Thinking caps on chaps!

Also, could you reduce the jerking on the mooring by fastnening your mooring lines together a few feet away from the boat using some strong bungy cord.
 
Thanks guys, I think you are setting me on the right track.

I was trying to analyse the motion at 6 am but with 40+ knots of wind and rain plus a night with little sleep I couldn't get my head round it. It looked as though the stern was swinging sideways through the water but with two barn-door rudders I couldn't see how that could be the case. On reflection I think the rudders were anchoring the sterns and the side thrust on the mast was making the bows fall off.

I had thought of some way of introducing side drag by some form of drogue off the bows. I also considered reducing lift on the mast. One way of doing that is to reverse the mast so the trailing edge is forward - this reduces lift by 40% but as the pivot is near the leading edge, rotating would bring the CE forward and cancel the reduced lift.

The CLR of the underwater profile excluding rudders is close to the CE of the mast but adding that of the rudders means she is quite unbalanced. The problem thus becomes one of moving the CE forward of the CLR. I'll look at some sort of riding sail/air rudder, a drogue off the bows and a forward dagger board. Any other notions welcome.

BTW I had a chat with the owner of a Walker Wingsail recently. He said that of half a dozen extant boats, only 1 is still using and active computer-controlled system. All the rest are manual/passive. What impressed me in relation to mine was that the ball-bearings meant the rig weathercocks in even a light breeze. My plain bearings need quite a bit of force on the boom to rotate the mast so I don't see any solution that involves the mast turning being feasible.

Just to add further complication, she sits on a drying mooring so when there is a windshift while she is dried out the wind could end up coming over the stern till she floats. The ground is soft mud so she sinks in till the mud is 12" below the waterline. Any protrusions need to be undamaged by being pressed down into the mud.
 
snowleopard said:
It looked as though the stern was swinging sideways through the water but with two barn-door rudders I couldn't see how that could be the case. On reflection I think the rudders were anchoring the sterns and the side thrust on the mast was making the bows fall off.

I had thought of some way of introducing side drag by some form of drogue off the bows. I also considered reducing lift on the mast. One way of doing that is to reverse the mast so the trailing edge is forward - this reduces lift by 40% but as the pivot is near the leading edge, rotating would bring the CE forward and cancel the reduced lift.

The CLR of the underwater profile excluding rudders is close to the CE of the mast but adding that of the rudders means she is quite unbalanced. The problem thus becomes one of moving the CE forward of the CLR. I'll look at some sort of riding sail/air rudder, a drogue off the bows and a forward dagger board. Any other notions welcome.
Click to expand...

How about mooring stern to? Then you have the drag of the rudders at the 'front' (nearest the buoy), with the boat weathercocking better behind, and the lift of the mast not only reduced, but position further 'back (away from the buoy).
 
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SL

in order to prevent the mast 'sailing', it must point directly into or down wind.

If you don't have the mast freely pivoting and weathercocking, then every proposal using water flow is just going to set the mast across wind (and generate unwanted drive) at some stage as wind and tide conspire to be at different angles to each other.

When she has taken ground, this is especially true as the wind will blow where it listeth, and not conveniently fore and aft.

The only guaranteed way to align the mast and wind direction is a freely pivoting mast, either driven by a 'rudder' at the outhaul end of the boom to counter the jib boom's windage, or a sophisticated drive system with sensor and power.

Or an aerial version of a trim tab self steering ? Now that could provide some non-electrical power to move the mast.
 
As an afficionado of the yawl rig. could this be adapted to your cat? A collapsible mast and boom (maybe on a traveller of sorts) attached to your arch.
 
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Hmmm.
Firstly, nice looking rig, clearly it is powerful and all boats are that darned compromise..
Secondly I spent a very windy night behind a breakwater on a big HR , 50 kn showing all night and the boat sailed around like a barstard- so
much so that the company had supplied an anchor sail for the backstay which helped... A little

Without spending too much time and money at this stage, I would be tempted by;
1) hanging an anchor and chain over the bow to drag the seabed as a dampener just to see if that is all that is required. Crude I know.

2) ditto two heavy buckets slung from the two sterns, and
3) the double vee- shaped anchor sailcloth wrapped around the mast and the the two clews sheeted out at a effective angle to the ships quarters, ....I suspect that some of the sailing energy once the boat sheers, is being fed in from the fore and aft boom as it comes athwart the wind. So any Vee sail that can blanket that somewhat will help?


To the other poster with junkrig: mine never sailed around at all, the trick might be to lower the sail/batten/ package to deck level if strong winds imminent.
 
Factory chimneys used to fail because of resonance, due to the development of Karman vortex streets. The answer was a 'vortex breaker' which spiralled up the outside of the chimney and desynchronised the vortex.

I doubt whether your problem is due to vortex streets, but the answer could be similar. Hoist a thick rope to the masthead, then spiral it round the mast. If nothing else, that should help to spoil the aerodynamics of the mast.
 
In my youth I owned a wide, flat bottomed monohull sailing boat that was unmanageable at anchor in a breeze. I tried everthing without success until one windy night I attached the anchor to the stern. Problem gone, it behaved just a 'proper long keel yacht'.

Might be worth a try?

Peter.
 
Could you design a wind vane type auto helm system so that as soon as she starts moving she'll turn up into the wind.
 
Anchoring or mooring by the stern has occurred to me but only as a last resort as the cockpit is nice & sheltered when the wind is from the bow. When moored to a pontoon with stern to the wind life is much less pleasant. I'll try it on the mooring to confirm it works but for anchoring I think it's a non-starter as all the gear is up the pointy end(s).
 
I too like the idea of a spoiler, but I'd try to work out how one could be pulled up the mainsail track. I think you could some make a form of flap that extended transversely which could be pulled up the track , ie like a T on the back of the foil? I think that it would cause trailing edge stall, which should substantially reduce the sideways lift being generated from the mast. There would be an increase in drag, but I think that this would help the boat lie better on its mooring anyway.
 
Hanging by the sterns, with the rig pivoted through 180deg, would seem to put a lot of things in the right places (CR/CE)- and improving the shelter in the cockpit might be easier than some of the other suggestions.
 
Stability is best achieved, not by having no forces but by having two opposing forces in balance. I think dje67 has the makings of the solution when he says use an asymetric bridal to bias it to one side........ I would go further and also bias the rig. Position it so that it tries to make her pull the opposite way.... ie. so that the rig is pulling her one way and the bridal is pulling her the other.

You said that you can't use a riding sail because you don't have a backstay but your picture does show a rope going from the top of the mast to the back end of the "boom"........ Could that rope be used to hoist a free flying riding sail? It would be rigged with the long side towards the stern and the "tack"pulled forward and made fast somewhere on the deck. You have enormouse beam (sorry, the boat does) so the riding sail could also be used to bias the boat in the opposite direction to the way the bridal is pulling her.
 
peterb said:
Factory chimneys used to fail because of resonance, due to the development of Karman vortex streets. The answer was a 'vortex breaker' which spiralled up the outside of the chimney and desynchronised the vortex.

I doubt whether your problem is due to vortex streets, but the answer could be similar. Hoist a thick rope to the masthead, then spiral it round the mast. If nothing else, that should help to spoil the aerodynamics of the mast.
Click to expand...

I thought someone was likely to beat me to that solution. Easy to try, simple to remove, nothing to be lost as far as I can see.
 
bignick said:
I too like the idea of a spoiler, but I'd try to work out how one could be pulled up the mainsail track.
Click to expand...

I envisioned a spoiler, too, but was thinking of something more like a spinny snuffer. In other words a sleeve around the mast (asuming it is plain all the way up, with no spreaders as I imagine it must be).

To really remove the aerofoil shape the snuffer would have to be made more cylindrical. This tumescence could be achieved by a couple of sausage bladders running up inside the snuffer which get inflated. I refuse to say what this is modelled on...

Mike.
 
SL has a mast of approx 100 ft sq. No amount of aerodynamic spoilers are going to prevent that having a considerable driving force through drag alone, if the mast does not trim easily to face the wind, and if the cat is turned either by tidal action or by being aground, at an angle to the wind.

If it were a question of generating assymetric lift then spoilers might well help.

Just think of a structure about 50 ft long and 2 feet wide with the wind blowing at 90 degrees to it.

The only solution is for the mast to be able to trim autonomously to minimise drag and negate any lifting component. The boat must be capable of doing that even if the hulls are pointing away from the wind through action of the tide and the mooring arrangement, or by being on the putty.
 
snowleopard said:
OK, here's the problem: my boat sails about on its mooring and at anchor. The cause is the wing mast which means there is 100 sq ft of 'sail' area set at all times. For those who haven't seen, here's a pic...

snowleopard.jpg


In moderate winds she swings from side to side but when it gets really strong she starts to sail from side to side until brought up by the bridle whereupon there is sharp deceleration and her head whips round to sail off in the opposite direction. It's uncomfortable, alarms the neighbours and of course the jerks on the mooring with the risk of breaking it.

So far I have 2 solutions. The mast maker recommends setting the mast atwartships. It does work fine at low wind speeds but puts more tension on the mooring and if the wind shifts suddenly it can develop forward drive with potentially disastrous consequences. The other I thought up at 6am today with 45 knots of wind over the deck - I put both engines in reverse at tickover so the boat couldn't accelerate. While they were running she just swayed 20° either side of the wind.

I have tried to think of ways to cut the surging that don't involve engines or excess loading on the mooring.

One obvious option is some sort of riding sail but of course we don't have a backstay so that would be tricky. Nor do we have space for a mizzen with riding sail.

So - I'm looking for some ideas.

p.s. other than that, it's a brilliant rig!
Click to expand...
A call to Z Spars for a normal rig?
Hee hee
Stu
 
snowleopard said:
I'll try it on the mooring to confirm it works but for anchoring I think it's a non-starter as all the gear is up the pointy end(s).
Click to expand...

It's not much effort to anchor from the pointy ends then walk the warp back to the stern (and vice-versa when the time comes to leave). Point taken about a draughty cockpit though.

(Only time I've ever been on a boat that was anchored by the stern was during race training, when the skipper would anchor that way while we did drills for spinnaker gybes and peels, without worrying about where the boat was going. You need to do it on a day when the wind is going the same way as the tide.)
 
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