by GreenLake » Wed Oct 29, 2014 2:19 pm
Your original post was not totally clear on your intentions. But it looks like you have things well in hand.
I've found it challenging to translate a theoretical curve onto the actual blade when I built my rudder. I did make a template by printing out the curve at full size, then gluing it to cereal box cardboard with epoxy. Unusual choice of glue, I admit, but it makes the cardboard into something that's easier to cut along the line, you can even sand it. It's using the template where I think I didn't quite figure out the optimal technique.
On my next attempt, whatever that will be, I'm planning this approach. Build an epoxy sealed blank with at least one layer of glass so that it is inside the dimensions for the template. Apply a layer of fairing compound with a notched spreader, notches running down the length. The idea is that the ridges end up proud of the final profile. Before that hardens, use the template and press it into the fairing compound to get lines that are at the level of the profile. Then sand the ridges until they are flush with these profile lines. Fill all remaining hollows (grooves). Sand flush. Seal with epoxy, paint and done.
I don't think it would be much more work than "eye-balling" a curve. Especially if the trick with the notched spreader results in being able to get to the final shape in fewer iterations.
However, I would love to know how sensitive the final performance is to getting the optimal curve. Do you lose most of the theoretical performance from the first few percent of deviation, or is it much more gradual? The latter would mean that your approach would already deliver most of the benefits. I don't think I've seen that discussed anywhere. But I suspect, it's not unlike sail trim, where even small corrections can have noticeable results.
I see the main benefit of the throughbolt in reduced flexing of the CB trunk. Instead of a sideways force on the wall of the trunk, the through-bolt delivers an up/down force inline with the wall. Which it is far more able to resist. K.C. ended up reinforcing his CB trunk wall, looking at mine I just don't see the movement. Anyway, the way I have it was the way I got the boat. I'm not sure I would have made the choice retrofit it myself.
~ green ~ lake ~ ~