fuel economy

Discussion in 'Powerboats' started by whitepointer23, Jan 12, 2011.

  1. whitepointer23

    whitepointer23 Previous Member

    hi everyone, i have purchased a savage lancer 26 flybridge with twin 225 mercruiser ford v8's. for people who are not in australia, the lancer is a mid 70's heavy fibreglass planing hull, moderate v, 26 feet long and about 3 metric ton. shaft drive. what sort of fuel consumption should i expect cruising off the plane at about 8 knots.
     
  2. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    More than I can afford I'm sure.

    At that displacement and length, 8kts is likely to be an unhappy speed for fuel economy and will probably carry a pretty big wake. 6kts is more like a top speed without the above issues.
     
  3. CDK
    Joined: Aug 2007
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    CDK retired engineer

    About 6 knots, as Tom said, while consuming 15-20 l. per hour if the engines are in good condition. The engines won't like it for long because they cannot reach normal operating temperature: they will cough a lot of (expensive) soot.
    To get better economy you need another set of props with a considerably higher pitch and forget about planing speed.
     
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  4. Submarine Tom

    Submarine Tom Previous Member

    OR, you could sell it and buy a sail boat.

    -Tom
     
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  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Even though your hull is heavy, you have the HP to plane and this will be the most comfortable "zone" the 450 HP worth of twin Ford V8's will enjoy. Naturally, tossing this much power at a set of props can be costly, but reducing the speed to 8 knots isn't going to help you much. You'll have to work out her best/economical cruising speed, but I suspect you'll be running in the mid teens when you find it. At 8 knots you're pushing her "up hill" a fair degree as Tom mentioned (about 1.7 S/L) and you'll have been chewing fuel like red meat at this point. At 6 knots (1.25 S/L) you've cut your fuel use nearly in half, though the engines probably don't like chugging along, barely off idle. You'll probably carbon foul pretty regularly, asking the engines to just loaf along like that, so bring an extra set of spark plugs with you.
     
  6. Typhoon
    Joined: Mar 2009
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    Typhoon Senior Member

    A friend's uncle had a Savage Lancer, nice boats. They'll easily run to 30kts with those engines, if everything is right. Once on the plane they do get fairly economical, being a deep v hull, they don't much like displacement speeds.
    As said above, it'll be best to pop it up on the plane and throttle it back so it's just on plane.
    My friend's uncle used to run his on one engine at displacement speeds when he ran at those speeds, helped with economy. But, he bought a planing hull and used it as such, speed is fun.
    If they're fresh water cooled engines, they won't foul up, they're not diesels.......
     
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  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Typhoon, I mean the combustion chambers will foul, if you lug 1970's era engines along at the RPM levels required for 6 knots. They're likely 302's with points ignitions.
     
  8. whitepointer23

    whitepointer23 Previous Member

    thanks everyone for the replys, all good points.
     
  9. Willallison
    Joined: Oct 2001
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    Willallison Senior Member

    I grew up cruising on a Sonair 26, which was designed by my father and built on the hull of the Savage Lancer hull. (My avatar is a pic of me aboard it) Ours was fitted with a pair of 120hp mercruiser sterndrives, which were only really just big enough to push the boat - it would've been better with a pair of 6 cylinder engines.
    1st thing, your boat almost certainly weighs rather more than 3 tons. More like 4 and possibly a little more than that if you've got a fair bit of gear aboard.
    If my memory serves me correctly, the realistic displacement speed for the boat was more like 5 knots. As others have said, forget 8 - if you want to do 8 knots then I'm afraid you've bought the wrong boat. And I hate to say it, but if economy in general is at the top of your list, then a heavy shaft-driven petrol-engined planing hull doesn't exactly tick all the boxes either!
    Having said all that, I'll doubt that you'll do all that many actual running hours per year, so the cost of fuel will hopefully not be all that significant.
    At sensible planing speeds - say around 18 knots I'd guesstimate that you'll probably use around 2 - 3 litres per nautical mile.
    The Lancer is a great boat - solid as a brick... well... you know - I'm sure you'll have fun with it
     
  10. whitepointer23

    whitepointer23 Previous Member

    hello, thanks for the reply, i certainly have not bought the wrong boat, i ask questions to get peoples opinions but i am certainly not new to boats, i have owned and worked on several from 12 ft to 48 ft. 7 or 8 knots is definately possible with the large trim tabs it has on it. fuel usage is not a big issue, i just wanted a rough idea. my two v8 are far more economical than 2 little 120's pushing a boat that size. definately well under 4 ton. my 30 ft diesel cray boat only weighed 5 ton and that was carvel with 1" jarrah planks.
     
  11. Willallison
    Joined: Oct 2001
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    Willallison Senior Member

    Whitepointer... no offense was intended... if I did so, I apologise... just trying to help.
    I wasn't suggesting that you can't do 8 knots. But to do so, you will be operating within the most inefficient speed range for that boat. Better to either do 5 or 18 ish...
    Whether the 2 V8's will use less fuel than the 120's nobody will ever know... as I said, they were a bit marginal. The inefficiency inherent in the shaft drive setup will weigh against you, but that doesn't become so apparent until you reach planing speeds.
    As for the weight.... my experience is that 90+ percent of boats weigh more than their owners think they do... especially after a few years of gear accumulation. I know the weight of the boat we used to own because we weighed it....
     
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  12. whitepointer23

    whitepointer23 Previous Member

    no need to apologise, i wasn't offended in any way. i respect everyones views and appreciate you taking the time to reply, what people think is offensive on forums is not normally. if we were having a face to face debate over a beer we would make the same comments with out even thinking about it. as far as shaft drives i agree with you, but they are better than legs at low speed, the boat is trimmed a lot better with the engines forward. the reason i believe the 120's would use more fuel is because they be would at full throttle when the v8's are probably at 1/2 throttle. i looked at a searay with 2 454's but got scared of having 2 big blocks, i spoke to the surveyor who looked at it and he said he worked for searay for 16 years and drove all the boats he fitted with engines and the big blocks returned better economy than the small blocks every time.
     
  13. whitepointer23

    whitepointer23 Previous Member

    i will fill the tanks and get accurate fuel usage figures for fast, slow and cruise speeds and post them on this forum, should be in a couple of weeks.
     
  14. WickedGood

    WickedGood Guest

    those are pretty small engines. Are they the Ford 351 Block detuned?

    You could just pop out those engines and drop in a new pair of PCM fuel injected Excalibur 343s that will push the boat a respectable 30 knt speed.

    You will most likly burn somewhere areoun 40- 50 gallons per hour as the lancer has a lot of deadrize and is heavy. Of course the Function of the boat is to blast around the lake and attract Babes in Bikinis so you will have to stock the wet bar frequently also.
     

  15. whitepointer23

    whitepointer23 Previous Member

    302 fords were around before 351's, windsor blocks which is what these are and what you have in the states come in 289 ci 302 ci 351 ci.
     
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