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Old 06-06-2018, 01:39   #1
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Help me improve VMG

I know I shouldn't believe the internet (except everyone on this forum of course). Looking at the claims made when sailing upwind my tacking angles seem pretty crap but speed and degrees to apparent seem good.

I'm hoping to improve VMG.

Yesterday I was able to run the boat at around 30 degrees to apparent on both tacks and it seemed happy there. If I went a couple of degrees closer to the wind I fell out of the sweet spot and lost drive, the tell tails looked good so I believe I was close to the maximum angle of attack but maybe that's not necessarily what I'm after ?

If I work my numbers out for true wind direction we were at 50 to 52 degrees to true most of the day so my theoretical best tacking angle would be 100 - 104 deg. My trace on navionics looks about 110 degrees maybe a bit more which looks about right. Discounting fantasy numbers or much better boats are numbers close to a 100deg between tacks really possible on similar boats, if so how do I improve my numbers.

As far as I can see the slower you go the better your tacking angles and the worse your VMG.
  • I had about 4 degrees of rudder on..........so I was slipping 4 degrees to windward ? Does it work like that?
  • Average breeze was 18kn apparent
  • Average SOG 8.5kn
  • Dagger boards down
  • No reefs
  • 120% jib
  • 0.75m chop
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Old 06-06-2018, 02:29   #2
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Re: Help me improve VMG

My summer trip every year for the last 4 years required me to get 1500 miles upwind every time, so I've spent a lot of time (and money) working on sailing upwind.

I would say you're doing fine.

One thing to be aware of -- we sail in water and only in water, but we can't really measure the effectiveness of our upwind work except over ground -- because of leeway. So you're measuring everything with the right measure -- tacking angle over ground -- but bear in mind that any current will distort that greatly.

In a catamaran, you are even more dependent on speed to keep down leeway, than we are, because you have less power in your underwater foils, so you will notice that when you sail too close to the wind and speed starts to fall off, that you will get a big increase in leeway, which spoils your tacking angle over ground. You will have to experiment to see the optimum balance between speed and angle, but on a multi, you will really want to keep the speed up at all costs. I would say that if you are getting 100 degrees without any current you're doing well already. Few cruising boats mono or multi are able to do much better than that.

Note also that your tacking angle over ground is highly dependent on conditions. You need enough wind to sail fast but not so much wind that you need to start to reef, and you need the flattest possible sea state. Any variation from these conditions will reduce upwind performance.

Obviously sail trim is all-important when going up wind, and sail condition. Getting upwind is a fight between lift and drag. The right balance between lift and drag is different in different conditions -- it takes experience. Also getting the angle of attack right is critical -- easy enough for the main with a good traveler, but complicated for the jib. Upwind, jibs are exquisitely sensitive to clew position so you might want to barber haul the clew inboard. Sometimes just a few inches makes a big difference. If you have a choice of headsails, a non-overlapping jib generally works better when you're going for maximum upwind performance, even in fairly light conditions.

As to rudder angle -- you are right to be looking at this, but you are drawing the wrong conclusions. Rudder angle does not directly show your leeway angle -- it shows how hard the rudder is working. The rudder is a foil just like your dagger boards and you need lift from it to go upwind, so you must have some rudder angle when going upwind. Too much rudder angle is too much drag in the water and shows that something is wrong -- too much canvas in general or trimmed for too much drag or bad balance. On a mono, it also means too much heel. It varies by boat, but 4 degrees is pretty moderate and probably appropriate for moderate conditions on a well-balanced boat. Up to 10 degrees in stronger conditions might be not too much, depending on the boat. Note that this does NOT necessarily mean that you are making 10 degrees of leeway

Good luck and let us know how you get on. Going upwind is the biggest challenge in sailing. For some people it's just a PITA; for others it's a fun challenge. In any case, if you want to sail rather than motor most of the time, you need to be able to do it. Just by the numbers, the APPARENT wind will be ahead of the beam a good deal more than half the time

Another thing -- the term you are after is "VMG to windward", as simply "VMG" means velocity made good to anything -- to a waypoint, for example.
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Old 06-06-2018, 02:45   #3
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Re: Help me improve VMG

I'm assuming the 4 degrees of rudder was weather helm? If so, it's not bad, but maybe you could slightly ease the mainsheet. The emphasis being on Slightly.

You're right about your tacking angles. Sailing higher and slower might result in a track that looks better, but will be slower to the windward mark.

At 8.5 knots and around 30', there won't be many cruising boats staying with you.
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Old 06-06-2018, 03:29   #4
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Re: Help me improve VMG

Tacking angles are very flexible. When I raced Lasers we could tack, in 12 knots and flat water at about 80 degrees. In light winds and chop the tacking angle would increase to 110 degrees or so.

Our boats have high air drag which is not good for pointing. If we could cut off the bridgedeck then we could reduce the drag of our boats. Anything done to reduce drag will allow you to point higher. If you tow a dinghy or have a rough bottom, then you will lose height because drag goes up. The angle between the lift produced by the underwater sections and the drag is called the drag angle. The rig also has a drag angle.

A bridgedeck cat will have trouble pointing as high as a mono as monos have less aero drag. Also monos quickly get to the maximum stability and bleed off power by pointing higher. We don't do this in cats because we don't need to bleed off power until much later than our mono friends.

I would not worry about what you read on the net. I would trim the sails properly, genoa nicely trimmed, telltales breaking up top before those down low. The main is where you get height. Pull it on and keep winding until the leech telltale 1/4 of the way down the leech starts flicking back behind the leech. (The telltale will stream when eased off). This is the absolute gun of a telltale. Pull on till it flickers and then ease till it just streams - you can't pull it more than this. This will give you as much height as you can get without stalling the lee side.

Then the boat will let you know where it can sail to. In light winds and chop you sail lower. Flat water and more breeze you can trim on and go higher, more confused conditions will hide that telltale and you will have to ease main and genoa and bear away.

It can end up being silly for people to talk about how high their boats can point in terms of a single angle. In 18 knots, with full sail, flat water, sailing on leeches only with someone bleeding power, any boat will sail much higher.

As for the rudder angle, that sounds fine to me. Have a rudder at a positive angle of attack is normal performance boat design. It means that the rudder provides lift as well as the daggerboard.

I raced against a fast Schionning in a Gladstone and the owner said he had a gun sailor on board to get him to sail faster "Keep her low, keep bearing away" was the advice and the owner said it made a big difference. The boat I was on had Jeff Cruze on it and he said cats never should be pointed up to bleed power - keep her low.

So the fast guys don't obsess about angles - you have a fast cat. Listen to it and it will do better than almost anything else out there.

cheers

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Old 06-06-2018, 04:23   #5
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Re: Help me improve VMG

Hi Dave, I am interested in the subject and spent quite some time myself to improve my VMG. Looking at your number I don't feel like giving you any advice, they are just excellent ! Maybe your fast boat can do even better, I don't know...

Quote:
Originally Posted by Dockhead View Post
As to rudder angle -- you are right to be looking at this, but you are drawing the wrong conclusions. Rudder angle does not directly show your leeway angle -- it shows how hard the rudder is working. The rudder is a foil just like your dagger boards and you need lift from it to go upwind, so you must have some rudder angle when going upwind. Too much rudder angle is too much drag in the water and shows that something is wrong -- too much canvas in general or trimmed for too much drag or bad balance. On a mono, it also means too much heel. It varies by boat, but 4 degrees is pretty moderate and probably appropriate for moderate conditions on a well-balanced boat. Up to 10 degrees in stronger conditions might be not too much, depending on the boat. Note that this does NOT necessarily mean that you are making 10 degrees of leeway
Everything I have read in this thread sounds good expect this part. You can definitely go upwind with 0° in the rudders, and that's what I am always trying to achieve. 10° seems enormous to me, I usually do everything to stay below 5°. But well, I realize it is just a personal feeling on my boat not based on any particular sailing theory.
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Old 06-06-2018, 04:53   #6
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Re: Help me improve VMG

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Originally Posted by rom View Post
. . . Everything I have read in this thread sounds good expect this part. You can definitely go upwind with 0° in the rudders, and that's what I am always trying to achieve. 10° seems enormous to me, I usually do everything to stay below 5°. But well, I realize it is just a personal feeling on my boat not based on any particular sailing theory.
Sure, and it also depends on the boat.

Some monohulls hard pressed and at maximum efficient heel (that's 20 degrees on my boat) might want 10 degrees of rudder. Some boats with long keel and full skeg rudder might want even more. A light boat with high aspect spade rudders might never see 10 degrees. It varies a lot. But concerning the OP -- I think 4 degrees is not a large amount of rudder angle on any boat.

Every boat has a GROOVE where everything is in balance -- that's what you have to find.

But as to going upwind with 0 degrees -- sure, if you don't need lift from the rudder to drive you forward (that's the vector which counteracts the force blowing you off to leeward). But 0 degrees rudder is not efficient on any boat I've ever been on. All boats, as far as I know, are tuned to give at least a little weather helm, and that's for this exact reason -- so that you can keep some rudder angle on to get some lift.

The underwater foils on sailboats have no CAMBER, unlike and airplane wing. They are symmetrical. Therefore, they provide no lift without being presented at an angle to the water flow -- the angle of attack.

It is true of course that 0 rudder angle will put the rudder at the same angle of attack as the keel. But the rudder works in the turbulence behind the keel and needs more angle of attack to work.

Here's some good basic information:

Ocean Sail Articles: Keels and Rudders
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Old 06-06-2018, 05:53   #7
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Re: Help me improve VMG

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But as to going upwind with 0 degrees -- sure, if you don't need lift from the rudder to drive you forward (that's the vector which counteracts the force blowing you off to leeward). But 0 degrees rudder is not efficient on any boat I've ever been on. All boats, as far as I know, are tuned to give at least a little weather helm, and that's for this exact reason -- so that you can keep some rudder angle on to get some lift.
Correct me if I am wrong but weather helm forces you to to "pull the bar", so that the lift below WL drives the boat downwind, not upwind. Because the lift above WL drives the boat upwind too much. So you can actually go upwind without any rudder at all It's the sail plan taht drives the boat upwind.

Anyway, I totally admit some, most, (all?) boats may go a little faster with a little more pressure on the main, so a little more weather helm, and so a little more rudder angle.
Everyone has to find the sweet spot on his own boat, weather conditions, set of sails, etc ...
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Old 06-06-2018, 06:37   #8
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Re: Help me improve VMG

Quote:
Originally Posted by rom View Post
Correct me if I am wrong but weather helm forces you to to "pull the bar", so that the lift below WL drives the boat downwind, not upwind. Because the lift above WL drives the boat upwind too much. So you can actually go upwind without any rudder at all It's the sail plan taht drives the boat upwind.

Anyway, I totally admit some, most, (all?) boats may go a little faster with a little more pressure on the main, so a little more weather helm, and so a little more rudder angle.
Everyone has to find the sweet spot on his own boat, weather conditions, set of sails, etc ...
No, if you think about it -- "pull the bar" up to windward and the rudder goes to leeward, pushing the stern up to windward and helping the keel hold the boat up to windward, counteracting leeway.

This explains the role of rudder angle in sailing upwind:

https://www.sailingworld.com/how-to/...e-rudder-angle
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Old 06-06-2018, 08:14   #9
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Re: Help me improve VMG

I have to say, you are on the right tack here (so to speak!)

You get so many people here bragging on how well their boat goes to weather and the numbers make no sense, or are physically impossible. And they talk about "tacking angle" but sometimes talk about AWA, sometimes TWA. Almost always ignoring leeway. As you suggest, lots of fantasy.
Looking for best VMG is the right answer.

For all boats, the best VMG is a little further into the wind than the point where speed starts to drop off, on my boat that is past the point where the tell-tales start to lift on the windward side.

VMG is a good number to look for, but is virtually impossible for a human to steer to. Every time you point higher into the wind, the VMG goes up... for a short period of time, then falls. If you bear away, the opposite.

A suggestion: Use your autopilot. Steer to a constant AWA, average the VMG for a few minutes, then go 1 or 2 deg higher or lower and see what happens. My AP (B&G) does this automatically, optimizing VMG over the course of 5 to 10 minutes. It's not always perfect, but it really helps.

Be sure your sails are set right. Leech and luff tensions are critical, and variable depending on conditions. Get the draft in the right place, and the twist right. Use your traveler and jib car position to make sure things are right.
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Old 06-06-2018, 08:27   #10
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Re: Help me improve VMG

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. . . Be sure your sails are set right. Leech and luff tensions are critical, and variable depending on conditions. Get the draft in the right place, and the twist right. Use your traveler and jib car position to make sure things are right.
And get the jib clew in the right place. Barber hauler is your friend.
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Old 06-06-2018, 09:16   #11
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Re: Help me improve VMG

Don't forget that the leeway angle is in effect your angle of attack. For many boats about 5 degrees. So non a angled rudder can be faster other things being equal. If the sail plan does not balance without some helm then so be it. Unless you can tweak the sails to achieve neutral helm. Good luck
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Old 06-06-2018, 10:44   #12
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Re: Help me improve VMG

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Don't forget that the leeway angle is in effect your angle of attack. For many boats about 5 degrees.
Just to be clear for everybody, this is the angle of attack of the keel to the oncoming water.

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So non a angled rudder can be faster other things being equal. If the sail plan does not balance without some helm then so be it. Unless you can tweak the sails to achieve neutral helm. Good luck
"All other things being equal" a straight rudder will ALWAYS be faster because it generates less drag. But you are missing the point. Going up wind there are things to consider other than just maximizing STW.

A slightly angled rudder causes the keel/rudder combination to generate more lift at the same angle of attack. That means you can reduce the angle of attack, and still get the same lift, you point higher, and your VMG upwind is better.

Of course, if there is too much rudder angle, the added drag defeats the added lift and all is bad.

The boat trimmed with a LITTLE weather helm will beat to the windward mark the same boat trimmed to a neutral helm.
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Old 06-06-2018, 11:25   #13
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Re: Help me improve VMG

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. . . A slightly angled rudder causes the keel/rudder combination to generate more lift at the same angle of attack. That means you can reduce the angle of attack, and still get the same lift, you point higher, and your VMG upwind is better.

Of course, if there is too much rudder angle, the added drag defeats the added lift and all is bad.

The boat trimmed with a LITTLE weather helm will beat to the windward mark the same boat trimmed to a neutral helm.
That's right!

And that is one reason why virtually all sailboats are designed to have a bit of weather helm.

It's said by some that the rudder needs to have more angle than the keel because it's working in the turbulent water behind the keel.

I've also heard it explained that the angled rudder makes a kind of virtual camber (like an airplane wing or a sail) when seen together with the keel.

Maybe no one has a complete understanding of it, but I think it's widely accepted that you sail faster upwind with a bit of weather helm and rudder angle.

As to this: "That means you can reduce the angle of attack, and still get the same lift, you point higher, and your VMG upwind is better." I would just add that if more lift is generated, this will automatically reduce the angle of attack, which is created in the first place by leeway


But whatever the theory -- it sure FEELS good when the boat gets in her groove upwind.
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Old 06-06-2018, 13:32   #14
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Re: Help me improve VMG

I had the boom pulled across to just windward of centre (maybe 2deg) and the jib pulled in until the air flow between the sails was just crushing the front of the main.

I should have tried a bit more to see if it might point higher or faster but all I could think of was the articles that say not to have the boom past the centreline and I thought there may be another reason I wasnt aware of. I tried less, both with the traveller and the sheet but both lost power.

Is there a safety reason not to have the boom a few degrees windward or can I try a bit more?
How much crush on the front of the main is too much?

Thanks all for your comments and links... all good reading,
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Old 06-06-2018, 14:02   #15
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Re: Help me improve VMG

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I had the boom pulled across to just windward of centre (maybe 2deg) and the jib pulled in until the air flow between the sails was just crushing the front of the main.

I should have tried a bit more to see if it might point higher or faster but all I could think of was the articles that say not to have the boom past the centreline and I thought there may be another reason I wasnt aware of. I tried less, both with the traveller and the sheet but both lost power.

Is there a safety reason not to have the boom a few degrees windward or can I try a bit more?
How much crush on the front of the main is too much?

Thanks all for your comments and links... all good reading,
No problem having the boom above the centerline -- experiment away.

I normally have the boom up above the centerline when hard on the wind in light to lightish conditions.

I would suggest experimenting with the jib clew position as well.
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