Downwind Lift

There have been several comments regarding Bill Hagerups sliding mast arrangement. Angus thinks it provides no advantage. I believe that with some minor modifications it could provide significant lift at the prow.

The present arrangement moves the base of the mast forward. My first thought was to tilt the top aft at the same time, to give a lift component to the sail force. But a much simpler method would be to slide the outhaul inboard, which will allow the foot to billow forward, much like a spinnaker. The McCormack rig is well suited for this, but care must be taken to avoid putting any turning forces on the mast pivot.

This will have some advantage without moving the mast, but its efficacy will be improved by sliding the mast forward. The objective is to raise the prow, not the whole boat.

There will be secondary effects, in that it will reduce the projected sail area, which might be beneficial downwind. But it might also ventilate the sail better, which will have the opposite effect. It might cause bad things if initiated too soon, like on a reach.

Obviously, winter has come, and the golf season is over, so we have time to contemplate all sorts of things.

I attach two ideas that I tried out quite a number of years ago on a 36-600 Graupner model of the 8 Metre ‘Gracia’. The first involves a rubber band to hold the jib out when running on the starboard tack in flukey winds. (It has not effect otherwise, but sometimes is a hindrance in very light air.)
The second results in tightening of the clew when extra closehauled, but allowing the mainsail to become ‘baggy’ while running.
Both ideas work quite well, but are not legal on Solings (my current fancy) so I have not pursued them.

Photos did not attach

Pictures were too large. I guess I’m learning by doing, in the best pedagogical practice of the day!

Rod -
I like the idea of a clew tightner for upwind/downwind sailing. It seems to have some merit.

However if the rubber band is holding the jib out, how do you gybe on wind shifts or in tactical situations? If close hauled is the band loose enought to allow the jib to swing to port if so desired?

This idea has been used on the Victoria, with an improvement to avoid the problem that Dick mentioned. The rubber band is tightened when running, and loosened when close-hauled, by attaching one end to a hole in the sail arm. I have tried it, and it worked nicely, but it has another problem. In a close encounter with another boat, it is the first thing to get snagged.

Rod had suggested a neat method of controlling the outhaul. However, for my suggestion to work, it needs a very large movement of the outhaul, and only when running. A Rube Goldberg combination of levers and cams might be necessary, but the imaginations of hundreds of Footy sailors will eventually find something very simple.

The rubber band only holds the jib club out while running. It is overcome when the jib sheet is hauled in. The difficulty occurs in very light air as the jib is held at the fully closehauled position but is still on the starboard side, so coming across the wind while tacking can be almost impossible.
The mainsail clew outhaul really only tightens if the sheet hauled in, and then the centering adjustment on the transmitter is used to pull it in even further than usual. The ‘bagginess’ of the main while running depends on the exact adjustment of the point of attachment of the mainsheet. I’ve never used either idea in competition with another boat.

If you gentlemen are interested in increasing the “bagginess” or camber in the mainsail for offwind points of sail the simplest method is to place the gooseneck (pivot point of the main boom) farther aft of the mast. Trimmed in for pointing the sail looks as normal, but when the sail is let out the arc the sail travels pivoting from the mast is different than the arc the boom travels.

Here is an extreme example: The sail foot is say 9 inches. The main boom pivot point is 1/2 inch aft of the mast. When the sail and boom are closehauled they appear the same as they would with the gooseneck on the mast. In this example or with the gooseneck on the mast, for the sail to go from closehauled to out for running it would travel in a quarter circle with a 9 inch radius. The boom pivots from the hull centerline and is 8.5 inches long. When the boom is let out for the run it’s arc has an 8.5 inch radius. The difference in the radii with the boom being 1/2 inch shorter than the sail foot length puts more camber in the sail.

The Hoyt gun mount rig is an example from sit-on boats, but it was standard practice on vane Marbleheads thirty years ago.


You have made an excellent suggestion. The next question is how to apply it to the McCormack rig, and how to limit its maximum effect to the downwind leg. You have created a flood of ideas, and one of them looks like it might work reasonably well. I have attached a top view of the deck arrangement to show how it would operate. The basic idea is a double-ended outhaul line, terminated forward of the mast pivot, going to turning blocks at the aft end of the boom. It needs to be double-ended, otherwise it would only work on one tack, since the mast pivot would get in the way on the other tack. The two ends are mounted off center, separately, to control the mast angle at which the loosening starts to occur.

I have also attached a side view to show how the loosened foot improves the pitching moment. Essentially, the movement of the foot forward creates an angle on the face of the sail, which causes the thrust vector to point slightly upward. This means the tail of the vector is lower where it crosses the normal from the center of flotation. Therefore the downward pitch moment is reduced. It is apparent from the picture that this method works best when the mast pivot is further forward.

It remains to be seen whether the added compexity is worth the effort.

Please feel free to comment on the validity of my physics. I have been known to err.

I don’t see how your scheme would work. As the rig / boom turns to one side, one of your outhauls would loosen while the other tightened. The tightened line would further tighten the outhaul and draw the clew even further out. Even if you had a turning pulley at the clew of the sail, the position of the clew would remain unchanged.
I will try to diagram another arrangement for a follow-up posting.

Here is the scheme. The principle is that the tension on the mainsheet is less while running downwind, than it is when the sail servo has fully tensioned the sheet for close hauled .

I tried the rigging method that is shown in my earlier post, and it does actually work as shown. I probably didn’t explain it very well. One side goes slack when the boom goes out in one direction, and the other side goes slack when the boom goes out in the other direction. The line doesn’t start to go slack until the boom angle exceeds the angle of the tie points from the mast pivot. The position of the tie points will control the sytem. Further forward makes more slack, further inboard makes the slack occur earlier. Because it is a double-ended outhaul line, when either side goes slack, the outhaul will be free to move inboard.

The system that Rod recommended will also work, and is simpler, but provides less control

Yes, I see now. I assume that the loop of line at the clew slips through the thimble in the clew, so that there is, in effect, a larger loop at that point, thus slackening the outhaul. In your trial of the system, did you use any kind of block or pulley, or did the outhaul line just slide through holes in the sail and on the aft end of the boom?
The scheme I suggested could use levers pivoted at their centres, with the outhaul sheet attached at each end, instead of pulleys. I have made tiny oak blocks with brass sheaves and steel centre shafts, and it is a lot of very fiddley work.

Interesting…but are you not putting the cart before the horse??
First one needs to establish if easing the outhaul downwind is an advantage before inventing ways to control it.
Perhaps sailing 2 identical boats downwind ,one with a eased outhaul and the other not will first prove if this discussion is worth the time and trouble.
Correct me if my simple thinking is missing the mark.

Brett is absolutely right about the need for testing on the water. Unfortunately, our ponds are iced over right now, so testing will have to wait.

To say nothing about the almost impossibility of even finding two identical boats.
At our local university there is a Boundary Layer Wind Tunnel, to which I have written suggesting that this problem of Footy aerodynamics and hyrdrodynamics would provide an ideal project for a graduate student, lasting about one year only. The chance to work on a ‘full-sized’ subject which would require no extrapolation to ‘real sizes’ would, I think, give a student, a really interesting project, with free labour to build the models.
So far, I have not received any answer. Will persist.

[QUOTE=rod;42882]To say nothing about the almost impossibility of even finding two identical boats.

You don’t find identical boats…you build them.

While I would never wish to pour cold water on an idea - the original theme was lift from mast tilt.

The Cosine tables don’t give very much comfort in this direction.

My recollection of windsurfing is that certainly lift is there (and GREAT) but it needs a serious lean into the wind - approaching 45 degrees.

Still think my hydrogen-filled fat dirigible sail has possibilities


Although I can hardly claim to be an expert on the subject, on every racing sailboat I have ever crewed, the protocal was to ease the outhaul when running, and then “harden up” when beating upwind. My understanding was that the deeper draft in the sail would do a better job of trapping the downwind breeze, whereas a more flat airfoil profile would be more efficient when heading up. I’m pretty sure I read the same thing in Tom Whidden’s excellent book “The Art & Science of Sails”.