So How High Will a Cat Point?

[estarzinger]

Originally Posted by daddle

10kts of breeze, My AWA, 30 degrees. Tacking angle around 70.

Originally Posted by 44'cruisingcat

the only way your AWA could be so close to the TWA is if you were going pretty slow.

Daddle, can you help us understand this?

If your tws was 10kts, AWA 30 degrees and TWA 35 degrees (1/2 of your 70 degree tacking angle), then by definition your boat speed was 1.75kts - which does not sound very good!

To be perfectly honest the track you posted looks like a boat motor sailing upwind - 35 degree true wind angle is tighter than even the current America's Cup multi-hulls sail!

[Factor]

Originally Posted by Joli

.... Do you carry the same sail area in 20 knots regardless of point? App is what we sail in.....

I take your point and I dont want to be argumentative, but true is what I sail in and apparent is what I deal with. Being aware of true is critical for any boat but extremely critical on a multi, and more so on a quick one. My last Tri might do 12 - 15 knots on a very broad reach in 20 knots of wind for example. If all I worried about was apparent I would say that I am sailing in 8 knots or so. If I came up to 35 off the wind quickly I would be in a whole different world. You must deal in both wind thoughts, you must sail in apparent but remember what the true is so that you can plan for changes.

[daddle]

Originally Posted by estarzinger

Daddle, can you help us understand this?

If your tws was 10kts, AWA 30 degrees and TWA 35 degrees (1/2 of your 70 degree tacking angle), then by definition your boat speed was 1.75kts - which does not sound very good!

To be perfectly honest the track you posted looks like a boat motor sailing upwind - 35 degree true wind angle is tighter than even the current America's Cup multi-hulls sail!

It's all accurate. All thru this thread the terms are getting confused. Apparent vs. True. Pointing vs. VMG. And I wasn't perfectly clear either.

In the pic above Joli is correct. It's a SC50 monohull. I'm a multi sailor too. I was sailing in about 10kts true wind, maybe a bit more. I almost never look at the TWS display. High teens apparent. Boat speed was rather unknown as I'd left the speedo/fun-meter/crab-home sensor out of the hull. But I was moving along smartly, probably 7 kts. No motor. That would be cheating as well as noisy. The current was negligible. The waters protected. Did I mention the 86 degree clear water and ice cold beer? The numbers should crunch properly. AWA might be less than 30 at the masthead. This boat really moves.

Nobody commented on the track crossing shoals? Those were coral reefs that were easily seen and avoided.

Pointing angle (not tacking angle) is governed by the headsail sheeting angle on the typical mono or multi. If the boat is properly designed, the sheet block tracks will be in the right place. On a performance mono about 7 to 9 degrees from the centerline. On a multi a few more. Plus you need to be able to grind the headsail flat. Which implies a new-ish sail.

With eight 'heeling moment engineers' on the rail and a race 155% genoa that tacking angle could be a few degrees tighter and the VMG higher.

I cannot do those angles in a multi. Just a few degrees more. But I can come way closer than most here would imagine with proper sails and sheeting. And good race winning VMG too.

[estarzinger]

Originally Posted by daddle

I was sailing in about 10kts true wind. High teens apparent. Boat speed was rather unknown as I'd left the speedo/fun-meter/crab-home sensor out of the hull. But I was moving along smartly, probably 7 or 8 kts. The numbers should crunch properly.

Well, no, they don't. Not even close. Your reported apparent and true wind angles are just simply too close to allow for any boat speed (1.75kts is the result as I mentioned above).

Let's take 17kts apparent wind speed and 30 degrees apparent wind angle and 7 kts of boat speed. That would produce a 47.7 degree true wind angle = 95 degree tacking angle (with no leeway). That would all be perfectly reasonable and understandable and in fact quite decent performance for a cruising multi, but does not correspond with the70 degree reported 'tacking angle' or the track you posted.

Or let's take 35 degrees true wind angle, 10kts true wind speed and 7kts of boat speed. That produces a 20.7 degree apparent wind angle, which is closer than even the most close winded AC mono-hull will sail, and obviously closer than the 30 degrees you report!

The math does not lie. So, there is a problem with this story somewhere. On our 'slow' mono, we often pull the apparent wind almost 20 degrees forward of the true in 10kt winds

[Joli]

Evans, awa for a SC 50 is probably closer to 24 or so. That gives BS of 7.5, twa of 13 and awa of 24.

Those numbers work and yield an upwind vmg of 6.1~6.2.

I don't know target though.

Originally Posted by estarzinger

Well, no, they don't. Not even close. Your reported apparent and true wind angles are just simply too close to allow for any boat speed (1.75kts is the result as I mentioned above).

Let's take 17kts apparent wind speed and 30 degrees apparent wind angle and 7 kts of boat speed. That would produce a 47.7 degree true wind angle = 95 degree tacking angle (with no leeway). That would all be perfectly reasonable and understandable and in fact quite decent performance for a cruising multi, but does not correspond with the70 degree reported 'tacking angle' or the track you posted.

Or let's take 35 degrees true wind angle, 10kts true wind speed and 7kts of boat speed. That produces a 20.7 degree apparent wind angle, which is closer than even the most close winded AC mono-hull will sail, and obviously closer than the 30 degrees you report!

The math does not lie. So, there is a problem with this story somewhere. On our 'slow' mono, we often pull the apparent wind almost 20 degrees forward of the true in 10kt winds

[estarzinger]

Originally Posted by Joli

Evans, awa for a SC 50 is probably closer to 24 or so. That gives BS of 7.5, twa of 13 and awa of 24.

Those numbers work and yield an upwind vmg of 6.1~6.2.

I don't know target though.

Joli, I believe the numbers and track Daddle posted are for his multi, not the SC (could be wrong about that)? But in any case he is the one who said 30 degrees AWA.

Let's say we are dealing with a very close angled 24 degree AWA mono. There is still a problem with the story - lets say AWA = 24, BS = 7.5 and true wind angle=35. That implies TWS = 16 to get those tacking angles - which is rather windier than the quoted 10kts.

I don't know what/where the problem is, but the numbers just don't add up somewhere/somehow.

As an aside question - Can an SC50 actually sail 7.5kts in 10kts (true) at 24 AWA in the real world (which just fyi would still produce a greater than 70 degree tacking angle, 84 degrees). Or is that the design polar? The SC50 was I thought optimized for downwind not up? Just curious - Hawk manages 27 AWA (with new sails and a clean bottom) and I thought that was pretty good.

[Joli]

Certainly we have to be aware of true, otherwise we'll both be repairing expensive gear.

I think much of this thread was led astray by a question that isn't germain. The real question is, what is the upwind VMG for a multi?

The short answer. It depends on the multi.

Originally Posted by Factor

I take your point and I dont want to be argumentative, but true is what I sail in and apparent is what I deal with. Being aware of true is critical for any boat but extremely critical on a multi, and more so on a quick one. My last Tri might do 12 - 15 knots on a very broad reach in 20 knots of wind for example. If all I worried about was apparent I would say that I am sailing in 8 knots or so. If I came up to 35 off the wind quickly I would be in a whole different world. You must deal in both wind thoughts, you must sail in apparent but remember what the true is so that you can plan for changes.

[tsmwebb]

Just for fun the attached is what Ian Campbell modeled for USA 17 here. Despite some surprises it is close to what they actually achieved.

Tom.

[Joli]

Could be the numbers were a guess? Does any of this suprise you?

Most folks don't have processor driven instruments with sampling rates high enough to give meaningful numbers. Other then maybe you, me and Tom who really gives a **** about upwash angles, shear and target driven polars?

For the record, our numbers are awa 26, bs 10.4 and aws 24 yielding a vmg of ~7.5 with a full crew and a 155%.

Honestly though I would rather go reaching, maybe the multi guys have it right? Palarran seems happy enough to reach when he can then motor upwind when he can't.

Originally Posted by estarzinger

Joli, I believe the numbers and track Daddle posted are for his multi, not the SC? And he is the one who said 30 degrees AWA.

But, let's say we are dealing with a very close angled 24 degree AWA mono. There is still a problem with the story - lets say AWA = 24, BS = 7.5 and true wind angle=35. That implies TWS = 16 to get those tacking angles - which is rather windier than the quoted 10kts.

I don't know what/where the problem is, but the numbers just don't add up somewhere/somehow.

[tsmwebb]

Originally Posted by Joli

The real question is, what is the upwind VMG for a multi?

The short answer. It depends on the multi.

Aha! I agree with you completely here!

Tom.

[estarzinger]

Originally Posted by tsmwebb

Just for fun the attached is what the Ian Campbell modeled for USA 17 here. Despite some surprises it is close to what they actually achieved.

Tom.

Thanks, that's an interesting tidbit in the multi-hull speed debates. So, in 10kts true that's suggesting a 44 degree true wind angle for max vmg. WHich is also very close to what I understand the AC45's are doing.

But they are doing vmg 2x wind speed!!! That's almost not sailing as we know it. HAve to come up with a new name for this

[tsmwebb]

Originally Posted by estarzinger

That's almost not sailing as we know it. HAve to come up with a new name for this

Roughly speaking sailing twice the wind speed, VMG of 1.5 times the wind speed, Apparent angles at VMG less than 15 degrees (closer than an IACC v5)... It is not remotely like sailing performance as I am ever likely to know it! But, I think it's kind of cool to know it's out there. "DOG speed"?

Tom.

[Nicholson58]

My 'toy boat' is an international Tornado. - An older high performance cat. It gives up about 15 degrees leeway on point with boards up and has weather helm. Boards down leeway is about 3 degrees and the helm is totally balanced. Not the same as a cruiser but the trend is instantly clear. It will also out-point any monohull I have sailed with.

[daddle]

Originally Posted by estarzinger

I don't know what/where the problem is, but the numbers just don't add up somewhere

I think your vector calculations have gone astray on instrument error.

The OpenCPN track plot is real. Honest. It is affected a little by my tacking on shifts if allowed by the shoals.

The boat speed is a guess on my part. It seemed like 7-8 knots. The GPS read in that range when I happened to look.

Apparent wind can have significant errors in measurement. The masthead genoa bends aft and accelerates the wind at the masthead. Boobies glide up there so apparently the wind is actually going up at the masthead...and as the top telltail tends to indicate. A very long stick on the masthead sensor might help, but then it is ruined for downwind sailing where I really need it.

A well set up boat, mono or multi, can point high like this. Especially on flat water...as the polars assume.

I don't sail upwind by the instruments. I trim the sails to 'look right'. Steer by the telltails and shifts.

[estarzinger]

Originally Posted by daddle

A well set up boat, mono or multi, can point high like this.

hmmm . . . Its impressive and I congratulate you, but I would say you are in quite elite territory with a 70 degree tacking angle. What other boats have you sailed that could actually achieve a less than 80 degree tacking angle?

I don't think I know any cruising boats that can do that, and not all that many race boats. Most racing polars I look at suggest an optimum true upwind angle in the 40's (80-90 degree 'tacking angle', excluding leeway). And even pretty good cruisers tend to be in the 90-100 degree range.

Many sailors just don't understand how brutal the math is. If you are going fast, you ARE going to be pulling the wind forward, and that DOES make the tacking angle broader, unless perhaps you have a rigid wing sail. It is hard to make the math work for 70 degree tacking angles in 10kts, unless the boat can sail at 20 degree apparent wind angles; but as you say perhaps there are some significant instrument errors and it was windier than you thought.

Just FYI, for the "Alpha" C-class (one of the most high performance rigid wing multihull boats available) the polar angles are 90 degrees up to 8kts TWS, 86 up to 12, 84 up to 16.