catboat minimum freebord

Discussion in 'Boat Design' started by Gianf1041, Feb 28, 2022.

  1. Gianf1041
    Joined: Sep 2018
    Posts: 68
    Likes: 6, Points: 8
    Location: italy

    Gianf1041 Junior Member

    I ask what can be the minimum height from the lwl to the sheer line of a catboat with a length of 7.30 meters, the relationship between the various dimensional measures of the cat.
     
  2. TANSL
    Joined: Sep 2011
    Posts: 6,980
    Likes: 553, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    For such small boats there is no regulation that establishes the minimum freeboard as such. But it must be avoided that in the worst load condition, with the passage to the side, the deck submerges. That may give you the data you are looking for.
     
    BlueBell likes this.
  3. BlueBell
    Joined: May 2017
    Posts: 2,000
    Likes: 594, Points: 113
    Location: Victoria BC Canada

    BlueBell . . . . .

    It depends on the boat design.
    What kind of boat is it?
    Is it custom, are you designing it??
    Pictures?
    Sketches?
    Drawings?
    CAD (Gawd forbid...)
     
  4. Gianf1041
    Joined: Sep 2018
    Posts: 68
    Likes: 6, Points: 8
    Location: italy

    Gianf1041 Junior Member

    Preliminary drawing ??
     

    Attached Files:

  5. BlueBell
    Joined: May 2017
    Posts: 2,000
    Likes: 594, Points: 113
    Location: Victoria BC Canada

    BlueBell . . . . .

    Thank you for the attachment.
    I'm sorry, I don't know the answer to your question.
    Nice lines though for a Cat boat.
    All the best,
    Cheers
     
  6. Ad Hoc
    Joined: Oct 2008
    Posts: 7,286
    Likes: 1,178, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    It does vary...
    For motor vessels - which yours is not - of less than 7m, is to have at least 300mm freeboard at the lowest point on the sheer line.
    If the deck is continuous or not stepped.
    If it is stepped then this maybe reduced to 200mm.
    The next rule is for greater than 18m..and then interpolate between the two values... but 7.3m is clsoe enough.

    For sailing vessels over 15m, the min freeboard is 300mm + 25mm with marking.

    So, if you have at least 300mm, you should be good to go.

    Or...alternatively worst case, draw a waterline at 7degrees see what freeboard you have (it must be positive), and then add 75mm to that freeboard.
     
    BlueBell likes this.
  7. Rumars
    Joined: Mar 2013
    Posts: 1,417
    Likes: 743, Points: 113, Legacy Rep: 39
    Location: Germany

    Rumars Senior Member

    Do you intend to have a self draining cockpit? If yes how do you want to sit in it? Do you plan on a high cockpit combing continuing the cabin sides like some traditional examples exhibit?
    All of this decisions influence the minimum freeboard. A traditional catboat is a working inshore craft and has low freeboard. There is no reason a recreational boat has to be the same, other then looks.
    Here two very different examples, Atkin Cupid least freeboard 400mm small combing, Atkin & Co. - Cupid http://www.atkinboatplans.com/Sail/Cupid.html and Benford 128 least freeboard 800mm, plus a healty combing 22' Cruising Catboat or Cutter - Cruising Sail - Benford Design Group http://www.benford.us/cruisingsail/cutter.php
     
  8. rxcomposite
    Joined: Jan 2005
    Posts: 2,542
    Likes: 474, Points: 83, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    Depends on where you want to sail. But at 7.5 m length, there is not much you can go. Say you will sail at 1 meter wave, 1/2 of that is the minimum freeboard so that your deck gets wet only some of the time. If you are going to encounter 2 meter wave (hope you survive), 1 meter freeboard. Too much freeboard will act as a sail surface, pushing the boat sideways. It can add to the capsize your boat.
     
    BlueBell and hoytedow like this.
  9. Gianf1041
    Joined: Sep 2018
    Posts: 68
    Likes: 6, Points: 8
    Location: italy

    Gianf1041 Junior Member

    Ok for your support, reading the book - the design elements of a catboat - by Fenwick C. Williams, indicates the freeboard aft and bow ............ or aft can be one and a third time the minimum freeboard, forward can be the sum of the minimum freeboard and the stern freeboard. ??
     
    BlueBell likes this.
  10. Gianf1041
    Joined: Sep 2018
    Posts: 68
    Likes: 6, Points: 8
    Location: italy

    Gianf1041 Junior Member

    preliminary dwg in progress ???
     

    Attached Files:

  11. Gianf1041
    Joined: Sep 2018
    Posts: 68
    Likes: 6, Points: 8
    Location: italy

    Gianf1041 Junior Member

    preliminry dwg..........
     

    Attached Files:

  12. gonzo
    Joined: Aug 2002
    Posts: 15,818
    Likes: 1,221, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Catboats were originally fishing work boats. They had very low freeboard to allow the crew to handle crabpots and other gear. Also, because of the sail center of effort being rather forward, the centerboard must be forward too; not in the center like a sloop.
     
    hoytedow and BlueBell like this.
  13. Gianf1041
    Joined: Sep 2018
    Posts: 68
    Likes: 6, Points: 8
    Location: italy

    Gianf1041 Junior Member

    They are in the preliminary study phase, everything can be questioned to arrive at a definitive result acceptable from the design point of view, as well as the position of the centerboard and other "adjustments" of the project ....... !!
    as regards the minimum freebord argument, I agree with what you have reported to me, that is, it can be defined taking into account the "heel" angle of the hull under the force of the wind by dimensioning the height of the perimeter profile of the cockpit in order to avoid that in navigation not too much water enters.
     
    TANSL likes this.
  14. Waterwitch
    Joined: Oct 2012
    Posts: 122
    Likes: 28, Points: 28, Legacy Rep: 20
    Location: North East USA

    Waterwitch Senior Member


  15. rxcomposite
    Joined: Jan 2005
    Posts: 2,542
    Likes: 474, Points: 83, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    If you want to dig deeper, see attach. One of the hull form is similar to yours.

    If you want more on the freeboard, I have a spreadsheet but deals with more complex subject as it is ship design. In the meantime what AH has advised you will suffice.
     

    Attached Files:

    Last edited: Mar 5, 2022
    DCockey likes this.
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.