bulbous bow

Discussion in 'Boat Design' started by gkevin, Jan 12, 2013.

  1. gkevin
    Joined: Jan 2013
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    Location: sitka,alaska,usa

    gkevin New Member

    i want to install a bulbous bow on my steel 46#14#6 hard chine fishing [troll/longline] vessel. i will be doing this my self and hope to reduce fuel consumption. when trolling for king/coho[silver] salmon my speed is 2.7 knots. running speed is 7 knots. main is a 4-71 detroit, rebuilt 3 seasons ago . i am also going to install a hydrogen generator. remember it is not a scam if you believe. what do you think ? is this worth doing ?
    thanks for your thoughts
  2. Number4

    Number4 Previous Member

    Hi Kevin,
    Welcome to the forum.
    Have you found the search function yet? The are thousands of pages of fascinating information on this site.
    eg http://www.boatdesign.net/forums/hy...ulbous-bow-15m-wooden-fishing-boat-44776.html
    I look forward to finding out what an "expert" has to say, I am sure one will post soon.
    Is there any chance of a picture of the beast?
    What sort of distances are you covering? At which speed? I think these are the important questions.
    Best Wishes,
  3. Submarine Tom

    Submarine Tom Previous Member

    Probably not.
  4. Stumble
    Joined: Oct 2008
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    Stumble Senior Member


    A bulbous bow is highly unlikely to do anything more than increase fuel burn. They add a lot of drag right at the air/water interface if designed incorrectly, and even when done perfectly crate a lot of drag. There are a few circumstances where the reduced bow wave is worth it, but generally only when operating at close to hull speed for long periods of time.
  5. Milehog
    Joined: Aug 2006
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    Location: NW

    Milehog Clever Quip

    Think about how the boat will handle in a following sea with that rudder-er-bulb on the bow.
  6. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    In the Spanish Mediterranean coast, in the last 3 or 4 years, many fishermen have added bulbous bow on their boats. I have participated in the design of 6 bulbs and testing of ships processed. The fishermen say, not me (I have my doubts), that in an operation of about 70 hours per week, they save on fuel to about 180 liters per week: trawlers between 20 and 24 m.
    See attachment a theoretical (????) study of power / speed of a boat, with bulb and without.
    In a so thorny issue that everyone think what he wants.

    Attached Files:

  7. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    I leave the bulb comments to others with experience with that fixture.

    As for the hydrogen generator............... I am pretty skeptical about that gadget. I have friend who installed one of those on his Toyota truck. After a couple of months, he got over the embarassment of being hoodwinked. He confessed that it did nothing for output or economy.... for a mere $200.

    I do believe that Exxon, BP, Shell and the others know more about fuel than some backyard chemistry wizard who figured to make money from his "invention".. The conspiricy theories about the petroleum giants participating in some sort of scheme to defraud the fuel user is ludicrous.

    Refiners do use hydrogen for several purposes. Among the terms used that involve hydrogen are:..... Hydrocracking a refinery process in which heavy streams are cracked in the presence of hydrogen to yield high quality distillates,........... hydrosulferization; a refinery process in which sulfur is removed from petroleum streams by treating with hydrogen to form hydrogen sulfide which can be removed by stripping,........... Hydrophylic group; an organic group that has an affinity for water such as the hydroxyl group (OH) or an acid group.

    Refiners use some chemicals such as WASA an additive that reduces the tendency for wax to settle out on storage of diesel fuel. They refer to another as WAFI, an additive that improves the cold flow characteristics of a diesel fuel and also reduces the tendency for wax crystals to settle during storage. These guys are pretty good with petrochemistry.

    Cetane number is a measurement of the tendency of diesel fuel to ignite when sprayed into a diesel engine. The higher the cetane number the easier the fuel ignites. The refiner fiddles the cetane number by manipulating the n-hexadecane and heptamethyl -nonane to arrive at an appropriate cetane value. Too high a cetane number and the fuel ignites too soon in the cylinder. Too low and the engine is difficult to start.

    Fuels have a specific capacity to produce heat. Typical gasoline has a specific heat of 115,000 BTUs per gallon. (42.7 MJ/kg) Unfortuneately you will not extract that much energy from the fuel because a modern reciprocating engine delivers only about 30% efficiency. The addition of home brewed hydrogen in the air intake stream is not likely to change the maximum amount of heat that your fuel is capable of producing at stoichiometric air /fuel ratios. Or any other ratio for that matter.

    Sorry about all that commentary that you did not ask for. If you read that stuff, above, do you really want to mess with your air fuel mixture? One more rhetorical question....Do you think that Caterpillar, GM, or Kubota would hesitate to build a hydrogen generator into their engines if it gave their engines a competitive advantage?

    End of rant.
  8. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect


    At trolling speed 2.7knots your Fn is roughly 0.12. At crusing speed it is roughly Fn = 0.31.

    Just looking at these basic numbers and comparing with "best" typical BB used effectively is in the Fn range 0.24-0.57, immediately suggests it isn't worth it. Even though your cruising range just overlaps, there is far more to it than just these basic numbers.

    All you will do is add drag as noted above. Also depending upon its size, you could also serious affect the directional stability and worse its seakeeping.

    A modification like this should not be done without a degree of investigation on the effects of your boats handling with and without. That is the more import aspect than whether you'll gain any benefit in fuel consumption, which I cannot see you could, based upon your limited data and scope provided above.

    Keeping your hull bottom very clean (power wash) on a regular basis and any one of those new generation "super-slippery" (low friction) paints will be far more beneficial.

  9. MikeJohns
    Joined: Aug 2004
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    Location: Australia

    MikeJohns Senior Member

    As others have said already, and to reinforce this:

    Neither the bulbous bow nor the hydrogen generator have any merit in this application.

    Bulbous bows are designed for a specific speed and need model testing for proper refinement. They also don't work very well in a seaway on small craft.

    Adding a small sail may give you the fuel savings you seek.
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