Optimum heel angle

[Blether]

Traditional sailing advice says 'sail the boat flat'. These days we see part/whole crews sitting to leeward while the boat is still heeled that way (that is, intentionally allowing the boat to heel to leeward).

Intuitively, more power comes from the sails if they are upright: hull performance at different angles varies with hull design.

Is it possible to state rules of thumb for the optimum heel angle for going upwind, for different boats ?

[Olav]

Hi Blether,

I can only imagine one situation with modern boats where heeling to leeward is desirable: light airs. In my opinion the "traditional sailing advice" is still right. As you mentioned you'll get more power from the rig, more power from the foils (with lower down forces), and of course lower wheather helm you then would have to compensate with the brake (=rudder). In light conditions it may be clever to heel to induce shape to the sails (if you don't have full battens).

A different story are catamarans/multihulls (to get one hull out of the water to reduce drag), hard-chined scows (to reduce wetted surface area and to get a sharp entrance at the bow), and traditional boats with large overhangs (to increase waterline length).

I am an Int. Moth sailor and we use to sail our boats with windward heel upwind in strong breezes. This increases righting moment, gives lift from the sail and a momentum to leeward to compensate the windward helm that comes from mast rake.

So as a conclusion I don't think there is a rule of thumb as long as you don't have a specific hull in specific conditions in mind.

All the best, Olav

[Blether]

Thanks Olav.

Yes, I'd always believed in the traditional advice: and of course at the very light-wind end there are gains in using gravity to maintain sail shape.

But recently I see 30- and 40-foot yachts sailed as I described, and today I read on the net that a Laser's hull is most efficient upwind, heeled 20 degrees to leeward. I can understand that - it's very flat, so one can picture a reduction in wetted area with the heeling. It's been a few years since I sailed a Laser, and I never raced one, so I don't know how this balances out with the lowered sail power.

Those who race a particular type and know it well, what balance is effective ?

Designers, how do you recommend owners sail your yachts, wrt lateral balance ?

[BrettM]

The only way to make a laser fast upwind is to hike hike hike hike hike hike hike hike hike hike hike to keep it flat. And that hurts.

Very light airs to keep shape is a different story.

[dionysis]

It is always recomended that you sail a boat flat, for the above reasons: aero and hydrofoils work at their most efficient etc., but on big boats, that are not dependent on movable ballast, sailing flat ultimately depends on the righting moment of the boat. Designers have to juggle a lot of factors and make a lot of compromises - the upshot of which is: if you graph the thrust to sideforce of conventional foils asa function of heel, you find there is a point; around about 30 degrees, beyond which increasing heel gives less and less drive.

In other words you do not lose too much efficiency of foils up to about 30 degrees, but beyond this you lose efficiency very quickly.

I hope this is what you were getting at Blether

[SailDesign]

Strangely, we found with one of the first fat/flat Open60s that the VPP, which said "sail at 20-23 degrees in 12 knots" was correct. It took a bit to get there, but we gained 0.5 knot or so. It was not comfy, but it was fast - probably due to a narrower waterplane at that angle, and there was _plenty_ of sail area available on the beast.
Steve

[tspeer]

Inland lake scows are heeled 15 degrees to reduce wetted area upwind, and sailed flat for planing. Their boards and rudders are canted to be vertical when the boat is heeled. Most dinghies go best when upright, but may need to be sailed more bow-down in light winds. So it depends on the design of the boat.

See Frank Betwaite's "High Performance Sailing" - he has 1/3 of the book devoted to dinghy handling.

[SuperPiper]

So with enough movable ballast, a small keelboat would be more efficient heeled to windward?

[dionysis]

Yup, in a breeze that is - The lift vector together with the heeling vector has an upward component, instead of being either horizontal or downward when the boat is heeled to leeward. This means that there is less heeling moment, but together with this, a component of lift is actually lifting the boat out of the water.

In sailboard sailing, this heel to windward enhances lift. Tom would have a far more substantial contribution to better understanding of this enhanced lift effect.

[thesailman]

Heeling to windward downwind in light airs raises the sail and puts it in more wind. To heel to windward when going to windward would increase lift.