RPM minimum

manyboats said:

So when a boat is burning 5gph and at WOT (propped correctly) and burns 10gph at WOT it is at 50% load. It's "running your boat at 50% load or running your engine 1700rpm at 50% load.

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Where this fails is lets say you are trying to run with a massive load of barnacles on the prop. Push it up to 1700 and that is all it does. Lets say at 1700 full power is 7.5gph, and at normal rpm full power it is 10gph. That would calc out at 75% load, even though engine can't make any more power.

Still not clear to me how the various mfr's actually figure this.

With regard to the Ford of England Dorset diesel, the base engine for the FL120, I will never forget what we were told by a chap we were introduced to during one of our narrowboat trips in England. He had worked for Ford in their engine division during the the time the Dorset and Dover engines were developed and in production. This is his direct quote:

"The Dorset was a bad engine that we fooled into thinking it was a good engine by using it in applications that didn't overtax it."

We had recently bought the cruiser we have today, and it has two Dorset's (FL120s) in it. There wasn't anything we could do about it at that point, so we have operated them in the manner we were advised to operate them by people with an intimate knowledge of them. They have worked flawlessly for us for the last 16 years, although I must admit we are always a bit amazed, knowing what we know about their history, every time they start up when we push the start buttons.

We have come close several times to changing them out but something more important came up each time. So they're still there, hammering away under the floor. But we're glad we have two of them and not just one.

Ski,
I think we've been using the wrong word/expression.
Power output or something similar may be a better choice.
When I think of load I think of how far I've got my foot into it going up a hill in a car. Not max power output.
Or we could just say "I'm running at about 50%" But that would get all kinds of subjective stuff mixed in like noise and throttle position. My 50% rpm is 1500rpm but my boat is making far less than 50% power at 1500. It probably would be more like 25 or 2600rpm.

Marin said:

When our boat was new to us I occasionally got doing things too fast and shifted into gear at the too-high rpm of about 1000. The difference between that and proper shifting at 650 or so is pretty significant. At 1000 rpm there is a definite "shock" that can be felt throughout the boat.

At 650 the only way one knows the shift into gear has occurred is the boat starts moving. There is no bump, no clunk, no shock, nothing at all.

That tells me that all those whirlybits down in the engine room are a whole lot happier with me shifting at a nice low rpm than at a higher one.

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Thanks Marin,

It was a pleasant surprise to return to the internet world and see your back. I really appreciate your summary of the Lehman engines.

Maybe my experience can help put some light on this issue. My SP135 idles about 600 to 700, but it's not a happy idle. It's rough. So as soon as the engine starts, I raise the idle to 8 or 900 and it's so smooooth.

Then when I get underway, I make sure the throttle is at its min stop and put it in gear. Clearly, to shift it at higher rpms, as I have done a few times in moments of PANIC, is not good.


I also appreciate your sharing your 2.5 sec observation. My gut told me it was about that and I always try to give it at least a few seconds, unless I panic as mentioned above

I'm back from the Supertramp.Ich have the idle speed reduced to 680 RpM. At 650 RpM the engine runs a little poor because i have mounted to the engines the air compressors for the stabilizers.
With 680 RpM switches the transmission smoth and quiet.
Supertramp has the Transmission Velvet Drive 1013 /CR2

And now the max RpM ( max is 2600 RpM )
Under way the cruising speed is 7,5 Knots with 1700 RpM, ( 1700 RpM is the max Torque from the FL 135 SP, the consum is 2,3 Liter Per Miles )
__________________
Norbert

Amazing how we drifted from Minimum RPM to Max RPM. But, no bad thing.
I was taught gear changing is not Fwd>Reverse and vv; rather it is a deliberate Fwd>Neutral>Reverse, involving the pause others referred to.

BruceK,
That's the way of conversation. We do it all the time.

Most people don't even think of starting a new thread much less do it. And I don't have a problem w it until I go looking for a thread or information. We could have a few more mods and let the mods do it but there would be a lot of definitions on where TC warrented a new thread.too many opinions may get involved.

Has any forum found a solution to this? On the Willard site there is only one thread. Now there's some thread creep.

You're spot on re shifting.

Just a note reg. the idle speeds. I hope we are all talking photo timed verification. If not then do we know what we are talking about? I would tend to agree with the owners manual recommendations. If shifting at the proper rpm setting is causing slamming I would be seeking the advise of a knowledgeable mechanic with plenty of transmission experience. I don't think the answer is to significantly lower the rpm.

manyboats said:

...

Most people don't even think of starting a new thread much less do it. ...

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More than once I've taken a quote from one thread to start another. I should do it more often.

I just started one on Continuous Rated Engines, figuring that was a drift too far. But, threads go where they go, because people find interesting tangents, and that`s no bad thing.

markpierce said:

More than once I've taken a quote from one thread to start another. I should do it more often.

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I thought "starting" the last single vs twins debate cured you of that









Sorry for that thread split btw Mark

So on our FL120 today I noticed the idle reads 650 on the ancient tach. at start-up. At 1700 rpm the Standard Horizon plotter says I'm going about 8 knots in my semi-planing hull. I have never pushed it harder than that so I have no idea what would happen. Probably Armageddon.

I think they fooled a lot of people into thinking it's a good engine! Maybe because it has a pretty good reputation as a big iron, dependable, efficient engine. I had a single FL120 in my CT35 and a pair of them in Lollygag. It didn't work in trucks but it's great in boats!

Apophyge said:

I think they fooled a lot of people into thinking it's a good engine!

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The retired Ford fellow I quoted didn't mean they fooled people into thinking it was a good engine. He meant they fooled the engine into thinking it was a good engine.

Marin said:

The retired Ford fellow I quoted didn't mean they fooled people into thinking it was a good engine. He meant they fooled the engine into thinking it was a good engine.

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“I think I can. I think I can. I think I can. I know I can.”


― Little Engine That Could
acknowledgement to Wilbert Awdry

The FL 120 moto.

eyschulman said:

. I don't think the answer is to significantly lower the rpm.

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No one was suggesting that.

With any reciprocating engine the designers select idle and cruise to be at RPM that balance well and feel smooth..

Apophyge said:

I think they fooled a lot of people into thinking it's a good engine! Maybe because it has a pretty good reputation as a big iron, dependable, efficient engine. I had a single FL120 in my CT35 and a pair of them in Lollygag. It didn't work in trucks but it's great in boats!

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I've been on the Supertramp only two main engines, which are Ford lehmann.
These are the best engines I've ever had in the Supertramp
________________________
Norbert

manyboats said:

Engines are designed to do everything I've talked about and more.

If you've got a weak engine and need to treat it like an old lady so be it. But the rest of us can run our engines fairly hard and the wear isn't worth talking about

I think most engines are rated to run at WOT for at least 30 minutes to an hour. And probably run 85 or 90% after that continuously.

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I love your statement, Manyboats. So true! This has been an interesting thread. It is impossible for me to believe that occasionally running a marine diesel at WOT will cause damage.

I bring my diesel up to WOT in gear for one or two minutes at least once per month to ensure all is well and I can a reach my target of 3400-3600 RPM. I may be in an emergency situation where I actually need the HP; and, knowing my prop is pitched correctly (not under-propped), I can confidentially deliver full HP at maximum RPM! My Volvo Penta manual suggests not running WOT for more than 10-15 minutes as I recall, which is a long time in my book and this is probably conservative.

Thank you VT and see new WOT thread to avoid further TC.

supertramp said:

I've been on the Supertramp only two main engines, which are Ford lehmann.
These are the best engines I've ever had in the Supertramp
________________________
Norbert

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And they will be for years to come.

I can't even believe there is any question that Lehman's make good marine engines. If the original builders had to "fool" the engine into believing it, then they did a heck of a job of it.

Are Lehman's the latest and greatest? No.

Are they long running, easy to maintain, forgiving of abuse, fairly fuel efficient, etc. engines? I'd say those questions were answered in the affirmative years ago.

If none of that is true, somebody show me all the posts somewhere where there are lots of complaints and questions about Lehman engine failures and repeated systems issues?

The Ford Dorset diesel is a reliable and long-lived engine IF it's operated at a relatively constant rpm at a moderate load in the 1500 to 1800 rpm range. That was the Ford guy's point. Run it that way-- which is the very definition of marine service in a cruising boat--and it's an excellent albeit outdated, noisy, overweight, and polluting-- engine.

Run it harder than that--as in heavy truck service which is what Ford designed it to do-- and it is, in the terms of the Ford engineer I met, "complete rubbish."

BTW, Lehman had nothing to do with making these engines. They are solely Ford of England products. All Lehman did was, like a lot of other companies on the planet, design a marinization kit for it. Lehman had nothing whatsoever to do with the design or manufacture of the base Ford engine.

So I'm not saying the FL120 is a bad marine engine. It's not as evidenced by the thousands of boats in which it has given excellent service as Capt. Bill points out. The Dorset also did great in agricultural service in the lower powered tractors and combines of the day.

Where it's a "rubbish engine" is in applications that force it to run hard and fast. Operate it that way in a boat and one runs the same risk of problems as the truck operators who were unfortunate enough to have one of these engines installed in their vehicle.

I'll try to be move specific in the future. But I'm guessing everybody knew what I was talking about when I used the word Lehman where I should have perhaps used Ford.

As to them being complete rubbish as truck engines, who cares. Last time I looked, most trucks don't float very well.

Capt.Bill11 said:

As to them being complete rubbish as truck engines, who cares. Last time I looked, most trucks don't float very well.

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It's only relevant if a boater who has these engines runs them hard to get more "modern" speed out of their boat. I've met over the years three or four people in our marina who did this. And in each case, they were bemoaning the fact their "reliable" FL120s had failed catastrophically in some manner.

Marin said:

It's only relevant if a boater who has these engines runs them hard to get more "modern" speed out of their boat. I've met over the years three or four people in our marina who did this. And in each case, they were bemoaning the fact their "reliable" FL120s had failed catastrophically in some manner.

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Maybe that statement is more to the point. We have covered this ground in the past. ?
Without a doubt- most any Lehman is GREAT in a "trawler type" application. If you want a motor yacht... KEEP SHOPPING!!!


1983 Present 42 Sundeck
Twin Lehman 135's

So Marin,

You've got a graveyard all arranged for your Lehman engines do you?

Better make room for your Bruce anchor too.

As to them being complete rubbish as truck engines, who cares. Last time I looked, most trucks don't float very well.

True , But smaller trucks are driven by folk that do not usually own the truck.

If a truck engine can live with constant abuse , overreving , or lazy shifting and lugging , it should make a good candidate for marinization for a go slow cruising boat..

Sport Fish , run on the pin ,must go to industrial rated engines .