Gas engines / verses Diesel on larger boats ??

[smitty477]

Agreed. Plodding along at 6.5 - 7 kts I can only manage somewhere around 1.2 - 1.3 nmpg with twin 454s. At 17 - 18 kts it's more like 0.5 - 0.6 nmpg. A modern pair of diesels would get the same hull to about 3 nmpg at the lower speed, 0.9 - 1 at higher speed. So about a 40% improvement for high speed, but easily 60% at lower speed.

Of course, at low speed the gassers are nice and quiet (especially up on the bridge) even with my boat not having a lot of sound insulation on the engine room. On plane, it's a different story with plenty of intake howl and other general engine noise (exhausts are still fairly quiet though). But it was pretty cool running through some of the fast sections of the Erie Canal up on plane and realizing I could hear the engine intake noise escaping through the hull sides and vents and echoing back off the banks of the canal.

"A modern pair of diesels would get the same hull to about 3 nmpg at the lower speed, 0.9 - 1 at higher speed."
A good guess...not really off that much from what we got with our 38' twin diesel boat.
At 6 knots it would get 4 nmpg and at 15-16 knots it was always above 1.2 but often near 1.4 nmpg.
Contrary to what some might think the 5 cyl 4 stroke diesels were not noisy at all at most any speeds as they exhausted thru mufflers and discharged well out the stern. Generally the boat was 38'2" molded hull with a 13'5" beam weighing in at about #20,000 dry and unloaded.

 

[rsn48]

The Merc 6.2 liter isn't automotive based? I thought it was just a re-tuned and marinized variant of the GM 6.2 liter LS engine (which is a very solid engine already).


And I quote:

"Like the company's 2014 introduction of the 4.5L V6 sterndrive, the 6.2L is specifically built as a marine engine – replacing the MerCruiser 350 MAG and 377 MAG models – and is manufactured at Mercury's world headquarters in Fond du Lac. The 6.2L gains the technological improvements of the 4.5L and a few additional features, including a new air-intake resonator and Active Trim (which will eventually be applied to the engine builder's lineup from 40hp and up).

On-water testing aboard a series of 23-foot-and-up bowriders displayed the 6.2L's responsiveness, power and torque as well as its ability to deliver a quiet and smooth ride on numerous vessel types.

“With the introduction of our new 6.2-liter V-8 sterndrive engines, Mercury continues to build on its success of designing and manufacturing propulsion systems that deliver the most intuitive, powerful, worry-free, smooth and quiet boating experience,” said John Pfeifer, President of Mercury Marine.

Mercury has been quick to point out that its latest generation of sterndrive blocks are made specifically for marine use, rather than adapting and ‘marinizing' a GM automotive engine. The addition of the 6.2L brings the company's lineup of marine purpose sterndrives to four, including the 4.5L, 8.2L HO/MAG and 8.6L 540/520."

 

[smitty477]

Agreed. Plodding along at 6.5 - 7 kts I can only manage somewhere around 1.2 - 1.3 nmpg with twin 454s. At 17 - 18 kts it's more like 0.5 - 0.6 nmpg. A modern pair of diesels would get the same hull to about 3 nmpg at the lower speed, 0.9 - 1 at higher speed. So about a 40% improvement for high speed, but easily 60% at lower speed.

Of course, at low speed the gassers are nice and quiet (especially up on the bridge) even with my boat not having a lot of sound insulation on the engine room. On plane, it's a different story with plenty of intake howl and other general engine noise (exhausts are still fairly quiet though). But it was pretty cool running through some of the fast sections of the Erie Canal up on plane and realizing I could hear the engine intake noise escaping through the hull sides and vents and echoing back off the banks of the canal.

"Agreed. Plodding along at 6.5 - 7 kts I can only manage somewhere around 1.2 - 1.3 nmpg with twin 454s. At 17 - 18 kts it's more like 0.5 - 0.6 nmpg. A modern pair of diesels would get the same hull to about 3 nmpg at the lower speed, 0.9 - 1 at higher speed. So about a 40% improvement for high speed, but easily 60% at lower speed."

Taking your exact numbers many folks would look at these comparisons differently - say your 1.2 nmpg for gas vs the 3 nmpg for diesel.

The comparison that would have value would be that the diesel engine boat would achieve 250% of the range on the same gallon of fuel (3 / 1.2 = 2.5).
Similarly two boats one with gas and one with diesel each with 300 gals of usable fuel available would have ranges of 360 vs 900 miles.
Using your numbers at higher speeds the difference would be about 200% increase in mileage (1.0 / 0.5 = 2.0) or 150 miles vs 300 miles for that same 300 usable gallons of fuel.

 

[Baker]

Not one single mention of safety....which is the number 1 reason I choose diesels. There is bascially ZERO carbon monoxide threat and basically ZERO explosion threat. Longevity and fuel efficiency are just a bonus to me. There is no way I could sleep soundly with a gasoline engine running in the bilge. My fear would be I would sleep a little too soundly and never wake up!

 

[rslifkin]

Taking your exact numbers many folks would look at these comparisons differently - say your 1.2 nmpg for gas vs the 3 nmpg for diesel.

The comparison that would have value would be that the diesel engine boat would achieve 250% of the range on the same gallon of fuel (3 / 1.2 = 2.5).
Similarly two boats one with gas and one with diesel each with 300 gals of usable fuel available would have ranges of 360 vs 900 miles.
Using your numbers at higher speeds the difference would be about 200% increase in mileage (1.0 / 0.5 = 2.0) or 150 miles vs 300 miles for that same 300 usable gallons of fuel.

And you've nailed the exact reason why I'd love to put diesels in this boat. There's also the safety improvement as Baker mentioned, although that one doesn't concern me too much. But the extra range would be nice from a trip planning perspective. And it would take the cruising range from "enough for basically any coastal cruising or loop scenario" to "enough for any coastal cruising or loop scenario at 18 kts".

I wouldn't want to give up speed in a re-power, as being non-retired, it greatly expands my cruising envelope by letting me trade fuel for time on the un-interesting transit portions of a trip (being that just taking a longer trip isn't always an option). At 6.5 - 7 kts, home port to the mouth of the St. Lawrence to get to the Thousand Islands would be almost 11 hours, so a fairly long day. Or I can burn twice as much fuel, but make the same run in about 4 hours, 15 minutes, leaving me half a day to continue to somewhere interesting and do some exploring.

Only problem is, even with that savings, assuming a full re-power (engines and generator) could be done with modern diesels in the 350 - 400 hp ballpark for $120k, it would still take something like 3000 hours of running to make it up in fuel cost (using the somewhat high prices at my home fuel dock of $3.99 diesel, $4.39 gas). At 50/50 running slow vs on plane, the gas engines will burn something like 56,250 gallons in 3000 hours, while the diesels would burn 31,800 gallons. That's a cost of $246,937.50 for gas, $126,882 for diesel, or a $120k fuel savings in 3000 hours.

Good guess on the 300 gal of usable fuel by the way, as that's exactly what I consider my usable fuel to be (420 gal total).

 

[smitty477]

And you've nailed the exact reason why I'd love to put diesels in this boat. There's also the safety improvement as Baker mentioned, although that one doesn't concern me too much. But the extra range would be nice from a trip planning perspective. And it would take the cruising range from "enough for basically any coastal cruising or loop scenario" to "enough for any coastal cruising or loop scenario at 18 kts".

I wouldn't want to give up speed in a re-power, as being non-retired, it greatly expands my cruising envelope by letting me trade fuel for time on the un-interesting transit portions of a trip (being that just taking a longer trip isn't always an option). At 6.5 - 7 kts, home port to the mouth of the St. Lawrence to get to the Thousand Islands would be almost 11 hours, so a fairly long day. Or I can burn twice as much fuel, but make the same run in about 4 hours, 15 minutes, leaving me half a day to continue to somewhere interesting and do some exploring.

Only problem is, even with that savings, assuming a full re-power (engines and generator) could be done with modern diesels in the 350 - 400 hp ballpark for $120k, it would still take something like 3000 hours of running to make it up in fuel cost (using the somewhat high prices at my home fuel dock of $3.99 diesel, $4.39 gas). At 50/50 running slow vs on plane, the gas engines will burn something like 56,250 gallons in 3000 hours, while the diesels would burn 31,800 gallons. That's a cost of $246,937.50 for gas, $126,882 for diesel, or a $120k fuel savings in 3000 hours.

Good guess on the 300 gal of usable fuel by the way, as that's exactly what I consider my usable fuel to be (420 gal total).

"Only problem is, even with that savings, assuming a full re-power (engines and generator) could be done with modern diesels in the 350 - 400 hp ballpark for $120k"
Or you can just take a fraction of those funds and add it to the resale value of your boat and replace with whatever you prefer.
There are always choices to consider …..

 

[rslifkin]

"Only problem is, even with that savings, assuming a full re-power (engines and generator) could be done with modern diesels in the 350 - 400 hp ballpark for $120k"
Or you can just take a fraction of those funds and add it to the resale value of your boat and replace with whatever you prefer.
There are always choices to consider …..

Yup. I kinda have it in my head that I'll run the existing 454s until I have a reason to replace them. And then depending on when that day comes, repower costs and available money I'll either put in some more modern gassers, build up a pair myself targeting durability and efficiency, or go for diesels. Or the really cheap option of just new long blocks and basically change nothing.

 

[Art]

Only problem is, even with that savings, assuming a full re-power (engines and generator) could be done with modern diesels in the 350 - 400 hp ballpark for $120k, it would still take something like 3000 hours of running to make it up in fuel cost (using the somewhat high prices at my home fuel dock of $3.99 diesel, $4.39 gas). At 50/50 running slow vs on plane, the gas engines will burn something like 56,250 gallons in 3000 hours, while the diesels would burn 31,800 gallons. That's a cost of $246,937.50 for gas, $126,882 for diesel, or a $120k fuel savings in 3000 hours.

3000 hrs run time to break even = 20 years at 150 hrs per year or 15 yrs at 200 hrs per year. Those are typical hour usage rates for a large portion of the boating community. Also, Although taking your calculations as accurate for repower cost and fuel usage/per gallon-cost there is still maintenance costs to figure in [which are usually higher cost on diesels]. Then we get into the what ifs in regard to any major breakdown/repair costs as well as potential for fullon engine replacement costs after using any type engine for 3000 hours in 15 to 20 or more year time span. Diesel replacement costs are then ouch, ouch, and ouch / Gas engine replacement costs are just ouch... for another 15 to 20 yr usage!! By the end of all that you're 30 to 40 years older with a 30 to 40 year older boat that started out as used with some years on it from the get-go! OMG - LOL

To me... in my way of thinking: Purchase a boat that already has low hour, well maintained, good condition engines of a type and HP you can be satisfied with... for the long term. Then go out and enjoy boating!!

In boating [as with most of life] everything is a trade off [often even more so in boating than other portions of life]. Myself, because we love to boat and also love to not spend too much money on family toys. I believe that shoping carefully, purchasing wisely, and selling correctly is a good axiom to follow in satisfying conditions that exist my family's boat-crazed toy world!

Happy Boat-Power-Choice Daze - Art

PS: Reason for three boats shown above is because we just added another! For having boats... It's sorta like having kids... you fall deeply in love with and then love each for their own individual good points!!

 

[kartracer]

The money I saved by buying my Bluewater with 454's paid for the 900 mile trip we took and still have a lot more in the pocket.

 

[Nomad Willy]

rslifkin wrote;
“ So about a 40% improvement for high speed, but easily 60% at lower speed. ”

Way way off at WOT diesel and gas are almost equal. Not even close to 40%. More like five percent. But I read that some time ago and both diesel and gas engines have changed considerably since then.

 

[smitty477]

rslifkin wrote;
“ So about a 40% improvement for high speed, but easily 60% at lower speed. ”

Way way off at WOT diesel and gas are almost equal. Not even close to 40%. More like five percent. But I read that some time ago and both diesel and gas engines have changed considerably since then.

"Way way off at WOT diesel and gas are almost equal"
Certainly not on the boats that we are familiar with that are powered by both gas and diesel engines as produced for direct comparisons.

 

[smitty477]

Yup. I kinda have it in my head that I'll run the existing 454s until I have a reason to replace them. And then depending on when that day comes, repower costs and available money I'll either put in some more modern gassers, build up a pair myself targeting durability and efficiency, or go for diesels. Or the really cheap option of just new long blocks and basically change nothing.

That would work as well - my thoughts were to consider replacing the boat with a diesel powered choice.

 

[tiltrider1]

This is an Apple vs Orange conversation. Both engines have their strengths and weaknesses. The safety comments are fearmongering, plenty of diesel boats out there with propane on them. Boat size and use dictates which engine makes sense.

A Viking 43 liveaboard should be gas, the cost savings just might be more than the total fuel bill. A commercial 43 fishing boat should be diesel, the fuel savings alone would be worth it not to mention longevity of a diesel over gas.

If the boats purpose is long range cruising, 500 miles between fuel stops, then money means nothing and diesel gets the nod. If I am looping and then selling the boat, money is an issue and a cost analysis with have to be done.

Then there is a whole different equation, a Viking 43 with dual 454 has a big engine room, same boat with dual 3208’s has no engine room left.

 

[rsn48]

I post so much about gas and diesel, it must seem I'm anti-diesel and pro gas. But as tiltrider1 comments about fear mongering seems to reflect, their is a biased towards diesel which may not be reflected in reality. Personally I don't think it is fear mongering so much as Joe who read something from Bob that diesels are safer, who read it from Bill that diesels are safer, who read it from John etc. etc.

This from David Pascoe about myths concerning diesel:

"Myth #1: Diesel is safer than gas.
For some reason or other, the fear of gasoline explosions, which are very rare, but had caused some rather spectacular accidents thirty years ago, just won't die. The facts are that gas engines are very safe and you probably stand a better chance of dying or being injured in an airline crash that you do in a gasoline fire or explosion. Yes, gas engines do pose a carbon monoxide hazard, but most of this hazard comes from gas generators.

Diesels are safer from the standpoint of explosions as diesel oil vapors are not explosive. Prior to the advent of water cooled turbochargers, statistics show that fires caused by diesel engines ran nearly 5 times the rate over gas engines. With the introduction of water cooled turbos, the rate of fires has come way down.

Of far more concern is the issue of carbon monoxide poisoning. Diesel exhaust produces far less CO than gas exhaust, though diesel exhaust produces sulphur dioxide that can quickly cause nausea, but is not life threatening. Gas generators are responsible for most instances of CO poisoning, with leaking exhaust systems and station wagon effect a very distant second place. If you plan to do much overnighting at anchor with a generator running, diesel is definitely the way to go."

One of the TF members in another thread about diesel versus gas debates looked up the main cause of fires in boats and found wiring was the culprit. This has really become an issue with older boats and owner modifications which may have not been properly equipped, installed and supported. It is rumoured insurance companies are going to demand stricter electrical surveys on older boats before insuring.

The following is a video carried out by Mercury Marine back in 1957 running two boats on a lake for 50,000 hours illustrating that the then "newer" outboard motors could take a beating. It kind of backs up the claim a well used engine outlasts a little used engine:

[For some reason, even when I down load this video from youtube, it won't play, but if you hit on the sentence to play it on youtube the video will play]

 

[boatruptcy]

Not one single mention of safety....which is the number 1 reason I choose diesels. There is bascially ZERO carbon monoxide threat and basically ZERO explosion threat. Longevity and fuel efficiency are just a bonus to me. There is no way I could sleep soundly with a gasoline engine running in the bilge. My fear would be I would sleep a little too soundly and never wake up!

Totally agree, gasoline has no place on a boat in my opinion. It's amazing more don't blow up each year, and of course the carbon monoxide issue as well.

 

[boatruptcy]

I post so much about gas and diesel, it must seem I'm anti-diesel and pro gas. But as tiltrider1 comments about fear mongering seems to reflect, their is a biased towards diesel which may not be reflected in reality. Personally I don't think it is fear mongering so much as Joe who read something from Bob that diesels are safer, who read it from Bill that diesels are safer, who read it from John etc. etc.

This from David Pascoe about myths concerning diesel:

"Myth #1: Diesel is safer than gas.
For some reason or other, the fear of gasoline explosions, which are very rare, but had caused some rather spectacular accidents thirty years ago, just won't die. The facts are that gas engines are very safe and you probably stand a better chance of dying or being injured in an airline crash that you do in a gasoline fire or explosion. Yes, gas engines do pose a carbon monoxide hazard, but most of this hazard comes from gas generators.

Diesels are safer from the standpoint of explosions as diesel oil vapors are not explosive. Prior to the advent of water cooled turbochargers, statistics show that fires caused by diesel engines ran nearly 5 times the rate over gas engines. With the introduction of water cooled turbos, the rate of fires has come way down.

Of far more concern is the issue of carbon monoxide poisoning. Diesel exhaust produces far less CO than gas exhaust, though diesel exhaust produces sulphur dioxide that can quickly cause nausea, but is not life threatening. Gas generators are responsible for most instances of CO poisoning, with leaking exhaust systems and station wagon effect a very distant second place. If you plan to do much overnighting at anchor with a generator running, diesel is definitely the way to go."

One of the TF members in another thread about diesel versus gas debates looked up the main cause of fires in boats and found wiring was the culprit. This has really become an issue with older boats and owner modifications which may have not been properly equipped, installed and supported. It is rumoured insurance companies are going to demand stricter electrical surveys on older boats before insuring.

The following is a video carried out by Mercury Marine back in 1957 running two boats on a lake for 50,000 hours illustrating that the then "newer" outboard motors could take a beating. It kind of backs up the claim a well used engine outlasts a little used engine:

[For some reason, even when I down load this video from youtube, it won't play, but if you hit on the sentence to play it on youtube the video will play]

There is no myth, it's absolutely true, diesel is safer than gas. Please don't give people false security about explosions like it could never happen to them. There is a reason they put blowers and ignition protect everything in a gas boat bilge, vapors go boom.

 

[psneeld]

And the reason they are there is to make gas boats safer....maybe not perfect but within the bounds of NOT being paranoid.

Saying gas has no place on a boat is a statement made out of total disregard of reality.

 

[boatruptcy]

I personally know a couple that were literally blown off the fly bridge of a trojan after taking on gas, luckily they survived.

 

[boatruptcy]

And the reason they are there is to make gas boats safer.

Saying gas has no place on a boat is a statement made out of total disregard of reality.

I said it's my opinion, but why ever take the chance? Maybe a bow rider but a cruiser? Hell no, never again for me, the only reason you see them is because of initial price, there is nothing a gas engine does better than a diesel in a cruiser application, that's reality.

 

[psneeld]

I personally know people who have died all kinds of ways.

Big deal, until the root cause of an explosion is thoroughly wrung out ....stories are just statistics with no meaning.

 

[psneeld]

I said it's my opinion, but why ever take the chance? Maybe a bow rider but a cruiser? Hell no, never again for me, the only reason you see them is because of initial price, there is nothing a gas engine does better than a diesel in a cruiser application, that's reality.

No, just opinion and even that depends on the boat and it's skipper.

 

[boatruptcy]

Big deal? Yeah it's a big deal. The cause was ignition of GASOLINE vapors from a bilge blower. You probably won't get it so whatever. I've also been on a boat that ruptured gas tank, bilge filled up, gen running, a miracle it didn't go up. You can argue a lot of things but not that gas is as safe as diesel on a boat....I mean you're trying but you look foolish.

 

[psneeld]

Yeah, my experience and I am trying to look foolish.

As opposed to someone arguing that probably 80 percent or more of all recreational powerboats are way too dangerous to operate. Because they are gassers.

The following are your words...and they don't differentiate about boat sizes, types, models, construction, operation, etc.. etc....

"Totally agree, gasoline has no place on a boat in my opinion. It's amazing more don't blow up each year, and of course the carbon monoxide issue as well."

 

[rslifkin]

rslifkin wrote;
“ So about a 40% improvement for high speed, but easily 60% at lower speed. ”

Way way off at WOT diesel and gas are almost equal. Not even close to 40%. More like five percent. But I read that some time ago and both diesel and gas engines have changed considerably since then.

Modern diesels are definitely more efficient than a gasser (particularly if it's a turbodiesel, which are somewhat more efficient than a naturally aspirated diesel). And definitely more efficient than an old, carb-ed gas engine like mine. For example, a 425hp Cummins QSB 6.7 burns 21.7 gph at WOT according to the Cummins charts, so it makes just about 19.6 hp-hr per gallon. From the limited numbers I can find, my 340hp 454s should be darn close to 30 gph at WOT, so only making 11.3 hp-hr per gallon.

Mind you, the average marine gas engine isn't tuned for optimum fuel economy, it's tuned for idiot-proofing. So you could definitely get the WOT economy of a gas engine closer to the diesels (although probably still a little worse). But by the nature of having a throttled intake, gas engines have more pumping losses at light load, so their efficiency will always fall off more at light load than a diesel will.

That would work as well - my thoughts were to consider replacing the boat with a diesel powered choice.

That's also a thought when the time comes, depending on our boating wants and needs at that point in time. But unless we're looking to go bigger, I'd have a hard time finding something with a better layout in this size range without going to a slow trawler, I think. Full walk-around side decks, 2 cabins with good size bunks (no v-berth), decent galley layout, and a hull that runs very nicely up on plane without the huge sport fish type digging a hole in the water wake makes a pretty decent package.

 

[boatruptcy]

Yeah, my experience and I am trying to look foolish.

As opposed to someone arguing that probably 80 percent or more of all recreational powerboats are way too dangerous to operate. Because they are gassers.

The following are your words...and they don't differentiate about boat sizes, types, models, construction, operation, etc.. etc....

"Totally agree, gasoline has no place on a boat in my opinion. It's amazing more don't blow up each year, and of course the carbon monoxide issue as well."

Experience doesn't make you right, just arrogant from what I can see. It's pretty clear what boat I was talking about here, just read the name of the site you're on. Still waiting for you to tell me what a gasser does better than a diesel in this application, should be easy with all your experience to enlighten me.

 

[psneeld]

If you start being selective we have a discussion instead of a broad brushed irrational fear.

True for most Trawlers, diesel is well suited over gas.

Yet for small Trawlers, gassers could be a suitable powerplant especially if room dictates a sterndrive or outboard application.

 

[JLD]

While there have been some interesting posts in this thread, I think the thread does not have much value in helping someone find a boat and that's because the OP hasn't shared with us how he intends to use the boat and what some of his boat criteria might be.

What are the OP's requirements: budget, age, length, beam, flybridge (ladder or stairs) speed, tankage, etc.?

Seems pretty silly to me to ask if gas or diesel is best without knowing any of this information. If the OP wants a trawler, is going to likely be diesel. If the OP wants a motor yacht, then the choice of gas or diesel is likely going to be influenced by the size of the motor yacht. A smaller motor yacht, generally 36' or less will be gas and over 42' will often be diesel. Between 36' and 42' there might be the option of either.

Jim

 

[ksanders]

(Whew) Thanks for that, John! I've felt like that for quite awhile!

So have I

A well maintained power cruiser can go anywhere and do anything 99% of the “trawlers” here can do.

No they cannot cross oceans, but from being here on TF for a long time now it seems like ocean crossing capable boats are certainly not the majority of “trawlers”

 

[ranger58sb]

I personally know a couple that were literally blown off the fly bridge of a trojan after taking on gas, luckily they survived.

That sounds like you're blaming the gasoline, and not whatever it is that everyone did wrong to let that happen.

?

I said it's my opinion, but why ever take the chance? Maybe a bow rider but a cruiser? Hell no, never again for me, the only reason you see them is because of initial price, there is nothing a gas engine does better than a diesel in a cruiser application, that's reality.

Lots of reason's diesels are "better" but then there are also a bazillion folks actually boating today because they can afford a boat with a gas engine. I suspect if there were no gas boats, there would almost be no boats in the marketplace at all.

-Chris

 

[rslifkin]

On older boats, there's also the which engine fits the use case better dilemma. Power density on diesels was historically a lot worse than gas engines, although this isn't really the case anymore. Looking at my boat, diesels were a factory option. But they were older Volvos rated at 230hp. So if you go for that, you end up with a boat that's 2000 lbs heavier and has 2x 230hp compared to 2x 340hp for the standard gassers.

That's a big difference, as in, with the extra weight, it's probably not comfortable on plane much below 17 kts. And 17 kts is about the best you'll cruise at with the diesels, as with the reduced power, you'd probably make 20 - 21 kts wide open. The gassers comfortably cruise at 17 - 19 kts without pushing them too hard (and are nicely on plane down to 15.5 - 16). And wide open, they're good for 27 - 28 kts.

Personally, putting diesels in this hull, I'd want to power it for a typical planing cruise of 19 - 20 kts at somewhat below the manufacturer's max continuous rating for the engines, leaving a little more on the table for a fast cruise when desired. Top speed would be whatever you get with the engines that meet the other requirements.

Personally, I'm in the "any hull that can plane well should be powered well enough to do it" camp, as it's not worth having the downsides of a planing hull if you can barely get it on plane. In the case of my boat, with the engines available when it was built, the gassers were just the better choice for the hull. Doing that same analysis with engines available now, the answer would be different, as the only reason to go gas would be to save build cost. A pair of Cummins QSBs would power the hull quite nicely and with ancillaries included, the whole setup would only come in about 800 lbs more than the gassers. JD 6068s would also be appropriate power, but they're heavier.

Of course, for the average non-planing trawler, a diesel makes more sense, as efficiency is important. And weight is mostly a non-issue.