This is the first time I have built a guideboat where I have had long enough stock so that I can cut the bottom board out of a single plank. Always before I have had to scarf two planks together to get the required length. Problems always occur when you go to glue the scarfed planks together. They always want to slide apart at the scarf.
So I obtained a 16 foot plank of quarter sawn white pine 10″ wide from Blue Line Hardwood in Long Lake. It was just what I needed but a bit unwieldy. I laid out the dimensions of the bottom board on the plank and then got my son to help me run it through my band saw to rough cut it. Here we are doing the rough cutting. We had to turn the saw 45 degrees and run the plank out the window to get enough room.
The next step is to trim the board with a bench plane to to bring it to its final shape.
The hard part comes next. The board must be beveled so that the bevel exactly matches the angle of each rib between its foot and lower arm. You start by laying out the distance from the edge of the bottom board inward to where the bevel ends. You will end up with a rolling bevel, one that starts out amidships with a gradual slope but that becomes steeper as you move towards the stems.
To get the width of the bevel at each rib stations I went to my reference book, Tale of an Historic Adirondack Guideboat…, Table 4 . Then I took my bench plane in hand again and started removing material until I got close to the final slope. You have to be careful because if you take too much you will cut into the top of the bottom board and it will not be a pretty sight! When I get close to the final shape I switch to a cabinet scraper. It gives me more control of removal and eliminates any rounding that comes about when I use a plane.
I always check my work by putting a rib at its station to see if the angle of the rib matches the bevel. I do this before I get too close to the final slope. The bevel at each rib station was off by enough to make a difference. I was really puzzled by this.
So I went back to the drawing board and to a method I use to lay out the bevel that is fail safe. It relies on the geometry of right angles. Here it is below.
What you do is to clamp at its station. Back the rib away from the board so that a straight piece of stock held against the lower arm of the rib just touches the top of the board. This forms a right triangle with hypotenuse formed by the stock, the distance Y is the bottom board thickness, and X is the distance you are looking for. It is the distance back from the edge of the bottom board to the back edge of the bevel. If you use this distance for each rib you can’t go wrong. I did this for each rib station and these are the half-widths for the bottom of the bottom board.
Station Number Half-width, inches
0 2 11/16
1 2 11/16
2 2 9/16
3 2 7/16
4 2 1/16
5 1 13/16
6 1 11/16
7 1 3/8
8 1 5/16
9 1 1/4
10 1 1/8
Here I am checking the slope against a rib to make sure we are now OK.
That hurdle passed, we now lay out the holes for the screws that will fasten the ribs to the bottom board. I wanted to make sure that the holes were perpendicular to the plane of the bottom board since any deviation off perpendicular one way or another could cause a problem. The ribs are not very thick and we don’t want screws coming out the sides of them.
There are such things a screw centering devices so I ordered one. It cost about $12 and was very nice. The problem was that it would not take a screw as small as a #6. So I made one of my own from a small block of cherry. I drilled a hole in it with my drill press so I knew any holes drilled using it would be square. Here I am using it.
I would check to make sure the holes were true every once in awhile.
I put the drill bit in the hole and checked for perpendicularity with my small square.
So now the bottom board is ready for attaching the ribs. We will tackle that next time.