Help me improve VMG

[catsketcher]

The hard thing for our cruising boats to do is to go upwind well under autopilot or when we want to zone out and take it easy.

Have a watch of the AC 45s during the Americas Cup. The main is going in and out all the time. These really good sailors are adjusting twist and sheeting and talking about "high mode" "VMG mode" and "low mode" all the time. It is great to watch.

We don't want to have to sit on the helm and adjust for every phase of breeze so we have to also put in "easy mode". On my last boat I could crank everything in for a slightly better high mode but if the autopilot was a bit off the weather helm would over power it, the rudder would stall, and she would end up head to wind. So I usually sail a little eased off from high mode to let the autopilot have more time to react. It can't feel like a good helmsman.

Pulling the boom to windward used to be for masthead rigged monos only. THe TP52 monos started doing it years ago and it seemed weird. Be careful about going too far but the boat will tell you, the speed will drop, the bow will come up a little and the leech telltale will hide away because of stall. Just ask the boat and it always tells the truth.

Sheeting angles. How does this work? - Sailing Anarchy - Sailing Anarchy Forums

As to the rudder, all fast racers load the rudder. Having the rudder at about 3-6 degrees angle of attack increases drag only slightly but produces a huge amount of lift. This allows the centreboard to operate under less loading and much of the drag from the centreboard is induced drag, drag from having to make lift. Foils are tricky but it makes little sense to have one doing all the work and operating at a high drag condition and having the other just sit there being pulled along - get it lifting too! The real design trick is to get it so that easing main gets you back to neutral helm - Farrier designs are excellent at this.

cheers

Phil

[Dave_S]

Originally Posted by Dockhead

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.

Good to know, that gives me some experimenting freedom for next time.

For the jib I've got two rows of traveller rails on each side of the mast about 400mm apart running fore and aft where you can pull up a pin and move the car along the rail to about 8 set positions. I'm on the inside rails now. It's a chore to change rows as the sheets run through a series of runners and clutches so I might run another sheet through the unused ones but only attach it to the clew if I need it.

The problem with the traveller car set up is once it is loaded you can't move it (you probably could but it would go really fast). I did move the car forward from my start position as the top of the jib was more open than the main but I can only do this between tacks, it would be nice to be able to adjust it on the fly.

Thinking about moving the boom farther to windward, maybe I could use the unused second jib sheet (if I fit it as above) from the other side so I can pull the jib clew closer to the centre line? A problem might be this could choke the jibs airflow between it and the mast ?

[44'cruisingcat]

Originally Posted by Dockhead

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

Weather helm is one area where cats differ from monos.

Monos have weather helm because they heel. The boat is being pulled forwards by the mast, held back by the hull. This produces a turning moment to windward.

Cats heel very little, and what heel there is, is a result of the leeward hull sinking and the windward one lifting.

Which produces a turning moment to LEEWARD. Which is pretty much balanced by the windward turning moment of the mast.

So cats can sail with no weather helm. Any weather helm you see is caused by the main, pushing the stern to leeward.

A little weather helm is not a bad thing. It means the main is driving. Too much, and 4 degrees is more than I usually see, could mean that the rudders are slowing you down.

However, Schionnings are somewhat known for having small rudders.

[44'cruisingcat]

Originally Posted by Dave_S

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,

With my old round roached main, when it was getting a bit baggy and hooked in the leach, I pretty much always had the traveller to windward, and in light air it would be well to windward, with the sheet eased so the boom was slightly to windward too. This helps get the leach to open in light wind.

With a square top, the leach always opens. It's almost too easy.

[Dave_S]

Here is a 90degree trace from Roam. Pretty credible guy.

That's going to keep me thinking.

WOW


Quote


How's those upwind angles! Figured out how to make Roam do 90's.
Full main, no head sail, who needs a self tacking jib?
I didn't leave the wheel once... but Liss did play the traveller a bit to make sure we didn't get stuck during a couple of tacks.
No fossils were harmed in the making of this picture 😎

[44'cruisingcat]

Sure. Sail slow or in strong wind and your tacking angles improve. It's because as you sail a smaller percentage of TWS, the difference between AWA and TWA gets smaller.

Doing without the headsail is a sure way to go slower.

[Dave_S]

Originally Posted by 44'cruisingcat

Sure. Sail slow or in strong wind and your tacking angles improve. It's because as you sail a smaller percentage of TWS, the difference between AWA and TWA gets smaller.

Doing without the headsail is a sure way to go slower.

Your right, I have been trying to work out what sorts of speed and angles he must have been running at and I think I'd rather ***coughcough*turnthemotoron*coughcough***.


I think he must have done it just to see if he could.

[Dockhead]

Originally Posted by 44'cruisingcat

Sure. Sail slow or in strong wind and your tacking angles improve. It's because as you sail a smaller percentage of TWS, the difference between AWA and TWA gets smaller.

Doing without the headsail is a sure way to go slower.

Really?

One definitely good point in this is that we don't care a fig about the angles, we care about VMG to windward, and obviously speed is key. Speed keeps leeway down; speed gets you upwind -- that's what they always taught us anyway.

But do the ANGLES improve sailing slow? Leeway goes way up when you slow down, especially in a cat, no?

[44'cruisingcat]

Depends on the cat. Minikeels work OK at low speed. And even with a daggerboard boat, there wouldn't necessarily be a huge difference in leeway between sailing at 9 knots and 5 or 6. But there could be major differences in AWA vs TWA.

Our best tacking angles over the ground have been when sailing to windward in over 25 knots, (in an enclosed waterway) deep reefed, sailing at a comparatively low percentage of windspeed.

BTW, I'm not suggesting sailing slow is a way to improve VMG. It's not. But it is a way to make your tacking angles look better.

[catsketcher]

Originally Posted by Dave_S

Good to know, that gives me some experimenting freedom for next time.

For the jib I've got two rows of traveller rails on each side of the mast about 400mm apart running fore and aft where you can pull up a pin and move the car along the rail to about 8 set positions. I'm on the inside rails now. It's a chore to change rows as the sheets run through a series of runners and clutches so I might run another sheet through the unused ones but only attach it to the clew if I need it.

The problem with the traveller car set up is once it is loaded you can't move it (you probably could but it would go really fast). I did move the car forward from my start position as the top of the jib was more open than the main but I can only do this between tacks, it would be nice to be able to adjust it on the fly.

Thinking about moving the boom farther to windward, maybe I could use the unused second jib sheet (if I fit it as above) from the other side so I can pull the jib clew closer to the centre line? A problem might be this could choke the jibs airflow between it and the mast ?

IIRC Schionnings have a second outer set of genoa leads for the screecher. This allows you to sail very close to the wind with the screecher up in light winds. It isn't for the genoa.

I haven't sailed on many boats that can move a loaded genoa car. Usual practice is the look where the lead needs to go, move the windward side, tack, check and repeat. On some boats with barber haulers you can move leads under load but it is rare.

Pulling the genoa in further may help but may make you slower. In Tasars, a nice performance dinghy, the jib leads go athwartships. We only have them fully in when the wind is light to moderate and the sea is flat. As soon as the chop increases you have to ease the sheet or the boat stalls. In medium breezes the leads go out or the slot gets choked and the main starts backwinding a lot. Heavy air - get the lead out of the main just flogs. So your leads will be a balance between tight in for light and wide out for heavy. About 12 degrees sheeting angle is normal for cats.

[44'cruisingcat]

Our headsail sheeting angle is 8 degrees.

[Dave_S]

Originally Posted by catsketcher

IIRC Schionnings have a second outer set of genoa leads for the screecher. This allows you to sail very close to the wind with the screecher up in light winds. It isn't for the genoa.

I haven't sailed on many boats that can move a loaded genoa car. Usual practice is the look where the lead needs to go, move the windward side, tack, check and repeat. On some boats with barber haulers you can move leads under load but it is rare.

Pulling the genoa in further may help but may make you slower. In Tasars, a nice performance dinghy, the jib leads go athwartships. We only have them fully in when the wind is light to moderate and the sea is flat. As soon as the chop increases you have to ease the sheet or the boat stalls. In medium breezes the leads go out or the slot gets choked and the main starts backwinding a lot. Heavy air - get the lead out of the main just flogs. So your leads will be a balance between tight in for light and wide out for heavy. About 12 degrees sheeting angle is normal for cats.

ooops

I assumed the second lead was for anything other than close hauled with the Genoa. I'm told my other sail is a reacher but I can't find a good description of one to know for sure but it is a flatter sail than the code 0's and is made of a laminate on a furler so I have no reason to doubt it. It is a big sail, it comes back too far to go through the genoa leads. The boat has two non-adjustable positions for the reacher sheet. A pulley on the very outside of the hull behind the helm and another beside the cabin just forward of the helm.

I'll have to measure the sheeting angle, at a guess I'd say it's between 8 and 12.

[catsketcher]

No oops, I could easily be wrong. I have a hazy recollection of my friend with a Waterline 1320 telling it was so but I could be wrong. It is probably best to ring Schionnings themselves and ask.

[catsketcher]

More mea culpa - I did some more reading and find that some people go down to 7 degrees for sheeting angle. I will have to measure my boat next time but she does have pretty wide angles - I put them there. But she does go pretty well in a chop.

[arsenelupiga]

this is not exactly what title is about but i think my experience is still relevant if you out there in open.

we had 3m steep short waves, presume generated by currents, and sailed upwind against them in 30 kn app . Boat was crashing under sails and it was not comfy at all and my wife stressed. Issue was that boat accelerated too much and when speed increased above 6.5kn just too fast for the waves and crashed.

Tried several things and found winning formula.

turned on both engines, with very low revs (setup did not work with 1 engine) . Left only mainsail reefed 2x. Set revs so that max speed when wave timeout was just below 6.5 kn so no crash when next 3m came. Engines did not accerelate beyond 6.5 kn. And crashing was completely gone and my wife happy Still felt wavy but no boat stress and no crew stress.

ok, now say all these things about lagoon