Cross beams/aka's for a 6m (20ft) trimaran

Discussion in 'Multihulls' started by Aaron_de, Jun 6, 2016.

  1. Aaron_de
    Joined: Jun 2016
    Posts: 13
    Likes: 2, Points: 3, Legacy Rep: 10
    Location: Avoca Beach, Australia

    Aaron_de Junior Member

    Thanks for the replies, based on your feedback and other research and conversations I've settled on 100mm aluminium tube with a 3mm wall. Plus a reduced beam from 5.5m to 5m.

    Next I'd be keen to hear your thoughts on waterstays vs. fixed aluminium struts.

    Here's what I've been thinking about so far... (please correct any of my thoughts if necessary)

    Waterstays are obviously much lighter, a good thing for any sailboat.

    Waterstays win

    The fixed struts provide up & down vertical support, while waterstays only provide tension preventing the ama's from upwards movement.

    I understand, however, the mast shrouds would provide opposite support to the waterstays although I want to limit mast compression where possible.

    Struts win

    Ease of assembly
    Waterstays would be made from dyneema with a simple purchase system for tension. Installing eyes to the hull and aka's for dyneema is fairly straightforward.


    I found reasonably priced 8mm quick release pins for the fixed struts with a breaking strain greater than 63,000 Newtons. To pullout the pin without depressing the button requires 3000lb+ of force. I believe the Ultralight 20 by Warren used quick release pins.

    Struts win (just)

    The manufacture of the aluminium struts plus the mounting brackets to hull sides and aka's will require professional help.

    Off the shelf hardware is available so cheaper and faster to build using waterstays.

    Waterstays win

    So far it's neck and neck so the last factor is...

    Sailing performance
    This is the real unknown for me. What are the thoughts from those in the know?


  2. tamas
    Joined: May 2009
    Posts: 38
    Likes: 1, Points: 0, Legacy Rep: 15
    Location: Brisbane

    tamas Junior Member

    Hi Aaron,
    Boat speed has been good, very quick to accelerate, best to date is 14kts (2 sail close reach) in about 16knts of breeze. When boat is doing better than about 8kts it feels very smooth and out of the water. At 14kts it feels just as nice, amas sitting high in the water and not pushed at all. I sail 2 up only. I don't think 20knts is out of the question give how easy it gets to 14knts and how smooth it is.

    My struts do splash in waves so to try and eliminate that I have wrapped them in a type of foil (wing) section so as to go through the water smoother. It seems to work ok.

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.