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Old 05-19-2011, 05:12 AM   #21
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RE: Running single on a twin to save fuel

Very rare in this country to see a commercial boat with more than one engine.
In the merchant fleet the same applies except when getting into very large HP ships such as box boats.
I sailed on one product tanker ( not large 25000 tonnes) with twins but this was thru a single CP prop and each engine had a 1500 KW gen set attached.
All power to gen sets and prop was transmitted via air bag clutches.
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Old 05-22-2011, 08:14 AM   #22
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RE: Running single on a twin to save fuel

I believe the original comment/question was can a*planning hull*boat operate more efficiently on one engine below planning speeds. I started this exact same discussion last Oct:*http://www.trawlerforum.com/t38913265/operating-a-twin-on-one-engine-and-fuel-economy/?r=548802
My conclusion and experience was that it can and the savings can be sufficient to do so. Not all agreed with me, but my calculations showed that it could.*
I recently cruised for an hour at 7.5 kts swapping engines every 15 minutes to keep the tranny's lubricated. My calculated savings were about 35%.
However in the realm of pleasure boating running about 100 hrs a year, it just may not be worth the effort to do so. When fuel runs upward of $5/gal we'll probably have this discussion again.*
The 2 vs. 1 engine will always be a personal choice. However a planning hull boat requiring the power necessary to plane will more than likely have a high output engine that's turbo charged. This introduces a lot more failure prone machinery and hence the necessity of 2 engines. A normally aspirated Yanmar, Perkins or Lehman on a displacement-hulled boat is far less likely to experience a failure and perhaps the necessity of 2 engines is diminished.*
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Old 05-22-2011, 09:25 AM   #23
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RE: Running single on a twin to save fuel

In the discussion on Boatdesign.net it was noted that some boats (commercial charter types..I think) ran from Seattle to SE Alaska on one engine but they removed the prop on the engine not to be used. But to run on one and drag the other prop through the water seems to be a very poor substitute for a good economical boat. And if you ran your twin engined boat all the way to Alaska on one engine to save fuel would you then switch to twins when you get here? If the answer is no then I'd suggest this person needs a different boat. One that works much better and more economical on one engine. As an alternative one could remove one engine all together including the shaft and struts. One would want to insure that the prop walk turned the boat in the direction of the remaining engine. If there were port and stbd fuel tanks the one on the engine side could be removed. Also batteries and other heavy equipment could be moved to the light side. The boat may handle badly in following seas from one side and have other vices not so obvious. But this is all a bad idea as one should have a boat that is optimised for what one does.
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Old 05-22-2011, 10:30 AM   #24
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RE: Running single on a twin to save fuel

Seems the best solution is to acquire an as-designed*single-engined vessel to begin with.
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Old 05-22-2011, 11:42 AM   #25
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RE: Running single on a twin to save fuel

Per

You raised an interesting point saying engines are the most costly part of maintaining the boat. For our total boat ownership costs, this is not the case. Good maintenance normally keeps engine costs well in check. For us, far bigger ownership*numbers are:
<ul>[*]Annual moorage*[*]Upgrades (diesel heat, bow thruster, enclosed fly bridge*etc)[*]Fuel[*]Exterior upkeep such as bottom paint,*waxing,*FRP repairs, varnish[/list]And we have twins!
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Old 05-22-2011, 11:53 AM   #26
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RE: Running single on a twin to save fuel

Quote:
sunchaser wrote:
Per

You raised an interesting point saying engines are the most costly part of maintaining the boat. For our total boat ownership costs, this is not the case. Good maintenance normally keeps engine costs well in check. For us, far bigger ownership*numbers are:
<ul>[*]Annual moorage*[*]Upgrades (diesel heat, bow thruster, enclosed fly bridge*etc)[*]Fuel[*]Exterior upkeep such as bottom paint,*waxing,*FRP repairs, varnish[/list]And we have twins!
*Well said Tom
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Old 05-22-2011, 05:54 PM   #27
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RE: Running single on a twin to save fuel

Until I gave it away, my Espar heater was the most costly bit of maintenance on my twin engine boat. second was the fridge, as it required a huge commitment to supplying amps, and the batteries couldn't possibly keep up. the twin engines are still way down the list.
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Old 05-23-2011, 04:10 AM   #28
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RE: Running single on a twin to save fuel

"Annual moorage "

Dont use a marina dock, get a mooring and dink


"Upgrades (diesel heat, bow thruster, enclosed fly bridge etc)"

One time expense for most


"Fuel"

Go at SL .9 and the fuel bill gets smaller.


"Exterior upkeep such as bottom paint, waxi

Good bottom paint is every 3 years, A can of Collonite is under $10. retail, exercise is good .



The point is expen$es are what you choose to make them , not fixed.
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Old 05-23-2011, 07:47 AM   #29
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RE: Running single on a twin to save fuel

FF -* You forgot to add another way to save money is keep a navy launch in my Florida backyard with a 6-71 for power. I'm so envious, some of us have all the luck.
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Old 05-23-2011, 12:06 PM   #30
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RE: Running single on a twin to save fuel

if you upgraded your twins, i bet that would be the most expensive cost in the lifetime of the boat.
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Old 05-23-2011, 01:37 PM   #31
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RE: Running single on a twin to save fuel

Per* --* Quite the contrary. On newer boats, twins are often cheap in comparison to buy once you get above 45'. I recently made an offer on an expensive Brand X single engine boat. Fortunately they turned the offer down so I can*cruise with*my cheap twins for the rest of the year it appears. Until another expensive Brand X single comes on the market that is ----.

This discussion reminds me of the guys who buy a* Lexus, Infiniti*or Porsche hybrid*to save money on gas.
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Old 05-23-2011, 01:41 PM   #32
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RE: Running single on a twin to save fuel

Quote:
sunchaser wrote:
FF -* You forgot to add another way to save money is keep a navy launch in my Florida backyard with a 6-71 for power. I'm so envious, some of us have all the luck.
*FF,*

Have you met the guy who has a navy launch he keeps at Rialto Harbor. We rafted up with him and his wife for dinner and the night 2 months ago. I believe he lives in Ft Myers. Very nice job of converting her.*
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Old 05-24-2011, 03:25 AM   #33
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RE: Running single on a twin to save fuel

Very nice job of converting her.


For someone that wants a nice cruiser , has a couple of years , and the skills and background to do the work its a nice way to go.

There would need to be a special Desirement , that a stock cookie cant meet to make it worth the effort.

One advantage to a 50 ft hull is one could liveaboard very early in the conversion.

The low time hulls with running , mostly cummins power, are running about $35K in Boats and Harbors.
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Old 06-07-2011, 04:24 AM   #34
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RE: Running single on a twin to save fuel

white vapor at the tail pipe (over fueling)

White smoke is underloading or poor compression or low cylinder temps.

BLACK smoke is too much fuel.

The trailing prop is a big drag , one cure is power feathering. A small 1 hp or so electric or hyd motor is installed to spin the prop, but not push the boat.

This will allow centered ahead rudders , and no prop drag.

Alternators and DC motors are not efficient,, but way better than a dragging prop.
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Old 06-07-2011, 08:11 AM   #35
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RE: Running single on a twin to save fuel

Quote:
boatk9 wrote:
*The corresponding fuel flow*was*3.1 gph (per the chart).* That's about a 23% improvement over twin operation...far more than I expected.* I attribute the improvement to bringing the turbo charger on line. *



-- Edited by boatk9 on Monday 6th of June 2011 12:52:43 PM.
*My experience is very similar to yours. I have a planning hull with turbo charged after cooled engines. I believe the turbo's kick in around 1400 rpm. I set both engines at 1300 rpm and achieved 8.3 kts with a fuel flow of 4.9 gal/hr. For my boat this is displacement hull speed. I shut one down and left the remaining engine at 1300 rpm. Speed dropped to 7.1 kts and fuel flow was cut in half to 2.45 gal/hr. A whopping 41% improvement in fuel mileage.*

I attribute this improvement to several factors. The engines are huge compared to the boat displacement in order to achieve 25 kts. At displacement speeds only a small amount of power is distributed to the prop but a larger amount of power is used just to keep the engine running, ie alternator, raw and coolant pumps, etc. Shutting one engine down doesn't really cut the power to the props in half, but does eliminate all the other ancillory items from consuming fuel.*

My props are close together so assymetrical thrust is minimual or at least less than perhaps other boats. A 3/4 turn of the wheel into the stopped engine is all it takes.*

My guess is if you were to leave the throttle setting the same ie did not increase the remaining engine to maintain speed, your fuel mileage would be even better. I believe the tubo only increases performance at the top end, above 50% power thus the reason it kicks in at a higher rpm.*
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Old 06-07-2011, 10:08 AM   #36
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RE: Running single on a twin to save fuel

The very existence of this conversation indicates someone has the wrong boat. Do you guys think this is a solution to your problem? I wonder what it would cost to convert to single engine? Weight is a huge part of a boats resistance (especially a planing hull) so you would be shedding not only the weight of the engine removed but half the fuel, perhaps a start battery, a prop and shaft and likely other stuff. Could be 2 tons with a boat that size. But resale value may go down*** .... it may go up but not likely as a prospective buyer could buy a regular single engine boat. Thinking out loud.
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Old 06-07-2011, 11:52 AM   #37
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RE: Running single on a twin to save fuel

Quote:
nomadwilly wrote:
The very existence of this conversation indicates someone has the wrong boat. Do you guys think this is a solution to your problem?*
*Wrong boat?? *Solution to our problem??

Not sure what the problem is. Discussing the most economical way to operate a boat does not indicate someone has the wrong boat.*

Your boat is perfect, OK nearly perfect for you. You can take whatever those Alaska waters can throw at you cruising along at 7 kts.

For me in So FL cruising the ICW where waves rarely exceed 2 ft takes a different mind set. I like sitting up high in the breeze watching the sea life and shore go by, sometimes at 20 kts. I also like my wide beam, full size bed that I don't have to climb into, relaxing sundeck, wide salon with wide screen TV and stairs from the swim platform to the sundeck. Yea, I know, I've gotten soft and comfort trumps sea worthiness, but have you never had the desire to get somewhere quickly, to beat a storm or anchor before sunset, or just relax before it gets dark. If so then Eric, may I humbly suggest that perhaps you have the wrong boat.*

*

Attached below:

Bridge view of Florida Straits, 1/4" following seas, 20 kts, 70 mile run in 4 hrs, 70 gallons
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Old 06-07-2011, 08:48 PM   #38
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RE: Running single on a twin to save fuel

boat9 and timjet,

I'm really sorry guys. I had the idea you were trying to operate your cruisers as trawlers. Yes the practice does save fuel and it looks like now and then you're taking advantage of that. Perhaps some winter I'll come down there and see what it's like. I did post on BoatDesign but I did'nt start the thread. I would never have thought of that. I just wanted to tap the knowledge and information that came from it and share on TF. Sometimes the same discussion is on TF and BoatDesign and some on TF (like me) are on BD as well. I like to think out of the box and I like to share my thinking with others and I know I sound rather uppity and come out like a know-it-all fairly often. I like to say what I want to say and share my opinions freely. My comments like changing to a single screw or converting a sailboat to a trawler are completely speculative also unless otherwise presented. When it comes to a good seaworthy small and economical trawler I do have a good boat but ther'es lots of features of the W30 I don't like. And I did or still do think I have the wrong boat and spent lots of time this winter shopping for another but the Willard is close enough considering that most likely I'd jump into a a project boat or nearly so so I decided to invest my time in the Willard and do more cruising. Speaking of cruising you'll get a break from me as I'm headed for Sitka in a few days. Anyway I'm sorry about the misunderstanding and I'll try hard not to do that again.
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Old 06-08-2011, 04:40 AM   #39
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RE: Running single on a twin to save fuel

"So you're saying a smaller set of injectors wouldn't help reduce incomplete combustion at low power settings? "

YES , the load is so light the compression pressure (after ignition) is too low.

Much of your fuel use efficiency comes from getting the turbo to work , instead of being an intake restriction.

For most engines at least 1 pound of boost is required to get ant efficiency.

There are waste gate turbos , and dual spool units that solve this at big cost.

Ship engines today use 4 turbos which can be taken off line as required , now that "slow steaming" is in vogue for some portion of operation.
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Old 06-08-2011, 10:02 PM   #40
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RE: Running single on a twin to save fuel

No disrespect but I do'nt see how a planing hull can be run w only one engine (with it's asymmetrical thrust and necessary rudder deflection and dragging prop) and be "quite competitive with full displacement." in fuel burn. I think a planing hull will have 2 to 2 1/2 times as much resistance as a full disp hull run about 15% below hull speed without any asymmetrical thrust or dragging propellers. Remember that FD boats don't run at hull speed. Hull speed is their TOP speed unless they are overpowered. It just dos'nt seem possible. Feel free to beat me up on this if I deserve it.
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