relative fuel economy

[jpceir]

Does anyone have data on the relative economy of running at displacement v. planing speeds? For example, will it cost the same in fuel to make a 100nm passage at 10 kts (displacement speed) or at 20kts (planing)?

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[ChrisP]

Think you'll find that it's dependent on the hull shape loading and engines. you'll have to do some pertty complicated maths with the data from your boat to get fuel consumption rates for different speeds. Alternatively go out and do a series of sea trials at differing speeds and tide condtions and build your own database. From there you should be able to make a reasonable prediction. Don't forget to take into account the fouling of the botton, fuel additives, fuel quality and the cruising extras which will all add weight to the boat and affect the performance.
Each boat will perform differently. As a rough average mine gives approx. 1 gallon per mile per knot over 16 knots. I.E. 16kn = 16 GPH, 18kn = 18GPH, 24kn= 24GPH whilst 27 Kn = S**t loads.

ChrisP

<hr width=100% size=1>What do you mean the sea gull in front's walking !!!

 

[ccscott49]

Fairly complicated question, but I knoiw that at 6.5 knoits, I use 1/2-3/4 gal an hour per engine, at 10 knots, 5 gal an hour per engine, I bet you can guess what speed I travel at. But of course I'm a displacement hull. I think you'll find that at displacement speeds a planing hull is very inefficient, which means fuel, at planing speeds, with good trim, possibly less fuel, overall. A planing hull is designed to plane.

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[kimhollamby]

Very dependent on length of boat. Short boat, say 30ft, with a planing hull, might well burn more at 10kt than 20kt; you would have to drop to 7kt to get a real advantage.

Longer boat, say 50ft plus, would more happily deal with 10kt economically compared to 20kt.

All very general though...depends on hull shape, beam, weight, engine(s) and so on.

Do you have a specific example in mind?

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[TroyTempest]

What a coincidence, last night I fitted the fuel sensor on Stingray, will be experimenting this weekend and will post relevant figures.

I'm trying to convince my father that I use less fuel at 20kts than I do at 10, but he won't have it!

Anyway, the old goat choker is coming up to Scotland this weekend, so we should have some fun.

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[Alistairr]

How are you enjoying Largs? Mark..



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[gjgm]

on boattest.com they have tables of revs and speed against consumption etc for the boats theyve tested.Cant remember if its in the results anyway, but you can recalculate distance ag fuel consumption. On the sports boats I looked at there is generally a noticeable hump just before getting on the plane.. ie its more efficient to be on the plane than just off it... but you dont have to go much faster before you lose that advantage! If you find a similar boat and engine to yours, you can drop the data into excel sheet and chart a rather horrifying picture of how you re guzzling the gas ! Damn eye opening though, I warn you !

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[gjgm]

on boattest.com they have tables of revs and speed against consumption etc for the boats theyve tested.Cant remember if its in the results anyway, but you can recalculate distance ag fuel consumption. On the sports boats I looked at there is generally a noticeable hump just before getting on the plane.. ie its more efficient to be on the plane than just off it... but you dont have to go much faster before you lose that advantage! If you find a similar boat and engine to yours, you can drop the data into excel sheet and chart a rather horrifying picture of how you re guzzling the gas ! - at some point it just goes more or less vertical!

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[andyball]

depends on the hull/engine of course. For smallish boats(under 25') there are figures from 1000rpm to red-line using various outboards <A target="_blank" HREF=http://www.yamaha-motor.com/products/otb/perfbull/performance_02.html>here</A> which show the mpg at each speed. Pick a boat with similar size/weight/power to yours & you'll have a very good idea of what to expect.

Used to be other tests at www.yme.com, but can't find them now.

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[TroyTempest]

Hi Alistair, Largs is great, lovely weather yesterday, fitted the fuel sensor and then had a pint outside Nardini's at the Marina - Life doesn't get much better.

Give me a shout some time if you want to "bunk off" for the afternoon and we'll take the boat out!

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[Alistairr]

You'll not be doing much today, there's a hell of a wind blowing.
Bit of a change from yesterday..

Sounds great. i'll need to look you up the next time i'm over.
Let me know your berth no.

cheers..

Alistair...



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[Alistairr]

You'll not be doing much today, there's a hell of a wind blowing.
Bit of a change from yesterday..

Sounds great. i'll need to look you up the next time i'm over.
Let me know your berth no.

cheers..

Alistair...



<hr width=100% size=1><A target="_blank" HREF=http://www.hamptonandmcmurray.co.uk>Hampton and McMurray</A>

 

[TroyTempest]

Birth Number? Don't talk to me about Birth Numbers!

Everytime I get to the marina the damn boats been moved!

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[Alistairr]

"Birth" number, What have you father something?
I said berth no. not birth no.

Can they move it without your permission, have you not paid for a permanent bErth?
Why do they keep moving her?



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[TroyTempest]

Whoops, yes, I have paid for a bErth, but the only guarantee is that you have a berth, not where it is!

The main problem is that there are a lot of events at Largs, so most peoples boats get shunted about!

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[Alistairr]

Thats terrible, is that the same for all bErth holder? That means you can't have your warps spliced to lenght!!!

Did they move you for Stan the Mans weekend?



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[TroyTempest]

It's bloody terrible when any fenders that you tie to the pontoon go missing after your boat is moved!

Stan the Man?

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[Alistairr]

Prossers Sealine Demo Weekend!



<hr width=100% size=1><A target="_blank" HREF=http://www.hamptonandmcmurray.co.uk>Hampton and McMurray</A>

 

[TroyTempest]

Nope, didn't get moved then.

Are you attending this weekends festivities by any chance?

Or will you be raking up a few more hours on your new boat?

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[Renegade_Master]

Re: Kim

Spot on Kim Neils Fairline 50 was cruised at 10kts for most of its trip to the Med and he managed to cross most of Biscay at that speed, (290nm in 29 hrs) and still had plenty of fuel to spare. He has 600gall capacity

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