program on bbc iplayer

last night i watched an interesting program about the airbus380 (apparently the biggest commercial plane) on bbc iplayer. now the plane stuff itself was boring. however they also went into the wing design. by having a lip on the wing tips it increased efficiency  by stopping tip loss. i was just thinking this could apply to foils aswell. ok with daggerboards its more difficult due to fitting it down the slot. however on the rudder it could work. im not thinking T-Foils here, just a tiny lip say 1cm to eliminate tip losses. this apparently gave the plane 8% more lift. if we got 8% more lift we could have a foil 8% smaller and therefore actually use more power from the rig due to the tripping effect of the board being higher up as well as reducing drag by having smaller boards. RS boats have a slight lip on the bottom of the rudders. (its a piece of plastic pipe running along the bottom edge. i think this is more for durability though.

what im wondering is whether this theory is applicable to boat with water being a denser medium and the speeds being significantly lower.

The gates on the ends of the wings help reduce induced vortices.  ie, reduce pressue leakage from the underside of the wing to the upper side.  Hence the wing becomes more efficient.

You could try them on your rudder and I think I saw a National 12 with them many years ago.   You could try them on the top of your mainsail !   But I think the eliptical "Spitfire" wing or sail shape is pretty efficient without them.

It may be better to have the "gate" on the boom.   There is a picture in Marchaj's Sailing Theory and Practice book of a yacht with a very wide boom.  The foot of the sail is on sliders.  The idea is is let the foot of the mainsail slide to leeward end of the boom leaving a big flat shelf  on the windward side acting as a gate.  It probably worked but without proper measurement, who knows ?

I do think that the foot of dinghy jibs should be cut so they are sheeted tight to the foredeck upwind for the same reasons.   And, OKs and Finns sail upwind with the boom on the deck

Edit:  I've always wondered about the efficiency of loose footed mains.   A main sail with a "lens" foot should be more efficient.  

 

Edited by boatshed

A fatter-headed sail suffers less from tip losses (than a narrow-headed or pointy sail).  If you make a fat-headed sail and can stop the top from twisting off excessively then it's harder for pressure to escape around from the high pressure side to the low pressure side - difficult to explain in words and I don't have the wherewithal to draw a diagram.  Bethwaite's book explains how the bent-top 18 rig works so well in this respect.

Mike

Ah, good answer Noah, and I agree with you that the jib-on-deck thing is very worthwhile, and much more so than
the jib overlap which it affects. But the verticality of the jib leech is an irrelevance, it's the angle of the
luff wire which dictates the movement of the jib back/forwards as it goes up/down. And the sheeting angle can be
adjusted to suit the change in position, so we needn't worry too much about that either.

Of course, the actual back/forwards movement of the jib on a Fireball over the sensible range of jib heights is
minimal, and perhaps irrelevant in the real world. I'm just interested to know, all other factors being equal,
whether or not a greater overlap is a Good Thing or not.

Mikey,

Thanks for the jib luff vs leach correction - 'twas late & post beer & curry . You might have every-which-way jib sheet adjustment, but mine only goes in and out

I seem to recall that I14's used to have overlapping jibs / genoas, but nowadays they don't. Is my memory OK or playing tricks? What's the reasoning behind this? (Just plain faster / self-tacking / rules re sail sizes ???)