Setting-up and Gybing Asymmetrical Spinnakers (Using a Conventional Spinnaker Pole)

[bbhflts]

Recently reading North Sails U-Trim I found the comment on pg 146 that a symmetrical spinnaker is not an optimal shape specifically on the luff and leach length and that this compromise is due to the fact that they must be interchangeable. The commentary then goes onto talk about rigging an asymmetrical with a normal pole. It's also described nicely here:

Quantum Sail Design Group AY Promotion

I normally run an asymmetrical on a bow sprit so my question to the forum is if this described method would still be optimal to achieve a better VMG closer to a run. Normally the use of an asymmetrical on a bowsprit forces one to reach down the course more so than one would with a symmetrical. To clarify further, the described method would enable one to move the tack and luff further to the windward side out of the shadow of the main, as you can with a symmetrical. My guess is this would be a great trick to improve VMG but there may be an issue with the resulting sail shape. With normal asymmetrical setup with the bowsprit fully extended, the luff is the correct length, but with the tack on a normal spinnaker pole, it's moved aft and windward, so I'm guessing the Tack distance to the head shortened. This would mean the sail draft would have to increase significantly to still fill.

Has anyone tried this? Does it result in a less than optimal sail shape or work perfectly? Would I need a different size and shape A sail compared to my normal Gennaker? Any thoughts in general.....

Cheers.

Ben.

[Hud3]

I can't attest to the details of sail shape, etc., but a friend of mine does this regularly with his asym. He's able to sail dead downwind with the rig, and keep the sail filled.

[bbhflts]

I think I'll have to give this a shot. Just need to find the right length spinnaker pole.

Cheers.

Ben.

[bbhflts]

I'm also wondering if this would impact IRC rating. Mmmmm, will investigate or I'm sure there will be a protest the first time I do well in a race using the method.....assuming it works well;-)

[elangley]

Ben,

Since you are looking for opinions...

I think that trying to get very close to dead downwind would not be desirable for several reasons.

1) Danger of auto gybing. A small wind shift can auto gybe the boat. You'd have to stay on your toes all the time, which is tiring. I run my asym on the auto helm with a tack angle. Since I am well up from dead downwind I don't have to pay attention every second. Even waves can cause an auto gybe simply from a rocking boat.
2) It's slow. Do the math, use your polars. If you go 1.5 knots faster further reaching upwind you'll probably make better overall VMG then dead downwind.
3) It's uncomfortable. Depending on the true wind speed you'll feel little or certainly less breeze. Come up a little and you get a nice breeze on the shirt from the apparent wind.

IMHO,

Eric

S/V Devante's Dream

[elangley]

Ha! I was going to ask if you are racing but didn't. So some of my opinions don't apply to racing, such as how it feels, tired, etc..

However, your class rules will determine if you can use your spin pole with an asym.

If you are going to all that trouble why not get a real chute

Eric

Originally Posted by bbhflts

I'm also wondering if this would impact IRC rating. Mmmmm, will investigate or I'm sure there will be a protest the first time I do well in a race using the method.....assuming it works well;-)

[Bash]

the downside is a more complex gybe--and by that I mean more complex than a dip-pole gybe with a conventional chute AND than an inside-sheet gybe with a sprit on an a-chute.

the upside is in light air where you don't have to run after-guys on the clews. On an a-chute the tack is always the tack and the clew is always the clew, which gives an advantage for light-air sheeting.

[bbhflts]

Eric.

My original thought process is on the basis of the comments in the North Sails U Trim book that a symmetrical sail shape is not optimal and a compromise. So I began thinking that if an A sail is more optimal (shape wise) but as Bash mentioned more complicated and I'm willing to deal with the additional complications for superior performance, why not. Last year racing from Muscat to Dubai we had wind for nearly two days from behind. With only an asymmetrical, our choice was to limp along at only a couple knots, or significantly deviate from the rhumb line. If we had the advantage of a symmetrical, the the more efficient shape of the asymmetrical we would have had the optimum canvas for the race.

[elangley]

Originally Posted by bbhflts

Recently reading North Sails U-Trim I found the comment on pg 146 that a symmetrical spinnaker is not an optimal shape specifically on the luff and leach length and that this compromise is due to the fact that they must be interchangeable. The commentary then goes onto talk about rigging an asymmetrical with a normal pole. It's also described nicely here:

Quantum Sail Design Group AY Promotion

I normally run an asymmetrical on a bow sprit so my question to the forum is if this described method would still be optimal to achieve a better VMG closer to a run.
Cheers.

Ben.

Ben,

I read the article you referenced. It is really just like gybing an asym with the addition of moving the pole. I personally don't like gybing mine. I use a snap shackle on the tack, blow that, douse the sail with the snuffer and then reset it on the new gybe. It's far safer and doesn't put the sheets in the water or require sheets to be twice the length of the boat.

Your question is, "will this be better VMG close to a run?" You don't mention what kind of boat you have. If it's a production built vessel it probably has polars, showing boat speed at various wind speeds and angles. I think you'll find that the closer you are to dead downwind your boat speed will be slower. So sailing higher should give you a better VMG.

There is a really good article about VMG and, specifically, VMG going dead downwind that you can read here;
Why VMG Matters - a knol by John Navas#
It is normally faster (higher VMG) to sail a hotter angle than dead down. It's really the reverse of sailing into the wind.

Eric

[barnakiel]

We fly the asymmetrical from the pole ... The gennaker from the bowspit. But I want to redesign this and have the gennaker on a movable bowsprit (little beam here).

I think it very much depends on the sail design - the newer asymmetricals set well from the bowsprit, because that's how they were built, the older ones do not.

The stuff at Quantum site works as advertised.

b.

[rodney_k]

The boat I race on does exactly as Quantum describes. It really works well and we can run pretty deep with the Asym on the pole. If you think about the luff, when you are reaching, you want the luff tight, and when running, the luff should be eased to make the Asym fuller. When reaching you'll have the Asym on the sprit and can tighten the luff as required. When running, moving the tack from the sprit to the spin pole will ease the luff as required for running deep. Sail shape seems fine in both "modes". We race under PHRF, and took a 6 second per mile hit for using the Asym on the pole. Having the Asym on the pole and being able to run deep more than makes up for the 6 second hit though.

[Joli]

When we were racing heavily we flew and jibed the assy exactly as the giude suggests. We did not have a penalty pole though so our jibes were outside most of the time.

When racing W/L we almost never flew the assy's but sailed with sym's because they were so much more tactical.

Cruising, hard to beat an assy.

[barnakiel]

I do not think the assy works for an average cruising boat either (broad reaching or running). Unless you have something very beamy. I think the kite will have to be flown to the windward (an adjustable bowsprit) and then probably the clew poled out too.

My probably most eye opening experience was sailing beam reaches inside the Great Barrier Reef with the genoa clew poled out and the sail sheeted tight. Very efficient, wonder why I never see people doing just this.

b.