Solomon Technologies

Advantages

Prop Size Matters
To make full use of our motors’ powerful torque and regeneration ability, we recommend a large-diameter, high-pitch, three-bladed, fixed propeller. The bigger the prop and the steeper its pitch, the more water it pushes when motoring, and the more power it produces when spinning under sail and turning the motor/generator to generate electricity. Our Cherubini 44 installation carries a 20 inch diameter 16 pitch prop. Our Saga 43 installation has an 18x18 prop, as does our recent 51’ Gold Coast cat installation. Our 35’ Tektron cat installation sports an even more aggressive 16x20 prop. (See Selected STI Motor Replacements.)

Two ways to go – feathering or fixed.
If you race, you are a candidate for a feathering prop. You can’t race with your motor on, so you can’t afford the drag created by running without the motor turning your fixed prop. Does that mean you can’t buy STI electric drive? Not at all. Simply use the same solution available to a racing sailor with a diesel auxiliary: a feathering prop. It works fine with STI drive and can still regenerate electricity under sail. (See Regenerative Motor Sailing.) Note, however, that the blades must feather and be able to lock in the open position. A folding prop, whose blades typically will not lock open, cannot be used for regeneration. The force of the water from sailing folds the blades back instead of turning them.

The blades of a feathering prop, however, can be opened in reverse orientation by running the motor briefly backwards until the prop blades lock open. The prop and motor then freewheel and regenerate just as well as they do turning forward. Water pushing against the blades holds them open. To start motoring again, the motor control lever is switched to forward. The blades flip back to normal orientation and push the boat ahead. To sail without regenerating or any motor use, the racing helmsman places the motor in neutral. The blades feather as they are designed to do, with their orientation parallel to the water flow.

A feathering prop isn’t as efficient as a fixed prop for either motoring or regeneration. But if your overriding goal is maximum speed under sail and racing competition, feathering props are the ideal solution. You’ve still got all the other advantages of STI electric drive: quiet, fume-free, fuel-efficient motoring, instant-on power, immediate full-speed reverse, fingertip control, near-zero maintenance and an abundance of electricity for your house power needs.

Cruising sailors also want to sail as fast as possible. But most of them also want electricity-hungry creature comforts, along with a powerful, dependable auxiliary propulsion source. Until Solomon Technologies came along, their only power choice was the “demon below,” a noisy, dirty diesel (and occasionally gasoline) engine -- and often a separate and usually noisy generator as well.

Hybrid-electric STI drive has exorcised that demon. Motoring can now be clean and quiet. Regeneration recharges batteries under sail. And the water-cooled generator is always available for quiet backup to keep auxiliary systems powered.

As for motoring power, there is no comparison. Large-diameter props turned by STI advanced, compact lightweight motors provide far more propulsive power than the undersized props required by bigger internal combustion engines. A 20-40 hp diesel auxiliary simply doesn’t have enough low-speed torque for the kind of prop that our 6, 10 and 12 hp STI electric motors can turn. The same prop on a diesel would simply cause it to stall out at low speed. STI motors have near-maximum torque at low rpm and can turn as big a prop at one rpm as they can at 1100 rpm. So we size our props aggressively to use this torque to its fullest. Drag is minimized by keeping the motor on and the prop turning. And that brings us back to regenerative motor sailing.