Electric Propulsion

Powering your boat with an electric drive has never been easier. There are 6 different configurations available: open frame drives, sealed drives, water cooled drives, direct drives, serial hybrid drives, and electric outboards. Over 20 different electric drive packages insure there is one that is perfect for your sailboat. All of the drive packages work well with Polar Power's DC genset.

The Gearboxes have an integral thrust bearing. The gearboxes also increase the height of the motor above the bilge for additional safety.

We strive to optimize efficiency and durability to give you longer ranges and high dependability.

1) Required Thrust is determined by the characteristics of the boat. The major characteristics are length, weight, beam, windage, underwater profile, underwater obstacles (ie: through hulls, depth sounder transducers)

If your boat was previously powered by a diesel or gas motor, please send the following information to the email address at the bottom of this page for a system quote:

---existing diesel motor make, model and h.p., reduction gear ratio, rpm of motor at desired cruising speed, and propellor pitch and diameter---

2) Power : Power is measured in kilowatts consumed. Power (KW) = Voltage (Volts) multiplied by Current (Amps)

3) Voltage: Higher voltage systems are more efficient than lower voltage systems. However higher voltage systems require additional safeguards to protect the occupants and are more expensive. The general rule of thumb is to only use the voltage that you require and no more.

Battery packs are no greater than 48 volts, or 4 batteries in a string with a resettable circuit breaker in the positive lead and a battery switch in the negative lead. Higher voltage systems are configured with a central high voltage bus located near the controller. For instance a 72 volt system is configured as two 36 volt battery banks coming to a central 72 volt bus. A 144 volt system would be 3 48 volt battery banks coming together at a central 144 volt bus. This architecture limits the exposure to higher voltage on a boat to just the central bus area. All high voltage wires are limited in length and require additional protective sheathing.

48 volt systems are easy to work with because of the plentitude of 48 volt equipment available like inverter chargers, solar chargers, battery chargers and DC to DC converters.

72 Volt equipment is not as commonplace and is more expensive. 72 volt inverters, chargers, solar chargers, and DC to DC converters are available but we have yet to source a true sine wave 72 volt inverter/charger.

4) Current: Lower current systems are more efficient than high current systems. Additionally current is limited by the size and length of the battery cables. Current should not exceed 100 amps inside an engine space for a 2/0 cable on systems higher than 48 volts.

3) Efficiency: Power mulitiplied by each different efficiency determines net power which determines thrust.

d) Thrust Bearing Efficiency: All rotational energy is converted to thrust by the propellor which must be applied to the boat for propulsion. A properly sized thrust bearing is important for optimum efficiency. Thrust bearing should neither be too large or too small for any application.

e) Efficiency of Propellor location: Propellors located in an aperture are less efficient than propellors located in clear water. Propellors are more efficient the closer their shafts are parallel to the hull surface, and the closer the hull surface is parallel to the water level.

f) Propellor efficiency: propellor efficiency changes with rpm. The propellor size determines the gear ratio.

95% motor efficiency x 95% controller efficiency x 95% gearbox efficiency x 60% propellor efficiency = 51.44% overall efficiency.

If a system consumes 7 KW and is 51% efficient, then net power of that system would be 3.6 KW.

Electric boats are capable of sailing in more wind conditions with more power and better handling than their diesel counterparts.

An electric drive turns a propellor shaft from 0 rpm all the way up to full boat speed where a diesel turns the propellor from 300 rpm up to boat speed. Electric drives are optimized for lower power and diesel drives are optimized for higher power. This fact has a profound affect on boat handling. My most recent island trip on Kapowai produced some interesting results. A very small amount of energy in these lower power settings has tremendous affects. The propellor becomes invisible at 100 watts. This adds 1 knot of boat speed in all conditions for very little power. This zero thrust setting is capable of being easily generated by a solar panel.

In the case of very light wind conditions, the first knot of boat speed takes very little power to create. Three or four hundred watts is capable of pushing her at 2 to 3 knots, enough to create wind. Usually there is some wind, 1 knot in some direction. Couple that with 2 or 3 knots of boat speed and the sails stop luffing and boat moves along quite nicely under her new "apparant' wind. Kapowai can motor sail in almost no wind for less than 400 watts.

Even the smallest amount of boat speed, 2 - 3 knots, is capable of providing directional control against swells.

An electric drive can regenerate from the propellor turning. The regenerated power in high wind conditions can be used in low wind conditions. Therefore you have more than a days "energy buffer". Slowing the boat through regeneration acts like a variable drogue, pulling on the boat to help handling conditions in very rough weather and further adding to precise handling control of the boat.

An electric boat is capable of power tacking on demand to avoid completely or remedy being stuck in irons. An electric boat is capable of motoring on demand into the wind to change sails.

The only limitation that an electric boat has over a diesel boat is immediate range. Long range is better for an electric boat because the boat regenerates as it sails and never runs out of energy. If immediate range is necessary, then a diesel or natural gas generator can be fitted into the system, which is definitely the ultimate power package for a sailboat.