With the memories of the unforgettable moments Corsair 31 gave us against the huge waves of the Atlantic Ocean being fresh, I took my position behind its cockpit. However, this time, the aim was not to travel, but to test the performance of Bravo I FS propellers fitted to the new twin 250hp Optimax which were mounted on its transom.
As we have seen in a previous article, Bravo I FS is a pro finished propeller which was «born» from special interventions made in the design features of the standard Bravo I, which made it «lighter» for our engine.
In practice, this means that we can switch from a standard Bravo I to a Bravo I FS longer pitch propeller, while maintaining the same rpm in our engine.
The detailed results of our measurements are presented in the table below.
Despite the heavy loads and the open tents that we had during our test, the results were particularly impressive:
- the rib was getting on plane easily at 2700 rpm
- the engines reached their max rpm at WOT, despite the heavy loads
- our cruising speed at 4000 rpm was 36 knots with a consumption of 1.7 litters per nautical mile
- the accelerations were great and the throttle response impressive at the whole rpm range
- the handling of the rib and the propellers’ grip were excellent even when we were trimming excessively out the engines.
The relatively high slip numbers at the whole rpm range are expected because of the modified characteristics of the Bravo I FS propeller. Besides, this is its main characteristic which allows us to use it in longer pitch.
Basically, the choice of specific propellers with specific pitch is totally satisfactory for the particular engine-boat combination and for the normal use with the particular loads.
We could suggest a spare pair of 25΄΄ Bravo I FS which would be necessary when the rib carries lighter loads, achieving this way higher top speed, higher cruise speed at midrange rpm and of course impressively lower fuel consumption almost under the 1.5 litters per nautical mile.