Yamaha 90 hp 2 stroke Outboard WOT … … 4-blade ‘ Stern lifting ‘ Stainless S. Propeller

3 cylinder 2 stroke Part1 Full Throttle @ WOT . Full Trim,no "cavitation"/ventilation 37.5 knots at 5300 Rpm. ( I need a Jack Plate )
Full Throttle @ WOT,,,LOWER TILT 35 knots. Rpm, I don't recall
Yamaha Specs Recommended Min-Max RPM 4500-5500 @ WOT
for this 90 HP! I have a 70 hp 2 stroke Yamaha and it has Recommended Min-Max 5000-6000 RPM. More info further down why it is Important.



"Conventional" Loop Charged 2 stroke carburated outboard
1140cc 90 hp lightweight " 121kg " outboard engine.
Propeller, 4 Blade Original Yamaha, 13 1/4 x 18 =Very good grip in the water and planes at 2600 rpm!
It would have been impossible with a 3 blade ; )

It may go faster with a 3 blade prop but i don't think it would be that much more ,and i would lose all the benefits the 4 blade brings


One "custom modification" ...
Drilled new holes for the mounting so high that the holes for the bolts are 1.5 cm from the top of the transom
And the engine sits in the 4th hole.
Higher up is impossible without a Jack Plate.

Yamaha has four holes to mount bolts in,
If you mount the motor on the lowest holes,,,the higher up the engine will be........obviously : ) .

Lift up your outboard 1 or 2 holes
even if you drive with an aluminum propeller, it will go much easier in the water, the less rig you have in the water = the less drag

And you save fuel because of lower drag
And maybe get more speed out of the boat.

Why slow down the boat unnecessarily with a low-mounted outboard.

If you mount your rig too high The Aluminium Propeller will start to ventilate (take in air ) you can hear this clearly,
Lower the outboard one hole and test again,
Or try a Stainless prop with the same pitch.
And I can assure you that it will not ventilate (losing grip in the water).
Maybe you can raise the engine further without the propeller loses its grip.Higher Performance!!

If you have lets say a 19" Aluminium prop on And replace it with a 19" Stainless Steel , It will drop the rpm at WOT ( Full throttle ) and lose performance.
Because the 19"ss is more "aggressive"( the most ss are ) then the Alu dito
If you are going to have the engine at the same hight rpm try a 17"
If it still have lower rpm at wot,Elevate the outboard

Propeller Calculator
http://continuouswave.com/cgi-bin/pro...

Important !
You must also remember not to go below or above the recommended RPM range at wide open throtte for your outboard.
Find out in the specifications for your outboard.
Warning !
Do not forget the cooling water intake, if you raise the engine above the intake, the engine can overheat.
But there are solutions for this also.

There is so much to say on this topic, so check out more on the web to learn more about Propellers.
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That's why I want my outboard higher up.
It does not loose the grip even at full tilt (Trim) and make 5300rpm
I want to reach 5500 rpm (Maximum recommended RPM) for this Yamaha 90 hp 2 stroke.

Since its not ventilate at the highest trim, It could probably be raised further with a Jack Plate