Monday, November 14, 2016

Finishing Tips for a Good Boat

Amateur boatbuilders are able to create boats of remarkable quality, sometimes rivaling the finishes and detailing that comes out of the best of professional boat shops. Having built a few boats myself, I know that I have the experience and the skills to do work that is as good as many professionals, as long as I stick to fairly standard detailing and don't try anything very fancy.

I see work of similar or better standard from other amateurs but I also see some boats that are somewhat "agricultural" in appearance, with very rough finishes. Much of the problem is related to being unaware of, or ignoring, some fairly basic principles that will make a big difference to the finish without adding a lot of work.

It is worthwhile to do as good a finish on your new boat as you possibly can. The extra effort will pay off later in the price that you can get when you want to sell it and also in the level of pride that you will have in your boat when using it and when showing it off to others. You will put in a lot of time and money creating this boat, which may be wasted if your boat is sub-standard. The cost won't be any different if you follow these tips but the standard will improve considerably. So, be good to yourself and do a good job of the build.
Interior of Hout Bay 33 built by Sergey Fedorov in Russia. Note the lack of sharp corners on all of the woodwork, giving a soft appearance and a feeling of quality. 

In no special order, here are some tips to help you to create that high standard of finish.

1) Sand wood rather than coatings.
It is easier to get a smooth finish on wood than on epoxy, paint or varnish. Do yourself a favour and get the wood as smooth as possible before you apply your first coat of anything over it. This will give you a good foundation on which to build a nice standard of finish on the coatings that will come later.

2) Round off all external angles.
Here I am talking of the exposed corners of framing, trims, bulkheads etc., in fact every external angle in the boat.

There are multiple reasons for this. First, it looks much nicer, due to softening the appearance by removing the visual harshness of the sharp corners.

It allows the coatings to adhere better and be of more constant thickness so that they give maximum protection. Paint and epoxy is pulled away from hard edges by surface tension, leaving those edges with minimal cover and protection. Rounding them off allows the coating to spread itself around the corner, for a smoother finish.

It removes the sharp corners that can cause damage to human skin and bone if fallen against at sea, bumped when cleaning bilges or getting items out of lockers. Those sharp corners can also damage hoses, electrical wiring and other items of boat equipment due to constant movement and chafing at sea.

Rounding off the corners of framing like stringers, joinery cleats and trims is most easily done before installing them in the boat. Do so with a router fitted with a 6mm radius corner round bit on all edges that will be exposed on the completed boat. The simplest way to do this is to use a router table, with the router mounted below and the wood run through the cutter on top of the table. For corners of bulkheads, lockers etc. use a 10mm radius corner round bit on a router than can be run along the edge of the plywood.

Don't think that just because an edge is inaccessible it doesn't need to be rounded off. If you want that piece of timber to have long-term resistance to rot then it needs as much protection as you can give it. That means rounding the edges then coating properly with epoxy, even if you will never see it again.
This DS15 was built by Jim Foot in South Africa. This boat has a wet deck, with all spaces under the deck sealed in and never to be seen again. Nevertheless, all corners have been nicely rounded and all wood surfaces are smooth, ready to take the epoxy coatings. This ensures effective protection for the timber and improved durability of the boat, as well as higher resale value.

2) Smooth off all framing
There is no sensible reason to use timber that is rough on any exposed surfaces. Rough surfaces have many little exposed corners, so coatings will run away from those corners, just as they do from edges that haven't been rounded off. You also increase the risk damage to skin, hoses etc. as described above.

You can buy wood that is planed all round, in the sizes that you need them to go into the boat. However, that is the expensive way to build a boat. It is normally cheaper to buy your timber in wider planks then cut them down to size yourself. Buy a table saw to do this job, it is a valuable piece of equipment for a boatbuilding project. Fit a carbide-tipped blade with 40-50 teeth. That will rip the wood quickly and leave surfaces that need minimal or no sanding.

The saw doesn't have to be a big one, costing loads of money and needing lots of space in the workshop. I built the CW975 "Concept Won" using a skill saw mounted under a portable saw table. When not needed I could pack it away while I did other work. At the other extreme, I built the Didi 38 "Black Cat" using a very nice radial arm saw.

For large boat projects it is worthwhile to buy a bench belt sander with 4" wide belt, which will allow you to run framing over the top of it to remove any roughness if needed. It will also allow you to sand smaller items to a nice finish before fitting them into the boat and to fine-tune the ends of smaller pieces of framing that need to meet neatly at intersections. Attention to these smaller details will make a big difference to the professional appearance of your boat.

Don't sand any frame surfaces that will be glued, rather leave those surfaces slightly rough or clean-cut. Sanding will block the pores of the wood, reducing penetration of whatever glue you use, thereby weakening the bond.

3) Take care with fillets.
Take care and time to make your epoxy fillets constant in radius and shape. A fillet that sags is not pretty and is also weaker than one with a smooth curve that feathers out against the two surfaces that it connects. That can sometimes be difficult to achieve because a high density fillet formed with epoxy, cabosil and wood flour cures very hard and is hard to sand. A little too wet a mix and it will sag, whereas too dry a mix drags when you run your filleting tool over it. A low density fillet is easier to sand out imperfections after it has cured. It is not as strong, so must be larger for equal strength. If you have an ugly high density fillet and can't rework it to look better then add a low density fillet over it to hide it.

4) Sand between coats.
Sand your wood surfaces before applying the first coat of epoxy, paint or varnish. After that blow off all dust with compressed air or vacuum it away. If you don't, you will be rolling dust and wood fibres over the surface when you work. They will be set into the coating and stay there, creating bumps and texture on the surface. The only way to remove this will be by sanding the coating before applying the next coat.

Some of the surface fibres of the wood will often stand up when the first coat is applied. Don't ignore this and paint over it, this will require more coats to cover it. Instead, it will need only a light sanding to smooth the texture before applying the next coat.

Sand lightly between coats if more time has passed than the over-coating time recommended by the manufacturer. For epoxy this is normally 12 hours, for paint it varies. It is also worthwhile to do a chemical wipe with acetone or mineral spirits to remove any surface contamination that may have come from skin contact (body oil in the shape of hand prints may be the most common form of inter-layer failure in painting of cars, boats and furniture) or other sources of contamination. A diesel generator running nearby can ruin your paint job due to oils in the exhaust gasses raining down on everything downwind of it.

5) Feather glass edges
If the boat that you are building has glass-taped joints or areas that are reinforced with fibreglass, sand the edges of the glass to a feather edge then apply a final coat of resin to fill the weave and seal any exposed fibres. Fair the glass surfaces where needed with epoxy fairing compound, as well as along all edges. The fairing should be no thicker than needed to fill any hollows, with minimal thickness over the humps. Sand it smooth to make the glass reinforcement disappear into the surface once it has been painted.
This is the chine of the Didi 950 being built by Mike Vermeersch. It has 2 layers of glass tape, which has been sanded to feather edges, faired and sanded smooth.

The finished chine with epoxy primer, ready for paint.

Achieving a great finish on your new boat should be a major goal. You will experience much more pride and pleasure from a boat that looks really nice than one that is very obviously an amateur build due to inferior surfaces. Challenge yourself to work to the highest standard of finish that you can. You will surprise yourself.

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1 comment:

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