moving lower shroud chain plates

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Steveandelfrys

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My recently purchased Westerley Centaur has had the lower shrouds moved from the coach roof to the deck - the deck is lifting in this area - does any one know
1. what is the core material of the deck in that area?
2. have you had success in moving them yourself?
3. do you reckon a metre long piece of angle iron will solve the problem?
I can expand on all these question if it helps me get an answer <span style="color:blue"> </span>
/forums/images/graemlins/laugh.gif Thanks
 
No way should that have been done without the designer's approval
The new postions need to be properly reinforced and the rig will need to be altered too. This sounds like an absolute No-No
 
"do you reckon a metre long piece of angle iron will solve the problem?"

Well... a better solution might be to take the tension down to a chainplate lower on the hull side. This can be s.s. rod, strip or wire and bottle screw. The reason they were moved may have been to do with position of windows in the cabin side.
I don't suppose there is a hndy bulkhead to use ?
Ken
 
As posted before chainplates loads should be transfered to a spot somewhere lower down the hull.A fiberglassed over plywood web big enough to spread the forces involved should be laminated to the hull.Be careful not create localized stresses that might give way to distortion.Epoxy resin an glass roving are the best materials for the job.Decks are not usally ment to have shrouds attached to .
 
The load path for a shroud is from the mast top to the chain plate thence down to the keel. Then from the keel to the mast base to the top of the mast. The distance the chain plate is out from the mast gives the support to the mast in the horizontal. So there will be pressure to pull the chain plate in toward the mast.

Ok so I reckon the simplest fix is to fit a pair of of saddles. or a U bolt type chain plate so that the deck can be squeezed between nuts and bolts with an attachment for wire underneath to take the tension. You should fit another chain plate to the hull somewhere near where the chine would be on a hard chined boat.

The inside chain plate can be a flat piece of SS with a piece welded on to the middle to attach a wire or turnscrew. The flat SS has lots of largish holes drilled through it so it can be epoxied onto the inside of the hull and have a f/glass layer laid over the top such that it is bonded through at each hole.

Ideally the inside chain plate should be located so that the pull is in a straight line down through the shroud through the deck to the inside chain plate. The wire from the inside chain plate to the under side of the deck chainplate is tensioned so there is no lifting of the deck under load.

I agree the chain plate should not have been moved from its original location on the cabin side but I am sure you can add the necessary strength if you pull from the under side of the chain plate.
Or as suggested you can fit a plywood and fibreglass web to reinforce the deck where the chain plate is now fitted.

If the deck is so reinforced from underneath you should not have to worry too much about the deck repair just fill the cracks to keep the water out.

Yes you could fit a piece of angle metal across the under side of the deck. This will spread the load to a larger area of deck which may be strong enough but transfering the load down to the hull is a much more certain fix. good luck olewill
 
I generally agree with other posts but as I have in fact looked at the Centaur structure in detail before I can perhaps add something. The original position of the lower shroud chainplates on the coachroof was abysmal. You will in fact see many Centaurs where the coachroof has lifted and flexing has taken place which is a major reason for the windows on these boats to leak. It is therefore an excellent idea to move them but to where?
The good news is that the hull of the Centaur is built like a brick outhouse. The deck itself in this area is just balsa cored though and will not take the load on it's own. I supervised the conversion of 2 Centaurs in the distant past to having chain plates bolted to the hull sides with stainless steel plates bolted to the inside, but as yours have already been moved to the deck I would suggest the following.
A. Remove the chain plates. (U bolts?)
B. Make up two marine ply knees to fit either side of the bolt holes to come as far inboard on the deck and as far down the hull sides as possible.
C. Fit them in position with Sikaflex for a temporary fit.
D. Glass over them generously (having abraded the area well with an angle grinder and flap wheel first) making sure that the area between them is at least 1/4" thick where the bolts are going to go and the glassing is continuous down the inside of the knees. You will then have effectively made an angle bracket that takes the load off the deck and transfers it to the hull sides. Then drill through the holes and fit longer bolts if necessary. It would not be a bad idea to make up a stainless or aluminium plate to act as a "double washer" between the reinforcing knees too.
E. Refit the U bolts or whatever, with plenty of Sikaflex sealant and don't do the bolts up tight until the sealant has cured. Don't whack the bolts up too tight or you will compress the balsa core. You can fit spacers if you like but it's not really necessary as all the load is upwards on the bracket and inner skin which takes the load off the core. Good idea to lock two nuts together on the inside though
Hope this helps.....
 
I'm sorry but the idea that people are going to radically alter their boat design on a DIY basis is ridiculous. This is not a job for an amateur as anyone will find out when you try to get insurance or make a claim. It is absolutely essential to get a yacht designer's drawings and calculations for this work. I seems pretty obvious that this hasn't been done hence the decks lifting. The decks aren't the only problem. The mast will have less support due to the reduction in rigging angles. The rigging tension will have to be increased to give the same support.
I'm afraid if the yacht has been modified in this way it's a pup that shouldn't have been bought.
 
Thank you - I am gob smacked at the quick and useful responses - this is an excellent resource that I will use and contribute to from now on - I'm off to the boat to consider some of these options! /forums/images/graemlins/smile.gif
 
"reduction in rigging angles"

Surely the moving of the plates to the deck will have increased the angles ? So there is less stress. /forums/images/graemlins/ooo.gif
Almost any position is better than the original - which has, and continues to cause problems in these boats. Unfortunately, builders do not always follow designers plans in mass produced boats like these. Have you seen any recently ?
Ken
 
[ QUOTE ]

"reduction in rigging angles"

Surely the moving of the plates to the deck will have increased the angles ? So there is less stress. /forums/images/graemlins/ooo.gif

Ken

[/ QUOTE ]Er........ No, not on the mast and rigging.. It does depend of course on how much further in we're talking about
 
"depend of course on how much further in we're talking about ".
We are not talking about "in". We are talking about out.
The deck is further out from the mast than the coachroof. The angle of the shroud to the mast is greater and the forces are less. /forums/images/graemlins/smirk.gif
Ken
 
Although I agree in principle with majority of what you say .. I think you have gone over the top in condemnation ... also I cannot understand how you can say: "The mast will have less support due to the reduction in rigging angles. The rigging tension will have to be increased to give the same support. " If the stays have been moved from coachroof to deck - they in fact have been moved outward - giving greater angle and support - till the deck failed anyway. (Maybe I have read original post wrong .....)

The Centaur chainplate design has generally survived well - but odd ones do show trouble on coachroofs - IMHO because to get support - the tension is higher due to the angle from that location. It also suffers greater stress by virtue of that acute angle when mast works.

Personally ? I would re-instate the original c/p's ... possibly with a bit more backing than original. I would then have the decks repaired where lifted ... as the core will suffer if not sorted ...
 
You are of course absolutely correct. Why anyone should want to move chainplates out would be a mystery to me, I wouldn't expect it so I didn't read closely enough. The original chainplates must be a bad design but I would still get proper advice before changes are made. Apologies for the mistake.
 
Hello Savageseadog it is intrigueing how our approach to yacht design differs. To me one of the joys of sailing is to be able to do my own thing in terms of modifications especially to rig. No I don't think the designers is always particularly cleaver and often is more budget driven than by good design. He can however benefit by experience as more copies of a design are built. I spent my most recent 30 years dealing with among other things defects with small aircraft design as they appear in operation. Experience certainly shows up the design short comings. So while we hope we can rely on the design of our aircaft or boat to be good, it is often seen that the design can be improved.

I am a bit horified at the idea of increasing the static stay tension because the shrouds are further inboard. (I realise we have decided the stays are not further inboard in this case)

It would be far more correct to stay the stay tension when sailing hard will be greater with a smaller stay angle. (That is simple geometry) I don't believe that means the stay static tension should be greater. In fact I don't believe in the huge static tension many text books promote anyway.

Chain plates should be as far outboard as possible for best mast support but they need to be as far inboard as possible to get the best sheeting angles for the over lapping genoa jib. So the designer goes for a compromise.
The structure of the chain plates must be adequately strong if it is not you see movement and the beginings of failure.
All IMHO olewill
 
"as far inboard as possible to get the best sheeting angles for the over lapping genoa jib. "

For a Westerley Centour ?
Please - A close reach is the best we ever got, compared to a good fin keel.
Ken
 
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