R21EC Over-propped?

[greenghost45]

I have a deal pending on a 2006 R21EC with the Yanmar 30 hp. I was not able to attend the sea trial but i did have a mechanic aboard. The WOT speed as confirmed on the plotter was 7 kts (sog) @ 2,900. rpm. Does this sound unusual for an R21EC? I think that the rpms should be a bit higher, thus perhaps the boat is overpropped. The prop is a 4 bladed bronze; I don't know the diameter or pitch. The mechanic felt the engine was running well and it only has 370 hours. I'm not worried that the speed is too slow for me (former sailor), just want to be sure that the boat is performing normally. Thanks for any advice!

 

[Stevan47]

HI 'Green Ghost 45': I have a 2009/2010 R21-EC with the 3YM30 Yanmar diesel engine. I have managed to get around eight knots on a flat calm day, no wind, reasonable depth (as you would appreciate, if it is too shallow you will get a suction effect which draws the hull down towards the seabed and thus reduces your speed somewhat: this is known as 'shallow water effect' and from experience usually occurs in shallow channels approaching a harbor or in rivers). I never crank out to WOT as I do not want to 'push the envelope' and risk a mechanical failure or put unnecessary stress on the engine, albeit this has never happened. The most I ever 'ring down' to the 'engine room' is 3400RPM, which as I have just mentioned, gives me a little over eight knots on a good day. I believe 3600 RPM is WOT or 'redline' - in any case, I have never exceeded 3600RPM. With full fuel and water tanks, plus ancillary equipment, provisions and a few extras I managed to get just over eight knots. I also have the four-bladed bronze ACME prop which came as fitted with the vessel. Hope this helps. Regards, Stevan

 

[greenghost45]

HI 'Green Ghost 45': I have a 2009/2010 R21-EC with the 3YM30 Yanmar diesel engine. I have managed to get around eight knots on a flat calm day, no wind, reasonable depth (as you would appreciate, if it is too shallow you will get a suction effect which draws the hull down towards the seabed and thus reduces your speed somewhat: this is known as 'shallow water effect' and from experience usually occurs in shallow channels approaching a harbor or in rivers). I never crank out to WOT as I do not want to 'push the envelope' and risk a mechanical failure or put unnecessary stress on the engine, albeit this has never happened. The most I ever 'ring down' to the 'engine room' is 3400RPM, which as I have just mentioned, gives me a little over eight knots on a good day. I believe 3600 RPM is WOT or 'redline' - in any case, I have never exceeded 3600RPM. With full fuel and water tanks, plus ancillary equipment, provisions and a few extras I managed to get just over eight knots. I also have the four-bladed bronze ACME prop which came as fitted with the vessel. Hope this helps. Regards, Stevan

Thanks for your insight!

 

[Two killicks]

Mine is a 2012 with the Yanmar too. I can go all the way to 3750 rpm with it at WOT. This give a speed of 8,5 Kts fully loaded at WOT. I normally cruise at 2200 rpm for a cruising speed of 5,5 knots.

 

[Stevan47]

Hi Pat: thanks for your input too. I will compare next time I am out on the Sound and give it a burst. Kind regards

 

[Stevan47]

Hi Pat, et al: was out on the Sound today. Wind at about 13 knots on the port quarter and a little bit choppy, but still managed to reach 9.3 knots @ 3600 RPM. It didn't maintain that speed, due to weather and current conditions I guess, however it only dropped back to about 8.9 - 9 knots overall. Eventually I throttled back to 3400 RPM and it stayed around 8 knots after that. Interesting - thought I would share. Regards, Stevan

 

[Two killicks]

Hello Stevan,

We almost have the same configuration. If my boat is not fully loaded for a long trip, I will get pretty much the same speed as you in the same RPM range.

 

[greenghost45]

Turns out, the owner during the sea trial never used WOT. He thinks that the speed of 7 kts. and 2,900 RPM was all the tug should be run. I will report back to this thread when I have had a chance to run the boat myself.

 

[Two killicks]

Yanmar recommend to run the engine at wot for 5 minutes every hours...

 

[Stevan47]

Thanks Pat, et al: I was not aware that I should run at WOT that often. I will start doing that from now on - after all, it does make sense to work a diesel hard every so often, otherwise it will tend to 'coke up'. For the record and just to confirm for my peace of mind, is 3750 RPM the official benchmark for WOT? Stevan

 

[trailertrawlerkismet]

Question....has the boat been in the water any period of time where growth of slime, barnacles or alga could be impeding the performance of the boat? If so this could be a factor.

Jim F

 

[Solitude]

My guess would be that you are running an Acme #224 prop, which Ranger had on these for some time. I understand they switched to an Acme #650 in order to achieve the proper WOT RPM, which is better for the Yanmar. I have both and choose to run the #224. We are usually lightly loaded and I like the higher cruise at a lower RPM. If we were running heavy, loaded down, more often I'd likely put the #650 on. Acme doesn't make a prop that is between these two that fits this boat.

 

[greenghost45]

We finally did get her on the water last week. It was a calm day and with 5 aboard, WOT delivered about 8.4 Kts at about 3,600 RPM. Just about bang on based on the experience of other people kind enough to reply and share their experience. And the Heatcraft heater was brilliant. Kept the cabin toasty warm on a day cloudy day with an air temperature of about 1C. Guessing that the water temperature was around 8C. Thanks to everyone who replied! 😀