As I was looking at the Technohull SeaDNA 999 and two of the most famous and well designed 4-blade propellers, I couldn't resist the temptation of a comparison test.
Revolution 14 5/8΄΄ x 25΄΄ against Hydromotive 14 ¾΄΄ X 24΄΄. Two propellers with approximately the same diameter and pitch would allow us to focus on the individual characteristics of their design.
The pair of 300hp Mercury Verados that was mounted οn the small brackets performed very well with remarkably low fuel consumption, mainly due to the overall design of SeaDNA. The engine's mounting height for these propellers was ideal, as shown by the data, since at high speed the rib performed wonderful, recording very high speeds, while it also got on plane quite quickly at low rpm. A combination for which it took many hours of testing and observations.
We chose a windless day without heavy load (2 people, 120 litters of fuel and the necessary equipment) and went out to the sea for testing.
Both pairs of props got the rib on plane just at 2000 rpm, with speeds that varied from 15 to 18 knots. Without the bow rising up, we continued pushing the throttle levers forward and were travelling with 30 knots at 3000 rpm. When we reached 3500 rpm our speed climbed to 36-37 knots, depending on the propellers we had.
At 3700-3800 rpm we were travelling with 40 knots keeping the fuel consumption constant below 2 litters per nautical mile.
Any boat would envy these excellent performances as well as every pilot would like them.
In the photo below we can take a look at the Revolution, to the left, and the Hydromotive, to the right:
40 knots are for SeaDNA a very pleasant and normal cruising speed with these propellers.
Pushing more the throttle levers, the hull responded immediately and gave us a very sweet and perfectly weighted ride, even when we reached 69 knots. We felt completely safe and actually enjoyed this speed as the hull clearly showed us that it could run even more with absolute stability.
The Rev prop test results.
First of all we observe that both propellers manage to get the SeaDNA on plane at 2.000 rpm. The Revolution, however, gives us higher speed at 2.000 and 2.500 rpm, having very smaller numbers of slip than the ones of Hydromotive.
This is due to its blade area which is much larger than the Hydromotive's one, so as the Revolution seems like 5-blade propeller related to Hydromotive.
It's worth noting at that point that the Revolution has lightly smaller diameter.
Comparing the two propellers in the range of 3.500 to 4.500 rpm we observe their excellent performance, both in speed and in the rate of slip.
We note that at 4.500 rpm the Revolution exceeds the Hydromotive 3, 5 knots with significantly less slip rate.
Even also at the range of 5.500rpm to W.O.T. the Revolution run faster with considerably smaller slip rates.
At this point it should be emphasized that the overall design and the individual characteristics of each propeller enable them to work very well, like surface propellers.
The bigger size of cupping and mainly the higher angle of the rake of Revolution than the ones of Hydromotive enabled us to trim up the engines more and eventually reach 69 knots.
It is obvious that the Revolution is capable of retaining more water to the surface of its blades and its hub, a fact that restricts its ventilation and sliding, thereby allowing higher angles of trim, resulting in an increase of final speed.
All the referred above result to a greater bow lift at the medium rpm and the W.O.T. which means less resistance producing better performance.
In the particular combination of boat and engines, with the particular mounting height of them, the Revolution matches better ... and win on particular points.