Tinny Hydrodynamics

Discussion in 'Hydrodynamics and Aerodynamics' started by the_big_ragoo, Jan 21, 2015.

  1. the_big_ragoo
    Joined: Jan 2015
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Ballarat

    the_big_ragoo New Member

    G'day all,

    I have been assigned with building a pulse jet for a fishing boat. I am fine with most of the physics exept for the hydrodynamics.

    The key problem is I dont know bugger all about this boat and have little way of finding out. What I do know is that it's a fairly standard tinny.
    Can anybody help me figure out what it's drag will be, ballpark figure?
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    A pulse jet, is what, exactly ? Sounds like the V1 "buzz bomb" of 1944.
     
  3. the_big_ragoo
    Joined: Jan 2015
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Ballarat

    the_big_ragoo New Member

    Thats about the size of it. Yup.
    Without the bomb though...I hope. :/
     
  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    So what is the object of the exercise, and what are the details of this propulsive device ?
     
  5. the_big_ragoo
    Joined: Jan 2015
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Ballarat

    the_big_ragoo New Member

    The objective of the exercise is to strap a pulsjet to a fishing boat. :)

    I have to design the pulsejet around the fishing boat. So I need to figure out what drag the fishing boat will have in the water. I can then detremine the acceleration needed, which tells me how much thrust I need.

    I can then design my pulsejet around providing that amount of thrust.
     
  6. Ad Hoc
    Joined: Oct 2008
    Posts: 7,773
    Likes: 1,678, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Welcome to the forum t_b_r

    Well, unlike most who seem to think design can be plucked out of thin air, we need some facts and figures. Just asking for drag values with no vessel is religion based not engineering based design :D

    At the bare minimum, you'll need to provide:

    1) General Arrangement or Lines plan, along with Principal dimensions of the hull
    2) Displacement of the vessel at the given water line
    3) Target speed

    This would give a start. But it still would require many if's and butt's that'll it only just be a ball park figure.
     
  7. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I'd say you should look at the normal hp requirements of the boat you have chosen to host your exotic drive device, and work backwards from that. You may find a thread somewhere on the forum that dealt with the thrust figure ( pounds) of various hp outboards. Use the search function. Small electric outboards often are rated to pounds of thrust, but of course they are not big enough to power the type of boat you mention, to the cruising speeds they are designed for. I'd say the required figure would be in the area of 300 pounds, give or take, to have a 4 metre tinny skating around happily.
     
  8. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    The victim, I mean skipper, of the Pulse boat will need to submit a chiropractor's report about the effects on the human body of the intermittent thrust. :D
     

  9. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I hope the pulse jet hasn't flat-lined.
     
Loading...
Similar Threads
  1. Alan Cattelliot
    Replies:
    17
    Views:
    2,554
  2. Brennan McDermott
    Replies:
    0
    Views:
    1,176
  3. johnnythefish
    Replies:
    8
    Views:
    1,537
  4. SET Project
    Replies:
    15
    Views:
    2,936
  5. seth godin
    Replies:
    10
    Views:
    2,056
  6. craphy
    Replies:
    1
    Views:
    3,059
  7. DouglasEagleson
    Replies:
    13
    Views:
    2,366
  8. flboats
    Replies:
    20
    Views:
    5,848
  9. mydauphin
    Replies:
    1
    Views:
    1,889
  10. cmckesson
    Replies:
    18
    Views:
    6,969
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.