Sail Design: Foot attached or not?

I currently have a Hobie 16’. It and most boats that I’ve seen in the past (although I may not have been that observant) have the Foot attached in a track in the boom.

I'm looking at some boat plans by various architects. However, some of the designs I’ve seen lately have main sails attached only at the Tack and Clew. The sail maintains the same camber all the way to the Foot versus flattening out. Can someone comment on the relative pros and cons of these two methods?

 

Inquisitor,

At a very general level, there are three options for the foot of the main: loose foot, shelf, and traditional. The shelf is a section of cloth cut to match the designed maximum camber of the sail and which is intended to be horizontal when the sail is flying. With the traditional style foot, the lower section of the sail must develop the camber between the straight line of the boom and the mid-section of the sail, so some of your sail is not going to be a foil. The loose foot permits the whole sail to be a foil.

For sail shape, you're generally best to go loose foot or shelf and, of those two, probably loose foot. The decision is generally based on the mechanics of dealing with the sail when it is lowered or reefed - sometimes the loose foot is a pain (and sometimes it's better). People will comment on the end-plate value of the non-loose foot arrangements, but I don't think that this is material.

 

I don't believe, I've ever seen the shelf version, but that makes sense.

I’m guessing by your descriptions that the attached foot since it has reduced camber and thus reduced lift at the edge would also have smaller end vortices. The loose foot would have higher lift, but larger energy wasted by larger end vortices. And the shelf version acts like a tip sail (fence) blocking the high pressure bleeding over the foot to the low-pressure side of the sail (wing).

I was wondering on the affect of these (now three) designs on performance. In the real-world are there any noticeable differences? And if so, do you have to constantly watch it or could an average sailor see the benefits?

 

Loose foot is the current fast fashion. The loose foot will generally permit better sail-shaping, depending on the available controls.

I doubt that the differences in speed will be significant on a typical application, hence my use of the word 'fashion', but I'd go loose-foot.

I don't think you'll get any material end-plate benefit from a shelf as the pressure will be bleeding around the boom. For an interesting experiment in end-plating boomed sails, have a look at Steve Dashew's try-out of placing a skirt between boom and deck at:

http://www.setsail.com/c_central/techtalk/endplating.html

 

Go for the "shelf foot".
I've heard it referred to here as a "lens" foot.
When cruising (40') with that gentle breeze we ease off the foot a little, climb in and lay back, can't get any better than that.
Don't forget and try it with a loose foot.

 

Holy Commolli! I hope my foot is attached....

 

The "old" way is a Park Ave boom.

The top of the boom is a wide flat plate with sail track run across and the bottom of the sail has simple mast slides . you get the great shape of a loose footed sail AND he end plate effect.

Not bad for a 100 year old idea.

FAST FRED

 

Loose lips sink ships! What do loose foots do?

 

What do loose foots do?

Allow the camber of the sail surface to go right to the foot, no area lost ataching to a boom.

FAST FRED

 

Maybe cause booms that are too flimsy to bend or even break in compression as well as in bending. With an atatched, foot you have a distributed load along the boom. With a loose foot, you now have two point loads, one on each end of the boom where all of the load at the foot is concentrated. If your sheet tackle is between them, watch out.

This of course can be engineered around. You can make the boom stronger and you can move the sheet tackle to the end of the boom. Or you can do any combination of the above.

Another problem is that the overpressure on the windward side of the sail can pour out the now open bottom of the sail. Maybe thats why the shelf was invented.

My guess is that, if loose footed sails were really better than atatched footed sails, we would see them almost universal in racing fleets.

Bob

 

For offshore work the Wishbone is a fine sailing companion.

The Wishbone boom takes all the main clew + outhaul loads , so the sheet pulls the sail in , but NOT down , the boom did that.

Very nice but a pain to lower or reef rapidly .

Nothing is "perfect",

FAST FRED

 

They are. I doubt there has been a high tech racing mainsail built in the past 10 to 15 years that wasn't loose footed.

 

A "loose" foot is cheaper to build, and is lighter in weight over all. Also composite boom without a slot in it is cheaper to build, and stronger for the same weight. Other benefits are that the outhaul is more reactive, because of less friction, and you can install the mainsail by yourself more easily. Also on boats that take the kite down into the main hatch you can pull the the sail down through the slot between the boom and the foot of the mainsail, so you are less likely to tear the spinn. on the end of the boom.

That is the long and the short of it from my perspective.

 

In addition to Doug's observations, you can also put a generous foot-round on a loose-foot main and gain a bit of area downwind.

Yoke.

 

End Plate? looks like a 'bonnet' to me! Didn't Columbus use them when he invented America a few years ago! Silly me! so that's why they went out of fashion! (I know Artemis but I can't help myself, it's so much fun!!!