Waterski Cost effective composite with a high strength to weight ratio

[mobefive]

Hello all,

I am in the waterski manufacturing business and we are building trick skis. I need some information and advice regarding composites. Today's high-end skis are built using aluminium honeycomb cores and prepeg carbon fibre layup overtop, this is an expensive process. The skis we have built so far have used an expanded PVC core and a fibreglass layup, mostly a combination of triaxial and normal glass. This is totalling around $100 Australian per ski. It is vacuum bagged onto a sheet of curved steel to gain the required 'rocker' shape (curve on the bottom of the ski).

I do not mind putting costs up a little, but within limits. I do not know what difference to the strength of the ski the triaxial glass makes and if it helps, I just know that I put a lot of resin into them and they are turning out heavy. I would not mind experimenting with perhaps a layer of carbon on the top, but I do not know what difference this will make. A trick ski is roughly 42x11.5" with rounded ends and about 1-1.5cm thick. Also there is an aluminium plate that is 20+" that covers teh top centre of the ski and is covered by a layer of glass.

The main problems that have been found with skis in the past, including honeycomb cored skis is that skiiers often push their back heel through the surface of the ski and out the bottom destroying the ski. Also after much use, (especially jumps and flips) the forces on the skis have caused them to loose their shape in the rocker line (the profile from side-on), and this is definitely not desired.

It would be great to hear from anyone who can help me here with any advice or suggestions as to good composite layups and perhaps a better way of laying up the composite as to save weight and gain strength.

If you need any more information please do not hesitate to contact me, and any help would be very much appreciated so as that this project can go on.

Cameron Leake

MobeFive Trick Skis

http://www.mobefive.tk

 

[G1DESIGN]

this may be a dumb idea

could you put a keel strip insde the ski along its length
ive done some work using this idea on bike frames but know nothing about water skis however when i lived in the US a good buddy of mine made surf boards


this got me thinking
however you could come up with a pretty good solution using a moulded ski with a keel strip built in, almost like two hollow moulded halfs joined in the middle but with no join if you like ,ive used this on bikes too to produce monocoques and the technology required would be quite cheap we had to build our first one on a tight almost no money budget and it was as good as the version with the honeycomb core oh and the resin content is pretty near 35% using this process

drop me a line and ill show you some pictures and the way its done might be a good starting point a monocoque ski

dunno if this helps

if not it was a suggestion

 

[mobefive]

A surfboard is a great example, only a trick ski is smaller, thinner and needs to be way stronger. This is the main concern when choosing a core material/design and layup process. Its a cost vs weight vs strength issue. Stringers are a great idea that I had previously had mentioned to me but had not thoroughly investigated, I would be really interested to see how you used it to your advantage. Stringers in the shape of the rocker may stop it from loosing its shape, what type of material did you make the strigners out of?

However I dont think that a hollow-cored ski is a good idea. We are currently using Expanded PVC for its excellent stength to weight ratio, will stick with this until I find something better, I will however consider additions for strength.

G1DESIGN, you can email me at mobefive@hotmail.com if you would like to send me those photos.

Cameron Leake

MobeFive Trick Skis

http://www.mobefive.tk

 

[Gerrd]

hi

i have a friend doing surf science (sound like a lazy course i know,but it aint)he recons its posible to create stringers out of the top or bottom layers of fibre simply by formingthem in to a U shape. it a bit tricky to discribe, but simply its a chanal running the lendth of the bored which you fold a layer of fibre into, then layup a flat layer over the top. should be a compatable method for a foam core system.

if theres a problem with parts of the surface being compresed try laying up carbon in that regon under neith the glass. fibre orientation should always be in the direction of the load.

hope its some help.

 

[benno]

Would a switch from PVC foam to Al honeycomb provise you with any kind of appreciable weight saving? I would think that the primary weight saving on the carbon/Al honeycomb ski would be in the laminate. If you use PVC foam it limits you to wet layup as prepreg curing temps would damage the foam. My suggestion would be combine your current methods with carbon/kevlar mix cloth. Careful attention to your cloth weight and bagging methods should yield a laminate that is way superior/lighter than triax glass. Additionally, you'll have your shape preserving foam in the construction and a more durable product all round.

Ben Roberts

Broadcast Engineer

Sentient being.