Deck fittings - One for the engineers:

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doug748

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I am reseating this U bolt on the foredeck.

Is it man enough to anchor an inner forestay for use with a heavy weather jib?

InnerForestay.jpg


Thread size is 1/4" BSF, the U is 5/16" dia.
1 1/2" between centres.
The sail size is nominally 90 sq ft. 32ft boat.

Thanks.
 
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To a certain extent, it depends what sort of material and how thick your deck is. Having done some work on a Moody, I actually laminated in some stainless plates pre-drilled into the inner deckheads to guarantee strength as the owner was a belt and braces type of guy.

As a minimum, you'll need a good sound deck with some sort of backing plate or heavy duty washer type arrangement I'd imagine.
 
Think I would prefer to use the Wichard ones with the plate and sealing boots. The M6 version is 32mm between centres and has a BL of 2900kg and the M8 is 36mm between centres and has a BL of 4800kg
 
Bolting a U bolt through the deck for an inner forestay is not good enough. A backing plate under it is not good enough and a "washer type arrangement" most certainly isn't acceptable. You should not be loading the deck, loads should be transferred to the hull. Exactly how you transfer it to the hull will depend on the boat, but you can use various methods such as rods or vertical plate, angled plates etc. Think along the lines of a chain plate.

I would also agree with Tranona, regarding the Wichard type of U bolt.
 
PaulRainbow said:
Bolting a U bolt through the deck for an inner forestay is not good enough. A backing plate under it is not good enough and a "washer type arrangement" most certainly isn't acceptable. You should not be loading the deck, loads should be transferred to the hull. Exactly how you transfer it to the hull will depend on the boat, but you can use various methods such as rods or vertical plate, angled plates etc. Think along the lines of a chain plate.

I would also agree with Tranona, regarding the Wichard type of U bolt.
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I tend to agree, but he's probably better off breaking his corroded old skinny u-bolt than ripping the deck off?
I'd want the loads going into some structure with some stiffness vertically. That could be something like a partial bulkhead like the aft face of an anchor locker.
The loads on the tack of the jiband forestay are not small, and for a storm jib arrangement you want a decent safety factor, after allowing for the shock loads of hitting waves etc. All that force has to be distributed into the hull to make its way back to the foot of the mast.
 
I am happy with the deck as it has been beefed up.
I just wondered about the U bolt itself. Glad to hear it is not a silly idea though I will go up to the 8mm Wichard if I can find one locally.
Thanks all.
 
The WLL for that size is about 1500 pounds. The 1/4" thread is limiting. Reduce that based on age. I'd probably go to all 5/16".

The forestay WLL you can gauge based on cross section. It is probably considerably greater, but the inner stay is not working alone.

The central problem is support. Would you place a 1-2 ton weight on the deck in that location? If not, then the chain plate comments are correct.
 
Regardless of whether you are happy with the deck it is not the way to go. It either needs to be secured to a bulkhead or substantial cross member under the deck preferably bonded to the hull or a bulkhead.
 
Fr J Hackett said:
Regardless of whether you are happy with the deck it is not the way to go. It either needs to be secured to a bulkhead or substantial cross member under the deck preferably bonded to the hull or a bulkhead.
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Be carefull with broad statements. Many boats are designed with load bearing roof tops. My current boat has a carbon fiber frame for the mast and my prior boat had a hidden carbon fiber beam that carried the inner forestay load.

But I doubt that is the case here.
 
I used pad eyes, a pair on deck, one underneath through bolted to the ones on deck. The underdeck one was then connected to the reinforced anchor bulkhead, and then connected to a through eyebolt to the stem. the interior pad eyes and eyebolts were connected with turnbuckles to get them all tight. All of course in line with the storm jib forestay.
 
doug748 said:
I am happy with the deck as it has been beefed up.
I just wondered about the U bolt itself. Glad to hear it is not a silly idea though I will go up to the 8mm Wichard if I can find one locally.
Thanks all.
Click to expand...

Force4 usually have them in stock. Alternatively Baseline Marine have an M8*32 in the same style also in 316 at half the price.
 
Tranona said:
Force4 usually have them in stock. Alternatively Baseline Marine have an M8*32 in the same style also in 316 at half the price.
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Yes thanks for that , I have been quietly following up your suggestion.

Mailspeed offer the short series for £6.99...... Force4 (which is local) £18.20 !

The key reasons I was thinking of re-using the old kit is that the deck is over an inch thick and I will need the 100mm length which would probably have to be ordered, more time wasted; secondly I really need to check the new unit against the stay fitting, as it is a tight fit - so tight that a new Wichard probably will not accommodate it. If I had to add a toggle or shackle it may mean I have to shorten the stay. - which would turn a small job into a marathon effort involving riggers.
Finally I don't want to be too far out with the centres, in order to use the existing holes, though this should be ok with those 8mm jobs.

So, as usual, a simple question/job grows like a snowball.
I would rather just use the ald thing, if at all sensible - hence the specific question about it's probable strength. :nonchalance:

Those concerned about the strength of the deck can rest easy. The stay has been fitted for over 30 years. The deck 30mm thick, supported by the anchor locker vertical bulkhead and backed up with a 5mm, double gusseted, stainless steel fabrication, through bolted. Which is why I said I was happy with it.
 
doug748 said:
Yes thanks for that , I have been quietly following up your suggestion.

Mailspeed offer the short series for £6.99...... Force4 (which is local) £18.20 !

The key reasons I was thinking of re-using the old kit is that the deck is over an inch thick and I will need the 100mm length which would probably have to be ordered, more time wasted; secondly I really need to check the new unit against the stay fitting, as it is a tight fit - so tight that a new Wichard probably will not accommodate it. If I had to add a toggle or shackle it may mean I have to shorten the stay. - which would turn a small job into a marathon effort involving riggers.
Finally I don't want to be too far out with the centres, in order to use the existing holes, though this should be ok with those 8mm jobs.

So, as usual, a simple question/job grows like a snowball.
I would rather just use the ald thing, if at all sensible - hence the specific question about it's probable strength. :nonchalance:

Those concerned about the strength of the deck can rest easy. The stay has been fitted for over 30 years. The deck 30mm thick, supported by the anchor locker vertical bulkhead and backed up with a 5mm, double gusseted, stainless steel fabrication, through bolted. Which is why I said I was happy with it.
Click to expand...

There you go!
 
My little boat (21ft) came with a similar fitting on the bow for attaching winch for winching onto the trailer. I used this fitting as a primary mooring attachment and it failed after a few years. The point where the bulky U bolt is cut down to 1/4 inch thread is the fail point. I replaced it with a 5/16 sized saddle with ordinary 5/16 bolts. This has survived many years since . Despite the fatigue producing sideways and tug loads. I would not use that fitting. ol'will
 
Taking on board some of the advise, like upgrading the 'U' bolt (but there are suppliers other than Witchard, Lewmar, Ronstan and Harken come to mind) then you might want to look at the other components. The block you illustrate looks a bit undernourished, but that might be the image, even for the 'U' bolt in your opening post and if you consider the 'U' bolt inadequate then you might want to upgrade the other items. Little point in having the best 'U' bolt available if the block is questionable.

The minimum size of your existing 'U' bolt is 1/4", it is probably 316 (it might even be marked), I'd look up the strength of a similar sized 316 shackle - that will tell you the strength of a similar but new 'U' bolt.

I confess that when I am making an addition like yours - I always add a new backing plate made from stainless plate - whether I need it or not. You simply don't know what the construction is of the deck (or whatever) - you know what it is meant to be but not what it actually is. Adding a backing plate is easy repairing damage due to the absence of a plate - less easy :(

Sadly these tasks grow like Topsy - but you need to think of a complete and compatible package.

Jonathan
 
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