Friday, July 31, 2009

[Electric Boats] Static Thrust was Re: Trolling Motors

 


dennis wolfe <dwolfe@dropsheet.com> wrote:
(snip)

> Its static thrust (bollard pull) is not relevant to how fast it will push the
> boat. Thrust is a stupid way of comparing motors as the boats are not used
> tied to a stationary dock.

Denny:

I'd like to explore this a bit, as, on the contrary, I consider static
thrust a very relevant selection criterion (which, unfortunately, is never
published by outboard manufacturers). I have two Yamaha 9.9HiThrust gas
outboard motors on my 36' sailing catamaran which have served me wonderfully
for seven years of cruising (each has about 2600hours on it). My top speed
with both engines wide-open is 7.8kts, which, quite frankly, I only did once
"just to see what she would do". My normal cruising speed is just below
5kts.

My criteria is indeed static thrust because over the years I have faced
situations whereby I had to maneuver the boat in confined spaces into some
very strong winds whereby the boat is barely moving with the engines wide
open as you head into and try to turn across the wind. This to me is a most
important selection criteria as, in my example, an equivalent 9.9hp motor
with high-speed prop and gearing fails miserably in this situation.

Staying on topic of electric boats, I am exploring adding an electric drive
(outboard?) as a tertiary drive system since I have excess solar and battery
capacity. I've been comparing static thrusts for the above reason.

Perhaps you would care to elaborate as to why I'm looking at the wrong
specs?

JoeS.

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