Epoxy laminating techniques

[C08]

In a couple of weeks I am going to fit a bow thruster. I have all the supplies-solvent free epoxy, powder bound CSM, woven cloth etc and I am comfortable with epoxy/laminating procedures having done structural repairs and made new parts on a few boats over 25 years and I am clear how I plan to do this so this is not a query "how to do" but rather how would you do this installation.
1 in order to achieve the optimum bond of the 1st layer to the tube and hull what would you use? Tissue, CSM or thin cloth? Assume correct surface preparation in all cases.
2 As the laminating around the tube is tight and circular, CSM would be easiest perhaps with some layers of cloth. How would you do this all CSM, all cloth or a mixture?
3 In building up the hull tube join would you start small and increase the layer width or start wide and progressively decrease. Assume a little fillet as a starter.
Thanks-I know there are some real experts here and I am interested in their views.

 

[Tammany]

Never done this but this may help.

http://www.westsystem.com/ss/installing-a-bow-thruster/

 

[William_H]

I imagine the biggest problem area will be corner between the tube and the hull. As you say use a fillet of epoxy with filler first. You then want the cloth that you choose to be as flexible as possible to fit in with no air bubbles. I might be inclined to suggest buying "twill weave cloth" or cutting ordinary glass cloth diagonally (on the bias I think it is called) so strands are at 45 degrees to the cut. Make a strip or strips to initially wrap around over the fillet in the circumference of the mating joint.
Several layers wrapped around tightly should hug the fillet. The cut on the bias makes the bend easier. I would go small pieces first then expanding in size. (width) Once you have bulked out the joint area so the bend of cloth is not so sharp you can consider CSM. I am not sure CSM will bend well in the first stages of filling the bend as CSM is just strands about 3cms long and orientated in all directions so many strands will resist the sharp bending. good luck olewill

 

[Len Ingalls]

A pro installation: https://www.youtube.com/watch?v=cl0_T-_Drmw
There are several other videos including DIY info.
https://www.youtube.com/watch?v=Zcnr5aCcNd4

Getting it horizontal may be the interesting part.

Good luck / Len

 

[macd]

I might be inclined to suggest buying "twill weave cloth" or cutting ordinary glass cloth diagonally (on the bias I think it is called) so strands are at 45 degrees to the cut.

Not sure what you mean by twill weave cloth, olewill, but the best cloth for complicated and compound shapes is stitched bi-axial: very strong and very easy to use compared to anything else. It somewhat mimics your 45 degrees idea, but is much more adaptable to curves and corners.

 

[Javelin]

It depends on a few factors how I approach the laminating.
Often the best location for the tube provides very poor access internally, especially underneath where the tube meets the hull.
In this case if on a heavy layup hull I will chamfer the hull aggressively below the tube and laminate from the outside or on thinner hulls (1/2" or less) laminate a glass cradle for the tube to sit on and bond.
Unless the hull is made using epoxy I generally use polyester and 450g csm and then 600g woven biaxial, bulk out with core mat and top with 250g biaxial and gel
I've heard of some near disasters using epoxy on polyester hulls on boats less than five years old so I won't risk it plus working with polyester is much faster.
Not keen on using cloth for initial layup as it can peel and csm has a better bond.
On sailing hulls I incorporate a scallop aft of the tube instead of an eyebrow as it gives vastly better hydrodynamic performance.
Whilst this is more complicated to do it does result in a much stiffer result which is important as the tube is in the pounding area.

 

[William_H]

Not sure what you mean by twill weave cloth, olewill, but the best cloth for complicated and compound shapes is stitched bi-axial: very strong and very easy to use compared to anything else. It somewhat mimics your 45 degrees idea, but is much more adaptable to curves and corners.

I havn't seen twill weave for a long time. Just remember it was described in training as the best cloth for tight compound curves. If I remember rightly it is a peculiar weave of over one under 3 or something similar. Perhaps superseded by biaxial
or maybe same stuff different name. olewill

 

[Keith-i]

I'm not sure powder bound CSM wets out properly in epoxy.

 

[Javelin]

You can get csm specifically designed for use with epoxy, it uses a different binder as opposed to the one that dissolves in styrene with polyester resin.
Personally I don't like laminating with epoxy on a polyester hull.
More than happy to use it to bond, fabricate and stiffen however.

 

[Keith-i]

Not wanting to thread drift, but what is the concern over using epoxy with polyester hulls? Can you provide any further detail?

 

[Quandary]

As far as I know epoxy binds well to polyester but not the reverse, so if you chose to use epoxy to repair polyester then you have to stick with that medium in subsequent repairs. Myself, I have had no compunction about repairing polyester skinned rudders etc with epoxy, I have found that it gives a more secure and stronger bond. Polyester resins seem to be a bit more tolerant of low temperatures but you can buy special epoxy products for low temperature use.
The glass mat used with epoxy resins is 'powder bound'.
Google 'epoxycraft' and join, it is a good free source of information on techniques and projects though the technical details are sometimes separate from the ideas.

 

[Javelin]

Epoxy will not bond well to polyester until the styrene has vented off.
Usually this takes a few weeks.
However it can take much longer with some lay ups especially on sprayed lay ups.
That said it should be fine on a hull that's years old.

I pointed about above that it's my personal opinion and it's based on seeing a few failed repairs in the past where epoxy was used to fill in old skin fittings holes and there was obvious delamination, not dangerous but certainly could have developed that way.
Also a couple of epoxy glass repairs on rib hulls which were starting to peel off.

Now these could all be due to poor prep work during the repair or contamination or in the case of the rib repairs the repair was much stiffer than the surrounding glass and the differing flex could have been the issue.

The other possibility is the styrene issue even on an older boat.
Once you grind off the gel coat, on some lay ups you can smell the styrene in the exposed laminate.
It's well known that styrene adversely effects expoxy performance whilst actually helping polyester.

So my thoughts on the subject are my own based on my experience without any great scientific backing other than anecdotal and off the record conversations.

 

[C08]

Thanks for all the replies particularly Javelin taking the time to answer amateur's queries. I was not aware of the styrene issue with epoxy, this should not be a problem for me with a 35 year old hull but I will look out for a styrene smell (what does that smell like) when grinding the gelcoat. I also like the idea of making a cradle under the tube if access undernieth is tight. I think my hull is only about 12mm and I would have to re-position a bulkhead to have a recess at the tube rear so I think it will be an "eyebrow" at the front edge. On an old slow overloaded cat it probably makes little difference anyway.
Just a week to go fingers crossed for the hot spell predicted to carry on for a while- boat not been out for about 8 years and been on drying moorings so it will be be good to see the bottom of the keels (well no keels really just the hull bottoms) and how they are wearing so maybe more epoxy slapping!

 

[C08]

In Chichester Harbour recently we saw some foiling dinghys.. They were not close but they were traveling so fast that they were only in vision for a short time so we did not get a good look at them. The speed was amazing and it was the first time I had seen a foiling boat of any sort. Is there a class that races there?

 

[Quandary]

I'm not sure powder bound CSM wets out properly in epoxy.

It does for me, I started to use it as it is specifically intended for that purpose and is what most purveyors recommend. Mind you the 'binding' is very light but no trouble wetting it out.

 

[guardian]

I dont understand why you would use CSM other than to 'bulk-out' a laminate schedule seeing as it has no strength and drinks loads of resin, stick with 450 g bi-ax cloth though, also forget about that Wests rubbish and go to Reactive resins and get yourself a gallon of Syntac non-blushing resin and any one of their Synamin hardeners depending on what conditions you're working in and let us know how you get on.

Also nearly forgot, for filleting the interior intersection of your bow thruster tube to the hull get yourself a small pack of cabosil to mix in the epoxy with to a good stout consistency, top tip icing bags - fill one up with the thickened mix and pipe around the tube and with a tongue depressor, waxing stick, large lollipop stick go back round and there you have a nice even radius all the way around the tube for the cloth to take to.

Jobs a gooden!

 

[C08]

I am going to use Professional Epoxy Coatings sold by Fynne Boats which is solvent free epoxy. I have used it a few times and am quite impressed with it. Also it is 2:1 so easier to get the mix right without recourse to pumps etc. A bit slower to initial cure than West or SP but that is not always a drawback.
Thanks for the tip about an icing bag I will have to sneak into the kitchen at the dead of night

 

[guardian]

Sounds like a plan C08, post some pics when you're done, also reference the icing bags i meant to say get disposable ones, your missus will thank you in the long run!:encouragement:

 

[Tammany]

Was always under the impression that epoxy was the only resin you can use on an older GRP boat for repairs as polyester doesn't bond to old GRP?