What, exactly, is a tacking angle

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homer

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In boat tests, they always quote a tacking angle; 85 degrees, 90 degrees or whatever. Simple question, but are they talking about the angle between the headings on each tack or the angle between the course made good (i.e. including leeway). Can be quite a difference on some boats!
 
homer said:
In boat tests, they always quote a tacking angle; 85 degrees, 90 degrees or whatever. Simple question, but are they talking about the angle between the headings on each tack or the angle between the course made good (i.e. including leeway). Can be quite a difference on some boats!
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The angle between the headings on each tack.
 
As far as I am aware it is the difference between the headings as indicated by the compass

It was often quoted in the days long before GPS was available and able to easily display COG.
 
VicS said:
As far as I am aware it is the difference between the headings as indicated by the compass

It was often quoted in the days long before GPS was available and able to easily display COG.
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+1 except I would expect a guess of leeway taken into account. Although this makes it very ambiguous :eek:.

Hence forth with or without GPS people can argue in bars about which boat has a smaller one :D
 
onesea said:
+1 except I would expect a guess of leeway taken into account. Although this makes it very ambiguous :eek:.

Hence forth with or without GPS people can argue in bars about which boat has a smaller one :D
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Surely once you take leeway into account and compare wake courses you would ( in the absence of tidal effects ) be talking about COG.
 
Whoever the merits of each approach I can say that I have had several journalists on board doing articles and when checking the tacking angle they have all used the compass.

So, what you read in their articles is heading.
 
'Tacking angle' is a totally erroneous computation invented by yachting journalists.
It has no merit even when applied to a single (individual) vessel let alone as a comparator between different designs!

Eg. If a vessel can tack at 45/45 = 90 - and do (say) 4 knots @ 45 Deg - what does that mean if the same vessel can do 50/50 = 100 and do 7 knots by not pinching?

VMG means something - 'Tacking angle' means nothing.
 
VMG means something - 'Tacking angle' means nothing.
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If someone tells me their "angle between tacks" is 80° it means that their boat will sail much closer to the wind than mine will

If someone tells me their VMG is 5 knots it tells me nothing other than that they were making 5 knots towards their destination...
 
VicS said:
If someone tells me their "angle between tacks" is 80° it means that their boat will sail much closer to the wind than mine will

If someone tells me their VMG is 5 knots it tells me nothing other than that they were making 5 knots towards their destination...
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I can ' Sail' i.e. fill my sails at 70 degrees (35/35) if I stay in irons - what does that tell you? Please give an accurate number in terms of my achievement.

If I put solid sails on (eg. sheets of plywood) they will not flap at 0 degrees - am I 'sailing' ??
 
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I can ' Sail' i.e. fill my sails at 70 degrees (35/35) if I stay in irons - what does that tell you? Please give an accurate number in terms of my achievement.
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That tells me that once your angle to the wind exceeds 35 you will start to make progress through the water .... a darn sight sooner than my boat will.


If I put solid sails on (eg. sheets of plywood) they will not flap at 0 degrees - am I 'sailing' ??
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That tells me that you are just being stupid

good night!
 
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Tacking angle

Everything so far said is correct. Nevertheless to check your tacking angle when beating can be an interesting exercise. That is the angle that you tack through from the heading you had when you reckoned you were sailing correctly. I find it is useful to have a speed readout so that you can see how you are going.

Most of our kind of boats have a max useful speed something above hull speed ie when running or reaching but beating will be around 70% of that speed. This all assuming plenty of wind. (and correct sail area for the wind) So when beating a quick check of speed will identify if you are pinching ie going too slow even at a closer angle to the wind or if you are too far off the wind for efficiency in best CMG. (course made good which is the outcome you want)
Of course to sail really close to the wind but not too close (ie with tell tales on the jib just lifting) means that any wind shift will become obvious which means you can take advantage of the lift or respond to the knock. This takes real concentration which is part of successful racing. ie makes it a sport.
incidentally if you get a chance to see any Womens Match Racing in the olympics have a look for some really fantastic sailing and crew work in 6metre boats. good luck olewill
 
Thank you all for that - confirmed what I suspected. I reckon that the angle between COGs would be more meaningful - and easy enough to measure nowadays. (I agree that you would need slack water (or tide exactly between tacks) to be accurate.
 
It depends what you want to know.
On my dinghy, the tacking angle is about 80 degrees, i.e. the number on the compass changes by 80 when I tack. A bit more in rougher conditions
This tells me a lot about windshifts, because I use it to compare headings between tacks.

Leeway is of no interest, because I'm not doing DR, I can't change the leeway and it's much the same for everyone. Knowing my simple tacking angle is useful in watching windshifts and doing well in races.
Using GPS, you could get the same info, but it would include leeway, and be subject to the delays and averaging of your gps, whereas compass course is instant (ish) and you can mentally filter out any bits where you are pinching or sailing free or ducking a stbd boat etc.


If you are doing DR, you will need to allow for leeway.
If you are sailing in tide, you might only care about your COG on the two tacks at any given time.
 
tacking angles

I agree that it is VMG you are after more than just tacking angle. But using a GPS with tracking on, and sailing a real upwind course, computing the tacking angle via COG (i.e. including leeway, etc.) will give you a tacking angle that can be highly useful for comparing boat performance. Timing and measuring your legs will give you your VMG's.

That said, real world performance, at least for cruising boats is often far off of the magic 90 degrees. I have run the above tests for my boat in racing conditions, where I performed in line with a wide range of other cruisers and racer-cruisers (tartans, older sabre's, C&C's, full keels, fin keels, etc.). 70 is the best I can do. Only the 'go-fasts' seem to do significantly better than this.

Interested to hear results from others who may have done the GPS COG angle test.
 
KellysEye said:
The tacking angle by definition includes lee way.
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Seems to depend on whose definition you use!

I agree that including leeway seems more useful for comparing different boats (currently I'm rather interested in what I can expect to get out of a Westerly Storm) and also for planning (can I get to X in one tack?). But with some people reporting it as the difference between headings and others the difference between ground tracks (plus a few in between), it can be hard to properly compare.

Pete
 
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