Advice required on MK 1 floorboard creation

GP14 Sailing Forums Forum Advice required on MK 1 floorboard creation


This topic contains 10 replies, has 7 voices, and was last updated by  Arthur 3 days, 5 hours ago.

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  • #20013



    We’ve decided to make some floorboards for our MK 1 GP14 as it currently only has the base hull floor and we are fearful of damaging it this season. I’ve found the references in the rules regarding board widths and it says the minimum is 300mm and maximum is 380mm. However at the back of the boat the width of the floor is around 127cm, which will mean the 380mm maximum boards will not cover much of the floor.

    Also I’ve seen mention of 2′ x 4′ boards being used, but the available floor space from front buoyancy tank to the transom measures 278cm, whereas an 8′ board is only 244cm long.

    There are 2 blocks on the floor (one either side) which the boards would sit on and have turnbuckles on them, and a block at the centre of the rear floor which also has a cleat for the elasticated cords from the plastic flaps over the 2 scuppers.

    Should I use 6mm plywood with width wards battons underneath, with one board down each side of the centreboard casing, meeting at the back on the rear block? Is marine ply essential or is well sealed and painted regular ply sufficient? How far forward should the floorboards go? Level with the front of the centreboard casing or further forward?

    Any advice would be most appreciated, as we can then get on with making some templates, test fitting them and then purchasing the ply and getting on with the job.

    Many thanks in advance


  • #20014

    Oliver Shaw

    Have a look at the discussion which is (at present) two strings down from this,  “Old Fibreglass Boat”.     Part of that deals with floorboards.

    Steve White is our resident expert on the early GRP boats.

    Fitting effective floorboards is vitally important,   not least because the GRP hull was never designed or intended to take the localised weight of a person standing on the hull skin,  and it may not be strong enough;   the load needs to be properly spread.    Having said that,   unless you intend racing the boat at the highest level of competition,  which is probably unlikely for a boat of this age,  my own personal view is that I cannot see anyone seriously objecting if your floorboards are wider than the Rules permit.

    And I would also expect that the 380 mm maximum width is for each side of the boat separately.    The normal arrangement is to have the floorboards in the centre of the boat,  extending out approximately as far as the side buoyancy tanks,  and with the outer edges continuing in much the same line as far as the Mk 1 stern tank.   So,  on the Mk 1,  I suspect that the outermost part of the hull skin abaft the side tanks is not covered by floorboards.    I will see whether I can find some photos;   if so I will post them later.

    Hope this helps



  • #20015

    Oliver Shaw

    A recent post “Seeking info on my GP14!” has a photo of the interior looking aft,  and clearly showing the floorboards.

    This is actually a M2, 2 boat,   so there  is no stern tank and instead the side tanks extend all the way aft,   but I am sure that if you make the floorboards to that sort of pattern they will be entirely suitable for your Mk 1 boat.

    Hope this helps,



  • #20016


    Hi Robine,

    There is no problem with an 8ft sheet, the boards only need to go to the forward edge of the aft deck, not all the way to the transom. I have just measured a board I had in an old boat, it looks like 4mm marine ply but I reinforced the edges with strips of 40 x 6 mm. The ply was 1 ft wide ( sorry about mixed terminology) and the reinforcing projected slightly, maybe 5mm either side.  Be careful about making them too wide as it can be a bit of a fiddle threading them under the thwart when installing.  Well painted and maintained you can get away without marine ply. You will also need a short filler piece between the centreboard case and the aft deck.

    Good luck, Norman

  • #20018


    If you have a look on the posts on “old fiberglass boat” I have put on some info about making floorboards.

    Hope this helps you !

  • #20020


    “Well painted and maintained you can get away without marine ply.”

    I agree, and I will say that if you are going to the effort of making the floorboards, and they are not considered disposable items, then making them from the ply which has waterproof glue and minimum voids is an investment in time sailing over time maintaining.

    Grades of plywood are for other forums to discuss at length, but make sure that the wood glue is waterproof.

    When I made the floorboards for 9121 (now a training boat at my local pond) I used a big piece of cardboard to make a template, and made the boards out of a single sheet of 1220 x 2440 BPW plywood sliced directly along the centreline, with appropriate stringers. As another poster has said, the floorboard needs to be flexible enough to bend and twist to get over the stern and under the thwart in an action which very much suggests that once fitted will stay in the boat.


    • This reply was modified 2 months, 1 week ago by  sw13644.
    • This reply was modified 2 months, 1 week ago by  sw13644.
  • #20181


    My series 1 boat has the floor boards ending at the forward edge of the aft deck, they do not extend all the way to the stern.


    If Oliver can excuse some unofficial modifications to my boat in the shape of a rear bulkhead and two sealed bouyancy tanks (that now have screw in openings for access) You can see where I also added a plank to either side to extend the floor further to the sides of the boat. I have removed my buoyancy bags and am currently working on making some sealed foam blocks to fit between the ribs that will be held in place with plywood to replace them. I camp cruise aboard my boat, the bags took up too much space for storage and sleeping.

    My boat was also missing the bow and stern bags, so nothing lost.


    • This reply was modified 1 month ago by  Arthur.
  • #20183

    Oliver Shaw

    I like the modifications!    If you do not intend racing her you can make what modifications you like,  but be aware that they may take her out of class;   however the primary effect of that,  if you do not intend racing,  is only to possibly depress her eventual resale value.   That may well be of no relevance to you,  and at the age of your boat and in a country where there is not a lot of GP14 racing anyway it is very questionable whether that would happen.

    Do however make sure that the final positive buoyancy which you end up with is sufficient.   Essentially,  positive buoyancy necessarily takes up space.



  • #20185



    I would agree with Oliver’s comment about ‘ positive buoyancy takes up space’, the bag used in each side of a Series 1 boat provide 150lbs of buoyancy each, so a total of 600lbs, the area under the foredeck originally held a triangular pillow which filled about half the height of the space, later we got Crewsaver to make double height pillows which completely filled the bow space.  With this buoyancy when the boat was righted after a capsize the water level will be below the top of the plate case making it possible to clear the water with out the boat continuing to fill up!!.  Later boats and as a retro fit many of us fitted a bulkhead forward of frame 2, either full height to the underside of the deck or if wanting some forward storage a part height tank with the top on the stringer, difficult unless you have the foredeck off!!.

    BUT beware of not having enough buoyancy, also are you replacing the capping over the centre board case? without it water will splash up when moving, even with a slot gasket.


  • #20200

    Oliver Shaw

    Regard the 600 lb figure for the buoyancy as the absolute minimum.    I think you will find that in addition to the two built-in tanks which you have created at the stern that requires fairly large buoyancy units under the side benches and also abaft of them,  as well as a large unit in the bows.

    The two built-in units which you have created at the stern look very neat,  but appear to be only about half the size needed in the quarters.    The normal standard is either a stern unit filling the space beneath the stern deck,  right across the boat (which used to be the normal arrangement),   or alternatively (the more modern arrangement) a pair of units in the quarters,  extending from immediately abaft the side bench seat knees right to the transom,  and of a diameter to only just fit under the stern deck.   So far as I can judge from the photo,  your two tanks appear to each be about half one of those quarter units.

    See the attached photos.   These show the side and quarter units,  and also just discernible (but in deep shadow) is the built-in bow tank,  complete with large (11-inch) diameter ventilation and access hatch.

    It may be only in the event of a capsize in rough conditions  –  and a capsize should never be allowed to arise except in very rough conditions  –  that you discover the hard way if your buoyancy is insufficient.   Even a deliberate swamp test,  useful though that is,  is normally carried out in smooth water;   so although it will tell you whether your buoyancy works,  and whether it leaks,  it does not always tell you whether you have enough of it.



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  • #20323


    Yes, I refitted the cap, that picture was taken when the varnish was still drying on many parts and I had just reinstalled the freshly done floorboards.

    I also have the bow sealed off with a hatch in the bulkhead at Frame 2 and I am currently building epoxy coated foam floatation forms to fit between the stringers to be held in place with a varnished strip of 4mm okoume plywood. I also intend on adding some to under the deck to keep her more afloat when on her side. All told I should have roughly 330 to 350 pounds of flotation plus the sealed bow and stern compartments.

    Unfortunately, and I hate to admit it, the first few times I sailed Spark I had no flotation at all. The two bags she came with would not hold air they were so far rotted.

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