RT 21 EC Max RPM way up there

[Two killicks]

I was doing a research in the forum this weekend to compare my max RPM with the other RT 21 max RPM with the Yanmar engine. I noticed that mine is way up there! when I cruise, my Max RPM is 3800, I noticed that most of your tugs are between 34-3600. Is this something that I should be worried about?

I try to go at WOT for 5 minutes every hour, as recommended. I wonder if I should just lower the rev to 34-3600 rpm... or go all the way because of my set up?

I normally cruise at 24-2600 rpm, this keep me in the 5-6 kts range.
if I respect the 80% max load, this gives me around 3050 rpm range to operate.

What are your thought on this matter?

 

[Irish Mist]

on my 29 my max is 4000 .. that is Yanmar 6YB.

 

[rt11002003]

I seem to recall the MAX RATED RPM for that engine is 3,400, which means it should have a prop that allows that rpm to be attained at a specific boat weight (normal load on board). Usually a prop tech will have things set so that a hundred or so rpm above MAX RATED RPM can be attained to allow for the additional weight we tend to accumulate on our boats.

At the rpm you stated your engine is running at less than the desired load on it. b/t/w, whether running under or overloaded applies across the rpm range.

All this is dependent on your tach reading correctly.

That engine, with the transmission in neutral, should run at 4,000 rpm, max. +/- approx 25 rpm.

This thread has been discussed at length on this forum. Various members reported MAX RATED RPM's on their engines at a variety of different rpm's. You might want to search and see what has been reported.

 

[SGIDAVE]

I was doing a research in the forum this weekend to compare my max RPM with the other RT 21 max RPM with the Yanmar engine. I noticed that mine is way up there! when I cruise, my Max RPM is 3800, I noticed that most of your tugs are between 34-3600. Is this something that I should be worried about?

I try to go at WOT for 5 minutes every hour, as recommended. I wonder if I should just lower the rev to 34-3600 rpm... or go all the way because of my set up?

I normally cruise at 24-2600 rpm, this keep me in the 5-6 kts range.
if I respect the 80% max load, this gives me around 3050 rpm range to operate.

What are your thought on this matter?

Hello Pat,

What propeller is on your tug? Probably either an Acme #224 or 650; given your higher WOT rpm, it's probably the #650. Unless you've got a 'rogue' unknown prop of some kind.

While you're checking the prop specs, make sure the prop is mounted correctly. That is, ensure there is no slippage o the shaft - is the key is in the keyway, nut tight, etc.

Finally, the Yanmar 3YM30 engine is supposed to reach 3600 rpm WOT. Theoretically, it is to be propped such that a new boat reaches 100-200 HIGHER rpm to allow the "loaded" boat to continue to reach 3600. This information is in the owners manual which is available on line if you didn't get one with your boat.

In my experience, the Acme #224 allows WOT of 32-3300 rpm whilst the #650 allows more like 3700. I prefer my boat's handling with the #224 although it is, academically speaking, OVERpropped somewhat. In practical terms it works out well. There are lots of these engines used in Genset applications where they are governed at 1800 rpm, so I don't worry about the 300-400 rpm WOT deficiency.

dave

 

[rayzickrick]

Your RPM is quite a lot higher than mine.
For my 2014 21EC with the Volvo D1-30
my RPM at WOT is 3150 with gear, 2 adults,
and a full tank of fuel.

 

[Two killicks]

Dave, I will check the spec on the prop in the spring when I go to get my tug out of winter storing.

 

[tlkenyon]

Max unloaded RPM on my Yanmar 30 is about 3900. I can get about 3800 max while underway and lightly loaded. Yours seems to be about right on the mark.....

 

[Two killicks]

I looked at the prop this weekend, there is nothing written on it to tell me what it is... the prop is tight on the shaft.

On the engine information plate there are two # written;

continuous power Kw 19.4/3489
fuel stop power kw 21.3 3600

is this the # that I should use to calculate my 80% for my cruising speed regardless of my actual max rpm of 3750 rpm?

 

[rt11002003]

The 3600 rpm from your data plate is "Max Rated RPM" as previously mentioned by SGIDAVE. Using the normal rule of thumb of 200 rpm more than Max Rated RPM to allow for additional accumulation of "stuff", you're spot on at 3800 rpm.

I'd assume the 3480 rpm on the data plate is the mfg. suggested max operating rpm, IFF you were pulling the 3600 rpm. Since you're pulling 3800 rpm, you could probably use the ratio of 3480 divided by 3600 and multiply it by 3800 rpm to get a MAX continuous RPM.

However, for long term continuous operating rpm, I'd go with 80 percent of the 3800 rpm.

Diesel engines like to operate under load at a steady rpm. But, they're not thrilled to operate at max rpm for extended periods.

 

[Two killicks]

Thanks for answer Gene much appreciated! This would give me a 3000 rpm cruising rpm if at 80% of 3800. Perhaps I was running the boat rpm too low, at 22-2400 rpm lately it is so more quieter at 2200...