The first thing you have to do when making the boat 3d is to build to the centerboard box, which means you need to know exactly how wide your centerboard is going to be, which means you really should have a finished centerboard ready to go. So, time to build the centerboard (and rudder since the procedure is exactly the same).
In order to make these heavy enough to counteract their own boyancy and actually sink when you deploy them you have to add weights to both. A lot of people will custom melt lead, but the idea of that is just completely nasty - lead is an awful chemical you really don’t want to get on you. So instead, I went to nfmetals here in Seattle and had them cut me some custom lead sheet to hit target weights.
They had 1/2" lead on hand, so I had them cut me two pieces - 6" x 17.6" (for a target weight of 22lbs) and 4.75" x 2" (for a target weight of 2 lbs). That weight for the centerboard is bang on, but according to the wisdom of the forums I should have gone a little heavier on the rudder - likely 2.5 lbs would have been best. I can add this later if needed.
The trick here is figuring out where to locate the weight, and then how to exactly match that location in each of the two halves of the rudder or centerboard so that it doesn’t have the option of rattling around.
The approach I took was:
- given how thick the lead plate itself is, and assuming half of that width would be taken up in each half of the centerboard/rudder, count out how many layers of the plywood you need. You should be able to easily tell how long/forward you can position the lead and still have lots of thickness on the outside edge to hold the weight in.
- put the two halves of the rudder/centerboard together, and make some reference marks around the outside edge
- connect those reference marks using a straightedge on each half of the rudder
- From the outside of the centerboard/rudder, eyeball roughly where it should go based on thickness of plywood (and keeping the weight as low as possible). Draw the outline of the weight.
- measure offsets of the outline in relation to the reference lines. Transfer those measurements to the other half (understanding that it’s mirrored) and draw the same outline on the other half!
This should be good enough to actually get you to the point where you have a box and you can route out the position. I just freehanded the router (using a spare piece of wood to set the depth correctly), it worked ok.
Ready to route
How did I know it worked ok? After routing out each half of the centerboard and rudder, put the lead weight into it, put the two halves together, and see if there is any offset or whether the two halves line up easily. You could also potentially try and shake it to see if the lead moves around - both mine were pretty good!
Complete and lined up nicely!
Time to glue the two halves together. Put a bunch of glue in the routed out area specifically to hold the lead in place, and then put a bunch across the interior surface of the rudder or centerboard. Here’s the classic shot of my centerboard glued up, using some unopened epoxy bottles for weighing the center down and as many clamps as I have arrayed all around the edge.
Oh so many clamps
The last step, once everything has dried, is to get rid of the various epoxy drips around the edge. And nothing, and I mean nothing, is as effective at that as the good ol’ shinto rasp. Worth it’s weight in gold.
If you don't own a shinto, buy one, now.
Next up, a little garage organization followed by some jig building!