Friday, June 14, 2013

End of Bilge Board Saga ..... For Now

Boards are done and installed in the boat.  As an experiment, I decided to foil shape just one board and leave the other flat and square edged.  The plan is to record a bunch of GPS tracks of Egret's tacking angles using each board and compare the results.  It will be interesting to see if there is any measurable advantage to the shaped board.

 Trailing edge epoxy pour.  Since the volume was pretty high I filled the trailing edges in two pours to prevent a runaway exothermal disaster.  Even so, the epoxy was too hot to touch.

The pivot pin and pennant holes got filled and re-drilled.

In the spirit of gettin'er done, the board pivots remain as originally designed with new 3/4" bolts.  This is what $40 of 316 SS looks like.

I used ply templates to get a consistent shape to the leading and trailing edges.  The templates are based on the shapes I used when building the Goat Island Skiff.  Since water flows diagonally across the boards I marked off guide lines and aligned the template parallel to the water flow, in theory...

After laying out appropriate guidelines I used the plunge router and fence to cut progressively deeper grooves in the leading edge.  These grooves act as guides for the belt sander.

When the grooves disappear you are done sanding.  Takes a bit of finesse with the 36grit belt.  Minor imperfections were filled with a final skim coat of thickened epoxy.

  Same deal on the trailing edge except the guide grooves are further apart.

Almost there.

Not too shabby.

Done except for final skim coat.

Comparison of shaped and unshaped boards just before installation.  The leading edges are facing up.

Looking down on the trailing edges.


  1. You will be a "machine" up wind now... :-)

  2. Simon, you've got an impressive idea of "git'erdone." If that shaped board isn't faster, I'll eat my (key)board.


    1. You may want to start looking for a nice keyboard seasoning. We did not spend any time doing careful testing but just sailing around I did not notice a significant improvement. Then again .1 kn is a huge difference in racing but not noticeable just sailing around.

  3. Simon, did you get any good data on your sail around the IRL yesterday?

    - Tim Webb

    1. Did not record any real data. Just a couple GPS tracks. They don't look good. I just found a GPS app that records speed at track points so will be able to plot speed vs tacking angle in the future.

  4. Nice job. If you don't get additional upwind performance or speed, don't despair for I'm sure you have achieved some level of low-speed maneuvering performance, which is where I really find the foils shine. What's the rudder like?

    I love how the Goat can peel off a dock at minimum speed/no momentum and maneuver out with grace, upwind, rather than cursing and frantic fending off.

    1. No despair. The boards needed to be fixed whether I get better performance or not. The rudder is typical sharpie super low aspect ratio. Same construction as bilge boards. Egret has a very large weather helm angle so there is room for improvement.

      Yes love what the Goat can do at low speed, in close quarters. Unless a gust comes as your sheet tangles ......

    2. I don't know what you're talking about. Mess in the cockpit? Never.

    3. Smoke in the cockpit? Often.