Would a Von Karman Vortex Street have saved the capsized catamaran?

JF
John Foster
Sat, Feb 24, 2007 1:33 AM

Cat being delivered in Atlantic flips, reminiscent of Catshot delivery
capsize in Pacific storm.

Ketchum man rescued after boat flips in Atlantic
http://www.mtexpress.com/index2.php?issue_date=02-23-2007&ID=2005114300

  • Idaho Mountain Express /23/02/2007

http://www.mtexpress.com/index2.php?issue_date=02-23-2007&ID=2005114300

Would a Von Karman Vortex Street have saved the capsized catamaran?
/

First lets be sure we are both discussing the same things when we use
certain words. For me:

"Heave To" has the ship in an attitude about 50 degrees to the wind.
(That 50 degree angle seems to be important in the generation of the
protective slick upwind) Headway is stopped and the ship is making a
drift (at a rate of 1/2 to 2 knots) to leeward, straight down wind. At
that angle of heading, the flow around the hull and keel is stalled and
a turbulent wake will appear on the weather side. This turbulent wake
has the effect of smoothing down breaking seas on their approach

The scientific name for the turbulent field caused by your hove to ship,
with or without a para anchor, is a Von Karman Vortex Street.

To quote from Pardey's book (Storm Tactics Handbook (Modern Methods of
Heaving-To for Survival in Extreme Conditions) (ISBN:0964603667) Pardey,
Lin/ Pardey, Larry. Approximate Price: US$ 21.93 ) on page 83:

" I have sat on deck during Force 10 winds and watched while almost
pipeline like waves toppled onto our slick, then crumbled into heavy
foam coming close to the boat. Yet the same pipeliners, with their
overhanging crests, kept their shape and power as they broke fore and
aft of where our boat lay. To write this on paper does no justice to the
drama of watching the slick sap the power of the waves"

Although a boat produces its own Von Karman Vortex Street, the parachute
anchor, upwind some 300 ft of so, also produces a Von Karman Vortex
Street so the protection from breaking waves is far better than without
the parachute anchor.

The 4th edition of Drag Devices Data Base ( by Victor Shane. ISBN
1-878832-03-4 Approximate Price $36.95 ) has a lot of multihull case
histories should you need additional opinions besides those reported in
detail by the Pardeys.

Oh yeah, one more thing, I have not been misled into thinking that a
bigger sea anchor would be better than one that is the correct size for
your boat. The generation of the protective Von Karman Vortex Street
depends on the boat drifting slowly, quite slowly actually, straight
down wind. Too large a chute, too slow a drift, and hence, no protective
Von Karman Vortex Street.

See also the Earl Hinz book "Heavy Weather Tactics using Sea Anchors and
Drogues", printed 2000, ISBN 0-939837-37-4

Earl spent a lot of pages on the need to have the para anchor and the
boat about one wavelength apart.

All the best

John

Cat being delivered in Atlantic flips, reminiscent of Catshot delivery capsize in Pacific storm. Ketchum man rescued after boat flips in Atlantic <http://www.mtexpress.com/index2.php?issue_date=02-23-2007&ID=2005114300> - *Idaho Mountain Express* /23/02/2007 <http://www.mtexpress.com/index2.php?issue_date=02-23-2007&ID=2005114300> Would a Von Karman Vortex Street have saved the capsized catamaran? / First lets be sure we are both discussing the same things when we use certain words. For me: "Heave To" has the ship in an attitude about 50 degrees to the wind. (That 50 degree angle seems to be important in the generation of the protective slick upwind) Headway is stopped and the ship is making a drift (at a rate of 1/2 to 2 knots) to leeward, straight down wind. At that angle of heading, the flow around the hull and keel is stalled and a turbulent wake will appear on the weather side. This turbulent wake has the effect of smoothing down breaking seas on their approach The scientific name for the turbulent field caused by your hove to ship, with or without a para anchor, is a Von Karman Vortex Street. To quote from Pardey's book (Storm Tactics Handbook (Modern Methods of Heaving-To for Survival in Extreme Conditions) (ISBN:0964603667) Pardey, Lin/ Pardey, Larry. Approximate Price: US$ 21.93 ) on page 83: " I have sat on deck during Force 10 winds and watched while almost pipeline like waves toppled onto our slick, then crumbled into heavy foam coming close to the boat. Yet the same pipeliners, with their overhanging crests, kept their shape and power as they broke fore and aft of where our boat lay. To write this on paper does no justice to the drama of watching the slick sap the power of the waves" Although a boat produces its own Von Karman Vortex Street, the parachute anchor, upwind some 300 ft of so, also produces a Von Karman Vortex Street so the protection from breaking waves is far better than without the parachute anchor. The 4th edition of Drag Devices Data Base ( by Victor Shane. ISBN 1-878832-03-4 Approximate Price $36.95 ) has a lot of multihull case histories should you need additional opinions besides those reported in detail by the Pardeys. Oh yeah, one more thing, I have not been misled into thinking that a bigger sea anchor would be better than one that is the correct size for your boat. The generation of the protective Von Karman Vortex Street depends on the boat drifting slowly, quite slowly actually, straight down wind. Too large a chute, too slow a drift, and hence, no protective Von Karman Vortex Street. See also the Earl Hinz book "Heavy Weather Tactics using Sea Anchors and Drogues", printed 2000, ISBN 0-939837-37-4 Earl spent a lot of pages on the need to have the para anchor and the boat about one wavelength apart. All the best John
BP
B. P. Hawkins
Sun, Feb 25, 2007 9:36 AM

Some more information on the Haley including the USCC time-line on a side
bar article from The Royal Gazette, Bermuda's only daily newspaper.

http://www.theroyalgazette.com/siftology.royalgazette/Article/article.jsp?ar
ticleId=7d72a93300301a2&sectionId=60

Some more information on the Haley including the USCC time-line on a side bar article from The Royal Gazette, Bermuda's only daily newspaper. http://www.theroyalgazette.com/siftology.royalgazette/Article/article.jsp?ar ticleId=7d72a93300301a2&sectionId=60