Multi-masted sailing cats

[Chris Ostlind]

Originally Posted by Fanie

Chris, those sails, one in each ama's, could free some hull space up... Any drawbacks to using it like that ?

Additional structure/additional weight out at the locations where I'd like to keep the boat as light as possible, reduced mast bury in the hull (self-supported rigs), interesting complications for reefing.

[BigCat]

Here's a catamaran rig with two unstayed carbon fiber masts, that is self tacking, and has a luff pocket that isn't hard to reef-in fact it's dead easy to reef. The masts and sails are identical, so easier to build, the sails' method of inducing camber isn't affected by mast bend, and don't require the services of a sail maker to create. See: http://bigcatcatamarans.com

[marshmat]

Interesting idea, BigCat.
It looks like you've essentially split the battens into two parts- one foil-shaped segment that wraps around the mast and one straight segment hinged to the trailing edge of the first?
How do the foil-curved battens slide on the mast- is it actually just a luff pocket, or are there tracks hidden inside there?

[Fanie]

Thanks BigCat,

That was along the lines I was thinking !! Nice idea to do the beam reaching too, so there is no direction of sailing with two sails side by side that would be a problem.

Big cat, nice music too

[Meanz Beanz]

Schionning had issues with the Radical Bay 800 (biplane rig) turning in heavy air at sea. Apparently in 30+ knots she wouldn't tack and I think had some issue gybing. I read a first hand account of it, will see if I can find it again. Does anyone know anymore about that? It was put down to the rig --> just wondering if it had been resolved.

[ThomD]

I talked to the guy who did the sails for White Wings, and some other Newick boats with the Lungstrum rig on it, possibly Pat's. His reaction was that it was a huge effort to get them right. Of course anything new is that way, but the simplicity aspect of it was not apparent to him.

[Steve W]

Peter Spronk did quite a few large lapstrake plywood cats down in St Croix some years ago with both ketch and schooner rigs.
Steve.

[sigurd]

robherc: when you sail a jib you trim the jib after the wind, there is not much room for using its sheet to balance CE, as you get bad turbulence immediately when it is not right.
In my experience the main is more forgiving, probably due to the fat leading edge or the downwash from the jib.

[brian eiland]

Originally Posted by Steve W

Peter Spronk did quite a few large lapstrake plywood cats down in St Croix some years ago with both ketch and schooner rigs.
Steve.

There is a Spronk at the bottom of this page:
http://runningtideyachts.com/design-references/s8.php

...and Peter Wormwood here:
http://runningtideyachts.com/design-references/s2.php

...they thought alike

[Gary Baigent]

An early 32 foot trimaran Atria was designed by Jim Young for Dooley Wilson and launched in 1964. This yacht had classical sheer in the main hull and because of this low freeboard amidships, placed the beams too close to the water surface, an early multihull design mistake, for the beams slowed the boat when driving through waves – a common problem with trimarans at that time. Wilson raced Atria in Tauranga for some years and then sailed it to Wellington where it was sold. Then in the mid 1970’s Young designed Wilson a 40 foot open wing deck trimaran named Bladon Racer; called a sketch for it was neither ketch nor schooner because both masts and mainsails were the same height and carried the same sail area in two roached, fully battened mainsails. “This was a low sail plan which kept the centre of effort down and reduced the tipping moment,” said Young. Although Young drew water ballast to be carried in the windward float to provide extra power, this was not fitted by Wilson. In the clever drawing, tanks which were linked to the centre board cases, could fill or empty to produce either buoyancy or lever arm weight.

[fng]

I sailed on the radical bay in thailand the morning of our sail it was blowing in the twenties and it was wing against tide. I found the boat very similar to my beach cat to tack, and always got it round. the trik was to leave the new windward main sheeted and ease the leeward. As you gained speed you would bring the leeward main in. to bring the leeward main in too soon the boat would begin to stall. The only other point to note is that the thailand versions don't have the wing mast as does the aussie version. At times reaching we felt a little overpowered but it did handle it very well and the whole platform felt very safe. Yes there was a time where one main blanketed the other but by heading up or down a few degrees this problem was eleminated.
There is a large Kelsall cat with a bi-plane rig sailing in NZ's bay of islands, and by all accounts they say the wouldn't have it any other way

[ancient kayaker]

Originally Posted by fng

I sailed on the radical bay in thailand the morning of our sail it was blowing in the twenties and it was wing against tide. I found the boat very similar to my beach cat to tack, and always got it round. the trik was to leave the new windward main sheeted and ease the leeward. As you gained speed you would bring the leeward main in. to bring the leeward main in too soon the boat would begin to stall ...

That makes sense, especially if you think of the rig as the wings of a biplane. There is no reason why the leeward and windward sails should interact negatively if the alpha is kept below stalling point. The rule of thumb for biplanes is, ensure the wing spacing is at least equal to the chord, at which point the second wing is operating at about 75% efficiency. However, a single high-aspect ratio wing (or sail) is always more efficient, so monoplanes rule the skies today except for planes designed for aerobatics.

[mdcf]

Originally Posted by ancient kayaker

That makes sense, especially if you think of the rig as the wings of a biplane. There is no reason why the leeward and windward sails should interact negatively if the alpha is kept below stalling point. The rule of thumb for biplanes is, ensure the wing spacing is at least equal to the chord, at which point the second wing is operating at about 75% efficiency. However, a single high-aspect ratio wing (or sail) is always more efficient, so monoplanes rule the skies today except for planes designed for aerobatics.

You have the interesting problem that the effective stagger is against you as well.

[ancient kayaker]

Originally Posted by mdcf

You have the interesting problem that the effective stagger is against you as well.

Biplanes usually had the upper wing ahead of the lower, positive stagger, but negative stagger has also been tried. I'm not sure which is theoretically the best, but I assume since positive stagger is by far the most common it is considered to be optimal. Presumably with positive stagger the upper wing is moved ahead of the turbulence coming off the lower wing, but the turbulence off the upper wingtip would then be more likely to influence the lower wing. I never did figure out the pros and cons.

I think those rare planes with negative stagger may have been to improve downward visibility from the cockpit. When going to windward a "biplane" boat would have negative stagger.

[mdcf]

Originally Posted by ancient kayaker

Biplanes usually had the upper wing ahead of the lower, positive stagger, but negative stagger has also been tried. I'm not sure which is theoretically the best, but I assume since positive stagger is by far the most common it is considered to be optimal. Presumably with positive stagger the upper wing is moved ahead of the turbulence coming off the lower wing, but the turbulence off the upper wingtip would then be more likely to influence the lower wing. I never did figure out the pros and cons.

I think those rare planes with negative stagger may have been to improve downward visibility from the cockpit. When going to windward a "biplane" boat would have negative stagger.

That is my understanding as well, at high alpha you get a reduced interaction by placing the top wing forwards. Fortunately for a biplane the airflow is close to perpendicular to the plane of the Cps (e.g. within 15 degrees, when not stalled) for the biplane cat, this is not the case and you approach a position where during a beam reach the stagger completely blankets the following wing. Unless the sails can work in close coupled mode the efficiency of the rig would be compromised dramatically. It is a great shame as I can see the rig being structurally good. Of course if the boat is very fast effective direction of the wind moves forwards avoiding some of this....