Kite boat foiling is fantastic


Did I mention that foiling is amazing?

Let’s call it a long weekend – hence this epistle on Tuesday rather than Monday.  (OK, maybe “epistle” is over the top…alternatively, perhaps foiling has spiritual dimensions? Amazing!)

It’s been a long time between outings on the Nacra 5.8.  You may recall that back in October, Alec broke my boat….and it may have taken rather longer than it should have to design and build new rudder boxes.  I had one or two other things on…. Suffice to say that, the new rudder boxes are seriously strong.  We’ve also added some serious steel strengthening against bending loads to the vertical foils (aluminium extrusions).  (Note the casual use of the first person plural, “we’ve also added..” – OK, I bought it, then GS inserted and put it together and did most of the rudder box as well.)

Unfortunately I have no (direct) wind data, track data or video to verify performance – that’s handy… I can make it up. 

Did I mention that foiling is astonishing?

We’d rigged an 11m, then put it away in favour of a 14 as the breeze dropped.  I mistakenly took another 11m kite out and pumped up before realising it was the wrong one – that cost us more time.  By the time I was launching the 14 from the beach, there was not enough breeze to launch.  I eventually got it up …and flew it overhead for half an hour…not enough breeze to get on a board.  Meanwhile the crew were out on the nacra on anchor waiting…where there was slightly more wind.  Eventually the breeze came back and I could kite out to the boat where the foils were already down.  Some messing around to get  on board and the ki­te attached….and then.  OMG.

We probably had a solid 17 knots for the next half hour while we kited/sailed.  PG noted that we disappeared upwind very quickly – he stayed in the support inflatable.  It certainly goes upwind.  AW, you probably recall how we were smashing the bows coming out of Wynnum into chop without the foils?  None of that yesterday!  Probably doing close to 15 knots at a very good angle upwind….The wand and heave control system on our Glidefree foils is all on the main foils – unlike moths/Waszps etc which have the sensor wand on, or even protruding from, the bow.  The bows are more than 3m forward of the foils.  So it’s inevitable that in flight upwind into chop, we’ll hit the chop…but we were generally only hitting the top of waves and quite gently?  A very comfortable ride.  Did I mention that foiling upwind is incredible?

But downwind was even more amazing.  I’ll have to work through the apparent wind angles – but we were foiling and probably doing 15knots – with the kite lines directly off the bow… occasionally they were even to windward, slightly, of our course.  I felt sure that we would run under the kite ….but never went close.  Foiling – wow.  (To you sailing techos, I know I should be disappointed that our apparent angle was, by implication of the kite position, so deep – a fast boat always sails to a tight apparent wind angle.  But the depth we were sailing, the comfort of the magic carpet ride and the stability of the kite at quite reasonable speed  were truly weird!)

During most of our flying, I was feathering the kite (ie dumping lift) so that we would keep our speed down.  With some more experience, it’s likely that we’ll get more confident of what these amazing foils can do when combined with a stable platform and a kite.  We were quite high a few times…at least it sure felt like we were high!  But we always came down very gently (this is not how I’ve generally come down off a foil board on which I’ve gone too high!)  The port hull flew higher than starboard…so we’ll change the trim on that foil slightly.  The main foils are about 700mm below the hull.  Design sailing height is 400mm.  I’m sure we’d have heard ventilation if the main foils, or rudder foils, came too close to or breached the surface.

How fast will it go?  We might have to get a crew with more _____ than me to find out.  Zebb/Ryan?  We were generally either sailing tight upwind or deep downwind – only went through the fastest point of sail a couple of times when gybing…and didn’t put the pedal down at those times.    

When we were high it was definitely lift from the foils, not heeling moment, that was lifting us – sometimes it was the leeward hull and sometimes windward.  The kite tow point was close to the leeward gunwale near the forebeam.  With the vessel flying high on the foils upwind, this would produce some heeling moment – but on a moment arm of order 1m rather than the 7m or so that would arise with a conventional rig. 

Incredible.  The theory and stability of these foils  (congratulations, again, Peter and Ian (Glidefree)) is such that we should be able to go pretty quick very safely with a kite…

Enormous thanks to GS for all the work to get this machine going – what a pleasure to work with you and see good practical engineering in action.  And PG, thanks again for the help yesterday (notice that I have no complaints about the 2 stroke outboard used to tow the Nacra out to deep water…might be worth having someone who knows about such things “on board” as standard procedure!).