Just like all Mar.co models, R-Evolution 36 is characterized by its excellent manufacturing quality with remarkable attention even in the last detail, offering to its owners the highest degree of what we call «Ribbing experience».
R-Evolution 36 shares exactly the same features with R-Evolution 35, from which it differs only on the surface of the swimming platform which is much bigger due to the bracket’s addition.
R-Evolution 36 was born to satisfy the most demanding customers who desire to install a third engine, as R-Evolution 35 can support up to 2 x 350hp as maximum horsepower due to the lack of the proper space on its transom for mounting a third one.
With the addition of a 60 cm fiberglass bracket, R-Evolution 35 got longer and became R-Evolution 36.
The mounted bracket, which of course has the required space for a third engine installation, is an extension of the hull and actively participates in riding while its keel is shaped to a wide pad, which is very important for achieving the maximum possible buoyancy that is necessary for the support of the third engine and the minimization of the bow’s raising due to the heavier weight on the transom.
Of course, proper modifications and reinforcements have been made to the transom and hull structure components so that they can safely manage the extra power of the third engine.
As far as the design of R-Evolution 36 deck is concerned, there is no difference from R-Evolution 35, the presentation of which you can see in our previous article: MAR.CO R-Evolution 35 with twin 350hp Verados.
As we have already highlighted, the strongest points of the deck is that it ensures ergonomics and absolutely freedom of movement, while the helm station with the highly appealing Hard Top steals the show.
Three Mercury's 400R engines were hung on our test rib, which with a gear ratio of 1.75: 1 were turning 16"x19", Eco Enertia three-blade stainless steel propellers.
With 280 litters of fuel and 4 people on board, R-Evolution 36 was getting on plane at 2800 rpm with 14 knots, while it was reaching the speed from 3 to 30 knots in time just a little over 6 seconds.
Despite the three engines’ heavy weight, R-Evolution 36 was maintaining a very good ride attitude across the whole rpm range, while the high degree of the hull’s deadrise provided a very soft ride, which in combination with the robust construction of the rib is a guarantee for comfortable trips even in rough seas.
At 3500 rpm, Mercury's multi-function display was showing a speed of 25 knots, consuming 3.1 litters per nautical mile, making it the most economical cruising speed for this particular rib-engines combination.
At 4000 rpm our speed reached 31 knots with a fuel consumption of 3.9 litters per nautical mile, while at 4500 rpm we were running with 37 knots burning 4.7 litters per nautical mile.
Due to the high waves on the day of our test, we were unable to keep the throttle wide open for a long time, nor to trim out the engines as much as we would like.
So we did not manage to overcome 6100 rpm, where we recorded 52 knots of top speed.
In any case, however, we were far from the area of 7000 rpm in which the 400R Verado engines should reach.
Therefore, it becomes clear that in order to allow the engines to reach their maximum rpm range, we need to go to shorter Eco Enertia propellers by two inches, which is particularly important for the proper operation of the engines.
If we calculate the slip values, we will see that at 4000 and 4500 rpm the slip is respectively 14% and 7.5%, while at 6100 rpm it reaches 4.5%.
These numbers seem initially satisfactory, but if we take under consideration the fact that we have three propellers in the water, then obviously the slip percentage is quite high.
It is worthwhile trying to raise the engines one hole higher, a fact that is allowed not only due to the numbers we recorded but also to the overall feeling we got, in order to achieve a reduction in the engines’ load and thus to gain about 200 extra rpm at WOT.
It would also be quite interesting to experiment with smaller diameter propellers, which is allowed by the triple outboard engine installation which limits the need to use large diameter propellers, and thus to reduce the great drag that the large diameter propellers present after 40-45 knots and negatively affect performance.
With this choice, we will be able to fit propellers with longer pitch so as to achieve a much higher top speed as well as considerably higher cruising speeds, with a corresponding reduction in fuel consumption.
Suggested propellers for test are the 4-blade Revolution with a diameter of 14 5/8" and Bravo I LT with a diameter of 15¼", depending on the intended use of the rib.
Sea-trials are the ones that will give us the answer for the best possible set-up!
Twin vs Triple engine configurations
In general, keep in mind that when going from twin to triple engine installations we will not have a proportional increase in performance in all fields.
For example, it is certain that acceleration from a standing start and planning time will be greatly improved due to higher horsepower and the additional propeller which maximises the thrust. In these cases, where the velocities are not high, the additional drag of the third lower unit in the water does not significantly affect the performance.
Regarding the top speed, however, improvement levels will be not proportionately increased.
The higher the speed, the greater the drag gets.
The reason is that the extra power of the third engine is confronted with both its extra weight and mainly its lower unit’s drag which is increasing exponentially in relation with the increase of the speed.
MAR.CO MARINE COSTRUZIONI
Via Edison 64, 20835 Muggiò (MB) Italy
Tel.: +39 0392787336