Italcraft 35 fast, get on plain problem

Discussion in 'Boat Design' started by tonipu, Jan 18, 2021.

  1. tonipu
    Joined: Dec 2014
    Posts: 126
    Likes: 0, Points: 16, Legacy Rep: 10
    Location: croatia

    tonipu Senior Member

    Can you send me e link where you find this picture, i cant find?

    Yes the flaps can fully retract, and the stracture and the mehanizam are very strong, but i dont understand fully mr. Efficency What you sugest
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,603
    Likes: 820, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Like this:

    TAB.jpg
     
  3. tonipu
    Joined: Dec 2014
    Posts: 126
    Likes: 0, Points: 16, Legacy Rep: 10
    Location: croatia

    tonipu Senior Member

    Ok, and you dont sugest to make it wider, or jo sugest that i do both, hinge and widening the flaps?
     
  4. tonipu
    Joined: Dec 2014
    Posts: 126
    Likes: 0, Points: 16, Legacy Rep: 10
    Location: croatia

    tonipu Senior Member

    I mean wedge, not hinge
     
  5. Ad Hoc
    Joined: Oct 2008
    Posts: 6,812
    Likes: 773, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

  6. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,603
    Likes: 820, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    It would be dead easy to fit a wedge to both flaps, as an experiment, widening the flaps a bigger job. Wider is certainly better than narrow, but you could get a big increase in lift from wedges, it becomes a matter of how aggressive (angle of attack) What is ideal might vary according to the characteristics of the boat, obviously a wedge does have an increase in drag, but the nett effect of drag from the boat+tabs is likely to be a reduction of the planing hump. It probably depends on the amount of drama involved in removing the boat to and from the water, balanced against the complexity of the modification carried out, but my initial impulse was a wedge was worth a try.
     
  7. gonzo
    Joined: Aug 2002
    Posts: 15,129
    Likes: 900, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    12 people plus seats is about 1 ton on the stern. The boat is overloaded and the CG shifted aft by quite a lot.
     
  8. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,603
    Likes: 820, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    He appears to be happy with the boat at speed, but looks to get easier planing, and presumably better ability to stay on plane, backed-off. The tabs appear to be area to concentrate on.
     
  9. TANSL
    Joined: Sep 2011
    Posts: 6,457
    Likes: 375, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    The mission of the tabs is not to increase the planing surface but to create a force that helps correct the trim. Therefore, longer tabs produce a force farther from the hull's axis of rotation, increase the lever arm of the force generated by them and increase, without varying the total force, the trim correction moment.
     
    BMcF likes this.
  10. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,603
    Likes: 820, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    They produce more lift by being wide rather than longer, the leading edge being longer.
     
  11. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,603
    Likes: 820, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I assume the semi-cylindrical ducts/shrouds are used to turn the boat ? Perhaps a downturned lip at the top of them, might create lift when taking off, but not be in play at speed, but maybe loading them up at the end may be putting too much strain on them.
     
  12. BMcF
    Joined: Mar 2007
    Posts: 1,037
    Likes: 66, Points: 48, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    We built a small surface effect ship that had two of the early "Levi Drives" installed. Late 1980s. The take-off performance of that setup was terrible, and despite several changes to the propellers (Levis was directly involved in the project), the craft never behaved well. This picture is, in fact, one of the only ones ever taken of the craft "on plane", moving along at over 40 knots. It was quite light but with a number of 55-gallon barrels full of water placed on the deck in forward part of passenger cabin. Only moments after this picture was taken, the craft executed a hard-over uncontrolled turn directly in front of the 35-meter surface effect ship that I was taking the pictures from. The barrels full of water went nearly through the side of the passenger cabin...

    And those steering shrouds..ugh...not very effective as it turned out.
     

    Attached Files:

    bajansailor likes this.
  13. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,603
    Likes: 820, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Not having those drums tied down sounds like negligence.
     
  14. tonipu
    Joined: Dec 2014
    Posts: 126
    Likes: 0, Points: 16, Legacy Rep: 10
    Location: croatia

    tonipu Senior Member

    Yes, once it get on plain with 12 people, it got without problem 30kts at 2450rpm.
    Other issue of this drive is that you can go 10, or 25kts and cant crouse in betwen, for exemple you cant cruise 20kts, with Will help in heavy sea, but actauly it is good and seaworthy boat

    Other issue is the turning issue, if you dont align it with flaps very well the boat go in one direction, oposite of your steering direction, i was thinking to add litle bit of surface to this semitunel
     

  15. BMcF
    Joined: Mar 2007
    Posts: 1,037
    Likes: 66, Points: 48, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    In hindsight...it probably was. Nobody was anticipating any violent maneuvers or motions in the flat calm conditions. Fortunately, the only injury was to cabin bulkhead.
     
Loading...
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.