On Thursday, March 27, 2014 4:20:46 AM UTC-7, Bruce in Bangkok wrote:
That is a cover for the raw water intake for your engine. It goes on
the bottom of the boat covering the water inlet.
See
http://www.westmarine.com/metal-plum...-hull--6606842
for a similar device which includes the thru hull fitting, that will
give you an idea of how it is used.

Thanks for the explanation and link, ... Peter E.