To keel or not

Discussion in 'Stability' started by rfleet1066, Oct 1, 2014.

  1. rfleet1066
    Joined: Feb 2012
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    Location: New Kent, VA USA

    rfleet1066 rfleet1066

    I have been constructing a large pontoon vessel for two years. Please see the old thread, "To Keel or not to Keel"

    I weighed the vessel and found that with 8000 lbs on the deck, she will draw my ideal max waterline at 26" 30" is a redline draft, as that is half the diameter of the pontoons.

    This may make the difference between a boat and a submarine.

    All that said, I would like to pose again the question about the keel requirement. With three hulls submerged 56' long is the keel less likely to be required?

  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Is that 8000 lb evenly distributed or do you have a safety factor? If the weight is mobile (passengers and crew), you need to calculate what happens if they all stand in one side.
  3. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    At that length I assume you will have an outboard engine on each of the outer pontoons. This will give you good steering control. Why do you want to add keels? Am I missing something???
  4. rfleet1066
    Joined: Feb 2012
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    Location: New Kent, VA USA

    rfleet1066 rfleet1066

    no outboards

    This particular vessel is designed for river and protected water operation.

    I am building a Caterpillar Diesel powered longtail drive. I have built a turntable for the engine at the rear of the deck with a yoke in which to mount the engine. This is essentially a gimble mount. It will swivel tor steering and tilt when running over logs in the river. The entire drive will tilt up enough to swing around and rest on the deck for cleaning, service, prop exchange, etc.

    Hydraulic thrusters are fitted fore and aft on the starboard hull.

    So, no outboards will be employed.


  5. Nick_Sinev
    Joined: Aug 2014
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    Location: Sydney

    Nick_Sinev Junior Member

    Re: river + protected waters

    As far as I know.

    You need to consider.
    1) List (i.e. roll) because of unfavourable weight distribution in the worst case scenario (everything moved to one side as assymetric as possible).
    2) List because of a wind gust. It is usually assumed as 2*list produced by a steady wind.
    3) List when turning on max speed with min radius.

    The vessel is supposed to withstand all 3 factors simultaneously.
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