SS anchor chain deck plate thickness?

[Andy Kirkpatrick]

Hi, I'm going to fabricate a small triangular deck plate at the bow of my boat, with a matching SS backing plate, and wondered about the ideal thickness (boat is only 22 feet). I see boats that have used ½ inch (10mm) plate, but this seems too thick?

Thanks

Andy

 

[Neeves]

We need more information. 'Small' means different things to different people. But a 10mm plate of stainless does seem a bit extreme - unless their yachts are good bit bigger than 22'

What function is your proposed deck plate to perform.

Jonathan

 

[zoidberg]

Should this assembly be required to take anchoring loads, then it is important that the deck AND the hull/deck join locally be adequately reinforced to take the strain. That's quite easy to do, albeit messy.
The under-deck plate then performs the function of a large washer to help spread the stress/strain from your bolts into the reinforced GRP. I'd suggest 3-4mm is plenty thick enough.

 

[Andy Kirkpatrick]

We need more information. 'Small' means different things to different people. But a 10mm plate of stainless does seem a bit extreme - unless their yachts are good bit bigger than 22'

What function is your proposed deck plate to perform.

Jonathan

My boat had a steel plate (about 30cm wide) under the fiberglass, that the bow roller bolted through, but it rusted away badly, so I need to cut it out and maybe re-glass (unless I can get the plate out without damaging the fiberglass). I thought it would be much stronger to have a triangular sheet of SS over the fiberglass, that the bow roller, and fairleads, maybe even the box cleat bolt through, with a corresponding SS backing plate. I thought this approach would add strength and protect the bow more.

 

[Poignard]

My boat had a steel plate (about 30cm wide) under the fiberglass, that the bow roller bolted through, but it rusted away badly, so I need to cut it out and maybe re-glass (unless I can get the plate out without damaging the fiberglass). I thought it would be much stronger to have a triangular sheet of SS over the fiberglass, that the bow roller, and fairleads, maybe even the box cleat bolt through, with a corresponding SS backing plate. I thought this approach would add strength and protect the bow more.

A plate above the deck is not necessary, since the forces involved are not downwards.

All you would be doing is adding weight where you least want it.

 

[Neeves]

Should this assembly be required to take anchoring loads, then it is important that the deck AND the hull/deck join locally be adequately reinforced to take the strain. That's quite easy to do, albeit messy.
The under-deck plate then performs the function of a large washer to help spread the stress/strain from your bolts into the reinforced GRP. I'd suggest 3-4mm is plenty thick enough.

Zoidberg's comment needs to be addressed.

The more weight you add to the bow the more negative the impact on sailing performance, see Poignards comment.

Your idea of a stainless steel plate is sound but it will only be as strong as the structure, fibreglass, to which it is attached.

If you want a maximum of "PBO" support tell us what model of yacht you have and maybe take a picture of the bow. Also describe what is 'under' the proposed location, is it a bow locker or the forepeak. A picture of the existing rusting plate might be useful - the fact it has rusted suggests it is not stainless (and may need the deck at the bow needs to be replaced (if the rusting plate cannot be cleanly removed).

If the rusting steel plate has been attached with sealant it will be possible to cut it out with no damage to the fibreglass - if it has been glassed in it will be slightly more difficult. You can cut sealant with a hacksaw blade slid between the existing fibreglass and the plate

The more information you provide (a picture is still worth a thousand words) the more detailed will be the advice.

Your project is not unusual - lots of expertise here.

Jonathan

 

[Neeves]

A plate above the deck is not necessary, since the forces involved are not downwards.

All you would be doing is adding weight where you least want it.

A plate above deck might be necessary if part of the plan is to dump anchor and chain on the bow during retrieval and wants to protect the gel coat.

Until the OP gives more information we are guessing, we are really good - but not that good - which is no use to the OP at all.

Jonathan

 

[dunedin]

Hi, I'm going to fabricate a small triangular deck plate at the bow of my boat, with a matching SS backing plate, and wondered about the ideal thickness (boat is only 22 feet). I see boats that have used ½ inch (10mm) plate, but this seems too thick?

Thanks

Andy

What is the actual purpose of the “deck plate” as that would make a big difference to the thickness needed.

Note that for securing the chain when anchored, a stretchy rope snubber is much better than a solid fixing

 

[Neeves]

What is the actual purpose of the “deck plate” as that would make a big difference to the thickness needed.

Note that for securing the chain when anchored, a stretchy rope snubber is much better than a solid fixing

But the stretchy rope snubber (use the forum search function for 'snubber') needs a solid fixing, somewhere - ideal at the transom or at worst at the bow.

Jonathan

 

[andsarkit]

My original bow roller had a backing plate about 60mm x 40mm and when it was hit while unattended on the mooring the bow fitting was knocked off. (26ft boat). I had the bow roller fitting welded onto a triangular 4mm plate about 25cm across the long side. This now also held the fairleads. I glassed in a backing plate a little smaller than the top plate and much larger than the original.. This had the advantage that the top plate would cover the alterations and look tidy and was much stronger than the original fitting.

 

[dunedin]

But the stretchy rope snubber (use the forum search function for 'snubber') needs a solid fixing, somewhere - ideal at the transom or at worst at the bow.

Jonathan

Most boats already have at least one cleat if not two at the bow, and two at the stern - or the snubber could possibly be taken to the genoa winches.
Just seemed an odd question - about an “anchor chain deck plate” which is not a term I have come across before.

 

[Neeves]

Most boats already have at least one cleat if not two at the bow, and two at the stern - or the snubber could possibly be taken to the genoa winches.
Just seemed an odd question - about an “anchor chain deck plate” which is not a term I have come across before.

I would agree with you and hopefully the OP is taking pictures and providing a bit more background.

In the absence of an update from the OP the thread will die.....

Jonathan