WOT only 4800 RPM

[Bigmuz7]

Well If I found out someone was revving the nuts of my motor in a no load situation, I'd not be happy about it either. There's so much power available when throttling up god knows how fast it actually spins
The noise you hear when your prop leaves the water is as much to do with the exhaust outlet leaving the water, cant say I deliberately go out to do that, but I know some on here do

Anyway OP .. the sizes are stamped on your prop .. and you can measure the diameter no need to speak to your dealer

[Hightower]

What is there to be gained by revving to the max of the engine without load? Absolutely nothing!

So don't do it!

[Hightower]

Originally Posted by Bigmuz7

The noise you hear when your prop leaves the water is as much to do with the exhaust outlet leaving the water, cant say I deliberately go out to do that, but I know some on here do

A good helmsman should be able to read the conditions and be ready to reign in the throttle when needed.

[Jon Tallis]

I recon you might be a shade over-propped.

My very similar rig - Humber Destroyer 6.0 / Yam 150 HPDI with 19" standard Yam prop tops out at 5600 revs (lightly loaded, fully trimmed), which gives spot on 40kts (46mph).

You are getting a shade higher top speed but at 800 revs lower.

I'd be interested to know what prop you've got on as I was considering changing to a 21" but don't want to spend a load of cash for less acceleration and no higher top speed.

How do you find the HPDI? Mine's a 2001 and I've owned it for 7 years. Goes like a scalded cat and never misses a beat - love it!

[poulner6]

I'm out this weekend, so I'm going to double check all out again, then will advise.

[poulner6]

Originally Posted by Jon Tallis

I recon you might be a shade over-propped.

My very similar rig - Humber Destroyer 6.0 / Yam 150 HPDI with 19" standard Yam prop tops out at 5600 revs (lightly loaded, fully trimmed), which gives spot on 40kts (46mph).

You are getting a shade higher top speed but at 800 revs lower.

I'd be interested to know what prop you've got on as I was considering changing to a 21" but don't want to spend a load of cash for less acceleration and no higher top speed.

How do you find the HPDI? Mine's a 2001 and I've owned it for 7 years. Goes like a scalded cat and never misses a beat - love it!

She just gives an excellent overall performance, push the throttle and she just's bits in the water and takes off...

[boristhebold]

Take a good look on the internet and read up on issues with prop choices, how to select the right prop etc you will learn loads. Sounds like a prop issue. You need to determin what diameter and pitch would suit your boat and what you want to do on it. Some props will give higher top speed but reduce acceleration and vica versa, there is a trade off, depends what you want to do and what is correct choice.

[colcreate]

Few thoughts:
Is your tachometer telling the truth?
Are you getting full movement on the throttle linkages?
Cables operated systems can stretch and wear!

A 1" decrease in prop pitch will increase the revs by about 200rpm
Stainless props will give different results to Ali props of the same pitch and diameter.
See if you can borrow another prop to try.

44mph isn't too shabby, but your optimum is 150hp @ 5,500rpm
Is the motor mounted too low on the transom?

[poulner6]

Well hopefully can close this chapter. Cracking cruise today 3 persons on board a full tank of fuel and WOT at 5200 rpm and 50mph. Well that's sweet got a bit of chime though so had to back down to 39mph and running sweet as