Rounded hull strength for docking

Discussion in 'Boat Design' started by Stein Helge Skjong, Oct 30, 2020.

  1. Stein Helge Skjong
    Joined: Oct 2020
    Posts: 1
    Likes: 0, Points: 1
    Location: Norway

    Stein Helge Skjong New Member

    Good evening gentlemen, I wonder if anyone could enlighten me (or point me in the right direction) on this subject.

    I have a self-built (not by me..) catamaran from Norway, a TC1060. I installed inboard engines with saildrives 11 years ago and even if I've avoided any accidents so far I'm thinking of adding a sort of skegs/small keels to protect the saildrives (they are about 18cm deeper than the hulls).

    Normally when staying on shore the boat sits on 4 polystyren block 60x60x60cm but I've also been ashore in Lanzarote with wooden blocks and wedges.
    I would however like to be able to put my boat in a slip to dry out for maintenance, cleaning etc.
    But I have no experience if the hull can take the load without spreading the load over a larger area.

    But, I would think that there is some way of calculating or estimating (a ball-park figure?) the area needed to absorb the weight when the hull radius and the (singleskin) polyester laminate thickness and strength properties are known?
    I'm away from home now but as far as I remeber the laminate was about 10 mm thick and the hull radius about 90cm..
    I guess using a wooden plank at contactpoint would be a good idea anyway, and I'm also considering a very shallow docking keel in addition to the existing daggerboard.

    I would like to keep the increase in wet surface as low as possible, so I'm thinking a docking keel starting out at an inch deep in front and ending in a depth sufficient to protect the saildrives. Might of course be a really bad idea all of this though :)

    I've searched the forum as far as I could and read the threads I've found on keel designs but I could not find the answers I'm looking for. And hopefully I'm not posting in the wrong place now?
  2. jehardiman
    Joined: Aug 2004
    Posts: 3,690
    Likes: 1,077, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Blocking diagrams are based around two concepts, the weight distribution of the vessel and the structural configuration of the vessel. For MOST small vessels, the hull strength is sufficient to support the hull if the blocks are placed under the structural bulkheads and deep floors. Right now there is probably a designer/builder provided diagram of where to lift and block the vessel. Contacting the designer would be my first suggestion, otherwise make sure the keels have sufficient strength directly under the structure to pass the loads up into the longitidunal stringers and transeverse frames. NOTE: I have seen 18mm 80 ksi steel dented in 100mm by landing wrong on a block...tread carefully.
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