Optimum speed for best fuel consumption?

[ianainge]

I am attempting to find out the the optimum speed to travel at to get the best consumption.i know load sea conditions etc play a part but MBY manage to give an indication on their boat reports. Princess strangely dont publish any indication and i cant find one done by MBY on My Princess 360 with Tam 63p.

Looking back through past Editions it appears that semi displacement hulls achieve the best result at 10 knots whereas planing hulls at about 40 foot achieve the best at around 500-600 rpm off of their max revs. However a 50 foot planing hull reverts back to the semi- displacement figures ie Astonda 50 GLX.

if any one knows the figures for my boat or has a back issue with a princess 38 or Phantom 38 test with the same engines that would be helpful.

I`ll send Moose a Pm as he has a similar boat with same engines in case he has some idea.

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[jfm]

There are several boat tests with the 63p engines, most recent that nice Spanish trawler yacht in MBY about 4 ish months ago (forgotten the name of it)

Volvo do a pdf data sheet with fuel curve <A target="_blank" HREF=http://www.volvo.com/volvopenta/uk/en-gb/marineengines/powerforleisureboats/diesel_inboard/tamd63/>http://www.volvo.com/volvopenta/uk/en-gb/marineengines/powerforleisureboats/diesel_inboard/tamd63/</A>

If it were driving a truck the answer would be easy, best mpg = idle/minimum rpm in top gear. The prob with a boat is that it is affected by whether the boat is planing or not, so you really need data for your specific model of boat rahter than some other one. You can however compare rpm with boat speed on your own boat, then get the fuel burn rate data off the volvo graph, and kind of plot a mpg vs rpm graph

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[itsonlymoney]

Thats easy Zero mph = best mpg
Ian /forums/images/icons/smile.gif

<hr width=100% size=1>Play the best game you can with the cards you've been dealt ! ! !

 

[hlb]

Not scientific but I recon 18 knots is about right for anything planing. Much slower and your likely to drop off the plane and anyway it feels like stopped.

<hr width=100% size=1> Get Yer Flags ear</font color=red>
Haydn

 

[jhr]

<A target="_blank" HREF=http://www.boattest.com/main.aspx>Boattest</A> publish consumption figures at various rpm with their reports. However, they're an American site, so don't cover everything, and may or may not have info on Princesses - but might give you a steer for a similar craft.

I'd have thought your W.O.T. less 5-600 rpm would be a reasonable benchmark.

Hope this helps


<hr width=100% size=1>Je suis Marxiste - tendance Groucho<P ID="edit"><FONT SIZE=-1>Edited by kimhollamby on 22/06/2004 15:12 (server time).</FONT></P>

 

[Observer]

Actually that's the worst. Zero distance for infinite fuel (if the engine's running).

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[jfm]

Volvo digi display, fred drift

Observer I notice from the website you have those Volvo EDC electronic displays, the 4inch square things. I am contemplating retrofitting these to our boat (I think they just plug and play with a network cable into the EVC system) mainly to get mpg and therefore range data (with a NMEA data feed).

My question is, do I need one or two units?
(a) Are the displays configurable so they show port engine and stbd engine data on the same display, and if yes is it shown simultaneously or sequentially?
(b) Alternatively do you need 2 display units to monitor 2 engines?
(c) Or indeed, do they add together the fuel burn data so one unit gives you combined mpg for both engines?
(d) can you program in your fuel capactiy to get a range figure on the display?

Thanks

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[mjf]

Ian, I have the curves for my boat and also the Fairline Phantom 38.

If you pm your fax # I will send over.

Are you up and running again yet?

Michael

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[DavidJ]

I've got 2 points on the graph for you with a Sealine S37 with twin KAD 43's Last year long distance cruising (ie 100 miles) at 22 knots (3200rpm) gave 2mpg. This year same sort of treck at 28 knots (3500rpm) gave 1.5mpg. I don't think any slower than 22 knots would work out any better. My max rpm is about 3800.

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[Jinks]

Be careful regarding US figures as their gallons are different to ours.

UK gallon times 1.2 = US gallon.

Apologies to those being taught how to suck eggs.

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[Observer]

Re: Volvo digi display, fred drift

Hi jfm,

(a) & (b) Needs one for each engine.
(c) you have to add the fuel consumption data for each engine. From memory, the display has four 'pages'. Page one gives analogue engine speed boat speed and fuel consumption as galls/litres per nm. Page 2 gives digital or analogue engine speed, coolant temp., battery charge (volts) and oil pressure; page 3 gives trip (engine) hours, trip fuel, current consumption as galls/litres per hour and total engine hours. I can't remember what page 4 is - maybe system setup. You can self-program next service due so when the number of hours clocks up the display shows a 'service due' message at power up.
(d) No - no capacity to compute or display range.

If you want chapter and verse, I'll try to get hold of the manual.

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[Wiggo]

From what I read, it should be at 85% of WOT, so for me that's about 3250rpm (KAMD43's), which bears out what DavidJ said. The TAMD63p should be most economical at 2380rpm, in theory.

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[DPH]

Something to ponder is the strength and direction of the tide.

I try to cruise at 3200 going against a tide and 3000 with it. Not very scientific but makes sence to do this in my head.

I'd love to know what the maximum revs for crusing with KAD300s is.



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[coliholic]

According to www.boatdiesel.com it's 3,800 rpm.

http://boatdiesel.com/index.cfm?CFID=2467803&CFTOKEN=78712640&CFApp=19&&Red=NRU&CFIDC=NRU2



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[Observer]

Dave,

On our Sealine S41 (KAD300s), the DIC displays suggest that there is little difference in fuel consumption (expressed as galls per nm) between 3200 (25 kts cruise) and 3800 rpm (WOT about 32 kts). Anywhere in that range seems to give about 0.7-0.8 galls per nm (0.3-0.4 each engine). Galls per hr is about 8 at 3200 rpm, 10 at 3500 rpm and 12 at 3800 rpm (each engine). These were taken in flattish conditions. I haven't collected data for a range of different conditions.

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[Jinks]

What's WOT please?

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[Observer]

Wide Open Throttle

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[Planty]

I used a calculation from a book I think is called Power Master?? Anyway it uses the given speed at given Revs, plus the optimum Torque of engines and the waterline length of boat in some longwinded calcs that eventually gives you consumption at each 100 revs etc. Thus the optimum cruising speed can be found.
On our F43 having done speed trials across Poole Bay last year in a flat calm, on our twin Volvo 74's it suggested 2100revs was optimum fuel consumption. This gives 24-25knots, good cruising, and we reckon has dramatically reduced our fuel bills.
The book is on the boat, I'll try and remember it and post the calc on here next week, if that would assist. Paul

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[tcm]

erm surely most economical for a boat, planing type or otherwise is most certainly not planing, nor at most of WOT? Suncoasts gang brought a fairline 50 over monster ranges through biscay at under 10 knots. Borin, but cheap.

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[Benny1]

Planty,

If you could post it next week, that would be v interesting. I love a good experiment!

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