Gas v/s diesel for trawlers

All modern diesels ranging from the Volvo D3, Yanmr BYs, Cummins QSB/C, Volvo D9, Cat Acerta, etc all make about 20 hp per gallon per hour of fuel burned at maximum hp at WOT.

Great, but most operate WAY below WOT and there the diesel falls flat.

For anyone contemplating a gas engine simply look up the cost of a brand new "crate engine" from the mfg of the boats engine.

You may find a new gas engine costs less than a simple rework of the injectors on a diesel.

The old Ford Lemamn Econo Power injectors are mechanical and really cheap to do, but a modern electronic injector can be a $1000 each! and just the brain box more than a new Crusader, complete.

At 200 hours a year , even if only normal PM is required , with gas at $3.13 and diesel at $3.90 , there will not be much "saving" from a diesel.

For the kind of blue water and coastal boating we do I'd never consider gas. But flashback to the 60s, 70s and 80s when large recreational MV use exploded (no pun intended) with gassers common in boats up to 44' like the Trojans or CCs. The only diesel that seemed to make any sense then was a big, heavy and expensive 6-71. And who can forget the common gasser Atomic 4 buried in the bowels of many sailboats up to 45'.

During the 80s I spent much time around St Louis. We had a 36 Trojan woodie with twin Chrysler 383s. No problem making 1.5 mpg at about 9 mph and it would still do 22 mph at 3800 RPM . Thousands of similar sized (and much bigger) gassers plied the rivers from Louisville to Mobile to Chicago. Houseboats that would run 25 mph and were up to 50' ran with gassers. All this is still going on today. For seasonal use in the USA interior, gas is still the most popular way to go due to cost, weight and simplicity of upkeep. As mentioned by Eric, FF and others, the simplicity of gasser maintenance is not a trivial advantage.

The OB revolution has injected a new concept too, with Searay now offering a 37' boat with twin OBs hidden in a waterproof sea cover. It looks very nice with interior and cockpit space aft rivaling a much larger vessel. Offshore fishing use by big diesel SFs had dramatically declined with the advent of big gas OBs on wonderful vessels like Gradey White etc.

I understand the safety factor, but with gas still outnumbering diesel on new builds up to 40' by several orders of magnitude, best let our diesel notions reside where they matter.

I wouldn't put a gas engine in Willy either but mostly as it would destroy it's resale value because of "in the box" thinking like Mark's comment about diesels being a part of trawlers and it wouldn't be a trawler w/o a diesel. When they took coal out of Battleships and installed oil boilers that didn't make the Battleship something else or even less a Battleship. But this dosn't pertain to the OP.

Great stuff that last post Tom. You can definitely think out of the box seeing things as they really are.

So nobody knows what parts or what else will make the modern gas engine less dependable than the diesel? If so I'll need to conclude that the gas engine IS as dependable as a diesel.

Yes Marin they were almost ALL gasoline powered. Flathead 6s mostly.

So it looks to me like the only real reason to shun gasoline power is the safety issue. So what recent improvements or new technology is in place to make the gas engine more acceptable? Much better sniffers???

Unless putting hundreds of hours a year on your engines, I think fuel economy and durability are hard to justify diesel instead of gas. The main selling point, IMO, to go diesel instead of gas is safety and vastly improved handling in close quarter situations. In those 2 regards diesel wins every time, no matter what, even if you only put 25 hours a year on your engines. A friend has a 30 or 33' power catamaran with twin 115hp outboards- gets fuel economy as good as any trawler but he can also get up on plane. That boat is probably the best of both worlds. Only way I would go gasers is with outboards due to the safety issue! I've personally seen 2 boats blow up at the fuel dock in the last 4 years.

Woodsong said:

Unless putting hundreds of hours a year on your engines, I think fuel economy and durability are hard to justify diesel instead of gas.

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Diesels hold their value MUCH longer and depending on the boat can hold the value of the boat up over that time as well.

A trawler needs diesels in my opinion. Naturally aspirated, slow turners at that.

Might trawler is 33 years old and the engines hum right along and sip fuel all day. Just under 3,000 hours young.

Marin said:

... made the run from Bellingham up into to SE Alaska with no need to refuel along the way. We can't do that with our 36' GB.

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We could probably make it. 600 gallons of fuel at a conservative 4-5 GPH would get us about 120-150 hours of running at 8 knots. That would give us a range of 1200 or so miles.

Everett to Juneau is something just over 1,000 miles? Lots of fuel between here and there though.

Eric wisely began this thread in post # 1 wherein he copied from another thread a post where I’d mentioned to him regarding gas – vs – diesel, i.e. costs, efficiency, explosiveness, and quietness in boats under 45’... his and my boats included therein. Good Job Eric, in thoughtfully opening this thread and applying your commentary throughout.

It’s interesting to read every post; much old and new, as well as just developing, gas and diesel engine and fuel “revelations” have been highlighted. Do understand that what Eric quoted from me to begin this thread was only meant as a broad brush swath for diesel or gas engine use in what I call fun-time pleasure boats (pleasure trawlers?)... or, as Marin likes to term them, “Toy Boats”. :lol:

Way I see it:

There is nothing wrong with competent use and maintenance of either gas or diesel power sources in applicably sized/styled/outfitted boats. Having for decades been around, utilized, and/or owned these power types in boats, and enjoying each power type for their individual attributes, it is my considered opinion that I better enjoy the use of smaller pleasure boats with gas engines due to overall reduced cost comparisons, minimized maintenance needs, and greatly quieter noise conditions while underway. With twin screw gassers running and our boat traveling 7 to 7.50 knots (approx hull speed) engine noise is minimal at 1.75 to 2 nmpg fuel usage. With one screw running at 5.75 to 6.25 knots and 2.5 to 2.75 nmpg engine noise is barely discernible. At full plane of 16 to 17 knots cruise speed mellow voice discussions are easy to hear in our boat’s salon while engines turn 3,400 to 3,600 rpm at 1 nmpg. In so far as my purchasing any craft... its power source type is not my end-all consideration, but rather the condition of said power source and what foreseeable costs could arise does play a strong part in my decision of buying nearly any motorized vehicle type – boats included.

That said, I feel there will be great improvements engineered that apply to both types of fuel-source engines during this decade, and, I hope our next craft holds opportunity to take advantage of at least some of these improvements. Currently my/our “Toy Boat”, “Pleasure Cruiser”, “Pleasure Trawler” is a good condition 1977 34’ Tollycraft tri cabin that is fully equipped with all amenities for long duration cruises or general hooking in bays for R&R vacations. It is correctly propped and well powered with real nice running, low hour, low cost, and low maintenance 350 cid, 255 hp Mercruiser gas engines, i.e. “If it Ain’t Broke – Don’t Fix It!

BTW: I am in communication with owner of the exact same model Tolly as we own (his is 4 years newer). He replaced his gassers and with Yanmar diesels while he refurbished his entire 1981 34’ Tollycraft tri cabin to pristine condition. Cost evidently $100K + when all was said n’ done... diesels’ full installation approx $60K. I guess he gets pretty good nmpg now... heard he can cruise 16 knots at approx 2 nmpg, that’s not bad at all.

So... let’s run some hypothetical #’s (based on reality #’s - at least as best as can be now ascertained):

1. At 100 hrs per year engine run-time doing 16 knots (1,600 nm traveled at 16 knots) his fuel-use savings (at 2 nmpg / compared to my 1 nmpg) would be - - > him 800 gal / me 1,600 gal = 800 gal less he uses than me. At avg $5 per gal = $4,000 less he annually spends on fuel than me.
2. At $60K to replace Mercruisers with Yanmars and $4,000 annual fuel savings = 15 yrs to recoup Yanmar installation cost via his fuel cost savings. Cool!


At that point (15 years from now) regarding inflated, value-less dollar for dollar ratios my boat may still be worth somewhere near an equivalent to the small amount I originally invested. His 15 yr old $100K refurbishment (inc, $60K repower cost) has enormously depreciated. For a “Toy Boat” I just can’t see reasoning behind this! Unless ya gots $$$$ to burn and no place of constructive value to put it!

We carry 400 gallons in the new tank system installed by th PO. This is less than the boat was built with but that's good since fuel doesn't stay on the boat as long.

At 1650-1700 rpm we burn a total of something over 5 gph at eight knots (2 FL120s). Actually its probably closer to 6 gph. We could burn less if we backed the power off a bit but eight nots is already too slow and anything less would be unacceptable.

So this gives us a theoretical range of about 600 miles. But our real range is a lot less than that because of the kinds of currents one encounters along the way. So there is no way we could make it up the coast to Alaska on one load of fuel. Actually I don't think we could even make Prince Rupert on one load of fuel, not that we would let our fuel get that low even if we could.

Fortunately, as SomeSailor says, there are plenty of fuel stops along the way.

On a long haul, the tides will be a wash. You ride an flood for 4 hours and an ebb after that. Your average speed would be unaffected. (Unless of course you chose to run against the tides more than with them)

I´d rather Diesel, In Brazil the Diesel is too cheapper than the gas and I think its more safe and reliable

SomeSailor said:

On a long haul, the tides will be a wash. You ride an flood for 4 hours and an ebb after that. Your average speed would be unaffected. (Unless of course you chose to run against the tides more than with them)

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That's the theory but in talking to a people over the years who've made that trip, particularly in slow boats, it doesn't work out that way. Partly due to the nature of the course itself where, like in the San Juan and Gulf Islands, even when the overall water flow is ebbing or flooding there are sections where you'll be going with, across, or against it, and depending on what section you are traversing at the time and the state of the tide at that time you may get more against than with.

And also because partway up up the whole system goes the other way.

But the people in our club who have made the trip in sailboats (under power almost exclusively) and in cruisers have all told me the runs usually took longer than they had calculated and they burned more fuel than they had calculated.

I don't know the fuel capacity of that 36' troller Donna I posted the photo of earlier. But its little gas engine-- and I'm sorry I don't remember the make; the owner told me-- must be really miserly with fuel if he could make it up the Passage without needing to refuel. I think it's just a five or six knot boat. Perhaps he really worked the currents carefully to be in his favor as much as possible. He told me people often repowered boats like this but he got it with the original engine and kept it that way.

Yeah... and it's uphill both ways in the snow...

Really?

I think you'd argue with a fence post if given the opportunity.

No, just trying to convey accurate info in a media where there is precious little of it and what little there is is often too simplistic and general to be of any actual use to anybody.

[
Art said:

"For a “Toy Boat” I just can’t see reasoning behind this! Unless ya gots $$$$ to burn and no place of constructive value to put it!"

To me, and most others on this Forum as evidenced by another current thread, a boat is indeed of constructive value and a great place to pi$$ money away. If I don't blow it on boats and such, those so listed in the will sure as heck will and have all the fun.

sunchaser said:

[
Art said:

"For a “Toy Boat” I just can’t see reasoning behind this! Unless ya gots $$$$ to burn and no place of constructive value to put it!"

To me, and most others on this Forum as evidenced by another current thread, a boat is indeed of constructive value and a great place to pi$$ money away. If I don't blow it on boats and such, those so listed in the will sure as heck will and have all the fun.

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Good point! sc :lol:

Marin says;
"There ya go again Marin listening to other people when you should be listening to your own brain.

On a long haul the tides will be a wash. SomeSailor is absolutely right. HOW COULD IT BE ANY OTHER WAY. The only difference is that when bucking current there comes a time when there's no movement at all or one even goes backwards but when going with the current one just goes faster. But if you keep going (as I did on my trip so) 50% of the time you'll be bucking and 50% of the time you'll be running with it. But this has not got to do w gas engines. So start a new thread if needed.

SS if the fence had anything to say he would.

So it looks like the only reason the gas engine shouldn't be considered for a trawler is because of the safety issue.

manyboats said:

Marin says;
"There ya go again Marin listening to other people when you should be listening to your own brain.

On a long haul the tides will be a wash. SomeSailor is absolutely right. HOW COULD IT BE ANY OTHER WAY. The only difference is that when bucking current there comes a time when there's no movement at all or one even goes backwards but when going with the current one just goes faster. But if you keep going (as I did on my trip so) 50% of the time you'll be bucking and 50% of the time you'll be running with it. But this has not got to do w gas engines. So start a new thread if needed.

SS if the fence had anything to say he would.

So it looks like the only reason the gas engine shouldn't be considered for a trawler is because of the safety issue.

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Eric - Pretty much! That is is the Captain does not feel competent to handle items related to the gas issue.

Yes Art.
Often times we do things that don't stand up to objective analysis because we have strong emotional issues regarding it. Trawlers seem heavy duty and it would seem they should be powered by a heavy duty engine and diesels have that reputation of being heavy duty.

If I was going to put an engine in a tug boat, a fish boat or a bus I'd go w diesel but on a pleasure boat that does not need an engine that lasts longer than a good gasser the gasoline engine could be the best choice for the trawler.

But I think almost nobody's going to do that because of emotional reasons or notions trawlers will remain diesel. Unless the notions change and I don't see that happening soon.

I just wanted to kick this around to see if I was imagining things. And because I'm analytical and like a dark horse I could'nt resist. Thanks all.

manyboats said:

Yes Art.
Often times we do things that don't stand up to objective analysis because we have strong emotional issues regarding it. Trawlers seem heavy duty and it would seem they should be powered by a heavy duty engine and diesels have that reputation of being heavy duty.

If I was going to put an engine in a tug boat, a fish boat or a bus I'd go w diesel but on a pleasure boat that does not need an engine that lasts longer than a good gasser the gasoline engine could be the best choice for the trawler.

But I think almost nobody's going to do that because of emotional reasons or notions trawlers will remain diesel. Unless the notions change and I don't see that happening soon.

I just wanted to kick this around to see if I was imagining things. And because I'm analytical and like a dark horse I could'nt resist. Thanks all.

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Eric, you're a forum champ! Each to their own and own to their each, regarding choice of power source... or anything else on a boat, for that matter - - > LOL :lol:

This has been an interesting thread you started and hopefully even more input will be brought forth. When day comes that we up-size to a larger boat (45 to 65') for extensive coastal cruising I currently imagine that newer version diesel power will be my engine(s) of choice. Till then, our Tolly’s simple gas engines are just fine for the amount of cruising we like to accomplish.

BTW: Being a careful Captain, each time before turning any electricity or other energy sources on aboard when we first board after boat's been left idle for some time (at night I use flashlights hanging at the ready) I always open salon floor hatches, lean way in, and give it a "deep sniff test". Then blowers on for ten minutes, then electric cord hooked to dock and electric power item activated on aboard. Also, even if only shutting engines off for a few minutes I always turn on blower before restart, same for genset. And, just outside slider doors I have perfect access to exterior hull vents just under gunnels where I get direct blower air-way exhaust for sniff tests. All our hoses and fittings are like new with connections kept tight. Being a consistent early riser, there is nary an early morning time-slot when we are out and about that I’m not in the engine compartment checking everything twice... just makes me happy and starts my boating day off with complete confidence that mechanical and fuel items are A-OK for another day!

Happy Boating Daze! - Art

manyboats said:

Marin says;
"There ya go again Marin listening to other people when you should be listening to your own brain.

On a long haul the tides will be a wash. SomeSailor is absolutely right. HOW COULD IT BE ANY OTHER WAY.

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If this was an armchair theory class--- which I guess this forum is most of the time--- I would totally agree with you. I've not taken a boat all the way up the Inside Passage so I can't argue the point from direct experience. I have always assumed the currents would cancel themselves out over that distance as far as their effect on your fuel usage is concerned.

But I can tell you that everyone we have talked to directly about cruising the Inside Passage--- something we want to do if we ever get the time and so have a very high interest in--- has told us that the theory does not hold true in reality. The current effects they encountered over the course of the run did not cancel themselves out. And that fuel burn was almost always significantly greater than they had calculated using the assumption that everything would cancel out in the end.

Their explanations were always as I stated above-- the currents did not affect their boats equally because of the routes they take through the islands. Maybe the current would cancel out if you went straight up Georgia Strait, straight up Jonnstone Strait, straight up Queen Charlotte Strait and Hakai Pass, and straight up Princess and Grenville Channels and straight across Dixon Entrance. But the folks we've talked to don't do that. They take a much more convoluted route and bypass as much of Johnstone Strait as they can, for example. They have said there have been days when all they seemed to have was contrary currents despite the fact that the tidal flow for the whole area was going the other way.

So while I certainly understand the cancel-out theory, I'm going to take the word of the people we've talked to at length about cruising the Passage who've done it, sometimes numerous times, and went over with us the records of their route and their fuel burn and their SOG.

You can take the word of whoever you like.

Understand one can ride the flood upriver a lot longer on the San Francisco estuary as opposed to riding the ebb downriver, leastwise when there haven't been heavy rains or dam releases.

Marin,
Here we are at thread creep again as I just noticed what thread we're on. From now on I'll need to check the thread before responding to your posts.

I made a post to Marin but then I saw it was way off topic so I sent it to him via PM.

manyboats said:

Marin I'm not as interested in what your friends say as what YOU say. How bout telling us what YOU think for a change.

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You never ask the easy-answer stuff, do you? If it was anyone else I'd blow you off but since it's you......

I think my friends are right because all the evidence they have presented to me has convinced me that they are. And we have experienced what they told us about currents on a much smaller and shorter scale driving a slow boat around in the San Juan and Gulf Islands and up to Desolation Sound.

If I have experienced something myself I can tell you what I think based on what I have done. And I will use that experience of doing it to defend what I have said.

IfI have not experienced something myself, wouldn't it be stupid of me to tell you what I think as if it's right, even though I don't know that it is?

So I will do the next best thing which is tell you what I have learned. And I will tell you how I learned it, which will usually be from talking to or reading material by people I judge to know what they're talking about.

It's then up to you to decide if what I have learned is valid or not.

Some people on this forum believe that if you have not experienced something yourself you have no business talking about it. I don't believe in that because that attitude negates passing on information from credible sources. Actually, it negates the whole idea behind school.

So I'm happy to pass on information I may feel is relevant to a subject even if I have not experienced it myself as long as I feel the information I'm passing on is coming from a credible source. And I'll tell you what that source is.

Whether someone else chooses to believe information I pass on is irrelevant to me.

Opinions, of course, are a whole different deal.

I agree that emotion plays a big part in engine choice, like most other choices in boat gear selection. Trawlers are "working man" boats, and diesels are "working man" engines. Grunt grunt
Is either one more cost effective overall? I dunno. I doubt there is much in it worth arguing about, unless you are doing a circumnavigation or are a full time fisherman.
Of all the costs associated with running a large recreational boat, and the difference between gasoline/diesel is a miniscule percentage of the total.

Tidal currents equaling out travel time...
I may not have come up with the correct explanation, but here's how I thought it worked for us not making our calculated miles at 5mph on the ICW in our sailboat.

Let's say there's a 5mph current, so I'm either going zero mph (against), or 10 mph (with). There are inlets at various places, and as I cross an inlet the current reverses.

I always spend a full 6 hrs at zero while bucking, then go 10 mph for 6 hrs, OR until I cross an inlet, at which time I'm bucking again at zero. It's possible to spend more than 1/2 the time bucking, but I can never spend more than 6 hours riding. No matter what actual speeds you use, you will ultimately spend more time bucking than riding = more fuel and more time than the numbers predict.

At least that's how I made sense of the phenomenon.

To me the big problem is too many folks think "efficiency" is measured in fuel cost per mile.

Actually it should be measured in total cost per mile.

Engine replacement , oil volume and price , routine maint and PM all factor in , not just GPH.

When considering the replacement cost alone the 3x to 4x price of a simple drop in replacement diesel (never mind a better newer engine) compares well to the engine life.

2000 hours can be had from most FW cooled gassers , 6000 is about right for a seldom used , lightly loaded diesel.
Ideling for batt charging eats engines worse than operating at modest load.

Contemplate all the engine /fuel / repair costs for a perhaps different view of gas in a rec boat.

Seven years ago I looked at a 44 Tolly gasser at Lake Powell. The Crusader 454s had about 3000 hours on them and ran perfectly. The owner ran an auto repair shop and was pretty smart on maintenance. This immaculate fresh water boat was sold to a guy in Sidney BC who was going to install Cat 3208s he had sitting around once the gassers gave out. I lost track of how long the gassers ran once in salt water, but it was more than a fortnight and diesel desire finally took over since his 3208s were parked nearby, waiting and waiting ---------.

jeffnick said:

No matter what actual speeds you use, you will ultimately spend more time bucking than riding = more fuel and more time than the numbers predict.

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But that also assumes you're silly enough to spend SIX HOURS making ZERO headway.

I have this scenario when transiting Deception Pass, Tacoma Narrows, Swinomish Slough... you name it. I simply time my departures and transits to make the best use of my time.

Sometimes it means leaving later... sometimes earlier... All part of the deal.

My original estimates were conservative. If I got to the point of ZERO headway.... it's time for lunch on the hook.

FF said:

To me the big problem is too many folks think "efficiency" is measured in fuel cost per mile.

Actually it should be measured in total cost per mile.

Engine replacement , oil volume and price , routine maint and PM all factor in , not just GPH.

When considering the replacement cost alone the 3x to 4x price of a simple drop in replacement diesel (never mind a better newer engine) compares well to the engine life.

2000 hours can be had from most FW cooled gassers , 6000 is about right for a seldom used , lightly loaded diesel.
Ideling for batt charging eats engines worse than operating at modest load.

Contemplate all the engine /fuel / repair costs for a perhaps different view of gas in a rec boat.

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Fred - I agree with you.

If placed on a long-term spread sheet (let’s say 30 year duration) I believe for pleasure boats (averaging 200 hrs per year engine run-time) that overall costs of diesel - vs - gas engines would show just about a push. These numbers would need to represent equal quality new engines of both types with each type engine experiencing equally correct/careful care.

Some primarily undeterminable factors (if not carefully checked into) come into play for purchasing used boats containing used engines of either type ("cost-weight" of each factor strongly determines boat owner’s overall "engine/fuel" expense):
1. Is engine on its first go-round from initial manufacturer or is it a rebuild, and, if a rebuild, who was the rebuilder... was it a qualified, reputable firm... did fluids test clean upon professional inspection?
2. Was engine properly broken in and then consistently cared for from day one of operation and how many hours are on engine as compared to that type engine’s “normal” lifespan?
3. If engine is getting “long of tooth” due to hours use what are the full costs for oncoming replacement or rebuild and how much longer is engine expected to continue operation before break down?
4. Is engine model of a type that has history of providing substantial duration of trouble free useable hours?

For experienced boat owners with decades of knowhow these four factors (and others not mentioned) for understanding the quality of used engines in used boats are pretty much a slam dunk paint-by-number exercise when purchasing any craft. However, for new boat buyers with little to no background in used-boat/used-engine purchasing or ownership these factors consist of a steep learning curve. One that if not correctly addressed might break their bank and in so doing would likely sour their desire to join and enjoy our boating community.

So... Any newbie to used-boat/used-engine purchasing needs to locate a very experienced marine mechanic who will thoroughly check-out the engines and who already well knows the background on that type of engine for clear counsel to the buyer. Otherwise the newbie could too easily, too soon be facing (for twin engine boats) $10 to $20K on new gassers or $30 to $60K for new diesels. OOOUUUCCCCHHHHH!

Diesels always hold their value better. Part of it because the plants are such a huge percentage of the boat's value. Re-powering with gas over diesel takes away value in my opinion.