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On rudders.....
It seems to me that using only side thrusters to steer would work of
course, but as Vance described, there are limitations to the effectiveness under
some scenarios. For sure it would work OK on a tiny sub but maybe less so
on a larger one like a K boat.
To steer a straight course using only side thrusters there would need to be
constant adjustment of the motor speeds which would possibly use more electrical
power.
With a rudder, small adjustments to the rudder position could be made while
using a steady speed on the thrusters. Any forward movement would make the
rudders act as "control surfaces".
On Git Kraken I opted for a combination of these. I have the two rotating
side thrusters mounted midship for use as depth control and fine maneuvering "on
location". Up, down, left, right. forward, back.
The stern thrusters ( 2 ) are mounted into prop rings with "rudder vanes"
and my hope is that a "vectored thrust" effect will be achieved. With 120
degrees of angle and both props turning in unison the vectoring effect should
push the ass end around for a relatively tight turning radius.
The "rudder vanes" are large enough that even without the rear props
spinning they should act as rudder control surfaces as long as
some forward movement is made. The main benefit is that the rudder
angle is changed with just a small "bump" of the rudder actuator which uses very
little electric power.
As a quick "burst" all 4 motors can be activated. In theory that should
give 404 pounds of thrust. With the two rear thrusters at full speed it's 202
pounds pushing the stern side ways. Each thruster can be activated alone so any
amount of thrust can be applied up to the maximum.
Each motor circuit is completely separate from the others including
dedicated individual battery banks, speed/direction controllers, thru-hulls and
motor.
One problem I'm expecting is that both props in the rear turn in the same
direction. If this turns out to be a problem as I suspect it will, I'll need to
get a left handed prop to fit one of the motors. My hope is that the vanes in
the prop rings will reduce the problem to a minimum but only testing will
confirm what's needed here.
On oil compensating......I think having each motor compensated
separately would be safer. No chance a leak in one would foul the others. A
common "bellows" could still be used if the plumbing connecting it all together
had some sort of "trap" in each line so water couldn't get to an adjacent
motor.
The "air cushion" from a truck looks promising as a bellows. I know they
can take some abuse without failing.
Frank D.
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