AvastMark
regular
Reged: 28/11/2006
Posts: 304
Loc: Nottingham
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Hi all,
I fiited a new log to my boat, and the diameter of the new skin fitting is slightly less than the old. So the original hole is to to large leaving a 5mm gap all the way round the fitting.
The flange on the outside of the fitting is wide enough to cover this gap, but I'd prefer it to be a nice snug fit, so my plan is to fill the whole and then redrill with a correctly size hole cutter.
I used a file to bevel the edge of the hole to roughly 60 degrees and plan to fill it with SP Epoxy thickened with microfibres. Most of this will go to waste when I redrill, but never mind.
Any comments on the suitablitly of this technique and materials are most welcome.
But my question is, should I used slow hardening epoxy, or will the fast stuff be OK. I have fast on the boat, but will have to buy slow hardener especially for the job. The hull is about 10-15mm thick, so I'll be applying epoxy to that depth.
I'm guessing that the fast epoxy may generate heat while curing and get too hot, which can affect its stength. Is this correct and will it be a problem for the job I'm describing? I can build up the filler in layers if necessary, if so how what length of time should I leave between applying each layer and what would be a sensible thickness. Say 3 x 5mm layers with 2-hours between each, for example.
Or am I being to much of a worrier. It's only a little job. Can I just slap the stuff on?
Comments and advice much appreciated.
Thanks,
Mark.
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Captainslarty
regular
Reged: 12/08/2007
Posts: 2012
Loc: Currently La Coruna Spain
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Yes, you are worrying lol ! 
Slap it on, but consider the thickening agent. Microfibres are ok, but a better solution is to use an offcut of chopped strand mat.. cut with scissors to around 1/4 inch length or less to make a small pile of tiny strands.. mix with the epoxy and use that. Better than microfibres for its use.
Use a teak or similar wood backing plate shaped to the hull curvature and bond that in with the same mix prior to drilling.. coat pad with neat epoxy.. (Grind hull inner first with course sanding disc)
Luvverly job..
ANother tip is to get a piece of thick card, cover with clingfilm, tape to the ouside of the hull over the hole to make sure the outside is neat.. when you have drilled the new hole through the epoxy and wood pad, give it a quick coat of unthickened epoxy to seal it - seal the transponder with polyurathane adhesive sealant..
Happy days.l
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PM me for info re SSB's etc. Bought, sold, repaired, fitted and optimised.
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AvastMark
regular
Reged: 28/11/2006
Posts: 304
Loc: Nottingham
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Thanks Captainslarty. Thought you'd pop up with some advise. Is chopped strand mat OK with epoxy as a filling agent? I was told that for general lay up work it shouldn't be used because the epoxy doesn't disolve the substance (styrene?) that binds the fibres together. But don't know if this problem applies if its simply used as a filler.
I have some woven roving fibre glass tape stuff. I can chop that up. I also have some chopped strand mat all chopped up, so can equally use that, but wasn't going to because of the styrene issue.
Cheers,
Mark.
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yoda
regular
Reged: 12/12/2001
Posts: 793
Loc: Devon
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Use fast hardener. I would clcean and champher the inside of the hole, tape the outside with duck tape and then use 5 or 6 layers of cloth on the inside of the hull. Did the same for one of my hull fittings and you can have confidence in the final strength of the job. Took me about 2 hours in total on a good warm day. I used polyester resin but epoxy is stronger and more expensive.
Yoda
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Tranona
regular
Reged: 10/11/2007
Posts: 1377
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Use glass cloth not mat as the binder in mat reacts badly with Epoxy.
Although, to be honest if you put a new backing pad bonded to the hull, internally and drilled to the right size (just clearance) you could back fill the gap in the hull with epoxy filler, or if the new outer flange still has plenty of mating surface to the hull just bed the whole lot in Sikaflex. Why make extra work for yourself?
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Captainslarty
regular
Reged: 12/08/2007
Posts: 2012
Loc: Currently La Coruna Spain
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Hi Tran, in which way does it 'react badly' ?
Have used this for donkeys, with no worries.. it simply disolves the binder >> ? works superbly.
Joe
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PM me for info re SSB's etc. Bought, sold, repaired, fitted and optimised.
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oldsaltoz
regular
Reged: 04/07/2001
Posts: 2628
Loc: Australia, East coast.
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G'day Mark,
The hole should be ground back on both sides to form a capstan shape, this will ensure it will fall out if stressed.
Use cloth designed for epoxy, chopped strand mat and epoxy lay up is a no no, the CSM has too many voids and you end up with too much resin and not enough glass, making the whole repair weaker.
CSM and poly resins use a 3 to one ratio, 3parts resin to one part cloth by weight.
Epoxy resin and cloth uses a ratio of one to one.
Micro-fibres and epoxy make a very strong fillet or glue, and with a gap of only 5 mm to fill they should be fine.
Though I would prefer to use epoxy, fast cure and cloth.
Hope this helps.
Avagoodweekend......
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Growing old is unavoidable. However, growing up is still optional.
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AvastMark
regular
Reged: 28/11/2006
Posts: 304
Loc: Nottingham
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Hi all,
Thanks for the feedback.
Further question.
I usually measure the epoxy by volume not weight. So I pour, say 50ml into a mixing pot then add the correct amount of hardner. What is the density of epoxy? Can I assume 50ml equates to 50grams? I'm not looking for exact science, but I want to be sure its roughly right.
The weight for cloth I can do, as its normally given per square meter right? so 300g CSM, or cloth, would be one square meter weights 300grams, half a square meter is 150grams etc.
So...if I chop up a 1m strip of 5cm wide cloth (I have some cloth tape on the boat) that will be one twentieth of its weight, which I'm not sure of without the packet in front of me so lets assume 450g which sounds familiar. One twentieth of 450 is 22.5g, say 25g, which is 25ml of epoxy?
So 1mx5cm 450g fibreglass cloth should need 25ml of epoxy. Does that sound sensible? I can make as many batches as I need to fill the hole.
In the past I've just mixed it up and slapped it on, but I'd like to start working a little more accurately, especially as to much or to little can weaken the job.
Thanks,
Mark.
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Tranona
regular
Reged: 10/11/2007
Posts: 1377
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To be honest, I don't know, only repeating what my local epoxy manufacturer/supplier says, and I have seen it in the press as well. I have always had good results with cloth.
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Tranona
regular
Reged: 10/11/2007
Posts: 1377
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Mark
You seem to be making a big meal of this. Follow mixing instructions on your pack. Manufacturers differ. I use both West and Blue Gee. West 105 is 5 resin to one hardener by either weight or volume, Blue Gee A is 2 resin to one hardener by volume.
If I were doing this job on my own boat I would make up an 18mm ply pad (you need a pad anyway) about 50mm larger all round than the diameter of the transducer, drill a clearance hole for the transducer, coat the whole lot in epoxy and bond with epoxy to the inside of the hull. You have already said the outer flange is larger than the existing hole and if you are worried about the sealing area, then back fill the hole with epoxy thickened with wood fibres and microballoons flush with the hull but leaving enough room from the transducer to go through. There is no load on the hull, your transducer is located by the pad and you only have to be able to make a watertight seal between the outer flange and the hull using an appropriate mastic.
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