Testing the above propellers is a very good opportunity to realize once again that the type of our hull is the most important factor which defines the proper diameter propeller that should match in order to ensure the necessary thrust over the whole speed range.
So we have two propellers with completely different characteristics. However, their almost similar pitch helps us to see the role and influence of the relationship of diameter-number of blades-total blade surface, in this hull.
We tested these propellers in a Marvel 930 powered by a Suzuki 300hp. The tests took place at the same time under the same conditions.
The propeller of Suzuki:
- was keeping the rib on plane at lower rpm
- gave us higher cruising speed at 4000 and 4500 rpm by 3.5 knots
- was slightly more fuel efficient at 3500 and 4000 rpm
- gave us higher top speed despite its lower rpm at WOT and its shorter pitch
- showed lower slip numbers over the whole rpm range and thus always was giving us higher speeds. In the following data we can see its excellent slip rates that at WOT are reaching only 4%
- as far as its behaviour is concerned, it gave us the feeling of better bite in the water, quicker throttle response while it was gripping slightly better.
Below we provide detailed measurements of both propellers
If we take a better look at the data can see that:
- apart from the gear ratio of the engine, the type of the hull is the major factor which finally determines the appropriate diameter of the propeller.
- the diameter of the propeller has the first role while the number of blades and total blade’s surface area are the following ones
- although Hydromotive is a very well-designed propeller with excellent features (great amount of blade cup, very high rake angle and especially intense cupping on its blade tip) which improve its grip, reduce its slippage and allow it to operate efficiently at very high mounting heights, however its smaller diameter only just by half-inch doesn’t allow it to show its capabilities in the particular hull.