We have a little confusion here;   is your boat built of wood or fibreglass?    Unfortunately your description “Don Marine Mk.1 12801 is contradictory,  and in order to best assist you we need to establish exactly what you have!

Boats designated by Mark numbers (Mk 1 through to Mk IV and IVa) are fibreglass;   boats designated by Series numbers (either Series 1 or Series 2) are wooden.    Don Marine built in wood,  and I am fairly sure that they later also built in plastic;   but not as early as the Mk 1 boats so far as I am aware,  and the sail number does not tally with Mk 1.    Mk 1 was succeeded by Mk 2 in 1969,  with sail no. 7930.   Your sail number dates your boat at 1987,  at a date when the FRP plastic boats were being produced.

If you can clarify what boat you actually have we will be very happy to try to assist you.

Oliver

• This reply was modified 6 years, 7 months ago by Oliver Shaw.

Yes,  she will be a Series 1,  built only a couple of years before the introduction of the Series 2 design.

Side benches first.    These are secured at either end,  so even without any remedial action they should be structurally secure;   the primary problem in respect of the failed joint to the thwart is keeping water out,  in order to prevent rot,  and to achieve that objective you need to seal that joint in some way.    Epoxy is a marvellous tool,  provided you can apply it to clean dry surfaces,  but I am not convinced that in this situation it will be possible to meet that condition (i.e. clean dry surfaces),  or to achieve an adequate spread of the epoxy over the whole of the joint surface,  without dismantling first.

So I suggest that you have two options,  either take out the side benches,  properly clean up all the joints,  and then reassemble,  bonding the cleaned up joints with thickened epoxy.   Don’t omit to thicken the epoxy.    Alternatively,  inject a suitable sealant into the gap between side benches and thwart,  in which case I suggest that for this application there are better (and incidentally cheaper) alternatives to epoxy (see end of this post).

The first route is arguably the best one,  but it is also the longer and potentially the more complex.    If you decide to go down that route you will have to separate the joints at either end of the side benches,  between the side bench and the supporting knees.   In older boats these joints may or may not have been glued,  but will certainly have been secured by wood screws.   In a boat of your pedigree I don’t know whether the builder bonded the joint,  nor what adhesive he used if he did.   If he used screws (either on their own or as well as an adhesive) I would quite expect that the heads may be recessed and capped by circular wood plugs which match the surrounding wood.

It would be worth a look:   if there are no screws visible look for circular wood infills where you would expect screws to be,  where either you can see the outline of the circle or where the grain probably does not quite match the surrounding wood.   If you can find these wood plugs you can carefully remove them (drill,  followed by either a very small chisel or a craft knife around the edge),  taking care not to damage the screws.   Then remove the screws.   If you are in luck at this point,  either the joint will not have been glued in the first place,  or the glue will have failed,  in which case the side bench will simply lift off.   If it won’t just lift off,  a smart blow with a mallet,  underneath,  driving upwards,  as close to the joint as possible,  may free it;   don’t worry unduly if that results in the break being not entirely clean,  and slightly splintered,  because when you reassemble that will glue up again strongly and almost invisibly.

If even that fails to lift the side benches,  or if they are bonded in place rather than being screwed,  they will probably have to be cut off.   Cut horizontally,  as accurately as possible along the glue line.  The traditional tool for this sort of job would have been a dovetail saw (like a tenon saw,  but smaller,  and with finer teeth),  but I have heard of owners doing this sort of job very effectively with electric oscillating multi-tools,  and although I have never used one I think that would be my tool of choice for this particular job;  a very fine cut and probably easier to deploy in the somewhat obstructed space around that joint.    Don’t worry unduly about the thickness of the saw cut;   if necessary you can insert hardwood shims into the joint when you reassemble,  but my guess is that if you use the tools suggested you may not need to do so because the saw cuts will be so thin that there is a good chance that heights will match well enough.

Once you have the side benches removed,  then clean up all the joints;  then reassemble,  bonding all the joints with epoxy.   Wood plugs,  if you need them,  are readily available in teak from many chandlers,  commonly in a choice of 8, 10, or 12 mm diameters.   Note that wood plugs are not the same thing as wood dowels;   quite apart from being made of a marine hardwood,  which many commercially available dowels are not,  plugs differ from dowels in the cosmetically important feature that the grain is across the plug rather than along its principal axis.   Alternatively,  if you buy a set of plug cutters you can cut your own plugs out of solid wood,  but be warned that I have tried this and I find that the diameter of the resulting plugs is slightly smaller than the nominal diameter expected,  so it may be difficult to find a drill size (for drilling the hole to be plugged) which matches accurately;  and certainly you need to cut your plugs first and measure them before you finalise the size of the recessed screw hole.

Insert the plugs into the screw holes with the grain of the plug parallel to the grain of the surrounding wood,  bonding the plugs in with epoxy,  and leaving some of the plug standing proud;   then when the epoxy has fully cured cut off the surplus wood from the plug (plane or chisel,  possibly preceded by dovetail saw if there is a lot of surplus to cut off),  and finally sand it smooth.    I don’t know what wood your builder used for the side benches at that period;   their earlier boats used mahogany,  but in later ones he took to laminating the thwart and possibly also the side benches from contrasting light and dark coloured wood.   Teak plugs in mahogany are not a perfect match,  but by the time the job has been sanded smooth and then varnished,  and then had a season’s sunlight on it,  they will be barely noticeable.

The alternative approach,  very much simpler,  is to force up the middle of the side bench so far as possible,  and then inject a sealant using a cartridge gun.    I have two recommendations for this;  either a polysulphide sealant or a sealant adhesive such as CT1,  which is described as a “hybrid polymer sealant”.   Either are more likely to be successful than epoxy in this situation,  and both are better than silicone sealant (and at about the same price).  https://www.sealantsonline.co.uk/ProductGrp/Ct1-unique-all-in-one-sealant-adhesive

This same supplier also lists polysulphide sealants,  but I have no first-hand experience of them;   however back in the eighties I regularly used Life-Calk,  another polusuphide sealant,  on my vintage wooden yacht,  and I was so impressed with it and used it so much that I kept a cartridge of it as part of my permanent onboard spares & repair kit.   It is still manufactured,  but it is an American product and I am not aware of any current UK importers apart from Amazon;  and Amazon,  somewhat unexpectedly for them,  sell it in only minuscule quantities and at an astronomical price.

In both cases,  the instructions may be summarised as “Ideally apply to clean dry surfaces.   If necessary apply to tolerably clean damp surfaces.   In emergency can even be applied underwater.”   Impressive!   Be warned however that it sticks to everything,  voraciously,  so try to avoid getting it where it is not wanted.    Clean up any gross surplus with copious quantities of kitchen towel,  and then when only a smear of excess remains use kitchen towel dampened in meths  –  and I would guess that acetone would work equally well.

If using this sealant route,  you may wish to also screw the side benches to the thwart.   If doing this,  avoid brass screws;   although once popular for mass production boatbuilding they are not  a truly marine quality material,  and tend to dezincify,   leaving the metal not only badly discoloured by also structurally very weak.   The top quality alternatives are stainless steel screws,  which are readily available,  or bronze screws.   The latter are expensive,  but you will need only four of them.    Few suppliers stock bronze screws;   I get mine from Classic Marine:  https://www.classicmarine.co.uk

Hope this helps.

This is enough for one post.   I will try to respond later to your other two queries.

Oliver

• This reply was modified 6 years, 7 months ago by Oliver Shaw.
• This reply was modified 6 years, 7 months ago by Oliver Shaw.

Floorboard supports:

First an explanation of the construction.

The timbers across the boat supporting the floorboards are of two different types,  although beneath the floorboards themselves they superficially look identical,  and they alternate.   One set are frames,  which form part of the structure of the boat,  and which help to determine the shape of the hull;   there is one of these (the famous frame no. 2,  which sets the limit in the Class Rules of where the bulkhead of the forward buoyancy tank may be placed) immediately ahead of the centreboard case,  another one (no. 3) in way of the after part of the case (from memory,  in way of the centre of the thwart),  and another one (no. 4) about half way between the after end of the case and the aft end of the cockpit.   These frames can be recognised,  once you know what to look for,  by the fact that they comprise two separate parts,  a lower part across the bottom of the boat,  and an upper part extending up the side of the boat,  with a substantial area of overlap where the two parts are jointed together with a glued joint.   Alternating with the frames are floorboard bearers,  which serve no function other than taking the weight of the floorboards (and anything placed on them,  including the occupants of the boat);    they are much more lightly secured to the boat,  and as a minimum,  at the outer end they rest on the chine pieces (and are probably screwed to them),  and at the inner end they usually rest on the hog.   There is some means,  which varies between builders,  to keep the inner end in position and prevent it just flopping around.   In the middle they may (or may not) rest on the stringer,  and they may (or may not) be screwed to it.   One of these floorboard bearers,  midway between frames 3 and 4,  lies immediately abaft the case.

The detail of how they are fitted varies between different builders,  and I suspect that this detail may well not be shown on the plans.   At different times,  around 30 years apart,  I have owned two professionally built Series 1 GP14s,  both by top builders;  the earlier one,  no. 4229,  was by R. R. Sills,  who were widely regarded as the Rolls Royce of GP14 builders of their day,  while the later one was a Don Marine boat only modestly older than your one,  no. 11930.   If memory serves correctly,  and after nearly fifty years perhaps I may be excused if it doesn’t(!),  the construction at the inboard ends of these timbers different between these two boats.   The Don Marine boat had the ends apparently housed in a mortice in a piece of thick ply on the side of the centreboard case.   The Sills boat did not,  and the bearers just terminated against the case  –  indeed I cannot be sure that they even touched the case,  and there may possibly have been a small gap;   however I suspect that on that boat the floorboard bearers may have been screwed to the hog,  and they may also have been screwed to the stringer.   In any case,  once the floorboards are fitted they themselves will be sufficient to keep the bearers in place,  and it is only when the floorboards are removed that there is any need for a specific provision to retain the bearers in position.

So,  your repair:

Clearly the decayed ply will have to be removed.    Now have a good look at the construction of your particular boat,  and decide whether any mechanical support for the floorboard bearers at that point is actually needed (and likewise for the the one frame  –  no. 3  –  which is split where it would otherwise cross the centreboard case);  you may decide that it is not.   If you decide that no support is needed you could simply leave a gap there.   Alternatively you could use CT1 to fill the gap,  as you suggest,  and since it is both a sealant and an adhesive this would also provide light support if you feel that is necessary.    I would expect that this may well be sufficient,  but I don’t currently have the opportunity of looking at a Don Marine boat to assess for myself.   In the fairly unlikely event of you deciding that more substantial support is needed the easiest would probably be to cut replacement plywood pads,  suitably morticed.

While you are working on this part of the structure,  may I invite you to check that the limber holes are clear.   These are holes at the inboard ends of the frames and floorboard bearers,  intended to allow water to drain through the hull.   The can easily become blocked by dirt and debris,  and when that happens any water gets trapped.   As well as being an inconvenience,  if trapped water is left long enough that then becomes a breeding ground for rot.

I will leave the matter of your mainsheet pillar for a little,  to see whether anyone who is familiar with the internal construction of this pillar chips in.    I am not,  although I have some ideas of how I would approach the job myself;   but input from someone who has actually repaired one would be most valuable.

Hope this helps,

Oliver

• This reply was modified 6 years, 7 months ago by Oliver Shaw. Reason: Removed unactioned formatting commands
• This reply was modified 6 years, 7 months ago by Oliver Shaw.
• This reply was modified 6 years, 7 months ago by Oliver Shaw.

Mast step:   Yes,  clean up,  treat with epoxy,  and then overcoat the epoxy with either paint or varnish.    Cosmetically you would probably prefer varnish.    Overcoating is essential because the epoxy does not contain a UV inhibitor,  and so it degrades in sunlight.

If the step is merely screwed in place  –  and I don’t know whether Don Marine did or did not glue it in place  –  this job is most easily done if you take the step out of the boat first.

That is always provided that if you have the original (square) mast step and mast foot sitting directly on top of the hog,  you do not use excessive rig tensions.    If however your mast step is a track,  sitting on a plinth about 12 cm above the hog and with a long support piece underneath,  and the mast step is a tenon (longer fore-and-aft than it is wide) which slots into the track,  then your boat has had the approved mast step conversion done,  you can use modern high rig tensions in perfect safety.

The boat was designed in 1949,  long before anyone even thought of applying today’s modern high rig tensions.    Nonetheless the boat is so heavily over-engineered that there is still reasonable latitude for increasing the tension beyond whet was achievable when the boat was designed.    I have always believed that tensioning devices up to and including a Highfield lever are fine with the original construction,  provided the boat is in sound condition.

But an 8:1 muscle box or 9:1 cascade tackle,  tailed in either case to a further 2:1 inside the boat,  giving either 16:1 or 18:1 purchase respectively,  is definitely so far outside the original design criteria as to risk serious structural damage,  which in the worst case could see the mast pushed through the bottom of the boat!   Modern race fleets,  when set up for stronger winds,  typically set the static rig tension at 440 lb-f,  and that is before the wind loading even starts.    That static loading alone can impose a load of up to around 3/4 ton force on the mast step (depending on how the genoa halliard is brought out of the mast and terminated),  and remember that this is before the wind loading even starts;    and the boat was never designed for these loads.

There are two solutions available,  arguably three.

Solution no. 1 is to limit yourself to the sort of rig tensions that the boat was designed to accommodate.   If you limit tensioning devices to a toothed rack across the halliard,  or alternatively a Highfield lever,  or alternatively a simple block and tackle (I suggest no more than 3:1 purchase,  possibly 4:1 if you are brave),  you will be fine.

Solution no. 2 is to fit the approved mast step conversion,  which entails some woodwork surgery,  and which is designed to strengthen that region of the hull specifically in order to accommodate modern rig tensions.    Plans and details should be available from the Class Association office.

Oh,  and solution no. 3?    This one is surprisingly popular,  but how well it works is another matter:   hope for the best,  and pray hard!

Hope this helps.

Oliver

• This reply was modified 6 years, 7 months ago by Oliver Shaw.
• This reply was modified 6 years, 7 months ago by Oliver Shaw.

Hi,

Lots of good advice from Oliver, can I follow up on his solution 2 for your mast step problem.  I would suggest fairly strongly that carrying out the mast step conversion is by far the best was forward, I have completed this on 3 different Series 1 boats with good results in all cases.  It is not difficult as the drawing and instructions from the Association are easy to follow and if the bottom of your mast is showing signs of corrosion there is the added benefit that you will be cutting 100mm off the mast before fitting the new mast heel.

One other point is where to source the hardwood for the new mast support –  if you are willing to look again at your side benches the class rules allow you to take out the inner side benches, to move the outer one inboard.  This gives you more room inside the boat but less seating when sitting inboard, but makes sitting out more comfortable, in my opinion!  The side bench knees also need to be reshaped but this can be done with them in place.  You then have two very nice pieces of hard wood which can be used to form the vertical mast support,  two pieces are bonded with epoxy resin, shaped to fit the curvature of the hog extending forward into the front buoyancy tank and then coated before fixing in place.  Another piece of one side bench is shaped to form the horizontal platform for the new mast step, this piece runs back over frame 2 into the center board case.  You will then have a very strong boat which can take any loads you may wish to apply to the rigging.

I have some pictures of the mast step conversion I did on 13003 in 2012 along with retro fitting through deck genoa sheeting – but that is another story!  Also some pictures of 12091 showing the inner side bench modification.  If these are of interest send me an email to scorbet@btinternet.com and I will send direct.

Steve

Thank you for the compliment,  Steve,  and in the long term I concur wholeheartedly that the mast step conversion is the way to go if Ben is keen to race the boat at top level.   But in the short term,  he has only just bought the boat,  described as being “in excellent condition and ready to sail”,  and he is rarin’ to go.

Assuming that the boat is indeed in sound condition the mast step conversion can wait a little,  perhaps scheduling it as a job for next winter,  provided he is content to sail with more modest rig tension in the meantime.    And he can then enjoy some excellent sailing as soon as he can get her in the water.

But when the time comes for him to do the mast step conversion I am sure that your encouragement,  and your photos,  will be most valuable.

Oliver

If you need to know anything specific to your boat Glyn Walker probably built it and works at SP Boats. He’s very helpful and likes to hear about his old boats.

Hi Ben,

I have 12811, another Don Marine boat, still going strong and built in the same year.

I did the mast step conversion- definitely the way forward.

As regards where the floor bearers meet the cb case, after thoroughly drying out the boat, I ran a structural fillet of thickenened epoxy around the joint. This, with the conversion makes for a very stiff case.

Obviously, if you have any leakage around the case, think very carefully about this approach. Heat will get it apart again, but you’ll  have to refinish the case.