Max Engine RPM on R29

[Nancy & Hugo Shaw]

We have a 2014 Ranger Tug 29 with the Volvo Penta engine. When fully loaded with water and fuel + 2 people on-board what should I expect my max engine RPM to be. I get 3250 - someone told me it should be higher? Apppreciate any feedback.

Thanks

 

[adodson]

Volvo Penta would like to see an end user RPM of 3400-3600 RPM. Most people will never run their boats at that high of an RPM but, if you can only achieve 3250 at 100% engine load your engine is working harder than it should and burning more fuel than it should at various RPMs.

 

[Levitation]

Before blaming the engine you need to insure that the bottom and prop are spotless. No barnacles, crud, line wrapped on the prop shaft, etc. which causes drag.
Then you need to pull your truck/trailer up to the boat and empty it of all the gear. I would even weigh the gear to see the total load, but that's me :mrgreen:
Make sure the fuel filter is new and clean.
Now take it out for a run in three directions 120 degrees apart and record the max RPM on each heading.
If you are still low on RPM at full throttle then the prop needs to go to the prop shop, most likely.
Last thing I would attack would be the engine/exhaust system, for several reasons. First would be the cost of having so called 'experts' mucking around with your engine. A lifetime of dealing with 'experts' has left me - Once Bitten (many times) and Twice Shy (the 2 is an exponent)
Another reason is that an engine that runs and sounds OK but misses full RPM by roughly 5% does not have major internal problems - though it could have a fuel obstruction, an intake air obstruction, or an exhaust obstruction.
Let us know how it turns out.

 

[Nancy & Hugo Shaw]

Thanks for the advice -I will do the checks you suggest.

I don't think it is build up on the hull/ trim tabs as I have had this lower engine RPM right after getting the bottom cleaned.

I have heard that the max engine RPM under full load at 3250 may be ok - but other have told me the volvo should be up at 3500.

 

[tugnnaweigh]

The acknowledged standard is boats must be “propped” to achieve the rated maximum engine RPM at WOT. If not, they say you’re “over propped” and straining the engine throughout the RPM range.

It’s likely you can get your engine to demonstrate its actual WOT RPM capability by placing the transmission in neutral and advancing the throttle fully. My guess it will make the factory spec, here 3500?

Once you know the engine does achieve correct WOT RPM you’re just working at quantifying the amount or % your off, someone above said 5% currently?

On your throttle runs take advantage of the “load to throttle percent” reading on the instrumentation, another way to quantify the percent your off.

Then you have to mix in “duty cycle” ratings, (80% or so?) your typical operating/cruising RPM, water conditions, current weight of vessel, comfort of the passengers, moon phase, etc. etc.

This brings you to the typical RPM most folks tend to run at being around at 80% or so of maximum and that would be 2800?

I’d not worry until RPM drops more than 10%, these diesels are up to the task. Keep in mind you have a 20% increase in weight, (fuel/water is 220 gallons total times 8 plus gear and two people: say 2000 pounds or so added to a dry weight of 9750) for only a 5% decrease in RPM.

However if you do choose to chase the RPM drop, they say de pitching a propeller one pitch results in 200 or so more RPM for each de pitch and also de cupping can help too, just not as much. Perhaps at your next haul out when you need a bottom job? Hope this helps, rich

 

[adodson]

The engine will not reach full RPM if you put it into "throttle only" mode, I think that the max RPM the system allows is 1500. While you are only missing 250-350 RPMs the engine is working harder through the entire RPM range than it should; is it enough to damage the engine, not likely. Tugnnaweigh has a good suggestion, at the next haul out figure out if you want to take an inch or two of prop out, an inch is usually 100-200rpms. Here is a link to the Volvo Penta RPM recommendation for your reference. It is a dropbox link since I couldn't figure out how to get the PDF in this message.

https://www.dropbox.com/s/ino5v3xee6leu ... s.pdf?dl=0

Note: Volvo Penta says New Boat full load = Boat loaded to full capacity (fuel, water, gear, canvas, bottom paint etc...) Passengers load to full capacity. When we test new boats we do a full load capacity and only have your typical passenger capacity instead of full passenger capacity.

 

[knotflying]

There are several variables that affect your RPM including salt or fresh water, altitude on inland lakes, weight, bottom paint type, bottom growth, trim tab settings, current, wind etc. Over time my R-27 with the Yanmar has exceeded the 4,000 RPM max by 40 and has been as low as 250 below. As long as I am within the historical RPM's and I take into consideration the other variables at the time of evaluating performance I don't worry about the degradation of the RPM's. If it starts to fall out of the limits under specific circumstances than I would do a little investigation to determine the cause.

 

[rt11002003]

Some of my comments have been touched on already. Max rated rpm is based on the engine design. It is a parameter on which performance is based for a specific load (boat). Usually a prop is selected to allow the boat to reach that rpm level. Some mechanics recommend a prop that allows 200 rpm more, to allow for accumulation of growth and things that get added. That 200 rpm prop adjustment reduces engine load across the entire rpm range. Any prop adjustment affects the entire rpm range, either loading, or unloading the engine.

Maximum rpm is the level the engine will reach before a governor cuts in. You can get that level by disengaging the gearbox and advancing the power lever. I've owned a couple of R21EC's using both Volvo and Yanmar engines. On both engines maximum rpm is/was 4,000, plus approx. 50 rpm. On my current R21EC, Volvo engine, maximum attainable rpm, under load, is a shade over 3,000. Hopefully, that number is close to max rated rpm; it should be, if propped correctly. My older R21EC's, Yanmar engines, pulled slightly less rpm than max rated. Never a problem.

I owned an Albin trawler with a Yanmar engine. It ran exactly at max rated rpm.

Most mfg's suggest operating their diesels at anywhere from 80 to 90% of max rated rpm, depending on mfg and engine.

Ranger does a good job selecting the appropriate prop. However, I'd think because of mfg tolerances, optional equipment selected, "stuff" and people added, one should NOT expect to attain max rated rpm unless the prop mechanic"tweeks" it some.