IS USING JUST ONE ENGINE FALSE ECONOMY

Some sea spots, instead of engines talk...

Glad to serve as far as Italian coasts are concerned - bits and pieces below, with just a few non-IT places, just to see who can spot them.
I don't think my boat would be so interesting on the other hand, her OB rating is in the same order of magnitude as Magnum's P72, just with the opposite algebric sign... /forums/images/graemlins/smile.gif

1
CT2.jpg


2
ST1.jpg


3
ML.jpg


4
ST2.jpg


5
SR.jpg


6
GS.jpg


7
CT1.jpg


8
CF1.jpg


9
VR.jpg


10
ZS.jpg


11
UW.jpg


12
HP.jpg


13
PL.jpg


14
CF2.jpg
 
Well - bet you didn't expect all that? What an interesting thread this has been, so thanks for kicking it off.

From all the answers above, the likely answer, I think, bearing in mind you're 30' LOA (so hull speed will be ~6kts), is that you're probably using less fuel on two engines at 6 kts (but lose possible saving on service costs) and less fuel on one engine at 4 kts. If you reduce speed through Poole Harbour to 5kts, you may use less fuel on one engine and have the service cost benefit as well.

Either way, you may want to check that your gearbox will not be damaged by windmilling prop on stopped engine.
 
Hi Observer,

Just got back to the forum.

I agree with 1 and 3, but not 2. Even if you reduce the drag of the windmilling prop by stopping the shaft turning and causing the prop to stall (point 1) the assymetric thrust causes crabbing which demands additional rudder which both causing additional drag, plus there is the additional drag from the non-powered prop. All cause an increase in fuel burn to keep the same speed.

So in my book, one burns more than two at all times, provided props are either side of centreline, of fixed pitch, and not foldable.

Now I'm going looking for the Passage Maker mag with the duscussion article on this. Do I still have it....?
 
I agree with much of what you say, Piers, about asymmetric thrust and so on but you're omitting to take account of the element of speed, which intuitively (to me, anyway) is significant. You also discount the observations that I and several other posters on this thread have reported.

I think you're probably completely correct if boat speed is at or approaching hull speed. Why don't you try for yourself at (say) 5 kts which is ~50% of your hull speed and let us know what you find. I won't get the opportunity to test for myself for a few weeks at least.
 
Whilst looking, I have just remembered an implication of running on one engine which is the strain on the rudder stocks. I checked with Fleming for Play d'eau, and was assured the Fleming rudder stocks could take whatever I threw at them (thankfully).

But I know that the artice I've referred to above, stated that some vessels should not be run at near max displacement speeds since the rudder stocks could not take the strain with obvious consequences.
 
Interesting. We've just got back from a week of pottering about, often running on just one engine. Have no idea of fuel economy figures but the increase in speed using both engines at any given revs was a mere 1.5 kts. This is for a pure displacement vessel. So I sort of assume that running on one engine, for me at least, must be more fuel efficient. This now has me interested in fitting a fuel flow meter to make a proper judgement.
 
So I have just taken delivery of a Sealine 365 with triple 200's, my question is this....

If I use the central and starboard engine will I save any more than if I use the central and port engine, or shall i just use the two outer engines....

Sorry could not resist, that should see this post to another hundred....
 
Ha with the price of fuel I'd take out both the port and starboard engines and fill the holes with pollyfilla.. Then flog the engines and keep the boat out on the hard. Then you won't use any diesel at all............
 
Re: Some sea spots, instead of engines talk...

Mapis, great pictures. The cave thingy is, is, is, ....is on the tip of my tongue. I know I've seen it before but can't remember the place.

Your boat looks fascinating and I would very much like to see some more shots of her.
 
Agreed that more sophisticated governors do control fuelling relative to load and rpm throughout the rpm range
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All diesel governors perform like this though some are more sophisticated than others.

The human interface is the speed lever which has a min and max setting, The governor instructs the engine to follow up on the speed setting and will hold that speed even if you lift the boat out of the water or stick the prop in a bowl of syrup.

It is interesting watching the governor on a ship working in heavy weather where the best indication is from the turbo speed and whine. Set the revs at 75 RPM and the turbos will go from idle to full tilt as the load varies with the prop rising and falling in and out oof the water . Your governor will do likewise however the speed is not so finely regulated.
 
If there is energy being absorbed by the windmilling prop - where to god is it going?

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It is producing extra load for the working engine and adding to its diesel consumtion .
 
As an aside, it is a fact that on a ship, slowing from full speed to dead slow is achieved more efficiently by slowing the engine speed rather than stopping it. Never understood why but it works (only a simple sailor rather then a naval architect).
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Yep we saw this with our Rustons where we had clutches to the gearbox.

Engines to Idle and declutched we went for miles as opposed to leaving the prop clutched in and slowly coming down on revs...Just a wee MoBo....30,000 Tons
 
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I'm not saying it does'nt just that on older engines, the governor only controlled idle and max speeds, that's all otherwise I agree with you

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I've seen ancient tractors where the throttle lever controls the engine via the govenor, never directly. As soon as the revs drop due to load at any speed possible for the engine, the govenor will adjust the fuel to keep the engine speed constant within its design limits.

Steam engines were the same. /forums/images/graemlins/shocked.gif
 
Re: Some sea spots, instead of engines talk...

Great photos Mario. Are they all pics of Sardinia? How about some more shots of your boat? She seems like a solid piece of kit
 
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