Help me improve VMG

[catsketcher]

This may have been the reason.

When we reef the typical fractional multi rig, the leech of the main comes forward and the genoa gets reefed too, bringing its CE forward. This causes the cat to want to get lee helm and bear away, going too fast in nasty conditions as you crest a wave.

You can get the same effect as you got without motoring by putting up a small staysail on your screecher furler (use the storm jib if needed). This brings the CE back to balance and the boat can sail smoothly at lower speeds.

You don't have to motor a cat to get it to perform well.

[fxykty]

A little off thread here, sorry.

Our boat’s reefing guide stops at 50 knots AWS with a triple reefed main (about 35% of the original area) and 20% of the jib. After that it says downwind only with triple reefed or no main.

The centre of effort of just the deep reefed main is far enough forward that it balances the boat quite well on a reach or upwind without any jib at all, though we haven’t sailed in more than 40 knots of wind yet.

When I asked Outremer if they recommended fitting a storm jib rather than a deeply reefed furling jib their reaction was ‘why would you want to do that? Our boat sails perfectly well the way we describe in the reefing guide.’

But I’m not sure that saying we can go off wind only in over 50 knots is sufficient. Time for a fourth reef (rather than the PITA of a trysail) I think. And perhaps a storm jib on an inner stay, though it would be about a metre behind the furled jib and may not have any decent flow because of that.

For the OP, sailing slow and high is fine for ex-America’s Cup 12 metre boats, but death for a performance cruising cat like yours. Other posts have described why in certain conditions more speed means wider angles on the ground - your challenge is to figure out the combination of heading and speed gives you best VMG to windward for any particular wind speed. Set a waypoint directly upwind a long, long way away (so your tacks back and forth don’t affect it too much) and have your plotter show your VMG to that waypoint. Then experiment, high and tight and slow vs low and wide and fast. Somewhere in between likely will be best.

[arsenelupiga]

Originally Posted by catsketcher

This may have been the reason.

When we reef the typical fractional multi rig, the leech of the main comes forward and the genoa gets reefed too, bringing its CE forward. This causes the cat to want to get lee helm and bear away, going too fast in nasty conditions as you crest a wave.

You can get the same effect as you got without motoring by putting up a small staysail on your screecher furler (use the storm jib if needed). This brings the CE back to balance and the boat can sail smoothly at lower speeds.

You don't have to motor a cat to get it to perform well.

thanks for the hint. I do not have staysail and going out at night to attach staysail in such conditions not part of my sailing plan except in life threatening conditions.

I was amazed how movement improved, stress on crew and boat has gone, and I found it myself

[OceanSeaSpray]

If you own a high performance monohull, the answer to upwind VMG tends to be "slow down and point higher". You don't lose much speed and the angle makes all the difference.
In very light winds, you have no other option: the higher the speed, the further forward the apparent wind moves and the more this forces you to bear away. In the end, you are just sailing across the wind and going nowhere.

If you have to keep the speed up to reduce the leeway and sail low, there might be an optimum somewhere there, but the result is unlikely to be flattering. A racing multihull can overcome this with speed, but not the average cruising cat or fat cruiser with a stubby keel.

Many cruising boats these days have far too much windage. Windage and resistance have a crippling effect on upwind ability and it gets worse as the wind gets up: Heavy weather dynamics: the behaviour of yachts sailing upwind in high winds | Nordkyn Design

So if you really want to improve your VMG, reduce your drag, but at some point you come against the limitations of the design itself.

[Dave_S]

Thanks all, I tried a few changes yesterday and was able to improve TWA but couldn't improve AWA (STRANGE? maybe not, I'll have to think about that) 30° was still awa anything closer and speed fell off quickly. TWA was 48.5° -2.5° better. TWA I guess is the mark I'm chasing for good tacking angles anyway.

The true wind was gustier and the sea state a bit rougher around 1m, the leeward side hull putting up lots of spray. Boat speed over ground was less than last time at around 8kn SOG with a bit more true wind and less AWS, around 13kn TWS, and 19.5kn apparent, against the tide, I guess a knot? (Moreton Bay) last time I had the tide in my favor, so I think I did significantly better this time = +1.5kn. I didn't need to tack, I made it home on that course. I regret not doing it just to look at the lines. I had about the same, if not bit less rudder but had more trouble keeping course. Hand steering both times.

I.joined the "sailors that have run around club yesterday too :-( " but that's another story.

I scrubbed the hulls this time - cheating! The boom was in about the same place - I started from more windward but moved it back. The leech tighter, the luff looser (I would have liked to tighten this but it was too rough and no one on board who could bring the boat back to find me) The Genoa car further back and tighter.

Judging by the leeward shrouds I had a lot more power in the sails, they were very loose, I'm wondering if they need retensioning or was I pushing too hard, it didn't fell like it. I also had a lot more crush in the bottom front of the main from the Genoa air choking the front of the main.

I think there might still be some more in it

[44'cruisingcat]

You discovered what I said before. Sailing at a lower percentage of TWS gives you better tacking angles.

But it's not necessarily the fastest way to go.

[OceanSeaSpray]

Upwind AWA is strongly influenced by the rig and sail trim and it varies a lot less than TWA, people using wind vanes are always very aware of this.

In order to improve AWA, you need to be able to sheet closer in and you can't do that unless your keel/centreboard/daggerboard can also produce a lift matching the side force. The minimum AWA is largely determined by the characteristics of the design. AWA will improve if you reduce the drag.

Sailing in a current makes the situation much more confusing. Pay attention to the tacking angle on the compass. It doesn't include leeway, but it is not screwed up by the current either. Same about the speed. SOW is what you are actually achieving through sailing.

[fxykty]

Originally Posted by Dave_S

Thanks all, I tried a few changes yesterday and was able to improve TWA but couldn't improve AWA (STRANGE? maybe not, I'll have to think about that) 30° was still awa anything closer and speed fell off quickly. TWA was 48.5° -2.5° better. TWA I guess is the mark I'm chasing for good tacking angles anyway.



The true wind was gustier and the sea state a bit rougher around 1m, the leeward side hull putting up lots of spray. Boat speed over ground was less than last time at around 8kn SOG with a bit more true wind and less AWS, around 13kn TWS, and 19.5kn apparent, against the tide, I guess a knot? (Moreton Bay) last time I had the tide in my favor, so I think I did significantly better this time = +1.5kn. I didn't need to tack, I made it home on that course. I regret not doing it just to look at the lines. I had about the same, if not bit less rudder but had more trouble keeping course. Hand steering both times.



I.joined the "sailors that have run around club yesterday too :-( " but that's another story.



I scrubbed the hulls this time - cheating! The boom was in about the same place - I started from more windward but moved it back. The leech tighter, the luff looser (I would have liked to tighten this but it was too rough and no one on board who could bring the boat back to find me) The Genoa car further back and tighter.



Judging by the leeward shrouds I had a lot more power in the sails, they were very loose, I'm wondering if they need retensioning or was I pushing too hard, it didn't fell like it. I also had a lot more crush in the bottom front of the main from the Genoa air choking the front of the main.



I think there might still be some more in it

YMMV regarding rig tension, but with our boat we were told by Outremer that the leeward shroud should be just loose tension but not moving at the top of each reef, and definitely not moving around loosely. Check with your rigger and the factory - it is unlikely that the shrouds should be very loose.

Regarding pushing too hard, where were you on your reefing guide?

On a racing monohull it’s common to loose the forward half of the main when in pointing high mode. But I’m not sure that pointing high mode is ever appropriate for a cruising multihull. Make sure that your genoa sheet angle relative to the centreline is correct - I expect it should be no less than about 28 degrees, but your rigger or the factory should be able to tell you.

Your main boom should not be above the centreline, except in very light airs when you need a loose leech. In general the boom should be at or below the centreline for upwind.

Set your main upwind by sheet tension first, then adjust the traveller. Basically your leech tension is determined by your top leech telltale - it should be hiding 50% of the time. Tension or ease the mainsheet so the top telltale is behaving as it should. Then adjust the traveller so that the back half of the top batten (or if you have a squaretop, the second batten - the first one parallel vertically to the boom) is at the same angle horizontally as the boom. If it’s hooked to windward and sheet tension is correct then down on the traveller. If it’s to leeward of the centreline then up on the traveller.

Now adjust the genoa sheet so that it’s luff breaks at the same time as the upper main sail telltales collapse - that provides your optimum upwind angle. The genoa luff should break evenly or slightly earlier at the top, so adjust the fore and aft position of the genoa sheet - forward if the top breaks too early, or aft if the bottom breaks too early. If you have inner shrouds, the foot of the genoa should not be tight against that shroud. For monohulls, distance off the top spreader is the guide. A slightly looser genoa sheet makes it easier to steer to it and provides a bit more power.

That’s for flat water. Allow more twist off in both the main and the genoa in chop or waves to provide power, and head 5 degrees lower to keep speed up and reduce leeway.

Or just set the autopilot to 38 or 40 degrees or whatever AWA works for your boat and the conditions, set the sails a bit looser than just right, and relax with a chilled beverage.

[Just Another Sa]

Originally Posted by Dave_S

Thanks all, I tried a few changes yesterday and was able to improve TWA but couldn't improve AWA (STRANGE? maybe not, I'll have to think about that) 30° was still awa anything closer and speed fell off quickly. TWA was 48.5° -2.5° better. TWA I guess is the mark I'm chasing for good tacking angles anyway.

Originally Posted by fxykty

Make sure that your genoa sheet angle relative to the centreline is correct - I expect it should be no less than about 28 degrees, but your rigger or the factory should be able to tell you.

Or just set the autopilot to 38 or 40 degrees or whatever AWA works for your boat and the conditions, set the sails a bit looser than just right, and relax with a chilled beverage.

Dave said awa 30° as quoted above.
28° or more genoa sheet angle does not work at awa 30°.
There is no point setting autopilot to steer AWA 8 to 10 degrees wider than the boat is doing when steering manually when wanting to go upwind.
I guess you did not pay any attention what Dave said about AWA in the post you quoted. Or maybe you just didn't believe that to be true?

[Just Another Sa]

Originally Posted by Dave_S

Thanks all, I tried a few changes yesterday and was able to improve TWA but couldn't improve AWA (STRANGE? maybe not, I'll have to think about that) 30° was still awa anything closer and speed fell off quickly. TWA was 48.5° -2.5° better. TWA I guess is the mark I'm chasing for good tacking angles anyway.

If you could keep the same AWA of 30° for all TWA, you would get the best upwind VMG = 50% of TWS when TWA is exactly 60°. That is a mathematical fact, not opinion. Any tighter pointing and you get VMG less than 50% of TWS.
In reality you can not keep the same AWA for that case, but as long as AWA remains (withing accuracy and precision it can be measured) the same 30°, point lower with better speed to improve VMG upwind.
In practice VMG will not reduce until AWA increases, as your boat is not capable of keeping that AWA at TWA = 60 degrees or beyond that.

[44'cruisingcat]

Originally Posted by Dave_S

Thanks all, I tried a few changes yesterday and was able to improve TWA but couldn't improve AWA (STRANGE? maybe not, I'll have to think about that) 30° was still awa anything closer and speed fell off quickly. TWA was 48.5° -2.5° better. TWA I guess is the mark I'm chasing for good tacking .

It'snot strange at all that AWA stayed the same. That's basically your boat's upwind sailing angle. In very light wind you may find a couple of degrees lower is better.

The relationship between AWA and TWA is a function of boatspeed compared to TWS.

If you sail a higher percentage of TWS, there's a bigger difference between AWA and TWA.

At zero speed they're the same.

Because the wind was stronger you're probably sailing at a lower percentage of TWS, which would account for the better looking TWA.

On a fast cat, don't go looking for really tight tacking angles. Unlike most monos you're not constrained by hull speed, so going faster is an option, and up to a point, it works better for a cat.

[44'cruisingcat]

Originally Posted by Just Another Sa

If you could keep the same AWA of 30° for all TWA, you would get the best upwind VMG = 50% of TWS when TWA is exactly 60°. That is a mathematical fact, not opinion.

Sorry but this is absolutely NOT fact.

The AC 72s were sailing at very similar AWA on both the upwind and "downwind" legs. There was only about 4' difference.

However the boatspeed changed by about 200%.

Which meant VMG to windward changed from about 90% TWS to around Minus 200% TWS.

[StuM]

Originally Posted by Just Another Sa

VMG = 50% of TWS when TWA is exactly 60°. That is a mathematical fact, not opinion. Any tighter pointing and you get VMG less than 50% of TWS.

That is not a fact, it is a terminological inexactitude.



VMG = 50% of SOG* when TWA is exactly 60°


Are you really saying that any boat will do 15 knots VMG at 60° TWA in 30 knots of wind?


*if you assume no leeway

[fxykty]

Originally Posted by Just Another Sa

Dave said awa 30° as quoted above.

28° or more genoa sheet angle does not work at awa 30°.

There is no point setting autopilot to steer AWA 8 to 10 degrees wider than the boat is doing when steering manually when wanting to go upwind.

I guess you did not pay any attention what Dave said about AWA in the post you quoted. Or maybe you just didn't believe that to be true?

30 degrees AWA is for a relatively slow boat (to TWS) so I think it may be useful for the OP to experiment with wider AWA to see where best VMG actually is. On our boat at the top of each reefing guide best VMG seems to be at 36-38 AWA. Hence my suggestion. I’m not being prescriptive and encourage the OP to experiment. He’s been trying 30 degrees AWA, now he could try something quite different.

Multihulls definitely behave differently from monohulls and point high and go slow is generally not an effective way to get upwind in a cruising cat. For a monohull, absolutely it is - an IOR 2-tonner back in the 80s I raced hit it’s polars upwind at 22 AWA in lighter air and 28 degrees in stronger winds.

[44'cruisingcat]

No, 30' AWA isn't for slow boats. The AC 72s pointed much higher than that.

On our boat the Simrad autopilot has a VMG optimiser, and it usually settles on 30 - 31' apparent.

It really depends on how well set up your boat is for windward sailing. Few production boats will sail to windward as well as home built ones.

Some upwind sailing on our boat:

https://youtu.be/34qgJRprAlE