Samphire 26 Compression Post Design

Discussion in 'Sailboats' started by samphy, Dec 23, 2022.

  1. samphy
    Joined: Dec 2022
    Posts: 2
    Likes: 0, Points: 1
    Location: United Kingdom

    samphy New Member

    Hi all,

    I am currently renovating a Samphire 26 yacht. The survey picked up gel coat fracturing around the mast mounting plate; the mast step had subsided by a couple of millimetres in the area of the mounting plate. Also, on removing the mounting plate I could see the plate had partially fractured width wise across the centre. I ground off the exterior of the mast step and inspected for evidence of a rotten/weakened fibreglass or wood interior but found no obvious issues. So I got a new, larger footprint mounting plate manufactured, and then started looking at the cabin roof area underneath the mast step for other possible causes of the subsidence.

    Several variants of Samphire construction in the area under the mast can be seen in the following images. The first shows a fibreglass arch that runs athwartships with a supporting compression post. This fibreglass arch is offset from the bulkhead by about 30cm, at the edge where the second level of the coachroof rises up. The shrouds are through bolted at the obvious lower corners of the arch.
    The following example is similar except the arch has been covered with wood panels.


    In the following image (of my yacht), the amidships part of the arch has been removed back as far as the point where the shrouds bolt through. The wooden compression post supports the cabin roof directly. The ends of the remaining port and starboard parts of the 'arch' can be clearly seen where the headliner is split.


    I am not sure if this latter variation is a change in manufacturers design or something that previous owners may have performed to gain a little more headroom, but several similar examples can be found online.

    In all the examples here, the compression post is offset to port slightly from the centre line of the hull (in my case about 10cm), presumably to allow easier movement forward, although this is still very awkward in the case of my yacht. I can't imagine trying to go forward safely past this obstacle in even a slight seaway with wet weather and safety gear on.

    So we come to the crux of my post. The mast step area lies between the bulkhead and the current compression post position. Could it be that the unsupported span between the bulkead and compression post is not providing enough support for the mast step, thus leading to the slight subsidence of the mast plate on the mast step. An unanswerable question with meagre resources I suppose, but given this assumption I would like to find a better solution that provides sufficient mast support and also allows easy/easier movement forward.

    My first thought is to create a rectangle using two compression posts with joining athwartship top and bottom plates, with the bottom plate sitting on a keel stepped support along the centreline. This would allow me to move the compression posts closer to the bulkhead, directly under the mast step, and eliminate the obstruction. But this is a lot of work, expense, and unknowns as I simply can't afford to get someone to design this for me.

    Would offsetting the compression post to the edge of the keel i the bilge combined with some sort of coachroof support plate between the compression post and bulkhead work?

    Anyway, enough rambling. I would be interested to hear your thoughts and/or be directed to other posts that may consider similar issues.

    Many thanks all!
  2. gonzo
    Joined: Aug 2002
    Posts: 16,800
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    Location: Milwaukee, WI

    gonzo Senior Member

    The offset posts worked fine for several decades. If you rebuild it as before, the boat will outlast you.
  3. samphy
    Joined: Dec 2022
    Posts: 2
    Likes: 0, Points: 1
    Location: United Kingdom

    samphy New Member

    Hi Gonzo,
    When you say 'rebuild', what do you mean? Build a fibreblass arch? Not sure if there ever was one on my yacht. What are your thoughts on the mast step subsiding and improving forward access?
    Last edited: Dec 23, 2022

  4. skaraborgcraft
    Joined: Dec 2020
    Posts: 378
    Likes: 113, Points: 43
    Location: sweden

    skaraborgcraft Senior Member

    Many Albin Vegas had the same problem, allegedly caused by owners being over enthusiastic with rig tension. Anyhoo, many have added/beefed up beams between the bulkheads, rather than a single pole down to the floor. If an arch type construction gives you better access forward, nothing wrong with that as long as it is built strong enough and well attached.
    TANSL likes this.
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