For fast sailing boats (speed > 12kts) with a Cruising hydrogenerators, Watt&Sea has developped a Manual pitch propeller. This propeller can be used in a large velocity range from 6 knots to 30kts. It is suitable for racing boats which are not equipped with an automatic pitch Racing hydrogenerator.
Which angle for which speed ?
The basic principle:
- The more the blade is perpendicular to the flow, the more power it can extract, and therefore the more suitable it is for low speeds.
- The more the blade is feathered, i.e. aligned with the water flow, the less power it can extract, and therefore the more suited it is to high speeds.
If the hydrogenerator starts roaring, and the batteries are not full, this means that the hydro-generator is going overspeed. You'll need to change the angle of the blades to feather them. Leaving a generator in overspeed can cause it to overheat and shorten its service life.
Caution: the angle of each blade must be absolutely identical. To help with adjustment: dismantle the propeller and place it on a flat surface. Unscrew the headless screws and adjust the blade angle using thickness gauges between the leading edge of each blade and the flat surface. Instead of shims, you can also use the pages of a book to reproduce a similar thickness between each blade.
To sum up:
- Max power position noted "Pmax" = low speed 6 kts
- Min power position noted "Pmin" = high speed 30 kts
- Then adapt iteratively to optimize power, always avoiding overspeeding (roaring noise).
- Each blade must have exactly the same pitch ange (use shims or pages from a book).