Slowly lapping
I really must apologize for the paucity of blogs in the last month or so. All I can say I think that this condition will even out over time, but lately I’ve been a bit distracted. She has the most *amazing* hair. mmmm.
In the meantime, when my mind is on boats, I think about the binder. After fitting it to the boat and making sure that everything was fair, I took it back off the boat, and cut in the bead along the top inner edge. I wrote about that particular step on the binder I made a while back; unfortunately, adding that detail before I double checked the fit of my plank, made the plank unusable. If I’d waited to do the bead until after checking the fit, I would have possibly been able to do some more shaping to the plank to make it fit. Live and learn. Again.
So, the bead’s now cut, the plank is clamped in place, and the next step is to cut the lap between the binder and the sheer. This is essentially a very precise slope that is cut in both planks so that when they overlap they mate perfectly.
First step is to mark out how much the planks overlap. In this case, the overlap is 7/8,” a little fact we picked up by looking at the transom where the joint between the 2 planks is exposed.
So, we run a 7/8″ line below the top edge of the binder all along its length. This defines the lower edge of the lap and so we won’t plane below this line.
The next task to to make sure we know how to get the proper angle of the lap. The lap is a rolling bevel, meaning that it changes along the length of the boat. And since it’s a watertight joint, it’s got to be right on.
There are a number of ways to do this. Some folks modify a plane with a rod sticking out of the side that serves as a bevel guide (’ll get you a photo later), but we went a little more low tech.
In most lapstrake boats, the underside of the upper plank is flat, and you work out the angle of the lap by placing a straight thing like a ruler or a fid on the top of your plank and angling it down to touch a mark representing the top edge of the sheer. That straight line represents the underside of the upper plank. By looking at how it lies against the upper edge of your plank, you can see how much you need to plane off to get a perfect fit at the lap.
In our case, the sheer is also beveled on the inner edge, so we can’t use a flat stick. Instead we use a combination of a batten and a home made test stick. Here’s what it looks like.
You can see that we’ve got a 3/4″ batten set up in this photo. It’s screwed into the molds so that its upper edge lies on the top of the sheer. Now we’ve got a continuous surface that we can ride our test stick along. Actually it’s more accurate so say that now we’ve got a continuous Line that we can run our stick along, because the only point on this batten that we want to contact is the upper outside edge. That edge represents the line of the sheer, exactly 3/4′ out from the boat.
So, to compensate for the fact that the sheer is now 3/4″ high, we tack on a 3/4″ thick block of wood to the end of our stick. If the upper strake (in this case, the sheer) was flat on the underside, we’d be done with the construction of our stick. However, since the underside of the sheer also has a bevel, we put that same bevel on the underside of the block. The bevel on the stick extends exactly 7/8″ up the block to mimic the depth of the lap.
Phew. Now we can actually use this thing to guide the cutting of our lap. Hold the stick on the plank so that the lower edge rests on the 7/8″ line we drew earlier to define the lower edge of the lap, lean it into the batten and voila! You can see how much you need to plane down to get your angle right.
Plane plane plane, move down your plank, repeat.
After a bit you get the feel for how much needs to come off so you can go quickly to get in the ballpark, and then use the stick to dial in the bevel just right.
Almost there.
There.
Now, to do this properly, you have to have the inside top edge of your plank resting right on the frame. If the plank has pulled away from the frame at all, the angle will be wrong. All that backing out I did earlier left me with a plank that fit snug and tight against the frames.
That is, until the drying began. Insert ominous music, lightning bolts, maniacal laughter.
“Lord, why does anyone work with a crazy material like Wood? It’s just a stupid thing to do.” says our instructor, Warren. And he’s right. This stuff moves all over the place. Fiberglass just sits there where you left it.
In my case, the drying plank slowly began to cup outwards. In essence, the plank began to flatten, and this meant that the top and bottom edges began to pull away from the frames.
Oh for God’s sake. Did I dropkick puppies in a former life?
So, back to the steam box with it, and then back on the boat. This time I’ve clamped it to the frames to within an inch of its miserable flattening life. I finished cutting the bevel and got ready to cut the gains.
The gains are the sections of a lapped plank joint where the 2 planks go from overlapping to flush so that they can lie in the rabbet as if they were one plank. Our gain transition starts about 12″ from either end of the plank.
But for now, I’m taking a week to fly to Madison and build some storm windows for my house there. The renters complained of the cold last year, so I’m going to try to tighten things up a bit.
That should give this plank a little more time to dry, but this time it’s held tightly in place on the boat. Hopefully it’ll give up its shifty ways and stay put.
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