New to diesel power

[GeneM]

Thanks for the contrasting opinion. I've been told by mechanics to run the engine hard. You make me feel better about my slow running. I guess heating to op temp keeps it going well.

Originally Posted by Simi 60

I'll just leave this here.




https://www.sbmar.com/articles/low-s...arine-diesels/

[mvweebles]

There are a few schools of thought for planing speed power boats

1) get the boat up in plane, then back off the rpms a bit so she maintains plane.

2) run the boat at about 80%-85% WOT rpm (probably around 70% load of engine)

3) for slow, fuel efficient speed, run at around 1.2 swl and crank up to 80% rpm for 15-mins or so every couple hours.

You may want to ping TrawlerForum.com or TheHullTruth.com as they are primarily power oriented.

[mvweebles]

Would also add that all boats have a sweet spot where the vibration and noise settle into a steady, relatively smooth rhythm. Often, +/- 50 rpm will make a difference.

Use the boat. Don't worry about hurting the engine. Have a good time.

Peter

[Lepke]

What kills engine life is exhaust gas temperatures. Using 80% of hp or less greatly extends engine life. Running at 90 or 100% can cut engine life to less than half. And I've rebuilt 100s of engines I knew of their history, either by myself or people working for me. I got to see the results in many boats with the same engines but different operators.

The valves, rings, sleeves and injector tips don't hold up well to extreme temps. And it's a myth that large commercial engines go their life without overhaul. They get constant overhauls. Most have one cylinder per head and a single cylinder can be overhauled during a brief stay. They carry spare heads and probably enough parts do do several cylinders.

[Flatswing]

I'm curious as to the reason for extended runs at higher RPM's. While we all nudge the throttles forward to overcome adverse current, avoid bad weather, make a bridge opening etc. I'm not sure what you achieve running 4-5 Knots faster routinely. Fishing?
The more fuel you burn, the faster the wear. As an example, CAT rates its engines longevity on # gallons of fuel consumed, not hours of operation. Many of us run at WOT briefly each trip - if only to unmask hidden problems in cooling system, dirty bottom etc. Others will take the opposite tack and never, ever run at WOT, even refusing to allow it during sea trial!

[Stx]

The motor will wear a little faster, just because everything is moving faster but, it’s not going to cause an immediate and catastrophic failure if you run it under the max RPM. I’ve got about a dozen Diesel engines in vehicles, tractors and construction equipment. I run the construction equipment at max RPM whenever using it, especially the newer equipment with a tier 4. I have a skid steer with 2600 hours, a mini-ex with 2200 and a boom lift with 6600, all 3 have been run at WOT 90% of their operating hours and none of them have had engine failures. The biggest issues to,watch for with Diesel engines are bad fuel and not getting it up,to operating temperature. If your fuel is clean and it’s hot enough, but not too hot, it’ll run well and last a long time.

[chrisjbell]

I'm surprised no one has even mentioned hull speed. I have a 39' twin diesel powered boat - mine has a semi displacement hull so it will easily exceed hull speed (call it 8 knots), tops out just over 20 knots. The OP's boat sounds like a planing hull but the physics are pretty similar.

Around hull speed the engines are under light load, top fuel economy. That's probably the best speed for long engine life. One point that was made by a couple of posters can't be emphasized enough and that is to get the engine running *and up to operating temperature under load* frequently. Do not just go start it and run it at the dock under no load (there are many post's worth of "why", trying to keep it relevant).

But a well used, well maintained diesel will last thousands of hours regardless of whether you operate at 25% or 75% throttle. WOT is probably fine, for that matter - I've had a lot of diesel equipment fall apart around the motor at 10k+ hours in industrial applications - but you will use a lot more fuel and the sbmar guy has some good points.

If a diesel fails earlier than, say, 3000 - 5000 hours then it was probably not run much and / or maintained properly. You wanna pay for fuel, go for it. Run it slow? Also shouldn't be a problem, although I do open mine up to ~80% from time to time, WOT occasionally.

BTW, if an engine won't handle max RPMs for short periods of time it's a failure waiting to happen. It is capable of running at manufacturer's full speed - or there's something wrong with it.

As to "why" - it's simple navigation principles... I can go the ~50 miles from my marina to SF in half a day at hull speed but can get there in half the time if I want to burn some fuel. A boat that can go 25 kts will get there even faster so a three day Bay cruise in a sailboat (which I also enjoy) can be packed into a day or a weekend.

But we're recreational use and most people will not be "wearing out" their engines.