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Cat motion

Robert Phillips

Fri, Sep 24, 2010 2:14 PM

The R&C 46 is somewhere around two seconds, while our Cattech 29 is closer to
one second, almost so fast it seems to be vibrating.

In the world of yacht handicapping, we have been testing oscillation as a
means of determining stability, in this case the ability to carry sail area,
which determines upwind speed in a breeze. Most of the top race boats are
around three seconds, racer cruisers like Swans, Oysters, etc., 3.7 to 4.2,
long range cruisers 4.5 to 6.

What I found interesting was the similarity between commercial fishing boats
and true cruising boats, both groups which spend time at sea, in that they
preferred longer roll periods. Where performance becomes the dominating
factor, shortening the time at sea, roll period shortens dramatically.

It will be interesting to learn the roll period of Pat's displacement cruising
cats. I haven't been on a SWATH vessel and am interested in learning their
roll period if anyone on the list has experience with one.

Robert Phillips, Managing Director
Doyle Sailmakers BVI, Ltd
Tel: +284-494-2569
Mobile: +284-541-2206
VOIP US Tel: 423-285-8752
Skype: doylebvi

The roll period of a boat is an important indication of its stiffness, or resistance to roll. My 60' trawler is 4.2 seconds for a complete oscillation. The eighty foot Dutch North Sea trawler I owned was eight seconds. She rolled gunwale to gunwale when at sea, but in such a long period you really didn't notice it, which is probably why commercial fishing vessels are, generally, round bilged. The R&C 46 is somewhere around two seconds, while our Cattech 29 is closer to one second, almost so fast it seems to be vibrating. In the world of yacht handicapping, we have been testing oscillation as a means of determining stability, in this case the ability to carry sail area, which determines upwind speed in a breeze. Most of the top race boats are around three seconds, racer cruisers like Swans, Oysters, etc., 3.7 to 4.2, long range cruisers 4.5 to 6. What I found interesting was the similarity between commercial fishing boats and true cruising boats, both groups which spend time at sea, in that they preferred longer roll periods. Where performance becomes the dominating factor, shortening the time at sea, roll period shortens dramatically. It will be interesting to learn the roll period of Pat's displacement cruising cats. I haven't been on a SWATH vessel and am interested in learning their roll period if anyone on the list has experience with one. Robert Phillips, Managing Director Doyle Sailmakers BVI, Ltd Tel: +284-494-2569 Mobile: +284-541-2206 VOIP US Tel: 423-285-8752 Skype: doylebvi

Pat Reischmann

Fri, Sep 24, 2010 2:27 PM

The R&C 46 is somewhere around two seconds, while our Cattech 29 is closer
to
one second, almost so fast it seems to be vibrating.

In the world of yacht handicapping, we have been testing oscillation as a
means of determining stability, in this case the ability to carry sail
area,
which determines upwind speed in a breeze. Most of the top race boats are
around three seconds, racer cruisers like Swans, Oysters, etc., 3.7 to 4.2,
long range cruisers 4.5 to 6.

What I found interesting was the similarity between commercial fishing
boats
and true cruising boats, both groups which spend time at sea, in that they
preferred longer roll periods. Where performance becomes the dominating
factor, shortening the time at sea, roll period shortens dramatically.

It will be interesting to learn the roll period of Pat's displacement
cruising
cats. I haven't been on a SWATH vessel and am interested in learning their
roll period if anyone on the list has experience with one.

Robert Phillips, Managing Director
Doyle Sailmakers BVI, Ltd
Tel: +284-494-2569
Mobile: +284-541-2206
VOIP US Tel: 423-285-8752
Skype: doylebvi

Power-Catamaran Mailing List

Don't forget VCG, when it comes to rolling. The Manta 44 powercat has one of the lowest VCG, I have seen. Fuel low in the hulls, no flybridge, makes a big difference in pitch and roll. One of the reasons we used a freestanding mast in the custom cat I am finishing was to lower VCG compared to conventional rig. ----- Original Message ----- From: Robert Phillips<mailto:bob@doylecaribbean.com> To: power-catamaran@lists.samurai.com<mailto:power-catamaran@lists.samurai.com> Sent: Friday, September 24, 2010 10:14 AM Subject: [PCW] Cat motion The roll period of a boat is an important indication of its stiffness, or resistance to roll. My 60' trawler is 4.2 seconds for a complete oscillation. The eighty foot Dutch North Sea trawler I owned was eight seconds. She rolled gunwale to gunwale when at sea, but in such a long period you really didn't notice it, which is probably why commercial fishing vessels are, generally, round bilged. The R&C 46 is somewhere around two seconds, while our Cattech 29 is closer to one second, almost so fast it seems to be vibrating. In the world of yacht handicapping, we have been testing oscillation as a means of determining stability, in this case the ability to carry sail area, which determines upwind speed in a breeze. Most of the top race boats are around three seconds, racer cruisers like Swans, Oysters, etc., 3.7 to 4.2, long range cruisers 4.5 to 6. What I found interesting was the similarity between commercial fishing boats and true cruising boats, both groups which spend time at sea, in that they preferred longer roll periods. Where performance becomes the dominating factor, shortening the time at sea, roll period shortens dramatically. It will be interesting to learn the roll period of Pat's displacement cruising cats. I haven't been on a SWATH vessel and am interested in learning their roll period if anyone on the list has experience with one. Robert Phillips, Managing Director Doyle Sailmakers BVI, Ltd Tel: +284-494-2569 Mobile: +284-541-2206 VOIP US Tel: 423-285-8752 Skype: doylebvi _______________________________________________ Power-Catamaran Mailing List