Corsair 33΄ of Top Line is one of the best rigid inflatable boats of the international market, famous for its robust construction quality, excellent finishing and of course its outstanding performance.
Having already presented in the past the description of Corsair 33΄ deck, as you can see in the relevant article, Top Line Corsair 33΄ – 2 x 300hp Yamaha, this time we will be limited to its performance recorded by hanging on its transom two 300hp Optimax two-stroke outboard engines as well as the overall behaviour of its stepped hull.
At Corsair 33 of our test, the two Optimax 300hp engines with a 1.75: 1 gear ratio was turning two Bravo I 15 ¼" x 26" lab finished four-blade propellers.
With three persons on board and about 300 litters of fuel in our tanks, we hit a top speed of 65.4 knots with a fuel consumption of 194 litters per hour.
The most economical cruise speed was 26 knots at 2500 rpm, at which it was burning 1.69 litters per nautical mile, a particularly amazing figure for a 10.45-meter rib powered by two outboard engines.
Still, even at 3000 rpm, with a cruising speed of 31 knots, the fuel consumption was particularly low, remaining at 1.8 litters per nautical mile.
As we can see in the measurements we recorded in the PDF below, the fuel consumption exceeded 2 litters per nautical mile only at very high rpm.
And of course, the one-meter height of the waves that we had that day, it was not capable of disturbing our ride, but quite the contrary, it made it more enjoyable. By testing the ride quality of Corsair 33 under all waves’ direction, we were absolutely impressed. Even when we were running having the waves on our stern, Corsair 33 was keeping its bow steadily high, without any tendency to «stuck» in the backrest of the waves, a phenomenon that several stepped hulls present due to their excessive lift of their stern.
We all know its excellent performance in rough seas and its incredibly soft riding. And of course, in addition to the high top speeds that Corsair 33 can record, another amazing advantage is its incredibly straight ride to both the middle and high rpm. During the ride, its entire hull was running out of the water, so as the only drag were due to the gearcase and the propellers themselves, thus justifying its particularly low consumption and high speeds across the whole rpm range.
Therefore, in order to achieve even greater performance, we can only focus on the mounting height of the engines in combination with the most suitable propellers and the proportional weight distribution.
What is even more impressive is that its hull maintains the ideal angle of 3 to 5 degrees - or at least quite close to that number- with the water surface, which is extremely important because in this lower limit of degrees the lesser drag, the higher speeds and the greatest economy are achieved. If the above ride attitude becomes greater or less then the performance is suffered.
Corsair 33's stepped hull manages to stand within the limits of this ideal angle, which is absolutely due to its geometry, which combined with the aerodynamic design of the tubes minimize the resistances and thus achieve a unique performance.
Really, is there anyone who wouldn’t dream of a rib with racing performance, great riding in rough sea, without requiring too much fuel and of course ensuring a comfortable and quality living at sea?
Corsair 33 of Top Line is a pure high-performance rib which has managed to combine to the highest degree everything a rib and sea lover is asking for. Besides, this is the main reason due to which Corsair 33 enjoys its great success.
I have to point out that Corsair’s 33 hull was not designed, of course, by chance. It is the result of hard work, boatyard knowledge and accumulated experience gained from the numerous participations of Petros Kapleris in rib races, who started designing and building this fantastic hull on a white sheet of paper.
Being well aware of the fact that a stepped deep-V hull, unlike conventional hulls without steps, does not accept any designing errors and is very sensitive to weight distribution, having even significant restrictions in both the trim and the tight turns, I can say with confidence that the stepped hull design is not for any manufacturer, and of course the well not designed steps can lead to dangerous phenomena.
The distance of the steps, their length, their position and their relationship with the boat’s center of gravity, which is very easily changed, are just some of the parameters that play a very important role and determine the success of a stepped hull.
Knowing also that the boat's riding angle is constantly changing as the speed increases and the lift-force distribution on the steps dramatically changes, it is therefore obvious that even a minimum change on the dynamic center of gravity related to the pressure center is enough to convert a boat with a steady ride to one that porpoises or presents chine walking phenomena at several speeds.
In addition, as the speed increases, so the hydrodynamic lift of the steps increases too, and therefore it is necessary to estimate with relative precision the total cumulative stern lift of the steps and propellers, so as not to have any dangerous phenomena at WOT due to the unwanted sudden glue of the bow in the water.
There is no doubt that the design of a stepped hull is a complicated issue and a very demanding equation, for skilful solvers!
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