Every bow and stern thruster gets a score from 0 to 100% built from four factors, which maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating. Thrusters are grouped by rated thrust (under 45 kgf, 45 to 75 kgf, over 75 kgf) and use the same scale in every group.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per kgf of thrust | 40% |
| Efficiency | thrust per kW of motor power | 25% |
| Run time | longest continuous run the maker allows | 25% |
| Weight | thrust per kg of unit weight | 10% |
Where the numbers come from
Thrust, motor power, voltage, tunnel size, weight and run time come from the maker’s product page or manual: Sleipner’s product pages, Vetus’s webshop pages and spare parts guide, Lewmar’s installation manuals and Quick’s user manual. Prices are checked at Amazon. Anything a maker doesn’t publish is left blank. Vetus’s own table prints a 35 kg weight for the 45 kgf unit that looks wrong next to its other models, so that one is left blank.
Thrust is the maker’s headline rating. Makers rate at different voltages: Sleipner’s headline figure is the thrust at 10.5 V, the level a 12 V system sags to under load, and it also gives a higher figure at the full supply voltage. The rankings use the headline figure for every maker, and the product page shows the full-voltage figure where one is published. Only that rating is used, so a maker that rates at a more generous voltage gets a small edge that we can’t remove.
The factors
Value is the current price divided by the rated thrust in kgf, on a log scale, so halving the price per kgf always counts the same. $110 per kgf scores zero and $25 per kgf full marks.
Efficiency is rated thrust divided by motor power in kW: 14 kgf per kW scores zero and 21 kgf per kW full marks. It shows how much of the motor’s power becomes thrust, and so how hard the thruster works the battery bank for the same push.
Run time is the longest continuous run the maker allows: 2 minutes scores zero and 5 minutes full marks. Sleipner states a 2 to 3 minute duty cycle (4 minutes for the SX35), Vetus 2 to 5 minutes by model, and Lewmar powers its controls down after 3 minutes of continuous use. The top of a stated range is used.
Weight is rated thrust per kg of unit weight: 2 kgf per kg scores zero and 5 kgf per kg full marks. Weight is the maker’s net weight and leaves out the tunnel; the Vetus 45 kgf is left blank because its printed weight looks wrong.
What isn’t scored
Boat length ranges, tunnel diameter, number of propellers, bow or stern use and current draw are listed but not scored. A maker’s boat length range depends on the boat’s weight, windage and hull shape, so it is a starting point, not a rating. Control panels, which the makers sell separately, are not part of the price. Warranty terms are not shown: none of these makers publishes one on the product pages we use.
Missing data
If a figure isn’t published, that factor gets the neutral middle score (50) and the product page marks it as estimated.
Ties and discontinued models
Products are ranked by score within each group. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.