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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Sailboat Design and Construction > Cat rig VS. Sloop
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Thread: Cat rig VS. Sloop Reply to Thread
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Topic Review (Newest First)
02-05-2009 08:59 AM
Jeff_H As I read through this thread, a couple things jumped out at me. First of all, the thread starts out as a general theoretical design question comparing sloop vs cat rigs. Then it migrates to a very specific question about converting a specific design from a sloop to a cat rig. And then it does a non-sequitor and becomes as a discussion of catamarrans vs mono-hulls and ultimately ends up as a discussion of the egos of felines, and multi-hull and feline lovers. Cheez Louise.......You just have to wonder about this place sometimes.

Anyway, back to the original question, in steady state, moderate to low speed wind conditions a single sail is generally more efficient than multiple sails. But we don't sail in steady state conditions. we sail at a variety of angles to the winds, with gradient winds that require twist to the sails, in ambient winds that increase and decrease in speed, which is then complicated by the impact of apparent wind and velocity shifting, and so on. And in these variable conditions, the multiple sails of a sloop allow us to adapt to the changing boat and wind speed and direction not just for performance, but to balance the helm, reduce heeling, deal with waves or current and so on. This can be done on a catboat as well, but not as efficiently.

Its important to understand that the primary drive in a sail comes from its leading edge and not from its sail area. Increasing sail area without increasing leading edge will increase speed on a beam reach to a run, but does comparatively little for the boat upwind. If we compare a sloop to a catboat of equal mast height, the added luff length of the jib can mean that the sloop will have an extra 60% to 100% more leading edge over the cat. That is significant when close reaching to going upwind.

Of course you can increase the length of the mast on the cat rig in order to equal that of the sloop, but when you do you raise the vertical center of gravity making the cat rigged boat a lot more prone to heeling for an equal sail area and luff length.

Some catboats try to equal the sail area of the sloop while maintaining an equal mast height to the sloop by going to quadralateral sails (gaff or lug rigs). This helps a lot on reaches and runs but adds drag and so hurts windward performance.

The other advantage of the sloop over cat is the ability to maintain luff length while reducing sail area in higher windspeeds. What happens with a performance oriented sloop is that it will have several headsails that it can employ. These headsails are typically of different overlap and flatness, but they mostly all have similar luff lengths. Because of the ability to control headstay sag over a range of conditions, the fullness of any individual jib can be varied with the conditions as well. Because you can pick the right jib for the conditions, the sloop also offers practical advantage over a catboat which can only alter mainsail shape, and reef to deal with changes in windspeed.

More than any other single reason, this flexibility in adapting to changes in windspeed is the reason that larger racing sailboats are sloops and not catboats. The massive inherent upwind inefficiencies of multi-mast rigs is the reason that modern race boats are typically not ketches, yawls or schooners.

Which gets us to the second part of the question, What is the best rig for a puffer, which is the one that I suspect that the original poster had in mind when he started this. For their day, Puffers were a nice design all around. They came with a very efficient sloop rig and I would suspect that converting one to a catboat, even with a taller mast, and greater sail area, one would give up a certain amount of performance particularly at the upper and lower ends of the wind range. Its not because of any theoretical advantage that a sloop may have, but more about the physical properties of the puffer itself.

As to the felines, and multi-hull and feline lovers, go find your own thread.

Respectfully,

Jeff
02-04-2009 11:33 PM
tdw
Quote:
Originally Posted by AdamLein View Post
When did this thread start being about catamarans?

It was probably just a matter of time.....

Now look here chaps......please read thread before jumping in......

It's a multi hull thing really......mention (good heavens my tabby cat got the blue pencil) and they think you are talking about them. Total egotists the lot of them.
02-04-2009 10:35 PM
AdamLein When did this thread start being about catamarans?
02-04-2009 07:37 PM
sailingdog BS. There are a lot of catamarans smaller than 40' LOA that have proven themselves in making ocean passages. The main cause of capsize in a cruising size multihull is human error. If sailed properly, the risk of capsize is quite low. The risk of losing a keel or rudder on a monohull is higher than that of capsizing a cruising catamaran, provided you're sailing it properly.

Quote:
Originally Posted by InetRoadkill View Post
I'm still undecided over single hull sloop or going with a catamaran for a cruiser. I like cats, but from what I've read is that they need to be at least 40' to be safe on open water. I'd really hate to deal with a knockdown in a large cat. At least a monohull will generally un-turtle themselves (provided they don't flood).
02-04-2009 03:31 PM
InetRoadkill I'm still undecided over single hull sloop or going with a catamaran for a cruiser. I like cats, but from what I've read is that they need to be at least 40' to be safe on open water. I'd really hate to deal with a knockdown in a large cat. At least a monohull will generally un-turtle themselves (provided they don't flood).
02-03-2009 10:40 PM
tdw Weatherhelm ?
02-03-2009 08:00 PM
seamountie
Why you don't see Cat-rigs

Why a cat rig isn't seen in the America's Cup is the same reason you don't see a catamaran...either outright not allowed or so heavily penalized as to be not worth the effort.

Watch for them in unlimited racing, particularly ketch and schooner rigged. Have a search for Magi Noir (Black Magic if you are interested). Unfortunately it couldn't get enough sponsorship to compete, but the specs were real good.

Sloop rigs are most prevalent because of racing ratings. Cats end up being penalized quite heavily.

Your typical daysail cat rig isn't going to compete, to weather anyway, with sloops who's heritage is racing. Compare it to a purely cruising sloop, and it compares very favourably, and is generally easier to handle.
10-13-2008 09:50 PM
runner This question was answered today when I was able to retrieve the original mast and standing rig. Now I need to make a boom up. Ordering the correct gooseneck tomorrow I hope. My nephew is working on his first attempt to copy the old jib off the 16 foot dinghy. We both figure it is going to take several attempts to figure that out! I have three jib sails that should work on the Puffer. I still need a main sail. Hopefully by spring that will be taken care of.
We are using a very old pattern that seems to have always had a slide or a
bolt rope slot to make these first sails. The stretch pattern of the material we are using is closer to canvas than it is to dacron. I am not sure if this pattern will work as well for a loose footed sail, but i suspect that is how the Puffer will end up rigged. If the cloth isn't stiff enough, he has the ability to laminate it. I wish I could get sailcut to work so I could cut full sized panel patterns as we go. Without, we are going to be working from the old sails.
10-11-2008 01:14 AM
Delirious Sailing speed is not necessarily a bad thing. Whenever my wife & I have owned a "larger" boat (27 to 34 feet) we've also owned a smaller open boat of 17 to 19 feet. There's something about hiking out a few feet over the water that is lacking in a larget cockpit.

I can tell you a 17 foot Thistle charging on a reach at 12 knots is a life-affirming experience. Equivalent to running up a motorcycle over 100 mph. Larger boats are just as exhilirating at times, but it's just not the same.

It just comes down to everyone needs at least two sailboats ;-)
10-11-2008 12:35 AM
runner I bought a 1955 Y-flyer a few days back. It is in pretty bad shape with rot of some kind. I would almost say time has had it's way. Anyway, I got it mainly for the trailer, but the sails and mast came with it. Another person locally has a hull that needs repairs but is servicable maybe. I have to go look at it Monday. . The Puffer is for me to play with and learn on. The new mast is strong enough, but I keep bouncing between just changing the mast and sewing sails to fit the new rig, or changing it around to be a simple fishing relaxation type boat.
I have a confession! The speed thing may be getting to me! This picture of the Puffer with a 2 foot bowsprit and a full 9' foot on the main using a boat length boom or a touch better. Fairlead slides, a traveler, cunningham, and a boom vang seem to creep into the vision when I am looking in that direction. BFS may be contageous! When thinking the other way, a simple cat rig sounds nice for simple day trips of just a few hours where relaxing with a lure bumping behind the boat .
PS: the Y-flyer came with a fiberglass layup of the bottom hull of a Y-flyer where someone had started to build one sometime in the past. It was turned upside down protecting the old boat from the weather. Wait and see the questions when it is time for that project!
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