1. POTENTIAL ELECTROCUTION

2. POTENTIAL FIRE

3. LOW RELIABILITY

4. EXTREMELY SHORT DURATION OF OPERATION BY DESIGN

1. ELECTRIC MOTOR CURRENT SPECS. - 12VDC OR 24VDC.

    A. 5 HP @ 12VDC = 400 AMPS DC CURRENT/ 10 HP @ 12VDC = 800 AMPS DC CURRENT

    B. 5 HP @ 24VDC = 200 AMPS DC CURRENT/ 10 HP @ 24VDC = 400 AMPS DC CURRENT

2. EXCESSIVE HIGH CURRENT MAKES MASSIVE BATTERY BANKS NEXT TO THE TUNNEL NECESSARY FOR PROPER OPERATION OF AN ELECTRIC DRIVE SYSTEM TO SUPPLY ONE MINUTE OF POWER.

    A. VERY FEW ELECTRIC MOTORS CAN OPERATE AT THE ABOVE CURRENT LOADS FOR MORE THAN ONE MINUTE WITHOUT OVERHEATING AND SHUTTING DOWN VIA CIRCUIT BREAKER. DURING THIS PERIOD OF OPERATION THE HEAT BUILDUP IN THE MOTOR, AND REDUCED CURRENT FROM THE BATTERY BANKS WILL CAUSE A CONTINUOUS RPM SLOWDOWN, UNTIL THE PROPS CEASE TO ROTATE. THE LARGER THE BATTERIES, THE LONGER THE MOTOR WILL OPERATE AT EFFECTIVE RPM UNTIL OVERHEATING OCCURS.

B. THE WEIGHT OF THESE BATTERIES CAN BE IN THE NEIGHBORHOOD OF 300-500 POUNDS. LOCATED IN THE WORST SPOT, FAR FORWARD WHICH INCREASES THE TENDENCY FOR EXCESSIVE PITCHING WHILE UNDERWAY AND PUTS THEM IN THE PART OF THE BOAT THAT IS MOST VIOLENTLY POUNDED. NOT NORMALLY RECOMMENDED FOR ELECTRICAL COMPONENTS.

C. THE BATTERIES NEED LARGE DIAMETER ELECTRIC CABLES TO CONNECT TO THE MOTOR TO REDUCE EXCESSIVE VOLTAGE DROPS. THE CONNECTIONS AT THESE CABLES AS WELL AS THE CONTROL CABLE CONNECTIONS CARRY ENORMOUS CURRENT, WHICH CAN CAUSE FIRE OR WORSE ELECTROCUTION. ANY ACCIDENTAL CONTACT COULD PRODUCE LETHAL RESULTS. CLEARLY THE INTEGRITY OF THESE CONNECTIONS HAVE TO BE FLAWLESS, AND MAINTAINED IN THIS CONDITION, TO PREVENT A DISASTER.

D. SUSCEPTIBILITY OF ELECTRIC MOTORS TO THE MARINE ENVIRONMENT IS WELL DOCUMENTED. INSTALLING A REPLACEMENT MEANS YOU WILL HAVE TO DEAL WITH THE CRITICAL (SENSITIVE) HIGH CURRENT CONNECTIONS. A JOB FOR A COMPETENT BOATYARD ONLY.

E. BATTERY CHARGING BECOMES A MAJOR ISSUE THAT CAN NO LONGER BE DONE WITH STANDARD ENGINE DRIVEN ALTERNATORS. HIGH CURRENT ALTERNATORS ARE NEEDED IN ADDITION TO THE NORMAL ALTERNATOR CHARGING THE ENGINE STARTING AND HOUSE BATTERIES. THIS REQUIRES A DIFFICULT ENGINE MOUNTING EFFORT SIMILAR TO MOUNTING A HYDRAULIC PUMP TO THE ENGINE. HEAVY CABLES NEED TO BE RUN FORWARD TO CHARGE THE THRUSTER BATTERY BANK (SIMILAR TO RUNNING HYDRAULIC HOSE).

1. DURATION OF OPERATION CANNOT BE UNDERESTIMATED. AN EXPERT HELMSMAN CAN DOCK HIS BOAT EFFICIENTLY ENOUGH TO ONLY NEED HIS THRUSTER FOR ONE MINUTE. ARE YOU THAT GOOD? IF YOU RUN OUT OF POWER BEFORE YOUR DOCKING IS COMPLETE... WELL, YOU MIGHT WANT TO CHECK ON YOUR INSURANCE COVERAGE AND DEDUCTIBLE.
KEEP IN MIND THAT AT THE BEGINNING OF THE MINUTE YOU HAVE FULL THRUST AVAILABLE, AND AT THE END OF THE MINUTE YOU HAVE ZERO THRUST AVAILABLE. THE THRUST RAMP DOWN CURVE COULD BE AN ISSUE YOU MAY WISH TO INVESTIGATE, IF YOU CHOOSE A DC SYSTEM.

2. SYSTEM CAPACITY OR THRUST CAPACITY IS A THORNY ISSUE THAT MOST MANUFACTURERS CHOOSE TO DEAL WITH ON A THEORETICAL LEVEL.

AN ENGINEER IS HIRED TO MAKE CALCULATIONS BASED ON THE SCIENCE OF PHYSICS, WHICH PREDICTS THRUST. THESE PREDICTIONS ARE PUBLISHED WITH ACCOMPANYING RECOMMENDATIONS AS TO WHICH MODEL IS SUITABLE FOR YOUR BOAT. IN OUR OPINION, THIS IS AN INADEQUATE AND MISLEADING METHOD OF PREDICTION. THE ONLY RELIABLE WAY TO PREDICT THRUST, IS TO HIRE AN INDEPENDENT TESTING LABORATORY TO TEST EACH MANUFACTURERS' SYSTEM AND DOCUMENT THE THRUST PRODUCED FOR A GIVEN LEVEL OF HORSEPOWER OR KW. I HAVE NOT SEEN THIS IN OUR INDUSTRY TO DATE. FOR THIS REASON, SHIPWRIGHTS DOES NOT PUBLISH THRUST FIGURES, WHICH ARE OBTAINED IN OUR LABORATORY IN A TEST TANK ON AN ONGOING BASIS. WE USE THIS INFORMATION FOR CONTINUOUS DESIGN REFINEMENT.

DESPITE THE ABOVE AND CERTAIN CLAIMS MADE BY MANUFACTURERS, WE BELIEVE THAT THE AVERAGE THRUST PRODUCED OVER A ONE MINUTE PERIOD BY A DC ELECTRIC SYSTEM IS CONSIDERABLY LESS THAN A HYDRAULIC DRIVE SYSTEM WOULD PRODUCE ON THE SAME THRUSTER FOR ONE MINUTE.

3. HOW MUCH THRUST IS ENOUGH FOR YOUR BOAT?

A. BEWARE OF CLAIMS MADE BY SALES PEOPLE THAT 5 OR 10 HP IS ENOUGH FOR YOUR BOAT SIZE, IF YOU WANT TO BE SAFE RATHER THAN SORRY. MAXIMUM HP AVAILABLE IN A DC DRIVE SYSTEM IS 10. THRUSTERS ARE NORMALLY SELECTED FOR THE MOST DIFFICULT CONDITIONS YOU EXPECT TO MEET.

B. WE BELIEVE THAT AS A RULE OF THUMB, A 5HP HYDRAULIC SYSTEM WILL PROVIDE SAFER MANEUVERING THAN A 10 HP DC ELECTRIC SYSTEM. BASICALLY, THE COMPARISON IS AS FOLLOWS: A 10 HP ELECTRIC SYSTEM OPERATING FOR ONE MINUTE AT AN AVERAGE OF 5 HP. A HYDRAULIC SYSTEM OPERATING FOR 15 MINUTES AT 5 HP CONTINUOUS. WHICH IS MORE APPEALING TO YOU?

4. COST COMPARISONS: WE BELIEVE THAT ANY $ SAVINGS ENJOYED BY BUYING AN ELECTRIC DRIVE SYSTEM PALE IN COMPARISON TO THE INHERENT ADVANTAGES OF A HYDRAULIC SYSTEM.

    A. ALWAYS COMPARE THE COST OF AN INSTALLED SYSTEM, IN ADDITION TO COMPONENTS. MAKE SURE THE YARD HAS EXPERIENCE IN BOTH HYDRAULIC AND DC INSTALLATIONS FOR A FAIR COMPARISON.

    B. IT IS OUR EXPERIENCE THAT A HYDRAULIC DRIVE SYSTEM IN THE 5-15 HP RANGE WILL COST 10% MORE THAN A DC DRIVE SYSTEM OF 5-10 HP.

    C. IT IS IMPORTANT TO EVALUATE THE THRUSTER COMPONENT IN THE COST EQUATION. ALL THRUSTERS ARE NOT EQUAL. IN PARTICULAR, UNITS THAT FIT PLASTIC PROPS INSTEAD OF BRONZE OR STAINLESS DO NOT ENJOY OUR ADMIRATION. WE FEEL PLASTIC PROPS ARE USED AS A DESIGNED IN WEAK POINT TO SAVE DAMAGE TO THE GEARBOX.