Nacra 15 FCS for fun

[martin 'hoff]

Now one thing I'm picking up is different between your NS DS and the official one is that yours doesn't conflict with the standard boom fitting. Is that right?

The 'One' DS mainsail
- has a smaller head, and smaller overall size than the standard main, and much smaller than the NS
- looks to be cut deep at the luff - similar to the standard, deeper than the NS
- needs to have the boom fitting removed :-/
- less power in light air
- probably easier to right solo

 

[PitPater]

Hi Martin

You are correct, it started out as being one for soloing and ended up being a full size decksweeper (which I prefer in hindsight...looks like it has more sail area than my regular main as well, definitely flatter though). I believe they modeled it off their F18 DS cut, additionally I was able to feed them photos and measurements of the lower mast area of the F15 so they made some modifications there as well (at bottom the DS sail is angled slightly upward toward the mast to go over the mast rotator when its angled downward). I have two boom fittings I can use, the lower one or the standard one (probably try them both out to see if there is any actual difference) ... no real interference though with the current boom fitting so no need to remove it), they also have a velcro strap loop on the tack of the DS so that I can pull the sail back toward the mast as need be (that helps with any interference issues, as well as it allow us to tension the bottom portion of the sail if need be).

It will probably be a bit of a work in progress as we start to use it, but so far alterations made from the first fitting have worked well (Ken and your point about not capturing the clew on the boom was correct now I think about it, originally it came without a strop in the clew and I made them put it on thinking it was supposed to be captured by the boom...they probably knew it wasnt). Anyway they have been very good to work with, going to feed them video of the sail in action so they can see if its doing what its supposed to be doing...we will probably make a few more mods over the winter months to fine tune the fit a bit ... but we will see if thats even necessary based on what happens when we load it up

 

[Kshack]

Decksweepers get their power lower in the sail than we are used to looking at.
Make sure you don’t just crank on the outhaul too tight. Don’t want the sail bending around the boom, but don’t want it more than an inch or two from the boom. May need a little piece of bungee from the boom to diamond wire to hold the boom horizontal.

 

[PitPater]

Thanks for the info Ken, definitely a different animal than I am used to. Original wind forecast was supposed to be for 10 - 12 knt tomorrow which would have been ideal for a first run with it at foiling speeds, but I see that prediction has dropped to 6 knts...looks like there will be nothing substantial until the weekend, hopefully they are wrong as usual

As to trimming one of these things, any thoughts...as indicated right out of the gate it looks quite a bit flatter than my normal sail..less cunningham required with these?

 

[Kshack]

Possibly bring rotation back more than standard sail, if you need downhaul. That will flatten the lower sail more, and that is where there is more power. Top already has less sail area. I usually trim to the top tell tails. You can try less spreader rake or less diamond tension to get a fuller sail.
I can take a look when I’m up there.

 

[PitPater]

We took it out yesterday in somewhat less than ideal conditions 10 - 12 knots of wind which weakened to 5 - 8 knots after about 45 minutes. Did manage to get up on the foils for a couple of downwinds. First impressions

1) Not capturing the clew on the boom and adjusting the outhaul as suggested by Ken and Martin made a huge difference in the sail shape, it was definitely restrained on the boom when it was captured.

2) While I have no proof, more instinct than anything, the impression was that upwind boat did not heel as much at a given speed. That is to say I felt that we should be heeling more when we hit around 10 knts of boat speed, and because you wernt heeling as much your brain seem to think that you wernt going as fast, yet the GPS told a different story...have to say it was wierd feeling

3) Boat appeared to tack and gybe faster and smoother than with the regular sail, again its an impression nothing you could measure

4) The boat appeared to be foiling more stably in these low wind conditions, usually we are chasing the wind and the apparent wind more at the lower wind range

5) The cut of this sail appears to be done extremely well, once the sail was in its uncaptured state it was easy to trim it from top to bottom, very little tweaking required (at least in these conditions) compared to the regular mainsail

Beyond that it is hard to put any quantitative assessment to it. Crew movements during tacking and gybing are going to be interesting in higher winds there is definitely a timing thing that needs to be worked out there

One observation was, that at times when dousing the spin there wasnt alot of crew room available on the starboard side due to the curvature of the DS boom, while we probably just need to get used to it is there any reason the boom cant be on the port side of the boat to free up space on the starboard side of the boat, my boom fitting on the mast is centrally located so rotating the boom over is all that is required.

Below is a bit of video from the first downwind foil with the DS, probably doing only 12 -13 knts boatspeed, given the low wind conditions it was surprisingly stable (almost casual) and as the wind dropped we seemed to be able to keep the boat up on its foils and skimming at boat speeds down to about 10 - 10.5 knts, while it will take more outings to gauge performance better I do think we are getting more power at the lower end compared to the regular main ... just an impression...will have track it with the Atlas and compare it with earlier runs in similar wind conditions. Going to interesting to see what this thing does when we get up into the 12 -14 knt windspeeds and above.

 

[martin 'hoff]

Sounds like you're reporting more power, lower CoE. That's great!

 

[PitPater]

Certainly feels that way upwind, need a few more outings to really tell for sure

@Kshack: Will see if I can out to Jericho on the 18th in the morning before you guys go out racing, got to go to a celebration of life for a friend of ours son who died in a climbing accident in Squamish on the 17th ... sad story that one unfortunately

 

[Kshack]

Sorry to hear about your friend.
Sunday would possibly work better because we drive up Saturday and things can get hectic.
Main reason for boom on starboard side is for starting watch. Otherwise either side works equally. What you are reporting is classic. More power down low results in less leeward heel and more stable flight.

 

[PitPater]

Had two days of 18 knt gusting to 24-25 knt....1st test of decksweeper and new North spinnaker under these conditions. The decksweeper definitely has some different characteristics in this wind than the regular main, took a while to sort out the right main setting under these conditions to get stability, it feels like we have more acceleration up to top speed...boat isnt waiting for us to get our shite together before it takes off...bit unerving at these speeds. Hit a new speed record downwind of 21 knts, I am thinking we are probably getting close to the max foiling speed limit of the boat (25 knts??), start to get some good vibrations and cavitation when the foil wash comes down on the rudders.

Martin, how fast have you had yours going? Noticed the N17s dont seem to get up over 25 knts (maybe now a bit more with the rakeable rudders?) think it must be a design limitation with the current Z foil design .... not that we need more speed!



Also felt the North spinnaker was a bit more stable in the higher wind range (we tried the Nacra one on one of the days and North one on the other day). North spin appears to be slightly flatter and longer .... nose of the boat seemed to stay up better, also could have just been slight differences in the wind and wave conditions. Loads in the snuffer bag a bit nicer with 3 spin take downs as opposed to the 2 on the nacra sail

 

[PitPater]

On both days we managed to foil upwind and to catch this holy grail moment on film. We are however stumped on what to do when the leeward hull starts to rise suddenly (aside from not letting it happen) as we did at the end of this video, nothing we tried (going up, going down, combinations of tightening the main, loosening the main etc) seemed to work aside from getting inboard as fast as you could ... managed to get up into the high 15 knt range at times...new speed record for us upwind

 

[Kshack]

Let your rotation off downwind. Your mast will last longer.

 

[PitPater]

Noted...shock cord on mast rotation line is too short and it cleats not allowing full rotation...needs re-adjustment...on my to do list

 

[martin 'hoff]

Cool vids! Quick notes
- impressed you guys are going so fast so soon. I think we've done 23-24kt for brief moments (but our speedpuck only "remembers" peaks lasting a couple seconds, and our other GPSs also do some smoothing so the most we have gotten from GPS tracks is 22kt).
- yes the mast rotator, in particular in a blow - you don't want to snap the mast so early - you can uncleat the line on the rotator itself, that's what's usually done right before hoist - fingers between ring and cleat
- in that big windy downwind I would recommend to trap way lower for RM and safety, stretch out, and have helm and crew a little bit further forward - coupled with more lift on main foils. the result is more constant pressure on the mainfoils and a much smoother ride.

 

[martin 'hoff]

We are now deep into training for Nationals so now with the C boards – slightly different set of skills. Here's a fun downwind in mild sea swell, 10-12kt https://gopro.com/v/36n7kOqErodgk

 

[PitPater]

Thats a great video Martin, clearly know who is wearing the captains hat on that boat....me thinks he is going to be a force to be reckoned with...probably find yourself into an N17 sooner than later. Interesting strategy to fly slightly nose up to avoid a pitch pole, that boat is still flying along at a really good pace with the C boards

Oddly I agree we do need more lift...although we were up to 3 in 18 knts, but it does seem to fly more stably with more lift, just hard to get yourself to dial more up as the boat really pops up its a bit un-nerving... hard to get down lower on the trap as we are probably still chasing the wind a bit more than we should be so the boat is rolling side to side....the stalls and subsequent falls seem predictable which has been a saving grace

 

[martin 'hoff]

lol thanks for the kind words. And yes, the young skipper drives with confidence.

WRT the lift, maybe keep the rake or a small nudge extra (3.5). The key thing is that at speed it should support a bit more overall helm+crew weight forward, so it's more stable.

Going back to the video – I don't know if you watched the second leg. It opens with us going in a comfortable angle to the waves. Then we gybe and we're going across the waves - they aren't too big, nor the conditions too taxing, but we'd still pitchpole by digging the bow into the next wave. The technique we were discussing there is to head up – go hot – so that you get an angle on the wave, and hit it with the side of the bow instead of the sharp end. Hot enough you think you're going over – as long as you get the nose over the wave and bear off, you're fine. May involve an ease on the spi.

Easier said than done.

In any case, I'm hearing that that works also in choppy conditions, semi-foiling, with the FCS kit. I think it's the technique on display at the medal race in Tokyo 2020 - https://olympics.com/en/video/men-s...cra-17-medal-races-sailing-tokyo-2020-replays
(actually the medal race had nice conditions - there were earlier races in Tokyo where I think I saw this).

 

[PitPater]

No question lots of confidence there, good to see

Actually now you mention it I would use a similar technique with the H16 on bigger wind and wave days, as jabbing a Hobie hull into a wave was not something you wanted to do on a regular basis given it propensity to dig in

Below is some of the drone footage from the other day, between the drone and the sunshine it makes it look like it was a serene day out on the water, it was anything but...wind was in the 15 knt to 18 knt range and gusts in the 25 knt range, wave state was actually pretty good not flat but not big or choppy either. The wind was steadier and stronger further upwind and out, while downwind and closer to shore the wind was gustier and came in squall like waves...which is where we had to be to stay in contact with the drone. Not one of our prettier days foiling, seemed to be all over the place downwind and probably the most banged up I have been on the boat all season, did get some better upwind foiling in at times...hulls were buried up to the crossbar at times after the hoist as the boat just started accelerating with nary little time to grab the spin sheets and jump on the trap. Video does show the magnitude of the hull drops a perspective which you dont seem to get with the GoPro footage. Day before was similar except the wind was probably stronger and steadier on average...didnt seem to have quite the same stability issues. I am sure part of it is learning to trim the new decksweeper in these conditions

Downwind



Upwind

 

[martin 'hoff]

No posts in a long while bc we've been training on C boards for Nationals which just finished. Great event.

We might switch back to Z foils. Had a chance to talk w folks in the know, and no plans for rudder differential for the N15. We might have to test that g10 plate experiment @PitPater .

 

[PitPater]

No posts in a long while bc we've been training on C boards for Nationals which just finished. Great event.

We might switch back to Z foils. Had a chance to talk w folks in the know, and no plans for rudder differential for the N15. We might have to test that g10 plate experiment @PitPater .

Hi Martin

How did you make out at Nationals? What did you come away with learning wise?

Yes not much chance Nacra is going to make a big effort at this point to give us raking rudders unless the class goes fully foiling and I guess there is not a push at the N15 grass roots level to go that direction because of safety issues? Have started to draw something out, definitely looks workable ... will send you something across in a week or so

Mostly solo sailing lately, finally got the nerve up to hoist the spinnaker in more than 12 knts ... not as bad as I thought it would be, definitely more stable with the spin than with just the jib

R