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Old 03-01-2015, 10:25 AM   #61
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What warranty? I'd never repower with a new engine(s). Secondly, the premise in this instance was to run the boat at reduced speeds/power, so the replacement engines would be in a much, much smaller package....probably fit through the hole for the stripped V12 block. If not, make the hole slightly bigger. Chopping a hole in the hull is crazy.

I've actually looked quite closely at repowering a stabilized Hatteras yachtfish or cockpit motoryacht with one mid sized turbo six...say in the 350-400 HP range... driving the two existing transmissions through a splitter gearbox (or a splitter chain drive box from Ramsey Silent Chain). The engine room in those bigger Hatts is begging for that set up. Spectacular stabilized coastal cruiser and live aboard for reasonable money. If you wanna go slow...do it in style.
I was thinking that you could leave the main engines in place as ballast and squeeze a straight 6 or 4 cylinder engine into the space between the two main engines; easy to fabricate plates to fit onto the main engine mountings.

This way you could place a chain drive to the two original gearboxes saving lots of money.....and of course the main engines could be fired up in an emergency!

The new engine could be a small 4gal/ hr/continuous to give about 7 kts.
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Old 03-01-2015, 10:32 AM   #62
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I was thinking that you could leave the main engines in place as ballast and squeeze a straight 6 or 4 cylinder engine into the space between the two main engines; easy to fabricate plates to fit onto the main engine mountings.

This way you could place a chain drive to the two original gearboxes saving lots of money.....and of course the main engines could be fired up in an emergency!

The new engine could be a small 4gal/ hr/continuous to give about 7 kts.
No obvious way to hook up to the gearboxes with the original engines attached. I guess you could hook up to the front of the two engine crankshafts and drive through the engines with their fuel shut off...heh, heh.
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Old 03-01-2015, 11:01 AM   #63
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No obvious way to hook up to the gearboxes with the original engines attached. I guess you could hook up to the front of the two engine crankshafts and drive through the engines with their fuel shut off...heh, heh.
On further consideration maybe the little new engine wouldn't be powerful enough to drive the massive twin props......

....so the new small engine would need a 3/1 reduction at least to get lots of torque. A chain drive direct to the gearbox output shafts/propellor shafts might work. When you think about it look at the length of chain drive to a motorcycle rear wheel; and some if those big Harley's have enough power to pull up stumps.

How about belt drive a la Harley choppers?
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Old 03-01-2015, 11:04 AM   #64
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Would it still be possible to run one prop in forward and the other prop in reverse with a 1-engine-2-props installation?

I could see a single engine in a Hatteras yachtfish, to be used as a "trawler" or LRC. If there were some with stairs to the flybridge (not ladders), I could maybe be all over that.

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Old 03-01-2015, 11:12 AM   #65
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Would it still be possible to run one prop in forward and the other prop in reverse with a 1-engine-2-props installation?

I could see a single engine in a Hatteras yachtfish, to be used as a "trawler" or LRC. If there were some with stairs to the flybridge (not ladders), I could maybe be all over that.

-Chris
Nice thinking....

Obvious solution: split the gearboxes from the main engines and move a couple of inches to the rear ( easy peasy), then fabricate a 2" wide spacer plate to fit between the old engines and the old gearboxes with a chain sprocket to take the drive from the new small engine.
If you were really keen you could machine a new long shaft adaptor to connect the old engine to the old input shaft of the gearbox, and slide a spocket with a locating keyway onto it to take the new engine drive....

This could actually work....!!!
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Old 03-01-2015, 11:35 AM   #66
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On further consideration maybe the little new engine wouldn't be powerful enough to drive the massive twin props......

....so the new small engine would need a 3/1 reduction at least to get lots of torque. A chain drive direct to the gearbox output shafts/propellor shafts might work. When you think about it look at the length of chain drive to a motorcycle rear wheel; and some if those big Harley's have enough power to pull up stumps.

How about belt drive a la Harley choppers?
The beauty of the Ramsey Silent Chain drives is that ratio changes are as simple as swapping the cogged sprocket-pulleys. Need to transmit more power/torque...use a wider chain. A belt won't cut it. Can't just drive the prop shafts as there's no reverse possibilities. Has to go through the existing transmissions. Same concept as the complicated one into two shaft drive system that's been around for years, but simpler, more flexible, and very likely less costly. The Ramsey chain boxes I've seen are very similar to the transfer case on many four wheel drive pickup trucks.
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Old 03-01-2015, 11:51 AM   #67
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Nice thinking....

Obvious solution: split the gearboxes from the main engines and move a couple of inches to the rear ( easy peasy), then fabricate a 2" wide spacer plate to fit between the old engines and the old gearboxes with a chain sprocket to take the drive from the new small engine.
If you were really keen you could machine a new long shaft adaptor to connect the old engine to the old input shaft of the gearbox, and slide a spocket with a locating keyway onto it to take the new engine drive....

This could actually work....!!!
Now you're making a simple concept complicated and expensive. Extract the junk V12s, install one reasonably modern engine, and use the excess space to install a huge black water tank (for the Great Lakes), a machine shop, a wood shop, bowling alley, some more fuel capacity, and a couple hundred 6V golf cart batteries in parallel. Then go cruising and anchoring out for a couple of years without ever visiting a marina. (Remember to keep those wet cells topped off).
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Old 03-01-2015, 11:58 AM   #68
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The beauty of the Ramsey Silent Chain drives is that ratio changes are as simple as swapping the cogged sprocket-pulleys. Need to transmit more power/torque...use a wider chain. A belt won't cut it. Can't just drive the prop shafts as there's no reverse possibilities. Has to go through the existing transmissions. Same concept as the complicated one into two shaft drive system that's been around for years, but simpler, more flexible, and very likely less costly. The Ramsey chain boxes I've seen are very similar to the transfer case on many four wheel drive pickup trucks.

Those look very interesting.
I'm guessing you would need about 80hp on a big boat to give you 7kts, so the drive system does not need to be enormously strong.

A small Yanmar 4 cyl only weighs 21Okg. and has 110hp max output. With gearbox they are being sold here In Europe for 10k,I guess $10k in the states. This would give you a reverse gear.

It would be very easy to position the output shaft on the new engine gearbox where you need it to drive either the prop shafts, or the original g'boxes if you split them and move them back.

Would the original g'boxes mind been driven by the new engine while in neutral?
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Old 03-01-2015, 12:06 PM   #69
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Now you're making a simple concept complicated and expensive. Extract the junk V12s, install one reasonably modern engine, and use the excess space to install a huge black water tank (for the Great Lakes), a machine shop, a wood shop, some more fuel capacity, and a couple hundred 6V golf cart batteries in parallel. Then go cruising and anchoring out for a couple of years without ever visiting a marina. (Remember to keep those wet cells topped off).
By the time you've cut a hole in the side of the hull to get out the old engines it would cost more than installing a new little engine!
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Old 03-01-2015, 12:12 PM   #70
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Those look very interesting.
I'm guessing you would need about 80hp on a big boat to give you 7kts, so the drive system does not need to be enormously strong.

A small Yanmar 4 cyl only weighs 21Okg. and has 110hp max output. With gearbox they are being sold here In Europe for 10k,I guess $10k in the states. This would give you a reverse gear.

It would be very easy to position the output shaft on the new engine gearbox where you need it to drive either the prop shafts, or the original g'boxes if you split them and move them back.

Would the original g'boxes mind been driven by the new engine while in neutral?
Maybe a clutch at the back of the new engine, but no third gearbox! The two chainboxes stack at the back end of the new engine's crankshaft (probably with a clutch in between). When the clutch is engaged both chains are spinning the input shafts of the original propshaft transmissions...just as when the V12's were running. The only down side of this arrangement is that there is no way to apply differential RPM when maneuvering, for example. Not a big deal with those huge wheels.
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Old 03-01-2015, 12:15 PM   #71
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By the time you've cut a hole in the side of the hull to get out the old engines it would cost more than installing a new little engine!
As I stated in an earlier post...I'd bet dollars to donuts that those engines could be disassembled and taken out from inside the boat in large pieces with much less destructive damage (and cost) than cutting a hole in the side.
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Old 03-01-2015, 12:28 PM   #72
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As I stated in an earlier post...I'd bet dollars to donuts that those engines could be disassembled and taken out from inside the boat in large pieces with much less destructive damage (and cost) than cutting a hole in the side.
Being new to trawlers my conclusion on fuel consumtion: (please make corrections)

Up to 34' and 6-7tons: about 2gal/hr at 7kts
36'- 40' twin engined up to 12 tons: 4gal/hr at 8kts
Above 40' - 50' anything from 7-8 gal/hr at 8kts

So.....

What would be the result of this small engine conversion driving twin props in a big 50' boat?
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Old 03-01-2015, 12:39 PM   #73
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I really like this idea, as you an pick up large boats with big engines for their scrap value.

You could have a fantastic large trawler that is economical to run at the same purchase price of a much smaller boat; nobody wants to buy an old v12 DD unless they own an oil well.
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Old 03-01-2015, 12:52 PM   #74
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I really like this idea, as you an pick up large boats with big engines for their scrap value.

You could have a fantastic large trawler that is economical to run at the same purchase price of a much smaller boat; nobody wants to buy an old v12 DD unless they own an oil well.
That's the concept (which I've occasionally pitched over the years).


I'd guess your fuel burn numbers are in the ball park for a modern engine. Of course power required to move the hull wouldn't change. The big efficiency gain would be from ditching the thirsty, inefficient 2 strokes that are being forced to operate at low rpm. And deep sixing a lot of weight. That said, weight distribution could be an issue. Depending exactly where the V-12's sit in the hull....I'd probably do a weight/cg/stability analysis and position the pin setting machine for the bowling alley accordingly.
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Old 03-01-2015, 01:07 PM   #75
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If not ballasted the stern will pop up like a cork. The bow will go down. 12V71s are very heavy. And, old 50 footish boats can be had cheaply but you gits what you pays for. They are not cheap just because they have old DD engines in them. A 53 Hatt with good running 8v92s and in good useable condition will not sell as cheap as a same model year CC powered similarly that needs lots of TLC. Some of these old boats are just money pits.
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Old 03-01-2015, 01:12 PM   #76
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Some of these old boats are just money pits.
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Old 03-01-2015, 01:12 PM   #77
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If not ballasted the stern will pop up like a cork. The bow will go down. 12V71s are very heavy.
Right. As I mentioned in the post before yours (you were probably writing when I pushed send)....I'd look carefully at engine location and do a weight distribution analysis. That said, lead is cheap...or bolt the V12 cylinder heads down in the lazarette.
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Old 03-01-2015, 02:37 PM   #78
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As I stated in an earlier post...I'd bet dollars to donuts that those engines could be disassembled and taken out from inside the boat in large pieces with much less destructive damage (and cost) than cutting a hole in the side.

A boat neighbor's MAN came out of his 50' Viking in smaller pieces. The replacement also went back in in pieces.

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Old 03-01-2015, 02:46 PM   #79
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Here's a video of a repower where the engines were taken apart both to take out and put in.
http://youtu.be/JzrRW7vthKY
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Old 03-02-2015, 06:13 AM   #80
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I've heard of people taking off one prop in a twin to get better mpg.
Running just one engine with the other prop freewheeling or locked doesn't increase mpg: So prop drag is the enemy.

So....
Run just one engine in your big twin boat, but take a simple v belt drive from the 'running engine' prop shaft to turn the other prop shaft so that's there's no drag: this would probably only need 10 or 20 hp.

Instead of freewheeling it would be 'power driven freewheeling' to cancel drag.

A single v belt with a jockey wheel/spring tension working as a clutch connecting the two shafts together would be a very reliable and simple solution:
Like they use in combine harvesters.

No alteration of the twin setup necessary: put v belt pulley on g'box output shafts of both engines, connect together with one lose fitting v belt which is rated at 20hp, place a spring tension jockey wheel half way between the two prop shafts with a Boden cable connection going to the helm position.

With no tension on the jockey wheel the v belt will just sit there and slip.
With tension it will engage with the pulley and drive the freewheeling prop.
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