Cutting Gains

One aspect of John Welsfords’ designs which seems to appeal to many people is the lap strake planking. While it is not as demanding of the builders woodworking skills as traditional clinker construction, those overlapping planks leave one tricky detail that has to be dealt with one way or another. What to do with the planks where they meet the stem?

Study a few photos of “other people’s boats”, and it soon becomes clear that there are some creative solutions to this problem area.

One method involves the use of copious quantities of filler to “blend” one plank to the next. I think it really spoils the lines of the boat, and it must use a lot of expensive epoxy filler.

Filler used to blend one plank to the next. (click images to enlarge)

A substantial improvement visually is to simply let the planks overlap all the way to the bow. To keep the planks vertical at the stem though, each one needs a packing piece – the higher the plank, the thicker this needs to be. As well as creating more work, this wasn’t quite the look I was after.

A nice alternative is the traditional method, where each plank tapers progressively into the one below so that they sit completely flush at the stem. This is achieved by cutting a shallow ramp called a “gain” into the top edge of each plank. It is easier to do than it looks, and I think the result is well worth the effort.

Trad craftsmen boat builders should probably start their grave spinning now. The ideal tool for this job is probably a rabbet plane, with the blade going to the very edge of the body. I had to find another way of cutting the gains on my Pathfinder. With a bit of practise it only took about twenty minutes per gain, and didn’t need gallons of epoxy to look good.

You will need a hand saw, a SHARP chisel and a pencil. A small plane and cordless driver are useful but not necessary. Before cutting each gain, I found it really helpful to dry-fit the next plank up, and trim its bottom edge as accurately as possible. This meant I could screw it in place periodically to check the progress of the cut. It also saved a lot of work later on, as it is far easier to trim the plank to a fair curve off the boat than on.

A related detail is housing the stringers in the stem. This means a large bevel can be cut each side of the stem for the planks to glue onto – the traditional term for this is “faying surface”. It takes a bit more effort, but makes the boat a bit lighter and a lot stronger – that has to be good!

Stringer housing cut into the stem.

Start off by marking a pencil line below the top edge of the plank where the gain will be cut. It should be parallel to, and slightly above the bottom edge of the stringer. This is also where the bottom edge of the next plank up will come to.

To get a consistent line I made a simple depth gauge from a nail and scrap plywood. Trim the top edge of the plank so that the nail can sit on the top edge of the stringer.

It is worth marking the entire length of the plank while you are at it, as it is a useful guide when planing the bevel for the next plank to sit on.

The next step is to figure out how long the gain needs to be. To get a rough idea, run a straight edge vertically from the plank you are about to cut into, up to the next stringer. At some point it will sit fairly flat on both the plank and the stringer. Put a second pencil mark across the first line where this occurs.

On my Pathfinder, this was about 40cm (16 inches) back from the stem on most of the planks.

Now the fun bit. The aim is to make a saw cut which angles through the plank about 3mm (1/8 inch) above the horizontal line, entering at that second pencil mark and just cutting through the full thickness of the plank at the front edge of the stem.

I use a sharp hardpoint handsaw – they cost all of $12 and go through ply like a hot knife through butter – in fact all the planks on my Pathfinder have been cut with one of these.

It is a bit awkward making this cut on one side of the boat or the other depending on whether you are left or right handed, hence the 3mm allowance. Don’t worry if it is a bit wonky – it will be fixed up later.

Making the first cut.

Once the cut is made, break out the bulk of the waste with a chisel. I have no photos of this stage, but trust me; it was pretty rough and looked very ugly.

As long as you don’t go deeper than the saw cut in too many places there is no problem. To (mis)quote Welsford's first law of boatbuilding, “the mistake has yet to be made that can’t be fixed with epoxy”. Use a sharp chisel or small plane to clean up the gain. My tool sharpening skills are a bit hit and miss, but it really is easier, faster and safer if you can get a decent edge on your chisels for this work.

Two views of the gain cut.

One trick which I found worked quite well was to use the saw as a long skinny rasp by dragging it diagonally across the face of the gain. As the saw blade is so long, it covers the entire length and only knocks off the high spots, making it easy to get things straight.

If you are like me, that first cut along the bottom edge of the gain probably drifted around a bit – trying to make a straight 30cm cut with a horizontal saw blade on a curved surface with your off hand isn’t easy!

To clean this edge up, sit the saw vertically on the little ledge along the bottom of the gain and cut straight down to the first pencil line.
It pays to dry fit the next plank up a couple of times during this process. I found that the rear end of the gains had to be faired out a bit further than I expected to avoid a lump in the higher plank. The end result should look something like this. Pretty cool eh!

One more to go.

By now you are probably sick of planing, so here is a speedy way of cutting the bulk of the plank bevels. Simply saw off the waste, using the pencil line you marked right at the start and the next stringer up as guides.

It works really well where there is a decent angle from one plank to the next (for example, the aft 2/3 of a Pathfinder) but be VERY CAREFUL as you get nearer the bow. It is very easy to cut too low where the planks flatten out. As long as the saw cut is above the pencil line you are pretty safe, and it saves a huge amount of planing.

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