Daggerboard - use of?

Originally posted by mike ellis but how much did you fall to leeward of them GRF?

Well you don't actually drop too far, and it only works when you've got a big
course with wide corners, don't go trying it on a lake. You're just playing the
same sort of angles as you do downwind, shallower faster, you just have to
develop a sort of instinct for when it will pay to go wide fast and low, as
against high and narrow. We're finding new stuff out about this boat all the
time, just how many of our windsurf skills are transferable and we had a
nice long beat on Sunday and we had a bit of a lead worth risking an
experiment on with the plate.

Originally posted by redback If we were a slow boat the slight leeway might be of benefit

Note that this has stopped being a beginner response in any shape or form - Sorry!

I'd need to see some measured data to be convinced this isn't a myth. A board needs to be sized for the worst case situation, which is coming out of a tack at slow speed with maximum side force and minimum flow over the board. The actual amount of area you need running deep in the light is tiny by comparison.

And then consider what actually happens if the boat were to be making extra leeway, which is really just having the hull going sideways against the direction of travel. The sails have got the same apparent wind at the same angle as if the boat were going straight, they are just marginally rotated compared to each other. And extra leeway can only really be achieved by running the foil stalled or semi stalled, in which case the drag must be tremendous.

Going deep with the daggerboard up has a number of effects - the centre of lateral resistance moves aft just as it would with a pivoting centreboard, because the side force is shared with the rudder. The wetted area of the foil and thus skin friction decreases as you lift a daggerboard. The induced drag of the foil stays much the same (unlike a pivoting board where it surely must increase).

But I've come to believe that nearly everything people "know" about leeway is wrong, because the wind and the sails neither know or care in what direction the hull happens to be pointing underneath them*. Leeway is really just the angle of incidence on the centreboard...


*at least until bits of hull or rigging actually get in the way of getting the sails at the right angle...

Edited by JimC

Originally posted by JimC Going deep with the daggerboard up has a number of effects - the centre of lateral resistance moves aft just as it would with a pivoting centreboard, because the side force is shared with the rudder. The wetted area of the foil and thus skin friction increases. The induced drag of the foil stays much the same (unlike a pivoting board where it surely must increase).

Think you might want to edit that para, Jim ("daggerboard up.... wetted area....increases" - eh?)

But I think we agree that you don't need so much board area offwind to achieve the same leeway angle?

So one question in light-moderate weather is: assuming the helm balance is still acceptable, does the drag reduction achieved by raising the board offwind justify the distraction of raising it? I'd tentatively suggest the answer is: only if the leg being sailed is a long one and you've nothing better to do (e.g. no kite to trim).

In windy weather, Frank Bethwaite advocates raising the board whatever (though probably not that much in percentage terms) in order to raise the centre of effort to enable more thrust. But when you think that the lever arm is from a couple of metres up the mast down to half a metre below the waterline, will a few centimetres really reduce the heeling moment appreciably? Isn't it more a case of making the handling/gust response more forgiving?

I've tried it in many classes and I can't honestly say i've noticed any benefit one way or the other; but then maybe I'm insensitive to such subtleties. There was one occasion, however, when I was sailing a Laser on a reach and it was not planing; I hoiked up the board and suddenly the bow rose and the boat shot forward onto the plane (but maybe I just cleared some rubbish off the board?!)

In summary, as people have suggested, there are many factors against raising the board: - helm balance, boat stability, space in the boat, and time/hands available. On the other hand there are potential benefits of drag reduction, and boat handling and (maybe) increased thrust in a blow. Whether the pros outweigh the cons will depend on the class and the conditions. So I'd suggest that people new to a class or sailing in general look at what the top guys in their class are doing and do the same - one of them will surely have tried doing it differently and at least found there was no significant advantage.

Well for me this discussion is very ironical.

Years ago I designed a windsurfing board that I had built at Parkers, and
it was there that I learned about all the various types of centreboard (I
picked up on gybing plates which is another entire thread). Prior to that I had
(and was probably the first windsurf sailor to do so)converted my then racing
board to accept a proper wooden foil and that it would retract fully into
the hull. The result was nothing short of spectacular.

This discussion just simply wouldn't take place in windsurf racing circles,
any wind above a force four and you kick the plate even if you sailing
quite
high angles, you drive off the fin. (But then our rigs are raked well aft).
We can feel every nuance of the resistance of the plate, so, that reducing
its area has a positive effect in a boat, I am in no doubt. Hence my logic for
not contemplating one without a fully retracting centreboard (that and our
dodgy beach.)
Imho the reason no dinghy or skiffy appears to be able to break the 25 knot
barrier is because of the drag, if you could some how kick back your Cherub
Plates for instance and offset the lee helm by bringing the mast foot back you
would notice a huge speed increase, the drag of a plate is immense and
when it's gone the whole craft (a three metre eighty long board in our
case) leaps forward, feels light and skips over the surface.

The same used to be the case of round bottomed division 2 boards so it's
not just the planing surface.

So the point of all this. Reduce the plate surface area in the water
whenever and wherever you can would be my advice, but within MedManiacs
suggestion, only if by doing so you dont lose out in another area. (One
of the reasons for us bringing the controls back to the helm once we get
round to it).

One final point, on a board, kicking it back or reducing it a little bit never
had any great effect, it was only dumping it entirely that made the
significant difference.

The problem obviously in doing that in a boat sailed by boat handling
numpties like us...

Where are you going to stand to get it back up again in order to put the
plate back down in order to get it back up again..

Edit, just another point I recall, without the plate kicked up on a board it
is damn near impossible to bear off around a mark above a force four..In
fact prior to retracting plates they just to call it the 'force four barrier'.

Edited by G.R.F.

Thanks to all for your input, all of your comments and discussions have gone a long way to proving what I was suspecting - that there is no straightforward "method" of using the daggerboard!

To quote Medway Manic: "In summary, as people have suggested, there are many factors against raising the board: - helm balance, boat stability, space in the boat, and time/hands available. On the other hand there are potential benefits of drag reduction, and boat handling and (maybe) increased thrust in a blow. Whether the pros outweigh the cons will depend on the class and the conditions. So I'd suggest that people new to a class or sailing in general look at what the top guys in their class are doing and do the same - one of them will surely have tried doing it differently and at least found there was no significant advantage."

I would say that this is most definitely the case; RYA training teaches "the basics" in a classic way and, as sailors progress, then boat handling does become more specific. Personally, I have noticed that various boat handling techniques adopted by Class Associations are usually the preferred or even fashionable way of sailing a particular class. In at least one case, I didn't follow a Class Association guideline and subsequently found a faster, easier method of sailing the boat.

This brings me back to my initial view that maybe it's best to watch what the fastest guys are doing in their boats, but also to experiment out on the water to find whatever method works best in different conditions. Trial and error (lots of it)...