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  #1  
Old 05-21-2011
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Comparing Upwind Performance / Tacking Angles

Was out yesterday for a short sail on my UFO 34 and whilst tacking upwind I had the nav software running on my computer recording the tracks. Then last night I was able to compare the tacking angles I recorded a few years ago on my 45ft Roberts ketch.

Now these yachts are radically different; a full keel 14t ketch compared to a 1980's 4.5t 34ft racer with a modern underbody. Therefore I would of assummed the performance would be fairly different. However I was surprised at the measurements; around 135 degrees for the ketch compared to 115-120 degrees for the UFO 34. Therefore it appears I am only getting 7.5 to 10 degrees closer to the wind on each tack.

Now as always I know it's difficult trying to carry out these comparisions considering the variables. For starters the wind strength for the ketch ranged from 12-20 kts, where yesterday it was ranging from 7-13 knots, which I know makes a big difference to the wave action. Both times was in the ocean with little shelter.

I also note that these tacking angles are no where as good as some of the figures I have seen quoted in various polar diagrams. For example, a Van De Stadt 34, which is fairly similar design to my UFO 34, is quoting tacking angles of around 90 degrees. I suspect that these measurements are done in "perfect" conditions; flat water, new sails and a racing crew with a well tuned boat. Comparing me bumbling along by myself with the autopilot running is never going to be as good.

So anyone have comments? I am doing the calculations all wrong?

Ilenart
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Old 05-22-2011
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I think both boats should point higher. My fat ketch frustrates me to windward, especially in a chop, but makes at worst 120 degrees. My previous boats, a fractional sloop and a yawl, would both do about 90. This is singlehanded, old boats, old sails, but in somewhat protected waters (Long Island Sound). The ketch will do better in smooth water with a fresh breeze. In addition, this is also course sailed, not made good. I'm judging by the compass, which doesn't account for leeway.
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Old 05-22-2011
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Thanks WS, my measurements are course made good, as detailed on the computer navigation software, which is recording a waypoint every six seconds, and some of the tacks lasted 2-4 hours. I then measured the angles using a range and bearing line function built into the software.

If I were to measure course sailed I would only need my ketch to point 7.5 degrees above course made good on each tack to get your reading of 120 degrees. From memory I think my ketch use to easily point 10 degrees above course made good (use to think I was sailing sideways sometimes ). Therefore it sounds like your measurements are not that far off from mine.

My measurements were also carried out virtually in open waters with a fair bit of wave action / chop, probably 2-5 ft yesterday and and 3-8ft when sailing the ketch. This would also widen the tacking angle.

Ilenart
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Old 05-22-2011
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I did this same thing last year while tacking up the Bay from Seward. GPS track was 90 degree changes. Tacks were about 1-2 miles long, 15-18 knots and 3 ft seas. The boat is an Omega 36.
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Old 05-22-2011
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No probably not. A pointing difference of 10º for tack is huge and will be what separates a very good boat from a poor boat. 20º in both tacks would represent a big distance in what regards speed made good.

Regarding the wind, if the waves are not short steeped the heavy ketch would have been in a better position with between 12/20K ...and 135º is really a poor mark.

I don't know the sailing ability of the UFO 34 with light winds, I would have expected more. There is a big difference between sailing with 7K wind and 13K and going upwind with those two different winds is a completely different story.

I am pretty sure the boat can do much better than that with enough wind and with sails in good shape. Sails in good condition are fundamental to get a good angle upwind.

On a recent Bavaria 36 with good wind (10/12K) and a long keel I can go a bit better than 90º, but not much better. A good modern performance boat can do 5 to 10º better than that, unless is one of those designed to go fast downwind and in that case it would not do much better.

Regards

Paulo
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Old 05-22-2011
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Thanks Paulo. I think I have worked out that a lot of tacking angles are measured via a compass looking at course sailed. So if you are measuring by the GPS track / course made good you have to take into account the additional angle you are sailing. My old ketch sailed very noticably at an angle, which may of been 10 or even 15 degrees above course made good. This would make the 135 degrees more like 115 to 105 degrees. Next time I am out on my UFO 34 I'll check the compass and work out what the average angle is.

Both times the waves were short and steep. I need to try this in more sheltered conditions. A couple of times on Saturday I hit a bad wave and the speed dropped from 5 knots to 3 knots in an instant. The boat was definitely geared in for power (curved main / jib etc) so be interesting to see what results sheltered conditions give.

Ilenart
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Old 05-22-2011
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Ilenart,

I was talking about the angle as it is shown on the course marked on the plotter. Normally 90º and if the sea is not really bad and on optimal conditions a little better. This corresponds at about 30/35º of the apparent wind as shown on the wind instrument. But I am talking about a 36ft boat wit 1.9 m draft and with premium cruising sails. I could go faster and closer to the wind than a Beneteau 39 of the same year, a fiend's boat

I think that a modern Benetau will make about 100º and a First or a similar performance boat with very good upwind ability should be able to do 75 to 80º on the plotter.

You should be able to do 90º if not maybe you need new sails.

Regards

Paulo

Last edited by PCP; 05-22-2011 at 06:46 PM.
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Old 05-22-2011
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Hello,

I race on a well prepared mid 80's C&C 34. New sails, hull and keel cleaned weekly, decent crew, etc. I have recorded many tracks on my GPS. We do about 100 degrees in the tracks.

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Old 05-23-2011
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Quote:
Originally Posted by Ilenart View Post
Was out yesterday for a short sail on my UFO 34 and whilst tacking upwind I had the nav software running on my computer recording the tracks. Then last night I was able to compare the tacking angles I recorded a few years ago on my 45ft Roberts ketch.

Now these yachts are radically different; a full keel 14t ketch compared to a 1980's 4.5t 34ft racer with a modern underbody. Therefore I would of assummed the performance would be fairly different. However I was surprised at the measurements; around 135 degrees for the ketch compared to 115-120 degrees for the UFO 34. Therefore it appears I am only getting 7.5 to 10 degrees closer to the wind on each tack.

Now as always I know it's difficult trying to carry out these comparisions considering the variables. For starters the wind strength for the ketch ranged from 12-20 kts, where yesterday it was ranging from 7-13 knots, which I know makes a big difference to the wave action. Both times was in the ocean with little shelter.

I also note that these tacking angles are no where as good as some of the figures I have seen quoted in various polar diagrams. For example, a Van De Stadt 34, which is fairly similar design to my UFO 34, is quoting tacking angles of around 90 degrees. I suspect that these measurements are done in "perfect" conditions; flat water, new sails and a racing crew with a well tuned boat. Comparing me bumbling along by myself with the autopilot running is never going to be as good.

So anyone have comments? I am doing the calculations all wrong?

Ilenart
Ilenart,

Let's see this again. I have been messing up things

Take a look:



What I was saying is that in normal conditions I get about a 90º angle on the plotter. Barry is saying the same, using a CC 34 with good sails and a racing crew.

This is in fact a good angle because to do that you have to point higher to true wind than 45º to compensate lateral drift.

So doing better than that is actually making a bigger angle on the plotter and what I wanted to say is that with very good conditions I can get a bit better than 90º but just a little bit.

I don't think that a fast modern cruiser racer with very good pointing ability can do better than 110º. That will represent a TW angle of 35º but in fact it will represent less, maybe 30º, to compensate lateral drift.

My confusion begun because you say that your ketch was capable to make an impossibly good 135º angle and that the UFO 34 was doing an also impossibly good angle (120º) but worse than the ketch and it should be the opposite.

Of course I can also have misunderstood what you mean. Take a look at the picture. We are talking about the true course of the boat regarding true wind as it is marked on the plotter. You are talking about the same?

Regards

Paulo

Last edited by PCP; 05-23-2011 at 06:00 AM.
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Old 05-23-2011
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Paulo, now you have confused me! But that's not hard I confuse easily

I don't think we are talking about the same thing. My plotter is not integrated with my navigation software on the computer, or with the wind instruments. My computer is linked to a handheld GPS only. Yea I know I should integrate everything together and it's on the (never ending) to do list

Below is a screenshot from the navigation software showing three tacks of the UFO 34 on Saturday. The total distance of the map is about 3.5NM from top to bottom. Wind was Southerly ranging from 7 to 13kts.

The information in red are the details from a "range and bearing lines" function on the navigation software. The first leg is showing 967m (range, which we can ignore) 132 degrees True and 134 degrees magnetic (bearings). The second leg shows 1.8 nm, 248 degrees T and 249 degrees M.

What I have done is taken the two true bearings and subtracted one from the other ie, 248 less 132 is 116. This is what I am assumming is my tacking angle, ie 115-120 tacking angle is the average for a number of tacks.

Paulo, I am not familiar with the system showing on your plotter. However if I understand it correctly if your plotter was on my boat I believe it would be giving a reading of 64 (rather than 90 or 120) using the bearings of 248 and 132 from the above example. However I could be totally confused!!!!

Ilenart

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