Last week I done back to back sail test in light winds ,I really can't decide which has the better power
a 2 cam sail or a 4 cam sail .
for sure the 4 cam is has better top end but down low was similar .or am I imagining it .?
theoretically more cams mean a more forced aerofoil shape/wingshape which resists backwinding and allows to sheet in tighter and forces the sail even more to become wing-like and generate power via lift as opposed to drag. This is obviously very desireable when you boost the lift further with apparent wind by going fast.
At slow speeds, especially reaching downwind you operate the sail more in drag mode so less cams will be better. In fact going on a dead run downwind course where the sail is in 100% drag mode doesn't even work on cammed sails as they often wanna rotate out of that position whereas vintage sails are so drag-friendly they really like going on slow reaches downwind and actually feel good to use.
Many years ago I was doing a similar test but with cams v non cam.
found it really came down to which sail could be rigged with tightest leach which in most cases was the no cam version. Plus the weight savings in the larger sized no cam and softer shape meant earlier planing and easier pumping onto the plane
however,
as soon as you plane into a lull the cam sail leaves the no cam for dead because it maintains shape.
On Lake George in marginal conditions, my observation and experience is that 4 cam sails are faster than 2 cam and no cam sails of the same size.
Define power.
there's a lot to consider. Does it mean the ability to get going? Does it mean the ability to keep going through a lull? Does it mean max speed on a deep angle? etc
each one will have a different winner.
Select to expand quoteSubsonic said..
Define power.
there's a lot to consider. Does it mean the ability to get going? Does it mean the ability to keep going through a lull? Does it mean max speed on a deep angle? etc
each one will have a different winner.
Good question .no reaching .point to point .wind was up and down 12-15 sometimes 11 knots .First hour I Had the M3 8.6 ,Severne made a tear in it ,had no tape ,so rather than keep sailing I went in and changed to the Ezzy 8,5 Lion ,both seemed similar in power but the power band was different on the Severne in areas .But in that wind strength the Ezzy seemed quicker to plane .it was hard to judge which was the winner 😐.with the bigger luff pocket on the SV I would say made it the winner just to stay planing longer ,this could be because of the extra speed it gained in the top end ,both where rigged on the same 490 mast 100% Duotone .both had good power .So yes you are right it came down to speed .popping on the plane Ezzy seemed better .still on the fence .
I find the Severne Turbos have a better bottom end than the Motos and Machs ( Prob Mach3 is my newest? ) .
For bearaways and control the Motos and Machs are better, but you need decent consistent power. I get annoyed at how gutless they are in iffy lighter winds and definitely wouldn't use them in lake chop. The big luff tubes take in too much water and weigh too much for this little black duck. 🙄
Select to expand quoteKit3kat said..
theoretically more cams mean a more forced aerofoil shape/wingshape which resists backwinding and allows to sheet in tighter and forces the sail even more to become wing-like and generate power via lift as opposed to drag. This is obviously very desireable when you boost the lift further with apparent wind by going fast.
At slow speeds, especially reaching downwind you operate the sail more in drag mode so less cams will be better. In fact going on a dead run downwind course where the sail is in 100% drag mode doesn't even work on cammed sails as they often wanna rotate out of that position whereas vintage sails are so drag-friendly they really like going on slow reaches downwind and actually feel good to use.
Ummmm...a shape can't really force a sail to "become more wing like", and there's no such thing as generating power via lift as opposed to drag.
Even if we assume that a "wing like" sail is one with a double surface then the presence of cambers has nothing really to do with it. Resisting backwinding by forcing a sail into a certain camber isn't really a thing in light winds, and if the angle of attack is wrong then having a "force' shape will do nothing. Either you will be under-trimmed or over-trimmed and stalling, and having a rigid shape won't effectively change the way the wind flows over the sail.
Generating "power via lift as opposed to drag" isn't really a thing in aerodynamics, unless you are talking different angles of attack in which cambers aren't really relevant. There can be high lift sails and high drag sails, but any sail that works must be creating lift (as some aerodynamicists use the term) and all sails must create drag unless going almost straight downwind. The aerodynamicists use the term "lift due to drag" because you can't really get one without the other.
Select to expand quoteGestalt said..
Many years ago I was doing a similar test but with cams v non cam.
found it really came down to which sail could be rigged with tightest leach which in most cases was the no cam version. Plus the weight savings in the larger sized no cam and softer shape meant earlier planing and easier pumping onto the plane
however,
as soon as you plane into a lull the cam sail leaves the no cam for dead because it maintains shape.
That may depend on what non cammed sail you're comparing with. Aerodynamically, the position of draft should normally move aft in light winds, so a sail that maintains the right shape for a gust will lock it into the wrong place for a lull.
Boat sailors have much more ability to change sail shape than windsurfers, and the good professional sailmaker/trimmers don't try to make sails maintain shape. Not only that, but guys like Mark Drela, world record holding aerodynamics professor/foil designer from MIT, say that the way a boat rig can change sail shape (not maintain it) as they move from gust to lull is the sort of thing that aircraft wing designers can only dream of.
