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Old 04-27-2014, 06:57 AM   #101
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Originally Posted by eyschulman View Post
I

When it is snotty I change gears and pop out of my usual hull speed travel.

Literally? Multi-ratio marine gears? Or did you mean that figuratively?

-Chris
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Old 04-27-2014, 07:13 AM   #102
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We keep being told that we will quickly ruin big diesel engines cruising at the speed that we enjoy, even by mechanics that I have known for years.

A few others have commented on this point, but I think it's worth emphasizing... that viewpoint is sort of an over-abbreviation of a not-so-complicated issue. And it's likely not well documented, in any case.

If you run "big diesel engines" at low RPMs but also at their optimum operating temperature, no matter what the resulting boat speed is, they'll probably last forever. Or if they're designed for 20K hours before major rebuild (for example), maybe you'll only get 19K hours.

Run the boat slow all day, give it a few minutes of higher RPMs while under load at the end of a long run, enjoy your sundowners.

IOW, it's no big deal.

IOOW, if you find a boat that otherwise suits you, but it has engines larger than you might have chosen... that doesn't have to be a big impediment. They are what they are. Enjoy the boat, even if it might cost you an extra .2 GPH when you run it.

FWIW, our diesels will achieve optimum operating temperature after about 10 minutes of idling while underway... at about 625 RPMs and about 5 kts. When we boost that to about 725 RPMs after the engines are warmed up, we run at about 6 kts... and I can do that all day long at less than 2 GPH total. In a boat designed for a 22 kt cruise speed.

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Old 04-27-2014, 11:08 AM   #103
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Ranger,
You are confusing engine coolant temp w valve temps, piston temps, cylinder temps ect.

Coolant temp is kept artificially high by the thermostat. If you took the thermostat out the coolant temp would be MUCH more representative of the actual temp of the engine parts that need to be hot enough to embrace the kind of luberication that promotes long engine life.

Forget about what the coolant temp is as it's not represetitive. Diesel engines need to work hard to get their internal engine parts significantly hot enough for healthy long term operation.

In my opinion it probably takes about 1/2 an hour of steadily increasing load to get (for all practical purposes) heat soaked. True stabilization (in temps) of all engine parts may take well over an hour. It only takes 3 or 4 minutes for my boat Diesel engine to achieve a coolant temp of 180 degrees .... At an idle.
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Old 04-27-2014, 11:36 AM   #104
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And for that, you get the title of "Guru?" Maybe I should rethink the whole trawler thing.
I am one of the rare breed that has one foot in sail.. and the other on trawlers..
15k offshore blue water under sail..
I speak from experience.. ever go to a pot luck with a bunch of sailors?
you would understand the comment...

the attached pic was taken during a delivery, the pic was taken about 600 miles East of Florida... on of all things .. A sailboat!

Please don't tell anyone though.. I have a reputation to uphold.

The comment was meant to poke fun at the sailors..

HOLLYWOOD
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Old 04-27-2014, 11:36 AM   #105
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Ranger,
You are confusing engine coolant temp w valve temps, piston temps, cylinder temps ect.

In my opinion it probably takes about 1/2 an hour of steadily increasing load to get (for all practical purposes) heat soaked. True stabilization (in temps) of all engine parts may take well over an hour.

I wasn't, and only meant ours as an quick example, but I see that isn't apparent the way I wrote it. Yours is a fair point and good you added that for clarification.

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Old 04-27-2014, 11:58 AM   #106
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Ranger,
You are confusing engine coolant temp w valve temps, piston temps, cylinder temps ect.

Coolant temp is kept artificially high by the thermostat. If you took the thermostat out the coolant temp would be MUCH more representative of the actual temp of the engine parts that need to be hot enough to embrace the kind of luberication that promotes long engine life.

Forget about what the coolant temp is as it's not represetitive. Diesel engines need to work hard to get their internal engine parts significantly hot enough for healthy long term operation.

In my opinion it probably takes about 1/2 an hour of steadily increasing load to get (for all practical purposes) heat soaked. True stabilization (in temps) of all engine parts may take well over an hour. It only takes 3 or 4 minutes for my boat Diesel engine to achieve a coolant temp of 180 degrees .... At an idle.
That's an interesting perspective. What is causing the coolant temp to reach that 180 degrees? Why do the engine manufacturers spec coolant temp as an particular operating specification? Once the thermostat is open, what would cause the coolant temp, pre-heat exchanger to be radically different than the engine temp? Just idle curiosity here, no hidden agenda.

Personally, my engines are spec'd to be in the 170-180 coolant temp range ideally, max about 200, and do not get to any of those temps unless the boat is underway. Thermostats open at 170. But then I would never idle them at no-load long enough to see if I could get them to 170. I like to take an infrared thermometer and measure oil temp at the filter on a regular basis, as well as coolant temp before it goes back through the heat exchanger. Usually around 210 (running about 20-30% load), right where DD says it should be.
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Old 04-27-2014, 12:08 PM   #107
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I am one of the rare breed that has one foot in sail.. and the other on trawlers..
15k offshore blue water under sail..
I speak from experience.. ever go to a pot luck with a bunch of sailors?
you would understand the comment...

the attached pic was taken during a delivery, the pic was taken about 600 miles East of Florida... on of all things .. A sailboat!

Please don't tell anyone though.. I have a reputation to uphold.

The comment was meant to poke fun at the sailors..

HOLLYWOOD
Wifey B: One foot on sailboat, one on trawler. Must be freaking painful when the boats head in the opposite direction.........owwwwwww

Poking fun....bad boy.....you should half know (as half sailor) they're a sensitive breed. Of course not sure the OP knows yet he's entering a world now where powerboaters laughing at sailors and then his sailor buddies going to poke fun at him for crossing to the dark side.
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Old 04-27-2014, 12:23 PM   #108
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There are lots of boats out there with high hp engines running hull speed and very low engine load. Dock lore has it these engine should fail because they are not loaded enough. Actual experience has proven that wrong. In over 20yrs making my living with marine diesels, I have not seen a single engine problem attributed to hull speed running. Not a single one. Lots of blown engines from hard running, none from slow cruising.

I have seen some gensets glaze cylinder bores due to too light a load, but not main engines.

Is it optimum for the engine? Maybe not. But experience has shown the risk is low or non existent.

In the case of my personal boat, in about 11000nm of travel, if I ran 20kts I would have burned about 6000gal or $24k of fuel. Most of that travel was at hull speed at 3.9nm/gal, about 2800gal or $11k of fuel. If I did glaze the kits, it costs a few $k in parts and a few days to swap. $13k in fuel savings would be worth it. But the engine is absolutely fine with minimal blowby and minimal oil use.

And the ability to run at 23kts to actually get somewhere is pretty valuable.

I figure the big engine penalty while running at hull speed is probably about 1/2gph over using a smaller engine at a higher load. Worth it to me.
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Old 04-27-2014, 01:36 PM   #109
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Ski is right on the ball. Diesel motors do not die early from lower rpm the contrary. Many experienced modern mechanics agree with Ski I say that based on about 5 years of my interest in this matter. What kills diesels early is high rpm-overload-overheating-poor exhaust geometry-poor maintenance and dirty water soaked fuel. Add salt to the list part of marine ageing.
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Old 04-27-2014, 01:43 PM   #110
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Ski is right on the ball. Diesel motors do not die early from lower rpm the contrary. Many experienced modern mechanics agree with Ski I say that based on about 5 years of my interest in this matter. What kills diesels early is high rpm-overload-overheating-poor exhaust geometry-poor maintenance and dirty water soaked fuel. Add salt to the list all part of marine ageing.
Just as further measure, diesel manufacturers use hours as a convenient means of estimating service requirements and engine life. However, they feel that gallons of fuel used is a more reasonable means.

Even the need to occasionally open the engine up a bit when running at very low rpm's isn't a matter of engine life, just a matter of keeping it running well at the low rpm's and preventing any build ups of lubricants or particles within.
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Old 04-27-2014, 02:28 PM   #111
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FD engines last longer as they don't have to go as fast.

There's no such thing as revolutions per minutes. It's about revolutions taking place in one min.

And our boats are powered by engines .. Not motors.

Been wanting to say that for years.
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Old 04-27-2014, 02:55 PM   #112
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rjtrane's boat is powered by a motor. But I don't know of any others.

Does that mean I have an enginesailer?
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Old 04-27-2014, 03:04 PM   #113
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FD engines last longer as they don't have to go as fast...
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Old 04-27-2014, 03:05 PM   #114
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FD engines last longer as they don't have to go as fast.

There's no such thing as revolutions per minutes. It's about revolutions taking place in one min.

And our boats are powered by engines .. Not motors.

Been wanting to say that for years.
Why is it a motor if it's an outboard and an engine when it's inboard?
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Old 04-27-2014, 03:07 PM   #115
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rjtrane's boat is powered by a motor. But I don't know of any others.

Does that mean I have an enginesailer?
No. Enginetraveler.
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Old 04-27-2014, 03:26 PM   #116
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Hmmm, so what's with referring to them as Motor Vessels or motorboats or motoryachts?
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Old 04-27-2014, 03:33 PM   #117
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Hmmm, so what's with referring to them as Motor Vessels or motorboats or motoryachts?
PS: Recovering from this Achilles Tendon rupture has given me way, WAY too much time on my hands as evidenced by posts like this. No boating makes George a dull boy. Watching all the boats go by on the Neuse on this beautiful spring day. Two months down and about two to go....aaauuuuughhh!

There. Thank you for listening.
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Old 04-27-2014, 03:51 PM   #118
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PS: Recovering from this Achilles Tendon rupture has given me way, WAY too much time on my hands as evidenced by posts like this. No boating makes George a dull boy. Watching all the boats go by on the Neuse on this beautiful spring day. Two months down and about two to go....aaauuuuughhh!

There. Thank you for listening.
Well, you always wanted to have an arm like Dan Marino, but somehow that got confused and now you'll have a foot like him.

How is your recovery going?

Four months, no boating. That is misery.
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Old 04-27-2014, 04:50 PM   #119
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Too much time on my hands?

Nail on the head as I've been quite sick foe 3 or 4 days.

You guys are OK. You responded exactly the way I expected.

That was pointed out to me some time ago and I finally started feeling silly say'in rpm's.

But of course I still say outboard motor and motorcycle.

When's Mark coming back. I think I miss him.
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Old 04-27-2014, 05:43 PM   #120
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Well, you always wanted to have an arm like Dan Marino, but somehow that got confused and now you'll have a foot like him.

How is your recovery going?

Four months, no boating. That is misery.
Yes I am definitely out for the playoffs. As a buddy said, "when you come back, we will have to reshape your game because from now on, you won't be able to simply rely on pure athleticism".
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