Gas vs. Diesel

Art said:

And - - > DON"T fall in love with any boat until after you have cut the best deal possible and you then own it "lock-stock-and-barrel". Reason for this: So you can walk away from any deal that shows signs of future boat problems. This suggestion can eliminate a lot of costs, efforts, and heart ache in future times.

Happy Engine-Choice Daze! - Art

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Yes, this I will say, it is hard, especially if you love boats in general. And the fact that all boats are future problems in the waiting regardless

SaltyDawg86 said:

The buying of the boat doesn't bother me, it's the costs that come with owning a boat that keeps me from pulling the trigger right now.

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Same. . .that's why I live on mine! At least the costs can be justified since it's your home

cool beans said:

I will say, it is hard, especially if you love boats in general.

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No, it's easy.

Never never never fall in love with a boat you do not already own.

Old saying about boats...

"Every portion of a boat in moving toward breakdown 24/7."

You just need to keep/have all boat portions in best condition possible and be ready to fix whatever may occur.

The one thing that keeps people from hiring me as a boat broker is my favorite saying for the young and still with family about boat purchases...


Fall in love with a boat...then buy the next model smaller as you will never use it as much as you think you will.

Yea my wife isnt down for living on a boat full time, already asked!

A good Diesel engine, well maintained and not overloaded, should give you around 5,000 hours before needing a rebuild. Gasses are more like 1,000 hours. Gross generalizations, of course.

How to overload a diesel? Overpropping is commonly cited. Running the engine over 80% of wide open throttle. Not cooling down the running engine before shutting it down (if your turbos were engaged). Not bringing it up to temperature before opening up the speeds. Ironically, you can also under load a diesel. Excessive idling with no load and running at slow speeds can promote carbon buildup.

Robster_in_edmonds said:

A good Diesel engine, well maintained and not overloaded, should give you around 5,000 hours before needing a rebuild. Gasses are more like 1,000 hours. Gross generalizations, of course.

How to overload a diesel? Overpropping is commonly cited. Running the engine over 80% of wide open throttle. Not cooling down the running engine before shutting it down (if your turbos were engaged). Not bringing it up to temperature before opening up the speeds. Ironically, you can also under load a diesel. Excessive idling with no load and running at slow speeds can promote carbon buildup.

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Rob - 1000 hrs for a gasser is low unless it's a high hp, high performance model and it's consistently abused at too high rpm with lacking maintenance.

Gasser's with regular %age hp to cid when used intelligently and well maintained can reach into the 3 to 4K hr zone before rebuild or replacement becomes required.

Of course... some well utilized diesels can last way over 5K hours too.

Robster_in_edmonds said:

A good Diesel engine, well maintained and not overloaded, should give you around 5,000 hours before needing a rebuild. Gasses are more like 1,000 hours. Gross generalizations, of course.

How to overload a diesel? Overpropping is commonly cited. Running the engine over 80% of wide open throttle. Not cooling down the running engine before shutting it down (if your turbos were engaged). Not bringing it up to temperature before opening up the speeds. Ironically, you can also under load a diesel. Excessive idling with no load and running at slow speeds can promote carbon buildup.

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The carbed, electronic ignition 454 gasser in my assistance boat is passing 5000 hours any time now (13 years of grueling service) with no signs of slowing down.

It has hundreds of hours of over temp and over pressure on it....towing and ungrounding are not good for any engine if misused...

It gets minimal maintenance beyond oil changes.

A lot of low power, idling issues of diesels aren't universal...just with those that HAVE those issues...and that is dependent on if you follow manufacturer recommendations to blow out/burn off the carbon. Also is the myth of of overpropping...it is the misuse of it...not the technique itself.

Robster_in_edmonds said:

A good Diesel engine, well maintained and not overloaded, should give you around 5,000 hours before needing a rebuild.

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A 5,000 hour time between overhauls (TBO) is extremely low for the typical diesel thats used in recreational boats. In fact I would say abnormally low. As in the operator isn't using it and maintaining it properly. The ancient Ford Lehman 120 is said to be (by people like Bob Smith who was involved in Lehman's marinization program back in the day) a 12,000 to 14,000 hour engine in recreational boat service if operated within its ideal parameters and serviced and maintained properly.

In constant and properly serviced industrial use the FL120 has gone more than 25,000 hours before needing an overhaul. A friend in Hawaii who runs a small fleet of 70' longliners all of which use Volvo diesels told me he gets very pissed off if he gets less than a 30,000 hour TBO with the engines in his boats.

Now an engine will need plenty of maintenance and repair during that time, particularly with its ancilliary components like pumps and whatnot.

Perhaps the newer-generation, higher speed, lighter weight diesels have a shorter TBO rhan the older ones, I don't know. But a TBO of only 5,000 hours woud in my opinion negate the whole reason and value of the very high cost of using this type of engine in the first place.

5000 hours is more in line with newer, lightweight, recreational rated diesels...not so much with old iron or commercially rated engines.


that is why bigger and more powerful gassers and outboards keep showing up.


as always, there are exceptions to rules of thumb.

When I was in field service working in Japan I saw industrial diesels running 24/7/365 for over a year without a major overhaul. Those same engines in a marine environment often last less than 2,000 hrs as they are often ignored for maintenance and their performance parameters are mostly violated. The diesels that last for many thousands of hours are reasonably maintained before failures occur and are always operated correctly.
When you buy a boat you are also buying the past owners like it or not so spend some time figuring out what type of service the engines and bot received before you take over the job.
Hope this helps

Everyone understands that buying an older boat is cheaper than buying a new boat for the simple fact that many of its systems may be nearing the end of their service life.


I would not buy a boat that I could not afford to replace major systems on. That includes engines and fuel tanks. If you can get away with running high hour engines and 30+ year old fuel tanks think of it as a bonus, and when they fail be prepared, and not surprised.

psneeld said:

The carbed, electronic ignition 454 gasser in my assistance boat is passing 5000 hours any time now (13 years of grueling service) with no signs of slowing down.

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Excellent post.

All I would have added is that running a diesel above 80% of rated power is hardly going to create any kind of issue as long as the rest of the propulsion system can do its job properly. A poorly maintained cooling system can kill an engine at 50, 60, or 70 percent power just as easily.

Scratch off another silly myth.

Users need to read and understand how power ratings are developed and what they have to do to operate within those ratings. Just picking a number because it sounds good is not good.

Most people here won't wear out a gas engine much less a diesel so why even talk about it?

The issue's are safety and fuel consumption.

"The issue's are safety and fuel consumption."


Where we are diesel on the water has always been cheaper to buy. This season at least 15% lower than gas but at certain places and times as much as 30% less.
After that you can figure out how much less you will consume with diesels.




"All I would have added is that running a diesel above 80% of rated power is hardly going to create any kind of issue as long as the rest of the propulsion system can do its job properly"


Yes , I agree. But running a diesel much above 1 hp used for every 2 cubic inches of displacement will also lead to a much shorter and dangerous life. So its the way it is used and the maintenance that adds to the longer life.


Hope this helps

manyboats said:

Most people here won't wear out a gas engine much less a diesel so why even talk about it?

The issue's are safety and fuel consumption.

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And cost...

You're right. But then fuel consumption is a lesser issue to those who would never wear out an engine.

And durability remains an issue for some, both for major work and minor.

The westerbeke 46 in my sail boat is 28 years old. It smokes a bit on start up, but the smoke disappears as soon as the engine warms up or is loaded. Other than that it runs just like a brand new engine - uses zero oil, starts immediately, hes plenty of power, etc. Maintenance is minimal. I just serviced the injectors (115) for the 2nd time since the engine was new. Other than that service is limited to changing oil and filters, changing the heat exchanger zinc and replacing the raw water impeller and fan belt every few years. I replace all the rubber every 10 years too.

Ddog said:

Everyone understands that buying an older boat is cheaper than buying a new boat for the simple fact that many of its systems may be nearing the end of their service life.


I would not buy a boat that I could not afford to replace major systems on. That includes engines and fuel tanks. If you can get away with running high hour engines and 30+ year old fuel tanks think of it as a bonus, and when they fail be prepared, and not surprised.

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smitty477 said:

But running a diesel much above 1 hp used for every 2 cubic inches of displacement will also lead to a much shorter and dangerous life. So its the way it is used and the maintenance that adds to the longer life.

Hope this helps

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All it helps is to continue spreading nonsensical mythology about marine diesels ...

All you have to do is look at the specs for a couple of very popular yachtie marine diesels to see the real numbers. A CAT 6.6 ACERT produces 275 hp from 201 cubic inches.

A relatively little MTU 2000 produces 1800 hp from 1635 cubic inches, an MTU 16V4000 as used on many large yachts produces more than 4600 hp out of 4211 cubic inches. None of those engines have a particularly "shorter and dangerous life" compared to any other marine diesel. They are selected by builders for their economy and longevity as well as performance and each is at opposite ends of the spectrum as far as size and power.

I didn't bother to run the numbers on the hundred other engines that more likely than not will return very similar displacement/power ratios. Even the 71 series DD's make that 1:2 thing look very silly.

"didn't bother to run the numbers on the hundred other engines that more likely than not will return very similar displacement/power ratios. Even the 71 series DD's make that 1:2 thing look very silly."


And typically result in a much shorter life as a result of it.

The Cat 6.6 is around 400cid.

Life depends on MANY factors. Better to run often. Better to run mid range of power band. Better to be not overloaded. Better to be maintained well. Better to be a good design. Better to NOT be spanked by the operator. Better to have an operator that can sense issues before they snowball.. Etc, etc.

Many examples of gassers logging lots of hours like PSN's example. Also many examples of diesels dying at 1500hrs.

Lots of examples of diesels going for 20,000 even 40,000hrs. But part of this is that gas engines are NOT spec'd for these kind of applications.

Lots of cars and pickups go over 300,000mi with no major engine work. At a life avg of 30mph, that's 10,000hrs. Often the car is retired then not because the engine has failed, but that the car is a ragged out rustbucket. Nothing to sneeze at there.

"All you have to do is look at the specs for a couple of very popular yachtie marine diesels to see the real numbers. A CAT 6.6 ACERT produces 275 hp from 201 cubic inches."


I do not know much about the Cat 6.6 acert engine bit I believe it is 6.6 liters of displacement or 403 cubic inches. They limit the hp on their 6.6 gensets installs to less than 220 Hp and about 12 gph max.

smitty477 said:

And typically result in a much shorter life as a result of it.

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I think claims that today's engines don't last like yesteryear and have shorter lives is without any real supporting evidence. I believe the opposite is true, that the technology continues to advance and the engines get better. Today there are many engine options available to builders based on the use of the boat.

One thing manufacturers like MTU do as well is match the engine to the expected use. There are many models of the same basic engine. For instance on the MTU 16V2000, there are at least 9 versions currently offered.

When we were chartering, before buying, one thing we did was look at the maintenance logs of the boats we chartered. These were often some high hour engines. The real problems during their lives were minimal. Some had as much as 7000 hours and ran like new. Look at the commercial side of things though and they have far more hours. I have no numbers to prove it but those I've met have talked about hot much better engines are today. Common Rail is one of the big advances.

It seems to be common on many things to reminisce about the good old days.

Maybe it's because I'm younger than some here, but I do not buy the "myth" (Rick's word, my opinion) of older engines being better.

Another thing that skews longevity stories: The old engines, and I mean Detroits, Cats and Cummins that are still running after 50-plus years of use are the survivors. There were lots of engines built way back then that were in the junk pile after ten or fifteen years. We don't see or hear about THOSE!!! We only hear about the good ones that passed the test of time.

Same things with old houses. Crawl around a 200yr old house and be amazed at the craftsmanship. What you don't see is the sloppy built houses of the same era. Long gone, those.

And the newer engines do have some stupid problems. Bud with MTU 2000's is shelling out $40k for cracks in turbos. Eight years old, not high hour.

RickB said:

All it helps is to continue spreading nonsensical mythology about marine diesels ...

All you have to do is look at the specs for a couple of very popular yachtie marine diesels to see the real numbers. A CAT 6.6 ACERT produces 275 hp from 201 cubic inches.

A relatively little MTU 2000 produces 1800 hp from 1635 cubic inches, an MTU 16V4000 as used on many large yachts produces more than 4600 hp out of 4211 cubic inches. None of those engines have a particularly "shorter and dangerous life" compared to any other marine diesel. They are selected by builders for their economy and longevity as well as performance and each is at opposite ends of the spectrum as far as size and power.

I didn't bother to run the numbers on the hundred other engines that more likely than not will return very similar displacement/power ratios. Even the 71 series DD's make that 1:2 thing look very silly.

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Going to side with Rick on this one. Someone forgot to tell my 8v82ti's what smitty's opinion was.

Here's one piece of advice: you are better off ignoring 90% of posts about engines here on the recreational boater interweb. Problem for a newbie is, you can't tell which 10% to pay attention to. A realy experienced mechanic who knows the engines in question is the most valuable, and osme of them can be found on boatdiesel.com.

smitty477 said:

I do not know much about the Cat 6.6 acert engine bit I believe it is 6.6 liters of displacement or 403 cubic inches. They limit the hp on their 6.6 gensets installs to less than 220 Hp and about 12 gph max.

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Oops, my mistake ... I was dividing by 2 and keyed in the wrong figure.

The 6.6 is rated at 275hp max. If one were to follow the 1 hp per 2 cubic inches then the max hp would only be 200 hp and that was the point of the statement.

The generator rating is just one rating ... it is not the maximum for that displacement.

I am glad to see people are researching the data though ... that was the other point I was trying to make - don't believe everything some guy says on an internet boat site ... look it up, confirm the story.

Ski in NC said:

And the newer engines do have some stupid problems. Bud with MTU 2000's is shelling out $40k for cracks in turbos. Eight years old, not high hour.

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What part cracks? The housing? Flanges? Compressor or turbine? Which turbo(s)?

To answer the original question; besides the Tollycraft, Bayliner made a nice 32' boat in the mid eighties to early 90's with gas and Mainship made a 36 Nantucket that was available with gas.
John
MS390

Ski in NC said:

Another thing that skews longevity stories: The old engines, and I mean Detroits, Cats and Cummins that are still running after 50-plus years of use are the survivors. There were lots of engines built way back then that were in the junk pile after ten or fifteen years. We don't see or hear about THOSE!!! We only hear about the good ones that passed the test of time.

Same things with old houses. Crawl around a 200yr old house and be amazed at the craftsmanship. What you don't see is the sloppy built houses of the same era. Long gone, those.

And the newer engines do have some stupid problems. Bud with MTU 2000's is shelling out $40k for cracks in turbos. Eight years old, not high hour.

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Great point. We only see those still running. While the craftsmanship in the old houses is great, to be livable they've had to have major renovations. The definition of old houses changes too. Our house is 20 years old and doesn't have the original roof, heat or air.