Exactly...However, fortunately for us sailors, the CE's sum of sails, hull and foils conveniently shows up on the rudder gear when sailing straight and steady. So changing the headsail will show up directly in the rudder. Automagically including changes due to speed, heel, leeway, etc."Center of effort" devised with the old 2D geometric method is not going to tell you what you want to know. I dont know how you calculate...
That's what I thought, but using 12 metre's formulas it looks as if the layman's 2 dimensional center of effort of the sail plan only moves aft about 10% of the headsail overlap (where the headsail overlap and "E" mainsail foot length are identical) when re-calculating CE for a 100% jib vs the existing 140%."Center of effort" devised with the old 2D geometric method is not going to tell you what you want to know. I dont know how you calculate what you are after and what you are after is the "center of pressure" ans how it changes as you change trim. That's a pretty complicated 4 dimensional problem. I haven't used the old method to calculate " C of E" for many years. It was not working. Today I trust my eye and my experience. It's not a 2D problem. I'm sure some clever fellow with a lot of time on his hands could write a program for this. It may have already been done. My bet is that it has. Can't be too complex on a solid wing sail. I'm sure the AC designers are not guessing.
Most, if not all the time, when you reduce the jib LP, CE will move forward, not aft.That's what I thought, but using 12 metre's formulas it looks as if the layman's 2 dimensional center of effort of the sail plan only moves aft about 10% of the headsail overlap (where the headsail overlap and "E" mainsail foot length are identical) when re-calculating CE for a 100% jib vs the existing 140%.
And I wonder how much of this amount of movement is likely lost or negated by the M & J sail trim angles.
Basically what I'm looking at is how much the CE moves aft if I put a 100 on with inboard sheeting (waaay inboard of current sheeting angles). Less total sail area, true (573 vs 681) but better pointing.
Hmmm.....
Agree that it would have helped the discussion if the OP should have indicated the reason why he wants to know. because if it is the latter of your statements, then yes it is a bit of a moot discussion.This is all very interesting but unless one is designing a boat and is trying to calculate the position of the rig I fail to see the purpose of it.
As the C/E moves during sail changes you have to account for it through the helm and sail trim, not through theoretical calculations.
I just like to include all possible variables in my decision making process', sometimes important considerations are revealed therebyThis is all very interesting but unless one is designing a boat and is trying to calculate the position of the rig I fail to see the purpose of it.
As the C/E moves during sail changes you have to account for it through the helm and sail trim, not through theoretical calculations.
Any chance that I could cajole you into helping me figure out the CEs for the sails on the AC75?Parma,
There is an app for that !
RigEdge is the only CFD program I have ever been able to get even the most basic handle on but it can do the sort of calcs that you seek. Here are some screenshots from a rig included in its library.
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I hadn't fired the program up in months and I was surprised that I was able to set up that model and get some results without going back to the tutorials. I guess I retained more of it care and feeding that I suspected. The parameters for a boat and rig can be entered parametrically in a series of rig data that looks like this. Much easier and quicker than how I usually meticulously build a virtual rig and sail model in Rhino3D and then you can't really do much with it. Once you set up a rig and sails model in RigEdge then you can proceed to full analysis pretty quickly.
We bought a license for use on the rig of the CG certified 49 passenger daysailing catamaran and it was worth if for just that one job, but getting the engineer to accept the analysis was another thing. Still waiting on some valid results from him on that rig! The important thing is getting some output that will pass muster with the Coast Guard and the classification societies. The people behind RigEdge are pretty sharp and they have full RINA approval and the bulk of their customers are for those huge Wally sloops and the even bigger Italian mega ketches. The ultimate module in the package calculated the G loads on a rig imposed by bashing into head seas which apparently is a major concern when rigs get up near 200 feet!
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Thanks. Actually, using XFLR5 and a reasonably decent profile of this "twin skin" mainsail, I have a good idea where the CE is located along the chord. It varies from 35-45% from LE, depending on the camber & windspeed settings.On a plane wing, the centre of effort is about 33% of the chord back from the leading edge.
For a guesstimate, I would use this value, I think it will be closer than the geometric centre.