Saildrive and two rudders: How do they handle?

[Dr. D]

A number of boats I have looked at recently have saildrive and two rudders. With the propeller relatively forward under the hull and the neither rudder in line with the propeller, I got wondering about low speed handling. When docking our boat (standard drive and single rudder) I make use of prop walk and prop wash. With their effect available with saildrive and two rudders, how do these boats handle at low speed?

[boatman61]

Not well.. delivered an Oceanis 331 with that set up.
Strong cross winds.. no chance..
Under 10kts her bow thruster was indispensable.
In the Portsmouth marina I started from we had to warp her across to the fuel dock from her berth.. it was windy.

[belizesailor]

Delivered a Jeanneau SunOddesey 30i years ago. Twin rudder version. You do lose the ability to effectively direct prop wash. However, this was a nice little boat, which sailed very well.

[Dr. D]

The handling of this boat is fine! Different procedures without prop walk and prop wash, but the new ones are effective. I am pleased.

[Snore]

Having run several twin rudder boats I agree with all the posts.

But reemphasize the bow thruster. Between the undercut forefoot on modern boats AND the inability to vector prop wash- the thruster is really critical.

[MartinR]

You just have to do manoeuvres with a fair amount of speed. If anything goes wrong....... .

Imho twin rudders with central sail drive is poor engineering. But all boats are compromises.
Bow thruster solves the problem, more or less. But then you loose some speed sailing. Compromises.

[TJ D]

At sea? Just great!


In the marina-not good. At all.



Rocket Science probably represents nearly the worst case scenario for close maneuvering-super light, very little keel cross section, and rudders way away from the prop, 10' apart at the tips. We also have no thruster.



All that said, I've learned to handle her just fine. We painted the hull 4 years ago, and are only sporting a couple of small scratches from rubbing on docks, after lots of cruising.


Martin has it about right-it's about confidence with carrying speed. If we're not moving a few knots either ahead or astern, we have zero control. That takes a lot of getting used to.



Probably the only thing that's really saved us is that bigger slips usually have generous approaches.

[Dr. D]

I am of a different mind on this topic, as noted above. (My wife says I have a different mind period.)

To achieve rudder control the boat needs to be moving, but only a hair over 1 kt and I have control. During the lesson yesterday I was tuned into boat speed and maneuverability and 1 kt is the threshold.

The boat will spin around. The radius is larger than with a standard set up using prop wash and prop walk, but not that much more.

Leaving a dock requires different techniques due to no prop walk/wash, but not that much harder.

For those who say a 34’ long boat of the sail drive with twin rudders configuration needs a bow thruster, what is the lower limit? Does a 30’ boat need one? A 28’ boat? A 25’ boat?

On the other side of the coin, a boat with a flat bottom may get the bow blown off easier by the wind, but that means it needs less counter force to overcome the wind.