Make Bunk Board For Small TrailerArticle By Shorty
Many boats see their roughest time on the trailer. There are a couple of big problems with the typical bunk boards that run lengthwise. The boat to the right is my friend's vagabond 14, you can see the depressions in the bottom of the hull from those lengthwise bunk boards.
1 - As the hull sits on the trailer, the bottom of the hull starts to form dents. This is both because of the weight of the trailer, and also the strap you put on to secure the boat to the trailer.
2 - As you bounce down the road, the bouncing / jarring action flexes the bottom very quickly, breaking fibers in the hull, weakening it. When you hit a pot hole, that quick snap thunking noise you hear is transmitted directly to the hull.
The solution I see is to make better bunk boards that support the hull. For light boats that don't have much structure built into them, a bunk which runs perpendicular to the hull that has a curve that matches the hull will spread all the force across the hull, and more importantly to the chine area (curves on the sides) which is a MUCH stronger area than the flat bottom.
Another important trick is to put foam padding between the bunk board and the carpet covering. Have you ever tried to hammer a nail into a board, while the board was sitting on carpet with foam backing? The foam absorbs shock very well, and you don't need that much of it either. The foam I use is concrete edging foam. It is 4" wide x 3/8" thick, and comes in 50' rolls. I used the leftover foam to make boat cushions and pads by gluing strips together, then cover with vynil fabric.
For this hull, I am making a curved bunk board that goes cross wise and will support the hull all the way across. I first setup the trailer so I knew exactly where the board would be crossing the hull.
This is my offset tool, it's real name is a splining block. I mark the curve onto the bunk board by pulling the stick and pen from side to side, as the point of the stick makes contact with the hull, the pen makes contact with the board, only offset by a couple of inches. The important thing to do is keep the stick vertical at all times, otherwise you won't copy the curve correctly.
Would you look at how well that cut matches the hull ? I once cut a perfect curve in a piece of plywood to fit around my toilet. That was a much tougher curve to match, and tighter spacing.
The bottom of the bunk board was a little on the thin side, so I laminated another board to the bottom of it, and on both sides.
Sorry I don't have a picture of this, but what you do before you put the carpent on, is to put some foam on the board. This acts like a shock absorber as you trailer down the road. I use concrete border foam - it is used around the perimeter of concrete pads so that they can expand and contract without cracking the neighboring concrete. It comes in 50' rolls, is black, about 3/8" thick and 4" wide.
Cover the foam and board with indoor / outdoor carpet, and we are ready for a cushy ride to the next boat ramp.
Burt Revell came up with this idea to make an adjustable offset tool, he added a screw to the end of the block so the distance can be adjusted in small increments. Neat !!