To determine if the Silver Star Ultra  ( or V60 ) speed controller is suitable for your boat requires knowledge of the motor current at full throttle.
Motor current is determined by :
            MOTOR TYPE / SIZE
            GEAR RATIO
            PROPELLER TYPE / SIZE
            BATTERY VOLTAGE

SEE SUITABLE TYPICAL SET UPS AT BOTTOM OF THIS PAGE
(SCROLL RIGHT DOWN).

MOTORS UTILISED IN SUITABLE SET UP
EXAMPLES ARE SHOWN BELOW
ONE GEARED 3.3 :1 AND ONE DIRECT DRIVE

Motors are Robbe 600/24 geared 3.3 :1  and EF76/2 direct drive.
These are low cost good performance 540 size motors and marked
around 8 volts. nominal.
If your motor is a similar size and weight - e.g. 57 mm long. 38mm dia
body and weight around 200grms. and marked around 8 volts it could
well be a similar motor.  

RECOMMENDATIONS USING ABOVE TYPE MOTORS
FOR A SINGLE SILVER STAR ULTRA OR V60
SPEED CONTROLLER ARE SHOWN BELOW:

SINGLE MOTOR SET UP RECOMMENDATIONS:
DIRECT DRIVE  2 blade 40mm dia. 36mm pitch PROP.12 volt battery.
              For lower power/longer run duration use 6 volt battery.

DIRECT DRIVE  3 blade 50mm dia. 42mm pitch PROP. 6 volt battery.

3.3 :1 Reduction   3 blade 50mm dia  42mm pitch PROP. 12 volt battery.
              For lower power/longer run duration use    6 volt battery.

TWIN MOTOR SET UP RECOMMENDATIONS:
DIRECT DRIVE  3 blade 50mm dia 42mm pitch PROP.
with series wired motors (6 volt to each) using a 12 volt battery.
For longer run duration use smaller propeller.

3.3 :1 Reduction  3 blade 50mm dia 42mm pitch PROP.
with parallel wired motors (12 volt to each) using a 12 volt battery.
For longer duration use 6 volt battery or series wired motors using
a 12 volt battery (6 volts to each motor).