You could consider building a low volume rectangular shaft below the waterline, with a casing around the leg that slides down inside this shaft and closes the hole when the motor is either up or down. The bottom and top pf the propeller duct would be shaped to fair the aperture, and the sides would be parallel faired plates to support the bottom plate. There should be sufficient tip clearance to minimise vibration induced by the propeller, and the structure should be stiff enough to limit vibration induced fatigue. There might be some friction losses, and the box-duct will provide some protection to the propeller, particularly if an intake grating is part of the structure, but then that is more drag. Some experimental work is expected.
Cheers,
Peter
From: harryproa@yahoogroups.com.au [mailto:harryproa@yahoogroups.com.au]
Sent: 06 June 2015 02:05 AM
To: harryproa@yahoogroups.com.au
Subject: [harryproa] Re:: Re: Retractable motors
Mike, "DEPTH OF WELL
Since the motor isn't going to be steered, I'm not sure the depth of the well is going to be an issue. Fuel and electric lines won't mind going up and down a few feet."
I think I have two primary concerns with putting the engine and prop in a well. The first is water in the well, especially with the engine down. I often see 4 - 5 foot waves along the hull and with an open bottom or a leak I could see that well filling very easily. Even if it didn't flood the engine, the well could easily be carrying a couple of hundred pounds of sea water to slosh around...
The second is the plate attached to the bottom of the prop, normally used to fair the bottom of the boat when the prop isn't deployed. It seems very hard to construct and very draggy and fragile.
If the plate isn't attached to the bottom of the prop and a door or hatch is used to cover the hole instead I am failing to come up with a nice elegant way to do that under a foot or two of water. Then sealing and pumping the water out could be interesting.
There must be a nice elegant solution I am missing.
Talador
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Posted by: "Peter Southwood" <peter.southwood@telkomsa.net>
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