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Old 15-04-2013, 18:43   #1
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Single John Deere or Twins for Offshore

Its an important question as ultimately the answer will determine the brand and model of the 58 or 64' Passagemaker I plan to purchase. I am NOT an experienced sailor but a quick study. I have been on a number of boats as a diver and own a small boat now.

Let's assume the running gear is not the issue as protection is there single or twin. But, sand or seagrass etc. could be sucked up into an engine and then you have a problem. Or an unusual problem the mechanic at your starting port failed to catch an issue or something simply broke. I know John Deere's are very reliable but anything man made can break. Twins give you the ability to have a full engine vs. powered by a generator driven get home certainly with the power you need to get home but you have twice the maintainence and expense, more fuel burned and more costs of spares etc.

So, assume I need the Idiot's Guide to Diesel Engines to try to get home where all I can do is change an impeller, pencil zinc, fan belt, the oil and/or fuel filter and that is the extent of what I can do... Do I go with a single engine or for the extra safety margin of dual engines.

Note: I am a stickler for proper maintainence when do. Engines would be NEW starting out.

What is the right choice here?


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Old 15-04-2013, 18:59   #2
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Re: Single John Deere or Twins for Offshore

For a boat of that size, I would have to say twins because of the manuverability.A boat of that size will be pretty hard to handle in close quarters with a single. IMHO

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Old 15-04-2013, 19:57   #3
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Re: Single John Deere or Twins for Offshore

The bottom line is there are a lot of trawlers and other types of power boats cruising around the world right now with single screws. There are trade offs with both and yes, you should and will learn to work on your diesel engine(s)

If money is not a consideration then you could go with twins, but you will be cutting in your navigational range by half since I would guess there is no opition for more fuel tankage. On the other hand you will be able to go faster, if that is your goal.

If money is being considered, twin engines will double your fuel and maintenance bills. Not to mention the initial outlay of funds for the second engine.

Bow and maybe a stern thruster, as well as a good prop walk, will compensate for close quarter manuvering on a single screw. So manuverabilty is normally not an issue when considering twin or single screws.

If you are worried about only having one engine, I would find out if they have the option of a take off unit on the Gen Set to be used as a "Get Home" motor. These are normally very slow as compared to the main engine (3 or 4kts), but does give you a back up, while you repair the main engine.

When I convert from sail to a power boat, mine will be a single screw with a bow thruster and a "Get Home" take off from the Gen Set.

Good luck with your purchase!
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Old 15-04-2013, 20:08   #4
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Re: Single John Deere or Twins for Offshore

Originally Posted by Terry.157 View Post
But, sand or seagrass etc. could be sucked up into an engine and then you have a problem.
If you're sucking sand or seagrass into the engine, whether you've got twins or a single screw, you've probably already lost the props.

Technology doesn't trump stupidity. Ask yourself how many screws the Costa Concordia had.
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Old 15-04-2013, 20:58   #5
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Re: Single John Deere or Twins for Offshore


I would point out that probably the best built long range power boat on the market is the FPB 64 by Steve Dashew. Which has a single screw. The real issue is that the majority of engine problems are related to fuel not engine issues, and if you have a fuel problem it will strike both engines at the same time.

That being said they did outfit one of the boats with a small (25hp if I remember correctly) Diesel engine. If I remember correctly it was placed slightly off center and added a folding prop. It wouldn't work for real running, but could maintain 3kn or so just in case the main diesel failed.

Correction: the FPB get home is a 100hp Yanmar that will maintain 7+kn in 30kn headwinds. Much larger than the engine I remembered.

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Old 15-04-2013, 20:59   #6
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Re: Single John Deere or Twins for Offshore

As a non turbo John Deere owner it depends on what sort of power you need to cruise.

I've found my 4045DFM likes it between 1500rpm and 2250rpm. Without checking the power curve I think that translates to roughly 20hp to 60hp and 4 to 12 litres/hour.

If you're after max fuel economy then a single 4045DFM might just about do the job, but would struggle at times.

If it were me then I'd seriously consider two 4045DFMs for long range cruising. Maybe gear them down 3:1 for a bit of extra oomph against a heavy sea and headwind.

From memory all the bigger six cylinder John Deeres are turbocharged, the smallest being about 130hp. Nice, but you'd loose the ability to run long distances at low rpms.

Conventional wisdom would suggest using two bigger diesels of (say) 180hp each and this would be an option worth considering particularly if you like a bit of speed.
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Old 15-04-2013, 22:14   #7
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Re: Single John Deere or Twins for Offshore

2012 Challenge 52 ft Passagemaker Power Boat For Sale -

If this is the kind of boat you want, then I would focus on a well installed Single Engine allowing you enough space in the ER for properly installed ancillary equipment, leaving space for maintenance and a work bench.

Too often designers compromise both engines by squeezing them into too tight a space with insufficient air changes to keep ambient temperature low.

Carry a full set of cruising spares and design the steadying sail rig to keep you out of trouble

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offshore, single

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