Fibre glass modifications

ongolo

ongolo

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Hi All,

I dont know too much about fiber glass, except the occasional successful repair of my bashed up dinghy.
I am considering converting two or three Russian double ender lifeboats. To add some keel and ballast, I would need to make strong fiber glass additions.

Another guys 50 footer ended up on the rocks last year and ius still being repaired. He got advice from "knowledgeable people" in Cape Town, that one cannot or should not repair/modify fiber glass with resin, but use epoxy. That is new to me, but the "experts" reccon, that unless epoxy is used, the job will last only 5 years before delaminating.

So, what is the verdict? Could I use resin or is there a good reason to use epoxy.

I am a metal man, so I need some help here. Thank you

Regards Ongolo
 
Using epoxy products onto polyester resin will grip very well provided you make sure you bond onto suitably prepared surfaces, ie they are dry and properly keyed. The drawback to using epoxy is firstly it is much more expensive and secondly you need to reprime between each coat.
A common mistake in using polester resin for this sort of work is not building up enough layers in a tapering way such that there is a strong bond at the join. The other common mistake is not fairing in the curves which leaves weak areas in the construction.
 
G'day Ongola,

Bonding poly resin to old poly layup is OK in some situations, however, adding a keel will require a strong and somewhat flexible joint. Poly to poly bonding relies on the mechanical bond only, so preparation must be meticulous, clean, very dry, no contaminants, solid base and so on.

Epoxy on the other hand has a secondary chemical bond and can be 40% stronger and weigh less.

It is also very important that the correct type of glass is used, this means NO CSM (Copped Strand Mat) as it has large voids that when filled with epoxy will the work weaker and very expensive.

Poly resin to CSM ratio is 1 cloth to 3 resin.
Epoxy resin to cloth ratio is one to one, so less resin is required.

Epoxy cloth has many forms, Crows foot or Bi-directional is a good one for this project, for extra strength add a layer of Woven roving's between every 2 or 3 layers of cloth depending on thickness.

The edge of each layer MUST finish inside or outside the last, this ensures a tapered finish and avoids hard lines or spots that can cause structural failure.

Epoxy resin and cloth MUST be well wet out and any excess resin squeezed out to ensure maximum strength and minimum weight; I find threaded rollers are best for this.

When you finish laying up any epoxy below the water line you MUST add at least 4 coats of resin, applying wet on tacky will avoid the need to wash and sand between coats.

If the resin cures between coats you must remove the residue left by the curing process BEFORE you sand it, or you will just rub it into the surface.
Run a hose and fresh water over the area, start at the top and work down, rub with a plastic kitchen scourer (Scotch-brite) till the water no longer forms beads, this is not a big job and takes only minutes.

Sand with a 200 grit to remove the gloss only, wash, wipe dry and clean with Acetone 15 minutes prior to applying more layers.

Clean up tools with white vinegar first this will remove most of the epoxy resin, finish cleaning with Acetone. Wear 2 pairs or Latex gloves when working so when things get a bit sticky you can peel one off.

Epoxy resin (most brands) needs the temperature above 20*C and relative humidity below 73%; this means don't start till around 10AM and the last bit of resin on by 2PM to ensure you don't end up with a milky moisture contamination.

There is some good advice on the "West System" site.

I hope this helps.

Avagoodweekend......
 
Thank you both for the good advice. The keels are not going to be fin keels, so the load is much less. I am considering twin keels for easy beaching, I am not interested about performance.

I am further considering converting these boats into "caravelle" replicas. How would that go down? Possibly with bronze canons. Ok I am nuts, so what. I just like old things.

Any experts on fin keels? On the canon bit I am quite an expert, have published a 512 page book on ballistics.

No letter bombs please.

Thanks

Regards

Ongolo
 
High Ongolo If you are building bilge keels for lifeboats the design will be quite critical. You will probably want to build the keels out of polyester resin for lower cost and ease of layup.
However I would suggest that you set a series of bolts into the keels and rely on bolting them to the f/g hulls. You would do well to consider building in reinforcing structure inside the hull to take the loads of grounding.

Even if you got a decent bond to the skin using epoxy you would need to reinforce the skin of the hull on the outside or inside to carry the loads into the whole boat. If not you could get the original skin cracking around the outside of the keel.
I think polyester would be OK for structural reinforcing provided that the bond to the old f/g is a large area and the new structure is thick enough to not be able to be peeled off. Preparing the old f/g is critical.

If you want balast you might consider casting lead in the keel shape with bolts cast in then covering it with a lot of fibreglass ie at least 5mm thick. good luck (yer mad) olewill
 
PS I reckon you might do better with a dagger board of f/g on wood down through a centre keel box. Make it a deep keel and you will get performance. If you had a cabin or structure above the keel to permit a tackle to raise it you might even consider a few hundred kilo of lead at the bottom of the dagger board. (mine on 21ft is about 1.6 metres long about 550mm chord and 100kg weight. with great performance. You will need under floor balast as well. olewill
 
Why not fabricate twin keels from steel and bolt then on with a support framework inside.

In the 60's in the UK there was a number for ply sail boat designs with steel bilge keels, the Lysander being one of them
 
[ QUOTE ]
Epoxy on the other hand has a secondary chemical bond and can be 40% stronger and weigh less.

[/ QUOTE ]
Could you explain more fully what you mean by this? My understanding has always been that there is NO chemical bond between epoxy and polyester - whether primary or secondary, so I'm assuming that you mean there is only a chemical bond between successive layers of epoxy - as indeed there is between successive layers of polyester laminate.

In other words, there is no chemical advantage in using epoxy but I agree completely that its mechanical properties are far superior.
 
Thank you all, I am learning. Yes I would also like to understand the extra 40% secondary bond of epoxy.

Regards

Ongolo
 
I agree with Rogershaw. It will be a lot easier to make them out of steel and bolt them through the hull than make them from fibreglass. As a general rule the longer your bilge keels are the more your turning circle will suffer....on the other hand if you go for shorter and deeper the weight of the boat is being spread over a shorter distance which is something to be aware of.
I'm not sure what the secondary bonding of epoxy means but I would not be surprised if epoxy joints were 40% stronger than polyester. If you do use polyester don't forget to seal it with an epoxy paint or eventually it will suffer from water ingress. /forums/images/graemlins/ooo.gif
 
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