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I’ve been reading diesel engine owner’s manuals for over 2 decades and between the last three boats I’ve had, and the 100’s that I have worked on, this term never came up? Did I miss something?

I think I coined that term about 10-12 years ago when I finally had enough of trying to explain the effects of salt water and the general marine environment that diesel engines operate in. It’s this marine environment that constantly takes its toll on marine components and has absolutely nothing to do with operation of the engine or vessel hours. I had figured out well over a decade earlier that many of the components in a marine engine that “go to crap”, so to say, are  way more related to early or premature failure due to having been in and or around salt water than actual engine hour use, or what most consider everyday “wear & tear”.

In fact, some of the most critical components of a “High Performance Marine Diesel” start the process of “Marine Age”-ing the very second these components come in contact with salt water. And because of their base design criteria, that in some ways forced the engineering of these components that direction, that the marine ageing process will   make or break that engine early on in its potential life long before the engineers thought it would, or could.

Think “Marine Age” and nothing else when it comes to a cooling circuit system on seawater inside of the engine it that is comprised of mixed metal alloys. The couch engineers that write maintenance intervals base everything on the engine hour meter – This is Completely Ridiculous! You have had seawater inside your engines cooling system for how many years? 3, 5, 7? and do you really think “Mother Nature’s” destructive work stops when you turn off the key? Think again…  And it’s just not inside as it starts on the outside too with small drips that does unbelievable amounts of damage over time.

A "Low Hour" Engine
A “Low Hour” Engine that has been externally ravaged by the effects of “Marine Age”

When you decide it’s time to purchase a used car, usually the first question to be asked of the current owner is “how many miles does it have?”. Well why not? …It’s a great question after all. If someone were to tell you that the vehicle had 225,000 miles on the original engine, you could surmise that the vehicle was probably well maintained but in all likelihood the vehicle has given the better part of it’s life and it’s just a matter of time before something “catastrophic” happens. Now on the flip side of the coin, if the current owner were to tell you that the vehicle had only 35,000 miles, you would say to yourself that the vehicle is just beggining to be “broken in” and that the purchase would be a prudent one. Why the drastic difference in assessment in comparison to boats and marine engines? Well unlike boats, cars exist in a much less adverse environment free from the corrosive effects of salt water. Barring any wildly outstanding circumstances, cars for the most part age the same which allows the assessment of mileage to serve as a standardized indicator for gauging the useful life of a road vehicle. The hour meter on a boat doesn’t even come close to indicating the true condition or real value of a marine engine… it’s much more complicated than that.

So why now? Why hadn’t this term, “Marine Age” surfaced or mean what I know it means today 30, 40 or 50 years ago when there were marine diesels even back then? Why is it we have 30, 40 & even 50 year old Detroit’s, CATs and Cummins diesels that “Marine Age” was not something you really did not think much of? But now, it’s the main ingredient that affects engine life today (not engine hours) – AND YET – it’s never mentioned in the books, owner’s manuals, in the “Captains Briefing”, or when you hire a “certified tech” or “engine surveyor” to come down to your boat for an inspection or perform normal maintenance? Seems everything revolves around the engine hour meter these days………………Talk about STUPID and one of the biggest fallacies of our time, and what’s even worse, 100’s of  people reading this have paid good money to “professionals” in this industry to get a good engine survey when buying a boat, yet it is never mentioned.

Why is Marine Age so Important Now?

Detroit Diesel
Detroit Diesel 8v71

As to why now and not before is real easy if you look at the way the high performance diesels are designed and cooled compared to years back. Two things really separate engines from 30+ yrs ago compared to engines today. One is WEIGHT and the other is power density. Once in a while I use the term “heavy iron” and when I do, I am usually referring to an engine design like that of a Detroit 8-71, CAT 3406, or Cummins 555, 903, or 855. With engines like this, weight and overall size were not really the focus of design. Back then, cooling parts were large and heavy and typically made of thick-walled iron and bronze castings with large passage ways throughout. Output Horsepower was low in comparison to both weight and engine displacement and because of this, rarely did a design need cold seawater to cool the air being pushed into the engine, or the lubricating oil in it, or even in the transmission. 30 HP per liter was about all these engine developed and a 350 HP diesel could easily weigh 3000+ lbs. (about 8-10 lbs. per HP was the norm).

Cummins “K” Engine
Cummins “K” Engine

Today, the real design focus for all makes of marine diesels used in pleasure boat applications is getting the highest power density possible by keeping the package dimensionally as small & as light weight as possible using aluminum, thin walled castings or fabrications in as many places as feasible, pumping cold seawater thru as many components as needed to allow them to be smaller and more efficient for cooling. Then comes the HP/per liter to make them competitive by fueling these engines so output horsepower is upwards of 70HP per liter of displacement while still maintaining a degree of reliability as to engine life based upon “operating hours” before the engines needs rebuilding from internal wearing of the main components. (There lies the crux of this article, “operating hours”,  we will get to that below)  …Seems that is what the market wants and is the driving force for these types of engine designs. Want to travel at 30~35 K’s in a 38 ft. Sportfisher getting 0.9-1 MPG? You could never do that with a old Detroit 8-71TI or Cummins 903 as the power density of those older “Heavy Iron” engines would never give you that type of performance.



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