rpm?

[popey]

My mercruiser 165 IL6 turns about 3'400 at max speed which is equal to about 32 knots. According to the manual this should be 3'9 to 4'3. The rpm meter is factory fitted.

When I get from about 25 knots up, it like 'bubbles' at the sterndrive. What is this related with? Prop? Trim?

Thanks for your reply.

Regards, popey

 

[Bondo]

Re: rpm?

When I get from about 25 knots up, it like 'bubbles' at the sterndrive. What is this related with? Prop? Trim?

Ayuh,.... are ya sayin' it ventilates, 'n the prop looses traction,..??

Ya it could be the prop or the trim...
What prop is it,..?? How beat up is it,..?? What's yer trim,..??

 

[Fishermark]

Re: rpm?

In the DIY section at the top of the page, there is a post with troubleshooting for low rpms. (Or you can click here to see it )

 

[popey]

Re: rpm?

Hi there

yes, ventilation is the right word. My prop is a 14 1/2 RH 17 Mercruiser aluminium. Trim is slightly up, too much gives more ventilation. I have a gauge indicating the trim, but as it is set, it is not showing it.

Best Regards,

Popey

 

[Bondo]

Re: rpm?

Hi there

yes, ventilation is the right word. My prop is a 14 1/2 RH 17 Mercruiser aluminium. Trim is slightly up, too much gives more ventilation. I have a gauge indicating the trim, but as it is set, it is not showing it.

Best Regards,

Popey

Ayuh,... Does trimming it Down help the ventilation problem,..??

My 1st guesses are ya trimmin' too High, and/ or yer prop is Beat.....

How High does it Rev when it's ventilating, with no traction,..??
Does the boat drop off plane, loosin' all yer speed,.....

Ignore the trim Gauge,...
I do... 'ell, I don't even have 1, it's pretty much meaningless...

As for the Tach, just because it's original, don't make it Right,...
Cross check it with a Known accurate Tach...
I use my timing light, as it has that function...

 

[popey]

Re: rpm?

Thanks a lot - will pay attention to find out.

 

[popey]

Re: rpm?

I was out today and tried it out. Left the trim in a neutral position, no ventilation, stable in the waves, no jumping. Might be, that the top speed is slightly lower, but that I don't care, it is more than fast enough. I guess, it is difficult not having clear trim positions, but only the engine to pull up or down. But seems to be ok - thanks!