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Tightening up tacking angles

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Prospector
Master Marine Consultant

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Canada
3159 Posts

Initially Posted - 06/10/2009 : 12:51:28

I got a new GPS toy that allows me to upload my race data to google earth, an dafter the dismal results at the past weekend's races I started looking at how to improve.

The first item I saw that needs addressing is my tacking angles. by exporting my Google-earth images to ACAD I was able to measure about what angle a tack took me on and was surprised to see that my tacks go from 103 deg up to 135 deg.

Who has tips on keeping this number down? What can I do differently to get more 100 degree tacks and fewer of the 130's?

The wind was really moving back and forth as you can see on the track, and we were getting constant lifts and headers, I promise my track isn't always that wiggly!

"Iris"
1984 FK/SR #4040
http://frosthaus.blogspot.com/

Take a minute to register your boat with the association!!
http://www.catalina-capri-25s.org/owner_questionnaire.htm

Edited by - on

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 06/10/2009 : 13:22:09

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Prospector
 
Who has tips on keeping this number down? What can I do differently to get more 100 degree tacks and fewer of the 130's?

<hr height="1" noshade id="quote"></blockquote id="quote">

Sail in a stiffer Breeze. Stay in phase and don't tack at all.

Aside from those two smart A comments:

Your angles are going to get larger as the breeze begins to die down. Nothing you can do about that. While having an idea of what your optimal angles are, it is more important to maintain boatspeed. The boat speed is going to drop drop during a tack especially in a c-25. If the boatspeed drops too much though, you have to have a bigger angle to build speed back up to get the boat back into the groove. So tip number one - keep boat speed up. Do this by making sure that you let the sails help drive you through the tack - don't release the sail until it backwinds and starts to push the boat. That will also help your crew get the sail around quicker and smoother. Next, while getting the sail around fast is great however it doesn't help you if they kill your boatspeed by bringing it all the way in "knot to block" too soon. The trimmer should bring the sail in about a foot to 18 inches and then slowly grind the sail back in as the boat speed comes up to the polar target. Help the boat accelerate to rebuild some of that lost speed.

Next - don't oversteer - Since you are already charting the angles keep a record of the angle relative to the windspeed at that time. (measure the angle where you think you are up to speed, not what your boat actually does) Then when you tack work at not driving the boat down below the prescribed angle. Don't live or die by this though, again boat speed is key. I'd work on all of this before and after a race. During the race you have better and more important things to do.

Mark your deck with a grease pencil with the tacking angles or laminate card and tape it to the deck. Put low medium and high tacking angles on both sides of the cockpit coaming. You can use this to spot up where you plan on being (remember to divide your tacking angle by 2) and can also help you to check your crossing angles. Whidden, I believe has a chapter or two in his book on this. I believe it is championship racing tactics or something. I'll have to check my shelves to see what is there.

Hope some of this helps

Edited by - on

Steve Milby
Past Commodore

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USA
5909 Posts

Response Posted - 06/10/2009 : 13:44:59

IMHO, the main cause of overly wide tacking angles is that people have heard it said by experts that you want to trim the sails full as you come out of the turn, to help the boat accelerate back up to speed. While that's true, people way over-do it. If the trimmer trims the sails too full, the helmsman can't steer the boat any closer to windward than the sail trim permits. If the sails are trimmed for 8-12 degrees off the wind, or more, then until they are hardened up for a beat, the boat is sailing in the wrong direction. When the racing experts talk about trimming the sails full as you're coming out of a turn, they're generally talking about something around 3-4 degrees. Occasionally you might need to increase that a little, such as when there is a chop or big boat wakes, and the waves are slowing the boat significantly as they strike the bow. That's when the sailing experts tell you that you need to "power through the slop." In a good turn, the winch handle should only have to be turned about 3/4 of a turn in order to give the jib it's final trim after coming out of a tack, but, when most boats are coming out of a tack, you'll see the trimmer madly cranking the winch round and round. The reason why he's doing that is that the helmsman is ahead of the trimmer, in turning the boat, and the trimmer is trying to catch up.

The work of the helmsman, tailer and trimmer all should be coordinated, so that the boat is turned and the sails are trimmed quickly and efficiently, because, in a well-coordinated turn, the boat doesn't lose so much speed that you need to bear off so much in order to bring it back up to speed.

Edited by - Steve Milby on 06/10/2009 13:55:42

DJAnderson
1st Mate

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USA
29 Posts

Response Posted - 06/10/2009 : 20:06:48

The "course over ground" angles here are interesting, but it looks like there was a lot more going on than just difficulty with tacking angles. Is this track all from the same day? In one part of the picture you're tacking out to sea and in another tacking up the coast. Huge wind shift? I also notice that in the section where you are tacking up the coast, your port tack segments are not parallel. Was the wind clocking to the right as you moved up the coast? It can be hard to tell what your actual sailing angles are from GPS which has recorded your course over the ground (COG). For example, if you were tacking into a current, your zig-zag track will look compressed with wider "tacking angles." Also, you are seeing some leeway in the GPS track which will make the angles look wider than they actually are relative to the wind. Did you have a lot of waves to contend with? For these reasons, a traditional compass will be a better measure of tacking angles.

All that aside, the shape and trim or your headsail is critical for upwind performance. Do you have a flabby, sagging furling headsial (like I do). Is it sheeted in far enough? Is it trimmed so that the telltales "break" evenly up the luff?

Edited by - on

JohnP
Master Marine Consultant

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1520 Posts

Response Posted - 06/10/2009 : 21:58:56

Sensible comments above.

I would be interested to see others' tacking angles. There must be others on the Forum who also have some of these images on your mapping GPS devices.

In the diagram below, that you may remember from my posting some months ago, I also learned that my tack angles were way above 90 degrees. Here are some of the details of my setup: C-25 SR/FK, the jib is 110%, and there was probably 10 knots of breeze of more, and there are no strong currents or tides in this spot. I almost always move the traveler up, to sail a few degrees closer (maybe 3-5 degrees?) to the apparent wind.

It's fairly easy to trim pretty quickly the 110% jib single-handed without a winch handle, and so my boat may go slower than a boat with a 135% or 155% jib, but the tacking angles may routinely be smaller.

I also see now that it looks like the wind shifted a little bit from start to finish of this course I sailed.

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 06/11/2009 : 06:49:37

Good additional info John, and great tips so far guys.

I sail/race on a large lake. No currents to speak of. During this race, we could see th eboat ahead of us go to the pin in a single tack, however the wind was shifting to the right, with about a 5 minute phase in oscillations (this is a guess).

We were flying our 110% jib, SR/FK, newer full batten Main. Our conditions are actually very similar to what John P has posted, only more open water around us. I am not sure of the strength of the wind at this point.

DJ. The race was 7 hours long, but yes, this is all the same day. Start was at about 11:00 AM and Finish was around 4:30 PM, so it is expected that the wind would shift in that time. (Westbound was Start, Northbound finish). We have foredeck call trim to keep the headsail shaped nicely. The headsail is hank-on, and very crisp.

Edited by - Prospector on 06/11/2009 06:56:05

DJAnderson
1st Mate

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USA
29 Posts

Response Posted - 06/11/2009 : 19:54:26

Well bummer. I was trying to help you find a good excuse to use

Pardon my asking, but is your bottom clean? Maybe you're not generating as much lift on the hyrdro side as you could to match the quality of the sails on the aero side?

Interesting track from John P, too. Can't tell from the 2D view, but I'd bet the wind blowing down that channel is bending considerably around each of those promontories. If you are calculating your angles based on straight lines from tack to tack you'll have a lot of variation depending on whether you tacked to windward or to leeward of each promontory and other factors. If you really want to know your tacking angle, you need to compare the closehauled compass heading immediately before vs your heading on the new tack once you're back in the groove (this will also help cancel out the error from less than perfect tacks.)

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 06/12/2009 : 06:29:58

New VC-17 bottom this spring.

I wonder if this was a case of too much leeway, although I don't think we were heeled all that hard.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 06/12/2009 : 06:54:37

Leeway could be it, which is why I would favor the GPS track over compass headings, particularly on a lake. Pointing and trimming too hard can induce leeway that you can't see--but the GPS knows. You can watch its heading as you adjust course and sails--your actual track can sometimes be a little higher by falling off a little and gaining better boat speed. (Speed reduces leeway.) This varies with wind speed.

Your real objective is Velocity Made Good to a waypoint, which your GPS can tell you. On a practice sail in light air, set a distant upwind waypoint and experiment with course and trim while watching VMG (easing the sheets just a little as you fall off just a little). You might be surprised. Then do the same in heavier air.

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 06/12/2009 : 08:13:28

Dave, I am going to try to get out tonight with the camera and take photos every 'n' seconds of the compass while running the gps tracker.

The difference between GPS heading and compass heading will be leeway.

My plan (based on info recieved here and elsewhere) is to:

1.) Make a windward run using my current methodology (traveller hard to windward, boom centred on cockpit, no cunningham, mainsheet centres boom)
2.) Make a Windward run with traveller held no higher than amidships, all other controls stay as current.
3.) Make a windward run with traveller held amidships cunningham applied.
4.) Make a windward run with cunningham applied, traveller hard to windward.

Over the weekend, I'll georeference the photos to the tracklog and see how much of a difference each pass makes. Any other ideas?

About the onlyu item that hasn't been brought up iun this discussion is jib sheeting angles. I pulled a "set and forget" with the jib sheets in this race. I wonder if they were set such that we couldn't get up close to the wind in their position. I haven't sailed with the 110% as much as I have withour 155%, so I wasn't sure of their position. The bottom 2 sets of telltails were streaming well, but the top ones were more hit & miss.

Sailing sure can ruin a nice day out on the boat :)

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 06/12/2009 : 08:36:20

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Prospector
 Sailing sure can ruin a nice day out on the boat :)<hr height="1" noshade id="quote"></blockquote id="quote">You said it, not me...

Regarding the jib, there's also the issue of sheet car position... Further aft in heavier air, to flatten the lower area of the sail and let the top twist off a little, and further forward for lighter air, to ease the foot and tension the luff, making the sail fuller and bringing the top more into play. The real power in a jib is in the lower half, and it generates much less heel per pound of driving force than the main does.

Back to compass vs GPS... That comparison can help you understand your leeway, which helps you understand your boat. But again, maximizing VMG (the rate at which you are reducing the true distance between you and the mark) is your real objective. In lighter air, pointing and hardening to the max does not necessarily do that, due to the lower boat speed and the leeway it allows.

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 06/22/2009 : 08:46:40

The tuning paid off...

This is this past weekend's race with a 155% in light to heavy air.

The angles look WAY better!

EDIT to Add:

This course was steered based on "closing Speed" on the GPS rather than telltales, heel angles, or number of martinis per mile.

Edited by - Prospector on 06/22/2009 08:59:59

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