fittings in steel hulls

[cormorant]

fittings in steel hulls

What is the correct method for mounting through hull fittings in an epoxied steel hull? I am of course thinking about galvanic reaction. Does the same apply to any deck fitting, i.e. a stainless steel bolt in an aluminium window or a stainless deck fitting?
Many thanks for all replies

 

[chibb]

Re: fittings in steel hulls

You really want to avoid metal through hulls with steel, use plastic if possible. Where dissimilar metals meet Durlac can be used which is horrible yellow stuff that sticks to *everything* ! Its also used for rivets in aluminium masts etc.

 

[Sui Generis]

Re: fittings in steel hulls

A question with too many answers. Not wishing to teach you to suck eggs, galvanic reaction happens whenever two dissimilar metals are in contact with each other and (usually)water. Water being universal in the marine environment (air included) means a serious subject so far as boats are concerned. Simplistic answer - isolate/insulate dissimilar metals from each other so far as possible and if not possible use a sacrificicial anode.

In a steel hull also pay attention to your electrics.

Don't be put off - my next boat will probably be steel.

 

[ean_p]

Re: fittings in steel hulls

So why are you going steel next time Rob and what are you with now please ?

Ian P.

 

[Mudplugger]

Re: fittings in steel hulls

Sorry Chibb. In process of fitting out Epoxied Steel hull under surveyors guidance....Not allowed to use Plastic skin fittings below waterline...ref RCDirective....Hence had to use s/s at exorbitant price to comply. Insulated to best degree with Sikaflex.

 

[cormorant]

Re: fittings in steel hulls

Thanks guys, I didn't think I would be allowed to use plastic below the waterline. Would it be acceptable to sleeve the fitting bolts with shrink wrap and wrap tape around the skin fittings? Use a ply backing pad on the inside and bond it all in with sikaflex? Even if the fitting is totally insulated from the steel can problems occur with corrosion around the seacocks for instance?

 

[zeehond]

Re: fittings in steel hulls

You can look for Marelon fittings-Forespar do a range and if you look on the web you'll get a lot of info about Marelon( a glass reinforced plastic). We have just replaced bronze seacocks with Marelon in the Head, having found 8 at a boat jumble. Our through hull fittings are stand pipes welded to the hull with the appropriate thread cut to accept the seacock. Hope this helps

 

[PaulJ]

Re: fittings in steel hulls

I don't like the idea of through hull skin fittings in a steel boat for all the reasons that have already been identified. One solution as has already been mentioned, is a steel standpipe welded in but where this is not practical, which was the case in my boat, I have welded in steel "tank fittings" and then used plastic seacocks screwed directly onto them.

Where the use of plastic was unavoidable, ie, for the depth and speed transducers, I have welded in a secondary steel "container" all around the transducer, with a bolt on access lid so that in the unlikely event of the plastic transducer failing the ingress of water would be contained within the surrounding container.

I have posted at length in the past about plastic seacocks so I won't go through it all again here but be very careful about the cheaper type of Forespar seacock..... they tend to leak. Forespar also make a "better seacock" which they call their 9000 range. These are MUCH better and are what I have ended up using.

Paul.

 

[rogerthebodger]

Re: fittings in steel hulls

Have a look at metalboatsociety all kinds of useful info for steel and alunimum boats from people who use and build metal boats. I am using stainless fittings insulated with fiberglass washers each side sealed with sikaflex.

 

[Das_Boot]

Re: fittings in steel hulls

It is best to weld in mild steel stand pipes and then fit the seacocks. The same goes for transducers. These if looked after will last for hundreds of years. Stainless steel is not an option. Dont believe that just because stainless steel works above the water line it will work below. It will Either corrode itself or cause the milder steel to corrode. Basicly all I am saying is be very carefull when putting disimilar metals in close proximity. Where I have unavoidable proximity I use rubber mat about 5mm thick between the two metals. I do everything possible to isolate them from each other. Even where this is done I check regularly and make sure I clean them with fresh water. I dont have any where salt water can acummulate.

 

[Das_Boot]

Re: fittings in steel hulls

In addition to my last post. Type in Rust prevention or corrosion prevention into google. This should keep you reading for a good while and give you sound and unbiased advice. There are lots of sites that have done inumerable tests and that give good advice.

 

[Ships_Cat]

Re: fittings in steel hulls

Stainless Steel sea valves are no problem at all and are the usual fit for metal boats if plastic is not used. If they weren't there would be lots of steel and aluminium commercial boats sitting on the sea floor. We put them in aluminium boats (insulated, of course) where any galvanic problems will be greater, as does everyone else.

My own boat is plastic valves and fittings. I figure if the fire has gotten to burning out the bilges, I will be long gone, as will the pipework hanging off them. In any event the transducers are plastic too.

John

 

[Das_Boot]

Re: fittings in steel hulls

Just to show you a post by the administrator of the Metal boat Society forum..
''When I refered to plastic seacocks, I was in fact referring to the Marelon variety, which is just another form of plastic. I was in particular referring to the type that are fixed directly to the hull plate. I would not have those on a boat, no matter what the ABYC says. The arrangement of having seacocks on the hull plate is very common, especially in wood or GRP boats, but on a metal hull, when it is so easy to weld in standpipes, then I would consider that practice unacceptable.
If mounted on a high standpipe, above the waterline, then Marelon valves might be fine. I would still consider the combination of standpipes and flanged valves the best way to go.
Brian

As you can see welding in of stand pipes is the recommended practice.
As the guy says the throught hull fittings need to be right. If you cant put in stand pipes dont make any holes in your hull.

 

[Ships_Cat]

Re: fittings in steel hulls

I think that you might find that what you quote would be regarded as a matter of opinion by most rather than the "administrator of the Metal boat Society forum" being the adjudicator of all that is right and wrong in metal boat construction.

In the end, there is no perfect solution, standpipes in a steel boat introducing their own problems as you will possibly come to discover with the passing of time.

John

 

[AndrewB]

Bronze seacocks in steel hulls

Bronze (or DZR brass) is close to mild steel in the galvanic scale and in practice there is not usually a problem. I have 20 year old bronze seacocks, with bronze skin-fittings, showing no electrolysis, either on the seacock or the surrounding hull. Ordinary brass seacocks (which most people deplore anyway) have caused a minor problem to the surrounding hull, though over a long period.

Either way, problems should be caught by routine dismantling and inspecting, at a maximum of three year intervals.

If you mount aluminium deck fittings with stainless bolts, as is common practice with window frames, use plenty of barium chromate paste (Duralac). However they are still likely to seize solid within five years.

 

[Das_Boot]

Re: Bronze seacocks in steel hulls

Stand pipes dont give problems any more than the steel plate keeping the water out. If you look after them in the same way they will last as long as the boat. The correct galvanic Bronze seacocks seated in mild steel stand pipes is the best practise any thing else is a compromise.

 

[Ships_Cat]

Re: Bronze seacocks in steel hulls

I agree, a real bronze or manganese bronze is of no real problem.

Another common area on steel boats with bronze satisfactorily fixed to mild steel is when a stern tube carrying the shaft bearings and seal is used down the propellor shaft log.

John

 

[claudio]

Re: Bronze seacocks in steel hulls

I agree, if the standpipes 'are looked after' there shouldn't be a problem.
I recently spoke to a surveyor who told me that the majority of vessels that sink in Holland are due to steel standpipes corroding internally and then being subject to freezing conditions. The water freezes in the tube and has no where to escape when it thaws. Just a thought ...

Claudio

 

[Das_Boot]

Re: Bronze seacocks in steel hulls

I used to agonize about mine freezing over in the winter and bursting but soon realised that the sea would have to freeze over. I also have a bronze stern tube by Vetus. When I pulled my boat it was as good as new. Even the prop was clean also by Vetus.
As said you have to clean out the pipes everytime you anti-foul and give the insides the same treatment as the hull they should last as long as the boat.

 

[Ships_Cat]

Re: Bronze seacocks in steel hulls

Still Learning I see - for someone who only a few months ago was claiming that steel boats could only be painted in a paint booth as you will get bits of stuff in it that will wick moisture through to the steel you have seemingly adjusted your views to now accomodate it being very easy to prepare (and repair) and paint up some pipe /forums/images/graemlins/smile.gif.

John