bumblefish
Well-Known Member
How big should a shroud backing plate be? Question in the subject, I know how long is a piece of string, but on a 30' boat, as big as I can fit or something else?
How big should a shroud backing plate be?
- Thread starter bumblefish
- Start date
Swagman
Well-Known Member
You are right with your bit of string. Your profile does not show boat model but if you advise on more then boat length, say rig height, sail plan, and the surface / material the plate is currently bolted to, it might help others give sensible responses.
Cheers
JOHN
Cheers
JOHN
G
Guest
Guest
Sensible answer .......
Doesn't need any info about boat .... as the sensible answer is - biggest plate you can physically get in to do the job.
Doesn't need any info about boat .... as the sensible answer is - biggest plate you can physically get in to do the job.
pappaecho
Well-Known Member
Is the plate to be glassed onto the inside of the hull?
oldsaltoz
Well-Known Member
I would think a 10 to 12 cm square plate of 6 mm stainless or 10 mm Aluminium would do the job.
Make sure the corners have a big radius and the edges are rounded all over, add some Microfibres and resin rather than timber cos it don't rot.
Avagoodweekend......
Make sure the corners have a big radius and the edges are rounded all over, add some Microfibres and resin rather than timber cos it don't rot.
Avagoodweekend......
Shanty
Well-Known Member
Started writing a long reply, but just scrapped it - you don't give nearly enough information for a meaningful response.
Are you building a boat - if so, who did the design, and what do they specify?
Are you repairing an existing boat - if so, what was originally fitted, and did it work?
Do other boats of the same design exist - if so, what do they use?
Do you think your existing fittings look too small / too big- if so, what is your basis of comparison?
Are you building a boat - if so, who did the design, and what do they specify?
Are you repairing an existing boat - if so, what was originally fitted, and did it work?
Do other boats of the same design exist - if so, what do they use?
Do you think your existing fittings look too small / too big- if so, what is your basis of comparison?
r_h
Well-Known Member
Is it for the cap shroud or lowers? If I remember rightly, you have an Elizabethan 30... many boats of that era (including Contessa 32s) had the cap shrouds very securely attached to a chainplate on a bulkhead or similar.
However, the lowers were often taken to a U-bolt fastened through the sidedeck. In this case the deck often lifts around the fitting - if that's your problem, as sbc says, the minimum fix (if you catch it early) is to add the largest backing plate you can fit underneath the fitting. If not caught early, more radical repairs may be needed...
However, the lowers were often taken to a U-bolt fastened through the sidedeck. In this case the deck often lifts around the fitting - if that's your problem, as sbc says, the minimum fix (if you catch it early) is to add the largest backing plate you can fit underneath the fitting. If not caught early, more radical repairs may be needed...
Swagman
Well-Known Member
Re: Sensible answer .......
[ QUOTE ]
Doesn't need any info about boat .... as the sensible answer is - biggest plate you can physically get in to do the job.
[/ QUOTE ]
Maybe.
But maybe the deck is lifting, in which case finding a vertical suface to take a side loading and extending the underdeck plate (as opposed to widening it) might be a better solution.
More info would be helpful, do you not think?
JOHN
[ QUOTE ]
Doesn't need any info about boat .... as the sensible answer is - biggest plate you can physically get in to do the job.
[/ QUOTE ]
Maybe.
But maybe the deck is lifting, in which case finding a vertical suface to take a side loading and extending the underdeck plate (as opposed to widening it) might be a better solution.
More info would be helpful, do you not think?
JOHN
bumblefish
Well-Known Member
I'll reply to my own post to give the extra information.
Elizabethan 30
mast 10m
mast head rig
balsa cored deck
fore and aft lowers, through deck U bolts, starboard side showing early sign of lift (surveyor)
cap shrounds also U bolts through deck, OK
at present 4'' x 2'' wooden plates
current plan is to put 6'' x 3'', 5/6mm stainless steel with pad of resin and microfibres (oldsaltoz)
not sure I can fit angled piece to topsides as well! very little space and deck hull join is very uneven, 1972 boat
how is that?
Elizabethan 30
mast 10m
mast head rig
balsa cored deck
fore and aft lowers, through deck U bolts, starboard side showing early sign of lift (surveyor)
cap shrounds also U bolts through deck, OK
at present 4'' x 2'' wooden plates
current plan is to put 6'' x 3'', 5/6mm stainless steel with pad of resin and microfibres (oldsaltoz)
not sure I can fit angled piece to topsides as well! very little space and deck hull join is very uneven, 1972 boat
how is that?
roly_voya
Well-Known Member
The size of the backing plate depends only on the combination of lead and compressability of the material the shroud fitting attaces to - all it is there to do is to stop you crushing the substrate when you tighten the bolts. Thats the easy bit.
The hard bit is how do you attach that piont to THE MAST FOOT. Look at the top of the rig, you have a cap shroud from the mast head to the deck braced out with a crosstree. The bottem is the same the load goud down the wire, is braced out at deck level (frequently by the deck or deck beams) then either through the hull or a bulkhead to the keel/mast foot.
Personally in you case I would look at putting a tryangular steel bracket at least 2' deep under the side deck bolted or VERY solidly bonded to the hull and then take the 'U' boltbolt through to that. Takes all the load off the deck and transfers it straight to the hull which on an elizebethan is pretty sound. I would never fasten a shoud to a composite cored deck its just bad design and will eventually fail, the load should always go the the hull somehow.
Tradittionally on a 30ft boat I would expect to see the load transferred from wire to hull by stee chanplates around 1 - 1.5" wide by a couple of feet long with at least 4 10mm bolts. There would then be either a well fitted and substantial bulkdead or couple of ring frames eqivelant to abou 3" x 2" timber. The mast would then either be keel steped or have a compression post.
To get a good idea of the loads involved look at the tensile strengh of the wire - the fixings should take that with a substatial safety factor. In other words would you feel happy that if you cranked the shroud up till it broke that you would not dammage either the anchor or what its fitted to?
Yes I do know lots of modern boats have a dinky 'U' bolt to a scrap of stainless under the deck and there are many boat repaire shops greatfull for the work entailed in repairing them!
The hard bit is how do you attach that piont to THE MAST FOOT. Look at the top of the rig, you have a cap shroud from the mast head to the deck braced out with a crosstree. The bottem is the same the load goud down the wire, is braced out at deck level (frequently by the deck or deck beams) then either through the hull or a bulkhead to the keel/mast foot.
Personally in you case I would look at putting a tryangular steel bracket at least 2' deep under the side deck bolted or VERY solidly bonded to the hull and then take the 'U' boltbolt through to that. Takes all the load off the deck and transfers it straight to the hull which on an elizebethan is pretty sound. I would never fasten a shoud to a composite cored deck its just bad design and will eventually fail, the load should always go the the hull somehow.
Tradittionally on a 30ft boat I would expect to see the load transferred from wire to hull by stee chanplates around 1 - 1.5" wide by a couple of feet long with at least 4 10mm bolts. There would then be either a well fitted and substantial bulkdead or couple of ring frames eqivelant to abou 3" x 2" timber. The mast would then either be keel steped or have a compression post.
To get a good idea of the loads involved look at the tensile strengh of the wire - the fixings should take that with a substatial safety factor. In other words would you feel happy that if you cranked the shroud up till it broke that you would not dammage either the anchor or what its fitted to?
Yes I do know lots of modern boats have a dinky 'U' bolt to a scrap of stainless under the deck and there are many boat repaire shops greatfull for the work entailed in repairing them!
William_H
Well-Known Member
As an option you could fit a saddle (U shaped metal with hole at each end) onto the U bolt nuts under the deck. Glass and or bolt in a plate to the hull 40cms below the U bolts and fit a turnscrew and wire tail between the two. This will both hold the deck down and transfer the load into the hull. Tighten the turnscrew until it starts to pull the deck down a little.
Ultimately you need to transfer the load to the bottom of the mast the hull and the keel. good luck.....olewill
Ultimately you need to transfer the load to the bottom of the mast the hull and the keel. good luck.....olewill
Swagman
Well-Known Member
Hi Bumblefish,
Thanks for the added info and it sounds like if you can transfer the load though the deck onto a bulkhead / topside / elsewhere - you should.
If its not possible then all you can do is go for your bigger plate and maybe strengthen the deck internally where the plate is fitted.
If your deck is balsa core and not already solid glass where the plates located, cut it back from inside and make it a solid area beefing it up with woven glass and resin.
If your topside internals are too rought to consider bolting on a angle plate, you could hit them with an angle grinder and consider running unidirectional glass from under your plate location, around the corner and maybe a foot os so down inside your topsides? Today - that is how most loads are transferred as opposed to metal brackets.
Good luck
JOHN
Thanks for the added info and it sounds like if you can transfer the load though the deck onto a bulkhead / topside / elsewhere - you should.
If its not possible then all you can do is go for your bigger plate and maybe strengthen the deck internally where the plate is fitted.
If your deck is balsa core and not already solid glass where the plates located, cut it back from inside and make it a solid area beefing it up with woven glass and resin.
If your topside internals are too rought to consider bolting on a angle plate, you could hit them with an angle grinder and consider running unidirectional glass from under your plate location, around the corner and maybe a foot os so down inside your topsides? Today - that is how most loads are transferred as opposed to metal brackets.
Good luck
JOHN
Graham_Wright
Well-Known Member
Easy! My surveyor said if you can lift the boat by the chainplates, they are big enough. If they rip the deck out;- fit bigger ones. /forums/images/graemlins/tongue.gif
bumblefish
Well-Known Member
Now I like that idea, I shall go and see how much access I have to the inside of the topsides, if I can do it I could increase the skin thickness under the U bolt (angled A bolt) and make it a lot smoother to take the backing pad. I could still fit a large stainless steel plate over the beefed up 'GRP chainplate'?
bumblefish
Well-Known Member
Another thought, to keep the weight/bulk down could I use kevlar or carbon fibre fabric?
dulcibella
Well-Known Member
As big as possible and bonded through to a bulkhead. On my old Halmatic 30 I had an inner shroud plate (about the size of a postcard) start lifting out of the deck half-way across Biscay in a SW 6. Very worrying. Fortunately the wind eased and backed so, during an overnight stop in Coruna, I rigged a "running shroud" to support the mast at spreader level. On arrival in the Azores we got a local vehicle conversion firm to cut and drill us some huge s/s plates that fitted under the deck, which did us fine until I could get a proper repair and upgrade done at home on our return. Avoid all this stress and put in the biggest possible plates attached to some bomb-proof bit of the boat.
