Bladerider Foil Mods

I’d like to get a new set of foils for MB1, but I can’t quite justify that expense at the moment.  That being the case I looked at my current foil package to see if I could modify it to improve the overall performance.  I’m currently running a home-built front foil designed by Gui and a Bladerider rudder foil.   I’ve considered cutting the tips of Gui’s foil, but I’m not going to go there quite yet.  That leaves the Bladerider rudder. It’s clear that the current trend is for symmetrical rudder foils and the stock Bladerider foil is far from symmetrical.  I looked at the foil shape and decided that it should be possible to make the foil more symmetrical by modifying the trailing edge.  Below is a typical NACA section that is pretty similar to the Bladerider rudder foil.  This foil really has a lot of ‘flap’ which can’t be very fast for high-speed sailing and probably produces a lot of drag at all speeds.  The red line shows what kind of section you’d end up with if you removed part of the trailing edge.  

 

This section looked quite a bit better to my eye so after a bit of checking to see how much carbon was in the trailing edge of the foil I simply took a large file and removed about 3mm of the trailing edge.  Then I thinned the bottom side of the edge to remove more of the ‘flap’ and repainted it.  What I was left with was a foil that still isn’t symmetrical by any means, but it is far more symmetrical than it used to be.

So far I’m really happy with the performance.  It may not have quite as much low-speed lift, but also seems to have less drag.  The largest benefit I’ve seen so far is that I don’t need to adjust the pitch of the rudder as much when going from an upwind mode to a downwind mode.  Previously it felt like I needed to decrease the pitch on the rudder when going downwind to keep the boat from getting uncomfortably nose-down and then increasing the pitch again when I turned upwind.  Now the boat feels much more stable in pitch on all points of sail.   It also seems like the foil is less prone to cavitation.  So should you take your stock Bladerider foil into the shop and grind it down?  I’m not going to go that far yet, it could turn out that grinding this much off the trailing edge weakens the foil, but I do think it improves the overall performance.  So if you have an old Bladerider foil laying around that you don’t mind breaking, it’s may be worth the 30 min it takes to modify it.