HELP: rotten wood & replacing transom

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This topic contains 4 replies, has 2 voices, and was last updated by  Tony Thresher 5 years, 11 months ago.

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    Andy Weir

    Hi all,

    In a fit of enthusiasm, and to take advantage of the good weather, I decided to tackle a couple of jobs on my Firefly…

    I should have seen it as a sign when I realised I’d mixed the epoxy the wrong way round (2 parts hardener, 1 part resin) to (re)stick the outer gunwale back on resulting in a big sticky mess (will be picking up a 5l can of acetone tomorrow).

    One of the other jobs I wanted to tackle was some cracks around the transom – my plan was to, remove the transom, clean everything up, then epoxy it back on again. Unfortunately, I found a big soggy mess, so it’s not going to be that straightforward:

    So my questions are:

    How do I tell the difference between rotten wood, and damp “good” wood

    What is a cheap, quick & class legal way to replace the missing wood (and ideally before the sun stops shining) – glass/epoxy/filler do the job? or will I need to patch in some marine ply?

    My transom is cracked in several places along the grain – is it worth epoxying it back together (some of the cracks are nearly all the way across), or am I better replacing the whole thing? what’s the cheapest/easiest way to replace a transom? does someone have a full size template?

    Sorry for all the questions – was hoping to race in Torquay, so want to get going asap


    Tony Thresher

    Having had a look at the pictures I think you might as well replace the transom. I seem to remember there was a good article by Steven Greaves in a past Bulletin giving a step by step guide to doing the job. I think there is something similar on the website he created when he converted his boat Cumulus to a MK4. I’ll see if I can find the link and post if someone doesn’t beat me to it. Might even be under Links on this site?

    As for the rest of the work it is difficult to assess from pictures only if you have got rid of all the rot. If the wood is just wet then if you gently push a bradle into the wood with light pressure it should only leave a dent, if its rotten it will penetrate the wood. I tend to cut and scrape away with an old chisle until I get to a point that i think i need a mallet and and a sharp chisel to make further progress. At this point I decide where I am actually going to work to, to make the repair and cut accordingly. Whatever you do make sure everthing is thoroughly dry before you start the repair.

    As your hull is painted and assuming you are keeping it that way you dont have to worry about cosmetics so you can use layers marine ply instead of veneers except on the inside where you might want to try and match the existing wood. In the long term if you have doubts about the soundness of the floor in your boat you might consider applying 3/4mm ply skin to the inside as described in the new class rules which will not only stiffen the floor but acts as a massive backing patch to work to when replacing any soft wood in this area. See the picture of 3173 on the boat register to get an idea. In the meantime you could start the process by epoxying say an 18 inch long 3/4mm backing patch either side of the hog covering the area defined by the edge of the hog and the MK4 sidetank sides which will give you sometghing to work too. You can then complete the process of covering the whole cockpit floor area as defined by the edge of the hog and MK4 tanksides in the future by butting up to these patches.

    Hope this helps and hasn’t complicated matters!! Contact me if you want me to talk you through the last paragraph.

    Tony Thresher


    Tony Thresher

    BTW you need to click on the picture of 3173 in register and another will come up showing the floor.



    Andy Weir

    Hi there Tony,

    thanks for the advice – I had an email from Steve today, with article, instructions, and photos – so I’m a lot happier with the prospect of replacing the transom.

    I’ve started to square things off (I’ve added more pictures), and re-attached the old transom so that I’ve got something to work to (3 layers of 1.5mm ply should be pretty straight forward to work with).

    I’ll probably just stick to ply for the moment, and make a “feature” of the repair in anticipation of a MKIV conversion at some point in the future.

    Is ply reinforcement class legal now? couldn’t seem to find anything about it in the class rules.


    Tony Thresher

    Ply floor stiffening was passed at the AGM as follows:

    Proposal 2) New floor repair

    (a) The hull shell shall comply with the Lines Drawing.
    (b) The hull shall be built in one of these forms:
    (1) Wood
    (2) FRP
    (3) Composite i.e. GRP shell with wooden decks.
    (c) A maximum of 2 internal longitudinal stringers may be fitted on each side
    of the hull shell. OR:
    Internal stiffening may be achieved by adding either marine plywood or
    solid wood veneers a maximum of 4mm thick that shall cover all the
    interior surface of the hull within the outline defined by the MkIV side and
    bow tanks, the hog sides and the transom.

    I’m 99.9% certain it has now been ratified by the RYA. I’m checking and will post when I get a response or perhaps someone who knows better than me will beat me to it!!!


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