Hard Cabin Sides Project

I have an older Lobster style boat. I want to fabricate Hard sides with a couple of sliding windows. This will protect from side spray and wind etc...
What would anyone recommend using for materials to build the sides? Also, how would you gel coat something like this?

 

I'm assuming you have a convertible and want to make a hardtop or at least cabin sides to partly enclose the helm area from spray coming over the side.

There are several methods to make cabin sides or walls with sliders in them. Plywood makes reasonably easy work of this. More traditional construction techniques would use solid lumber that's edge set and fastened with thru bolts (very important in boats heading into deep water) I've seen cold molded cabin sides and strip planked as well as typical GRP. Set your sides to lean inboard a touch. This will add a great deal of additional strength to the structure with little extra effort. If heading into deep water, where waves can board on the quarter or over the bow, through bolt the cabin sides to the deck beams and carlins. A wave can easily rip off a moderately sized cabin side without this feature, screws just will not be up to the task. If you build using all 'glass construction, then tab the sides well into the deck cap, coming or whatever you're attaching to. The 'glass layup (for the cabin sides) should be as the deck or topsides of the hull are. The size, style, shape and building technique will determine the construction details for these sides.

Gel coat isn't a very easy thing for the backyard builder to do well. Paint or other coating is much more likely to result in something you can be pleased with while under the big shade tree plugging away at you boat. Gel coat should be left to the folks with the equipment and experience, it's not a material that can be poured into a Wagner spray gun and shot on the sides of the boat and expect reasonable results.

 

Would you recommend if using plywood, to roll a couple layers of epoxy like West Systems on the plywood sides then paint them, or just bare plywood?

 

Plywood alone (most types) offers a limited amount of protection from the elements without a coating. CPES, epoxy and paint are the typical coatings and there are variations of application for these. Some say just a few coats of CPES and paint, others like myself, insist that most lumber used in marine grades of ply will require some reinforcement and epoxy to stop the surface checking possible and provide some abrasion resistance, then paint, others, all sorts of "magic" formulas. The tried and true (well tested) method is to seal the ply with thinned epoxy or CPES until the wood will soak up no more then a finish cloth (4 to 6 oz. cloth with it's weave filled) set in epoxy under the best paint you can apply or afford (prices can vary dramatically depending on the type of paint) Typically the two part polyurethane's are the toughest (also one of the most expensive and difficult to apply well) then the single part poly's, then epoxy based then oils.

Spraying produces the best finish, though is the most difficult to get right for the inexperienced. Rolling then tipping off with a good quality brush and paint can produce very good results, especially if the conditions can be controlled somewhat (temperature, humidity, bugs, etc.) I get very good results with a brush alone, though rolling and tipping off is a faster way to cover a large area needing paint. Controlling the "flow" of the paint is key, but frankly the trick to any finish job is surface prep. Finish work is 80% prep (maybe more) and 20% application. The better the prep, the better the finish will be.

I've just completed a transom replacement on a good size power boat. The transom is mahogany plywood, real pretty stuff and the owner was wondering why it was taking so long after installation to deliver the boat. He wanted a bright, natural finish. This means, starting from scratch (bear wood) three rubbing sessions with linseed mixture to fill the grain (a day each) a rubbed in thinned coat of varnish, (another day) five build coats of solid varnish (a day each coat) plus 5 more finish coats of varnish (yep, a day each coat) The actual varnish in the brush time (I sprayed the 5 finish coats) was just a few hours, the rest of the time was leveling the surface and creating a tooth for the next layer to grab onto. He now understands why it costs so much for bright work, as he sat in on several sessions during the process. This job was helped greatly by doing the work indoors and having control over the conditions. If done out doors the job would have taken twice as long. This is a show boat and I told him he needs more varnish, but he likes what he has now so . . .

 

For a 35 to 50 ft boat 3/4 airex core (or your favorite core material) with a layer of 3/4oz matt 28 oz roving ,mat , roving and mat last on both sides will make as strong as needed and weigh about 3 lbs per sq ft.

Ply burried in my experience has a 10 year life MAX,And has virtually no insulating value.

We replaced acres of ply (decks , cabin sides) in Tiwan Tubs over the years.

FAST FRED

 

Taiwan Tubs

I am currently replacing all the core on a 41' Taiwan tub built in 1980. Because the boat was originally designed for the heavy ply I am using it on all the lower decks and cabin sides. I'm using a honecomb core material for the flybridge,this will save a lot of weight high up and provide some insulation. I live in Hong Kong where it's hot and humid most of the year.

For added strength on the outside I'm using a "multi-mat" material on the walkways and where the deck meets the hull, this is a chopped strand mat the two layers of axial roving, this will be topped off with one final layer of chopped strand mat (CSM), 450grams. On vertical surfaces,to cover the ply, I am using 450g CSM on top and bottom and a 1mm layer of core mat between. On a small sample I made up I found the 1mm coremat to be stiffer than 850gram woven roving. As a resin I'm using vinyl ester. It's much stronger and more impact resistant than polyester and a fraction the price of epoxy. I also use a sealer on all surfaces before applying any resin. On another test piece this appears to increase the bonding strenght to the plywood by a large amount.

So far this appears to be much stronger than the stuff I just cut off and put in large trash bins! A local surveyer agrees that this is probably overbuilt but not a bad idea.

As a cheap way to stop spray getting in your face, it's only a 10 minute job