Proper Cruising RPM's Please

[GMUGMU]

I have a Parker 2300 with a yamaha 300 (142 hrs). What would be considered a cruising RPM range and a max RPM range? I tried other internet sources but came up empty. I did see a recommendation of 3800 RPM as a max cruise RPM. Many thanks in advance

 

[warthog5]

It varies....Load on boat, sea state..... 3800 is a little low, but if you can get away with it....Great. We would usually run it between 4200 & 4400 But it was a 2530....with a Crows nest....[More resistance]

Your question has a LOT of variables....

 

[GMUGMU]

Thanks for responding. I understand that 3,800 rpm would result in more speed if the boat has less wait on it and is in favorable seas. Lots of variables indeed. I am under the impression that any given outboard would have a "safe/healthy" cruising rpm range. That is, regardless of vessel or other variables, there is an ideal cruising rpm range for outboard motors. Is this not the case? Speed is probably dominant in most discussions, but I would think that rpm is a more important parameter in proper outboard care and longevity.

 

[Andy]

Thanks for responding. I understand that 3,800 rpm would result in more speed if the boat has less wait on it and is in favorable seas. Lots of variables indeed. I am under the impression that any given outboard would have a "safe/healthy" cruising rpm range. That is, regardless of vessel or other variables, there is an ideal cruising rpm range for outboard motors. Is this not the case? Speed is probably dominant in most discussions, but I would think that rpm is a more important parameter in proper outboard care and longevity.

Hi GMUGMU, I don't know if this will help, but one 'rule-of-thumb' tossed around by local O/B 'guru's' is that a 'good cruise' rpm for a 4-stroke o/b is around 25% off the top rpm. (of course the rpm will vary a bit with different prop selections), For example, If your top rpm is 5800.....
5800 rpm X .75 = 4350 rpm.
And in reality, with our Yamaha 300 on the 2520, we have found 4200-4400 to be our 'sweet spot'.
............. If what you've been hearing about is the importance of rpm with marine Diesel engines, yes, they are a different animal when it comes to Diesel's; the rpm is more critical. (And I mention this because we have found some recent Parker folks here with diesels). With the diesels it is best to run "around 12%" off the top rpm. For example, our last boat had a diesel that topped out a 2650 rpm. The 'best' cruise-rpm was 2650 X .88 = 2332. We 'cruised' at 2200-2300 rpm most of the time. Running Diesel's at too low of rpm can make them run 'too cool', (the engine temp is critical with Diesels) which causes a lot of issues like 'coking' up the engine, fuel blow-by, injector issues, engine oil temp and others. Even the fuel temperature effects the performance of a Diesel....

 

[GMUGMU]

Hi GMUGMU, I don't know if this will help, but one 'rule-of-thumb' tossed around by local O/B 'guru's' is that a 'good cruise' rpm for a 4-stroke o/b is around 25% off the top rpm. (of course the rpm will vary a bit with different prop selections), For example, If your top rpm is 5800.....
5800 rpm X .75 = 4350 rpm.
And in reality, with our Yamaha 300 on the 2520, we have found 4200-4400 to be our 'sweet spot'.
............. If what you've been hearing about is the importance of rpm with marine Diesel engines, yes, they are a different animal when it comes to Diesel's; the rpm is more critical. (And I mention this because we have found some recent Parker folks here with diesels). With the diesels it is best to run "around 12%" off the top rpm. For example, our last boat had a diesel that topped out a 2650 rpm. The 'best' rpm was 2650 X .88 = 2332. We 'cruised' at 2200-2300 rpm most of the time. Running Diesel's at too low of rpm can make them run 'too cool', (the engine temp is critical with Diesels) which causes a lot of issues like 'coking' up the engine, fuel blow-by, injector issues, engine oil temp and others. Even the fuel temperature effects the performance of a Diesel....

Many thanks. We're making progress do you determine top rpm buy pushing the throttle all the way forward? I have heard that you should occasionally run an outboard at top rpm. How often and for how long (pardon the change of topic).

 

[Andy]

Many thanks. We're making progress do you determine top rpm buy pushing the throttle all the way forward? I have heard that you should occasionally run an outboard at top rpm. How often and for how long (pardon the change of topic).

Yes, all the way forward. What you will see 'in print' in boat specs and such, is the term WOT. Which means 'wide-open-throttle'. Boating experts that perform the boat tests that you often see written up in boating magazines/spec sheets/ bulletins, as part of their evaluation of a boat, will most always run for a few minutes at WOT. In fact, they will jamb the throttles wide open, from a dead stop, to see how long it takes to reach plane, and how long it takes to reach 'top-speed'... (and of course noting the numbers, including top speed). They are also evaluating what the 'sweet-spot is (best cruise-speed/best mpg)... They tie fuel-flow meters into the fuel lines during the boat tests.
The 'recommendation' that we've heard about running WOT occasionally is likely a valid point as I've been hearing it for 40+ years! I've also heard it was more of a good idea with the older 2-stroke engines, as they 'run dirty' and need a 'burning out' occasionally; I've not had a 2-stroke outboard since 1975, so that might be old information; but, there are still 2-strokes operating in our area today; sturdy old beasts!..... With that said, with our Yamaha 300, I will pop NEAR WOT occasionally, well, because like you, I've heard it's supposed to be a good thing to do; if not, at least it won't hurt anything for just a minute or so.

 

[GoodChance]

Here is some data you can use to estimate your own fuel efficiency and what might be the best RPM for your best fuel economy. All of these measurements were taken in a river with minimal (no) current and minimal winds. All data is reproducible.

I have a huge Excel spreadsheet with numerous props tested on a 23 DVCC with both the 3.3l F250 and the 4.2l F300 that I'd be happy to email if you send me your email address.

 

[GMUGMU]

Yes, all the way forward. What you will see 'in print' in boat specs and such, is the term WOT. Which means 'wide-open-throttle'. Boating experts that perform the boat tests that you often see written up in boating magazines/spec sheets/ bulletins, as part of their evaluation of a boat, will most always run for a few minutes at WOT. In fact, they will jamb the throttles wide open, from a dead stop, to see how long it takes to reach plane, and how long it takes to reach 'top-speed'... (and of course noting the numbers, including top speed). They are also evaluating what the 'sweet-spot is (best cruise-speed/best mpg)... They tie fuel-flow meters into the fuel lines during the boat tests.
The 'recommendation' that we've heard about running WOT occasionally is likely a valid point as I've been hearing it for 40+ years! I've also heard it was more of a good idea with the older 2-stroke engines, as they 'run dirty' and need a 'burning out' occasionally; I've not had a 2-stroke outboard since 1975, so that might be old information; but, there are still 2-strokes operating in our area today; sturdy old beasts!..... With that said, with our Yamaha 300, I will pop NEAR WOT occasionally, well, because like you, I've heard it's supposed to be a good thing to do; if not, at least it won't hurt anything for just a minute or so.

Many thanks...I have some homework to do on my next trip

 

[GMUGMU]

Here is some data you can use to estimate your own fuel efficiency and what might be the best RPM for your best fuel economy. All of these measurements were taken in a river with minimal (no) current and minimal winds. All data is reproducible.

I have a huge Excel spreadsheet with numerous props tested on a 23 DVCC with both the 3.3l F250 and the 4.2l F300 that I'd be happy to email if you send me your email address.

great info...close to what I have experienced at 3900rpm...many thanks

 

[Swatski]

I must say, being new to this board, I find friendliness and informative tone here fantastic.
Or - maybe I'm just jaded by THT, it's been too long, lol.

Either way - great forum, thank you!

 

[GoodChance]

When I owned a 23 DVCC and the F300 (perfect combination), I would set the rpm at 3400-3600 for the best fuel economy, sound abatement, and overall cruising speed (which was about 30mph). The 2nd graphic that I posted above shows this to be true as well.

I've heard/read others say that the F300 when operated under 3600 rpms gets the best fuel economy. I forget why but there is a mechanical explanation.

 

[GMUGMU]

I must say, being new to this board, I find friendliness and informative tone here fantastic.
Or - maybe I'm just jaded by THT, it's been too long, lol.

Either way - great forum, thank you!

welcome

 

[sydngoose]

On my 2320 w single 300 Yamaha factory provided Reliance prop: my minimal planing speed is 3800 rpm at 21 mph.
Her best cruise is 42-4400rpm’s at 31-34 mph.
But sometimes I just got to let her eat at 5500rpm and 45 mph and WOT is 5900 at 49.8mph

 

[sailmaster]

Yes, all the way forward. What you will see 'in print' in boat specs and such, is the term WOT. Which means 'wide-open-throttle'. Boating experts that perform the boat tests that you often see written up in boating magazines/spec sheets/ bulletins, as part of their evaluation of a boat, will most always run for a few minutes at WOT. In fact, they will jamb the throttles wide open, from a dead stop, to see how long it takes to reach plane, and how long it takes to reach 'top-speed'... (and of course noting the numbers, including top speed). They are also evaluating what the 'sweet-spot is (best cruise-speed/best mpg)... They tie fuel-flow meters into the fuel lines during the boat tests.
The 'recommendation' that we've heard about running WOT occasionally is likely a valid point as I've been hearing it for 40+ years! I've also heard it was more of a good idea with the older 2-stroke engines, as they 'run dirty' and need a 'burning out' occasionally; I've not had a 2-stroke outboard since 1975, so that might be old information; but, there are still 2-strokes operating in our area today; sturdy old beasts!..... With that said, with our Yamaha 300, I will pop NEAR WOT occasionally, well, because like you, I've heard it's supposed to be a good thing to do; if not, at least it won't hurt anything for just a minute or so.

learned how to operate an doing the post cruise "burn" in the 60s with a LOT MORE OIL in the mix

 

[Andy]

learned how to operate an doing the post cruise "burn" in the 60s with a LOT MORE OIL in the mix

Yes! we did the same thing on my brothers 16' Larsen/65 hp Merc in the late 1960's.... be careful, we are showing our age! ☺

 

[warthog5]

.I have some homework to do on my next trip

Here's your Homework.....Run the boat at WOT , trimmed out and obtain Max RPM and Max Speed. For a min......or two.
There is your benchmark.......

Now run the boat at 3800.....Will it stay on plane? What the fuel consumption?

The Sweet spot is.....Max speed ,Lowest RPM and Best fuel mileage!

These are all played with.....Throttle setting......Engine Trim setting......Trim Tab setting.

 

[grouperjim]

For gas powered craft the rule of thumb for fast cruise is 75 percent of max output which is around 4500 rpm for an engine designed to turn 6k. The engine can run indefinitely without harm at 4500 rpm. Fast cruise is unrelated to fuel efficiency. On the hand, slow cruise is the most efficient rpm on plane.

 

[FINSOUT]

Here is some data you can use to estimate your own fuel efficiency and what might be the best RPM for your best fuel economy. All of these measurements were taken in a river with minimal (no) current and minimal winds. All data is reproducible.

I have a huge Excel spreadsheet with numerous props tested on a 23 DVCC with both the 3.3l F250 and the 4.2l F300 that I'd be happy to email if you send me your email address.

Good Chance,
I just got a 2018 2300 DV with the 300, I however don't even come close to the numbers you have seen. I have been out twice since I brought her home from SC. First trip 1.9 MPG second trip after installing a ATLAS JP 1.56 MPG. Now the second trip was offshore in 1-2' Occasionally 3's. I have a REV 4 17P prop installed and I read nothing but great things about the ECO prop. I am ready to pull the trigger to get a new prop so wIth you knowledge base, what with you recommend?

 

[GoodChance]

I sent you a message.

I recommend the Mercury ECO 18" for the absolute best performance. The Mercury Mirage or Yamaha SWS in 19" are both very close to the ECO in terms of performance/fuel economy at a much more reasonable purchase price over the ECO ...... I think the ECO is well over $1,000 now. When I was buying them, the ECO was a $550 prop just 1-2 years ago.

 

[FINSOUT]

Thank you I will do some price searching and pull the trigger on the ECO as a starting point.

/r
Eric