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Old 10-30-2015, 03:12 PM   #1
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Single Screw Twin Rudders

I recently read about a 75' Northern Marine with a single screw with twin rudders. In the blog post the owner stated that after he purchased the boat he noticed the rudder activity just wasn't right. He did some research and consulted with some naval architects and they recommended twin rudders on the single screw. After this modification the owner now states his vessel tracks like a slot car.

I did some googling and found a lot of information about large ships with single screws and twin rudders but I didn't really find anything substantial about this set up for smaller recreational vessels. That said, does anyone have experience with this type of set up on a recreational boat or know of a source for solid information on this topic?

Note: Not looking for personal opinions, unless of course you have first hand experience. What I'm looking for is researched evidence from professionals, good or bad, about twin rudders on a single screw recreational vessel, specifically a full displacement "trawler" type vessel.



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Old 10-30-2015, 03:28 PM   #2
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for me I count on the thrust against the rudder for maneuvers. Be that single shafts, or twin shafts. Even if they sport large rudder or rudders. Never had alot of control in reverse with rudders only at slow.

I would then believe twin rudder set up on a single have a continuous duty thruster or thrusters. Stern and or bow

But my experience is limited.

So just random thoughts

YMMV
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Old 10-30-2015, 03:42 PM   #3
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"researched evidence from professionals" on any subject concerning recreational vessels is virtually non-existent. But there's plenty of sales hype available.
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Old 10-30-2015, 05:13 PM   #4
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Quote:
Originally Posted by Tad Roberts View Post
"researched evidence from professionals" on any subject concerning recreational vessels is virtually non-existent. But there's plenty of sales hype available.
Sad, but oh so true!
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Old 10-30-2015, 06:32 PM   #5
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No experience with twin rudders and a single other than sailboats but downwind steering is enhanced greatly under sail. Our power boat has twin rudders as well as twin engines but that's a different kettle of fish.


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Old 10-30-2015, 06:58 PM   #6
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I'm fond of the twin rudders/single screw.

The prop wash is cone shaped therefor getting smaller than the dia of the prop a foot or two aft of same. So I'm thinking the drag of the propwash over the rudder can be dramatically reduced w twin rudders carefully placed. Also I suspect that the propwash/ rudder response will suffer little especially if the rudders were made a few inches longer. May reduce propwalk too.
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Old 10-30-2015, 07:32 PM   #7
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I suppose having less length with dual rudders versus a single rudder would have advantage when there's insufficient room for a single "barn door" rudder (but with extra expense.)
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