End Plate Effect

[ianabc]

I am about to build a 16 foot long boom for a 37 foot steel sailboat.

This caught my attention...

"Endplate" or seal off the bottom of the boomed sails. If you can achieve this for even half of the foot length, the increase in efficiency is dramatic. (Steve Dashew)

I am wondering if the end plate effect that can be used to optimize perfortmance of aircraft wings and sailboat keels can be used increase boom efficency by adding a "wing" to the boom.

Perhaps aluminum 4 inches X 1/8 inches standing out from the boom just below the sail track, and capped with aluminum rod to soften the outer edge.

I did notice winglets on each side of the boom on a one piece carbon fibre rotating mast/boom on a Trinitella. Noisy it seems downwind.

Any designer / experimenters / model boat racers / crazy oragami metal boat builders etc., input would be appreciated.

 

[sarabande]

On a few "fixed wing" boats, e.g. the Walker Wingsail, theier have been some endplates at thetop of the sail and the bottom. I think they need to be a bit bigger than you suggest, but it should be possible to have plates made of sail material which "fly" at right angles to the plan of the main sail. I'll look up some photos.

 

[Goldie]

How about fiting a 'Stack Pack' or similar and when under way, ease the lazyjacks and rig a lateral spreader (batten?) at the fore and aft ends of the stack pack so that the canvvas forms the end plate? I don't know, but it might work....

 

[Fin]

Some of the old large American racing yachts <u>used to</u> have "Park Avenue" booms (so called because the were the size of Park Avenue). The idea behind the winglets/large booms is to reduce pressure loss from one side of the sail to another.

The windward side of your sail will have a higher pressure than the leeward side, the air on the higher pressure side will always try to "get" to the lower pressure side by going around the sides. The bigger the pressure difference the stronger the flow from one side to the other. (Think about weather systems, and a high moving towards low pressure.) This is whats happening when you see the vortex coming off a wingtip, the harder the wing is working the bigger the pressure difference between top and bottom, so the bigger the vortex.

The harder that you make it for the pressure to equalize around the ends of the sails then technically the more efficient they become. There are lots of ways that this is achieved on aircraft the more obvious one is winglets. Lots of blah written about them but they try to reduce the vortex and turn it into either thrust or lift. The obvious one that applies to sails or wings is taper. The narrower that the wing or sail is then the smaller the pressure difference between windward and leeward because the sail hasn't got the width to change the air much as it flows over. The smaller the pressure difference the less the air wants to spill around the sides.

You can achieve the endplate effect on a smaller yacht boom, you will get small increases in sail efficiency but think about downsides, your boom will be heavier which will pull down and probably hook your leech; not fast. If someone doesn't move their head out of the way on a gybe, boom rash will develop into decapitation territory.

"1/8 inches standing out from the boom just below the sail track, and capped with aluminum rod to soften the outer edge." Soft?

If you want to speed up the boat, strip out all the weight that you don't need and you'll go faster than some guy thats bolted a plank onto his boom...............

 

[MikeBz]

An endplate at the head of the sail would have much bigger effect! You get a lot of pressure loss out of the tip (head) of a sail, which reduces efficiency. Typically the foot of a sail needs to be flatter anyway because it is close to the deck and therefore in a slower airstream (so it's apparent wind is further forward, hence the need to be flatter to be trimmed correctly vs. the upper part of the sail). Another thought which occurs is that if you're heeling then the tendency will be for air to flow up the sail rather than down it, so again the endplate at the bottom probably won't do a great deal.

Just my 2p.

Mike

 

[sarabande]

Just a further thought and pic. I endorse other comments about having structural endplates which might act a horizontal shears!

The pic shows a small wingsail with a squared off top and an endplate, and a structure about halfway up which not only controls shape (drive) but which will act as pretty effective (mid!) endplate.





The Amateur Yacht Research Society is bound to have lot s of reference material. Worth talking with them ?

Keep up the good work and let us know how you get on please.

 

[bobgosling]

Just a thought.

I really really really wouldn't like to be hit on the side of the head by a boom like you describe.
( I'm not an Iranian dictator's brother !!! )