Leaking Minimost Overhaul

Hi there, this is my first post, and I'm new to boat building but I've been reading all the posts for awhile now.

My dad built what I think is a "Minimost" (http://www.svensons.com/boat/?p=HydroPlanes/minimost) about thirty five years ago. Its built with regular cheap plywood and painted inside and out with Marine Paint.

After so many years of good service, and I'm sure much neglect, it leaks where the transom attaches to the rest of the boat on the bottom and both sides. In addition the front two pieces of plywood that were nailed together have began pulling apart and there is a small gap. Finally, along the cut in the bottom that I suppose was required to bend the bottom sheet of ply to make a curved hull, it also leaks. The wood seems in decent shape with some small "dry rot" in places.

I began the task of sanding it down a few years ago and hope to finish the refurbishing this summer, because we just purchased a new outboard I want to try .

My dad suggested to fiberglass the leaky seams with fiberglass cloth and resin. Then resin over all of the outside of the boat, grind that down and paint over top of it. I don't think this will trap all the moisture in because I plan to leave the inside of the boat raw. Is this a good Idea? Should I use fiberglass cloth or mat? I've heard conflicting reports and I really don't know the difference between the two. I plan on using EPOXY resin, because if its one thing I've learned reading these forums here, that its worth it to spend the extra dough and get a two-part? epoxy resin. Can you recomend a brand?

I want to paint over the resin that I have roughed, what weight of fiberglass with I have to use for the weave to be unnoticeable through the paint? I have purchased a spray gun and have a compressor and moisture removing attachment for the compressor, I want to do the paint myself as well. What kind of paint can I use with a HVLP gun like this and get a good finish (I am willing to do lots of sanding and many coats as I know it requires)? Then I suppose I can clear over it as you would with any other land vehicle? Can anyone recommend any brands of paint/clear?

For the inside I think I will cut a piece of ply for a floor and cover it with some carpet for a steady surface and leave the rest of the interior bare wood. Good idea?

Sorry for the long post, your help is really appreciated. Any questions, post and I'll try my best to answer them, but I'm far away from the boat currently and won't be able to see it until I will be working on it.
I know my dad would love to see his baby back in top shape for his birthday in September and I am itching to get at it when I get home from school in the summer.

Thanks,
Ryan

 

I'll see if I can get all of your questions answered.

The best thing you can do is to remove the known rot and replace the areas affected with wooden "Dutchman's". After you've removed and repaired the bad pieces, you can address the leaking issues.

This boat has seen lots of vibration, pounding and abuse on and off the water, plus is built of less then ideal materials and has had less then ideal care. This means most if not all of the joints are moving around and some of the plywood is delaminating. This is typical of plywood over frame powerboat construction and the real solution is to refasten the boat, so the individual pieces that make up the structure are tight again. Since this boat may have some sentimental value, it may be worth, uncovering all the fastener heads, removing them one by one and replacing them (usually with the next size up screw or nail).

Most of these boats were built with mild steel fasteners, which if not kept dry, will rust away if water has been allowed to be in contact with them for extended lengths of time. Stainless fasteners will last a little longer, but the age of your boat suggests unless the fasteners are bronze, then they're spent.

Another method to get some additional years of service from the old girl is to tape the seams. This means grind the exterior seams (chines, keel, deck joint, etc.) back to good wood, coat with epoxy then skin each seam with cloth tape, set in epoxy. This will add some strength to the weakened hull, but will require you take much better care of her in coming years or she'll rot faster then before.

Coating the outside just epoxy will provide some protection, but not much. You'll still have to paint it and have the additional issue of maintaining any dings and blemishes in the epoxy coating, where paint can be let go for much longer before addressing scratches, etc.

Use cloth with epoxy.

A trailer boat doesn't really need cloth sheathings if well cared for, so I'd just paint her after taping up the seams, repairing the rotted areas and replacing as many fasteners as you can.

Bare wood will absorb moisture, so paint all exposed surfaces (varnish is paint too). Carpet will accelerate moisture ingress problems on any wooden surface, so select a different flooring treatment that doesn't trap moisture between it and the wood. Carpet can work, but you have to remove it when you park the boat (each and every time), so moisture can dry up and not be trapped. This is true of anything that lies against wood, like coolers and gas tanks.

Finishing 'glassed surfaces is like finishing anything else, you sand, add filler, sand, continue to fair the surface, until you're happy enough to start painting. The weave of the cloth is filled with successive coats of material, cloth weight doesn't matter (except for the time it takes to fill it). It usually takes two coats of epoxy to fill a 6 ounce cloth weave, maybe more if the epoxy is particularly thin (like Raka's products). Further fairing can be done with reinforcement agents (fillers) added to the epoxy and smeared over the surface. There are other products that also will fill the surface imperfections, but don't use Bondo, it will rattle out and fall off from vibration.

If you're comfortable with your spray gun outfit then use a single part polyurethane paint. It's hard and durable. There is better paint, but not well suited for amateurs. Oil based paints can produce a nice finish, but not as glossy or as hard as the polyurethanes. The low buck route is acrylic (latex) porch and deck paint, which is okay, but very soft, not particularly durable, nor very glossy.

Try the search function at the top of the page and look up some of the subjects you are having questions about. Much information is available and you'll likely find all the answers you need.

 

Ok, thanks for answering all those questions, its a huge help.

As for the carpeting I was planning on, I was thinking of sort of laying a sub floor on top of the frame that is inside the boat (plywood) and just cutting it to the shape of the boat, and perhaps covering it with carpet, because you're sitting on the floor when you drive (or on a small pillow or chair). I plan on just laying it in and not fastening it down. Do you think this would work if I used the epoxy/Varnish/paint on the inside as you suggested? (Which is a the best choice for the inside coating epoxy resin/varnish/paint?)

What type of product could be used to fill the surface imperfections and provide a good surface for the single part polyurethane?

Is this polyurethane similar to the finish like you see on production boats? A "gelcoat" I'm told? If I spray with the single part polyurethane I just cover it with clear and I will get a nice shiny finish you are talking about?

Also, I was wondering what can I use on the edges to prohibit small bumps from scratching the paint job and even chipping it? I do not want what I'm told to have a "capped" boat, as it currently is.

Thanks again,

Ryan

 

If you use a cushion you'll be more comfortable and it can be removed after you've blasted around for the day. The same is true of carpet, just make sure it doesn't stay in the boat when not in use.

Painting anything is 90% surface prep and 10% coating application. The better the surface is prepped, the better the finish will be. Hundreds of man hours goes into making the plug for a 'glass boat perfect, so that each hull that pops from the mold has a nice smooth finish.

The same is true of a painted finish. There are several methods to fill the surface imperfections. It frankly would be the larger portion of a book to describe the techniques, materials and methods used. Much of this has been covered in previous threads and topics on this forum. There are also several books on this subject. Try the search function and take a look at what's available in the BoatDesign.net book store links above.

Typically the edge of deck will have a section "half oval", which is a hollow or solid metal (stainless steel or bronze) strip with holes in it. It is bedded and screwed to the deck edge or more typically a rub rail.