SS thru aluminium hull?

[FNQCairns]

How silly is doing this really? I have a couple of really pretty SS thru hulls I was going to fit to a glass hull but now I have an alloy boat.
How about brass? I know nylon is kind but are there any other good options?

cheers fnq

[lee8sec]

I assume you are talking STAINLESS STEEL when you say "SS".
Was in the local boat dealer the other day & had a look at a savage alloy with a SS bait table bolted to the transom. BAD corrosion all around the mounts, paint blistered, also had 2 SS rod holders in the gunnels, same corrosion. After seeing for my own eyes i will keep any SS away from my boat. Leigh

[tigermullet]

Very dangerous to go with stainless steel below the water line unless you can guarantee that the two metals are totally insulated. Even above the waterline it is a risk in a moist environment though it would be easier to insulate with plastic or nylon washers + sealant such as neutral cure sikaflex. Brass no go either. Fittings formed of aluminium would be best provided the grade of alloy is close to the hull alloy. Nylon is definitely the safest option provided the use of nylon is not for stuctural purposes.

Our boat has been in the water now for just on 9 years (on a mooring) it is all aluminium without any stainless steel below the water line and every piece of stainless steel above the water line is well insulated. Even the nuts that hold the sacrificial anodes are nylon because I could not tolerate the thought of stainless steel being anywhere near the aluminium. Togther with sufficient sacrificial anodes and all electrical leads held in conduit it has been a winning combination.

In the combination of stainless steel and aluminium, paranoia is your best friend;D

[FNQCairns]

Thanks for the repies, Tigermullet paranoia seems like the place to be on this, I was hoping there would be some magic way of coping with the stainless fittings, guess I will go with crappy plastic everywhere and plan to replace early, better than corroding the boat like in your example Leigh!!!!

cheers fnq

[snelly1971]

Hi FNQ....my big transducer housing is off course bolted through my pod below the water line and it is SS on aluminium....i use Duralac on all fitting and have not had any problems with corrosion....

[FNQCairns]

Snelly1971 how long has it been fitted?

cheers fnq

[snelly1971]

just on 12 months....my last boat i had for 3 years with a similar set up and no problems....

[SCOTTYGC]

I am about to fit a bow mount electric to my tinny

how would you best fit it to stop corrosion ?

SS bolts?

should i put some thin rubber between the motor and boat?

any ideas?

cheers
scotty

[stark]

Not all stainless steel is suitable for use in the marine environment. Normally CRES316 is used. CRES304 and 306 will corrode over time. 316 will last much longer. However, much depends on where it is and if other metals are in contact either through a saltwater path or direct contact. Best to seek an experts opinion before doing any major surgery.

Please also note Brass is NOT to be used. Use bronze. Brass contains Zinc and will pit & dissolve.

Cheers
John

[tigermullet]

I am about to fit a bow mount electric to my tinny

how would you best fit it to stop corrosion ?

SS bolts?

should i put some thin rubber between the motor and boat?

any ideas?

cheers
scotty


By rubber I take it that you mean some sort of plastic. There are a few products that look like rubber but, in fact, are not. Rubber contains carbon black and is very corrosive if in contact with aluminium. We have used a thin but dense plastic between the motor and what passes for a transom on our boat. In other areas such as insulating the bait tank (stainless steel) from the aluminium deck we have used some sort of plastic which is used in the kitchen for rolling pastry and is available very cheaply from discount stores. The bit about the pastry is a guess - that plastic could also be used as a protective surface for cutting things.
Who knows? - that's secret women's business.;D

There is not much choice for bolts - stainless steel has been proven to be okay if used in conjunction with Duralac (a great product) as has been pointed out in this thread. On top of that our bolts are heavily coated in Lanolin grease and that really helps too. We also use a length of aluminium which acts like a sacrificial washer between the transom and the mounting bolts, on the inboard side.

Those lengths of aluminium (or washers) are easily replaced every so often. We last checked them two years ago and the washer system was okay - the liberal coating of Lanolin grease seems to have helped there as well. A casual inspection a few weeks ago did not reveal any nasty surprises.

[zigfreed]

Duralac is the go, if you are still paranoid try some heat shrink ( used for electrical connections) and shrink it onto the bolt before you bolt it up with nyloc nuts.

If you want to use brass on an aluminun hull may as well drop a few snapper leads in the boat while you are there............ just to speed the process up a bit.