Carbon fibre on existing lay

Gordonmc

Gordonmc

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Ok, I have a wooden boat and know hee-haw about the black art of polyester/epoxy. But I am helping a friend whose boat has suffered depression of the (deck) mast step.
The boat has a cored two-skin coachroof. There's a compression post from the coachroof to keel. The tabernacle bolts go through both skins.
Its suspected the core has suffered from water ingress allowing the outer skin, plus tabernacle, to drop. The plan is to cut enough of the outer skin off to reveal all the rotten core, dig it out and replace with a mix of ply and West System + micro baloons.
My question is: can we reinforce the upper skin by using carbon fibre rod glassed to the underside before replacing it and making good.
Or would that be a waste of time.

Any thoughts on the proposed solution welcome.
 
G'day Gordon,

I doubt the core has rotted, the builder would, I suspect, have installed a marine or construction ply pad under the tabernacle, so expect to find soft ply.

You can preserve the deck finish by doing this repair from inside, cutting away the section after removing the compression post; I'm assuming the mast will be off the boat.

I would adding any carbon fibre for two reasons, to do any good it would have to extend outside the the area effected, this may then produce a hard spot and lead to stress cracking due to the lack of flexibility.

The good news is that as this area is under compression you can use standard resins and mat, reducing costs.

A plunge router makes short work of removing the section from inside with the advantage that it can be set to cut only the inside skin, a few stabs will show the extent of the timber pad, then run around it and lever it out.

An Allen Key with the short end ground to a chisel shape and placed in a drill will clean the foam / balsa from the edge of the exposed area ready for refilling.

When you replace the ply, it will help if you drill 1/4 inch holes about an inch apart and then lay a generous layer of resin and Micro-Fibres (not Micro-Balloons) on top and push it so that the trapped air and fibres can be squeezed thru the drilled holes, pop a sheet of plastic on top of the compression post with a small packer or two and slide it under the play till it has cured and it should be neat fit after laying the new glass on the underside.

I hope this helps.

Avagoodweekend......
 
It will be a sod of a job repairing this from underneath. Despite loading the resin up with colloidal sillica and micro fibers, gravity will always win. I'd cut away the deck with a dremel or something similar and build up the new layers that way.

Might be worth checking out the bottom of the compression post to ensure that the rest of the boat's structure is ok.
 
I did a similar repair on Avocet a few yers ago. I did it from underneath but it was a pretty horrible job and I came home looking like a Homepride flour grader for a few days! It's true that I saved the outer skin but as this had developed a few stress cracks anyway (once the mast step started to sink), I still had to do a few minor repairs on the outside anyway. In retrospect, I think that if I was doing the job again, I'd probably do it from the outside! That said, Avocet's interior is a bit different. There is no compression strut and the mast rests on the main bulkhead so there are quite a few stiffeners in the locality which made it very messy indeed!
 
What are you doing posting here Ian (Avocet), you don't have time for this. Get back out there and on that torture board or you will never her back in the water.

(Falls off chair laughing)

Avagoodweekend......
 
Yes carbon rods would be a waste of effort.

You need to determine if it is the core that has colapsed. As suggested that is unlikely as it should be solid wood under the mast.

If it is the core that has colapsed you might consider packing or extewnding the compression post from underneath. In other words leave the core compressed. It can't colapse any more and eventually you will have outer and inner skin pressing on one another which should be very strong in compression.

If you do decide to replace the core then you could try a few small holes and pump in from a syringe straight resin. It will be quite strong in compression when hard. Polyester would be OK.
A sdescribed you could drill a hole say 1/4 inch then put an allen key in to rotate around to clean out the core to eventually make a pillar about 1.5 inches diameter of solid resin which if repeated several times will also be strong in compression.
To cut out the top deck will mean disfiguring the surface which espedcially if it is antiskid roughened will be inmpossible to restore. good luck olewill
 
How about replacing the rotten area with a plate of steel or ss, or maybe even alu? I guess you want the material to match the existing tabernacle to avoid electrolytic issues. with the mast off, take out the compression post, cut a hole in the offending area in the head lining, measure and cut/have cut an appropriate plate, drill holes to match mast foot, bolt the lot back together... Feasability depends on the thickness of the gap I suppose, a 15mm lump of SS the size of a mast foot aint gonna come cheap!
 
With respect,I don't like it.
Plywood is easy to work and has relatively soft edges,whereas the aggro of sourcing and cutting a piece of s/steel...then presumably it will have to be cambered slightly and still bedded in epoxy-not fibreglass now,then once all is done the mast step will have to be resecured through the steel plate.Imho thats just creating lots of work that requires more expensive tools and materials..I would also tackle the job from within unless the guy doing the work is really good(in which case probably wouldnt be asking advice here).It is not that easy to neatly replicate or replace the outer deck skin fairly and in such a way that you aren't devaluing the boat to a degree(imo)
Take lots of piccies along the repair route.
 
If it's the kind of arangement I'm thinking of, it will be locally double-skinned just under the mast step and the space between the skins will have been filled with some sort of wood. If that's the case and there is visible compression of the top skin, I'd be amazed if there were no stress cracks in the top skin. If that's the case, you'll have to repair them anyway so the cosmetic appearance of your coachroof is going to change whether you like it or not! That being the case, (unless you really like having a boat (and eyes) full of fibreglass dust and getting resin in your hair), I'd still vote for going in from the top!

I'd also be a bit wary of filling the void with polyester resin as there could well be quite a volume in there when it is full and it is likely to generate a great deal of heat! You could replace whatever was in there with some more of the same - it lasted for quite a while anyway, or you could just do as I did and replace it with solid fibreglass. It will be a lot lighter than a piece of stainless and you'll have to use fibreglass for the rest of the repair anyway!

P.S.

OldSaltOZ!!! I've been doing my torture board duty all today and I'm absolutely knackered. In fact, I can barely type now, my arms are so stiff!

So there!
 
G'day Again Gordon,

No doubt you picked up on the fact that I missed the word NOT in my earlier posting, it should read:

"I would NOT be adding any carbon fibre for two reasons"

As this was really the only question you asked I hope it helped, however we now seem to be discussing the pros and cons of doing the repair from the topsides or below deck. You have indicated that you plan to work from above in your posting and at the end of the day that's your choice.

This is not an uncommon failure, I have done the job twice myself though never on any boat I owned, but rather for clients. The cause was as you pointed out in your post, water ingress, and almost always via the tabernacle bolt holes.

I only ever use marine ply because it's easy to work with, only requires an off cut, and can be made to any thickness without too much fuss.

However, there Four very important steps that I follow to reduce the chance of future failures.

First the ply is cut and shaped with well rounded corners (at least a 3 inch radius on the corners) and placed into position dry to ensure it's going to fit.

Next, the holes are marked while in position and drilled out at least 20 mm over size and more 6 mm holes are drilled to a grid pattern at 25 mm intervals; these smaller holes will allow the resin and Micro fibres to squeeze thru when placing the ply ensuring no air voids are trapped. This applies to working from above or below.

Then the ply is given a good coating of epoxy by mixing a small batch and adding Methylated Spirits at 40% by volume to thin the resin for better penetration, then after curing give it another couple of coats to seal it properly on the outside.

The last step is to fill the oversized holes with epoxy and Micro-Fibres do not use Micro-Balloons, they have little structural strength and are a soft filler only.

When fitting the tabernacle add a ring of non acid sealant around each bolt hole before you pull them down.

I hope this helps.

Avagoodweekend......
 
I would remove the mast

Turn the boat upside down. Perfect the exterior finish, polish it with GT wax. Then.....

Laminate 1/4 " thick Glass fibre in polyester resin all over the exterior of the hull, laminate in suppporting pads, channels etc to maintain the stiffness of the mould. Remove from boat.

Turn boat upside down, Make mould of topside in similar fashion, Take topsides of boat and remove internal furniture - save for making moulds,

Make mould of interior of boat using same methods, Lay sacrificial layer of aramid fibres at -45 degrees and +45 degrees to the longitudinal axis, lay on with the epoxy resin, and then use high modulous Carbon fibre to lay -5 degrees, +5 degrees , - 45 degrees, +45 degrees, -5 degrees, plus 5 degrees and a single layer of fine woven glass matting to act as the wear surface inside the boat. Cure off, lay appropriate thickness nomex core, which has had its back broken by rolling, then lay on the similar layer you have made from the outside mould epoxy the two layers together under vacuum. Finish off and then insert the parts made from the furniture moulds.

I God had intended men to keep using wood for boats he would never had permitted scientists to exist.

All IMHO of course! /forums/images/graemlins/cool.gif
 
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