Composite project Jetski hull help needed!!!!

General Composites Discussions Composites Talk
#1

Recently i started to rebuild a stand up jet ski, kawasaki sxi 1995, as a freestyle machine. basically this is a trick ski which needs light weight to work properly.
Long story short. i did not do my reaserch and the weight for my hull is way too much for this type of ski. therefore im looking to make a composite hull to reduce the weight in order not to loose the money invested on the machine.

i am looking for advice into:

  • the type of composite to use. (ex carbon fiber or carbon fiber with kevlar)
  • Type of fabric (ex 3k plain, 12k, unidirectional, etc…)
  • Layers required for sufficient stregth to support the stress on the hull.

The process im thinking to use is by molding the composite into a fiberglass mold.
Any input for this process, or if there is a better more efficient process for home made fabrications, i am deff open to new more efficient options. since weight and stregth is a concern, i was looking into adding a middle structural layer in between 2 layers of composite material, in order to reduce the layers required and add structural streghth to the hull.
*would this be a good structural set up for the ski, or would it be better to add layers.

  • if it is a good set up, what would be a good material to sandwich in between the layers.

that said… whatever you have extra to add to this project i would appreciate it very much. thank you for your input.

#2

Look into Diolen. It has some flex so it will take a hit or two. It is used in motorsport for Anti Intrusion panels.

#3

i looked into this material, it seems to be a polyesther composite. it is perfect in the sense that it reduces costs a bunch. however, my concern would be in the streghth of the material compared to carbon fiber or kevlar. what is the comparison as per stregth to weight of diolen versus that of carbon. would it be a good idea to combine layers to have a structure composed of both. or would i be able to use diolen by itself and have the same characteristics as by using equal layers of carbon or kevlar?

thank you for your input and knowledge sharing on this alternate option.

#4

You would use the diolen in the lay up with the carbon and/or Kevlar or whatever you want to use. Personally I would have several layers of carbon a 200gr surface then possibly one ot two layers of a 600gr carbon with several layers of diolen then a reversed repeat of the carbon so you have a balanced lay up,

#5

Hello,
look at this homepage.
http://www.rl-automobile.com/7.html
I build this kind of jetski with them. The quality is absolute perfect. If you just want a carbon fibre hull I would recomend to buy it.
Building it yourself will be much more expensive even if you do not have a lot experience in composites.

#6

i have experience in fiber glass composite. which gives me an edge in working with the material. however, i am not much experienced with carbon or kevlar. anyway, you are talking about a 6,500 euro hull, where i could probably spend $1500. tops $2000. us in materials to build the custom hull. plus the time involved. not to mention i will be able to keep my mold. While having the satisfaction to have a custom self build jetski. now there is that probability that my build will take time and there is always that failure posibility. however i am willing to take my chances just for the learning experience. Although i cannot lie that hull was beautifull. thanks for the advise, but i am looking to get help on how to build this hull not on purchase options.

#7

from my research, we are talking about a hull weighing approximatelly between 60 to 70 puonds. wouldnt all these layers bee too much weight to be within this range. although the less the better.

#8

Is that weight the empty hull?? If it is then the lay up I mentioned would give an area of about 20sq meters! Just to give you an idea of scale my Motorcycle seat/tank is a full monocoque and weighs in at 2.1Kg or 5lbs. That is fully self supporting. OK you need more strength but even with the layers I mentioned it would not be heavy if you were doing an infusion or usuing an OOA Pre-preg.

#9

Your calculation with the money is only in the beginning correct;) At the end you will think that you should have bought it, but I can understand your idea of building your own one.
I would build the lower hull section in sandwich, probably a 15mm foam core, for example a Airex C70-75 or a Rohacell core.
Layup maybe
200 g/m² plain or twill 0/90°
450g/m² biax ±45°
450g/m² biax 0/90°
Core
600g/m² UD 0°
450g/m² biax 0/90°
450g/² biax ±45°

no Kevlar, Diolen etc, only carbon. The Kevlar does not help you.

#10

I like the diolen for impact resistance and when used in Kayaks it can hit rocks and take some massive hits and still not sink. It adds some shatter resistance to the lay up over carbon only. persoanally I would do it in pre-preg with a VTF surface layer and I think a core does add some extra strength too. But that is just me…

#11

I just had a rough calculation of the lay up I mentioned… You say it sounds heavy with all those layers in there…

200gr per sqm surface. X1
600gr per Sqm Backing layer carbon X2
600gr per Sqm Diolen X2
600gr PER Sqm backing layer carbon X2
200 gr per Sqm surface (to balance it out)
This gives 4kg per sqm for the material if you add 40% resin for a pre-preg this brings it up to 5.6Kg per sqm for the material. Not sure how big the surface area is but i would think 3sqm would cover it giving 16.8Kg (37lbs) total (not including any core or inserts for internal features ect) I am sure you can get sub 50lbs easily…

#12

Also check into innegra fabric. It is flexible and when used with cf fabric you can have a strong very lightweight part that will absorb shock when your riding the jetski. The innegra I tested today produced a very flexible and lightweight part.