Cruising RPMs

[Solitude]

Find your 75-85% mark but....

(3) Are there abnormal vibrations or
noise?
Do not operate at speeds which produce
violent vibrations. Depending on the hull
structure, engine and hull resonance may
suddenly become great at a certain
engine speed range, causing heavy

vibrations.

When operating the engine at low
speed for long periods of time,
race the engine once every 2
hours.

Note: Racing the Engine
With the clutch in NEUTRAL,
accelerate from the low speed
position to the high speed position
and repeat this process about 5
times. This is done to clean out
carbon from the cylinders and the
fuel injection valve.
Neglecting to race the engine will
result in poor exhaust colour and

reduce engine performance.

[Gulfislander]

Thanks everyone. This has been helpful. I have found over the last 2 years of owning this boat that the "sweet spot" is around 2800 rpm's. She seems to like this. I just wanted to confirm that I was doing the right thing. Thanks again.

[Bash]

My 4JH3-TE has a continuous output level of 3,700 RPMS. The 4JH4-TE that replaced it a year later has a continuous output level of 3,100 RPMS.

Best cruising strategy for keeping Yanmars happy is to find the continuous output level in your owners manual and run at 80% of it.

[Tellie]

Originally Posted by neilpride

1200 rpms for charging bateries in a yanmar sounds to me wear and tear in the long term, what about 1500 rpms??? Cheers.

It's not just a diesels rpms, it's the load. Most alternators just can't provide enough load by themselves. If they could the engines performance in gear would suffer.

[maxingout]

We cruise at 2200 to 2500 rpm on our 3GM30F Yanmars. We have 4500 hours on each engine.

[robboa]

Originally Posted by GordMay

From Yanmar Help

Goto ➥ Yanmar Marine Engine Help

Website long gone - Here is the content I recovered.
---
Overview - Engine Operating Guidelines
If you forget to turn on the raw water supply before starting the engine, put the engine key on the sea cock every time you turn it off.
How long should I warm up the engine for before moving off?
Fresh water cooled engines: Today's engines do not require long warm up periods. By the time you start the engine, check all clear, cast off and get out of the marina or in a clear area the temp will be over 60deg C, 140deg F, you can apply full power to get on the plane. Displacement vessels can go straight to cruising power once clear of the marina.
Raw water cooled engines: As the operating temp is only 55degC, 131degF, provided the engine will keep running in gear, the clutch can be engaged. Apply cruising power about 5 minutes after you start moving.
All engines: Prolonged no-load operation of the engine may cause it to blue/gray smoke at low rpm with an associated increase in oil consumption. For every 3-5 hours low load operation (trolling) or no load operation (running the fridge or charging batteries) should be countered by 10-20 minutes near maximum continuous rated rpm.

When increasing engine rpm take about 10 seconds to move the throttle lever between low load and full load.
Let's cut to the chase..... If you want the engine to last past Christmas!

For prolonged running, a pleasure boat engine a good operating speed is around 85% of maximum continuous rated RPM (see the engine data plate)
assuming the propeller size is correct and the engine can reach maximum rpm).
See this list for approximate rpm:

GM - 4JH - 3/4JH2 series - 2900rpm
YM series Depending on WOT rpm - 2600-2900rpm
4LH and 6LY series - 2650rpm
6LP and 3/4JH3 series - 3000rpm
3/4JH4 series - 2400rpm
6CX series - 2200rpm

Operating for extended periods below 80% rpm may increase longevity but the cylinder bores could glaze causing an increase in oil consumption and blue smoke especially when new. If you're operating these engines COMMERCIALLY, different rules apply. For engines without a tacho, run it where it sings best. If the ship is shaking and growling, alter the RPM. If the engine VIBRATES unpleasantly at a particular rpm, don't operate it in that rpm band or it will eventually break! Yanmar TACHOMETERS usually read about 100rpm too high at maximum rpm so don't be pedantic about lining up the needle exactly. The latest Yanmar panels combined with combined tacho & LCD digital hour meter as fitted to some GM series and all YM and JH4 engines that have a VDO electronic taho that operates from the flywheel sensor on GM series and from aletrnator pulse on other models.
You may note that the MAXIMUM RPM of your engine under load is higher than the figure I have given above
USE THE MAXIMUM RPM IF YOU ARE IN TROUBLE, or to get the boat on the plane, don't be frightened, the engine will handle this for an hour provided it has been installed correctly. Once out of trouble or on the plane, reduce rpm to 85% for better fuel consumption and longer engine life.

I once had a complaint from a customer that his engine used too much oil.(3GM30C) The boat had been shipped to the Kenwood Cup in Hawaii and sailed back to New Zealand afterward. I found out by chance ( yes, that overheard conversation in a bar ) that the boys had been becalmed and motored home from the Fiji Islands with their foot literally hard down on the go lever for 1200 Nm! I gently explained to the owner that if he lined up his Porsche at the end of the motorway, selected low and put his foot hard down, how far did he think he'd go before the engine died, 1200 Nm? We refilled the oil pan and the engine didn't require any further servicing. I'm still impressed!