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Hi, Peter . . .
Thanks for the input on switches. On-off,
on-off, on-off - I can handle that! Not much circuitry
involved.
Regarding holding depth: you are correct in your
assumption. Using a VBT (hard tank) assumes theoretical neutral buoyancy.
Stating the obvious, thermal currents, obstructions diverting currents, salinity
changes, thermal contraction of the sub itself (changing internal volume), etc.
all have an effect on the boat's so called neutral buoyancy.
Which makes it clear that there really is no such
thing as neutral. Building with thrusters allows you to literally flip a
switch when you need stability. Using a speed control allows fine tuning
of your trim - nice to have. Something like a trim tab on a plane.
But, vigilance is always needed; a little less if you've automated the
process. But, the label says not to operate heavy machinery when . .
.
Needless to say, get as close to neutral prior to
using the thrusters.
All of the above having been said, if the boat will
be used in stable water or hi vis situations where you have external visual
references (or you don't mind keeping your eyeballs glued to the depth gauge),
VBT's may be fine. But, you still may want to install the thrusters anyway
for more convenient control.
Regarding rolling your sub, how much of a moment
arm is there? Simple terms: if your centre of gravity (keel ballast) is
far below your centre of buoyancy, the roll should be minimal - but probably
noticable. How far outboard will the MinnKota be installed? That
increases the leverage on the boat, as well.
Also, be prepared for some sideways movement due to
the roll. Thrust forces will be vectored to the side somewhat and the sub
will sidle a little.
If you keep the thruster well inboard, roll will be
minimized, and, hence, so will sidle.
Rick Lucertini
Vancouver, Canada
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