Devotti Single Hander

a traveller isn't essential the laser gets by with out one and the mustoskiff has a strop too, but there are times when the mainsheet tension and boom angle could be improved with a traveller which I guess your trying to solve with 2 strops on a blaze but I still think a traveller is better quality. on a finn if you need to point a little bit higher to hold your lane you can pull the traveller up a few inches or drop it to foot, I guess you can pull harder on the mainsheet to do get more height but its not the same.

Originally posted by sten its common to single handers,  centred mains are for boats with jibs. if you had the boom cetred on a single sailed boat it would stall. a jib helps keep the flow and you don't want to chock the slot with the main too eased.

That's quite interesting, I need to know why that is now..

I'm not disputing it, bowing to your experience of single handers.

It's just not the case with boards, you sheet it to the centre line or go
nowhere, in fact oversheeting can also have its place.

So what is it about a boat I wonder.

I thought it might be to do with those old school low aspect long boomed
sails, I can see them stalling, but as it's you saying it, then it must also be
true of the Musto..

I can understand it if you have a bit of way on and it's breezey, but are
you maintaining that even in lightish air you don't cross the centre line
with a single hander?

I vaguely recall a diagram that showed that the lift from an airfoil section is at 90 degrees to the 'flat'
surface (stop me if I get too technical here). So if you put your boom on the centreline then, if the book
is to be believed, the force will be at 90 deg to the direction you want to go and will all get soaked up by
the CLR.

But I'm not entirely convinced by this explanation. Anyone got a better one ?

Originally posted by Mikey 14778 I vaguely recall a diagram that showed that the lift from an airfoil section is at 90 degrees to the 'flat' surface...

Its a useful approximation for most purposes, but inevitably its gets a *lot* more complicated than that!

Sten has it right on there - on a board the sails are inherently more twisted so up from the foot of the sail the chord line as you move up its height will be at some angle of attack - also true about effectively sheeting out when the sail is pulled to windward, provided it is raked aft, else the converse is true!

 

 

With jib headed rigs the jib lead is always off CL, jibs when sheeted in are not very twisted until its windy. booms are sheeted at or close to CL largely to keep the slot geometry right, plus mains on jib headed rigs are usually a fair bit more twisted than unas like the laser/finn/d1.

The optimum amount by which the sail is off CL is a function of the aero and hydro drag angles (see aero/hydromechanics of sailing by marchaj, or sailing yacht performance, same author). These angles being essentially a measure of the efficiency of rig and hull/foils. So an IACC yacht or some of the TP52s sheet as close as 5deg I believe (big, slippery yachts, big, flat sails, very efficient appendages) The laser is at 9deg when sheeted to the corner I think, doesn't ever like coming much further inboard than this, likes to be sheeted further out in breeze. Finn similar. D1 prob too. All of these go upwind with well sheeted, very untwisted leeches. Most dinghy jib fairleads are around 7 to 11 deg ish off CL. Conversely an oppie would porobably be sliding sideways a fair bit at 9 deg since it is not the most efficient package.

Basically if you sheet too far inboard (sail higher than max VMG angle), you won't be able to sail as fast, there will be less water going over the foils so (assuing same righting moment, hence sailing sideforce) they'll be operating at a much higher lift coefficient than optimum, and the induced drag will be too high.

Conversely if you're reaching around at lower than opt VMG angle, more water will be going past the foils, lift coefficient (for equal RM) will be lower, such that you're suffering from having too much skin friction from the excessive wetted surface relative to the smaller amount of induced drag due to the lower lift coefficient.

Try out sten's traveller trick in the laser to experience this in real life.