Wednesday, July 16, 2008


i did a couple of maths and realised that some of my light-air trouble is possibly stemming from my technique, rather than from setup problems. (would be great if it turns out this is the case.)

Basically when i sit at the back of the boat and try and launch, i can get up to about 7 degrees angle of attack on the centreboard foil as the bow lifts up, and my boat's fat ass drags in the water. lifting off like this the wand starts moving the flap up, as the front of the boat starts to clear of the surface. in this configuration, with the flap down say 5 degrees out of 20, the centreboard Cl is 1.57 and Cd is 0.0193
If on the other hand i was to sit really far forward and keep the nose buried, i could keep the flap at say 15 degrees down, at the same stage of takeoff. in this configuration the centreboard angle of attack is 0 degrees, but with the extra flap deflection im still getting a Cl of 1.54 and a Cd of 0.0156. so this is better, same lift for about 80 to 85% of the drag. ill try it out on the weekend.

also i ripped off my crappy wand. finally. i laid up some new bits tonight that will allow me to adjust everything about the wand, and to use carbon rod and tube of varying stiffness and size. I have a choice of two wands to start with - a straight stiff one with flexible tip and a kinked, stiff one like the old prowlers, with a flexible tip as well. ill try both on saturday weather permitting. The aim of all this is to keep the flap at full deflection while the bow is within a foot of the water. the winning wand gets glory. and to stay on the boat. it is possible that they will both lose, in which case shame will be brought apon their families. and they both also die.

Saturday, July 12, 2008


went out today for a few hours to test the new modifications. conditions were like 3 to 12kts. anything above about 8 i was foiling, though probably needed 10 to go upwind and downwind propperly. everything worked well, no breakages, nothing moved at all. didn't capsize or crash, but i was playing it pretty safe. tried a foiling tack and almost threw myself off the back corner of the wing, holding onto the tramp lacing with my feet. it turns much quicker on foils!

The linkages work much better, and the rudder adjutment in particular is a massive step up from what i had. the wand vibrates when going slow, which is annoying, so ill take to it with the grinder and make it flatter on one side. also thinking about a flat surface on the end, so that not as much of it drags in the water.

i need a new sail.

im not quite happy with the angle of the centreboard. i noticed that i had the rudder trimmed back, flap up about 5 degrees, to the point where half the time it was actually pulling the transom down; you could see because the top gudgeon was touching the top of the gantry, rather than there being a small gap. seems to me the rudder foil could be smaller. before i go cutting stuf im going to make an F-box of sorts, a contraption that lets me adjust the rake fo the centreboard over about 5 degrees on the fly. also i want to put a small bulb at the T joint of the centreboard, to hide a wad of carbon uni that i will wrap around the leading edge at the T. the crack didnt get any bigger, but im not going to risk breaking this foil. so there's 2 or 3 projects to keep me busy(er).

Saturday, July 5, 2008

linkages relinked

just a quick note: the boat is nearly back in one bit again!
all linkages are now stainless, after much swearing at (breaking of) expensive taps/dyes. there is less slack and the ends are more robust, especially the new flap joint which is a beast. see below, pretty self explanatory. i think the bladeriders have a similar thing, with the benefit of having a nice thick bullet fairing to hide all the shit in. i reckon ill have to fair it a bit.
the main foil appears to be at a good angle to the static waterline, about +1.5 to +2 degrees; i think the flap was just jamming in the 'up' position after the linkage broke within 10 seconds of leaving the ramp, giving me that 'sucking' feeling. also theres a 10mm long crack at the t joint of the new centreboard, not sure if its superficial or not. im keeping an eye on it. be sailing soon, should be interesting.