Hydrofoil Project Notes January 2010

At the start of the season Merde exploded their rudder box and pulled both the front centrecase struts off the X frame. As it hadn't originally been built with foiling in mind we weren't really surprised that some things broke. Merde is probably the lightest Woof built and really didn't need much work at all. It definitely seems robust now and the few modifications necessary have given us a good idea of how much strengthening the older boats really need.

Wands and control systems

David implemented a tension based wand control system on Merde, using spectra, bungy and a couple of blocks. It seems to be working pretty well and will certainly simplify retrofitting foils to some of the older boats.

TheVirtual has higher gearing than the other boats and we found that as the boat went faster the wand was bending and reducing the ride height, Merde had a similar issue, so both boats added some uni to the wands. This worked well at Charteris Bay for TheVirtual with really smooth rides and much better height control. As the issue wasn't entirely resolved a second layer was added during the next week. The next time out, with the kite in 20kts and large seas, the cable was loaded up too much and bent. As L3 had already had a couple of cable failures, we decided to swap it all around to use the cables under tension rather than compression. This combined with the more rigid wand has resulted in an improved the ride, especially downwind. On 19th December we sailed in a classic 25kt NE and the boat handled really well both up and downwind. Downwind we went through the tops of a few of the larger waves as the boat didn't climb quite fast enough to clear the crest. Going through doesn't slow the boat down too much and is preferable to having the foil break out the other side.That only happened once, on a steep breaking wave, and very nearly resulted in a capsize. Sailing on foils in those conditions wasn't as difficult as we expected.

Since the Charteris Bay races at the end of November 2009, TheVirtual has been using a curved paddle (oblate section) on the wand. Prior to that a flat batten end was used, the new paddle tracks the surface more accurately and is more responsive in a big chop. Merde is now using one as well.

Sean has extended the prototype rudder vertical which was too short and was resulting in wipeouts at inconvenient times. They've also changed the wand system around as well to be tension based.

Retractable Foils

TheVirtual sheared off their main foil at the T hitting the mud at Charteris Bay, and another couple of boats have touched Granny's Rock launching at low tide. So far Merde is the only boat with retractable foils. They seem to work relatively well, but in a big breeze launching in our constrained facilities can be a challenge. I think a few more boats will implement them, but only use the facility on very low tides. The boats are still launched on their sides, this is because none of the boats have cradles that will work with foils retracted and we don't have a suitable floating pontoon from which to drop the boats. So you still get almost as wet launching and retrieving with retractable foils.

Working Sails

On TheVirtual we were in the fortunate position of having sold our old rig just prior to getting the foils up and working. This meant we were able to get a set of sails built which would be better suited for foiling. With the new high modulus 50mm mast, we went for a flat high aspect main with a big low drag roach profile. Jib flat with a slightly larger head than usual. As is fairly common, the mast has a stump (400mm in our case) which means we can reef by just removing the stump, zipping up the bottom of the main and shortening the rigging. This means the top of the rig still works properly.

The new working sails seem good and we're pretty happy with them. L3 also has a new set of sails as their previous set was getting pretty tired. They've opted for a slightly bigger head on the main and a smaller jib. Unsurprisingly all the foiling boats are reefing down a few knots earlier than the conventional R's due to the higher apparent wind.

There are a lot of improvements that can be made to the rigs, but that's for the future.

Downwind Sails

We've found that we do need a kite to be competitive downwind. On the one occasion we sailed a conventional R alongside a Bladerider (in approx 12kts) we found both boats sailed at pretty much the same angle and speed. In most conditions the R is underpowered without a kite. Boats with kites can sail deeper and hence get better VMG. In 25kts in big seas two sailing downwind on foils is nearly as quick as with a kite conventionally. A kite does make the boat easier to sail and more balanced. However, hoisting a medium size kite while foiling in 25kts with big seas is a bit tricky.

The conventional kites don't seem to fly very well as they're too full and prone to collapse. The foils provide plenty of lift, so mining isn't really an issue anymore. This opens up a new range of options for kite shapes. Phil Auger has just built us a flat Screecher. In the first test in under 10kts it showed promise, being quicker than a larger conventional kite. Unfortunately the second time out 10-12kts there were no other boats around, but the kite was quick. The Screecher makes it easy to keep the boat on foils when gybing and we found we were able to sail deeper than we expected. We're looking forward to trying it out in more breeze and in races.

Hydrofoil Construction

Sean has build another set of foils to replace the prototypes, and he's currently finishing off and fitting them to the boat. Steve MacIntosh and Tony Park have started building their foils: it'll be interesting to see how much impact the foils have on a 1995 hull and rig. The other two sets under construction are progressing slowly due to James' and Doug's other commitments.

Future

There is still a long way to go with optimising setup, tuning and systems. The guys just about to come onboard will be able to get up and running with a lot less hassle than the early adopters. Using their own ideas to build on known good setups should enable them to get quickly to the front of the fleet. Hopefully by the end of the season we'll have seven boats on foils here in Canterbury. Its definitely a great time to be sailing R's.