Gestalt said..
a cambered sail will help in gusty wind once planing because the sail keeps it's shape through the lulls.
the simmer mast is not ideal for the north sail. the simmer mast is heading towards flex top and north is pretty much middle of the road constant curve. for lighter wind its beneficial to have a tighter leach to induce more power in the sail. a flex mast in your sail will allow the head to lay off more.
sounds like a mast issue to me.
you either need a north mast or similar constant curve mast and rig to the dims or you need to rig the sail by eye to get it right on a simmer mast. you can't use the figures written on the sail. the etype is not a flat sail and if it is rigged flat then that is a sign all is not right and why you lack power.
try letting the downhaul off an inch or 2 and give the sail negative outhaul and then go sailing. if the sail feels very heavy then give it a cm more downhaul. set the downhaul for comfort when you are sailing.
in light winds rig your boom about nose/eye height and run longer lines. try 30in as an example. if you find you are kinda getting going but the nose of the board just won't break free then lift your boom 1cm and try again.
freestyle sailors use 5+m sails in 15 knots and plane with 20cm fins. it is very possible.
next is your board. maybe a wider board will help. how much do you weigh?
correct stance really helps to get going in light winds. hang off the harness lines to get going. pull down through the boom. it's best to not be a passenger and hook in and hope the wind does the work. don't hop in your straps until you are planning.
if you are 120kg + then yeah you need a bigger sail but try the other stuff first.
I'll try not to turn this into a.
"How's my rigging?" thread, but since its already headed down that path, and it's made me rethink what my aim was, I may as well provide some feedback - and who knows - one day it might be useful for someone else doing their own research.
Gestalt - I think you might be on the money.
The 2015 NorthSails catalogue says Simmer
is compatible with North - so I just assumed it was
'perfectly' compatible - but it may only be compatible to a degree. I'm pretty sure the 7.3 and the mast are the same vintage.
What's confused the issue for me is that my North Natural 6.2 (2012) seems to rig really well on exactly the same mast (460 CC Simmer SC3) and just seems to have heaps more get up and go - in not that much more wind - and that's why I expected the newer NS 7.3 to kick in to action earlier using the same mast.
So yesterday, I did what you recommended:
Winds: 13 gusting to 16 knots (on average) - very light conditions.
Rig setting: Minimal DH, neutral to negative OH, boom up 2 maybe 3 inches higher than normal (felt too high, but I left it for the experiment), Harness lines set at 31-32 inches.
Unfortunately - it was again an uninspiring light winds outing, no straps required - feet positioned forward to even out the weight, pumped and beared off where I could.
Apart from a handfull of short planning bursts through some of the higher gusts on a broader angle - the rest of the time was easily sub planning. Sea state was still a bit lumpy from the blow the day before - so not as flat as it could have been - which probably didn't help.
Due to minimal leech - the sail felt quite heavy. At the end of the session I applied more DH - loosened the leech and it obviously felt lighter - but certainly less power and the day was over anyway.
One thing I'm concerned about (even with minimal DH and minimal OH) is the battern overlap over the mast - I'm not sure that it is enough. It doesn't take much effort to flick the battens around - I would have thought that it would be much, much harder at the minimum settings. (Battens are tensioned to flattened out wrinkles but avoid over tightening.) So yeah - I think the mast is having more of an impact than I gave it credit for.
Something else I noticed. the bagged out sail touches the boom on the leeward side - and touches by quite a bit. Could this be hampering its shape and therefore its ability to extract that low wind power?
The boom is 160-210 and looks like a 'new-school' shape. The sail is approx 204cm boom length, but just because the boom fits, doesn't mean its the right boom shape for the sail. (see pics below)
I'm now thinking my next investment is not a bigger sail (or different board), but more likely a new boom (...and possibly mast!).
Once I do a few more rigging tests, I'll provide an update.
