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Old 28-06-2006, 03:21   #1
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Props aft of the rudder

Over the months I have noticed a few folks with concerns about boats with the props aft of the rudders. I have since sailed on two such boats, a Lagoon 380 and a Lagoon 470. I have to admit it looks kind of freaky when you swim under the boat, but I can't truly say that I noticed any severe issues. Both boats are harder to tack than some other cats I've sailed, but I'm hesitant to lay this at the feet of the prop/rudder configuration.

Objectively I would expect the prop handling in tight spaces to be better because the props are way aft, and perhaps you'd lose a little effectiveness with the rudder when you have steerageway on because the rudders are a bit forward.

With this setup prop wash works under aft propulsion not forward, but these not being monohulls, you don't really rely on wash because you have two screws to work with.

What the setup does do is put the diesel so far aft that both boats have engine rooms sealed off from the interior (no diesel under your bed) and with great 360 access to the motor.

Curious as to what others think about this setup.
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Old 28-06-2006, 04:35   #2
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When reversing into stern-to moorings in the Med, I would be nervous. The bottom often shelves very steeply, and I would rather touch with the rudder than the prop....

Also, while it is true you use the engines to 'spin' the boat while manouvering in close quarters, the rudder, being in the prop-wash, can impart side-thrust as well, which can be useful.

Having engine access outside has pros and cons too - balancing on the transom to do engine work when at sea, or in bad weather is not too attractive, and can be expensive in tools/screws. (plink-plink-plop).

Incidently, while the larger Lagoons seem to go OK, I have seen several bad reports of the 380's sailing capabilities - any thoughts?
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Old 29-06-2006, 01:21   #3
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Backing your prop into a hunk of concrete would be fairly objectionable.

As far as the engine access goes, on the 470 you'd just climb in and shut the lid. That way things go plink, plink, plink. The one I was on had plenty of room and a nice fluorescent light. Can't remember if the 380 was of a similar size but I do remember climbing in there too. I understand the heavy seas point but don't know if I want to be in the aft cabin tearing the mattresses out under those conditions any more than climbing in from the transom.

I thought the 380 sailed fine. Fine is not my highest rating. Fair trade for the interior volume if you're cruising though.
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Old 02-07-2006, 06:07   #4
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The only thing i would suggest is to lock the rudder when going backwards, so that the rudders are not brutally tilted and the dis-align (is that the right word for getting out of "parallel" ??)
In total i found the sailing "OK" so far. Of course it is not a racer, but in general it is OK. I would not say that it is faster than a monohull, but it is also not slower with a lot of space.
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Old 02-07-2006, 09:57   #5
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Mis-align.
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Old 04-07-2006, 02:23   #6
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Most catamaran steering systems are not designed on a parrallel basis, but on the same basis as a car (i.e. ackerman steering) where when turning to port you need the stbd rudder to have a steeper angle than the port rudder.

This helps to reduce the amount of skidding and tighten the turning circle.
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