df50 2008 wot and rpm

[bakalisk]

I am an owner of the DF50 model 2008 with 340 working hours.
My problem is that I can’t get close the WOT limit of 6500rmp.
I have two props (3 X 11 3/8 X 14 and 3 X 11 3/8 X 12). With the 14 pitch prop and only one person on board (total weight 600Kg) I can reach 5800 rpm. With the 12 pitch prop I got up to 6000 rpm. With full load (800Kg) there I got 5600 rpm with the 14 pitch prop and close to 5900 with the12 pitch prop. Shouldn’t there be a greater difference in rpm between the different situations? I hoped with the 12 pitch and one person to get near to the limit of 6500 rpm level.
I got the feeling that something is not right. I checked the cylinder compression, replaced IAC valve, replaced sparks, replaced fuel filters, cleaned the injectors and cleaned the throttle body.
Any suggestions?

[Harper]

Bumped to top for more exposure....

I'll take your word for it that the max RPM within the prescribed range is 6500. The new DF50A shows 5300-6300. In any case, if you're only getting 5900 with your NORMAL load, then perhaps you could go to the 10" pitch. Suzuki lists it at $150 or so. Personally if I had access to a reputable prop shop, I'd work with them on tweaking the 12" prop that you currently have.

[Hoosmatroos]

How low/high is the motor fitted? If it's mounted too low then there is a lot of drag. Do you have a picture of the motor on the boat out of the water?

[bakalisk]

Motor is mounted with the cavitation plate 2cm above the bottom of the boat. Also at cruising the cavitation plate is at water line.

[Hoosmatroos]

Are you sure that there is no water in the boat (sandwich bottom). Between the two props there should be a greater difference. If possible, you can try a 11 or 10 inch prop and see what happens.

[bakalisk]

Are you sure that there is no water in the boat (sandwich bottom).

My boat has three airtight compartments which are clear of water.

Between the two props there should be a greater difference. If possible, you can try a 11 or 10 inch prop and see what happens.

This is exactly what I can’t understand. Unfurtunally I don’t have any other prop for testing proposes.

[Moonlighter]

The difference between props is usually fairly linear IF the props are from the same manufacturer and are the same model. And if they are in similar new condition.

This is because different manufacturers props may have different blade shape, blade area and rake. So you can compare apples with apples. Also, it is not uncommon for prop measurements to be wrong!

That may or may not explain the differences between the props you tested.

I think that 6500 is an ambitious target. There was recently another thread where someone also quoted that for the 50, but the only Suzuki data I could find said it was lower. Like 6300 max.

If it was mine I would be very happy to get 6000-6100.

A good prop shop should be able to take some pitch out of your 12” prop and get you some extra revs and bite.

[bakalisk]

The difference between props is usually fairly linear IF the props are from the same manufacturer and are the same model. And if they are in similar new condition.

This is because different manufacturers props may have different blade shape, blade area and rake. So you can compare apples with apples. Also, it is not uncommon for prop measurements to be wrong!

That may or may not explain the differences between the props you tested.

I think that 6500 is an ambitious target. There was recently another thread where someone also quoted that for the 50, but the only Suzuki data I could find said it was lower. Like 6300 max.

If it was mine I would be very happy to get 6000-6100.

A good prop shop should be able to take some pitch out of your 12” prop and get you some extra revs and bite.

Thank you.
I would never thought that there could be major differences between prop manufactures. The 14” is the original Suzuki S1400 ant the 12” is from a Solas (model Amita 3). I will try to find an original Suzuki 12” prop to test it.
Regarding the rmp limit, I attached the DF40/50 specification of the model 2008.

[Hoosmatroos]

Oke, that is clear now. 6500 is the max.

And yes, there is a lot difference between the brands. Moonlighter is wright about that.