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Re: [PUP] Bulbous bows

BE
brian eiland
Fri, Apr 29, 2005 2:48 AM

Thought some might be interested in what Michael Kasten had to say about Bulb
Bows, http://www.kastenmarine.com/caution_note.htm
In fact he speaks quite a bit about trawler vessels.

"Several well known trawler designers seem to favor bow bulbs on nearly
everything that moves.  In my view, placing bow bulbs on relatively small
vessels cannot be encouraged for any vessel under around 65 feet or so, due to
potentially dangerous handling characteristics in following seas.  This is
particularly so for short and fat boats which will already exhibit excessive
yaw in following seas.  What is favorable in the towing tank is not
necessarily a benefit in the ocean, where wave-size-to-boat-size quickly
becomes an overriding factor.

Bow bulbs may often pandered on the basis of pitch reduction.  The benefits in
this regard are measurable.  It is important to realize though that the
benefit of using a bow bulb simply to attenuate pitch on a well designed hull
form is controversial at best.  For example, we have observed that on smaller
craft a bow bulb can increase the likelihood of slamming in short steep seas
due to its relatively flat bottom shape.  For more information on the possible
hazards of bow bulbs on small craft please see the article on "Running vs.
Heading Up."

Brian Eiland

beiland@usa.net
http://www.RunningTideYachts.com
distinctive multihull expedition yachts

Thought some might be interested in what Michael Kasten had to say about Bulb Bows, <http://www.kastenmarine.com/caution_note.htm> In fact he speaks quite a bit about trawler vessels. "Several well known trawler designers seem to favor bow bulbs on nearly everything that moves. In my view, placing bow bulbs on relatively small vessels cannot be encouraged for any vessel under around 65 feet or so, due to potentially dangerous handling characteristics in following seas. This is particularly so for short and fat boats which will already exhibit excessive yaw in following seas. What is favorable in the towing tank is not necessarily a benefit in the ocean, where wave-size-to-boat-size quickly becomes an overriding factor. Bow bulbs may often pandered on the basis of pitch reduction. The benefits in this regard are measurable. It is important to realize though that the benefit of using a bow bulb simply to attenuate pitch on a well designed hull form is controversial at best. For example, we have observed that on smaller craft a bow bulb can increase the likelihood of slamming in short steep seas due to its relatively flat bottom shape. For more information on the possible hazards of bow bulbs on small craft please see the article on "Running vs. Heading Up." Brian Eiland beiland@usa.net http://www.RunningTideYachts.com distinctive multihull expedition yachts