On Fri, 29 Oct 2004 08:44:03 -0400, nafod40
wrote:

My semi-informed opinion is...not much. Water is incompressible, so the
pressure change across the tunnel opening will not be a factor. Here's a
good site on bow thrusters.

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Absolutely incorrect. The aperature represents a discontinuity in the
hull form and will create a great deal of turbulence which translates
to drag.