Glass Selection for Repair

[Jim Herbert]

I will be repairing the bulkhead to hull tabing on my project Islander 36. The chainplates attach to the bulkhead, and the bulkhead pulling free is a common problem with these boats.

I am tempted to use woven roving simply because it looks strong.

All things being equal, would I acheive better strength and adhesion with a lay up of cloth instead?

I will be using West System and I understand that it's not so compatable with the mat reqiured between layers of woven roving.

Being just a fat old guy, I have no idea of the rational behind a lay-up schedule. Any insights would be appreciated.

Also any insights on getting your son to help with the new boat will be rewarded.

Jim Herbert

"Only eat produce from blue states".

[yokebutt]

Jim, What I like to use for tabbing (if it's not weight-critical) is alternating 10oz. cloth and +/- 45 deg. biaxial tapes. The benefit of this is that you can wet the two out together on the bench, (cloth under biax) roll them up, put the rolls in a bucket, and bring it all into the boat to install (cloth facing out).

The biax provides the bulk of the strength, since half of the fibers in the cloth are parallel to the joint, the cloth keeps the wetted biax from disintegrating when you handle it, but still allows enough movement to conform, it helps the biax stay put when you laminate, and it requires a lot less work to make it look good after it's all cured up.

But, before all that, make sure to fill any gap between the bulkhead and hull, (sand everywhere!) then a nice size radius between them with say West 404 (big enough for your hard roller to fit (sand it smooth before laminating)).

Put back at least as much glass as you took out, more if you're uncertain (you did remove all the old tabbing, right?).

As for dealing with your son, have you tried deprivation and violence?

Happy spooging,
Yokebutt.

[Ssor]

The incompatability problem with csm and epoxy has to do with the sizing used in the csm. some types of sizing are completely compatable with epoxy. You could however use vinylester resin and any type of csm-bi-ax combination. On my Islander 30 I chose to put the chainplates outboard and glass over those holes in the deck.

Alan Vaitses in his book "Fiberglass boat repair" recommends refastening tabing with 3M 5200 and screws into the bulkhead.

In Bietzpadlin the tabing didn't let go of the hull just the bulkhead. The leaky deck allowed enough rainwater in to rot the bulkhead. I had to replace the entire bulkhead.

As to a lay up schedule; it is always best to lay csm between woven layers, because the glass to glass contact area with woven fabric to fabric can be very small. If you applied resin to wet but not flood woven roving and laid another piece of the roving on top, then lifted the second piece off, you could see the contact points. laying csm between the two layers of roving and repeating the touch and look you will find the csm will separate and cling to both pieces of cloth.

[yokebutt]

Jim, just use epoxy and don't worry about using mat (csm or chopped strand mat).

[Jim Herbert]

I appreciate all the good advice. I suppose I will cut my own biaxial tapes along the bias of standard glass cloth material, or search the web for a supplier.

I am also intereted in Ssor's relocation of chainplates. The thought has occured to me but I assumed that the penalty in windward performance would be too great. How much does the loss of fors'l sheeting ability around the new outboard shrouds effect pointing / speed on your boat?

[Ssor]

Jim, The move to out board chainplates and shrouds involved about a six inch shift of the shrouds. If you routinely sheet very close to the shrouds now, then you might loose a degree or two going to the weather. On my 30 I used 1 1/2x1/4- 316 stainless steel and bent them to conform to the hull where they would be attached, and made sure that they were laying in proper alignment with the pull of the shrouds. I will look for a picture and post it.

[Ssor]

Posting a picture sure ain't easy.

[Ssor]

Originally Posted by yokebutt

Jim, just use epoxy and don't worry about using mat (csm or chopped strand mat).

Yoke, In another thread you commented about delaminations from appearently minor bumps. Leaving out the csm between the layers of woven will contribute to such failure.

[Herman]

One important thing:

When making the fillet between the hull and the bulkhead (the radiused joint between the two, with thickened epoxy) please be sure to clean up the area where the cloth or whatever will lie down, either by wiping it clean, or by sanding really good after cure. Worst thing for a good bond is a layer of resin in between layers, with a low density filler in it.

And the other thing: most repais outlive the original construction. They are usually done with too much material. So do not worry too much.

Is there a local shop that can provide you with biaxial material? The stiching in the biax will keep it together when handling. Here in Holland, as a supplier, we cut it as a service for our customers. They really like that (saves them a lot of cutting)

[yokebutt]

Ssor, Yes it's an apparent contradiction, but since Jim had already stated that he would use epoxy, and since the main reason for using CSM is to make up for the poor bonding quality of polyester. (secondary bonds with epoxy are typically an order of magnitude stronger) My thought was that the simplest way to approach this relatively straight-forward repair is to essentially replace the old roving layers (roving is a bitch to work with for tabbing) with biaxial fabric, and replace the CSM with 10 oz. cloth.

Embarrassingly simplistic, I know, but the old tabbing worked well enough for 20 plus years, so I didn't see any reason to get too carried away, as long as it's the same amount of glass or more, done with a better resin, and the line-bubble in the corner eliminated, it should work safely. (and not having to wet fabric in place is a plus)

That was the basis of my reasoning, but of course, balancing expediency against analysis-paralysis is a tricky thing, and always subjective.

As for my other posting, it has always been disconcerting to me when people claim that heavy, monolithic fiberglass boats are stronger/safer/better than cored ones, without appreciating that the extra mass (often added where it does no good) will contribute to making them more vulnerable. Coupling that with the fact that some of these boats were/are made with low-grade polyester and frequently have poorly thought out structural arrangements, leads many owners to have a false sense of security in their boats.

Now, I should add that I come from a background in lightweight racing sailboats, and that obviously affects my view of structures.

Thank you for your questions,
Yokebutt.