Measuring Angle of A "Tack".... (pointing)

[Squidd]

How do you measure the angle of a tack.... I hear people say there boats point at 40* or 35* (mine seems more like 90* between tacks)...

Lets say I want to go North (0*) and the wind is coming from the north...

Should I look at my compass on a starboard tack (say 40*) and then add the difference on a port tack (say 320*)...to come up with 80* and then divide by 2 for pointing angle...?

Or is there something else to the formula...?

 

[Squidd]

Whats the desired (preferred) pointing angle then....I know depends on boat/conditions of sails etc..

But in general what is the range of "normal" compared to what is too wide and needs to be addressed..?

 

[Jackdaw]

Nope, you're on it.

The tacking angle is the difference between the boats HEADING (not course) on two close-hauled tacks. Most cruising boats will tack through 90 degrees in a moderate breeze. Race boats will be 80 or below. The angle typically gets better in more breeze, worse in less.

When people mention numbers in the 35-45 degree range, then are simply talking about the boat's heading with respect to wind direction (1/2 of the tacking angle).

 

[justsomeguy]

Well, there's true wind, and there's apparent wind.

When it's blowin' good, my little boat seems to point much better into the true wind, but when the breeze is negligible, the apparent wind really destroys her pointing ability.

There may be some degree of operator error in my light wind sailing technique.

I'd have to guess that the most objective determinant would be relative to the true wind.

 

[Stu Jackson]

Tacking angles

Boats tack through apparent wind. The ONLY thing that true wind will affect is when you are head to wind, and unless you have instrumentation you won't know what true wind is until you are head to wind and the sails are luffing.

Don Guillette's excellent Sail Trim Book & Charts are the best information on this I have seen in 35+ years of sailing. He explains the differences quite well.

To the OP, Jack's right, but in your original post you did the math twice!

The reality, unless you're on a real racing boat, is that you won't get anywhere near the 80 degrees (40 on each side !) you mention. Most recreational cruising boats, including cruiser/racers will do more like 100 to 120. I've sailed our boat in a C34 one design fleet for over 15 years, and even the very best skippers in our fleet are really pushing it to hit 100. If you have a J boat then you're in a different category.

Good luck, you got the idea right.

 

[Jackdaw]

I've sailed our boat in a C34 one design fleet for over 15 years, and even the very best skippers in our fleet are really pushing it to hit 100. If you have a J boat then you're in a different category.

Good luck, you got the idea right.

Stu brings up a very good point. For optimal progress to windward, (called VMG), all boats will be better footing off slightly from their tightest angle. Cruisers farther than raceboats. So in a C34 race, although the boat might 'point' into 45 degrees true wind, a smart skipper will foot off to 49 and make more speed that covers the extra distance sailed, so he has better VMG to the mark.

 

[justsomeguy]

Boats tack through apparent wind. The ONLY thing that true wind will affect is when you are head to wind, and unless you have instrumentation you won't know what true wind is until you are head to wind and the sails are luffing.

-snip

Just goes to show you, if you want the right answer, post a wrong one.

However, it still seems to me that apparent wind has a much more deleterious effect on pointing at lower wind speeds.

I figure true wind (if it's consistant ) to be coming from mid-point of my tack angles.

 

[Stu Jackson]

I figure true wind (if it's consistent) to be coming from mid-point of my tack angles.

That's correct. Assuming your tacking angles are equal both sides. Many skippers have reported over the years that their boats sail at higher angles on one side or the other. While not gemaine to this discussion, I have never seen it in reality, although those skippers may have better instrumentation to be able to measure it.

 

[justsomeguy]

Ah, thanks for correcting my little spelling error. I hate it when I do that.

 

[Jackdaw]

Many skippers have reported over the years that their boats sail at higher angles on one side or the other. While not gemaine to this discussion, I have never seen it in reality, although those skippers may have better instrumentation to be able to measure it.

It happens. Normally the mast is not centered on the boat. That's a rigging issue. Or the keel is not centered. That happens more then most people might think.

Speed tip: if you keel is not vertical, center your mast to IT, not plumb on the waterline.

 

[Jackdaw]

One other thing:

Although your boat sails in apparent wind, tacking angles are always expressed in TRUE. Mostly because that's what your compass sees and measures. There is a notion of a Apparent Wind tacking angle, but its not very useful because its total and constant relationship to boat and wind speed.

 

[Stu Jackson]

Ah, thanks for correcting my little spelling error. I hate it when I do that.

Me, too. Oh, not when YOU do it, but when I do!

Download iespell.

 

[Scott T-Bird]

I don't really watch my heading but I do watch my apparent wind angle on the instrument panel. I try to keep the apparent wind at 45 degrees and I know that true wind is always a bit aft. So I know that my tacking angle is hopefully 100 to 110 degrees. I tell Sue to try to keep it between 45 and 60 because she wanders upwind when she's looking around and I get fidgety when the sails begin to luff. At 60 degrees apparent, the boat sails very nicely and I don't have to interject in behalf of the sail trim nearly as often, which makes it much easier for the both of us to get along!

When I look at the GPS track, I cringe because I can see it's not 90 for sure. The gusts almost always give me a lift ... it's not normally a wind shift, just apparent wind moving aft, allowing me to head up.

On those wind shifty days, why does the wind always knock me down? Saturday afternoon I felt like I was sailing at a 90 degree angle from my destination for long stretches on both sides. It was getting frustrating!

 

[justsomeguy]

snip-

When I look at the GPS track, I cringe because I can see it's not 90 for sure. The gusts almost always give me a lift ... it's not normally a wind shift, just apparent wind moving aft, allowing me to head up.

On those wind shifty days, why does the wind always knock me down? Saturday afternoon I felt like I was sailing at a 90 degree angle from my destination for long stretches on both sides. It was getting frustrating!

Me, too, when the wind is light. Frustrating for sure.

Image of track was with winds of about 3 kts, maybe.

 

[Joe]

Your tacking angle...when discussing degrees from one closehauled tack to the other is measured against true wind direction, it can vary with wind speed, or sea state on one tack or the other.....but you can easily determine that when you first go out. You can determine true wind direction by taking the average between the starboard and port tack headings when close hauled.......... those number will allow you to determine the lay line, whether you're ahead or behind another boat, or whether you are clear to tack across. On my boat, if I can get 90, I'm happy as a lark... but it there are waves or tidal issues it will vary... usually 100 is more common... I've never got below 90.

Apparent wind is used to trim the sails... if you keep your apparent wind at 45 deg...you will not sail a straight course if boat speed changes, OR if true wind speed and direction change. So.. once you set your course and adjust your sails and your AWD is 50, say, then as long as boat speed, true wind dir and speed, are the same then your AWD will stay at 50.... but... if your boat speed increases your AWD will move forward to 45 say... now you figure you're at your optimum trim angle (this is common for daysailing) so you steer the boat using the masthead fly (AWD) or jib telltales then check your course... guess what? Ask yourself why it's called APPARENT.... and TRUE.

So what do most folks do.. myself included... when they're out for an afternoon's pleasure... they trim the sails, then steer to the tell tales or use the AWD of 45 deg to keep moving pleasantly along, listening to their favorite remix or an Angel game and sipping a non-alcohol St. Pauli Girl....

 

[Rick]

If I could chime in with an observation more than a formula, it might help to just dumb it down a bit unless you are talking something really technical, which a boat of your stature does or probably cannot apply. Me personally I sail for fun and although I am an engineer just have a hard time digesting some of the stuff here from the skippers because we have some EXTREMELY smart people and I choose DUMB when I go sailing. (actually have a class win in the Newport to Ensenada Interntaional Yacht race though.. lol)

Are you rigged with a Jenny or a Jib, would be my first question? Looking at the stats on your really cool boat BTW, I believe personally that makes your decision a bit more interesting. If you have a Jenny then that is your sailing engine. A Jib probably means your main is your engine. I saw your boat rigged both ways in spec.

You can do alot of math or you can pick a moderate day, say 10 knot winds and test theories about your rig. Put your main to center and move the draft as close to the point where it is effective, say 40 percent draft. Now just tighten your Jenny or Jib until the foot is trimmed or as tight as you can get it with the overall wind component (apparent) at 45 degrees (keeping in mind tough to do with a Jenny). Now you have a rig configuration that will give you a control that you can work with albiet normal deviations. Keep pinching until you see the speed drop off or a luff and hang there. Note the true and apparent wind and are you inside of 45 degrees which is typically the edge of the no sail zone. Now pick a land mark and turn her 90 degrees. Adjust and see if you can get the same speed switching tacks, of course taking into account current, jib cars equal (now if they are you can actually measure your sheeting from the clew to the jib cars so you can get equal distance on either tack), etc. Whew.. take a tall pull off your cocktail! That will give you a base with "fixed" conditions AND will create your window and angle for a "standard" tack. After that the rest is adjusting to feel of the boat, trimming to telltales, and then all the good stuff Don talks about in his book. AND all the great advice guys gave about it actually being more than 90 and up to 50 degrees or greater to keep her effectively moving. The relationship of apparent wind and true wind is always "breathing" depending on boat speed. That sums up an overall "headwind" component that creates your "no sail zone".

Its quite fun actually with a cocktail and a fun crew. Course as mentioned above, public math can be a real biatch. Joe got it right.

Cheers