Hull speed

Discussion in 'Boat Design' started by Mike D, Jan 7, 2003.

  1. duluthboats
    Joined: Mar 2002
    Posts: 1,585
    Likes: 43, Points: 58, Legacy Rep: 779
    Location: Minneapolis,MN, USA

    duluthboats Senior Dreamer

  2. tspeer
    Joined: Feb 2002
    Posts: 2,244
    Likes: 216, Points: 63, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

  3. ErikG
    Joined: Feb 2002
    Posts: 397
    Likes: 12, Points: 18, Legacy Rep: 344
    Location: Stockholm, Sweden

    ErikG Senior Member

    To water Gary

    Well Gary since Mike D is no longer with us, he passed away some time ago he will not be able to respond to your post, but if you have any specific questions just ask and someone smarter than me will probably try to steer you in the right direction

    ErikG
     
    1 person likes this.
  4. ryab

    ryab Guest

    ryan

    how can i make a hull go faster
     
  5. Willallison
    Joined: Oct 2001
    Posts: 3,590
    Likes: 130, Points: 0, Legacy Rep: 2369
    Location: Australia

    Willallison Senior Member

    longer (displacement boats), lighter, more power....

    ps. You're right - we do miss him - Dim as well... :(
     
  6. schecter
    Joined: Jul 2004
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: denmark

    schecter New Member

    Extending hull to gain lift and speed?

    Hello michael
    Ive read ( some!) of your postings regarding hull speed. I have a 16 ton, 45 feet motorboat with two engines 375 hp each, that sits heavily in the water. Im planing to extentend the hull and the drive tunnels to gain lift at the back of the boat.topspeed full loaded is 20knots.
    How much extension do i need? And will it help?

    Pauli From Denmark
     
  7. sorenfdk
    Joined: Feb 2002
    Posts: 511
    Likes: 27, Points: 28, Legacy Rep: 394
    Location: Denmark

    sorenfdk Yacht Designer

    Hej Pauli
    Mike døde sidste år, så han kan desværre ikke hjælpe dig...
    Men det er der heldigvis andre, der kan. Her i DK kan du f.eks. kontakte CDE Danish Marine Design, der har lavet den slags før. Se hjemmesiden på http://www.cde-dmd.com.
    Og ja - jeg er involveret i CDE, så måske er dette ufin reklame. I så tilfælde undskylder jeg mange gange!

    And for the rest of you:
    I explained to Pauli that Mike sadly has passed away, but there are others who can help. In DK it could be CDE Danish Marine Design, with which I am involved. If this is unfair promotion, you have my excuses - it won't happen again!
     
  8. brian eiland
    Joined: Jun 2002
    Posts: 4,788
    Likes: 157, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    PowerSailer claims

    I guess I was away from the list a little too long.....I missed the notice of Mike's passing as well. He was a great source of good info he shared freely.

    I've wanted to bring up a subject that seems to be a trend amoung monohull folks lately. I can only think it has to do with the competition they are feeling from the multihull market. I continue to see these inflated claims as to their particular designs performance capabilities, particularly under sail.

    Case in point. Have a look at the new PowerSailer from NZ.

    Can you really believe that a 28 tonne (I would venture to guess heavier by the time its finished) monohull vessel will 'sail' at 18knts??...even with a 110' mast. The vessel is only 66' long and carries a 21' beam. And I imagine it will be very difficult to keep that underwater, retractable Z-drive housing/sea chest volumn free of sea water (lots more weight). And she's carrying around a 13.6 keel and twin rudders. Granted the small print says in a downwind surfing condition, but they advertise the vessel as though a perspective client should expect such performance....wishful thinking.

    I've seen some number of other monohull manufactures claiming some 'very optimistic' speeds for their sailing performance lately....can't recall the specifics at the moment, maybe someone else can fill in the blanks.

    Now to get to 'planing speeds' desired of this power sailer she's going to need 800hp....boy, that's not going to be light. Then how do you get the rt-angle gears of a Z-pod unit to stand up to a continuous hp rating of this magnitude??

    Plus they're going to have a retractable keel (more weight) to gain entrance into shallow areas. And the vessel is going to be unsinkable??

    It seems to me they should just accept the multihull motorsailer planform in the first place, as all of these goals (and there others) are met with this planform.

    Boy I wish I could find a boater such as this gentleman, who would wish to put the money and effort he has committed into a custom catamaran motorsailer design. We could do this sort of performance with a 75' mast, two 200hp engines, and a 3.5' draft.....probably cheaper too.
     
    1 person likes this.
  9. Corpus Skipper
    Joined: Oct 2003
    Posts: 606
    Likes: 8, Points: 0, Legacy Rep: 173
    Location: Corpus Christi TX

    Corpus Skipper Hopeless Boataholic

    I'm an ex-Navy destroyerman. I was on USS Stout (DDG-55), one of the new Arleigh Burke class (DDG-53). She is powered by 4 GE LM 2500 gas turbines at 36,000 HP each, through double reduction gears (about 25:1 if I remember right) to J blade CRP props, counter rotating. 100,000 SHP after geartrain losses. Shaft torque was limited to 1.2 million (I think) lb/ft. Top speed was about 34 kt., burning a modest 20,000 GPH. I believe displacement was around 8000 tons. She is 505 ft. long, with a 60 ft beam (sorry, don't know the waterline particulars). Most of the time, we chugged along at 7-8 kt on 1 engine, dragging the other shaft. Much better fuel economy, something like 800 GPH.
     
    1 person likes this.
  10. Corpus Skipper
    Joined: Oct 2003
    Posts: 606
    Likes: 8, Points: 0, Legacy Rep: 173
    Location: Corpus Christi TX

    Corpus Skipper Hopeless Boataholic

    Oops, didn't read far enough ahead to see that my previous reply won't be read by it's intended recipient. He will be missed.
     
  11. PCVdominica
    Joined: Feb 2011
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Dominica

    PCVdominica New Member

    My Hull: Disp, or semi-disp.

    Hey guys,
    My 43' Gran Mariner currently runs twin 120 hp Perkins. She cruises at 8 with a max of 11kts. I am looking into a re-power and want to understand the characteristics of my hull before I choose new power-plants.
    I have been reading and reading and I am still uncertain whether I have a displacement or a semi-displacement hull.
    Would any of you hull-gurus mind taking a look at my pic and offering your assessment?
    **Important to note: As you can see in the second picture, the props sit in hull recessions. I have heard this referred to as a tunnel drive system. Does that effect performance?

    Kind Regards,
    Marcus
    [​IMG]
    [​IMG]
    [​IMG]
     
  12. Corpus Skipper
    Joined: Oct 2003
    Posts: 606
    Likes: 8, Points: 0, Legacy Rep: 173
    Location: Corpus Christi TX

    Corpus Skipper Hopeless Boataholic

    Marcus, that is a planing hull. V bottom at the stern, and submerged transom. Your speeds are only due to being way underpowered... If you want to keep similar performance, treat it as a semi-displacement. The tunnels do effect performance, via increased drag. But they do allow for a shallower draft, so it's a trade off. Nice boat, by the way. I'd call it "home sweet home"!
     
    1 person likes this.
  13. PCVdominica
    Joined: Feb 2011
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Dominica

    PCVdominica New Member

    Thanks Skipper

    Wow, a planning hull! In that case I imagine I am missing out on a great deal of performance potential. In addition, I am not maximizing the efficiency of my hull when I am tooling around at 10kts. I've been forming calculations for various power options on this site: http://www.psychosnail.com/BoatSpeedCalculator.aspx

    I tend to like the equation that concluded i need 500 shaft hp to reach 30kts. I can find that kind of power in 6cly gas engines. Saving me some money.

    Comments/concers?

    Here us link to my photobuckt account, you can see many more pics if my 'Ever August' http://s35.photobucket.com/albums/d154/JTII/?action=view&current=DSCN0182.jpgpg

    [​IMG]
     
  14. duluthboats
    Joined: Mar 2002
    Posts: 1,585
    Likes: 43, Points: 58, Legacy Rep: 779
    Location: Minneapolis,MN, USA

    duluthboats Senior Dreamer

    Thanks PCV for bringing this thread to the top. It is a good example of the vast amount of information this forum holds.

    PS, Craig, Good to see you are still out there. ;-)
     

  15. Perm Stress
    Joined: Sep 2009
    Posts: 554
    Likes: 23, Points: 0, Legacy Rep: 323
    Location: Lithuania

    Perm Stress Senior Member

    Tunnels allow for less inclined prop shafts; this make thrust, essentially orientated along the shaft, to push-forward more, and lift-up less, thus increasing efficiency.
    Les oblique flow trough the propeller also increase efficiency and reduce vibration.
    Propeller tip losses for part of the disc may also be smaller, but I am not so sure about this last point...
    ____________________________

    As to speed, extremely important is weight, namely OVERweight. Ballpark figure I know from statistic analysis (certainly there are experts with more exact suggestions/numbers) is minimum installed power ~10-13kW/t to reach planing speeds.
     
Loading...
Similar Threads
  1. Doh
    Replies:
    59
    Views:
    2,954
  2. johnnythefish
    Replies:
    34
    Views:
    4,532
  3. Trixini
    Replies:
    9
    Views:
    1,698
  4. Phil Christieso
    Replies:
    36
    Views:
    3,793
  5. Jon E
    Replies:
    68
    Views:
    12,351
  6. devudegoa
    Replies:
    2
    Views:
    1,625
  7. Beachside485
    Replies:
    0
    Views:
    1,036
  8. nqb12179
    Replies:
    35
    Views:
    3,989
  9. William George
    Replies:
    29
    Views:
    9,889
  10. Dhutch
    Replies:
    24
    Views:
    12,619
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.