It was the first time that on the transom of Corsair 29 Racing the new Mercury Verado 400R was mounted, a totally unknown combination for us. We tested the Bravo I 15 ¼ ΄΄ x 26΄΄ propeller, having the Verado 400R at the same mounting height as the 300 XS Optimax, the former engine of Corsair.
After almost 50 miles of testing, we reached 65 knots with the engine turning at 6500 rpm.
What we mainly felt from the first time was the tremendous power and torque of the new engine of Mercury. Indeed, the Verado 400 Race gives us the highest power-to-weight ratio of all 4-stroke engines in its class.
We were excited by the new Verado 400R but not quite satisfied by the performance of the rib, since:
- the top speed was low
- after 65 knots, the rib was loosing its stable ride and its handling got extremely dangerous
- we were able to trim out the engine too little without ever being able to get to its neutral position, keeping our bow permanently low so as to «read» each wave thus losing boat control
- the behavior of the rib was getting very bad due to the lost of the propeller’s grip when we were raising the engine a little bit higher with the assistance of the power lift thus not being able to keep the rib in a steady course
- after 4000 rpm the slip numbers were consistently very high
- we never managed to reach 7000 rpm at WOT
The measurements of our test are shown in the table below.
Looking at the above data and measuring the engine mounting height in relation to its distance from the transom it was obvious that the setup was completely inappropriate. We had no doubt that the engine was set too high and certainly it should be lower.
Αs it has already been emphasized for many times the height of the engine is one of the most critical parameters in the achievement of the optimum setup.
In our own hull/engine combination, by lowering the engine we will:
- be able to trim out much more the engine, leading thus to a better control of the bow angle
- improve the position of A / V plate related to the water surface
- increase the engine’s rpm which will certainly reach 7000rpm at WOT due to the ability to trim the engine much more out
- reduce the «slip» percentage and increase the final top speed which will definitely overwhelm 72 knots
- have better handling and much better stability after 65 knots due to the better relation of A / V plate – water surface and also to the ability to trim out the engine further. In this way the foremost part of the hull will not take part in riding at all.
We also have to keep in mind that the boat setup is completely different when we use two-stroke engines than with the four-stroke ones. The weight and the great torque of four-stroke engines require their setting to be more right, lower and closer to the transom so as the boat to maintain its proper balance and in this way to achieve stable ride especially at high speed.