smaller boat sitting on top of small boat ??

Discussion in 'Stability' started by zurk, Mar 26, 2014.

  1. zurk
    Joined: Mar 2014
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    Location: Vancouver

    zurk Junior Member

    Looking to add my inflatable SIB which is 10.5ft and weighs in at 150lbs or so to the roof of my hardtop on my 16ft aluminum boat upside down. I know the roof can support it as I have climbed up there and its rated for 300lbs and I can extend the roof with a bolt on bracket using a quick release pin which will go thru the bench seats on my inflatable and secure it nicely. not worried about looks or the inflatable flying off but am worried about increasing/raising the center of gravity of my aluminum which weighs 700lbs dry (hull weight) without engine (engine is another 400lbs+300lbs or so gear/fuel).
    will 150lbs on my hardtop roof cause my aluminum boat to become top heavy and cause problems in rough seas ? hardtop is about 5 ft high above the boat sides.
    Specs of the aluminum boat are : Beam 6'-9", Freeboard 28", Deadrise 18°, Hull (lbs) 700, Bottom 3/16" x 6'-0 5086, Side 1/8" 5052.
    im basically going to be using the inflatable as a lifeboat in an emergency so i would rather carry it inflated on the roof out of the way then stuffed into a bag and rolled up near the front seats which then requires 5-10min for inflation in an emergency.
    any thoughts ?
     
  2. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    You could try a dockside test. Have someone who weights about the same as the inflatable sit on the hardtop, and then heel the boat. Compare how it feels without a weight on the hardtop?

    Another consideration is wind on the side of the inflatable which can cause the boat to heel. Worst case might be going forward when a gust hits from the side.

    Where are you going in a 16' aluminum boat with a hardtop which is about six or seven feet above the water (freeboard at the side plus "about 5 ft high above the boat sides") that makes you want a "lifeboat"?
     
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    It could turn out to be the emergency device that creates the emergency ! This is a bad idea imo, you are compromising the boat's stability by doing it, you don't see mini tuna towers on 16 footers, for the same reason.
     
  4. zurk
    Joined: Mar 2014
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    zurk Junior Member

    Strait of Georgia.
    Do you think a smaller hardtop height will help ? Whats the max hardtop height i should do on a 16 footer to carry the load ? i can cut down the height from its current to something more reasonable if required by cutting the pillars and bolting it lower.
     
  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Tow it behind your boat if you must have it, it is generally accepted than a self-draining cockpit is not a good idea in a 16 foot powerboat because it raises the centre of gravity too much, what you envisage is doing the same, or worse. Your boat is too small, a 16 foot boat needs all the help it can get to manage offshore conditions safely, without creating unnecessary 'top hamper".
     
  6. zurk
    Joined: Mar 2014
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    zurk Junior Member

    looks like i'll just drop it in a bag in the front then.
    thanks.
     
  7. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    buy a self inflating kit for it. pull a pin throw it in the water and jump in it.
     

  8. zurk
    Joined: Mar 2014
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    Location: Vancouver

    zurk Junior Member

    that would be amazing but i doubt you can get a kit for a SIB with 6 air chambers lol.
     
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