Cats Can't Sail to Windward....

[mark_morwood]

Originally Posted by belizesailor

I do it all the time, tack thru a physical angle of 110d (even have my AP programmed for that), then after gaining some speed, sheet in and head up to 45d AWA.

How does that "not work"?

Are you tacking through 110degrees True/Compass or AWA?

I think a number of us were assuming your tacking angle was True/Compass in which case for many of the boats here you would probably already be sailing higher than 45 AWA after the tack and if you were trying for max VMG upwind you would be be coming up to an AWA angle closer to 30 degrees.

If you were tacking through 110 degrees AWA then for many of the boats here that would be going from a reach (relative to True wind or compass) to the opposite reach.

As examples of the math, assuming 15 knots TWS and 8 knots boat speed
55 AWA = 88 TWA (if you were tacking through 110 AWA)
45 AWA = 76 TWA
30 AWA = 56 TWA (if you were tacking through 110 TWA)

Mark.

[44'cruisingcat]

Originally Posted by belizesailor

I do it all the time, tack thru a physical angle of 110d (even have my AP programmed for that), then after gaining some speed, sheet in and head up to 45d AWA.

How does that "not work"?

Already explained. For me to sail at 45' apparent, I'd be tacking through around 180' true.


But tack through 110', come up to 30' AWA works...

[belizesailor]

Originally Posted by mark_morwood

Are you tacking through 110degrees True/Compass or AWA?

I think a number of us were assuming your tacking angle was True/Compass in which case for many of the boats here you would probably already be sailing higher than 45 AWA after the tack and if you were trying for max VMG upwind you would be be coming up to an AWA angle closer to 30 degrees.

If you were tacking through 110 degrees AWA then for many of the boats here that would be going from a reach (relative to True wind or compass) to the opposite reach.

As examples of the math, assuming 15 knots TWS and 8 knots boat speed
55 AWA = 88 TWA (if you were tacking through 110 AWA)
45 AWA = 76 TWA
30 AWA = 56 TWA (if you were tacking through 110 TWA)

Mark.

That could be part of the sematics issue, I always refer to tacking angle as an absolute angle, not relative. Ive stated that a couple of times, but may have been missed.

If I'm sailing on a starboard tack at 45 AWA and I tack thru 110 actual physical angle, I wont be on a 45 AWA on port, I will be at a greater AWA (exact angle depending on boat speed after tack, which will be less that it was while sailing on stb tack).

[belizesailor]

Originally Posted by mark_morwood

Are you tacking through 110degrees True/Compass or AWA?

I think a number of us were assuming your tacking angle was True/Compass in which case for many of the boats here you would probably already be sailing higher than 45 AWA after the tack and if you were trying for max VMG upwind you would be be coming up to an AWA angle closer to 30 degrees.

If you were tacking through 110 degrees AWA then for many of the boats here that would be going from a reach (relative to True wind or compass) to the opposite reach.

As examples of the math, assuming 15 knots TWS and 8 knots boat speed
55 AWA = 88 TWA (if you were tacking through 110 AWA)
45 AWA = 76 TWA
30 AWA = 56 TWA (if you were tacking through 110 TWA)

Mark.

That could be part of the sematics issue, I always refer to tacking angle as an absolute angle, not relative. Ive stated that a couple of times, but may have been missed.

If I'm sailing on a starboard tack at 45 AWA and I tack thru 110 actual physical angle, I wont be on a 45 AWA on port, I will be at a greater AWA (exact angle depending on boat speed after tack, which will be less that it was while sailing on stb tack).

[belizesailor]

Originally Posted by 44'cruisingcat

Already explained. For me to sail at 45' apparent, I'd be tacking through around 180' true.


But tack through 110', come up to 30' AWA works...

Ah, you are referencing tacking angle relative to true wind right?

I am not, I always use the actual physical angle.

[44'cruisingcat]

Well unless there's a wind shift during the tack, the tacking angle relative to true wind should be the same as the actual physical angle...


Anyway, I was referring to the physical angle.

[44'cruisingcat]

Originally Posted by belizesailor

That could be part of the sematics issue, I always refer to tacking angle as an absolute angle, not relative. Ive stated that a couple of times, but may have been missed.

If I'm sailing on a starboard tack at 45 AWA and I tack thru 110 actual physical angle, I wont be on a 45 AWA on port, I will be at a greater AWA (exact angle depending on boat speed after tack, which will be less that it was while sailing on stb tack).

If you're sailing at 45 apparent and 55 true, (tacking through 110 actual degrees) you're not going very fast relative to the wind. ie about 2.5 knots in a 10 knot breeze.

[44'cruisingcat]

And a VMG of around 1 1/2 knots...

[thinwater]

Originally Posted by 44'cruisingcat

Well unless there's a wind shift during the tack, the tacking angle relative to true wind should be the same as the actual physical angle...


Anyway, I was referring to the physical angle.

Sounds like there is a problem (no specific poster) in terminology. Of course, I may have this wrong

• AWA. What is sounds like. What the gauge says.
• TWA. What is sounds like. True angle to the boat. Can get this from the compass.
• Physical angle. Could be TWA. But to me I would use this for angle over ground by GPS. Corrections are to be made for both current and leeway, that latter of which may range from 3-8 degrees, depending on the boat and course. Leeway, as we know, is major. Thus, the TWA and the physical angle probably differ by 6-16 degrees, which is ton. My TWA is typically in the 80s, but my physical angle 95-100, remembering that for cats there is a relatively wide bucket of TWA that gives the same VMG (sail faster, less leeway); the best choice depends on sea state, wind speed, and obstacles.
• VMG. This can be calculated either through the water or over ground by GPS. In the absence of current, only over ground makes any sense, since when the boat computes this leeway is often ignored.

So TWA is relatively meaningless in the absence of good leeway data and I generally ignore it. I know my AWAs and I check tacking angle over ground when I tack. I calculate VMG from GPS speed and GPS angles, since in that way leeway is included. Current is more complicated, but can often be inferred from the data. Surface current (induced by the wind) is another factor.

---

I'm guessing that not everyone enjoyed trigonometry.

[44'cruisingcat]

Hmm, but leeway would be the difference between your heading and your COG right?


I don't believe Belizsailor was referring to that. He seemed to me to be referring to the change in heading after tacking.


He even states that he has his autopilot programmed for a 110 degree course change when tacking. That would be from the compass, not the GPS surely?

[44'cruisingcat]

Raises an interesting question though - how would leeway compare between mono's and cat's?


I would have thought minikeel cat's might experience similar leeway to mono's. Monohull keels wouldn't be all that efficient (at preventing leeway) when the boat's heeled over.


Daggerboard cat's would be better than both, I'd expect.

[thinwater]

^^ Can't guess what some of these posts mean. Geometry is geometry. Vectors are vectors.

Understanding leeway is vital to understanding windward sailing. Just a few months ago I revised my keels significantly (10 inches longer) to resolve handling problems and compensate for an up-sized rig. MAJOR change, all positive.

I don't think hard and fast rules are good, data is better. Some mono fin keels go to China, some dagger boards are too small, mini-keels on cats vary a lot, and balance makes a huge difference (is the board over loaded by imbalance?). I've made a number of changes* to my boat that cumulatively increased VMG by about 30%; any simplistic rule based upon basic designs could would fail to predict the before/after difference.

I suspect that golden age sailor navigating by dead reckoning had a VERY good feel for leeway. I learned and practiced that, before GPS. IF you are not honest with yourself, it shows.

*Extended waterline, changed sheeting angles, keel mods, reduced weight

[belizesailor]

Originally Posted by 44'cruisingcat

Hmm, but leeway would be the difference between your heading and your COG right?


I don't believe Belizsailor was referring to that. He seemed to me to be referring to the change in heading after tacking.


He even states that he has his autopilot programmed for a 110 degree course change when tacking. That would be from the compass, not the GPS surely?

110 PSC (which in this case is the fluxgate compass of the auto pilot). I have it set for that for sinle handed tacking. Fluxgate has been swung recently and variation here in the W Carib is small.

Rather than continue to beat this horse, which likely just boils down to semantics and differences in boats, I will be back on the boat in a couple of weeks. Will try to play around and collect some data...even found a nifty little racing tactics app that should help with that.

Of course, my anomometer is out of comission, which is less convenient, but can sort that out other ways.

[thinwater]

In that case, the tacking angle over ground is probably about 110 + 12 = 122 degrees. Easy sailing, but not high.

When heading high my compass angle is about 85, but the result is closer to 100. At a compass of 110 I am full and by, not pointing.

---

As an aside, I did move the genoa leads in, but not so far that I can over pinch. If I try to point any higher than this the genoa shakes, which is my intention. In this way I do not over press the keels and slide. For boats with limited lateral plane, I think many over sheet and over pinch leads.

[belizesailor]

Originally Posted by 44'cruisingcat

Raises an interesting question though - how would leeway compare between mono's and cat's?


I would have thought minikeel cat's might experience similar leeway to mono's. Monohull keels wouldn't be all that efficient (at preventing leeway) when the boat's heeled over.


Daggerboard cat's would be better than both, I'd expect.

My initial thought was that mini keel cats would experience more leeway in moderate to heavy conditions, but Ive also sailed shoal draft monos which had major leeway in similar conditions (reefing early and deep helps on shoal draft monos).

So in the end it probably comes down to draft and lateral resistance, more so than number of hulls.