Hydrofoil Board (structural)

General Composites Discussions Composites Talk
#1

First off, what is hydrofoiling… the sport is a blast, but most all of the ski is made from billet aluminum and is heavy… 35+ pounds for the unit. My goal is to build a 20 pound composite ski. We can be really rough on these things, so it needs to be able to withstand some torture. On a bad spill @ 30mph from about 17 or 18 feet in the air, things have a tendency to break. Here’s a video of a bit of hydrofoiling:

http://www.foilfreaks.com/Videos/Oct2004/Firebird-Oct-2004.wmv

So I’m a newbie at composites and have tried to soak up as much book knowledge as possible. With no prior hands-on experience, I’ve created three different molds and have pulled 2 parts over the past month. So I know enough to be dangerous. I’ve mainly used Fibreglast stuff to do the molds, because they seemed to offer an easy to follow procedure for the complete newbie…I realize they are expensive, but now that I’m understanding things a little bit better, I can look elsewhere for parts/supplies, etc. Enough with the background info, so here’s my question…

I’m on to building the board for the ski and I want to use sandwich construction + vacuum bag. My plans are something like this…

Bottom Shell
1 ply of 5.7oz plain weave CF
5 ply of 9.0 oz T700 12" uni-CF
(bag with nylon peel-ply/breather - bag & cure)

Apply a small coat of resin – lay in the Nomex
(Helcel HRH-10 nomex, 1/16 cell, 3.4 lbs density, .5 in thick)
Wet-out a piece of Uni and lay it on top of the Nomex
4 more plys of the Uni
1 ply of plain weave
Release Film/Breather/Bag & cure

So in general, is this plan OK?

I’m probably going to lay some 45 and -45 plys, but with a hydrofoil board, strength and stiffness is key from tip to tail vs side-edge/side-edge. There are a couple of areas that will need a bit of extra reinforcement (under the tower & under the feet).

Right now I’m using FibreGlast Epoxy 2000 with 2 hr hardners. Is AeroPoxy the strongest RTC for structural? It seems like the properties between the two are very similar.

I’ve heard of some gotchas about getting the Nomex and carbon to bond properly and not filling the honeycomb with resin…any tips on this type of sandwich construction?

I’m also going to be drilling holes through the finished part to mount the tower and foot bindings. I’m thinking of through-bolting everything…rather than trying to figure out inserts. Any ideas?

When I’ve drilled into the board, I will need to make sure the hole is sealed so water doesn’t get soaked up into the Nomex core. Should I drill, then fill the holes with some type of lightweight filler, then re-drill the bolt holes?

Thanks.

I’ve attached a picture of the board mold…

#2

Wow, the success rate of landing a jump is pretty low. I don’t know how to achieve what you’re doing but I’m sure Evan can. This might save you some time though. http://www.foilfreaks.com/Pictures/04Carbon/04SkySki-Carbon.htm

#3

You would be better off inserting hard points for bolting stuff onto it. It’ll distribute the load better and also look cleaner then running bolts all the way through. If you use aluminum, make sure you cover the aluminum with a layer of fiberglass to insulate it from the carbon. Carbon and aluminum will cause galvanic corrosion.

I would highly suggest way over building the first one if you are only building one. If you plan to make a few, I would highly suggest doing static structual testing to make sure it is strong enough. Remember when carbon fiber fails, it fails catastrophically.

#4

Actually, I showed you more of a crash or carnage video, just to give an idea that the foils can get beat up. Success rates of landing are actually pretty good…you can look at other videos on the site if you want to see more ride-away stuff.

As for the carbon stuff on the site, yeah, that’s pretty much what I’m riding now and the ski is down to 29 pounds. But most of that stuff isn’t available for sale…only prototype parts that have dried up. So I have to learn how to make more in order to fullfill my habit.

#5

The previous boards have used G10 inserted into the laminate, but I have no clue on where to get or how to work with G10. As for using aluminum, I’ve heard not to mix aluminum (metal in general) and carbon…but I know people do mix the two. So is it as easy as wrapping the metal with fiberglass first?

Yes, I plan to make a few and I am overbuilding, like you suggest. I’ve had some carbon failures and it is pretty much a bust rather than a bend, i.e. no yielding. I think I know where the greatest stress points are and for right now, I’m going to lay down mulitple plies of uni CF. Even around the bolt areas, I think my first one will just be major build-ups of uni, rather than trying anything else, like aluminum or G10. But I’m definitely interested in figuring out how to work with these types of materials inside of the laminate.

Thanks - I hope I don’t waste too much money learning how to do the sandwich construction. :lol:

#6

You can buy cured G10 plates from: www.mcmaster.com As far as using aluminum withib your laminate wrapping it with glass is the correct way to do it to avoid galvanic corrosion. Another way to avoid the possibilty of corrosion is to paint the entire aluminum plate with resin and let it cure before you integrate it with the laminate to provide a barrier between the carbon and aluminum. In bike frame manufacturing this is a commonly dealt with problem. The main problem you will have is the difference in thermal expansion between the two materials. Carbon as you may know does not expand much at all with heat but aluminum is pretty much the other side of the spectrum. Even if you don’t post cure the foil in an oven leaving it in 100 degree weather (as in summer heat) could cause problems. However if the plate is fully embedded and it is oversized it might not be an issue. Another idea would be to use a titanium plate to avoid the CTE problem. Titanium of course doesn’t expand much with heat just like carbon. That’s what I would use. Just my $.02

#7

Ideally titanium is really good material to put into carbon fiber, except it cost even more than carbon fiber. It also galls and is not the strongest when threaded.

I wouldn’t thread into G10. G10 is essentially fiberglass. All the knives I own with G10 scales all have inserts for the threads.

If you are using a honeycomb core, what you would do with the hardpoints is cut out a section in the honeycomb and replace that with the hardpoint. Once that’s cured, drill and tap the holes. You can get threaded inserts for use in composites, Aircraft Spruce & Specialties sells them, the problem is positioning them. Even in F1, they drill and tap holes in after it’s cured to insure the holes are in the right location.

#8

looks cool, must be hard on the back!!!
have you see the guys that have taken that under water spoller and addapted it to a surf board with foot attachments. There catchin like 100ft waves. Iam pritty sure that there made from composites