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Old 10 December 2002, 17:04   #1
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Mercruiser 1.7 fuel

Hi all…….

Some time ago I was involved in a thread discussing the fuel consumption of my Mercruiser 1.7 Turbo diesel. Well, I now have some accurate-ish figures!

I filled the tank up to the brim at the begining of September. From then, until I re-filled to the brim again for over-wintering a couple of weeks ago, I did a total mileage of 255 Nautical Miles. (GPS derived, so slight inaccuracies over water here but over a period should have evened out!). Engine hours have been 19.5, so quite a lot of slow pootling about in harbours since an average speed of 13 knots! (Fuel cost £43)

The fuel needed to re-fill to the brim by can was 175 litres…. So the answer is….

Litres per hour = 8.97

Litres per Mile = 0.69

Again, this is over mixed speed. Obviously, full blast across the channel for 3 hours to Guernsey or somewhere would undoubtedly reduce the Litres per hour figure! More on that next year!

One other point of interest, I think she is a little over-propped at the moment. Maximum speed I’m getting, one-up with not much fuel in the tank is 33 knots. This reduces to about 31 knots with a full tank, 3-up…. and in that situation the maximum revs are barely 4,000. They should be 4,400! The engine has only done 35 hours total and needs to loosen but even so!

Current prop is a 23” Ally …. So if anyone has a 21”s/s that will fit an Alpha One leg that they don’t want, …. Let me know.

Hope this was of interest!

Mike C
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Old 11 December 2002, 06:21   #2
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Hi Mike
Am I having a dumb moment?
255 nmiles for £43
wow thats a lot more sensable than my old 2 stroke
Jelly
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Old 12 December 2002, 09:20   #3
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Hi Mike

As it happens I have the same size rib; ie a Parker 630 fitted with the same Mercruiser diesel 1.7 TDI. I have had it since the end of July 02 and have done about 50 hours. The same prop as you have that is the s/s Laser 21". The max speeed I can get out of my rib on calm waters is 33/34 knots. I have not done any calculations like you have as I am waiting to get a few more hours out of the engine but agree it is a very ecconomical engine. Also I like filling up for 24/28 pence a ltr. Some marinas on the mainland sell the red between 32/34 pence a ltr. The only real account I did was on the St.Malo cruise and having filled up to the top in Alderney (100 ltr tank) we went flat out to St.Malo. There cos we could not refuel we went to Chausey Islands and then to Jersey max speed to save fuel was 21 knots total miles 135 and we ran out of fuel when we about to berth in Jersey. Could not have been a better moment
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Old 12 December 2002, 13:34   #4
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Mercruiser 1.7DTI

Mike C, The 1.7 diesel produces only 2hp less at 4000rpm than at 4400rpm. In fact, it's only another 3hp less at 3500. Your prop sounds dead on.
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Old 12 December 2002, 15:39   #5
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Mmmmmmm, food for thought here!

Jelly,
No dumb moments.... (well apart from buying 2 stroke!). £43 for 255 miles is what I paid. My main re-fill was at the fuel barge up the Medina in Cowes. I bought 139 litres at 24 pence per litre. The rest, all about 30 pence per litre, I got in cans from my local canal marina. The twin 60hp two strokes I had on my old Ribcraft 5.85 used almost £1 per mile. A round trip to Cherbourg last year cost me £140. That's why I got the diesel! Even if/when red diesel goes, it’ll still be half the cost I was paying!

Andre,
Firstly, let me correct my last post when I said that full blast would 'reduce' the litres per hour.... I obviously meant 'increase' it. ie.... it would use more fuel per hour... (sorry, double negative brain storm there!). Anyway, it's interesting that you used 100 litres, (presuming you were full to start), for your 135 miles trip. That works out (100/135) to .74 litres per mile... which is not far from the .69 I reckoned I used (@ 13 knots average)! I wonder how long it took you? If you were doing 21 knots from start to finish it would have been 6.4 hours... which means you used 15.6 litres per hour. Rather more than mine at 13 knots. I'm not sure where this number crunching is getting us but it's fascinating non the less!
As far as prop is concerned, I've currently got a 23" Ally.... I WANT a 21" s/s. Most other people I speak to think I should be able to get 35 knots with no problem even with a full tank!

jwalker,
OK, maybe I DON'T need a 21" s/s!? 2hp isn't going to do a lot is it? I do wonder if the engine will produce enough extra power to get to maximum revs anyway, when it's loosened up a bit?! I think I will have to borrow a few props next year to see what difference they make! Most people I've talked to though do say a s/s is best with this engine and 23" may be a bit course. Until I try some, I will remain 'confused of Iver'.

Thanks for the thoughts!

Mike C
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Old 12 December 2002, 16:14   #6
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Mike
On that particular trip there was 3 of us, seating for 4 and a 100 ltr tank.double A frame so there was some weight. The first leg was 75 miles and here we we going flat out very smooth sea . The next day 2 legs each 30 miles and here to save fuel we did max 21 knots. And just as well. I use a 21 inch Laser prop and don't think would consider anything els. I suggest if you can try out the Laser 21" then do so , you never know .
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Old 12 December 2002, 17:02   #7
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Thanks,

I will try and find one to borrow next year. It will have to be quite a bit better though... for the extra few hundred!

mike c
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Old 13 December 2002, 04:41   #8
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Mike
I agree these are not cheap . My 21" Laser came with the rib package as standard equipment. Anyway where do you launch your rib cos if on the south coast we may meet one day and I could let you have a go with my prop unless you get one earlier.

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Old 13 December 2002, 19:13   #9
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Thanks, Andre,

I may take you up on that. I normally launch in the Solent somewhere.... Anywhere from Hayling Island to Poole in fact is OK. I will drop you a PM next year. The boat is away for the winter now! Or feel free to e-mail me anytime!

Mike C

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