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ashskett 02-13-2012 04:51 PM

Moving 1 Rudder aft...possible?
Hi there, I'm brand new here and have a limited knowledge in boat design so please bear with me!

I have a 47ft Lagoon catamaran, currently in Tahiti, that is just going into a yard-period.

We would like to replace one of our old and corroded Yanmar 3jh3e engines with a new Yanmar 3jh5E engine and KMG65E generator attachment.

The problem we have is space. There is currently almost no extra space in the engine bay to accommodate the generator attachment, which is 105mm in thickness and fits between the engine and sail-drive. So we need to find this 105mm.

There are two options for extending the engine compartment. We could move the aft bulkhead forward, into the master cabin and re-site the saildrive. It would need a lot of fibreglass work to do this and we would loose room in the master cabin, plus there could be a lot of unforseen problems.

I think the better option would be to find out if we could move the rudder aft.

I need to know how much of an effect on the handling moving the starboard rudder 110mm aft would have on the boat. I would have said very little, but being a mono-hull sailor what would I know!



daiquiri 02-13-2012 05:34 PM

From the hydrodynamical point of view, you will extend the rudder force lever arm by some 1-1.5% when sailing on port tack. That is an almost unnoticeable difference, if the blade submerged area remains the same.

Richard Woods 02-13-2012 08:26 PM

Tiller bar??

Height of transom steps?? maybe moving it means distance between top and bottom bearing is shorter, so more stock loads?

Lots of cutting and reinforcing in a very small space, maybe need to cut off the transom step for access?

Richard Woods of Woods Designs

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