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  • in reply to: centreboard repair advice #17470
    Oliver Shaw
    Moderator

    A secondhand board is indeed an alternative way forward.    But if you choose that route do make sure that you get only a Series 1 board;    I understand that the later Series 2 type won’t fit.

    Perhaps fortunately,  I would guess that Series 1 are the more likely to come up secondhand.

     

    Oliver

    in reply to: centreboard repair advice #17426
    Oliver Shaw
    Moderator

    The smaller crack,  first:     if we are thinking of the same thing  –  the very small one which I see across a screw hole,  I agree that this does not need any dismantling.   I would be inclined to clean it out with a very fine saw,  either a hacksaw or a coping saw or just possibly a dovetail saw,  so that you have a good clean surface.   Then fill it with either epoxy or a flexible mastic.    However there appear to be several screw holes in that recess,   so if it were me I would be inclined to drill all of them out to either 8 mm or 10 mm,  and then let in teak plugs (obtainable from good yacht chandlers) bonded in with epoxy.   Then your replacement screws will be going into new wood.   Do all the cutting first,  then fit the wood plugs,  and finally fill the crack with either epoxy or mastic.

    Note that wood plugs differ from dowels in that the grain is across the cylinder of the plug,  rather than along its length,   so you are not going to end up screwing into end grain.

    On the bigger split,  don’t worry too much about breaking the thin wood at the bottom end;   if it does break up you can regard that as a non-structural cosmetic detail.   Depending on your skills and your wishes you can either let in a small piece of new wood and then fair it in,  or you can repair any blemish with filler.

    Hope this helps,

     

    Oliver

    in reply to: centreboard repair advice #17423
    Oliver Shaw
    Moderator

    Oh dear!

    This centreboard is very well constructed,  but the splits are one of the few glued joints where the joint is actually stressed,   i.e. where the “handle” meets the body of the board.    You are absolutely right that the proper way to repair this is to take the joint apart,  clean it up,  and re-bond it with epoxy.    However because the joint has already started to split it may be less of a problem than you suspect.     It may also be a case of using your contacts and the camaraderie of your club to ask whether anyone in the club can give you a hand with the job.

    Almost anywhere else on the centreboard the joints are under very little stress,  and it might then be worth trying a suitable flexible filler.   But I think not here,  unfortunately!

    It would be well worth at least trying to split the rest of the damaged joint.    If the wood will come apart into two neat pieces the job is relatively easy.   Since the joint is tongue and groove (as seen on one of the photos,  showing an end view of the joint) you are unlikely to be able to plane it without access to either the specialist plane or a suitable router or spindle moulding machine.    However you can at least clean up the dirt and grot from the inside of the joint,  using a sharp scraper,  or a sharp knife,  or a sharp chisel,  held more or less perpendicular to both the wood surface and the grain,  and then dragged bodily along the grain.   Note my deliberate insistence that tools should be sharp,  and by that I mean seriously sharp;   it pays dividends to resharpen your tools frequently,  and this is a skill worth learning   –   and again there is at least a good chance that you may find someone in your club who would be pleased to help you there.

    Then you can reassemble the joint,   bonded with thickened epoxy;   coat both sides with neat (unthickened) epoxy,  and then while this is still wet coat one side with thickened epoxy,  assemble the joint,  and clamp the two parts together with a pair of sash cramps.

    That is straightforward.   The big risk is that the joint may not split cleanly,  and you may end up by splitting the wood rather than splitting the joint.    You can do a lot to mitigate that risk by driving a (seriously sharp) chisel along the unbroken line of the joint,  on each side of the board,  in order to force the joint apart;    since the joint has already failed at one end it is reasonable to expect that at least the part of the joint which is reasonably near to the split is itself not far from failure,  and your chisel can provide that additional impetus.    However don’t try to chisel through the tongue in the centre of the joint;   that would be trying to cut through undamaged wood rather than failing glue.   The tongue may or may not come out cleanly;   but if it splits,  at least that indicates that it is still strongly bonded to the adjacent wood,  and the splits in it will be clean and will provide a good surface for epoxy to bind to when the joint is reassembled.

    If you end up with part of the joint remaining  unbroken,  and the wood splitting instead,  all is not lost.   The likelihood is that this will be at the far end of the joint,  where the load will be least;   and (as with the tongue) the split wood will make a good clean surface for epoxy to bond to.    Simply remove any part of the split wood which is going to actually obstruct the joint from fitting back together again,  and then coat all broken surfaces with neat epoxy,  overcoat while still wet with thickened epoxy,  and proceed as before.    Thickened epoxy is an excellent structural gap filler.

    Once the joint has been reassembled and the epoxy is solid,  clean off any surplus from the face of the repaired centreboard.   If you manage to catch it at the point where it has become solid but has not yet fully cured you can cut off any protruding surplus with a sharp chisel held flat to the wood;    if you wait until it has fully cured it is much harder work.

    Once the epoxy has fully cured  –  and don’t be tempted to try this while it is still soft  –  sand it flat with a orbital sander.

    Hope this helps,

     

    Oliver

    • This reply was modified 6 years, 10 months ago by Oliver Shaw.
    in reply to: THICKNESS OF RIGGING #17410
    Oliver Shaw
    Moderator

    With apologies for the delay,   I have just measured up two sets of shrouds.   One set is 3 mm diameter,  and the other is 2.5 mm.    I have to say that  –  now that I have measured it,  and done the above calculations  –  I think the 2.5 mm pair are a bit light,  but I am reasonably confident that 3 mm should be fine in everything except the most strenuous conditions.

    Hope this helps.

     

    Oliver

    in reply to: Age of dinghy #17355
    Oliver Shaw
    Moderator

    Absolutely.   With only one exception to my knowledge,  sail numbers 1-1000 were issued 1950-56,  but I have no information on the distribution within that period.

    Do check,  though,  that the hull number corresponds to the sail number;   it is the hull number which is definitive,  not the sail number,  because sails can be bought and sold second-hand  –  and when that happens the new owners don’t always bother changing the numbers.   The hull number should be engraved into the hog abaft the centreboard case;   expect  to have to lift a floorboard to see it.

    For fuller information on the history of your boat a starting point is to ask the Association for a copy of the official records,  now in digital format.   Beyond that it is pure detective work …

    Do have a look at the Cruising & Vintage Boats page of this website (under About in the banner menu across the top of the page).   We would love to see you,  with your boat,  at some of our events.

     

    Oliver

     

    in reply to: THICKNESS OF RIGGING #17351
    Oliver Shaw
    Moderator

    I have recently been reading about the rescue of the erstwhile America’s Cup challenger Sceptre from a stripped down and gutted state (a conversion interrupted by the death of her owner,  resulting in an executor sale “as is”) into a prestigious cruising and racing yacht.   Bear with me;   this is relevant!

    One detail which I picked up was Uffa Fox’s dictum for the strength of shrouds;    the total breaking strength on each side of the boat should equal the displacement.   For a dinghy,  of course,  displacement is in sailing trim,  so it includes crew weight.

    Uffa knew a thing or two about boat design;   he and Jack Holt were immediate contemporaries,  and were the two leading dinghy designers of their period,  joined a little later in a claim to that accolade by Ian Proctor.

    This standard seems intuitively sensible,  but as a physicist I wanted to validate it.   And I suspect that Uffa may have been wrongly quoted;   I personally would prefer a safe working load of that much,  rather than just the breaking strength.  However it seemed to be backed up by a mental “back of the envelope” very rough calculation in a semi-drowsy state while I was in bed but not sleeping in the wee small hours of this morning.   I estimated the maximum forseeable wind loading in the windward shroud as perhaps 265 kgf,  for the situation where two 80 kg sailors are driving the boat to windward and sitting out seriously hard.   Given the mass for the bare boat of perhaps 150 kg,  the total displacement would be 310 kg,  so Uffa’s dictum seems sensible,  with just a modest safety margin.

    That estimate does rely on some fairly approximate estimates of the lateral distances involved in the calculation,  so it is no more than a very rough guide.

    Allowing a factor of 3 to convert from breaking strength to safe working load,  and using my mental “back of the envelope” figure,   we are looking for a safe working load of 265 kgf,  so a breaking strength of 790 kgf.    Note that this is for the wind loading when driving the boat seriously hard.

    Looking up strengths of rigging wire online http://www.riggingandsails.com/rigging-breaking-strengths.shtml#top  I find that 3 mm of 316-type 1 x 19 wire has a breaking strength of 720 kgf,  which would indeed seem to be almost sufficient.

    However this takes no account of static loading;   and in Uffa’s day the static load was far less extreme than in the modern GP14 rig.    But since you are dealing with an early boat and a wooden mast,  you won’t be using those extreme static loads either.

    So it does look as though you are probably right in thinking that 3 mm is JUST strong enough   –   provided you don’t push her too hard in the heaviest weather.

    Hope this is helpful.

     

    Oliver

     

    Oliver

    in reply to: THICKNESS OF RIGGING #17341
    Oliver Shaw
    Moderator

    If you can hang fire for another few days I will aim to measure the thickness of some of my shrouds as soon as convenient.

     

    Oliver

    in reply to: Cruising, and Vintage Boats #17334
    Oliver Shaw
    Moderator

    We have also now had an offer from a member living in North Brittany to run a cruising event there in August,  coinciding with his club’s Regatta,  with the option for participants to take part in both.

    See the Cruising page for further details.

    An interesting programme for 2019 is gradually coming together!!

     

    Oliver

    in reply to: THICKNESS OF RIGGING #17327
    Oliver Shaw
    Moderator

    A handful of other points.

    The lengths data document that Chris Hearn mentions is appropriate for the usual situation,  i.e. the modern boat.    However the height of the chainplates was not standard on the early boats,  and as originally designed they extended up through the deck,  and the shrouds were attached above deck (like most dinghies of the time).   Although the more modern system (chainplates below decks and the shrouds passing through the deck) was approved in (I think) 1952,  boats continued to be built to the original design for many years afterwards.   And even for the modernised version I doubt whether the detail was specified;   certainly I have known  –  in both cases on professionally built boats by top builders of the day  –  shrouds pass through the centre of the deck bushes (outside a pin placed above the chainplates and rigging screws) and shrouds bearing on the sides of the deck bushes and going direct to the adjusters (on the chainplates).

    Also,  on wooden masts it is not unknown for there to be some slight variation in the design of the tangs of the hounds band – and even slight variation in the height at which it is screwed onto the mast.   And where shackles are used to attach shrouds (at either end) the length of shackles varies.

    All these factors of course affect the length of the shrouds,  so measure up your old ones;   alternatively,  if more convenient,  step the mast on your boat and then measure directly.

    Forestay.   The original arrangement,  almost universally used on early boats,  was for both shrouds and forestay to be secured (and adjusted) by rigging screws.   Halliard tensions were very much lower,  and the forestay was responsible for supporting both the mast and the jib luff,  which was hanked on to the forestay.   With greater halliard tensions the situation changed,  gradually,  to the point where in modern boats the rig tension is determined by the genoa halliard and the forestay is often much smaller diameter than the shrouds,  and is secured by only a lanyard (albeit with several turns).   The forestay then serves only to support the mast when the genoa is not set,  and it normally goes slack (unless tensioned by a bungee cord) once the genoa is set and full rig tension applied.

    A half-way house in terms of rig tension arises in boats with Highfield levers to tension the halliard.

    So the question of whether to use a rigging screw or a lanyard for your forestay,  and what diameter the wire needs to be,  depends very much on how much rig tension you intend to apply,  and that in turn interfaces with what hardware you have for tensioning the halliard.

    Finally,  don’t be tempted to apply full modern rig tensions on an old boat unless she has had the approved mast step conversion done;   the original design never envisaged the tensions that would be developed many decades later,  and there is a real risk of structural damage.

     

    Oliver

    • This reply was modified 6 years, 10 months ago by Oliver Shaw.
    • This reply was modified 6 years, 10 months ago by Oliver Shaw.
    • This reply was modified 6 years, 10 months ago by Oliver Shaw.
    in reply to: Cruising, and Vintage Boats #17320
    Oliver Shaw
    Moderator

    And it is good to see the number of views of this post creeping up.   Perhaps I could encourage Members to consider taking part in one or more of these events.

    If every person who viewed the original post then booked for the Cruising Week we would have one of the largest on record!

    Seriously,  these events are highly enjoyable,  and we would love to see you at one or more of them.   In one sense it is the people who make the events!

     

    Oliver

    in reply to: Can't get sails to black bands #17266
    Oliver Shaw
    Moderator

    The answer from David Rowlands,  Chairman of Technical & Rules Committee,  and Jon Close,  Chief Measurer,  is that all is well;   it was worth asking the question,  but the sails are OK,  and the Rules as they currently stand can accommodate them.

    David had intended to explain the detail,  but in the event there wasn’t a convenient time in a very full meeting.   But the key point is that there is no conflict between these new sails and the Rules.

     

    Oliver

    in reply to: Fixing a Leak on Wooden Mk1 – 12934 #17171
    Oliver Shaw
    Moderator

    There is an alternative to selling her.

    In the course of looking for something else I have just unearthed a set of photos of a boat which is presumably leaking,  because the owner has named her Leaky Bottom.

    So perhaps continue to sail her,  and rename her Leaky Bottom II ?

    Seriously,  a partial solution,  if you can identify where the water is entering,  is to inject a polysulphide mastic from the outside,  or a specialised marine sealant such as CT1 (which is described as a hybrid polymer).   This will remain flexible,  so the repair won’t be harmed by subsequent slight movement.    Obviously I can’t guarantee success,  but it is a low cost approach that seems perhaps worth a try.

    https://www.marinescene.co.uk/product/4920/c.t.1-underwater-marine-sealant

    http://www.discount-trade-supplies.com/shop/product/2057-CT1_Sealant_Adhesive_ctec/

    https://www.sealantsonline.co.uk/ProductGrp/Ct1-unique-all-in-one-sealant-adhesive

    for three suppliers (there are probably others as well).

     

    Oliver

    in reply to: Fixing a Leak on Wooden Mk1 – 12934 #17141
    Oliver Shaw
    Moderator

    I concur with the diagnosis.   Immensely difficult to identify the source of the water problem without seeing the boat,  but checking the buoyancy tank is an obvious first step;   if you are still sailing at this time of year then having a look inside the tank immediately after sailing will tell you whether water is getting in there.

    I am less confident about dealing with cracks,  if found.    Injecting epoxy or other materials may stop the leak initially,  but I would expect that whether this works on a long term basis would depend on whether the crack is still subject to movement under load.   If such a repair amounts to no more than a (dubious) butt joint in cracked plywood it will have little structural strength,  and may well not prevent the crack moving under load,  leading to the repair soon failing.    Much may depend on the location of the crack,  and the strength and rigidity of the surrounding structure.

    If you are confident that the crack occurred before the mast step conversion was done,  and that the work already done will absolutely prevent the crack now moving,  then the structural rigidity is already assured and filling the crack may be all that is needed.    If not,  some serious woodwork may be needed.

    If it is a crack in the plywood (only),  and there is an accessible area all round the crack to make a structural repair,  a backing piece on the inside and/or a scarphed or layered insert of fresh ply would be stronger (but a lot more work).

    Good luck.

     

    Oliver

    in reply to: Looking for a bronze horse #17056
    Oliver Shaw
    Moderator

    However,  …   …

    I think the full width sheet horse,  with a suitable traveller,  does have a legitimate use even for cruising,  and particularly so on an older boat  –  i.e. an early rig,  as distinct from the modern rig with bendy spars and massively powerful kicker.   In stronger winds it allows the traveller to be let out to the full width of the transom;   this effectively “dumps sheet” to some degree,  which in stronger winds may be necessary when beating hard,  while at the same time keeping the sheet more nearly vertical and so flattening the sail and controlling twist.    And when off the wind,  when you need the boom further out anyway,  it is even more important to be able to control twist in the sail.

    On the modern rig,  the combination of a seriously powerful kicker allied to bendy spars will do that very effectively without needing assistance from the mainsheet,  but the early rig with more rigid spars and only a much less powerful kicker is not able to do that.

    That is why the full width sheet horse was developed.

    If you feel that your boat is old enough for historical authenticity to be paramount,  then the original bronze horse is undoubtedly the way to go;   and that is indeed the situation with my two vintage boats.   But if that is not a major issue,  and you want the best sailing characteristics,  then if you are ever likely to be caught in stronger winds  –  even if only occasionally  –  you may be better retaining your full width sheet horse.

    Hope this helps,

     

    Oliver

    in reply to: Looking for a bronze horse #17047
    Oliver Shaw
    Moderator

    I am likewise vaguely looking for one for a similar project,  although in my case the project has temporarily stalled.    However I have got as far as obtaining a working drawing,  which I attach,  and which may help you.

    Note that although the width of it appears to be reasonably standard,  and this one looks about right,  I have occasionally come across examples which are both significantly wider than normal,  and others which are significantly narrower.   Since I seem to remember that Spark has the uprights of her original horse still in place it would be sensible to adapt this drawing if necessary to the dimensions set by your boat,  so that you can use the same holes in the deck.

    I also have,  and have likewise attached,  a photo of one incorrectly fitted (on the outside rather than the inside of the transom),  but it does show the entirety of the metalwork rather than only the part which is visible (i.e. above deck).

    Good luck.

     

    Oliver

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