125 Force can`t get the RIB in plane

[rbjo]

I have an 125 Force which have 130 psi on all cylinders with full open throttle. The prop is an 13X17 steel.
The boat is an RIB 675 cm long ( 21" ). The weigth is unknown.
I am not able to get the boat in plane.

Is the boat to big for the engine or is it somthing else?

BR

RB

Norway

 

[Jiggz]

You need to find out the WOT RPM first before you can decide if its the size of the boat or the motor not running properly that is causing the boat not to plane. And then there is also the proper trimming of the motor. An over trimmed motor will make the boat "plow" through the water making it very hard to go on a plane.

 

[SkiDad]

I would think it would plane it but you could try a 15p ... maybe your a just at the edge -try moving all your gear up to the front as a test.

 

[Frank Acampora]

The boat is not too big for the engine. I had a Force 125 on a 21 foot cuddy cabin and not only did it plane quickly, but top speed was 34 MPH. I would expect an RIB to perform at least as well. So, with compression ratio high and equal at 130 PSI look elsewhere. Check timing and check synchronization of timing and carbs. Use the videos at the top of the forum. Check fuel supply. Especially check the spark on all four cylinders. These engines will start and run (not well) on as little as 2 cylinders.

 

[jerryjerry05]

Pic of the rib?
Load?
Is the motor mounted right?
The 17p stainless is equal to a 19aluminum.
Might be too much and like Mitzy said a lower pitch might help.

 

[Frank Acampora]

It is NOT possible to generalize about stainless versus aluminum props. IF the stainless is the same manufacturer and style as the aluminum (Like stock Chrysler steel and aluminum props) THEN, the stainless will turn about 200 RPM faster than the same pitch in aluminum with about a 1-2 MPH increase.--it simply takes less horsepower to cut the thinner blade through the water leaving more horsepower available to drive the boat.

Since brands are designed differently, a different brand of stainless may have increased area, or more rake, or even more EFFECTIVE pitch and will perform differently than expected. For example: On my Chrysler 140, a 21 pitch stainless stock Chrysler prop (made by Michigan) will run about 5200 RPM. A stock Chrysler 21 pitch aluminum prop will turn about 5000 RPM.The same pitch stainless Ballistic prop (also made by Michigan) will only turn 4500 RPM due to increased blade area, full cupping, and increased blade rake.

 

[rbjo]

I have started to move the brackets from one engine to another which have 150 PSI on all cylinders. Unfortunately the axel which hold the trim/tilt pump is stuck. Tried with a 40 tonn to press it out with no luck. Have to heat it up and try again.
I will go through all the good advices and take step by step.
Here is some pictures of the boat and the two 125 engines.
'

BR

RB

Norway

 

[rbjo]

Heres the pictures`, to big to send in postr

 

[rbjo]

Picture

 

[jerryjerry05]

A stainless prop will knock down the rpms not go faster. Can drop the rpm's as much as 500
It's a lot heavier.