Having the fin as thin as possible is the most important, then weight and
strength. Looks like a heat-treated Ti alloy is in fact the best choice,
other than some "unobtainium", LOL!

Thanks again for all your help, my goal is to travel our 330' course in 1.8
sec!



"Ed Huntress" wrote in message
...

"cavelamb himself" wrote in message
m...
Ed Huntress wrote:

"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

Is this really a materials issue?

Or Temper?

If the object is to have the highest possible stiffness and strength for a
given density, it's really a materials issue -- and metal-matrix
composites look to me like the winner. Since the volume of material is low
and the objective is very high, it may be worth the effort and hassle.

And it is a hassle. Just cutting the stuff can be a nightmare. BTW, most
of the aluminum composites available today are not boron-fiber reinforced,
but other ceramics, like aluminum oxide and boron nitride.

--
Ed Huntress