modifying a staysail schooner

[PAR]

Tad, the original sail plan for the above pictured Choy Lee, shows the main of the ketch and the fore of the schooner in the same location, which to me makes perfect sense from a production point of view. My examples of the construction, deck and accommodations plans don't show a schooner mainmast but the mizzen of the ketch, which divided the cockpit in half (typical). I would have to assume that they offset the companionway and dropped the main down to the sole, where a very heavy athwart bearer took it ("U" shaped?), as the shaft is directly under the main.

[drewcathell26]

No one answered my question about cutters. I am still interested in knowing if there is a value and a way to locate the center of effort when one sail is covering a substantial amount of another sail.

You did however answer a question I hadn't yet asked and that was going to be regarding the difficulty in locating a usable center of effort on a bunch of sails some of which draw poorly. It leaves one question unanswered... does a sail create a rotation based on its size even if it is lousy at providing drive?

One other question. When you are calculating the ratio of sail area to displacement ratio for a cutter how is the foretriangle calculated.

One last thought. I have spent my life working with strucural engineers who all know the answer to practically every question I need to put to them. I was always amazed at what would happen when you broguht more than one to the mix. I am glad to see that boat design\building provides such a wealth of things to disagree about. I would hate to think the rest of the world had been relaxing while we homebuilders were living in the fog.

[drewcathell26]

In regards to PAR's question about the location of the mainmast and the companionway see the attached photo. The main mast lands on top of the frame in the photo. It was one of my concerns about enlarging the mail sail and placing more load on that frame.

[Tcubed]

Despite what has been said and written about centers of effort it is actually a simplifying method for a very much more complex problem.

Each sail will have a pitching moment about its aerodynamic center (0.25 mean chord) dependent on its section.
Furthermore there is the interaction of the sails upon one another (superimposition of up/down wash streamlines) .
So there is for each sail a total force vector acting upon its aerodynamic center (not the center of effort) and there is a moment about its aerodynamic center as well. These can all be summed to produce the total aerodynamic force and moment. This also does not act at the boats centerline due to the general angle of heel.

So you see that how one measures overlapping or not is a matter of convention , one that has been found to be a reasonable general approximation to the full model of the process as outlined above. Yes overlaps and individual sails are used , not foretriangles. But you never know , as each designer tends to develop his own methods over time.

[robherc]

@Drewcathell26

Usually, it's easy enough to ignore the part of the sail that is masked by another, as it isn't directly exposed to oncoming wind. IMO
But, as Tad so well put it, you can easily move your CE to just about wherever you need it by tightening &/or loosening a couple of sheets.

[drewcathell26]

I appreciate each of you taking the time to answer questions that must seem incredibly basic in your world. I started sailing 10 years years ago at age 40 and have been amazed at how wonderfully complex sailing is.

Your comments support the conclusion that two different boats of theoretically identical design elements will still sail differently based on the skill and experience of the person making the decisions. That being said it doesn't reduce the value of great design. Or learning more about it.