Think of waves with a wavelength about 10m beam on. Both hulls sit on a crest then the crest moves under the deck with both hulls in the trough. Any conventional long shaft outboard will go from fully ventilated to motor cowling under water. They are simply not designed for the middle of a boat. The transom on a powered boat usually remains wet and the water parts at the hull line so virtually no variation in water depth at the motor.
I once had a small outboard on a moderate displacement deep keeler. It was fine in calm water but once in waves it could not maintain enough speed to get hull sinkage so the prop would begin to ventilate then the boat gradually comes to a halt with the outboard bobbing up and down creating lots of bubbles. Same things happens with a conventional outboard in the middle of a HP.
I have seen a very deep leg with a small prop off a diesel in the centre of a catamaran but it would be useless for serious powering.
On 04/06/2015, at 3:41 PM, "robriley@rocketmail.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
I was interested in what you were describing the location of the trough, I would have thought a bow wave forward rescinding into a trough that begins to dissipate aft of half way along the hull where the following wave begins to propagate. That might have made the aft beam location a reasonable choice?
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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