1 vs 2 diesels, insights please..

[Fletcher500]

I haven't read the entire thread, so someone may have mentioned this. Electronically controlled deisels have an additional factor that can cause them to be inoperable. If you fully understand and carry spares for all the electonic components then you may be equal with a mechanial engine as far as reliabilty, but I doubt it.

I've had friends with newer electronically controlled engines that have had to deal with electrical issues. One wouldn't run, and one would start by itself with no one around.

My old engines take a battery to turn it off unless I go to the engine room and push down on the fuel solenoid plunger. I think I could withstand a lightning strike and the engines would still be running - although I might be dead.

Oh boy.

 

[Delfin]

While I understand the sentiment here - that twin owners have more experience with engine failure due to prop exposure - the bulk of the assertions are bunk. There simply is no denying that twins offer some level of redundancy - what is debatable is how much risk is mitigated and what are the tradeoffs. That can be a really personal calculus, it is for me.

That said, there are twins with fairly well protected props but not many (DF44 and the Great Harbors mentioned above are pretty good, but standouts because of the rarity). These days, most have centerline skeg as a lowest extremity but that offers only modest protection compared to a full keel such as my Willard (which in all fairness, is also fairly rare - my boat can absorb an incredibly hard grounding unscathed). The growing popularity of outboards on distance boats is the epitome of exposed running gear.

After dozens of these single vs twin threads, I have come to the conclusion that some people are single people, some are twins. Their mind is mostly made up and they each have their reasons based on what they prioritize, prior experience, and their use-case. For example, I didn't worry much about skinny water when on the Pacific Coast. Florida is a much, much different matter. People in the PNW see logs all the time which is uncommon elsewhere.

I think every response to a thread like this should begin with "I chose <twins>/<single> because xxxx reasons that are impoetant to me.....".

Peter

So, you reckon that it's near impossible to find a commercial fishing boat, including Being Sea crabbers and East Coast long lines that have twins is because the operators on both coasts are believers in bunk?

 

[SteveK]

Yes, an extra on hand would have been helpful but the fact would have remained that I would continue to have a weak link in the drive line. After my two experiences with them, I will never have them in any boat I own. I replaced them with spacers supplied by Spurs Marine, the folks who make line cutters.View attachment 133953

I can accept your decision not to use them, but weak link is the reason to use them.
BTW, since it has happened twice to you, have you given thought of why it happened? They are designed to break, so what caused it. I can speculate that if the prop did not hit a solid object then the only other sudden stop/change of rotation would be shifting from forward to reverse and vice versa. Maybe not all at once but weakening over time.
If it is the latter, that shock load is now absorbed by the transmission.
Consider the possibility rpm is too high when changing rotation was/is the cause.

 

[rslifkin]

So, you reckon that it's near impossible to find a commercial fishing boat, including Being Sea crabbers and East Coast long lines that have twins is because the operators on both coasts are believers in bunk?

Plenty of the Bering Sea crab boats have twins. If you look at the portion of the fleet featured on Deadliest Catch, the majority have twins (a few are singles).

 

[Cold Duck]

This is a fun exercise. Mission, location, type of boating all will determine what is best for you. Have had 2 big twins, 3 singles. One 70fter when lost 1350hp engine the thrust was so bad I could not manuver in close quarters with asymetric thrust of other engine. Had to call Sea Tow to tow us into harbor. At one time or another every engine was lost, clutch, water pump, contaminated fuel. Single engine for 2 years Ca. to Panama. No Sea Tow etc. I just like options, on a Willard used steading mast for sails including spinnaker that would propel boat as fast as the 50hp engine. If you're coastal US, Sea Tow/Vessel Assist is your best aux to get home. Look at your mission, your capabilities and your comfort level then make the decision. There is no right or wrong answer.

 

[mvweebles]

So, you reckon that it's near impossible to find a commercial fishing boat, including Being Sea crabbers and East Coast long lines that have twins is because the operators on both coasts are believers in bunk?

The yard Weebles is in right now also services the local fishing fleet. At any given time, about a third to a half the boats are twins. The reason commercial boats are configured the way they are usually has to do with economics; and often to 'game' whatever fishery's rules at the time keel was laid. Comparing boats on this forum to commercial fishing boats is akin to comparing a Ford F150 to a OTR 18-wheeler.

It's possible to argue a single is reliable 'enough,' It's not possible to argue one single is as reliable as two singles. When PAE/Nordhavn sponsored their Atlantic Rally 20-years ago or so, it was open to all brands.....as long as they had two forms of propulsion.

But the 'bunk' parts (actual and implicit) of the referenced post are:

1. Singles don't experience running gear failures
2. Twin-owners would not have hit anything in the first place had they had a single
3. Singles take half the maintenance of twins
4. By implication, exposed running gear failure is the biggest issue
5. World's fishing fleets are all singles.
6. Commercial fishing boats run singles because they are reliable
7. The big-daddy whopper: singles are as reliable as twins.

Peter

 

[Mac2]

Maybe it would be more beneficial to state the safety factors of twin vs single. Disregard the maintenance cost-this is an individual choice. Consider factors that are out of your hands. All engines break. All boats will hit something-either debris or the ground. This is the starting point for your decision for twins or single. Now your decision comes down to where you are boating. Can you get help/tow? Are you willing to gamble with paying for damaged running gear? If you boat in the PNW for an extended period, you WILL hit a log(s). The area you boat dictates a lot of the choice.

 

[catalinajack]

I can accept your decision not to use them, but weak link is the reason to use them.

BTW, since it has happened twice to you, have you given thought of why it happened? They are designed to break, so what caused it. I can speculate that if the prop did not hit a solid object then the only other sudden stop/change of rotation would be shifting from forward to reverse and vice versa. Maybe not all at once but weakening over time.

If it is the latter, that shock load is now absorbed by the transmission.

Consider the possibility rpm is too high when changing rotation was/is the cause.

No thought required. Your speculation is incorrect. I had gone aground softly in Cayo Costa. While backing off the bar and applying a modest amount of power, the DriveSaver fractured. You seem to suggest that, without a DriveSaver, shifting forces are absorbed (entirely?) By the tarnsmission. I think not. Isn't it mitigated by the vibration dampener? I don't (can't) know the percentage of boats equipped with DriveSavers but I speculate that they are not in the majority. Anyone who feels more comfortable with having DriveSavers in their driveline, more power to you. But, remember one fact, getting a good alignment with a DriveSaver in place is impossible save blind luck.

 

[SteveK]

No thought required. Your speculation is incorrect. I had gone aground softly in Cayo Costa. While backing off the bar and applying a modest amount of power, the DriveSaver fractured. You seem to suggest that, without a DriveSaver, shifting forces are absorbed (entirely?) By the tarnsmission. I think not. Isn't it mitigated by the vibration dampener? I don't (can't) know the percentage of boats equipped with DriveSavers but I speculate that they are not in the majority. Anyone who feels more comfortable with having DriveSavers in their driveline, more power to you. But, remember one fact, getting a good alignment with a DriveSaver in place is impossible save blind luck.

Jack, I am going by the reason they are sold, to protect the transmission. But never mind. Thanks for a reply

 

[Delfin]

But the 'bunk' parts (actual and implicit) of the referenced post are:

1. Singles don't experience running gear failures
2. Twin-owners would not have hit anything in the first place had they had a single
3. Singles take half the maintenance of twins
4. By implication, exposed running gear failure is the biggest issue
5. World's fishing fleets are all singles.
6. Commercial fishing boats run singles because they are reliable
7. The big-daddy whopper: singles are as reliable as twins.

Peter

1. Where did I say that? Putting words in other's mouths to defend your position isn't terribly convincing.
2. Again, where did I say that?
3. So, two engines to maintain don't require twice as much maintenance as one? Fascinating math.
4. Yes, in many cases, exposed running great increases the risk of damage. You find this controversial?
5. Again, where did I say that? Very large vessels after more likely to have twins, but even large boats like Wizard and the Northwestern are singles. Bunk believers, apparently.
6. Commercial boats are frequently singles not because they are 'more reliable', but because they are cheaper to operate and usually less likely to foul lines and nets. True, vessels in the 100' + range are much more likely to use twins, but huge many taller owners on this site have 100'+ boats?
7. That's right Scooter. All the single screw commercial vessels out there choose single screw because like you, they know they are unreliable, and unreliable equipment is a requirement for making a living on open waters.

 

[mvweebles]

1. Where did I say that? Putting words in other's mouths to defend your position isn't terribly convincing.
2. Again, where did I say that?
3. So, two engines to maintain don't require twice as much maintenance as one? Fascinating math.
4. Yes, in many cases, exposed running great increases the risk of damage. You find this controversial?
5. Again, where did I say that? Very large vessels after more likely to have twins, but even large boats like Wizard and the Northwestern are singles. Bunk believers, apparently.
6. Commercial boats are frequently singles not because they are 'more reliable', but because they are cheaper to operate and usually less likely to foul lines and nets. True, vessels in the 100' + range are much more likely to use twins, but huge many taller owners on this site have 100'+ boats?
7. That's right Scooter. All the single screw commercial vessels out there choose single screw because like you, they know they are unreliable, and unreliable equipment is a requirement for making a living on open waters.

Frankly, I'm not sure what you're trying to say. I have a hard time seeing through the hyperbole. You clearly have strong opinions, but not entirely sure they are based on practical experience. Below is your original post - you made a number of far-flung claims, both directly and implicitly.

As far as doing the math on maintenance costs of single v twin, let's use a real-world example: two GB36s each with a single FL120, most likely in two different marinas. Compare the pair to a GB36 with a pair of FL120s. The only way your 2x math works is if you ignore costs for time, spares, variances in installation, etc.

BTW - Attached is a picture I took this afternoon of a very commercial vessel in the 45-foot range with twins getting ready to be launched.

Peter

Most single screw boats protect the wheel behind a keel. With twins, they are generally more exposed, so damage to one screw is certainly easier to see happen. What this means is that those with twins love them because they may have experienced damage to an exposed screw so are grateful for the other. Single screw folks don't have that experience since their prop is better protected. That, plus the 1/2 maintenance hassle may explain why most commercial vessels in the size we putt around in are singles.

 

[rslifkin]

Twins will have more maintenance than a single, but less than double. For an equally powered boat, a single will be a bigger engine, trans, shaft, prop, etc. So maintenance items will each cost more and potentially be more of a big deal on the single even though there are half as many.

 

[koliver]

Re cost of maintenance for twins v single.
I was able to make a valid comparison, due to owning a single 400hp diesel (in my Motorhome) at the same time as owning my trawler with twin 200hp diesels.
Everything on the Cummins ISL400 is more robust than on the Volvo TAMD41s. Just comparing the cost of an annual oil change, I shopped in the local Bumper to Bumper store. Th twin Volvos need 10l of oil each, total of 20l. The Cummins needs 20l.
The oil filter for the Cummins was exactly 2x the price of the Volvo filters.
The Racors on the boat are cheap, but yes, you need 2. The off engine fuel filters for the Cummins are not cheap, and there are two of them, so way more than the cost on the boat.
Time spent? Pumping out the sumps at 10l each v one at 20l? changing 2 oil filters v 1? Not enough difference to affect anyone's decision.

Other maint items are required so rarely that their cost can't be a significant deterrent to ownership of either engine.

 

[catalinajack]

Those that prefer twins do not likely care about the extra cost. I do not.

 

[Delta Riverat]

Yeah, if you are worried about the cost don't have a boat in the first place.

I've got way more expense with toilets and slip rent than the engine room.

 

[cafesport]

Twins biggest cost is to the first owner, from there it’s mostly a toss up. I must confess I too haven’t read the whole thread and most likely never will, but I’ve participated in enough of these twin vs single conversations to know that most of what is written in them is bunk as mvweebles has so identified. Most participants have an opinion about twins, but they also have little or no data to support their views. It’s too bad the archives are not easily searched because I remember doing a post or ten about most of these things years ago.

If I have internet over the next few days I’ll try to find past posts and create some links. Fwiw I have a twin engined boat that was also manufactured as a single. I also have done many hours on each. My choice and others who have experienced the differences don’t vary.

 

[NWboater2]

I read many of the threads on this imponderable question to test and confirm my own thoughts. Twins are easier to maneuver and have redundancy at the cost of half the room and twice the maintenance. If they have more total power they are faster but use more fuel. Haven’t yet read a thread about someone being saved by a wing engine. Dirona, the Nordy 52 with 12000 hours and pretty impressive gps track has a single jd and as far as I know hasn’t used its wing to escape anything. AT and NT and KK and Selene and many others have one. It’s a calculated choice, not a mistake. Figure out what you want to do, choose accordingly. Maybe you’ll end up with a freeman 42 cat with a pair of v12 600 hp outboards … It just depends.
Here is the port half of my engine room. Just part of the reason I bought this one. GB 42.

 

[backinblue]

Regarding manuverability, would you say a twin is more manuverable than a single with bow and stern thrusters? I think the redundancy of twins is overrated. All road vehicles do very well with 1 engine as do the majority of commercial fishing and other boats. Not that some don't have twins, but singles seem to serve very well for countless hours with no issues. Also, again genearlizing, you likely have better prop protection with a single. But what I find interesting is that this thread has over 100 opinions on the subject but very vew real world experiences. With the broad range of boats and owners on TF you'd think there would be more stories about how a single got stranded or how a twin lost one engine and got home on the other. Lacking that, I conclude that it's a matter of peace of mind or preference, but not a true advantage to having twins for the average recreational boater.

 

[mvweebles]

There are a lot of stories of twin owners losing one engine. I recall doing a lesson on a 42-ish foot Taiwan trawler with twin 120s and lost an engine due to a shredded impellor. I also was on a 42-foot motoryacht that broke a shaft of raw water pump and limped home. CatalinaJack is quick to relate his two failures, one of which was caused by failure of shaft saver. To the extent I agree with Delfin's sweeping statements, I can certainly understand how loss of an engine would cause someone to insist on twins.

I know of several sailboats that have lost use of their single engine. One I recall tried sailing into an open slip and came in incredibly hot, hit hard, climbed over the front of their slip, and mangled the pulpit and bow of the boat on the other side of the dock. Pretty rude, especially since they took the first open slip which wasn't theirs. When the slips' normal occupant arrived an hour later after a day sail, they were to being in trouble when they realized their slip was occupied and had to U-turn their MacGregor 65 sailboat in 25-kt winds (South San Francisco).

As far as twins being maneuverable, they usually are. But not always. I recall another set of lessons on a Marine Trader Pilothouse that was about 50-ft long with a pair 120s. I don't know what the problem was but it was a total pig. Maybe underpowered, maybe mis-propped. But I could not get the bow through the wind in close quarters in a modest breeze. Scary.

And then there are GB36s that, with a single, dance even without a thruster. Delightful boat in close quarters. My W36 and its big sister W40 are pretty good too, but not as good on close quarters.

I absolutely believe twins have an edge in redundancy and reduced risk of trip interruption. I worry more about it on the water than in a car for obvious reasons, especially as I contemplate distant travels where there are not towing options. Consequently, I maintain my single differently. Given my experience of a broken water pump shaft, I replace water pumps instead of rebuilding them (not too expensive on a Perkins). Hoses get a full replacement well before they get soft. Belts get replaced early too. I tolerate zero leaks. So much for "if it ain't broker, don't fix it."

But I totally agree with Backinblue re: issue with this particular topic is lack of candor/experience and too much flippant generalization (my words, not his). The oft-repated corollary about the world's fishing fleets is total bullshit. When you read TFs Lepke's generous mechanical advice, you get a sense of just how experienced these guys are at keeping an engine going, plus they effectively have an entire machine shop aboard. And yes, these boats still get towed-in every once in a while.

You have to be brutally honest with yourself about your boat, its limitayuins, your limitations, and what you want to do with it. For me, that means understanding my single engine boat has vulnerability. It means being honest about my mechanical abilities (I like old-school engines not because they are better, but because I am only a fair mechanic with electrics being a blind-spot - I believe modern common rail engines are superior but beyond my skillset). Without those types of admissions, I am blind on how to best minimize and manage risk. Too often in this topic folks just whisk away the risk. You can't fix what you don't acknowledge.

Peter

 

[backinblue]

Thanks Peter, great post and I agree with you. However I will comment on this:

I worry more about it on the water than in a car for obvious reasons, especially as I contemplate distant travels where there are not towing options.

I would bet a very very small minority of boaters travel to distant places where towing is not an option. More so on this site, but in general very few. Therefore, I'd still contend the comparison to road vehicles is somewhat valid. An inoperable engine is more of an inconvenience than life-threatening. In fact, some road trips could put you in situations where a failed engine could indeed be dangerous. Same with a single engine plane.

 

[mvweebles]

....An inoperable engine is more of an inconvenience than life-threatening. In fact, some road trips could put you in situations where a failed engine could indeed be dangerous. Same with a single engine plane.

Totally agree. With my boat in Ensenada and home base in Florida, I've driven cross country many times these last couple years. The Mojave Desert region of I-8 across Arizona and California can easily exceed 110F, and cell phone coverage is spotty. Yea there are passing vehicles, but few will stop. You could really end up in a dangerous situation.

But in a way, this reinforces my point. You have to be honest with the entire package you are dealing with. Vehicle must be in top condition, and it may not be a good trip for an elderly person, nor infants or toddlers. Or travel at night.

Up-thread, Psneeld posted "singles in populated areas, twins in remote areas." While I think you can make a case for otherwise, I think that crystallizes the risk profile pretty well. It takes heroic efforts to equalize. At least that's my opinion and approach.

Peter.

 

[sunchaser]

First post and thanks in advance to community.
Attending boat shows with wife as we prepare for cruising life in next 2-4 years. Identified trawlers as our preferred platform (liveability, no rushing around, shallow draft, etc) with East Coast, Bahamas and perhaps into Caribbean (USVI, BVI) as cruising grounds. Great loop an interest too. Looking at a range of brands (Kadey Krogen, Krogen Express, Norhavn, Helmsman, etc).

QUESTION: I'm leaning towards twin diesels for redundancy, safety - all the talking points from the twin engine crowd - that is comforting to me. That said, i really lean in and listen to the single engine trawlers group that say it's no necessary due to sea tows, cell /satellite services and so on. "The only thing that stops these diesels is bad fuel."

Am i wrong in thinking twin diesels is the way to go and the liklihood of failures across two engines is near impossible? I know this is a common question, thanks in advance.
Thanks!!

Greg

Back to post #1 and some random thoughts:

After thousands of posts on this question, just ignore the endless squabbles. Focus on a few boats you really like, checks most of the boxes and can afford. If you are in the 50' - 60' range and approaching $750,00 + that implies a used boat just as does a 35' boat for $50,000.

Then if the boat of your dreams shows up it may or may not have a single. The question is not relevant as can be seen from this thread with so many pros and cons ably debated.

A really nice single like a Nordhavn or Selene will be the most expensive to buy, by far. A really nice twin like a DeFever or Grand Banks will be much cheaper to purchase and have twins. Why? Look no further than original intended mission.

So Greg, once your intended mission is determined, size range and cost will logically fall out. Then pound the docks and wear out some boat shoes. Like galley up or down, what anchor or fly bridge or not; the single Vs twin question will drop away.

 

[rslifkin]

I don't worry so much about loss of propulsion from the needing a tow perspective. In plenty of places, you drop the hook, start working on the problem and call for a tow if needed.

But if you spend enough time in very confined waters, in and out of tight harbor entrances, etc. then redundant propulsion of some form becomes a safety concern. I can think of a few places where I'd have the wing engine running before entering on a boat with a single + wing setup. Loss of propulsion at the wrong time would put you aground (sometimes on rocks) faster than you could get the anchor down on all but a dead calm day (and even then, with the confined space, I'm not sure you could anchor without swinging into something dangerous, other traffic aside).

Realistically, the majority of cruising is more benign than those few minutes at a time of concern. In general, I worry more about having a propulsion setup that can maneuver the boat in question adequately, is reliable, maintainable, etc. Whether that comes as single or twins doesn't matter all that much unless I'm expecting a use case where prop protection is really important. And of course, if I like a given boat, to some degree my decisions will be affected by how that boat is offered as far as single vs twin.

Plus, not all twins have poor engine access. It really depends on where the other equipment is placed on a boat. Looking at the GB 42 picture where there are tanks outboard in the engine room, I can see twins being tight for outboard access. But on my own boat (38 feet LOD, 14 foot beam) with nothing mounted outboard of the engines (save for mufflers in the aft corners of the engine room), access is fine other than a slightly awkward crawl over the stringers to get outboard (and having to sit on the angled hull bottom with limited headroom). There's just as much space outboard as there is between the engines, so no real issues working on anything once you get the hang of it. The pictures below show looking outboard across the front of my starboard engine and then the space outboard of it. The muffler is 12" diameter for size reference.

 

[mvweebles]

Greg



Back to post #1 and some random thoughts:
........
So Greg, once your intended mission is determined, size range and cost will logically fall out. Then pound the docks and wear out some boat shoes. Like galley up or down, what anchor or fly bridge or not; the single Vs twin question will drop away.

Nice thought and good advice. FYI - the OP joined Sept 17th, made one post - the one that started this thread - and has not returned since. I'm guessing if he does return, he'll be stunned to learn how much verbiage he ginned-up. The internet version of pulling the pin on a grenade and walking out of the room....

BTW - Jeff Merrill's YouTube channel includes a few interviews with power cruisers. In this one, the recent buyer of a Diesel Duck takes it from PNW to Hawaii. Mid-ocean, his engine shuts down. Took a half a day to find and repair the vacuum leak.

Peter

https://youtu.be/blOJqzt8Rv4

 

[SteveK]

My sig line comes from an experience. As a DIY guy I enjoyed the use of the boat for nearly 2 months on one engine. I just did not want to work on it while the sun was shinning.
I cannot recall having a single since my 22 footer or my sailboat. All twins were 30+ and I still cannot imagine a single, with or without thrusters. Purely personal choice.
As someone said and I agree, I do not care if costs are double. I own a boat for goodness sake, if saving money was the goal I would sell the boat.

 

[Mako]

I can think of a few places where I'd have the wing engine running before entering on a boat with a single + wing setup. Loss of propulsion at the wrong time would put you aground (sometimes on rocks) faster than you could get the anchor down

Good point about the fuel tanks. Personally I don't like P&S fuel tanks in the engine room for exactly that reason, even with a single.

However, your comment above shows a very high level of risk-aversion, personally I'd say too high by my standards, but that just goes to reinforce that a twin is the correct choice for you.

I think the point has been made several times on this thread - there is no right/wrong answer, only personal preferences. Except for anchors... everyone is wrong and mine is right

BTW, Happy Thanksgiving to everyone!

 

[rslifkin]

Good point about the fuel tanks. Personally I don't like P&S fuel tanks in the engine room for exactly that reason, even with a single.

However, your comment above shows a very high level of risk-aversion, personally I'd say too high by my standards, but that just goes to reinforce that a twin is the correct choice for you.

I think the point has been made several times on this thread - there is no right/wrong answer, only personal preferences. Except for anchors... everyone is wrong and mine is right

BTW, Happy Thanksgiving to everyone!

As far as risk aversion, I'd still take a single into those places, but I'd certainly be a little more cautious about it particularly with other traffic. It's more the thought that long distance travel isn't when propulsion redundancy is most important to safety. But if you operate in a lot of confined waters or certain other environments, you'll have more times where loss of propulsion is a safety issue and not just an inconvence. Fortunately, for most of us those situations are a small minority of our boating time, so it's only a minor concern assuming that whatever propulsion is installed is reliable.

 

[markpierce]

Not unusual that a twin-engine "go-fast trawler" uses the same engines as installed in a single-engine, slow-speed version. That has a dramatic effect on maintenance-cost comparisons.

 

[Nomad Willy]

I agree w Caresport.
A very significant element of the question usually not present.

The question of a twin being better is mostly exposed in the fact that the original owner usually pays for most of the 2nd engine. A sizable sum. I wonder what advantage the original owner had in mind? It was speed or safety IMO. I’m quite sure it was safety.

Another thing that could be the elephant in the room is social status. One gets a much stronger male image as in it takes much more courage to go down to the sea in a single. What could go wrong? HaHa several thousand things.

But the thing that gets overlooked is the fact that most trawlers w either single or twin use the same engine. That makes an improperly designed boat IMO.
There’s a speed that every hull is designed for. Very wide as in a planing hull and very narrow in a FD boat. Most all trawlers are heavy boats and w a SD hull-form so lots of power will be required unless the boat is FD. SD trawlers need a lot more power and I’m sure this fits into the equation of single v/s twin. So the biggest elephant in the room may be power. One almost always gets double the power w a twin. Even the other popular engine is a different brand/make it still almost exactly the same power.

So for safety one would choose a twin. And for power one would choose a twin. One could include maneuverability and perhaps other details like prop and shaft vulnerability. Most dead in the water situations are caused by an engine (or engines) quitting.

So IMO the question is power or safety.

 

[Nomad Willy]

Not unusual that a twin-engine "go-fast trawler" uses the same engines as installed in a single-engine, slow-speed version. That has a dramatic effect on maintenance-cost comparisons.

Mark I disagree,
Most maintenance cost is for things like oil, filters and gaskets ect. An engine w twice the power will need about the same $ per hp. More oil, bigger gaskets filters ect. Close to half double the expense.

So the question is how much will it cost to maintain X amount of available power.