Performance indicators

[adapted from Torqeedo website]

Meaningful performance indicators

Torqeedo provides meaningful performance indicators for boat drives. Basically, the power of a drive is measured according to how much propulsion it actually delivers for moving the boat. This power is referred to as the output or propulsive power. It is calculated by the power times the speed and can be expressed in watts or horsepower.

Although the propulsive power forms an extremely informative index for boat drives, most manufacturers don’t provide it.
Suppliers of electric motors generally use the input power of their motors as the power rating. However, only a fraction of this value is actually available to the boat drive as propulsive power. The rest is lost – for example in the motor or propeller – as inefficiency. Manufacturers of combustion engines, on the other hand, usually give the power at the motor shaft as their index. Also here, only a fraction of this value is available as propulsive power:

Propellers on combustion engines of a lower power class cause some 70% of the motor shaft power to be lost as inefficiency that cannot be converted to propulsion.

The second important index is the overall efficiency. It describes the efficiency with which the drive system converts the available energy sources into output power and is calculated by dividing the propulsive power by the input power.

Torqeedo builds the most efficient outboards on the market by far, by means of consistent orientation towards propulsive power and overall efficiency. As the overall efficiency of a drive system is given by the product of the partial efficiency levels of all components, a single poor partial-efficiency level can have a significant negative influence on overall efficiency. For this reason, Torqeedo takes great care in the comprehensive optimization and interaction of all components.

Another commonly used motor index is the static thrust expressed in pound force (lbf) or Newton (N). In comparison to the propulsive power and overall efficiency, this index is less meaningful, as it only measures propulsion in association with the static bollard pull experiment. In this case, as the speed is zero, the effective power (power times speed) is also zero. As a consequence to this, the static thrust does not provide any information on the propulsive power that can be actually achieved and is therefore not a meaningful index when taken in isolation. It merely serves as an indication for the maximum boat size that the motor can be used on. Before purchasing a motor, it is recommendable to test the static thrust specifications
personally. In Torqeedo’s tests of competitor products, the manufacturers’ specified static thrust values could generally not be reproduced.

Manufacturers‘ specifications and test results of electric boat motors

Product	Maximum input power in operation (electromotors) in watts	Maximum motor shaft power (combustion engines) in watts	Maximum propulsive power in watts	Maximum overall efficiency of electric motors in percent	Maximum propeller efficiency of internal combustion engines in percent	Static thrust in pound force	Comments
Torqeedo Travel 401	400		175	44 %		40
Torqeedo Travel 801	800		350	44 %		68
Torqeedo Cruise 2.0	2000		900	45 %		121
Competitor 300W & 12V	300		60	20 %		20
Competitor 500W & 12V	500		100	20 %		35	Manufacturer’s specifications of static thrust: 55 lbf
Competitor 1000W & 24V	1000		190	19 %		55	Manufacturer’s specifications of static thrust: 80 lbf
Competitor 2200W & 36V	1800		600	33 %		88
Competitor 2.3PS / 4-Takt		1690	380		22 %	55
Competitor 4PS / 2-Takt		2940	700		24 %	71
Competitor 6PS / 4-Takt		4410	1200		27 %	112

A big test for small motors: Accredited test laboratory Potsdam Model Basin (SVA Potsdam) confirms unique efficiency of Torqeedo outboards.