Repair of Damage to Hull Bottom of a Unibond Hull

[malcHILL]

[Moderator's note: the original post asked multiple questions on many different topics. Starting threads in which there are multiple topics is not a efficient way to get answers. The original post has been separated into several different topics so that readers can offer advice without producing a mixture of topics in one thread.]

I have a c.1979 MONTAUK 17 boat which I received at no cost. The boat has probably NEVER been stored indoors. It was mostly kept year-round in the water without a cover, and more recently it sat for five years on a trailer with an old cover. The hull topsides have an immense amount of spider cracking, and particular so around the fixtures. The hull keel has several poorly-done prior repairs. The bow area of the hull bottom was likely sitting on rocks at some point. The transom is split at the bottom.

The teak (wooden parts) are in good condition, and they are already being restored.

The metal parts look good.

The boat came with a non-working engine, which will be removed and replaced.

My plan is to repair the boat and have it in the water by July 1 [of some unspecified year]. I know little about how to fix boats. I would like the repaired boat to be pretty.

Q1: how can the hull bottom be repaired?

[Remainder of questions are separated into their own threads--Moderator]

[jimh]

Q1: how can the hull bottom be repaired?

The best source for advice on how to make repairs to the unique construction of a Boston Whaler boat with a Unibond hull is give by the factory themselves. The factory sent out repair instructions to owners and dealers, and those instructions are reproduced in an HTML page in the REFERENCE section. See:

INSTRUCTIONS--HULL PATCH KITS
https://continuouswave.com/whaler/refer ... tions.html

Note that the REFERENCE section of the BOSTON WHALER section of the website contains many long, carefully-research, articles about Boston Whaler boats. Anyone new to Boston Whaler boats should read the answers to Frequently Asked Questions at

Frequently Asked Questions
https://continuouswave.com/whaler/reference/FAQ/

In addition to the factory instructions, a very nicely illustrated article (again, in the REFERENCE section) shows repair significant damage to a Unibond hull that adheres to the factory advice. See

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

Although the factory instructions (written in 1994) generally mention using polyester resin as the laminating and repair resin, a better choice for an adhesive resin for making repairs to fiberglass boats that were originally built with polyester resin is to use epoxy resin. An article describing minor repairs using epoxy resin gives extended advice at

The Epoxy Cure
https://continuouswave.com/whaler/refer ... epair.html

The reason to use epoxy resin is twofold: epoxy is more water-resistant than polyester resin, and epoxy is a stronger adhesive.

For more comments about using epoxy to make repairs to a Boston Whaler boat, listen to my interview with Jim Watson of WEST System epoxy that was conducted 25-years ago in the WHALER RADIO section of the website:

https://continuouswave.com/whaler/radio/

IMPORTANT: before undertaking any repairs to a Unibond hull in which the foam layer is exposed, the foam layer must NOT be wet with seawater or freshwater. The foam must be allowed to dry out so that a good bond to the foam can be achieved.

Repairs to the hull bottom generally do not need to be done with great attention to the color matching of the original hull color to the repair area, as the hull bottom is not generally visible unless the boat is on a trailer and someone crawls underneath to specifically inspect the hull bottom. As long as the hull bottom repairs are some shade of white or off-white, there is really no need to obsess about getting a perfect color match.

[malcHILL]

As a progress report (that I should have included initially), the boat is currently upside down on its original trailer (with the bunks modified to fit), in covered storage. I have re-fiberglassed the keel and the bottom of the transom. My intention is to sand and then paint the bottom of the hull before flipping it back over. At this point, my question are about sanding and gel coat resin.

Q2: what products should I use for sanding?

Q3: what products should I use for gel coat resin?

[jimh]

Q3: what products should I use for gel coat resin?

Q4: how large is the area of the bottom of the Unibond hull that will be repaired for which you plan to create a new top coat layer of gel coat resin?

Q5: what method of application of this new layer of gel coat resin do you anticipate you will use?