New Stringers

Discussion in 'Boat Design' started by helluvaboater, Feb 28, 2016.

  1. helluvaboater
    Joined: Jul 2015
    Posts: 50
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    Location: Maui

    helluvaboater Junior Member

    Installing new stringers in my 27 foot express cruiser fishing boat. Tons of pictures at...

    Boat was originally setup for twin stern drives. I built a new transom and I am converting to a single v-drive so the last 8 feet of the boat is gutted right now.

    I plan to install a 200HP Cummins 6BT engine but I might get a 370HP 6BTA one day so I am trying to build the boat strong enough for the 370HP option.

    The stringers I am installing are made 1.75" thick microlam LVL and are 8 inches tall. My question is in regards to the tabbing where the new stringers meet the existing stringers.


    The new engine stringers are in-line with the exsting stringers, which are made from 1/2 marine ply with some roving/mat over it. The existing plywood stringers run up to the deck. When I cut out the old plywood stringers, I only left 6 inches sticking out to "sister" the old stringer to the new stringers. In hindsight, I should have left more so I could sister them together for a length. Is it completely necessary to sister these stringers together?


    There are fuel tank glassed to the hull outside of the stringers that add some longitudinal rigidity to the hull. They pass past the bulkhead at least a few feet:


    I have begun strengthening the area where the new stringers meet the forward bulkhead. I so far did 4 layers of 1.5oz mat in all the inner corners to round them off. Then we laid 3 layers of staggered nytex 1708 strips in the following places on both of the stringers:


    I also did 2 more units of 18oz roving + 1.5 oz mat over the existing bulkhead which had maybe only 1 unit on it already.

    I also put in some smaller stringers outside of the engine stringers to add more lateral support. These are glassed in with 3 units 18oz roving / 1.5 oz mat:


    These run from the transom to the back of the fuel tanks that are glassed to the hull.

    My questions are:

    Is it OK to sister the new engine and existing stringers together with only a 6-inch "sister" joint like I am doing because the fuel tanks add the lateral support to the hull in this area?

    -What is the tabbing schedule for the engine stringers on the forward bulkhead and transom? Does mine look OK?

    -Tabbing schedule for non-engine stringers?
    Last edited: Mar 4, 2016
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