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Carbon fibre over balsa hull


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Following on from previous post regarding glassing balsa plank on frame, I was wondering if it's possible to apply carbon fibre twill over the hull instead of fibre glass, or over previously applied fibre glass? I would like to know if this would add to much weight.

I have seen Afew people apply carbon fibre over other items and I do like the effect plus strength, has anyone tried this out before?

Look forward to you replies and thoughts



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Of course you can. We do not need to tell you that you cannot use Carbon Fibre on an IOM hull

You can use just about anything, even an old cotton bed sheet. Anything that is wetted by the resin you have chosen.

But before you do this you really must identify what it is you are trying to achieve. .

A Balsawood hull is a very strong structure over all but lacks the ability to survive impact, particularly side impact and any point loading.

The purpose of the composite skin is to overcome this and it works by spreading the impact load over a larger area.

This impact strength is mostly due to the resin not the fibres.

Carbon fibre reinforcement will not actually increase impact strength noticeably above say glass fibre since the strength of this is not in that direction, the strength is in the plane of the skin unless a complex 3D cloth weaves is used.- which will increase the weight of the boat dramatically.

What the cotton, fibre glass or carbon fibre cloth does is to hold the resin into a controllable thickness and the hardness / strength property of the resin does the rest. There are a myriad of advanced resins available today intended for a number of purposes, some have surface hardness of around 90 Rockwell. – Nearly equal to some steel.

Over the years I have played with many fabrics – paisley pattern silk scarfs, floral pattern cotton fabrics from dress shops. You can get a good finish and they look different

So what is your objective – a pseudo Carbon fibre look – a 95 g plain fabrics that and not add too much weight.

You can cheat and use Black pigment in the resin and 25g or 50g Glass and no one will tell the difference.

But in all cases go easy on the resin - the Balsa Hull is already heavy. You can of course break the balsa away if you first wax the boat - but this is a horrid job.

If you do not wax the boat the resin will penetrate into the fibres of the wood and this will make it harder in the same way. Use a low viscosity resin like Z-epoxy Finish resin for this. It sands easily. This is always a good starting point because the better the base surface finish - the easier it is to get a good overall finish without massive weight pickup.

If the boat has already been glassed sand it back heavily using a block and finish with 120G to get an abraded surface for the new skin to key onto.

But what ever you do you are putting weight onto the boat and this you do not need in any class of boat

But what ever you do buy a mini scale say 50 or 100g ( 0.1g divisions )- cost about £5.00 to £10.00, I call it a Drug Dealers Scale and weight out the resin and hardener.


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Hi Dave

Thank you firstly for your in depth account found it very informative.

As yet, the hull is just bear balsa, I'm still going for the carbon fibre route, and from what I have gained from your article, I shall firstly cover the balsa hull with a layer of epoxy, to seal the balsa, followed by sanding down, then apply a layer of carbon twill, and as little coats as possible of resin to get to a finish.

I think I am right in saying applying a thin layer of glass fibre on bear balsa firstly is a waste of time and added weight.

Many thanks again



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I assume you are using an Epoxy resin not a Ester resin. These are two totally different families, the non-smelly and the smelly type.

Don't use the smelly type i.e. Ester resin.

Three good reasons:-

a) Your wife will NOT receive a custodial senesce for murdering you for stinking the house out. At best she will be cautioned.

b) Cloths, glass, and Carbon are coated with a binding agent. This binding agent is dissolved / wetted by the resin. But the two different resins are completely different:-

Epoxy - a miscible in water

Ester - miscible in Xylene - fundamentally a branched Aromatic

c) You will not find a suitable cloth carbon or glass for an Ester resin

Ok but enough with work -

The bottom line is that you need to use the correct cloth for the resin

Thinning Epoxy Resin

Epoxy resins contain coagulants to vary the viscosity for different applications. They can be diluted ( thinned ) but this is not a good idea particularly for the home builder. Ye Ye I have heard all about using XYZ and ABC but ....

It is far better to use the correct viscosity resin. The product I indicated i.e. Z-epoxy Finish Resin is ideal and not expensive about £12.00 for 12 oz which should be more than enough for 3 IOM hulls

It is easy to use and sands easily. Apply it liberally to the raw balsa and I mean liberally. Put it on and rub it in with your fingers or the edge of an expired credit card. The idea is not to get a finish but to bind / seal the wood, get a consistent base to block sand. Balsa tend to be inconsistent and the glued areas are much harder even if you have used an aliphatic glue... you probably used super glue which makes this process still more essential.

Temperature is a key point. Never work below about 25C. The resin will not wet out properly. And avoid working above about 30 C , the pot life of the resin is very short.

You 600 - 800 grade water paper with a dash of soap and water when blocking. The soap, use Fairy Liquid, stops the water paper blocking and use a orbital motion , not up and down. I am lazy and use an mini orbital / finishing sander but I still block out first by hand.

You clearly can use other soaps, Tesco, Sainsbury green , blue what ever but should not use one that contains Silicate of Soda. ( washing powder ) or Shampoo

But AGAIN I must caution



You will pick up a lot of weight using a 3D cloth. I think it starts at 200g / m2 dry and wetting it will take the weight up still further

The better and more methodical you work the better the finish will be and the LIGHTER the result

Personally I think you are being a little silly.

Two layers of 50g glass wetted with black pigmented resin. .Block down and paint it BLUE , not orange, there are far too many orange boats

Go sailing. this is not a concours d'elegance car show.

Other will admire your boat when it is leading a race and you cannot do that with an overweight boat and you cannot race in IOM class with a carbon fibre hull.

You can buy a plastic shrink covering that will provide a pseudo carbon fibre look. It work out to the same weight as 50 microns of paint

Don't paint the inside of the hull with resin - use sanding sealer FGS

Ok you have it all now. get to work


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I can see 'first build euphoria' setting in here. I felt much the same when I built my 10r. Its got 8 coats of varnish on it and a raised foredeck. Beautiful but definitely overkill. Dave has given you all the tips so let me consolidate a bit foryou. Carbon is prohibited in the hull of the IOM (read the rules. All of the rules. It saves a lot of time later) and excellent material as it is the impact resistance of one carbon sheathing layer is minimal to say the least. Glass is tougher. Think how you will feel when, on your first sail, you get T boned and come back with an interesting shaped letterbox in the side or worse, a trail of bubbles.One layer should be enough given Dave's preparation instruction and it weighs less. Regarding paint, I prefer 2 pack because when you want to clean those nasty bits of glue that remain where the deck patch was, the paint stays put as well as resisting the paint ripping off when you pull off the patches. Rattle can paint is a quick fix and gives a good finish that you can polish. Just dont take the solvent to remove the afformentioned nasty glue as it will bring the paint off too. Cellulose thniners or acetone will do a good job andthe paint will just wipe of

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