which thru hull fittings, plastic, s/s , bronze ?

E

eranb2

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Hi
which is the best to use?
the strongest ? anti corrosion ?
which is the best of the three , and why ?

Thanks
Eran
 
Re: which thru hull fittings, plastic, s/s , bronze ?

A Fibre Reinforced Plastic - quite tough however I would use Bronze fittings rather than plastic or Stainless Steel is I was replacing thru-hull fittings. FRP is fine for log fittings where there is little or no stress on the fitting but I would not trust FRP fittings in any other underwater application on the boat.
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"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
 
Sorry for barging in here, but while on the subject, my through hull cockpit drain fittings are plastic, and I dont like them, as they are the various hose size type where one cuts to suit hose size.
Can I get bronze fittings for these? and where?
I dont mind the plastic ones on the cockpit sole as they are well above the water line.
 
Re: which thru hull fittings, plastic, s/s , bronze ?

Strange. I was thinking about this this other day. Why do you say it is ok for a log but not anything else?

Are there any statistical failure rates on bronze v's plastic? I have never felt that comfortable screwing in my plastic log into a plastic skin fitting but put it down to irrationality.
 
Re: which thru hull fittings, plastic, s/s , bronze ?

[ QUOTE ]
FRP is fine for log fittings where there is little or no stress on the fitting

[/ QUOTE ]
It is easy to over tighten a FRP fitting not so easy with a Bronze fitting. Then consider the rassle fitting a pipe (even worse trying to remove one). I have never heard of a bronze fitting snaping off except due to very old age wheras I personally have experience of FRP fittings failing (outer flange breaking off - only thing holding the stub was Sikaflex!...

For above water line O.K. - FRP if one must or they are already fitted.
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hammer.thumb.gif
"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
 
I asked the same question of a yacht surveyor a few weeks ago, during a public questions and answers session. His reply was that any plastic is better than bronze, just buy from a reputable supplier. I don't necessarily support his answer, indeed, I asked the question, but that was the answer he gave!
 
Re: which thru hull fittings, plastic, s/s , bronze ?

[ QUOTE ]

Are there any statistical failure rates on bronze v's plastic? I have never felt that comfortable screwing in my plastic log into a plastic skin fitting but put it down to irrationality.

[/ QUOTE ]

My guess is that what you are getting is prejudice rather than the result of scientific investigation. Sailors are incredibly conservative.

Most people's boats are plastic, and these days not very thick plastic either. But it doesnt need to be thick because modern technology makes it incredibly strong. So why not fit plastic sea cocks to a plastic boat? They are very corrosion resistant and impervious to electolysis, much less likely to seize, no servicing needed.

In the absence of any real hard info, I would go for plastic seacocks if I were ordering a new boat. But the devil is in the detail as usual - which plastic, and made by whom? Marelon is usually quoted but I'm sure there are others.

Same problem applies to bronze of course. Whic quality of bronze? Made in UK or 3rd world? How thick? I've seen lots of boats fitted with domestic gate valves and those are definitely not marine bronze.
 
Re: which thru hull fittings, plastic, s/s , bronze ?

I refitted my Nasa log skin fitting the other day due to the previous fit being a total mess. Tightened by hand , a few days later I retightened by hand and the fitting broke, the outside collar sheared off. Beware reusing old plastic!
 
The issues here are the probability of strain or shock being applied to the fitting (and the possibility of accidental leverage increasing that strain) and the possibililties of corrosion.

Stainless steel in a through hull situation can suffer from oxygen starvation, in which situation a protective oxide layer may not form, and the 'stainless' will corrode. Not commonly used.

'Marelon', a fibre re-inforced plastic, has (I believe) been recognised as suitable for thru hull fittings by some building standard agencies (sorry, don't have time to double check) though I believe there were restrictions on the type of use. It does not corrode, is very strong (not as strong as bronze) therefore slightly more vulnerable to shock and levered forces.

Bronze is strong and corrosion free in itself. However, its fastenings must be an identical metal (and rarely are) otherwise electrolytic corrosion can occur. This potential for corrosion is what many surveyors criticise. Suitable embedding or design of a bronze installation can overcome this criticism.

Would any boat builder please correct the above - it's a long time since I last read it up!
 
I've just got rid of an unused plastic skin fitting - when I came to remove it the backing nut split off with very little force being applied. Very glad I decided to do something about it. In my view plastic skin fittings have no place on a boat. I'm rather shocked that a surveyor would suggest they are the best - obviously someone with little or no practical experience.
 
That's interesting. This is a valuable thread. I wonder if anyone has a link to other forums or published reports on this?

Maybe it is something that PBO could investigate for readers? It is a matter of grave importance if there are safety issues.

PBO, are you there?
 
Re: which thru hull fittings, plastic, s/s , bronze ?

[ QUOTE ]
A Fibre Reinforced Plastic - quite tough however I would use Bronze fittings rather than plastic or Stainless Steel is I was replacing thru-hull fittings. FRP is fine for log fittings where there is little or no stress on the fitting but I would not trust FRP fittings in any other underwater application on the boat.
--------------------
hammer.thumb.gif
"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

[/ QUOTE ]

Think you have made a valuable point here relating to plastic fittings being ok where there is no stress.

I recently had a plastic skin fitting break which is 4" above the waterline. This was a bilge pump outlet where there was moderate strain. I only noticed it when I went sailing and was putting the fenders away.

I have also had a metal skin fitting break off in my hand but this was due I think to age and again, an unfair load and strain. I think it may make sense to buy the best quality fittings available and consider wisely how we support them.
 
Re: which thru hull fittings, plastic, s/s , bronze ?

[ QUOTE ]
I think we should differentiate between 'plastic fittings' and Marelon.

[/ QUOTE ]I think you're right. This comes from Marelon


<span style="color:red"> MARELON® IS...
Marelon® is the only synthetic material to be approved by the Marine U.L. Underwriters Laboratories)
for use below the waterline and has passed the same stringent tests as bronze. It exceeds the ISO
standards and is approved by the A.B.Y.C. (American Boat and Yacht Council). Marelon® plumbing
systems are corrosion and electrolysis resistant and will not freeze or become brittle with age or
temperature extremes. Marelon® is the choice of top quality boat builders worldwide.</span>
 
[ QUOTE ]
I've just got rid of an unused plastic skin fitting - when I came to remove it the backing nut split off with very little force being applied. Very glad I decided to do something about it. In my view plastic skin fittings have no place on a boat.

[/ QUOTE ] Was it a nylon fitting at the waterline? Peculiarly prone to ultraviolet deterioration on the upward facing inside, leading to cracking in situ with no forces applied.

Several 'plastics' are prone to this UV deterioration. When used in waterline fittings they're a regular cause of vessels sinking at their moorings. Marelon is UV resistant.

Another cause of sinking at moorings is corrosion around the fastenings of bronze seacocks. These surveyors do know the principal causes of marine insurance claims!
 
Re: which thru hull fittings, plastic, s/s , bronze ?

[ QUOTE ]
I think we should differentiate between 'plastic fittings' and Marelon.

[/ QUOTE ]

Yes. The skin fitting that failed on my boat was plastic and very open to UV. Perhaps frost may also be an issue with plastic fittings. When I bought the boat the surveyor recommended that I replace all plastic skin fittings.
 
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