Tempest plus and Revolution are two well-known propellers with almost the same design, a fact that allows us to compare them each other and to draw safe conclusions about the effect of an additional blade on the propeller’s efficiency and therefore on the boat’s performance.
Perhaps they are the only propellers in which such a comparison can be attempted since it is very hard to find two propellers (a 3-blade and a 4-blade) with such common features.
So, we can almost see, how the addition of a fourth blade affects the behavior of a 3-blade propeller, how many rpm it costs for the engine and the ability that gives us to raise our engine on the transom.
We had the opportunity to test these propellers on a Technohull Seadrug 688 with a Verado 200hp.
The tests took place in the same day, at sea state 3-4beaufort, with the same loads.
Let's see the common characteristics of the propellers we tested
- exactly the same diameter
- the same pitch
- approximately the same shape and the same surface area in their blades
- almost the same amount of cup which extends and covers the tip of the blade
- highly raked blades
- they are both of them designed to run close to the water surface and so they «like» high positions on the transom
Looking at the table above we see that the Revolution:
- keeps the boat on plane at a lower speed and lower rpm<
- provides quicker plane times
- is faster at low and medium rpm and as the load increases, the difference in their speed increases too in favour of Revolution
- has better fuel consumption at mid-range rpm
On the other hand, Tempest plus:
- allows the engine to increase its rpm at WOT
- gives higher final speed
Concerning the behaviour of two propellers, the Revolution:
- runs more smoothly and softly, with no vibrations, providing better boat handling
- provides greater stability and balance
- offers more grip in rough seas and has a better bite in the water
- provides greater stern lift, helping the acceleration of the hull, especially in the back-weighted boats
- presents lower ventilation rate at the whole rpm range, but also in sharp turns
- has better accelerations
- has smaller slip numbers at the whole rpm range
These differences about the behaviour of the two propellers, which we indeed observed in other tests with different engines and boats too, we can say with relative certainty that are due mainly to the additional blade of Revolution.
When we switch from a 3-blade Tempest plus to a 4-blade Revolution of the same pitch, we should expect a reduction of our engine rpm at about 150-200 rpm. But we can also raise the engine higher on the transom, because the Revolution runs better at elevated engine heights, retaining the same rpm without having to decrease the pitch.