Going down the mine ...

Jim, is it fair to paraphrase your original conclusions as "the combination of bow up trim and mast rake enables both spinnaker and mainsail to create a lifting force" BUT that the spinnaker is most definitely pitching the bow down".

Sounds coo. But wouldn't the forces be developed along a vector that is dependent on the measurments such as luff rake/bowsprit length etc? If you had enough rake on the luff (ie enormous pole) wouldn't that create vertical lift enouogh to compensate for the pitching moment?

The Rs and 12s do sail with the bow up more than any other class I've ever seen, with a strange-looking lifting motion that makes them seem to float up over the troughs, so doesn't that indicate that the long pole does lift the boat?

Secondly, the 12 guys say that a couple of seasons ago they went to more "dangerous" kites, ie ones that lifted less - which indicates that kite shape influences bow lift. I think the change was to flatter head sections which possibly had the effect of reducing vertical lift in the head?????????????????????????

Obviously the lift is NOT enough to require guys to trap forward of the shrouds, but it may still be there. I can't think of another reason why 12s and Rs have the distinctive bow-up angle downwind (OK they are short and light compared to a 14, but is that all there is?)

In boards (where the raked rig seems similar to a kite, with the uni taking the role of kite tack, and the sailor's feet acting as mast/stays and sheet) the vertical/bow lift seems to be clearly related to the fore-and-aft rake. Obviously there IS that lifting-but-pitching effect you refer to (if I read it right) but when the rig is raked back, the lifting effect seems to become more pronounced and dominates.

I'm not questioning (I hope) the work you and Mikko did which is way above my head, but wondering whether the effect and results would change if you put a 12-length pole and massive kite into the equations.

Originally posted by Chris 249 In boards (where the raked rig seems similar to a kite, with the uni taking the role of kite tack, and the sailor's feet acting as mast/stays and sheet) the vertical/bow lift seems to be clearly related to the fore-and-aft rake.

I don't see how a board sail is anything like a kite. A kite can develop lift because of the part billowing out near the head. A board sail is more like a main and is almost invariably sheeted well in. Boards go "nose up" because they plane easily and furiously, not because the sail is lifting them. Jim's document shows that the lift a Cherub rig develops comes almost entirely from the kite, not the main.

I used to race boards so I have some direct experience here. You do not feel the rig lifting upwards. It pulls sideways and forwards.

Edited by Stefan Lloyd

The kite lifts the bow. But when there are waves the kite makes you go much faster and more likely to plow into the wave infront, so in windy wavey conditions it much harder to fly the kite, without stickin the bow in.

I agree a board sail can generate vertical lift if pulled over to windward. In racing, you don't normally want to do that; you want to keep the rig vertical. That, anyway, is what the RYA coach taught us!

Sheeting out will evidently slow you down, unless you were oversheeted in the first place. I suspect sheeting out to avoid jumps is as simple as that.

"The FW guys always seem to say (IIRC)" - sorry but I don't know what FW or IIRC mean.

 

chris 249, yep wave sails are flatter, and what you have said is true, however wave sails tend to be flatter as they are used in higher wind conditions. cammed sails have little cams (like teeth) that go round the mast these make sure the battens stay behind the mast creating the curve in the sail in any wind therefore they are quicker than rotational sails (wave/freestyle etc). however due to the cams they have larger luff tubes and are therefore a lot harder to waterstart.hence in waves you need the ability to get up and going quickly with a light sail for throwing around etc.

If you jump and bring the rig to windward you begin to create the lift hence the bigger air time, plus it is quit often done so that u are ready for the landing when the fin bites back in.!

with forward loops (i can do em - great fun!!) youre actually going forward and around so the sails CofE is goin forward and to leeward - it is only the top guys in big waves that can do end over end forwards!!

hope something made sense


Edited by ssailor