Long - Skinny Power Boats

Discussion in 'Boat Design' started by SAQuestor, Sep 24, 2004.

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  1. Boston

    Boston Previous Member

    Im actually kicking its *** day trading
    I posted my day in real time over on the global economic conditions for live aboard yachties thread
    if your curious go check it out
    my final post in the series Ill quote here as it was a good synopses of the day
    it was a series rather than one after close post because I wanted the times on the posts to correspond with actual market positions thus corroborating my buys and sells
    I figured people might want to actually see for themselves I was in fact keeping step with the market motions with my positions on the day

    I ended up having a great day but obviously could not have known that at the start
    I just wanted to honestly represent the uncertainties in real time

    my last post in the series was an effort to explain my reasoning and its results

    day trading is about the only way Ive managed to survive since the contracting biz fell flat on its face over the last few
    surprisingly, when so many people told me not to even think about it
    turns out Im good at it
    I think it just might pay for the yacht cause contracting sure isn't

    cheers
    B
     
  2. Tad
    Joined: Mar 2002
    Posts: 2,303
    Likes: 184, Points: 73, Legacy Rep: 2281
    Location: Flattop Islands

    Tad Boat Designer

    Boston...

    What the ........ does your day trading bs have to do with long skinny powerboats?

    Thread drift I understand....intentionally adding posts with no bearing at all on the subject makes no sense!
     
  3. Boston

    Boston Previous Member

    Rick had mentioned something about financing the project with day trading
    so I threw him some bs about day trading
    which turns out will likely finance a long skinny hull just fine

    sorry if it didnt make any sense
    cheers
    B

    pertinant question then
    Im working on my math skills
    submerged area, 60' hull 6' beam 2.75' draft
    when I crunch the numbers I get 2500 lbs of thrust to reach 20 knots
    or 100 hp
    Im sure you have a hull efficiency calculator in there somewhere
    whats it say when you input those numbers
    Im curious if Im close
    thanks
    B
     
  4. Guest625101138

    Guest625101138 Previous Member

    Boston
    Here is a test on one of my slender boats with a small motor operating at 200W. The motor is rated at 600W. It went to 10kph (5.4kts).
    http://www.boatdesign.net/gallery/data/500/V11JE_10kph.wmv

    I intend to use this motor on the 1/5th scale model faux-tri but it will be minus the big gear ratio.

    One of the sailors looking on could not imagine that a tiny motor could move me at that speed. The motor weighs 149 grams and is 40mm diameter I have a 12:1 overall gear reduction.

    Anyhow it demonstrates how little power a long slender hull needs.

    Rick W
     
  5. eponodyne
    Joined: Aug 2007
    Posts: 327
    Likes: 13, Points: 0, Legacy Rep: 171
    Location: Upper Midwest

    eponodyne Senior Member

    no can view on a Mac, sorry.
     
  6. Guest625101138

    Guest625101138 Previous Member

    Can you view YouTube:
    http://www.youtube.com/watch?v=GJedBprmSkk

    There is nothing particularly great about the video. The impressive bit is the little 140 gram motor pushing a person on a boat it 10kph.

    There is a little program called Flip4Mac that enable Quicktime to view wmv files.

    I use Mac for email and web viewing so it is handy to have.

    Rick W
     
  7. eponodyne
    Joined: Aug 2007
    Posts: 327
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    Location: Upper Midwest

    eponodyne Senior Member

    oh holy crap that sounds like a dentist drill moving the gates of doom into place. Sure, that's a dandy little powerful motor. Annoying as ****.

    Better you than me, buddy. I'm glad you're wiling to do the research and put up with it, because it would drive me to world domination or some **** like that.
     
  8. Guest625101138

    Guest625101138 Previous Member

    The camera seems to amplify the sound quite a lot. It is not anywhere as noticeable on the boat. My son also found it very annoying when I first viewed the video at home.

    My main issue during the test was lack of a third hand and fear of losing the remote control while filming. I was trying to run directly with the waves so it would stop the jerky roll before I tried full power. I later found I had collected some weed in that run and was able to nudge just over 10kph with a clean prop.

    When you compare noise with the equivalent ICE used for model planes it is silent.

    Rick W
     
  9. Boston

    Boston Previous Member

    ya as a kid we used to play with those RC planes a lot and dam
    they scream
    ok well then I guess my numbers may be at least close then cause I took a big guess at the wave resistance and assumed it was half at 20 knots
    basically I only figured for the fluid resistance and doubled it to get to 20 kts at 160 hp for a 32000 trihull with one 60x6x2.75 and two 40x1.5x2 sponsons
    the sponsons work out to 30 hp each at 4000 lbs disp and the primary hull works out to 100 hp at 32000 lb displacement
    or 160 hp to hit 20 kts
    so the 250 hp Im planing on should be more than enough to keep me ahead of weather

    funny part is at 8 knots
    it seems to work out to about 16 hp
    cant be right
    which Is why I was hoping some one would check my numbers
     
  10. Boston

    Boston Previous Member

    oh
    video played fine on my mac
    but I already have flip for mac installed
     
  11. Tad
    Joined: Mar 2002
    Posts: 2,303
    Likes: 184, Points: 73, Legacy Rep: 2281
    Location: Flattop Islands

    Tad Boat Designer

    Rick....

    What is the length, beam, and weight(total with you aboard), of the boat in the video?

    Thanks...that's interesting work.
     
  12. Guest625101138

    Guest625101138 Previous Member

    Boston
    The lowest drag hull for 15kts with max length of 18m, max beam of 4m and max draft of 1.4m is a mono. The beam of the hull is 0.8m. The wetted surface area is 62sq.m.

    It requires 66kW for 15kts and 115kW for 20kts.

    A catamaran requires 80kW and 153kW.

    A trimaran with a 1t minimum displacement amas requires 71kw and 132kW.

    So the best option from a powering perspective for these constraints is still the faux-tri.

    Rick W
     
  13. Guest625101138

    Guest625101138 Previous Member

    Tad

    Around 110kg total. LWL = 7.2m, BWL = 225mm, draft a little over 100mm.

    The two little VRLA batteries are 12Ah and weigh 7kg combined. I have done full discharge test on these and they give about 1 hour operation at 7A. The 12Ah is based on 20h discharge rate. These batteries die if you try to pull 12A. That is where the lithium batteries win out. With a 5Ah lithium battery you can pull 70A and they still hold voltage. A 1kg battery will allow me to get full power from the motor - not for very long though.

    I know it was cold so there has to be some motivation. I am truly impressed with these modern motors and controllers. They are very well engineered and do not cost much.

    Rick W
     
  14. Willallison
    Joined: Oct 2001
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    Location: Australia

    Willallison Senior Member

    Rick,
    What I want to know, is what on earth posessed you to go out in a pair of shorts on a cold Melbourne winter's day !?!;)
     

  15. Guest625101138

    Guest625101138 Previous Member

    That is my normal attire for pedalling when it is not sunny. Once I start pedalling I enjoy the fresh air. No pedalling was very cold. I was shivering it was so cold. All for the sake of scientific enquiry.

    With hindsight I should have set up the pedals so I could have got warmed up.

    Rick
     
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