Downwind sailing and yawing

[Chanquete]

Hello
I love my boat. I own it for more than 13 years. Downwind sailing in following seas requires a lot of attention.
Some years ago I increased slightly the rudder area (the rudder chord) with the result of much better downwind stability.
Nevertheless I would appreciate ideas about sail organization and trimming in order to reduce the yawing tendency in downwind sailing with strong winds.
In this course I observed reasonable behaviour beeing dragged by a larger jib and a reefed main...but I would welcome suggestios of optimal sail dispositions.

Thanks in advance

Chanquete

 

[Contest1]

I only use the headsail, furled to match boat speed to wave train.
Also sail off the wind enough to ensure no broaching!
This works on my Centaur up to a force 7, after that its engine and run for cover

 

[LadyInBed]

Use twin head sails (no main) with an air gap between head sails - think of a parachute, they only became stable when a vent was put in. The wind has to spill out somewhere and without the vent wind spilt from the edge causing oscillation.

 

[wotayottie]

Through inattention / complacency we got caught 18 months ago coming up the Bristol channel with 25/30 kn true and rollers from the SW. Gradual build up in wind, crew too busy talking. We were goosewinged with preventer on the full main and poled full genoa under autopilot ( brilliant robertson / simrad jobbie) . Hit 15.6kn down one wave before we hurriedly reefed. But even under these stupidly dodgy conditions, there was no yawing and no attempt to round up.

So I dont think its so much a matter of adjusting sails which we definitely didnt do, as basic hull design. The boat ( 35ft, 7 tonnes) has a barn door rudder on a half skeg, the whole lot behind a shaft log that effectively works as a second small keel. Stephen Jones design.

Not our proudest moment.

 

[johnalison]

The helmsman's skill and sail trim have a part to play in downwind comfort. Usually, the best trim is achieved when the sails are driving at their best, correctly sheeted and not over-trimmed, especially with the spinnaker.

Some older designs, such as many '70s cruiser/racers, have narrow sterns and will tend to corkscrew in a quartering sea, but a good helmsman can ameliorate this. The trick is to keep looking ahead and not worry about the waves coming from astern. It's a bit like driving a car; the further ahead you are thinking, the better you will steer. It takes some time to get into the groove, but I find that after about ten minutes I get into "Zen sailing" mode - the boat sails itself.

 

[ChrisE]

As an owner of a 70s IOR cheating boat, a Rival 38, I recognise the problem. As others have said good helming helps and on long passages towing something like a turbine helps the autopilot.

I know some that tow a fender or two to soften the boats wish to broach.

Hope this helps

 

[Rossynant]

Often forgotten thing - headsails are always set to wrong angle. Wrong for downwind, that is.
The headsail angle of incidence is always about 12 deg, no matter how much sheet is let, the angle is fixed for close-hauling in modern marconi rig. This pose a problem when going downwind, seldom understood.
That is forgotten, but important, and was obvious time ago. Try boomed headsail, like in traditional sailing boats, you'll see. It's sails that roll the boat. And then modern boats have unbalanced hull shape, they turn upwind when heeled. Another obvious thing, but long forgotten...

On my boat long ago I made a boathook to serve for a king of spinnaker boom or pole, for genoa - just so it was easy to put the end into a sheet thimble, and stuck the base at mast, then harden on sheet and everything stayed put. Length made so that the sail was set at 45-50 deg to the boat. This way sail works properly (aerodynamically) from close reach to downwind and up to 30 deg on other tack. Any time we went off the wing we rigged genoa this way.

Nobody from boats left astern understood why we were so fast
And no more downwind roll or broach.

This is naturally forbidden in racing rules

 

[ChrisE]

Often forgotten thing - headsails are always set to wrong angle. Wrong for downwind, that is.
The headsail angle of incidence is always about 12 deg, no matter how much sheet is let, the angle is fixed for close-hauling in modern marconi rig. This pose a problem when going downwind, seldom understood.
That is forgotten, but important, and was obvious time ago. Try boomed headsail, like in traditional sailing boats, you'll see. It's sails that roll the boat. And then modern boats have unbalanced hull shape, they turn upwind when heeled. Another obvious thing, but long forgotten...

On my boat long ago I made a boathook to serve for a king of spinnaker boom or pole, for genoa - just so it was easy to put the end into a sheet thimble, and stuck the base at mast, then harden on sheet and everything stayed put. Length made so that the sail was set at 45-50 deg to the boat. This way sail works properly (aerodynamically) from close reach to downwind and up to 30 deg on other tack. Any time we went off the wing we rigged genoa this way.

Nobody from boats left astern understood why we were so fast
And no more downwind roll or broach.

This is naturally forbidden in racing rules

Hmm, I think from your description you are talking about the standard rigging for tradewinds sailing, ie a boomed out headsail. If this is the case, believe me it doesn't stop downwind roll ....

 

[Rossynant]

Well, depend on the boat also
To stop roll the boat must have some damping ability, not common nowadays. Other way - a sail working at angle of 10-30 deg to the wind is actively damping the roll, but this normally takes place in close hauled going.
It's possible to rig a sail downwind that acts this way, against rolling, and you only have to read Slocum or Knox-Johnson - they used this technique. Small foresail sheeted flat, on both sheets, so it works "backwards".

P.S Downwind rig, like twin headsails, work on 90 deg to the boat, or the wind. This naturally will cause rolling motion. I was talking about setting the sail to about 50 degrees to boat. This way it still work acceptably dead downwind, while not producing rolling effect - in fact mostly gives stabilizing effect against yaw and roll. But the pole goes after the shrouds, so we could not use spinnaker boom, no attachment there. And not necessary to rig one, as hardened sheet keeps it put. Different angle.

 

[ProMariner]

One thing to try, if you have a boat with a decent kicker and boom, pull/wind on enough kicker that the leach of the main is standing up properly, when goose winging. Aim to always have the back third of the top baton parallel with the boom, so that as the boat rolls to weather, some of the energy is transferred into speed instead. Not easing the boom all the way to the shrouds helps too.

Also, some helms persons seem to make roll/yawing worse by overcorrecting, try the autopilot instead?

But some boats just like to yaw, and some like to roll, no matter what you do. And some helms will insist on spilling my tea, can't be helped. Sure they all have good points too. If the crew starts to look green/nervous, you can always change your plan, reach up a bit or try the other gybe for a bit, try a different destination etc. Now, who's going to suggest that the OP simply dosn't have enough hulls?

 

[SteveSarabande]

are you talking about rolling or yawing. Rolling is a lot more troublesome in my experience going downwind

 

[Neil_Y]

A lot is the result of the top of the main as the boat heels and turns slightly an eased main at the top will help the turn. Solutions are more kicker (when racing in IOR boats this works until the broach starts and then it gets dumped completely) or when cruising don't use the main, and if its more than a few miles the twin headsail works very well but the roll/yaw very much depends on hull shape and mass. It's worth playing around with to see what suits your boat. My old boat

 

[Rossynant]

are you talking about rolling or yawing. Rolling is a lot more troublesome in my experience going downwind

With many new boats this is connected. They turn when heeled.

 

[TimBennet]

Solutions are more kicker until the broach starts and then it gets dumped completely)

Careful with this! When you are dead running, a slack kicker will allow the leach to twist and the air flowing off this will cause a roll to windward. A very hard kicker/vang and boom adjusted so top batten is square to the direction you're heading, will help stop the 'to windward' component of any roll. Most cruising boats have their leaches far too open when running and this exacerbates rolling. If you dump the kicker as a 'safety measure' when dead running, you will probably wash the windex to windward.

However when broad reaching, ie the flow of the air is longitudinal across the mainsail and the telltales are streaming, then the air exited the mainsail from the leach is causing a turning moment of the bow to windward. This is a leeward broach as ultimately the mast will hit the water to leeward (as opposed to the windward broach above). Preventing a leeward broach can certainly be helped by early dumping of the kicker or vang, although on cruising boats it's long been time for a reef.

But all this applies to rolling which is not the same as the OP's original question about yawing, but it wasn't me that started the thread drift!

 

[Topcat47]

The expensive option is to get yourself a parasail or perhaps a parasailer downwiind sail. This lifts the bow at the same time as powering the boat. It's so much nicer downwind and can used in light windsup to a broad reach. I've had mine for three years now. i onlt wish I'd bought it sooner. I use it even when daysailing single handed and it's even better for extended passage-making

 

[TimBennet]

This lifts the bow . . .

Whatever the advantages of a Parasail, this old myth (or advertising claim) has been disproved years ago! You can't attach a huge driving force (the sail) to a boat via a very tall lever (the mast) and aft of the longitudinal pivot point of the hull, and have it 'lift the bow'.

All the forward drive of every sail ever made (accept kites and canted masts) are trying to drive the bow down. This rotational force is resisted by the buoyancy and the hydrodynamic 'lift' of the hull.

If you want to make your own 'research model', get a piece of plank, shape it a bit like a boat, put a piece of dowel in it to represent the mast to scale, then attach three pieces of string to mast and hull to represent the guy, sheet and halyard. Float your boat and pull each of the strings in a similar direction to a spinnaker (or actually any direction), and you will never get the bow to rise.

Even when we've put loadcells on boats flying huge asymetrics from long bowsprits like the Cork 1720, the net lift is negative. Any bow rise with speed is the same as seen on a speedboat.

 

[Topcat47]

The main difference between a parasail and a spinnaker, even an assymetric spinnaker, is the slot and the lifting foil immediately above the slot. I've flown a spinnaker from my boat, admittedly not often; it doesn't have any lift. The parasail is different. My tack is at the bow, the slot and foil provide lift and spill air from the top part of the sail, giving it's drive a more linear characteristic. Compared to my Genoa or my spinney, it does lift the bow, or if it does not, it drags the stern which rather has a similar effect.

 

[BurnitBlue]

The main difference between a parasail and a spinnaker, even an assymetric spinnaker, is the slot and the lifting foil immediately above the slot. I've flown a spinnaker from my boat, admittedly not often; it doesn't have any lift. The parasail is different. My tack is at the bow, the slot and foil provide lift and spill air from the top part of the sail, giving it's drive a more linear characteristic. Compared to my Genoa or my spinney, it does lift the bow, or if it does not, it drags the stern which rather has a similar effect.

TCM uses both parasail and spinnaker on Mojomo. He made many good and interesting points on his circumnavigation. See his webpage.

 

[Neil_Y]

a slack kicker will allow the leach to twist and the air flowing off this will cause a roll to windward.

I agree...

That's why I was suggesting more kicker as the over twisted main top causes the roll to windward, and ends up being rolls and yawing as the rudder loses its grip at an angle. It's a learning curve and many cruising sailors I've sailed with never play with controls so they don't learn what effect they have.

 

[monkfish24]

All very good if you are sailing on flat water, what if you are sailing in the real world (not a test tank) and your bow is pointing to the sky, what is the vector then off the lift from the sail?

I've been on a boat that has tried to pitchpole going downwind in waves. Spinnaker up, bow hits wave, bow stays in air after leaving wave (in 30kts gusting 40).

I can understand you are trying to break old thinking but I've actually been there in practice. I've also been holding onto a spinnaker pole when the downhaul has gone and I've very quickly ended up 10ft in the air, pole still in hands......