Jib question

Guys multis go to windward a lot differently from monos, no hull speed limit, so no desire to sail higher to increase VMG.

You also have to distinguish between the idea case of a fully optimised sail setup versus reality.

 

Excuse me are you looking to smack an entire homerun with one experiment? Usually these advancements come in little chunks...chipping away at the problem, and making incremental advances...like the previous 12 meters.

Within the class rules I'm sure they are.



I included this reference to Catbird Suite as she is one of the few big cats I could find that has done this 'full size' experimenting. If you had read about her a little more you might have observed these excerpts:

"For a long, passage-making tack, I attach staysail and main to fittings on the windward side deck and use one genoa, the genoa attached to the windward bow, so I then have the entire width of the boat for sheeting positions, so no booms or whisker poles are needed to maintain ideal sail shape as I go from close-hauled to reach and on to run. In other words, the sails are sheeted down to the boat itself, and thus the boat is the 'boom'."


"The sail plan thus, with sails attached to windward side of boat, looks like a cutter rig that is heeling, even though the boat is not heeling. And she goes to windward very well, like 30 degrees to the apparent wind, and there aren't many cruising boats that can do better than that."


"The leeward genoa can be added to this sail configuration, and, when close-hauled, a whisker pole is not needed, with the clew of the leeward genoa sheeted just outboard of, that is, to leeward of the leeward mast but still within the beam of the boat. However, easing the sheet to reach, in order to maintain ideal sail shape on the leeward genoa, requires a whisker pole, because then the clew of the leeward genoa is out beyond the leeward side of the boat. It can be done without a whisker pole, and about as well as on a typical monohull, but, of course, the clew will rise and the sail will have too much belly, not ideal."




"On the other end of the wind scale, in very light winds, my sails have an advantage over the sails on conventional, vertically rigged boats, in that their sails require a certain amount of wind just to lift the sails away from the vertical enough to set them into their proper aerodynamic shape for sailing to windward at all, and in winds of less than the required amount for lifting and filling and setting the shape of the sails, which is considerable on a big boat with heavy sails, the sails are worse than useless, they are all drag. That's why you move yourself over to leeward in a little sailing dinghy in very light winds, to heel the boat a bit and thus get your sails to hang and set properly by gravity. It would take a lot of heavy crew to accomplish the same effect on a big cruising monohull, and would be impossible on a catamaran. My sails, attached to the windward side, because they are "heeled" to start with, as soon as I unfurl them, they assume their proper shapes by the effect of gravity and I'm away with the gentlest puff of wind, rather than with sails drooping like laundry and the boat going backwards."

 

WHAT :!:

 

WHAT :!:
Are you assuming that someone moves the tack position without ever retriming the sail? That might be the only way your statement has any validity.

We are talking about flying the jib (or genoa) tacked outward to a new location....a new rig configuration. Then we might well retrim that original sail,...or even cut a new sail that works better in that leeward position. Bottom line is we might well go to weather at a higher angle.

I suspect there is a quickly diminishing return on this investment (not forever linear as Eric hinted at in posting #3), but some increase in pointing capability never the less.

 

idkfa has other half right (allmost), a slight depowering is possible but not necessarily bcs the apparent wind increases in the same time. There's also decrease in relative drag and better direction of aerodynamic force..

It's not the only option to sail higher if that's not desired, you can also go to the same direction faster..

 

"So it's going to weather faster by footing, rather than pointing. This is what you do in a high-performance boat. If you see a modern multihull sailing lower than the monohull fleet going to weather, it's not that the multihull can't point - if it has a deep daggerboard it can point with the best of them - rather it gets its best Vmg by footing off instead of pinching. Sailing faster but farther to get the mark first."

http://www.boatdesign.net/forums/sa...el-vs-dagger-boards-etc-35316.html#post415832

 

I think most multihull sailors realize this truism.

However if we look at the original question asked by the poster, "What would it take for a jib to improve pointing?"

What's to say that reconfiguring a 'std' sailing rig by offsetting the headsail to leeward, that the pointing capability might be improved WITHOUT detrimental effects to drag? That's what would be interesting to explore. Then the mono or multi might just improve incrementally?

I think back to that old twin asymmetric daggerboard Terrorist in the SORC races that really cleaned up on windward performance (new thinking), and then was promply rated out of further development the following year.

 

Usually these advancements come in little chunks...chipping away at the problem, and making incremental advances


Why ?

If the process is an improvement in pointing, as a direct result of the re-positioning of the jib position, even my 12 months trial period is excessive.

I cant see why one 8 hour sail, with anemometer, GPS and video camera couldn't put this long running discussion to bed .

True, Cats and Monos have different strategies for getting to the windward buoy, but a graph of pointing angles, ground speeds and wind speed isn't a lot of work.

 

Fossatti tells in his book, Aero- Hydrodynamics, how difficult and expensive such work is so it's not a piece of cake..

 

Gooday watson - Is all this very valuable knowledge from you vast experiences in "True, Cats and Monos" because I'd sure be interested in your successful exploits ??? We'd sure find your information or great value.

"have different stratigies for getting to the windward buoy" - oh really - very interesting - not what a heck of a lot of very experienced sailors, designers, builders & skippers have said in these forums.

I'd sure like to know of the sailing that you've done that can show us all an example of your comments & how to put them into practical use - please explain ??? I'm sure we'd all like to learn from your vast experiences over the many ocean miles that you have sailed, I know - that I'd be very grateful. ciao, james

 

Sure - I can contribute a bit. Silver can be as smarmy as he likes with "vast experiences over the many ocean miles", as he likes, but this is not a case of experience or vast knowledge. Its just a very simple test.

I totally agree that if you are doing a complete analysis of a boats sailing performance overall, in differing conditions, sail sizes , mast rakes, ad infinitum, it would cost a fortune in time and money for any boat.

What everyone is having fun discussing here is ONE variant of the rig. Just ONE !

The theory goes, that by changing the point of attachment of the jib, we should be seeing a better pointing angle.

To quote the assertion "Every degree of angle you swing the jib tack to leeward, as measured from the jib tack to the mast, you gain that number of degrees to windward."

So, it would be as easy as setting up an adjustable bowsprit on a mono, or a traveller across the front of a cat. Then running a series of tests of speed V wind angle and recording the wind strength at the time.

Two Polar graphs with the points plotted should show a really noticeable difference in performance. The speed at identical upwind angles, in similar wind speeds should be significantly greater with the jib offset.

Its not something great minds and rocket scientists have to ponder on for years - its that %*(^$^%^ simple.

 

A test, simple or not, is a remarkably intelligent way of discovering the truth. Assuming the test is done well.
Lets not loose sight of the fact that the proof of the original statement is not where we should be concerned. The real issue is - Is there ANY benefit to moving the jib to Leeward?

If you move the jib 10 degrees to leeward and don't get 10 degrees of pointing ability doesn't mean you failed. If you do get 2 or 4 degrees of improvement we win. Any improvement should be a win

Lets not be nit-picking engineers. Lets see if this relatively simple idea is an improvement in actual fact. (Although I think Brian's example already proved it- we just need more people confirming it so it will be accepted)
Wish I had a working catamaran so I could contribute something useful.

It might be interesting to see proposals on how to actually build a Jib which could be tacked (at the tack) either side of centerline. What would we be limited to - 5, 10, or 45 degrees? My ideal would be to have a jib which would be flown off the inside of the bow of a catamaran, sheeted to the outside of the same hull (going hard upwind).

Can you imagine the pressure to do this if the AC 45 boats showed this works?

 

If you get just few degrees, or even 10 degrees, what use do you make of it? If you get them by maintaining the same Vmg then you do win, and you also win if you get a fraction of a knot more Vmg. But if you only get few degrees of pointing angle, at the cost of sacrificing the Vmg, I don't think that's what one would call a win.

 

How is this for making it simple ?

The angle of attack of the boats hull is why the altering of the jibs position doesnt make for better pointing .

 

Daiquiri,

There is no more point in this discussion. Who has any real idea that your last possibility has any reality? I agree a person could screw up setting the sails to make it happen.

Rwatson,

No wonder this discussion is sterile, I have never seen a sailboat with either of those diagrams, assuming the wind is from the top.
Actually I have. I passed a guy who had never sailed who insisted on sheeting the jib to the windward side of the boat. He was having a terrible time just getting the boat to move.
Such a pity, this is an interesting subject.

Why was there no discussion of post #100? Seems like a practical application of the question. One of the few. No hard core scientifically rigorous measurements, but I have almost never seen any of those here.