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Old 15-06-2019, 18:10   #1
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Newb Multihull wind angle question

I had the absolute pleasure of sailing on a crowther cat today that had been stripped of all of its fat and is a very fast boat.

Like a lot of monohull people i found myself confused about the apparent wind angle. At one point we tacked through probably 140 degrees and i found we were close hauled all over again. The boat was moving at about ten knots in maybe 13-16 knots true.

So does making your own wind mean that you are confined to that vector of wind angle? Like, are you no longer able to tack through 90 degrees because your wind angle creeps up as you accelerate?

Iíve been sailing long enough and have watched enough foiling cat footage to know this by now so donít beat me up too bad with the answers. I just canít seem to figure it out.
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Old 15-06-2019, 19:10   #2
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Re: Newb Multihull wind angle question

You nailed it.

As the boat speed increases the apparent wind comes forward. So running close hauled let's say at 40 degrees apparent wind angle at 10 knots boat speed results in much broader tacking angles than the same 40 degrees apparent wind angle at 6 knots boat speed in the same conditions.
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Old 15-06-2019, 20:05   #3
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Re: Newb Multihull wind angle question

I go by my VMG gauge as well as seat of the pants.
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Old 15-06-2019, 20:14   #4
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Re: Newb Multihull wind angle question

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Originally Posted by unbusted67 View Post
...
So does making your own wind mean that you are confined to that vector of wind angle? Like, are you no longer able to tack through 90 degrees because your wind angle creeps up as you accelerate?
...
No. You almost certainly could have come up (reduced the true wind angle) and sailed at a slower speed with roughly the same apparent wind angle.
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Old 15-06-2019, 22:46   #5
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Re: Newb Multihull wind angle question

You do have to be careful on a fastish cat with full sails, when going to windward.

If the sails get loaded up they get fuller. If you steer off the tufts then you bear away and the sail gets fuller. I have a crosscut genoa and in winds over about 12 knots I can't steer using tufts - I have to steer using true wind angle. (I am soon to buy a nice triradial genoa).

So the proper way to do this is get some nice flat sails and sheet them flat. If you do this then you will probably go faster by bearing away as much as you can whilst keeping the leeward tufts streaming. This is what the gun guys on a Mojo told us about one Gladstone race - the owner wanted to come up into the wind like on a mono, but the gun sailor had him bearing away as much as his beautiful carbon sails would allow - which wasn't much.

So, it depends. With lovely sails sheeted close and flat you can steer off the tufts, otherwise, you will be better served finding a best target boatspeed vs windspeed and staying there.

In the 80s there were lots of stories of cats sailing away in long races and disappearing from view (well one major story anyway) and then whilst the shorthanded monos plodded upwind they could see the big crosscut genoa cat storming back from the horizon and crossing under their sterns. After that the crew just got to a set speed and started pinching, not caring what the tufts said.

cheers

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Old 16-06-2019, 00:54   #6
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Re: Newb Multihull wind angle question

Phil, I came up with a kina silly question whilst reading your post: With opaque (ie carbon) sails, how do folks read their leeward telltals? i don't see clear windows let into such sails...

Jim
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Old 16-06-2019, 01:45   #7
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Re: Newb Multihull wind angle question

Our old mono used to sail at a bit over 40' apparent, and tack through not much more than 90'.

The cat sails at around 30' apparent and tacks through around 100'.

That's what happens when you sail twice as fast!

If I sailed the same AWA as we did in the mono we'd be tacking through about 160' and sailing fairly close to wind speed.

You do have to trade speed for angle a bit.

Our autopilot has a VMG optimiser function, which makes life easy.
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Old 16-06-2019, 02:47   #8
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Re: Newb Multihull wind angle question

On fast multihulls, cat or tri, there is a distinct difference between tacking angle and sailing angle. You may tack thru a broader angle due to drop in AWS and the nature of pushing multiple hulls thru the water, but you can quickly come back onto close hauled AWA as you rebuild boat speed. However, the faster the boat, the broader your sailing angle to TWA due to creating so much apparent wind. On serious go fast boats (incl monos) the AWA is almost never aft of beam...even if running DDW to TWA.

This can be very confusing when you tack as suddenly you lose most of that AWS and feel mostly true wind again...from a very unexcpected angle. The first time I tacked a Corsair F27...I nearly did a full 360 chasing the wind angle!
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Old 16-06-2019, 03:05   #9
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Re: Newb Multihull wind angle question

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Old 16-06-2019, 08:45   #10
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Re: Newb Multihull wind angle question

The SailGP boats sail upwind at 13' apparent, downwind at 19' apparent.
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Old 16-06-2019, 16:51   #11
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Re: Newb Multihull wind angle question

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The SailGP boats sail upwind at 13' apparent, downwind at 19' apparent.
In some wind speed perhaps, but certainly not in all windspeeds.
During AC35 in Bermuda, ETNZ sailed at 3 times windspeed with TWA of 150 degrees, which results AWA as 13.19 degrees.
I don't think sailGP is any slower in similar conditions.

Of course the wing causes upwash in front of it, so any wind instrument could show some other numbers, like 19 degrees caused by that source of error, but that really doesn't matter, does it?
13 degrees awa sounds pretty close correct for upwind case in similar conditions, but not in the heavier stuff.
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Old 16-06-2019, 17:18   #12
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Re: Newb Multihull wind angle question

So let me see if I am getting this right: Multihulls, because of the nature of their design do not generally point as high as monohulls.

That info aside, in a fast multihull, you may find yourself close hauled even with the TWA well aft of the AWA due to the boat speeding up and therefore bringing the AWA forward. As the multihull points higher though, boat speed will fall off as you get the bow of the boat pointing closer to TWA 45, therefore it is important to have a good indicator of VMG.

Does that sound right? Am I way off? I guess what I am wondering is, since you could be close hauled with the TWA aft of the the beam, then what happens when you point higher? Certainly you don't go into irons because TWA is actually well aft of your AWA irons point right?
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Old 16-06-2019, 17:19   #13
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Re: Newb Multihull wind angle question

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In some wind speed perhaps, but certainly not in all windspeeds.
During AC35 in Bermuda, ETNZ sailed at 3 times windspeed with TWA of 150 degrees, which results AWA as 13.19 degrees.
I don't think sailGP is any slower in similar conditions.

Of course the wing causes upwash in front of it, so any wind instrument could show some other numbers, like 19 degrees caused by that source of error, but that really doesn't matter, does it?
13 degrees awa sounds pretty close correct for upwind case in similar conditions, but not in the heavier stuff.
I was told this by one of the F50 sailors in Sydney. But what would he know?
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Old 16-06-2019, 20:36   #14
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Re: Newb Multihull wind angle question

How can a boat sail faster than wind?
By producing its own wind.
If you want to learn this, sail a beach cat. Start on a broad or beam reach with full power sails. As you start moving forward, the sailor keeps sheeting in until on a close hall making very flat sails. Then it stalls and he has to start all over with full power sails.
A big cat can do this but needs wind. Mine needs over 15knots of breeze before it will start producing apparent north of speed.
Multi hulls need to keep sheeting in while increasing speed.
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Old 16-06-2019, 21:27   #15
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Re: Newb Multihull wind angle question

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So let me see if I am getting this right: Multihulls, because of the nature of their design do not generally point as high as monohulls.

SNIP
While there are poorly designed multihulls that don't point well (and the same is true for monohulls) there are also multihulls that point quite well. Back in the day (like in the 1950s when I was learning to sail) my Dad use to point out that you could pinch a boat and sail closer to the wind but if you fell off your boat speed would increase.

As noted earlier modern chart plotters have a VMG function which makes the best course much easier to hold. Another important consideration to me is what I call easy sea motion. To some folks it is more important to be comfortable on a boat than make it go as fast a possible. I often will fall off more than necessary to prevent things like slapping and uncomfortable hobby horsing.
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