filling and redrilling log impeller hole: fast or slow hardener?

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MarkGrubb

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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.
 
Yes, you are worrying lol ! /forums/images/graemlins/wink.gif
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

/forums/images/graemlins/wink.gif
 
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.
 
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
 
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?
 
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......
 
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.
 
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.
 
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.
 
Hiya,

My post on measuring wasn't to do with mixing the epoxy and hardner. I'm familar with that.

It was related to the one-to-one ratio for cloth and epoxy suggested by oldsaltoz. Be useful to know for this job, but more generally for lay up work when I use cloth and epoxy.

As I usually measure epoxy by volume, but cloth is done by weight, I just wanted to clarify that 50ml of epoxy would equate to 50g of weight. Then I know to use 50ml of epoxy when I'm using 50g of cloth, for example.

As we were on the subject i just thought I'd ask the question.

In terms of this job, I've already beveled out the hole from the inside, so backfilling will be difficult and there may be voids left. But thanks for the advice and I'll bare it in mind for future jobs.

I'll probably go with captainslarty's advise and use epoxy thickened with glass fibres, but use chopped up cloth instead of CSM, as I've also heard the about the binders issue, and Oldsaltoz commented on the voids.

I just wanted to check that i got the one-to-one cloth to epoxy ratio correct. So if I chop up 1mx5cm strip of cloth, then I think it will need 25ml of epoxy.

Thanks for your suggestions.

Mark.
 
OK, you will have to do it now. However, you are only filling a hole, it is not structural. Suggest you attach your mould to the outside - piece of formica or ply with a release agent and just put in one layer of cloth and wet out with resin. Ratio is not critical, just wet out with a brush until there are no white spots showing in the cloth. Don't break up the cloth. This when it is cured will give you a good base to build up the thickness from the inside. Do max 2 layers at a time as there is a danger of an exothermic reaction if you put in too much in one go in such a small area. The last layer inside should overlap the surrounding hull by 25mm or so or at least the area of your internal backing pad behind the nut. When you finish and take your outside mould off you may find voids in the bit that is going to remain when you drill your hole and these can be made good with filler. This will probably be the strongest bit of your hull!

Good luck
 
G'day Mark,

If using cloth not CSM then getting the ratio right is simple, when laying up, wet out thoroughly and after a couple of layers roll with a consolidating roller; it's a small diameter grooved roller that will remove any trapped air, as well as leave just enough resin, but you need to cover the whole area working in all directions and finish on the outer edges. the resin that is rolled out can be used in the next layers. The last layer should be fully rolled then the excess resin evenly spread over the work to ensure no end strands are protruding, I use a lightweight roving to finish.

Outside and below the waterline you need to apply at least 4 coats of resin, wet on tacky to avoid sanding between coats.

Hope this helps.

Avagoodweekend......
 
I would start with a flat cardboard piece taped over the outside of the hull. I would glue perhaps with super glue a cardboard tube into the middle of the card and central to your hole.( the tube is slightly smaller than your final hole size) A coating of wax over the cardboard may help to release/clean up later.
Cut circles of woven glass in the usual manner but with a hole in the middle to go over the tube. You may have trouble getting the rings of glass to sit right down into your chamfered edge. You could fill some of the chamfer with strands of glass teased out of cloth and layed around the perimeter of the inside tube and into the chamfer area. Preferably don't rely just on circumferential glass but rather have some strands running radially as well.
When the inside is nearly hard you can tear off the outside flat cardboard, hopefully leaving the tube in place then lay up in a similar manner the outside layers.
If the tube falls out or is just too fiddly then just glass all over the hole. The tube will however reduce the amount of resin you waste and make the drilling of the new hole hardly more than cleaning out the hole left by the tube. good luck olewill
 
Wouldn't it be much simpler and more effective to epoxy the through-hull into the hull - especially as you say it's flange is wider than the existing hole. Just push it through and hold it central with sticky tape while you put thickened epoxy into the 5mm space between it and the hull. I'm assuming that the log can be taken out of the through-hull fitting so making the through-hull reasonably permanent should be OK. Things glued in with epoxy can be removed by heating them to soften the epoxy.

If, for some reason that was not appropriate I would be inclined to make a 5mm wide ring to fill up the space. It could be made from ply using two different sized hole saws - do the outer cut first to retain the pilot hole. It would then be easy to epoxy the ring into the hole.
 
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