Building ultra like hull with honeycomb core

[BSR001]

Ive been reading alot about nomex honeycomb cores the positives and negitives about them.Im considering building a freestyle jetski using carbon,kevlar and honeycomb.My layup im thinking something like 3k carbon,
kevlar,
6kcarbon,
1/8 nomex honeycomb,
6k carbon
,kevlar,
3k carbon.
I will be wetlayup and vacume bagging.
my question is should i do my 3k and kevlar and bag that then do my 6k and honeycomb and 6k and bag that then my kevlar and 3k and bag it again to keep from filling the honeycomb with resin?
thanks

[marshmat]

Hi BSR,

Firstly, without knowing the actual weights of the fabrics you're talking about (3k, 6k are tow count, not weight), I can't calculate the exact properties of your laminate.

I can tell you that if you're talking about typical 8-15 oz fabrics, your hull will be about half as strong and four times more flexible than the outer shell of a solar car- and those only have to deal with air. Almost certainly, it would break up the first time it hits a wave at 20 mph. Take a look at a cut through the hull laminate of a production jetski- they are strong, beefy fibreglass structures.

If you want to use carbon and Kevlar, you will need to do a lot more research and learn how to engineer these materials. They are not easy to design with and are very expensive to use. Your initial estimate is off by about an order of magnitude in strength and stiffness.

What plans are you building from?

[Jimbo1490]

I trained and worked in aerospace composite manufacturing and repair and have been around the block a bit with the Nomex. A nomex PWC is possible as nomex has been used successfully for quite a number of racing power boats. A race team I used to do repair work for had a pair of 32' power cats that were Carbon/glass and Nomex cored.

But a racer's definition of a successful boat might not be the same as your expectations. Even if you do the math (or have someone do it for you) and get a proper layup schedule, you will face the fact that Nomex cored boats tend to be a bit fragile. They do not like to hit things (including waves) and are difficult to repair. Racers put up with fragility to win races. If it lasts a couple of seasons, they are OK with that. In a couple of seasons, the hull shapes may have 'moved on' anyway, so fragility is not that big a problem; they won't be crossing any oceans.

Now you won't be going any distances either, but I bet you expect to get a few years out of this craft, especially considering how pricey the advanced fibers (especially carbon) have become.

Also, hand-layup is not the best choice given your selection of fibers. Even with vacuum-bagging, it will be difficult to get really good fiber fractions with hand-layup. Without good fiber fractions, the capabilities of the advanced materials are basically wasted on a heavy, brittle over-rich layup with resin-soaked Nomex cells.

If you are really committed to this kind of construction, you might consider finding a shop (probably a race car shop) that has the expertise (and maybe even the material on hand) to build it properly from prepreg.

The price will certainly be shocking, but the result will at least do justice to the materials.



Jimbo

[BSR001]

previous hulls i have built are vinylester resin and the layup are
3/4mat
12oz biaxel
12oz Biax
12oz biax
12oz biax
then when i join the hulls togather i run a layer of 19oz carbon from top to bottom these hulls are around 75lbs and the thickness is around .180
I would like to get one in the 60lb range.any suggestions will be appreciated
thanks

[Jimbo1490]

Suggestion: Prepreg

Jimbo

[BSR001]

Suspose i stick to my layup that i have been using its not bagged.suspose i do bag that layup im gonna lose my thickness which will lose the rigity of the hull would just a layer of 5oz carbon be enough to gain my stiffness back or would i need more?

[Jimbo1490]

No, no no no no, you're doing it all WRONG! You don't use CARBON to add thickness, in order to gain simple bending stiffness! That's what the core material is for! Carbon is a high-strength reinforcement that you use for the skins.

If you want to take this to the next level, I think you are going to need a little bit of help designing a layup. I'll bet someone on this forum can help you. Just ask. If you get help from a professional, expect to pay for his services. But it will definitely be worth the cost; you can get it right the first time. He can even design the layup with your production method (hand layup) in mind.

Jimbo

[DGreenwood]

For impact resistance, ease of construction around all those tight radiuses, and cost, you are waaayyyy better off working with foam to start. If you can take few ounces off later in low impact areas with honeycomb then do some experimenting. Odds are very high you would end up wasting a lot of expensive materials.
Really listen to me here---start with Core-cell or some such. Even then you will end up busting the carbon for a while until you figure out where to concentrate the material.
Start by learning to bag the deck and get that to stay together.
Jimbo is dead on about getting the thing engineered. You'll save yourself a lot of hell before it is finished.