Backing plates for skin fittings?

[Tim Good]

Just curious but do people still use backing plates in best practice? My engineer said that with the new types of sealant they tend not to bother any more as ply eventually rots and hardwood tends to crack.

Does anyone else agree with this?

 

[macd]

I do for anything requiring load-spreading, although not necessarily any sort of wood.

Incidentally, northcave, are you planning on making a movie out of your skin-fitting saga? If so, can I suggest David Lean as director? You clearly need a specialist in epics.
(Only joking: ask all the questions you want.)

 

[Tim Good]

I do for anything requiring load-spreading, although not necessarily any sort of wood.

Incidentally, northcave, are you planning on making a movie out of your skin-fitting saga? If so, can I suggest David Lean as director? You clearly need a specialist in epics.
(Only joking: ask all the questions you want.)

haha. Well I'm learning a lot from a refit and when I come up with a question I could easily put in one long lingering topic I thought best to keep the questions separate for others like me searching the forum

Anyway I'm fairly confident I now know the best way to remove and reinstall which will begin tonight. All this is happening at the same time as lighting the whole engine simply to replace the prop shaft :disgust:

 

[Tranona]

Backing plates are overkill, particularly on a heavily laid up boat like yours. Often the main purpose is to provide a flat area on a curved part of the hull. Expect when your hull was laid up flat area were created where fittings were planned. Remember there is virtually no load that needs spreading.

 

[prv]

Remember there is virtually no load that needs spreading.

Till someone stands on the thing by mistake while clambering about in a cockpit locker. Or they're ramming the dinghy in and don't realise that it's caught on a valve, but they know it ought to fit so they shove it harder. Or, in an incident I heard of, a spare alternator falls off a shelf and lands on it.

Backing pads are commonly not used, including on my boat. But I sometimes think maybe I should have.

Pete

 

[Tim Good]

Interesting. Yes my boat is laid up pretty heavy and these are actually for waterline scupper type. Maybe I'll forgo the backing plates and use plenty of sealant.

291 is the standard right? Or is 292 better?

 

[prv]

291 is the standard right? Or is 292 better?

291 is a sealant with some adhesive properties. 292 is a full-on adhesive. Gluing skin fittings in place doesn't seem right to me. Use 291 (or possibly one of the alternative products that people will no doubt now suggest!)

Pete

 

[vyv_cox]

I use 291, or Puraflex PU40 that seems to be about the same stuff at less than half the price, for virtually every sealant job, including both the ones that you are currently asking about. This thread, and the one on screwing seacocks onto skin fittings. Once these polyurethane sealants have cured it takes some effort to dislodge them.

 

[Tranona]

Till someone stands on the thing by mistake while clambering about in a cockpit locker. Or they're ramming the dinghy in and don't realise that it's caught on a valve, but they know it ought to fit so they shove it harder. Or, in an incident I heard of, a spare alternator falls off a shelf and lands on it.

Backing pads are commonly not used, including on my boat. But I sometimes think maybe I should have.

Pete

But a asking plate won't help unless the hull was wafer thin, like when the fitting goes into a cored hull and the inner is removed. In that case there needs to be a backing plate to spread the load. On the Ops boat the skin fitting would break at a far lower load than needed to do any harm to the surrounding hull.

 

[sailorman]

In the days before tighter controlled lay up the inside of the hull was more irregular hence the need for a softer backing ring to accommodate those humps n bumps.