what fiberglass to use for tabbing bulkheads, stringers, bunks: 20 foot sailboat

[sailormanbob]

What fiberglass to use for tabbing in new bulkheads, stringers, bunks, on a 20 foot sailboat?

I care most about strength and durability, then cost.... and don't care how it looks. Thanks!

[sailormanbob]

I found this so far on Defender: the second one down,

"West System Biaxial, 15 oz, "727""

Marine Fiberglass Tape

I was thinking using three rows with this stuff. Any other recommendations would be awesome.

Thanks!

[Lepke]

Epoxy not polyester. I like West System because it's easy to measure small and big batches. They have a pump system for small batches that gives uniform mixes. And a gear pump for large batches. Where bonding to existing fiberglass, I sand with 40 grit.

[jimbunyard]

Don't know where you're located, but I've always liked Fiberglass Supply on the west coast. For instance, they have 8.71 oz 4" tape for 29.00 for 50 yards. You'd have to double it to equal the Defender/West 15 oz tape, so that's actually 25 yards for 29.00. If you give them a call and tell them what you're doing they may be able to give you some advice and recommendations.

Fiberglass Supply - Fiberglass Fabrics, Surfboard Cloth, S-2 Glass, Fiberglass Fabric Tape, Industrial Fiberglass Fabrics

You'll generally get much better prices from a fiberglass supply specialist than a general marine store, just takes a little research. If you find a good one they can also give product suggestions for your application.

As for what exactly to use, the tape you suggest is good, and depending on your application, three layers (45 oz total) is probably sufficient. I'm old school and usually use a combination of 18 or 24 oz roving and 1.5 oz mat, which I buy by the roll and cut to fit.

Epoxy gives better secondary bonds, the type you'll be making, but polyester is a bit more versatile and easy to work with, as well as being faster. The slower cure time for epoxy can, however, be an advantage for the inexperienced as you'll have a longer time to make adjustments.

For the small amount it seems you'll be needing the price difference between the two will be negligible...

[44'cruisingcat]

I used tri axial glass. That way you have fibres laying at 90 degrees to the join, as well as the 45 degree oriented ones.

[dpddj]

IMHO (from being in the business too long) epoxy is overkill for your project. And ... you will be hard pressed to go onto epoxy with poly at a later date. Polyester is adequate. Just be sure, that if you wait more than 24 hours between tapes, that you scuff the bonding surfaces with 60 or 80 grit, and wipe off with alcohol. Lots of people use acetone, though.
Tape? I'd use a biax or even standard 0/90° (neither too heavy), but be sure that the rovings/strands go into the corner at a +/-45 angle. Not sure if that made sense, but rovings/strands at 90° into a corner are not as strong and may spring out of the corner.
Your starting tab should be at least 3" onto the hull and bhd. Use several tapes, each one extending out onto the hull/bhd at least 1" more per edge.

[thinwater]

One more thing. Lay a filet in the inside corners and round the outside corners. The glass cannot conform to a sharp corner, inside or outside.

I find biax conforms better. Smaller pieces are often easier to work with, particularly in tight spots and 3-way corners, and so long as there is overlap, there is no difference in strength.

Have fun!

[George DuBose]

I retabbed all the bulkheads on Skylark using bi-axial and tri-axial tapes in varying widths. I used West System G-Flex, which I later learned is not recommended for laminating!!! In spite of the cold temperature in the hall where I was working, I could warm up the two parts of the G-Flex and carefully and thoroughly wetted out the strips of cloth. I used two heaters to keep the cabin warm and after a season of fairly hard sailing in the North Sea, all the tabs held.

I was inspired to replace all the tabbing in Skylark as Pearson used only one layer of cloth for tabbing the bottom of each bulkhead and in one place there was NO tabbing at all. I had had a hard sail on the Atlantic coast of France two years ago and noticed that the tabbing on one bulkhead had caused the laminate on the bulkhead to shear. The RUBBER CEMENT bond of the laminate to the plywood had failed. That meant the ultimate bond of the tabbing was rubber cement.

I have also used G-Flex to bond HDPE to fiberglass and bond pieces of black locust wood that I was using to add a stronger floor over a weak spot in the keel/hull joint at the aft end of Skylark's deep bilge.

So far all is good. I will have to wait until the boat is hauled for the winter to check on this repair.

[Colin A]

You can use Epoxy or polyester. I think of polyester as easier because that's what i learned with but, most people I know think Epoxy is more user friendly. Epoxy will be stronger but polyester is how it was likely built.

If you do use polyester a layer of fiberglass mat as the first layer is a good idea. Then something stronger. If you use epoxy don't use mat. Biaxial will work fine. I usually use 8" tape.

If your in New England Defender is good or you can CHeck out Mertons FIberglass. Joe who runs Mertons is a great technical resource.

[George DuBose]

The thing I noticed about G-Flex is that it is 1. more flexible than the regular West System epoxy and 2. it sticks to plastic, even the mixing cups that the regular West System doesn't stick to. Even sticks to HDPE after "oxidizing" the HDPE with a propane torch.

[puffcard]

Originally Posted by George DuBose

The thing I noticed about G-Flex is that it is 1. more flexible than the regular West System epoxy and 2. it sticks to plastic, even the mixing cups that the regular West System doesn't stick to. Even sticks to HDPE after "oxidizing" the HDPE with a propane torch.

G-Flex is a great product and sticks to about everything. But not the correct product for tabbing. First it doesn't wet out fiberglass cloth/tape. Plus it is very expensive. You can buy a gallon of boatyard polyester resin for the cost of one 8oz tube of G-Flex. On a small 20 ft boat which won't be dropping off ocean waves, I would use polyester resin at $27 a gallon and have a grand old time. Just use 9oz standard fiberglass tape and layer it up. You can go all hi-tech, but not required. Do use tape, it's much easier to work with, than cloth which is cheaper.

[Frankly]

You didn't ask this but if you haven't already run across the idea of taking a router and removing about 1/8" X 2" from both faces of the bulkhead edge. This gives a good rough surface to bond to, and a smoother finished look for however you intend to finish it off. Also an edge to catch the glass makes life a little nicer.


I am assuming that you are not using 1/4" plywood for the bulkheads .

[Pete7]

One thing I notice on my Moody is that the tabbing is also through bolted with large washes, something you might also consider.

Pete

[JOHNMARDALL]

Lots of good advice here, so a couple of points that may help:

Epoxy is a much stronger glue "secondary bond" than polyester resin and if you use West System products with their handy metering pumps and other gadgets (spreaders, etc.), user friendly. It's expensive, but there's much less waste and uncertainty than with fast setting polyester or vinylester resin.

Use combination fiberglass fabric or use layers of chopped strand mat between layers of cloth or roving

No matter which resin you use, over time the connection to wood will fail- with epoxy the face of the plywood will pull off. It usually doesn't have much effect as the plywood bulkheads are surrounded and trapped, but for stringers and other high load connections, consider screwing or bolting through the tabbing, after it has cured to make a mechanical connection. This approach can also help with existing tabbing which has let go, by filling the crack with adhesive and then through bolting or screwing.

Good luck
John Mardall
Vetus Maxwell Group