View Full Version : Sloop to Nuts?
02-23-2003, 07:57 PM
This particular topic has probably been covered before, but I cannot seem to find any posts in the archive that addresses it. If you can direct me there, I would appreciate it. If not, perhaps you can answer my question.
How does one go about changing a sloop to a cat rig? Specifically, I am looking at a 14ft skiff with fractional bermudan sloop rig with an SA of 101sqft. The main is 67.3sqft and jib is 33.7 sq.ft. I am looking to change because I am unfamiliar with the rig, would like to avoid the complexity of stays, and have a rig that when dismantled, fits within the boat.
Should the new sail have approximately the same area as the two combined sails? Should the CE approximate the CE of the two sails? Is there anything else I need to consider?
02-24-2003, 08:40 AM
I have no idea, but I think your topic should get the "Best Topic" award! :D
02-24-2003, 08:54 AM
What Ken said... :D
John of Phoenix
02-24-2003, 09:15 AM
Glen-L "Bull's Eye" 11' skiff
Sloop Rig: Fully stayed with loose footed main. Area main: 49 sq.ft., jib: 25 sq.ft. Total area: 74 sq.ft.
Cat Rig: Unstayed mast with loose footed, sock-type sail. Area: 56 sq.ft. Note that the mast is about the same height but farther forward than when sloop rigged. On this 11 footer it's about a 16" difference IIRC.
Sprit Rig: Classic unstayed, rotating mast with sprit boom. Loose footed sail with with luff laced to the mast. Area: 51 sq.ft. Ditto on the mast moving forward.
Note that the CE is positioned at the aft edge of the daggerboard on each rig.
I can dig out the plans if you need to get exact data. Hope this helps. smile.gif
http://www.glen-l.com/designs/sailboat/dsn-bselaa.jpg http://www.glen-l.com/designs/sailboat/dsn-bselab.jpg http://www.glen-l.com/designs/sailboat/dsn-bselac.jpg
[ 02-24-2003, 10:19 AM: Message edited by: John Teetsel ]
02-24-2003, 12:15 PM
There are a lot of things you need to consider. Without going into a lot of detail, different rigs have what you might call different effective areas, so simply adding up the sail areas will not answer the question because one rig might need more area to produce the same amount of power. A sloop rig on a small boat like this may well be less efficient than a cat rig so the cat rig may require less sail area, which could be good because for heavier wind conditions the cat rig may offer you fewer options for shortening sail. On the other hand, a lot will depend on just what sort of cat rig you want to use because each has its own peculiarities. (gaff, Bermuda, sprit, what the heck, even a Chinese junk rig can be set up as a cat).
Also, most hulls are better suited to some rigs than to others. For example, a hull with a lot of directional stability may need a more spread out rig like a sloop for it to tack effectively. Also, a hull with less stability will need a rig that keeps the sail area low, which some rigs do better than other rigs. On the other hand, a boat that is designed to be 'high-performance' may turn out to be a boring 'dog' if you put a lower performance rig on it.
On the CE, I think you should assume that the position of the CE will need to change if you use a different rig because it is not safe to assume that it won't. How it should change will depend on the particular rig and boat.
Yet another point you need consider is how changing the rig will change the loads on the hull and thus necessitate changes to the hull structure.
I have certainly not covered all of the issues; I have just tried to give you a sense for what you are up against. Since this is a small boat you are not taking that big a risk by making such changes, but you should go into it with your eyes open...
If I were doing this I would treat the information about the existing rig as only moderately relevant. More important to me would be information about similar boats with cat rigs of the type you are interested in (gaff, sprit, etc.). Find as many comparisons as you can (and ideally ones that are proven designs so that you are not copying previous mistakes) and check things like where the CE is relative to the CLR. Also, try to analyze the stability of the comparison boats so that can judge how much sail area is called for. Some will probably argue that I am going overboard here and that all this math is not required for a 14' skiff. My response would be that experience and knowledge can substitute for (and probably improve on) the math, but that for someone lacking the base of experience to know what is right in this sort of situation, math is probably the best fallback position...
I know this all may not seem that helpful to you, but I thought it was good to get some background into the discussion. Others may be able to supply some of the basic information you asked for but I am hoping that their information will be more helpful with what I have said as background. If not, well, they're just words... :D
Have fun whatever you do!
02-24-2003, 04:53 PM
Tod probably needs to answer this, but, if you get the overall CE in the same place with one, two or ten sails the boat will handle about the same. The problem is pure physics. That said, usually, the fewer the sails the more effecient the sail plan for a given sail area.
02-24-2003, 05:11 PM
Ken and Tim, thanks for the votes for "Best Topic," do I win a wooden boat? ;)
Bruce, thanks for the background information. It is helpful to me as I consider the possibilities. In another thread there was talk about changing existing designs for whatever reason. When I purchase plans, I generally do so because I like the hull, but am never satisfied with the suit of sails and so I would think that it would be the easiest part of the design to modify. After your post, I am not so sure. You are right, however, that I need to indentify the type of sail I am changing to and at the moment it is a toss up between a trad sprits'l and a balanced lug. Although a boomed lateen is tempting because it is so dog gone easy.
John, thanks for posting the information on the Glen-L design. I'm assuming that the various cat rigs are smaller than the combined area of the sloop because of Ed's observation that a single sail is more powerful for a given area than two.
It may be an option to build to mast steps and partners. One that would accomodate the original rig for the design (I should learn to sail a sloop), and another that will accomodate the cat rig. The design I am looking at is an Atkin Skiff, and so consulting him on this possibility is out of the question. Hence my seeking the wisdom of the WBF.
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