Designing Stringers

I am about ready to replace the stringers in our 1996 Moomba Boomerang after removal of the remaining rotten pieces. How do I design them to where they match the contour of the hull. It will have to be a two axis cut.

In the second photo, the stringers will be running parallel to the gray center area and forward to an uprising bow.

Thanks,
Mark

 

I suppose you could fit a temporary bulkhead forward where the stringers are going to terminate, and run some taut stringlines from there back to the transom, at the height you want the stringers to be, determined by the floor height needed. Then measure the vertical heights at close intervals. You might be able to avoid the complication of a two-axis cut by filling the v-shaped gap between wood stringer and hull bottom with a resin filler with q-cells or the like, won't be any weight penalty in that. Someone may have a better idea, though.

 

Use a laser level. This tool makes simple work of this sometimes tedious set of tasks. Naturally, you'll want to level the hull at least side to side, to get symmetrical shapes. You can mark the perimeter of the sole, tops of the stringers and sole supports, landing points of these same pieces, etc.

 

Laser Level

I was thinking about a laser yesterday. When you say level the boat from side-to-side, do you mean placing a level on top of the gunwales and see if she is level? I've been struggling in my mind about an index point or point of beginning. It is currently sitting on a trailer and of course the boat will only reflect the angle the trailer sits at. I am probably going way too far in my reasoning...this thing isn't going to be circling Mars. And finally, when measuring thicknesses of plywood, they are true...right? Not like the milled thickness of a piece of stock such as a 2X4.

Thanks,
Mark

 

Park the trailer on a level pad, then measure from the bottom, outboard transom corners, to the ground. If both sides are the same, then the boat is level. Don't trust the gunwales, use the part of the boat the water sees, not the blonde you're bringing along.

If the place you park the trailer isn't level, then place the level on a ladder, behind the boat and shoot a line to hit the outboard bottom of the transom. When the laser hits both corners the same, it's level. You can shim or let air out of the tires to raise and lower one side. You can also jack the trailer on one side to bring the transom level.

The fore and aft level will still be out, but you can eyeball this from the waterline, boot stripe or sole inside the boat. In other words, place the laser in the boat, near the transom on the centerline and shoot a horizontal line around the inside. Measure down from this to see how far up or down the front is from the back. Use the trailer jack to adjust up or down, then check the side to side level again to make sure it's still where you want.

Most soles have some aft slope to them. This is fine, level the boat to this so your string tops, sole support pieces and sole perimeter all hit on a common laser line.

 

Is she level?

Thanks for sharing your wisdom in this area. Great information.