Fuel Consumption of Larger Yachts

Discussion in 'Boat Design' started by Slimjim, Sep 14, 2012.

  1. Slimjim
    Joined: Sep 2012
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    Slimjim New Member

    Hi to all and thanks from a lurker.

    I'm thinking of getting a larger motoryacht to live aboard,as the values of the 10-15 year old yachts have really dropped with the meltdown and what not.
    I have ocean front property,so docking is no problem.

    I have looked and emailed brokers,but can't find any info on consumption at lower speeds-it's not so much the amount as we will use it rarely- just need to know what kind of range I may expect for a 75-85' yacht like a Sunseeker.

    Any hints will help and thanks again.

    Jim
     
  2. WestVanHan
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    WestVanHan Not a Senior Member

    Hi slim and welcome to the board.

    I've had those thoughts lately too..the prices have dropped,and any on the market have been so for years..so the owners need to get realistic.

    I have a small oceanfront cabin up the coast-but docking in front of it is not a good thing and as you know docking anywhere near Vancouver for something that big is very hard and $$$$$. :( Otherwise I'd be so tempted.

    Anyways,I was on a charter Sunseeker 84 Manhattan.
    Almost all of them came with the 1400hp Cat 3412-which is not a too desirable state of affairs.
    If they've been used to any of the hp potential they tend to have problem$$.

    Or when..and I mean "when" not "if" one of them drops a valve,a liner fails,a skirt breaks,or the aftercooler leaks and breaks your pistons-pull it out and throw in a reman Cummins QSB11 as the main driver.

    Anyways I remember at 10 knots/1000 rpm both engines/ it was 90 litres an hour.
    I don't see why not at 7-8 knots, you'd be down to 50-60 litres an hour.
    You'd want to open them up a couple minutes every hour.
    At 22 knots it's 400+ litres an hour.

    Look into Fairline,Princess/Viking-the Italian boats seem to be more expensive.
     
  3. TANSL
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    TANSL Senior Member

    Search with Google catalogs of engine manufacturer. They indicate consumption, generally, in grams / hp-hour. (about 200 gr/hp-h)
    They do not say that consumption occurs under ideal navigation conditions, with the engine at 80%, but is data that can be used with caution.
    See attached example.
     

    Attached Files:

  4. WestVanHan
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    WestVanHan Not a Senior Member

    Trying to be helpful tansl, but without knowing how much hp it takes to move the yacht at a speed-charts and specs are useless.
     
  5. TANSL
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    TANSL Senior Member

    Well, you tell me how you will meet the consumption?. Or do you think that yachts consume according to their length?
    B.R.
     
  6. Tad
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    Tad Boat Designer

    Princess V72
    C32 Cats
    1000 RPM = 11.3 knots and 40gph = range of 295 miles

    Sunseeker 70
    1550 HP MANs
    1000 RPM =10 knots and 23gph = 500 miles range
    1250 RPM = 11 knots and 42.5gph = 300 miles range
    1500 RPM = 18.3 knots and 51gph = 399 miles range (best mpg)

    Those are US gallons
     
    Last edited: Sep 15, 2012
  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    not to thread jack, but how about two engines on one shaft, so.....

    you aren't lugging a big diesel at lower speed, but still got full power with both engines running.

    Ideally, I'd have 6 and 12 cyl engines, so I'd have 3 possible power levels....6, 12 or 18 cyls.
     
  8. mydauphin
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    mydauphin Senior Member

    If you have to ask... You cant afford it. Owning a big yacht is not about fuel, everything else is expensive too. Keep it below 50' and you will save tons of money.
     
  9. Tad
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    Tad Boat Designer

    The question concerns range, not consumption.
     
  10. WestVanHan
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    WestVanHan Not a Senior Member

    tansl...read my first post-I already answered his question.

    He wants to know a rough idea of actual consumption,not charts to be used '"with caution"

    "Or do you think that yachts consume according" only to their engines?

    So you see,the figures that Tad was kind enough to post are quite close to what I posted...and I've said before,the big semi-d yachts get surprising fuel economy when throttled back.


    UR right squid..if I could find one with rotten engines for cheap,I'd throw in QSM11s and be happy to toodle around at 8 knots and with whatever top speed I got.
    100+ US gallons an hour at speed doesn't sit right with me.
     
  11. TANSL
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    TANSL Senior Member

    OK WestVanHan, sorry if I said something wrong but I do not understand why we can not use information that the engine manufacturer provides. Cautiously or wrongly, is often the best information we can provide. On the other hand, you're right, not only are the main engines that consume fuel, we must take into account all other consumers of fuel in the boat. So I think that neither yours nor my data can answer this question. Finding a yacht consumption, and therefore its autonomy, is quite complicated. But. if the manufacturer gives us a data, why not use it?
    It's not that I try to help but not answering the question. It is, in my opinion, that if we do not use data as I propose is very difficult to estimate the consumption / autonomy of a ship, with rigor.
     
  12. WestVanHan
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    WestVanHan Not a Senior Member

    Like I said..it's good to try and help,but unless you know the drag/hp needed to move it-charts are not useful.

    I have answered the question-again-my data is based on measuring and experience,not guessing off charts.

    If you think you can solve it-tell me what lph is at 14 knots and what lph is at 16 knots.
    Hint: 14 knots is off plane, 16 knots is on plane.
     
  13. WestVanHan
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    WestVanHan Not a Senior Member

    Jim; forgot to mention there's been a Sunseeker 94 docked here in Vancouver for 12-13 years.I know it had very very rarely been away from the dock up to 2009. I walked and biked past it almost every day.

    And the last 4 years AFAIK it' hasn't been away much either,I'd guess for haulouts or runs. It was on the market continuously until a couple years ago-but I'd guess they still think it's worth the $4M they were asking for it in 2001.

    Oh and the tankage on the 84 was 7500 or so..so at 10 knts you should go ~850 miles to empty-more than enough to circumnav. the Island and spend a year parked in the Broken Group if you wanted.
     
  14. FAST FRED
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    FAST FRED Senior Member

    "not to thread jack, but how about two engines on one shaft, so.....
    you aren't lugging a big diesel at lower speed, but still got full power with both engines running."

    Ideally, I'd have 6 and 12 cyl engines, so I'd have 3 possible power levels....6, 12 or 18 cyls.
    "
    The past 40 years or so the US Navy has been installing two engines tied to a gear box and single shaft on landing craft.

    My preference would be for a smallish diesel to operate efficiently at 80% power 90% rated RPM for long range cruising, and a stock motor for the times to make a big wake and de-fuel the boat rapidly.

    3-71 and 6-71 or

    80Hp Deere tractor with Intl DT 466 ,,more Modern , might use less fuel

    Engine can be disconnected under way , but requires shut down to engage to reengage either engine.

    No big deal.
     

  15. mydauphin
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    mydauphin Senior Member


    Yeah, I saw two and four 6-71 tied into a one tranny in a Landing craft. The tranny was used and and need to be shift manually to engaged or this engaged them. But I thought it was a great idea. The problem has to do with a prop that works at 6-12-18 cyl. You would need a variable pitch prop to match. The whole setup is very complicated and obviously expensive that is why you don't see them.

    Those sunseekers are not trawlers and not meant for range or efficient fuel consumption.
     
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