GP14 Sailing Forums Forum Leak in Mk 1 wood GP

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    • #3934
      Michael Forrest
      Participant

      Boat is # 9546 ie about 40 years old – home built from a Bell kit I understand – and hasn’t had a structural problem or a problem with leaks, until now …

      There seems to be a leak into the centreboard case, at the join between the case and the bottom ply panel I think.  I understand this is quite a common problem. Seems probable that a glued join has given up and it looks as if there is a very small amount of movement between case and ply.

      How can I fix this? I would REALLY like to avoid having to take the centreboard case out! In any case the boat can’t be worth much (even if repaired), but I would like to get a few more years out of it. Hasn’t done much racing over the last few years but has seen a fair amount of coastal cruising, and (until the leak) has seemed virtually indestructible.

      All advice gratefully received. Regards, Mike

    • #3936
      Oliver Shaw
      Moderator

      If you look at the Centreboard Case Refitting Procedure document in the Members’ Library you will find that before dealing with how to take the case out it discusses repair strategies leaving the case in situ;    see pages 2-4.    Depending on the condition of your boat you may find that this answers your problem;  at any rate it is worth a look.

      There is a reference there to the use of a top quality mastic;  this is called Lifecalk (yes,  that spelling;   it is an American product),  manufactured by Boatlife,  and I now understand that it is a polysulphide formulation (not a barium formulation,  as I thought when I wrote that paper).   Vastly better for this purpose than silicon sealant.

      Although this is an American product it is available in this country with a little online searching,  but I have recently been told that there is also a UK equivalent called Arbokol 1000.   I have no experience of the latter,  and I merely pass on the information on the basis that it might be worth checking out.

      Whatever mastic you use,  if that is your chosen way forward,  it seems that you need a marine grade polysulphide product,  and nothing else will do.

       

      Oliver

       

    • #3937
      Oliver Shaw
      Moderator

      And a further thought.     You are not actually being precise in referring to the join between the case and the plywood;  the hog comes between the two.     At first I had tacitly assumed that you were referring to the join between case and hog,  but if you are in fact referring to the join between hog and ply then this has nothing whatever to do with the case.

       

      It may be that you first need to establish precisely where the water is coming in.

       

      If the join which has given up is the one between hog and ply is this failing at the forward end,  around the mast step?   If so,  this indicates a structural problem,  possibly arising from too much rig tension for the (original) design,  and the solution to that is the approved mast step conversion  –  as well as of course rebedding the ply to the hog.

       

      Oliver

    • #3943
      Oliver Shaw
      Moderator

      Is it just me,  and am I being just a crotchety old man?

       

      A member is in a degree of trouble with his boat,  and asks advice:    “All advice gratefully received.”

       

      The problem may indeed have already been answered in a document in the Members’ Library,  but failing to realise that is an easy omission.   So advice is duly given,  later the same day,  and with a follow-up first thing the following morning.

       

      The best part of three days later we have not even an acknowledgement.   Not only do we not know whether the advice is helpful,  or appreciated;   we don’t even know whether the member concerned has bothered to read it!

       

      Hardly an encouragement to others to help!

       

       

      Oliver

    • #3944
      Michael Forrest
      Participant

      Oliver, thanks for your help on this.

      I looked for the leak with the boat ashore, putting a small amount of water into the bottom of the boat (starboard side, port was OK) and looking to see where it came out! which was out of the centreboard case.

      So that’s from the inside (top) surface of the ply panel into the case. Looking carefully at the join between the panel and the hog (that’s the plank running from well forward to aft, isn’t it?) I suspect that the glue join may have failed here.  So my initial thoughts were that filling this gap should solve the immediate problem but I would still need to reinforce the join; possibly by using some WEST first to seal the wood and then to make the glue join, first working on the centreboard side of the join then on the inside-boat side, while replacing (or doubling, if I can’t get them out) some of the screws – assuming the wood isn’t in too bad condition. Probably have a go at both sides of the boat, since if it’s gone on one side, the other is probably about to go too.

      The amount of water I used wasn’t enough to reach as far as the mast step.

      Does this sound OK?

       

      regards, Mike

    • #3945
      Michael Forrest
      Participant

      Reply crossed in the post, as you see.

      regards, Mike

    • #3946
      Oliver Shaw
      Moderator

      Apologies if I was a bit crotchety!

       

      I am still not clear from your reply,  and I suspect that neither are you (yet),  whether the water is coming in between the case and the hog,  or between the hog and the plywood.   I think further investigation is needed to determine this.   I would suggest,  if convenient,  that this is best done by getting the boat absolutely dry inside and then floating her.    Then absolutely as soon as she goes in the water look to see where the water comes in;   is it above or below the hog?    If necessary,  mop out the first bit of water than comes in and observe again.   But you will need to observe the very start of the flow;  once you have enough water in the bottom to cover the hog it is too late to see where it is coming in.

       

       

      <span style=”text-decoration: underline;”>If leak is between case and hog:</span>

      The detail of construction varies slightly between different boats,  and you won’t know what the detail is on yours without taking her apart!    But for a boat of this age <span style=”text-decoration: underline;”>expect</span> to find the case bedded down onto Prestik tape or similar soft flexible bedding material,  pulled down onto it by a number of large woodscrews driven upwards through the ply and the hog (the longitudinal structural timber  –  the “plank”  –  on the inside,  between case and plywood).   Whether those screws also pass through the keel (the hardwood on the outside of the plywood),  or whether they lie underneath it and at least a section of the keel has to be taken off before you can gain access,  seems to have varied between builders.

       

      Given that the original construction relied on screws for mechanical strength,  and a soft semi-sticky bedding compound for sealing,  and given also that you now have a failure of that seal and that the wood is wet,  I do not think that epoxy has any fair chance of making a secure bond if you do the repair in situ.   That is why I recommended a polysulphide sealant for an attempt at an in  situ repair;   this may or may not work,  but it is worth a try.

       

      If of course you do decide to take the case out,  then (and only then) epoxy becomes an excellent choice for refitting it,  with everything cleaned up first,  and any rotten wood cut out and replaced.    But at this present stage I understand that you are hoping to effect at least a good temporary repair (good for a few years) without  the need to take the case out.

       

       

      <span style=”text-decoration: underline;”>If leakage is between plywood and hog:</span>

       

      I have never personally met this problem,  although it is a known problem around the mast step as a result of either rot or excessive strain arising from too much rig tension.   When the boat was designed,  in 1949,  today’s ultra-high rig tensions were unknown,  so the boat was never designed to accommodate them.    The static load alone,  before the wind loading even starts,  results in a downward force of somewhere around half a tonne force (from memory;   I am not re-doing the calculation at this point) on the mast step at the maximum rig tensions in common use.

       

      If that is the problem,  then a different solution will be needed,  and it will almost certainly include doing the approved mast step conversion.   This is designed to strengthen the area around the mast step,  by spreading the load,  in order to allow modern rig tensions to be used,  but it is also a recommended structural upgrade whenever one is doing a repair to structural damage or rot in this area.

       

      I realise that this is not yet a definitive answer,  because we still need to establish the diagnosis more firmly,  but I hope it helps.

       

       

      Oliver

       

    • #3947
      Oliver Shaw
      Moderator

      Yet another option,  by no means a proper cure but “first aid” which has sometimes effected at least a significant improvement.  is to clean up and dry off the entire area and then press a suitable grade of Sylglas tape along the full length of the outside of the join,  pressing it down firmly onto the wood.

       

      This was a popular “first aid” approach in the sixties,  and on many boats it effected a significant improvement that lasted for several years.

       

      I see that the range of Sylglas tapes has substantially expanded since I first knew it,  when there was at first only the one,   so check out the range and use your judgement if you decide to try this.

       

      http://www.sylglas.com/

       

       

       

      Oliver

    • #3949
      Michael Forrest
      Participant

      Thanks Oliver, that has given me plenty to think about!

      I have, as I said, had some water inside the boat and watched where it came out of! and I’m pretty sure that there is a failure of some sort between ply and hog, not between hog and case; I’ll have another look, though, and start prodding about. I managed to control the position of the water in the boat (using Blu-tak!) so I’m reasonably clear how it got out of the boat. I assume the hog and ply are supposed to be firmly glued, so this might be a case for WEST once everything is reasonably dry.

      I don’t know, though, the details of the construction and whether the ply edge gets as far as the inside of the case. Maybe this varies between GPs, although I assume all Bell kits are probably alike. I assume that, for the water to get in, there must be a structural failure somewhere. One worry is that if water gets into the plies then rot can start inside the ply, which would obviously be serious; however ply shows no sign of deterioration so far.  I haven’t had a chance to invert the boat yet, when I do I might be able to see what has been going on.

      It seems quite likely that some of the screws have given up and need replacing. I used to think that maybe bronze screws had been used, but I doubt of Bell’s finance could have run to that! so presumably just brass, after all, which could have lost its zinc.

      I rather doubt if rig tension has had much to do with this, as the only means of getting tension in the jib luff has been a Highfield lever which obviously won’t produce a great deal of force.

      I like the idea of using non-adhesive mastic in some form; obviously, if I epoxy things together, and I subsequently decide I need to dismantle them, I have given myself a problem.

      I’m a bit reluctant to get the boat wet again, as it would take ages to dry out and I can’t paint or glue anything until it does.

      As I said, much to think about, and I need to take a really good look now, and the information you have given me will be really helpful, please bear with me if I take a while.

       

    • #3950
      Oliver Shaw
      Moderator

      You seem to have eliminated one of “the usual suspects”,  and the next step would appear to be for you to now investigate further,  and perhaps try things out.

       

      I will very willingly give what help I can,  but in that context please be aware that I plan to be at sea from the beginning of April until Easter,  and then away again from immediately after Easter for the following 10 days or.    So I will not be able to respond to queries during that period.

       

      You may also find a lot of help on the GP14 Owners Online Community site;   link should be this site,  or go direct to https://groups.yahoo.com/neo/groups/GP14_Community/info

       

       

      Oliver

    • #3951
      Oliver Shaw
      Moderator

      Thinking further about this,  once you are absolutely certain that the leak is between ply and hog,  and not between hog and case,  I think that you are probably going to have to turn the boat upside down,  remove the keelband (or at least that section of it.  and remove the relevant portion of the keel.

       

      Saw through the keel both ahead of the case and abaft it,  taking care to avoid (so far as possible) touching the surface of the plywood with the saw;     since there is a slight V to the bottom avoiding that will be a lot easier than if the bottom were flat.    You can afford to regard the keel as largely non-structural,  so a straight cut at right-angles is fine;  there is no need to do a scarf joint;    the internal framing together with the case will provide all the structural strength needed.    Strip off the paint on that part of the keel in order to expose the heads of the screws,  and remove the screws.   If you are lucky they will unscrew;   however you may well have to drill the heads off,  then cut off the shanks flush (and file them truly flush) once the keel is removed,  and use fresh screws in fresh holes when you reassemble.

       

      Again if you are very lucky you may now find that section of the keel lifts off;   much more likely,  however,   you may have to chisel it off,  and replace it with new wood when you have finished.   But the total amount of wood involved is not large.   Use a decent marine hardwood for any replacement.

       

      Once that section of the keel is off you have access to the ply,  and the joint between ply and hog,  and you can then get to work with epoxy and fresh screws.

       

      The original screws are likely to have (once) been brass;    with dezincification over the last several decades they are probably porous copper by now,  and structurally very weak,  and thus liable to either snap or break up altogether.   The choice for replacements is bronze (expensive,  and not always easy to obtain,  but Classic Marine can usually supply them) or stainless steel.   Stainless is the mainstream choice,  and they are readily available (and I think cheaper than bronze).    Reading between the lines of your post I suspect that preserving historical authenticity of a vintage boat is not one of your priorities,  so I would go for stainless.

       

       

      Oliver

    • #3953
      Oliver Shaw
      Moderator

      ” You can afford to regard the keel as largely non-structural, so a straight cut at right-angles is fine; there is no need to do a scarf joint”

       

      Even better,  simple vertical cuts to remove the section of the old keel,  but if your woodwork skills are up to it then when you are ready to fit a length of new timber bevel down the exposed ends at that stage (about 1 in 12 gradient) and scarf in the new wood.    That will provide the added strength of a scarf joint,  while avoiding the unnecessary awkward attempt to saw an accurate very shallow bevel when removing the old timber.

       

      Oliver

    • #4011
      Michael Forrest
      Participant

      Thanks Oliver.

      Incidentally, I have just had a closer look (been a bit busy recently – … retired? nothing to do? put your feet up? well, no, it’s not quite like that) and the ply panel is quite definitely coming away from the mahogany (?) plank (hog?) above it – it’s shifted about a millimetre or two to side, as can be seen from the line of varnish, and it’s just possible to get a slim knife blade in. This over a distance of a foot or so, if you will pardon the mix of units. So it might seem that all that is needed is to trickle some WEST in, but I suspect there is more to it than that. I need to turn the boat over and have a good look inside the case.

      Meanwhile, thanks for your comments, will bear in mind when considering Plan of Action.

       

      regards, Mike

       

       

    • #4012
      Oliver Shaw
      Moderator

      I am pleased that your investigations thus far have refined your understanding of where the problem lies,  and that we seem to now have a firm diagnosis.     And I am pleased,  but not surprised,  to hear that you find yourself still busy in retirement;   so do I,  but at least we can be busy about out own chosen activities,  and to some extent we can control the pace …

       

      I think it very likely that you will now need to turn the boat over and remove the relevant section of the keel.    Not only will this allow you access to the underside of the ply,  and to the fastenings;   it will also then allow more scope for the ply to be temporarily sprung away from the hog while you attempt to dribble epoxy into the gap.    Incidentally I would expect that you will find it easiest to dribble the epoxy in if you put the boat on her side for this part of the operation;    she will remain semi-stable on her side,  but for safety and security you will need to arrange for an assistant to help you set her up in that position,  and arrange props to support her there.

       

      We both hope that you will find that you are dealing with nothing worse than a glue failure,  and that all the wood is still sound,  but that will of course need checking once you have the structure opened up.    Even with just a glue failure,  you are likely to find that the inside surfaces of the joint are now contaminated with gunge,  which will need to be cleaned out.   A hacksaw blade may be helpful here.

       

      I have not yet used the product,  but if you go for epoxy you may find that the WEST product SIX-10 is helpful for this job;    it  is a thickened epoxy which comes in a cartridge which fits a standard cartridge gun.      It comprises the separate components within the cartridge and they are mixed in the nozzle as it is extruded.    The benefit is that it can be injected into the crack.    At least one GP14 restorer in the eastern USA speaks very highly of it.   It is available in this country from the usual WEST suppliers.

       

      If you decide that you are unable to clean out the inside of the joint sufficiently for epoxy to have a fair chance of sticking,  but can make a secure mechanical joint with screws,  you might consider injecting Life-Calk polysuphide sealant as previously discussed instead of epoxy.   It will have zero structural strength,  which is why you will need a secure mechanical joint by means of screws,  but it is a superb sealant and will stick to almost everything,  even if you cannot get the surfaces properly clean and dry.   “Preferably apply to clean dry surfaces.   If necessary,  apply to reasonably clean damp surfaces.   In emergency,  can even be applied underwater.”

       

      If you find yourself faced with rotted ply in the region of the joint,  unless the rot is extremely localised the simplest solution may then be to cut out the damaged ply and let in a replacement piece;   cut out a piece of sufficient width to take the outer edge well clear of the hog,  so that you have easy access to the edge,  and then use a backing pad (bonded with epoxy) to make a good strong joint to the surrounding ply.

       

      Please be aware that I shall be away and incommunicado for most of April.

       

      Good luck.

       

       

      Oliver

    • #5041
      Michael Forrest
      Participant

      Well, I now know a lot more about wooden boats! Boat recently spent a few days on Chi harbour and seems OK. Thanks for your help, Oliver

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