We’ve been fascinated by prop shrouds and articulating rudders for years, so when we passed this trawler in dry dock we could not help but take photos.
Lars Bergstrom used articulated rudders on many of his sailing designs to great effect. Rather than being a means of enhancing lift, he used tiny trailing edge flaps with which the skipper controlled the rudder (in the same fashion that airliner rudders are controlled). Whether with auto pilot or tiller, this is the most efficient means of adjusting rudder angle of attack – at some cost in complication.
The rudder above is flapped for a different reason.
This is to increase lift on the rudder and do a better job directing the propeller thrust. These are seen with some frequency on commercial vessels which require good maneuverability.
Of course, if you have the space the simplest answer is a bigger rudder, which in the end, has always been our answer.
The prop shroud is to keep nets clear of entanglement with the propeller. Some vessels which operate in ice have these as well, often with forward struts for additional support and to keep ice from jamming into the prop/shroud interface.
Posted by Steve Dashew (May 17, 2009)
May 17th, 2009 at 2:27 pm
I always thought prop shrouds were to improve the efficiency and effectiveness of the prop, rather like ducted fans on aircraft. Is that not the case?
May 19th, 2009 at 11:18 am
Ducting can help with high load situations, such as towing trawls or in tug operation. But the drag of the shround outweighs the benefits for lightly loaded props.
May 17th, 2009 at 8:57 pm
Steve,
Glad to see your trip is progressing well. Would you or did you consider a prop shroud on the 64? I would love to hear your perspective.
Continued safe voyages
May 17th, 2009 at 3:14 pm
A prop shield (or fence) did not make sense on the FPB64, unless operation in ice was the main goal. The skeg and rudder will give excellent protection from debris and the propulsion efficiency would suffer with the shield. With a metal hull, it would not be hard to retrofit at a later date, if the trade offs made sense
February 25th, 2011 at 2:41 pm
hi,
Here in Norway we call these rudders “Becker” rudders – most of the newer costal steamers have them, and the can go sidways by operating rudders and engines indepenantly. http://www.becker-marine-systems.com/
johan