.intlwaters.com/albums...anImage011.jpg

Oh, those are cool, Terry, and they look like a lot of fun. We were
discussing here recently that my uncle raced model hydros like that in the
1930s, in a 35cc IC class and in a steam class (he used gasoline-fired flash
steam). I sure wish I had the photos of those.


Wonder if one of the magnesium alloys might be better?

It looks to me like you have four engineering factors he weight,
hydrodynamic drag, stiffness, and strength. Magnesium has roughly the same
ratio of strength/weight and stiffness/weight of most metals (titanium is
somewhat out of line, having high strength/weight but low stiffness for its
strength). So magnesium would result in a thicker, if somewhat ligher, fin.

I couldn't begin to evaluate the engineering options, but as a materials
freak, the first thing I would look at is unidirectional boron-fiber
aluminum composite. The second thing I'd look into would be a boron-fiber
epoxy composite. I'm not making life easy for you with that one. d8-)

--
Ed Huntress