Diesel 500HP marine - straight-6 vs V12

Hello all
You are a group with a lot of technical interests and knowledge.
Boats - for a vessel with a single screw and about 500HP, or a
twin-screw vessel with about 1000HP (500HP each engine and gearbox drive)...
Some have a/two straight-6cylinder engine(s) like the Cummins K19(M?)
Some have a/two Caterpillar 3412 V12 engine(s)
Why?
The straight-6 would be - cheaper? simpler? The V12 would be - ... ?
Thanks in advance is you can help take this curiousity to its end-point.
Regards, Rich S
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That's about having two engines, regardless of what type.
For sure, the twin-screw boats are in a much higher class and capability. I as a welder with minimal boating skills can see that. The way they can rotate barges they are tethered to - very desirable. One engine forward and one engine astern. Our area is very tidal, with two nearly identical tides per day (12hr50min apart) (the Pacific has, in the main, just one tide per day??). So the ability to manoevre in big tidal ebbs and flows is especially needed. Plus - propellers do get damaged in estuary work, and having two engines it leaves you with one to get finished and get to a yard.
That I have observed - both manouvrability and surviving damage.
Then there is the question - what causes the choice between a straight-6 and a V12?
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On 23/3/20 5:43 pm, Richard Smith wrote:

No. Everywhere on earth, there are (almost) two tides per day, because the high tides circulate (roughly following the moon) on *opposite* sides of the globe.
It's like two dancers spinning around each other - both are flung outwards away from the centre.
On average, the moon contributes about 1 metre of tidal flow, and the sun about 0.5 metres. When these line up, you get 1.5m, and when they're at right angles, you get 0.5m.
Up to here, all this can be calculated from the gravitational equation, with knowledge of the orbits, masses and distances of the earth, moon and sun.
Places with very high tides are like the slosh in the corner of a square bucket - they're at "corners" of the oceans.
Clifford Heath.
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You are both right, depending on where you look. https://www.britannica.com/place/Pacific-Ocean/Tides
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Hi Jim, all
I've simply heard about this big difference of our Atlantic tides with the Pacific. Cannot make informed comment.
Here in South Devon - the "English Channel" side of Devon on the West Country peninsula - tide ranges are something like 4.3m on "spring" tides and 1.7m on "neaps (I easily found 4.5m range "spring" and 1.5m range "neap"). Working on marine tubular piles with a 4+m tide range has its interesting aspects ;-)
On the original question of engines: Wikipedia proved very useful https://en.wikipedia.org/wiki/Straight-six_engine https://en.wikipedia.org/wiki/V12_engine Other Web searches seeking to know the comparative advantages of I6-vs-V12 produced some more comment, like optimum bore/stroke ratio being different between the two types, etc. I don't have the ability to even collate the impressions gained and summarise.
Just one comment - the inherent excellent balance characteristics of a six-throw crankshaft means the V12 can have a 60degree angle - not 90degree as needed for most other "V"'s - so the engine can be notably compact - it's narrower for a "V" than it otherwise would be - advantageous for a boat where likely can accomodate length no penalty but width is strongly undesirable.
I do note that the "500HP" (commercial) Caterpillar V12 is offered in a leisure-craft-only variant giving 1300HP - which surely a 500HP straight-6 cannot morph to - I assume it sticks at 500HP and that's it?
Is there the case that Caterpillar saw a vast market for the V12, across many in-house earthmoving eqt. plus "external" industrial and marine applications, so took a deep breath and invested the cash building a high-volume production-line, much flattening the cost differential between their V12 and and anyone else's I6???
Best wishes, Rich S.
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On 24/03/2020 18:05, Richard Smith wrote:

Richard,
https://www.coxmarine.com/ as it's a 60 degree V8 for compactness which means it uses a flying web crank design for even firing. I know a bit about it as a friend was involved in some of the design.
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On 24/3/20 10:08 pm, Jim Wilkins wrote:

The diurnal tides are coastal, also caused by coastal slosh.
The ocean tides follow the pattern I described. There are many finer details in tide modelling too; about 10 different oscillatory periods in the models used by oceanographers. But to a first approximation, moon->1m and sun->0.5m, plus slosh, gets you very close.
I live on the Pacific coast, swim in it often, and always check the tide chart. Mixed tides, here.
CH
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wrote:

I'm no naval architect, and only have outboards. Nothing near that size. I would guess the V-12's advantage would be more compact size for boat design, as well as possibly higher rpm, different vibration qualities for easier soundproofing in high end applications. The sixes would probably be easier to maintain, not just because of less parts, but because the package shape would lend itself to better access in the engine room.
Just thinking on the keyboard here.
Pete Keillor
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Let's see if anyone with commercial marine experience responds. Your surmises are the sort of thing I would wonder. Regards, Rich Smith
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Peter - when surmising, you'd only have to miss / be oblivious to just one significant factor and the entire balance and therefore optimum solution is missed. Reason I asked the open-ended question. Regards, Rich
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