Repair of Damage to a Unibond Hull at the Chine

[pufferfish]

Give me advice on repairing damage to the chine the Unibond hull of a 13-footer. The gel coat layer has been abraded, and in the area of damage there is a soft sport. The edge profile is largely intact.

Fig. 1. View of hull damage at the chine near the bow, looking up from below the boat.

chine.jpg (38.16 KiB) Viewed 2323 times

Q1: should the repair be one-sided?

Q2: should the damaged area be ground back to expose the underlying laminate and where there is a gap between the foam and the chine a filler material installed, using the process illustrated in the article linked below?

Repairing Hull Damage the Whaler Way
https://continuouswave.com/whaler/refer ... epair.html

Q3: can chopped strand mat be used to repair the laminate?

Q4: should I use an $50 Harbor Freight angle grinder instead of an orbital sander to taper the laminate and gel goat at a 12:1 slope and reduce the time needed to make the repair?

ASIDE: I went to harbor freight and got frustrated because I couldn’t find a disc sander. I found “dual action” sander/polishers, and the angle grinders have that guard which limits how oblique an angle you can apply.

Give me tips or tricks or advice for making repairs.

Q5: what is a good fairing compound?

Q6: is use of new fiberglass necessary to make a repair?

[jimh]

Q1: should the repair be one-sided?

I do not understand your use of the term "one-sided." There is no way to get inside the hull to make a repair from the interior side of the hull, because the hull is completely sealed and filled with foam.

Q2: should the damaged area be [repaired]...using the process illustrated in the article linked below?

Yes, the cited article is an excellent example of repair to a chine line. It shows the repair of very similar damage, albeit in the article there is perhaps a deeper abrasion of the gel coat and laminate. If the underlying laminate is sound, you only need to repair the missing gel coat. If the laminate is damaged and weak, you need to repair the laminate first, before adding topping with new gel coat. You will discover which type of repair will be needed as soon as you begin to abrade the damaged area to get to solid material.

Q5: what is a good fairing compound?

A fairing compound like the TotalBoat Fairing Compound is often used to fill minor surface imperfections in a fully repaired fiberglass surface. But the fairing compound will not create a structural repair to damage laminate. It is just for smoothing minor surface imperfections prior to applying a new top coat layer.

Q6: is use of new fiberglass necessary to make a repair?

I think you are asking if there is a need to use cloth material in the repair. This is determined by the depth of the damage. Again, follow the method in the cited article above. In smaller areas of damage where the underlying laminate is completely intact and strong, a repair can be made by just using epoxy resin with filler to restore small areas of missing laminate and gel coat. Deeper damage to the laminate needs to be repaired with laminating techniques.

More advice on making repairs to a Unibond hull is given in the Frequently Asked Questions answers in the REFERENCE section. See

Q5: how is damage to a Unibond hull repaired?
https://continuouswave.com/whaler/reference/FAQ/#Q5

The damaged area should be thoroughly dried so there is no water in the foam or laminate before initiating repairs.

[pufferfish]

The above remarks make be think I am on the right track.

Q7: for repairs, should chop strand matting be used or should something something like 1708 (which is believed to be a) biaxial fabric?

[To better understand this question, readers should watch a recorded presentation on youTube and pay attention at eight-minutes and nine-seconds into the presentation, which can be seen at

https://youtu.be/4XoeGV2KhGc ]

After I start the repair I will follow-up with more information on the repair.

[jimh]

Q7: for repairs, should chop strand matting be used or should something something like 1708 (which is believed to be a) biaxial fabric?

I am not sure that watching a presentation on youTube for eight minutes is going to be useful in replying to your question regarding when cloth should be used or when chopped strands should be used.

Most of the hull laminate lay-up in the construction of a Boston Whaler Unibond hull was traditionally built up using chopped strands applied with a "chopper gun" method. Boston Whaler traditionally did not use a hand lay-up method with cloth sheets. However, in the instructions from the factory for repairs, under the section "Structural Repairs," Boston Whaler shows the use of "mat" cloth to create a strong repair. Boston Whaler instructs to fill damaged areas first with a mix of resin and chopped fibers, creating a "mash." Before this inner layer of mash begins to cure, Boston Whaler instructs to add "no less than two layers" of two-ounce mat, and allow to cure. Not mentioned but important is that the two-ounce mat material should be wet with resin. Here is the illustration from the factory repair instructions that shows the method:



Whether or not some other cloth material could be used in place of the cloth mat suggested by Boston Whaler is speculative. The instructions were written in 1994. In 1994 some of the more modern and recently introduced laminating cloth materials composed of particular fabrics and weaves may not have been in existence, so the instructions could not have mentioned them or given judgement about whether or not to use them.

My assumption is that many classic era Boston Whaler boats with Unibond hulls have been successfully repaired with the methods given in the factory repair instructions. Whether or not there might be some advantage to using a particular fabric with a particular weave that is now available on the market seems difficult to assess with any sort of validity.

If you think the repair method could be improved by using a different cloth material with a different weave, then you can certainly try that approach.

Exactly how one would later determine there was an improvement in the repair method from altering the advice from the factory also seems difficult to establish. About the only way to determine the ultimate strength of the hull laminate after a repair would be to test the strength to the point of failure. That does not seem like a particularly useful approach.

[pufferfish]

Thanks for your replies, it's been a while and I'll read them. I'm shooting for a early June trip with a friend on Brewster Flats and want to at least be able to use it then. I renewed my registration.

I'm thinking I can shore up the chine with MarineTex. My understanding is that MarineTex I'd be able to sand and grind away and do a proper repair this winter with a gradual taper once I get to good fiberglass.

Then I'll minimally install the SUPER SPORT interior that I already bought for three times the boat cost--$1500 for new SUPER SPORT 13 interior, $500 for the boat.

I think I can just put in the console, side pieces, and two plank seats like in a SPORT 13, but not seat backs or cabinet.

I want to temporarily sal the holes made for the installation of the interior.

Q8: Between 3M5200 and 3M4200. which can be removed?

I'll try and update once I make more progress.

[Moderator's note: a new thread about engine repairs has been created. Please do not post to this thread about hull repairs for updates on work you are doing on the engine.]