How to create Tube-fittings by G. Maroske

  • This document was last changed 10th Feb. 2001 - All copyrights by G. Maroske
  • Working with these materials is HAZARDOUS!!!

    What is this document about?

    This document covers the creation of very small Tube-fittings for hard-shell kayaks.
    It is decicated to the experienced fiberglass kayakbuilder and NOT for beginners.
    Beginners should take classes in fiberglass work.


    Why fiddeling with these Tube-fittings, if there are easier ones?

    The Tube-fittings were developed to transfer the maximum of the applied forces into a large deck area with minimum impact to the deck while installing.
    If the kayak has a strong edge where the upper part of the gunwale meets the deck (think of greenlandstyle plywood kayaks) the fitting can be placed right at the edge so the fiberglass will transfer a part of the applied forces into the hull. This brings maximum failure safety.

    hull_fittingfitting broad cut at gunwale edge

    The piece where the rope runs around has a large amount of glass in it which provides maximum support in comparison to a rod fitting. Instead of high stressed points the load is distributed on a large area (hatched area in the figure).

    Tube fitting
    fittingfitting length cutfitting cut broadside
    Rod fitting
    rod fittingrod fitting in half

    How to install Tube-fittings?

    Read the instructions at least twice BEFORE you start drilling holes!
    If you have never worked with fiberglass before get someone who instructs you.
    Resins, hardeners, dusts and fibers are no child toys and safety precautions should be taken at each step.
    Read the warnings above! If you do not know what you are doing stop here and do not proceed!

    The fittings are most easily installed before the deck is joined with the hull.
    But they also have been installed in complete kayaks.
    Warning!! If working inside a kayak, provide ventilatition of fresh air inside the kayak, wear breathing protection and NEVER work alone! Irritant fumes and loss of breathable air may occur!

    Buy non-reinforced soft-PVC-tube with an outer diameter of ~10mm (~3/8 - 4/8 inch) and a stiff rope with a diameter that fits tight into the tube. Cut a 12cm (~5inch) off the tube . Pull 16-20cm (7-8inch) of the rope through the tube. Use a needle to pinch a piece of twine through one end of the rope. The rope is needed to prevent collapsing of the tube while bended sharply.

    rope through tube

    Take adhesive tape and cover the deck area where the fittings shall be placed. Mark two holes in a distance of ~22mm (~7/8inch). Drill two holes with the diameter of the tube. Sand the area inside thoroughly where the fitting will be installed (wear at least a dust-mask or similiar, those dusts are harmful!).

    drillholes placement

    Make sure that you get a a snug fit of the tube in the holes to prevent spilling resin later. From the inside of the hull stick both ends of the tube to the outside. Leave a generous loop inside the hull.

    drilled holes with the tube loopadd fiberglass mats

    Push lots of fiberglass mats through it (do not take a stiff mat, use fine roving mats of 200g or less per square meter). There should be a reasonable buildup of glass. Cut some pieces 10x10cm (4x4inches) for covering (wear at least a dust-mask or similiar, those fibers are harmful!).

    Turn the boat upsidedown.

    pull the tubes tight

    Wet the mats in the loop with resin and pull both ends of the tube tight from the outside (wear at least skin and breath protection).

    ready for coveringthe glassed tube

    Cover the hump of the bended tube with glass and resin to end up with a watertight covering.
    To remove the tube pull out the rope first. Use pliers and pull strongly on both ends of the tube. When the tube is stretched, it's diameter decreases and it starts to loosen. This will reduce the adhesive forces. Cut off one end of the tube as deep in the fitting as you can with a surgery knife. Pull out the rest of the tube using the pliers.


    My boat with installed fittings.


    !!!WARNINGS!!! Working with these materials is HAZARDOUS!!!

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