Heel Angle vs. Leeway -- Calculation

[Joli]

Originally Posted by wingssail

Sailing on the favored tack sounds simple enough but there is more to it than which tack is closest to the rumb line.

First is it essential to know what your VMG is, because one tack or the other may be effected more by current and or leeway induced by sea state. Good instruments can help you determine this.

Secondly knowing what the true wind direction is helps you determine what heading and VMG you'll be able to make on each tack, therefore determining which tack is favored, and with good instruments you can see small shifts which otherwise you have to notice by watching the compass as you steer to the tell tails. Tacking to determine you heading on the other tack may be lost time towards the mark.

Finally, Having access to good polar numbers for your boat, along with anticipated wind and current information down the course, will help with routing.

So I agree with the approach that good numbers coming off the instruments is very beneficial especially when you cannot see the mark or your competition, which is often the case in long distance races, and when "what feels good" can easily be misleading.

But I also agree that the best helm's persons and the best navigators/tacticians utilize everything at their disposal, and that means boat feel, and head out of the boat, not just instrument data.

The thing is, when distance racing, you're not sailing vmg, you're sailing vmc using the ladder rule. This is for all angles of sailing whether you're upwind, downwind or reaching. The goal is to move up the ladder more quickly (ie. footing when sailing upwind, heading up when sailing downwind). The idea is that you give up height upwind to be bow out with the realization that the wind direction will switch prior to arriving at the mark. As an example, you're going upwind, you've given up 5 miles to weather but are 3 miles ahead. If you're headed they turn down to your transom, if you're lifted you reach up in front of them. The same concept holds for downwind legs. These tactics are vastly different then bouy racing because the wind will very likely change direction prior to arriving at a mark hundreds of miles away.

[donradcliffe]

Originally Posted by Dockhead

I

Heeling is a very reliable function of lateral vector of force on the sail plan.

Think what you just stated, and think about why I spent last night's race with the crew on the leeward rail.

As a tactician, I spend most of my time coaching owners how to steer their expensive boats. They spent their lives making money instead of messing around in dinghies. Some tacticians spend their entire races constantly telling the owner to 'head up', then 'drive off'. I find a get better results (and its a lot quieter) by giving them a target apparent wind angle to steer. That target is based on the boat, current sailplan, wind and wave conditions, how close they are to target boatspeed, tactical considerations, and a host of other factors. They are usually pretty good at following the instruments, and they quickly learn to be better than an expensive autopilot (computer driven boat).

I don't waste my time giving champion helmsmen target wind angles. I concentrate on strategy, tactics, wind puffs and shifts, current changes, and laylines. Some champions sail by the seat of their pants, but downwind at night, they usually want TWA if the instruments are working. Personally, if I'm driving on the edge of control in a squall at night with the spinnaker up, I focus on the analog apparent wind instrument--there is too much lag in the TWA.

On longer races, I can track the performance of the various helmsmen by plotting their VMG vs the polars on Expedition. The really good ones don't have the highest peak speeds, they have the highest average. If necessary, I have the Come to Jesus meeting with the owner--"If you want to win, don't let anyone but these three guys drive the boat, and here's why".

Overall, we still haven't gotten to the point where a computer can drive a boat better than a good helmsman for 2 hours. Of course, in RTW races where fatigue is a huge factor, the computer never gets tired.

[Dockhead]

Originally Posted by donradcliffe

Think what you just stated, and think about why I spent last night's race with the crew on the leeward rail.

Naturally, if you shift weight around, on a boat where crew weight can influence heel angle, all bets are off.


No one ever sits on my rail, because we only do long distance races, and because at 20 metric tonnes light ship (and probably 24 tonnes in real life condition), a few hundred kg on the rail doesn't really do anything anyway.

Originally Posted by donradcliffe

As a tactician, I spend most of my time coaching owners how to steer their expensive boats. They spent their lives making money instead of messing around in dinghies. Some tacticians spend their entire races constantly telling the owner to 'head up', then 'drive off'. I find a get better results (and its a lot quieter) by giving them a target apparent wind angle to steer. That target is based on the boat, current sailplan, wind and wave conditions, how close they are to target boatspeed, tactical considerations, and a host of other factors. They are usually pretty good at following the instruments, and they quickly learn to be better than an expensive autopilot (computer driven boat).

I don't waste my time giving champion helmsmen target wind angles. I concentrate on strategy, tactics, wind puffs and shifts, current changes, and laylines. Some champions sail by the seat of their pants, but downwind at night, they usually want TWA if the instruments are working. Personally, if I'm driving on the edge of control in a squall at night with the spinnaker up, I focus on the analog apparent wind instrument--there is too much lag in the TWA.

On longer races, I can track the performance of the various helmsmen by plotting their VMG vs the polars on Expedition. The really good ones don't have the highest peak speeds, they have the highest average. If necessary, I have the Come to Jesus meeting with the owner--"If you want to win, don't let anyone but these three guys drive the boat, and here's why".

Overall, we still haven't gotten to the point where a computer can drive a boat better than a good helmsman for 2 hours. Of course, in RTW races where fatigue is a huge factor, the computer never gets tired.

Nothing really to add to this, but a minor point -- AWA downwind? I find that useless -- you can go from an acceptable broad reach to a gybe-risk by-the-lee situation in a blink, on AWA. Give me TWA any day. Even inaccurate TWA is more useful than AWA because however infuriatingly obscure upwind angles are with uncalibrated instruments, it doesn't take long to figure out where DDW is, even if it's offset on inaccurate instruments. I have no problem with update speed on my instruments -- seems to be several hertz, calculated in my Zeus, based on 4hz updated wind, 50hz updated heading, and 20hz updated STW. Of course my boat is not a planing downwind sled either, where I guess the problems are different.

[Pelagic]

Originally Posted by donradcliffe

Think what you just stated, and think about why I spent last night's race with the crew on the leeward rail.

As a tactician, I spend most of my time coaching owners how to steer their expensive boats. They spent their lives making money instead of messing around in dinghies. Some tacticians spend their entire races constantly telling the owner to 'head up', then 'drive off'. I find a get better results (and its a lot quieter) by giving them a target apparent wind angle to steer. That target is based on the boat, current sailplan, wind and wave conditions, how close they are to target boatspeed, tactical considerations, and a host of other factors. They are usually pretty good at following the instruments, and they quickly learn to be better than an expensive autopilot (computer driven boat).

I don't waste my time giving champion helmsmen target wind angles. I concentrate on strategy, tactics, wind puffs and shifts, current changes, and laylines. Some champions sail by the seat of their pants, but downwind at night, they usually want TWA if the instruments are working. Personally, if I'm driving on the edge of control in a squall at night with the spinnaker up, I focus on the analog apparent wind instrument--there is too much lag in the TWA.

On longer races, I can track the performance of the various helmsmen by plotting their VMG vs the polars on Expedition. The really good ones don't have the highest peak speeds, they have the highest average. If necessary, I have the Come to Jesus meeting with the owner--"If you want to win, don't let anyone but these three guys drive the boat, and here's why".

Overall, we still haven't gotten to the point where a computer can drive a boat better than a good helmsman for 2 hours. Of course, in RTW races where fatigue is a huge factor, the computer never gets tired.

Interesting post about the human element and really not that dissimilar to the 1970's
....But for different reasons.

As navigator on offshore deliveries of (then) Maxis 60-70ft ....leeway & DR between fixes was a combination of wave angle and the sailing tendencies of the actual crew helming .

Accuracy was a much broader brush that balanced the art of interpretating weather reports over SSB with your own observations in making course adjustments.

Deliveries, was not Racing as our goal was to deliver without damages.

If I had part of the racing team as crew, the likelihood of damages was considerably higher.

[Don C L]

Originally Posted by donradcliffe

Think what you just stated, and think about why I spent last night's race with the crew on the leeward rail.

.

So here you are referring to waterline length trumping leeway concerns in very light air, yes?

[donradcliffe]

Actually reducing wetted surface trumps waterline length in light air. I had the boat heeled to leeward so gravity helps the sails keep their shape.