Re: [PSUBS-MAILIST] My PSUB Explorer

["Walter Starck" <wstarck@ozemail.com.au>]

Propeller diameter/pitch, motor speed/reduction gear ratio and vessel
speed are inter-related. Generally smaller diameter and greater pitch
are employed with higher speed vessels and larger diameter/less pitch
are used for slower/heavier craft. Likewise, reduction gears and 3 or
four bladed props may also be used for greater thrust with larger
heavier craft.

Some motor manufactures offer different pitch/diam props for different
size vessels.  Subs are heavier and have greater drag than the small
boats typically used with electric motors so what you are looking for
will probably be a propeller of larger diameter and less pitch than the
standard one.  If one isn't available for the motor you have it may be
possible to
adapt one made for another motor.  Props used for diver propulsion units
are another possibility.

It is fairly easy to push a sub up to 2-3 knots.  Above three knots the
power required begins to increase dramatically and no matter how
streamlined the sub and efficient the propeller a big increase in power
is required.  If you want to see how much, try towing the sub at
different speeds using a spring scale or even hand holding the tow rope.
Up to 2-3 knots you can hold it with one hand.  At 5-6 knots it will
pull you out of the boat if you try to hand hold it.

The bottom line is no matter what you do the increase in speed will be
small unless you dramatically increase power.

Walter Starck
Golden Dolphin Video CD Magazine
The premiere publication of diving and the ocean world.
www.goldendolphin.com