bow thruster tubes?

Discussion in 'Metal Boat Building' started by Jackphilps, Nov 7, 2009.

  1. Submarine Tom

    Submarine Tom Previous Member

    What does the manufacturer recommend?
  2. jehardiman
    Joined: Aug 2004
    Posts: 3,517
    Likes: 903, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    So you want shipfitting advice? As Richard and Gonzo implied, this is a relatively simple layout job. There are many ways to cut a hole like this in the yard, lots of shipfitter tricks and specialized cutters or custom built tool jigs. As you asked how to do it, I will assume that you don't have those yard skills and only common hand tools.

    Ok, here is an example of how it can be done, especially for large dimensions where you can't just buy or make a cutter bit. The more precise you are, the better the fitup, but remember it is always better to cut the first hole too small but in the right place:

    Locate and determine the level of the Baseline, the forward reference point, and any list as the hull sits on the blocks. Using a transit or laser level construct several level transverses perpendicular to the vessels CL in away of each thruster tube. Lift a set of offsets from the hull in way of the tube opening remembering to correct for list and trim as she sits, you will need both sides as boats are rarely symetric within throat tolerances. Regardless of any other way to make the opening in the shell, you will need to accurately layout the axis of the tube on the hull shell if you want it correctly positioned.

    Go to the loft floor and project the INNER intersection of the tube to the insert to the OUTER shell. This is also the time to lift from the loft floor the circumfrential offsets of the tube from CL so you can cut the tube to near net shape. From the outer shell projection offet a second ellispe the width of the cut kerf inward towards the axis of the thruster tube. This will mark the ellispe you need cut. Make the cut (at the proper list and perpendicular to CL, normally you drill a set of reference holes), then dress the throat and cut the bevel. Fit the tube and mark the trim line. Trim the tube, tack, then weld.
  3. SeaJay
    Joined: Jun 2007
    Posts: 211
    Likes: 5, Points: 0, Legacy Rep: 112
    Location: Sacramento

    SeaJay Senior Member

    Bow Thruster Installation Tool

    I just happened upon this and thought it might provide some ideas about how to cut the hole. I was planning to do something similar, but hook one of my lasers to the rod and just mark the hole before cutting. This is pretty slick.



  4. tunnels

    tunnels Previous Member

    Whats the hull Glass or what ??
    In glass boats they neen to be glassed inside and outside using a glass tube of the diamater thats required for the unit being used . Its helps to remember that is is in the water all the time so need to be done properly and strong !! :eek:
    It is in a place that could get banged and knocked so make it stong , plus it below water level all the time !!:D
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