Carbon epoxy tender

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#1

Hi to all,

Nowadays i start a new project about a 2,40m rib tender.
I have made the mold (hull & deck) and my first thought is to build it from epoxy and carbon materials than polyester and csm fibres.

In the past, the tender were set up from :

  1. 1 layer 450 csm matt
  2. 1 layer woven 600
  3. 1 layer 450 csm matt
  4. Simply polyester resin

This time my thought is the epoxy version of it.

My questions are :

  1. How many layers and what carbon fibre is better to use for this situation ?
  2. It’s better to put between the layers core material (like soric xf or coremat) or not.

Of course i know that an exact answer need naval architect but i want to know for the beginning your eperience.

Thanks for your time

George

#2

Soric is usually used with infusion process and this would be good if you plan on infusion.

Coremat is heavy, it’s like a sponge and absorbs resin until it is full so this kind of defeats the purpose of lightweight and expensive carbon.

Another option is to use a foam core and make it a sandwich. This then also reduces the amount of carbon you may need but it also adds labor compared to your original solid laminate.

You might also consider using a vinyl ester resin? this way you get near equivalent performance of epoxy resin and you can still make it with gel coats.

Possibly

Gelcoat
225csm
200g carbon cloth
foam or soric core
200g carbon cloth

Reasonably light and a gel coat finish with no further finishing needed.

You could also consider the 3D PET core (only comes as 100kg density) with the infusion process. Not quite as light or rigid as 80kg foam core but it works really well with infusion process and conforms to compound shapes easier than foam.

#3

Thanks Fasta for the reply,

Vinyl is a good choice but epoxy i thing it’s better.

You have right about corematt, absord a lot of resin.

With epoxy will be very expensive for the final customer but with the vinyl we almost have the same properties as epoxy with less money.

What thickness of 3d core you suggest for this tender ?

your thoughts ?

By the way…nice work Fasta

Regards

George

#4

I think maybe about 6mm-8mm 3D core should be ok.

With epoxy the bigger cost than the resin is the labour it will take to finish it with paint. And then for all that extra work you have hull that is not as durable or resistant to damage (scratches) as gel coat would be.

Gelcoat, shiny from the mould is the way to go.

#5

Thanks again fastacraft

I think that 2mm 3d core is ok. It’s a 2,00m tender. It does not need thickness more than 4-5mm.

Also somebody told me that i can use vinyl gel coat if i put epoxy resin and i can avoid painting at the end. Have right ?

Regards

George

#6

Take note that the core is often the lightest part of the laminate and you can gain lots of stiffness with just 1mm or 2mm more for very little extra weight.

I have just built a 2.4m kids sailing dinghy hull that it 6mm 100kg PVC on the hull bottom (3mm PVC sides, bow and transom) since the stiffness is good for the boat and this is also the area where they stand and run across the boat when tacking.

I think the 3D core only comes in 3mm and then 6mm.

#7

You use vacuum infusion in your boats ?

Thanks

#8

I would somewhat disagree with that Fasta… Gelcoat isn’t tougher than a good 2k polyurethane. In fact, the very reason it is used on aircraft like gliders and sailplanes is it is weaker and so will not hide damage to the underlying laminate. If the laminate underneath is damaged, the gelcoat will show it. A good quality polyurethane can be flexible and strong enough to not show any signs of stress, which isn’t ideal on something that is so heavily regulated.

That said, it is actually a big issue at the moment for CASA, as there is a new push to change the regulations for using gelcoat in the mould. All these aeroplanes that are now 10 or 15 years old are all suffering from crazing, and it is a massive massive job to fix as the gelcoat has to be entirely stripped without damaging the laminate underneath at all. It’s a 60-70 grand job for each aircraft, and there are dozens and dozens of them all over Australia that have badly crazing gelcoat.

I’m all for polyurethane, I don’t think in-mould gelcoats are the way to go at all. It’s a higher expense initially, but it is far more expensive to fix further down the track.

#9

Gel coat is more durable in special cases like boat hulls…the reason is the trailers when go up and down. I have a lot of damages for this in 15 years expirience on yacht painting.
But in the urethane have a lot choices about colours than gel coat.

#10

How many kilos is the 2,4m dinghy fasta ?

#11

What about the corners with foam ? It’s very difficult than 3d core to adjust

#12

Hanaldo, I know that gelcoats are generally brittle and will crack when the laminate is flexed etc but I am talking about general surface durability for long term good looking boats taking the little bumps and knocks from use on and off the water.

I always encourage customers to gel repair and polish an older hull rather than repaint if possible. Once you paint a boat it can look pretty average within just 3-4 years due to chips etc. Especially the decks.

That little dinghy was infused and weighs 22kg. In a hard chine hull like this the foam is cut and fitted to the corners.

I have also built many 3.3m moth class dinghy hulls in pre preg that weigh about 10kg. These were painted since it is lighter than gelcoat and gelcoats are generally also incompatible with pre preg process.

#13

The pre preg boats it’s better than infusion ? More durable or have problems with flexibility ? What core materials use in this situation ?

Thanks

#14

The pre preg is ultimate for weight saving but these hulls are just 1 x 200g carbon each side of 4mm 100kg PVC foam. Lots of work to hand finish and paint. Just for racing and must be cared for. Very stiff overall but the foam core can simply dent if it is hit with elbows, knees etc.

You need an oven too of course.

#15

Thanks fastacraft for infos

#16

An infused Hull with 3D Core can be as light as a prepreg hull with foam core.
The 3D Core comes in 3/5/10/15/17/20/25mm as standard thickness in several foams. If you want to save weight you can buy the 3D Core in Airex T10/110 or less, their standard material is a 100kg PET foam wich changed not long ago and takes up less resin.
It is easy to place except hard edges but there it is not needed because of geometric stiffness.
For such a boat 1 layer 200, 5mm core and 1 layer 200 would be enough, but then you can damage it when hitting something, so you top laminate should be shock resistant enough. You can vary your plys depending on the area.
Also the core, you can use 5mm in the bottom and 3mm at the sides and deck for example.
Also the 100kg 3D Core is similar to a Airex C70-130. Because of the resin honeycombs it has much better properties then other foam cores.

#17

Thanks DDCompound

#18

Whats your opinion between 3D core & Soric XF ?

Thanks

#19

Soric is easy to place in tight corners and radius and is little drapable. But Soric has a lot of resin uptake and will give a heavy laminate.
3D Core is a foam core that creates stiffness by the resin honeycomb but the foam does not suck resin. It is the much lighter solution and also perfect to infuse. We use the 3D Core wherever we can, in my oppinion one of the best corematerials available.