Prop changes

[Jkraft]

Hey all. I don’t usually load my boat up but I did last week and max rpm was just shy of 3800. Maybe 3780. I need to get more rpm

Current prop is 19x18

Base on the idea that 1 inch is 200 rpm what should I change it to? 19x17.5 or 19x17?

What prop specs are you 315 yanmar folks running?

[Norseman]

19X18 four blade.

Been experimenting with 2 props, had them both tweaked and balanced, happy with the end result, smoother than before, 17 knots at 3600 RPM, 4000 at WOT.

[Jkraft]

Weird that we have the same prop specs and I’m getting almost 200 rpm less. Wonder if I should drop to17 pitch

[Norseman]

Weird that we have the same prop specs and I’m getting almost 200 rpm less. Wonder if I should drop to17 pitch

Full fuel, full water/stores?
Dirty prop, dirty bottom?
Quite a few variables.
I hear about guys getting better cruise speed and better top speed with the Yanmar, but have a feeling they are over-propped.
Been spending quite a few hours on the boat diesel website, lots of warnings on not to abuse the Yanmars and to give them plenty TLC.

[Jkraft]

Weird that we have the same prop specs and I’m getting almost 200 rpm less. Wonder if I should drop to17 pitch

Full fuel, full water/stores?
Dirty prop, dirty bottom?
Quite a few variables.
I hear about guys getting better cruise speed and better top speed with the Yanmar, but have a feeling they are over-propped.
Been spending quite a few hours on the boat diesel website, lots of warnings on not to abuse the Yanmars and to give them plenty TLC.

Full on fuel and water. Prop just reconditioned and only been in the water 2 weeks since the motor work.

If you know me you know this is not a neglected boat. She gets all the TLC she deserves.

[Norseman]

If you know me you know this is not a neglected boat. She gets all the TLC she deserves.

.

I know, but what then?
(GPS out of whack?)

[Jkraft]

Speed isn’t the issue for me. At 3400 I’m running 18 knots. I’m willing to sacrifice some cruise speed if I can turn another 100-150 rpm at wide open. I just don’t want to lug the motor

[Norseman]

Speed isn’t the issue for me. At 3400 I’m running 18 knots. I’m willing to sacrifice some cruise speed if I can turn another 100-150 rpm at wide open. I just don’t want to lug the motor

Looks over propped right there..

[Jkraft]

Agreed, hence my original question. Should I drop to a 17.5 or a 17 pitch to get to where I need to be?

[Nancy]

Prop just reconditioned . . . what does your prop guy say about the R's?

[Jkraft]

Prop just reconditioned . . . what does your prop guy say about the R's?

Nancy, he said if we reduce the pitch a little I can get more rpm out of it. Which I’m fine with. I was really shooting to see where everyone else was at with their props before I decided what to do. I think I’m going to reduce the pitch by .5 and see what happens

[Nancy]

Sounds like a plan. Those prop guys usually know what they're talking about.

[Jeremyvmd]

I’m with Nancy. Let the prop guy tell you what it needs. That’s what your paying him for.

[hatchetjoe]

Here is what I found with mine a while back. I think there is a fair amount of difference in the weights of these boats or something else in the bottom that changes the resistance.
"Success! I got the new prop on a couple of days ago. It is a Michigan 4-blade DQX, 19 inch with 17 inch pitch and 5 cup. I haven't had good seas to carefully test the change but it looks like I gained about a 25% increase in speed. With full fuel and water it looks like WOT is back to 3900 rpm and 20 kts instead of 17. More importantly my speed at 3,000 rpm increased from 9.5 to 12.4 kts and at 3,200 we went from 11.5 to 14.5 kts. It's hard to describe but the boat also feels like it is moving easier in the water. I'll still have to find a time with less chop and see what it really does with more carefully obtained numbers."

[Norseman]

. With full fuel and water it looks like WOT is back to 3900 rpm and 20 kts instead of 17. More importantly my speed at 3,000 rpm increased from 9.5 to 12.4 kts and at 3,200 we went from 11.5 to 14.5 kts.

Wow, huge difference, I may try that as well, did not have any cup added when a tuned my prop. Thx