By Thomas P.

Continuing the evaluation of propellers we made a summary of their performance at 4.500 rpm:

testing propellers

From the data as above it appears that the Revolution 21'', with specific loads of course, has the highest cruise speed at 4.500 rpm, with good fuel consumption.
Nearby is the Suzuki 15''x21'', however with fewer loads, while Solas 16''x19'', which in the previous statistics was among the first ones, is now in the last position with 26.4 knots, but with more loads.

We even observe that the Solas 15 3/4''x22'' gives a good cruising speed, good fuel consumption related to the load, while in the table of top speeds it was in the last place.

Let's now take a look at the last data concerning the speed at which the rib gets on plane:

testing propellers

In this table we see again the very good numbers of Solas 16''x19'', which despite the high loads it gets the rib on plane at 3.200 rpm with13.5 knots. Here again the theory is confirmed that the larger diameter propellers get the rib on plane at lower speed than the smaller ones.
If we compare the 3-blade Solas 16 x 19 with our 4-blade propellers we can see that the large diameter of 3-blade propeller gives us lower speed on plane compared to 4-blade ones.

Evaluating the quality of riding

After comparing the numbers of data to end to the appropriate propeller, we should first consider the 'behaviour' of each propeller regarding the quality of our cruise. This is a factor certainly very important regarding the final stage of choosing the right propeller. The behaviour of the boat, its stability in different wave directions and the general sense of the handling is no doubt very critical data, many times more important than the best numbers recorded.

First of all we will take out of the competition the Mirage Plus 19'' and 21'', because, despite their good numbers and good stability that gave, they showed a clear inability to lift the bow, especially at the medium rpm.
We will also take out the Solas 15 1/4''x22'', because after 5.000 rpm it had very high numbers of slip, resulting in no desirable performance.

Therefore, the number of the candidate propellers is limited to the following five ones:
3-blade Solas 16''x19'', 4-blade Solas 15 3/4''x20'', 3-blade Suzuki 15''x21'', 4-blade Revolution 14 5/8''x19'' and 4-blade Revolution 14 5/8''x21''.

For these five propellers, it is worth mentioning the following:

testing propellers

The prop Solas 16''x19'' is definitely one of the first in the selection list, since it gave us:

  • 6.000 rpm with the specific loads
  • 42, 6 knots, final speed
  • 26, 4 knots at 4.500 rpm
  • Faster accelerations
  • It gets the rib on plane with very low speed.
  • Moreover, the feeling of rib's handling was very good, with very good grabs while it was obvious that the prop keeps the stern high and the boat in a straight ride.

The prop 4-blade Solas 15 3/4''x20'' gave us:

  • 6.000 rpm, running with the most loads
  • 39,5 knots, final speed
  • 25, 8 knots at 4.500 rpm
  • Very good accelerations
  • It gets the rib on plane with very low speed.
  • Regarding the feeling of rib's handling was very good, still without the grabs we expected.

The prop Suzuki 15''x21'' gave us:

  • 6.000 rpm
  • 44 knots final speed, which was the highest, compared the other ones
  • 30 knots at 4.500 rpm
  • Unsatisfactory accelerations
  • It gets the rib on plane with quite good speed.
  • Regarding the handling of the rib, we had very good grip at medium speed, our loads still were limited. This means that we are unable to overload the boat, because then, apart from the others, the engine's rpm will drop below 6.000 which are not desired.

The prop Revolution 14 5/8''x21'' gave us:

  • 5.900 rpm
  • 42 knots final speed
  • 30, 8 knots at 4,500 rpm, which was the highest from the others
  • Unsatisfactory accelerations
  • It gets the rib on plane at higher speed than the mentioned ones above.
  • Regarding the rib's handling we were satisfied, but if it is required to overload the boat the engine's rpm will drop below 5.900 which is not desired.

The prop Revolution 14 5/8''x19'' gave us:

  • 6.300 rpm
  • 41, 8 knots final sped
  • 27, 5 knots at 4,500 rpm
  • Very good accelerations
  • It gets the rib on plane with quite high speed.
  • Regarding the feeling of handling was by far the best propeller.
    The acceleration was great and its grip was impressive.
    The stability of the rib was remarkable even when reaching the limits, with the trim and the lift at the higher level, without having ventilation trends. Its ability to hold up the entire boat was clear.
    The drive was strictly controlled at W.O.T., wherein the Revolution seemed to maintain very good contact with water, even when we pushed it consequently to lose its "bite", while the thrust loss was minimal.
    And, of course, its very smooth and soft operation gave us an amazing feeling of biting in the water, without a trace of vibration, inspiring unique confidence, even when the hull was balancing on the edge of the stern sections.
    Moreover, it allowed the engine to reach its maximum rpm, which let us load the boat more without dropping the engine's rpm below 6.000.

testing propellers

Final choice

As we can see, there is no ideal propeller. Therefore, we must choose the right prop depending on the use of the rib.

Personally speaking, I would prefer the Revolution 19'', because it gives the best average performance at top speed, cruise speed and acceleration, and allows us to overload the boat as much as we want.

Furthermore, I belong to the category of those who would not sacrifice the feeling of handling for any 'number', no matter how great it would be.
And the handling of the rib with the Revolution19΄΄ was excellent. Moreover, I think the Revolution 19'' can give us even better numbers in speed general, since we can try it in lift's higher positions, because it is designed to run close to the surface.

If you asked me which propeller I would prefer as a second or backup, I think about either the Solas 16''x19'' or the Revolution 21''. If I chose the Revolution 21'', I would use it when the boat was lighter loaded.

Finally, it should be emphasized once more that the Rev 19'' is the right prop for the particular boat, with the particular engine, for the particular loads, and the specific use.

This does not mean that the remaining propellers are "bad". Besides, there are no "good" or "bad" propellers. There are just propellers that match better to a particular combination of engine-hull-load than others, which will surely fit better in another combination...

...keep Ribbing!