Deck Height of a boat?

Discussion in 'Boat Design' started by Titu, Sep 9, 2022.

  1. Titu
    Joined: Sep 2022
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    Location: Halifax, Nova Scotia

    Titu New Member

    Hello my fellow boat builders,

    I am new to this forum, this is my first post. Amazing forum, this forum is like the holy grail of information and creations.
    I am creating a 22 ft semi-V runabout boat. I can't seem to find any information on how high can I build my floor deck from the waterline without compromising stability. is there any rule of thumb?

    Questions welcomed
     
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  2. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    No useful rule of thumb. Stability is a function of numerous variables. Even deadrise angle plays into the stability question. Chine width, displacement of the boat and all that it contains, height and weight of any superstructure, weight and location of engine, and more.

    Describe your boat in detail and perhaps someone will offer a bit more information. Drawings would be helpful.

    When you say that you are "creating" a 22 foot boat, does that mean that you are designing it yourself?
     
  3. fallguy
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    fallguy Senior Member

    It is all relative. The higher you go; the less stable. Go too low and scuppers will run water into the boat when loaded. Then the higher you go; the higher railings must be to keep passengers safe at sea, etc.
     
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  4. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    +1 (or +2 rather) to the excellent contributions above.
    Please do post as much info as you can about your boat - such as drawings / sketches, and your design philosophy (if she is your design) - although it is possible that you won't be able to post attachments (as a 'new' member) until you have a few more posts 'in the bank' as it were.
    If this is the case, you could email anything that you would like to post to me, and I will post it for you, no worries.
     
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  5. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    +3....Context is everything. It depends on the form of the vessel; open, cabin, etc... Generally, modern open runabouts have the floors slightly above the waterline to be self draining. How much is "slightly"? As said depends on too many other factors.
     
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  6. Milehog
    Joined: Aug 2006
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    Location: NW

    Milehog Clever Quip

    Self-bailing cockpits aren't always worth the problems they create.
    Will your boat live on the water unattended where they are a necessity?
     
  7. Titu
    Joined: Sep 2022
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    Location: Halifax, Nova Scotia

    Titu New Member

    Thanks for all the reply, about the boat, I have designed, prototyped two of them. I have put a link of its river trial video. The boat is 22ft long, 5 ft wide. Its running on 8Hp diesel engine, with 3 blade propellers .
    Questions welcomed.
     
    Last edited: Sep 10, 2022
  8. bajansailor
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    bajansailor Marine Surveyor

    I have just watched both videos - they do look like nice boats.
    Are they in Thailand?
    Relatively narrow (L/B is a bit over 4) and they are going along very nicely with their 8 hp diesel engines.
    Is there a long keel under the hull, or is the propeller shaft supported on a 'P' or 'A' type bracket?
    Have you got built in positive buoyancy under the sole, and under the side coamings?
    Are you looking to raise the sole a bit on the next boat to make it self draining?
     
  9. Titu
    Joined: Sep 2022
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    Location: Halifax, Nova Scotia

    Titu New Member

    Thanks for the reply. It is from Bangladesh. The hull has a long keel with a P bracket for propeller. I have built it in positive buaoancy. Yes I want to update with self draining deck, as you can see there is a small manual bilge pump at left of the transom. I am concerned during the monsoon it will be an issue.
    Also I wanted to see how will it perform with a raised deck and 25 hp outboard engine.
    Questions welcomed.
     
  10. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    Depends on several things, like anticipated loads, sea state, and intended use for starters.
    Ocean going vessel should have self bailing decks, so decks should be well above waterline, even when heavily loaded.
    Lightly loaded lake boat, deck near or even below waterline can work.
    You can deck it over at gunnel height, if that suits your purpose, but then heavy loads will need to be carried below decks to maintain stability.
     
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  11. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    A friend on another forum built a Panga, but whenever the boat was loaded well, the scuppers would flood the boat, so occupants needed knee high boots to fish.

    If all you really want is a drier boat, for a river, hard to beat a working bilge pump or even a pump well where you can wash gear/fish blood to the stern
     
  12. Cacciatore
    Joined: Oct 2008
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    Cacciatore Naval Architect and Marine Engineer

    Please check the the waterline at " full load" condition and from this point raise the deck min 75 mm for Cat C (better 100 mm.) please check ISO 11812 to have a better overview.
     
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  13. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Realistically, you do it the other way around. Put the floor where you need it to be, then design the hull to be stable.
     
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  14. Titu
    Joined: Sep 2022
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    Location: Halifax, Nova Scotia

    Titu New Member

    Thanks so much everyone. I think I have got some valuable ideas now from all of you. Love this community.
     

  15. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    If all you really want is a drier boat, for a river, hard to beat a working bilge pump or even a pump well where you can wash gear/fish blood to the stern[/QUOTE]

    I would have to disagree, reliance on mechanical means to stay afloat is risky, although this seems to be considered normal on some craft, especially center console outboard fishing boats with huge motors.
    The OP is asking how high ABOVE the waterline he can safely (in terms of stability) build his deck.
    Without much more specific information regarding his build, no specific answer can be generated.
     
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