Cyberspeed in Catsailor says a SC21 is very difficult to tack

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Bill Roberts
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Posts: 515
Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Cyberspeed in Catsailor says a SC21 is very difficult to tack

Post by Bill Roberts »

How about that havliii? Is your boat hard to tack? What about this cyberspeed guy? Well, he doesn't understand "shared lift" or what makes a beach cat tack well/quickly. On the SC21 the daggerboard is moved forward of the main beam. It is about three ft forward of the normal position. In this location it carries or is exposed to less that 100% of the sideforce from the sails. To bring the boat back in balance an oversize rudder is used. The rudder is installed in a balanced condition so it can carry the balance of the sail side force without creating a heavy, hard pulling tiller.
What makes a boat tack? Now, when a centerboard boat tacks it tends to pivot about the CB. The rudder, located several feet aft on the transom, generates a side force and the aft end of the boat responds and moves in a circle around the pivot point, the CB. Torque created by the rudder makes the boat tack. Now in the case of the 21 with the forward located CB , the lever arm between the CB and rudder is increased relative to a boat with the CB located near the shroud chainplate and this longer lever arm makes more torque to tack the boat. Also the 22 has an oversize rudder which generates more side force and this increases the tacking torque also. So the unique geometry of the SC21 with shared lift makes the boat tack quicker not slower. Mr Cyberspeed doesn't understand. A SC 21 8.5ft wide will tack quicker than a SC20 12ft wide.
The thing that bums me is that this error comment was published in Catsailor and now many readers will think it is true. They do not know that a dummy said it.
havliii
Professional
Posts: 272
Joined: March 27th, 2011, 8:12 pm
Boat Make/Model: SuperCat 19, Modded SC20
Location: Fredericksburg Virginia

Re: Cyberspeed in Catsailor says a SC21 is very difficult to tack

Post by havliii »

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Bill Roberts
Expert
Posts: 515
Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Re: Cyberspeed in Catsailor says a SC21 is very difficult to tack

Post by Bill Roberts »

Havliii, this Cyberspeed guy owns the SC20 that Eric and I won the Steplechase with twice. He frequently sails in the Steeplechase and finishes last. Once he sailed his SC20 tall rig in the Round Island Race at Ft Walton Beach. At the first
bridge he decided to follow the H16s and not sail through the center span. BANG CRASH that was the end of the tall rig mast
and, 5 miles into the race why was he following H16s with a SC20 tall rig? His performance tells me that a SC20 tall rig is slower than a H16. I guess we can't deny facts. It must be true, a SC20 tall rig is slower than a H16.
Havliii, the bummer in Cyberspeeds lack of knowledge comment is that many Catsailor readers will read his comment and believe it. This hurts the reputation of the 21 and in general leads to a misunderstanding of what makes catamarans tack fast or slow.
havliii
Professional
Posts: 272
Joined: March 27th, 2011, 8:12 pm
Boat Make/Model: SuperCat 19, Modded SC20
Location: Fredericksburg Virginia

Re: Cyberspeed in Catsailor says a SC21 is very difficult to tack

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