Forums Forum Deck Replacement

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    • #4524
      Anonymous
      Inactive

      Hi everyone,

      Our Uni sailing club has been donated a wooden Mk1 GP, and seeing as everyone else sails strange little plastic things, I’ve been delegated the task of fixing it up ready to sail.

      The decks are pretty much completely rotten, and need to be replaced, but the hull and frame seem to be in pretty decent shape.

      The plan is:

      -Put the boat inside our container to let it dry out.

      -Lift off the rotten decks, pull out any nails or screws and generally clean up the surface underneath. Sand thwarts and floor.

      -Buy some 6mm exterior ply from a hardware shop because we can’t afford good marine stuff.

      -Using the old decks as a template, cut them to shape, sand rough edges.

      -Put a coat of West epoxy on what is going to be the top side, make sure the cut edges are completely sealed. Wait for it to dry, varnish both sides.

      -Put some epoxy filler onto the frame and hull of the boat where it will be in contact with the deck to make it watertight, and stick the entire thing down with copper nails.

      -Fill any gaps with clear epoxy and sand back until smooth.

      -Stick original gunwales back on using nails and epoxy (they seem to be in  okay shape, and even if they’re a little spongy, they will most likely be used as bumpers anyway)

      -Put on about 5 coats of varnish on everything, letting the boat dry fully between each one.

      -Replace fittings, dipping screws in epoxy before screwing in.

      -Sail boat, amaze everyone with my skills.

       

      Seeing as I’m basically an idiot when it comes to boat maintenance and repair, are there any glaring flaws in this plan, or advice the good people of the forum could give me?

      Many Thanks,

      Peter

    • #4526
      Oliver Shaw
      Moderator

      Deck ply;   you will find that 6 mm thickness of the proper stuff,  i.e. marine ply  –  which I appreciate you can’t afford  –  is far heavier than the boat normally needs,  and would make the boat unduly heavy.    The minimum is 4 mm,  but for heavy duty use (including training,  and cruising)  many people prefer 5 mm.     6 mm would be somewhat over the top.

       

      Since you are having to use an intrinsically less strong type of plywood,  you may in fact need the extra thickness,  but that is something for you to assess in the light of this information.

       

      A few other points about exterior grade non-marine ply:

       

      I used it once for a very temporary and experimental rudder blade on the big boat,   when I wanted to try out a new profile before making a good one with the proper materials.    I was horrified to find that top veneer of the brand new ply was starting to delaminate even in my workshop,  before being exposed to any weather,  as soon as I started to cut it,  and I also found breaks in the interior laminations.    So if you have to use exterior grade,  treat it with caution,  be very selective in whom you buy it from,  and also be very selective in checking the individual sheets before purchase.

       

      <span style=”line-height: 1.5em;”>When I made my experimental rudder blade I coated the finished blade with epoxy,  and then three layers of woven glass mat.   The result was that it was a little too good  –  so it stayed in service longer than I originally intended;    but it was nonetheless still not good enough,  and snapped off in moderate swell off the Farne Islands,  with around 20 miles still to go to make port at Amble.   So be warned …</span>

       

      I think that if I were doing the job in non -marine ply I would at the very least coat both sides of the ply in epoxy,  and all the edges.     Some of that is best done during construction,  rather than beforehand;  mark out where the joints are going to go,  and leave those uncoated,  so that when you assemble and glue up you can do so with wet epoxy direct onto bare wood.    If you coat everything first,  you will find considerable difficulty in getting neat joints because of the thickness of cured epoxy getting in the way of the joint you are trying to make.

       

      Finally,  given that you are thinking of a greater thickness than you would need for the proper material,  and the possibly greater expenditure on epoxy,  it might be worth doing two costings before you start;   one using 5 mm or 6 mm exterior ply,  and one using 4 mm marine ply.   Make sure that you include <b>all </b>the materials in the costing,  not just the wood,  and the marine ply doesn’t have to be the very swish stripey sapele;    basic marine ply may well be a less expensive choice and should be perfectly adequate.   Only when you have the total costings for both routes can you decide whether the cheese-paring approach is justified;   if the saving is going to be very modest and the end result is likely to be much inferior it may well be a false economy.

       

      That is before you even start to consider the value of your time …

       

      Hope this helps,

       

       

      Oliver

    • #4527
      Oliver Shaw
      Moderator

      A handful of other details:

       

      It seems that you are intending to remove the rubbing strakes,  and replace them once the work on the decks is finished.   Good.   In that case,  cut the outside edge of your new decks to slightly proud of the hull,  and plane / surform / sand it flush once they are fitted and glued down.   Then of course coat the newly exposed edges with epoxy,  preferably doing this as you glue the rubbing strakes back on.

       

      Epoxy the underside of the ply as well as the top,  particularly if you are using non-marine ply.    If you use genuine marine ply you would get away with not epoxying the underside,  although best practice for the best long term job would still be to epoxy both sides.

       

      5 coats of varnish is rather pushing your luck;  that is just about the absolute minimum.   I would normally expect to be just starting to get an acceptable finish,  and a coating that will last reasonably well,  at six coats,  and I normally aim for about nine.    That is not of course nine times the thickness of a single coat,  because I sand down alternate coats moderately heavily;    it is possibly – and I am guessing  –  about six times the thickness of a single coat once all the sanding is taken into account.

       

       

      Oliver

    • #4531
      Anonymous
      Inactive

      Thanks Oliver, that’s some really useful advice.

      So you’d strongly recommend against using exterior ply to do the decks? I thought it would probably be fine if it was sealed with epoxy, but if you said it was delaminating indoors in your workshop, that mightn’t be the best idea (which begs the question, if it can’t cope with conditions inside in a dry, heated workshop, what exactly is it good for, and why is it called “exterior ply”?). I’ll ask around suppliers, and see if I can get someone who can give me a guarantee. If not, probably marine ply is the way to go, and I’ll try and get the money out of the club somehow. We’re getting a free boat, so shelling out £100 on wood for the decks doesn’t seem too unreasonable, I just have to make the treasurer see that!

       

      Just looking at Robbins’ website now, a 2500x1200mm sheet of 4mm bog standard marine ply is £34.24, plus VAT.  That won’t quite do the foredeck, but if we get two, we’ll probably be able to get everything (I’m no joiner, but I don’t particularly mind if I have to do the side decking in two parts, and just pack the space between the two segments with filler. It’ll look awful, but hopefully be strong and watertight)
      Other than that, the approach seems okay to you then? No glaring basic errors?

    • #4532
      Oliver Shaw
      Moderator

      If you are joining pieces of ply for the side decks a scarf joint (a.k.a. scarph joint) is neater than just a butt joint.    I appreciate your comment that you are no joiner,  but I wonder whether you have a contact who could make that joint for you?    It is not technically difficult,  but it does require a modicum of skill,  and the use of a workbench (or other good sturdy flat surface) as well as a plane and other basic hand tools.

       

      Oliver

    • #4534
      Anonymous
      Inactive

      It’s something I would actually be willing to give a try. This is my first job of this sort, so there is definitely something to be said for me trying it on a boat that I am not going to make any worse if I mess the job up. The lack of any tools for woodworking is a problem though. My initial plan was to buy a small handsaw, cut the panels slightly bigger than needed, and rub them down to size with a power sander (which we do have). Getting any sort of accurate profile on the two halves of a scarf joint would be next to impossible with those tools

       

      The other option is I look around local joiners and wood suppliers, and see is there anyone who would cut the pieces to size for me for a reasonable price. That way I can just epoxy and varnish the pieces, and stick them down to the boat, and not have to worry about me messing up any of the cuts (or wring my hands about throwing away all of the inevitable offcuts of lovely wood). It’ll be a bit less satisfying for me, and possibly more expensive, although that part would be entirely down to how much wood I would waste if I was to do the job myself.

    • #4535
      Oliver Shaw
      Moderator

      I don’t know whether they are still doing them,  but Fyne Boats used to sell kits of parts for the GP14,  and have been known in the past to supply individual panels on request.    http://www.fyneboatkits.co.uk

      Local wood joiners,  or even boatbuilders (if any in your area) for the limited assistance you suggest would also be worth considering.

      Where are you based?

       

      Oliver

    • #4536
      Anonymous
      Inactive

      I’m in Glasgow, and there seems to be a very limited wooden boat scene up here, unfortunately. Unless there’s someone in Largs that I don’t know about I’d probably have to go down to somewhere in the north of England, which is about £50 in fuel for a return trip, so is likely to price out most of the options there, unless they can do me an amazing deal.

    • #4539
      Oliver Shaw
      Moderator

      Over to some of our Scottish members to now pick this up;    do you know of any local firms who may be able to help?

       

      Oliver

    • #4542
      Anonymous
      Inactive

      Thanks for the responses, it looks like I’m going to have no shortage of help and advice getting this boat on the water, which is great!

    • #4549
      norman
      Participant

      Re Oliver’s comment on scarph joint, you need a solid bench (or table) and a sharp plane.  The operation is not too difficult if you line up one piece of ply with the table edge (or a straight-edged sacrificial sheet). good side up.  Lay the next piece on top, wrong side up  and set back ‘x’ times the ply thickness, where ‘x’ is the ratio of the scarph. (I see Oliver suggests 12 in another mail, but anything over 6 is probably OK).  Lay a third piece of “spare” ply with a straight edge on top, again set back by ‘x’ times the thickness.  Rest the plane across the three edges and plane gently until the bottom sheet meets the table surface and there is no step between the two work pieces.  When gluing, ensure the pieces cannot slip before tightening any clamps.

      Re plywood supplies, I have a friend in Ayr who is having the same problem and resigned to ordering from southern England.  You might co-operate with an order. Contact me on 01292 570520 before Wed 18th if interested.

      Good luck with the project

      Norman

    • #4555
      Oliver Shaw
      Moderator

      I have just come back to this,  and checked a bit more on Robbins’ prices.   As you rightly say,  a 2500 x 1220 sheet of 4 mm (3-ply) bog standard Elite marine ply is £32.24 plus VAT.   The equivalent in 5 mm (5-ply) is £46.90 plus VAT.   The difference is not large,  and pales into insignificance by comparison with the total cost of the project,  and by comparison with teh value of your time;   the important thing is to make the right decision.

       

      It would be well worth considering carefully which of the two to go for;  if your the expected use of the boat the 5 mm is preferable it would then be a pity to spoil the ship for a ha’p’worth of tar.   The class rules specify 4 mm minimum,  but a great many boats are built with 5 mm decks.    I think that the “right” thickness depends on how you expect the boat to be used.

       

      I understand  –  very much at secondhand!)  –  that top racers are likely to prefer 4mm because it is lighter.    However their boats are lovingly caressed,  except when  driving hard during a race,  and in terms of ensuring that the boats never suffer abuse they probably have an easy life.

       

      For a boat used for cruising,  or training,  there may well be more risk of higher localised loads on the deck (e.g. someone standing on it,  rather than sitting,  or carelessly plonking something heavy down on the deck).   For a boat that may suffer that sot of treatment from time to time,  even if only occasionally,  it is probably worth going for 5 mm.    When I had a new series 2 boat professionally built for me in 2005/6 specifically as a cruising boat the builder (Tim Harper) opted for 5 mm as standard,  and the boat still came out marginally under weight,  so carries corrector weights;   and I have absolutely no worries about her strength.

       

      Oliver

       

    • #6822
      Anonymous
      Inactive

      A wee update on this. The deck is on! Big delay over winter as I was kicked out of the shed where I had planned to work, but it recently went on fire, and nobody wanted the space I had been using any more. Result!

      I used exterior ply in the end, as I didn’t want to waste nice wood on something I was very likely to mess up.

      Only 1800x600mm sheets would fit in my car, so the side decks had to be made in sections.

      Painted the inside of the cockpit grey, as the wood wasn’t looking that great anyway, she looks a lot cleaner inside this way.

      From astern

      From astern. The aft deck was the first section I cut, as I thought it was the easiest, and as you can see, the panels came out a little wonky. My skills improved as the job went on and the other sections ended up much better!

       

      From the side. Gunwales are now on, the horrible white stuff is the filler I used to stick down the decks and fill in the damage caused to the ply when the old deck was ripped off. It looks a lot better now than in the photo, as the gunwale mostly covers it. Wimped out of using scarf joints, and went for butt joints instead. There are some small gaps, but they pass the slidey-bum test without taking off any skin, so that’s good enough for me!

       

      From the front. I don’t think I’m going to bother with a splash guard on the deck, although I’ll see if any of my offcuts of ply will do the job if I get the time.

       

      From the helming position. The gaps in the deck I was planning to use as spinnaker bags and put a nice rounded section of deck at the sides. What do people think? Holes for the shrouds still need to be drilled as well, trying to hunt down a big enough drill bit to set the fittings!

      Looking forwards from the transom. Thwarts could use a clean, sand and another couple of coats of varnish, but I am getting there!

       

      And from the side. She’s definitely a GP!

    • #4821
      Anonymous
      Inactive

      In case anyone is interested in how the job is going, we’ve taken the decks off and are trying to get as much of the old varnish off as we can.

       

      We also discovered the hull number hidden beneath the floorboards. She’s number 4611, built by Honnor Marine. Does anybody know her? Has she got any interesting history we can find out about?

       

      Right now, our progress is:

      -The frame is pretty much prepped for a new deck to go on. We’re going to roughen it up so the epoxy binds better, at Duncan Greenhalgh’s advice.

      -I borrowed a hot air gun, and have been going at the external paint and internal varnish, with the intention of getting as much of it off as I can to let the underlying wood dry. Some places it’s going fine, and the varnish bubbles and scrapes off very easily. Others, it seems like the wood has been treated with something under the varnish, the varnish itself will bubble and scrape off, but leave a layer underneath it of something very thick and sticky, which is really difficult to scrape off. This seems to be the case mainly with the floor and centreboard casing. Any suggestions?

       

      I’ve also been taking some photos as we go along:

      How she originally looked

       

       

       

       

       

      And a few of how she’s looking at the moment:

       

       

       

       

      You can find the full albums at:

      Before: https://www.facebook.com/groups/652327968145561/permalink/816349068410116/

      After a wee bit of work: https://www.facebook.com/groups/652327968145561/permalink/835393143172375/

      As she is tonight: https://www.facebook.com/groups/652327968145561/permalink/841702692541420/

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