Stainless Steel to Aluminium

[Vanquishv12]

I’m attaching stainless U Bolts to my new aluminium RIB and would like to minimise risk of galvanic activity which I understand is a problem in a marine environment .
I intend to use a clear plastic film where the nuts touch the aluminium, but what about the hole and screw threads.
Anyone got a fool proof method ?

 

[rogerthebodger]

Plastic washers and Duralac on the thread and in the holes.

 

[rotrax]

Paint the duralac on and let it dry - it is a bugger to clean off if it drips.

 

[MystyBlue2]

When i used aluminium plate on back of transom and bolted with stainless bolts i used plastic shoulder washers and duralec, failing that i have used in the past a type of PU sealant such as Stikaflex, Tigreseal or Puraflex 40 to try and eliminate as much contact between the two different materials as much as possible, the more you use the better and wipe any excess off when wet.

The PU adhesive's double up as a sealant too

 

[AngusMcDoon]

Paint the duralac on and let it dry - it is a bugger to clean off when it drips and gets everywhere, including on the floor, in your butties, up your nose, under the dog, over the rainbow, amongst the pigeons, and on parts other jointing compounds don't reach.

I've corrected that for you

 

[noelex]

As has been said isolation (usually plastic) and/or products such as Duralac or Tefgel are the best options.

Tefgel works with a different mechanism to Duralac. It seems to have similar effectiveness, but there are pros and cons. Tefgel is more suitable for fastenings that are periodicly serviced.

 

[Rappey]

Stikaflex, Tigreseal or Puraflex 40 to try and eliminate as much contact between the two different materials as much as possible,

I had an aluminium boat for 18 years.. Yes your method does insulate the two metals but it also seals the aluminium which can quietly oxidises and turns to jelly under the sealant.
Every nut and bolt on my boat was aluminium..
I found bare aluminium fared well in sea water, but something as simple as a vinyl sticker could cause chaos underneath !

 

[MystyBlue2]

I had an aluminium boat for 18 years.. Yes your method does insulate the two metals but it also seals the aluminium which can quietly oxidises and turns to jelly under the sealant.
Every nut and bolt on my boat was aluminium..
I found bare aluminium fared well in sea water, but something as simple as a vinyl sticker could cause chaos underneath !

Thats why my first choice was shoulder washers and duralec, secondly was the PU Sealant which if done right and with care, can work partially well.

Ive had great success and the job i did 5 years ago with PU is still as nice as when i first did it.

 

[Rappey]

Regards to your U bolt, if it has some sort of base plate which will be on the outside then under that is where i would say most corrosion would occur. A thin piece of plastic would help.
I had a large outboard bolted on with stainless bolts which are not the easiest to seal, let alone insulate but the bolts and holes never suffered from galvanic corrosion..
Duralac certainly works well but as mentioned already, an absolute bugger to get off anything once dried !

 

[MystyBlue2]

Yeah the last thing you want is your new RIB to become one big sacrificial anode,

Pay careful attention to eliminate contact of the two materials and take time.

Best of luck ?

 

[Rappey]

I bought a dingy sized rib for next to nothing.. Its paint was worn off at the back of the hull and had been left in the water.. The ally was perforated and had pin sized holes in it..
I would have an aluminium dingy but never a full sized boat again, unless it was brand new. Its not like its easy to weld/repair either.. but on the other hand it is so light and strong..

 

[MystyBlue2]

I bought a dingy sized rib for next to nothing.. Its paint was worn off at the back of the hull and had been left in the water.. The ally was perforated and had pin sized holes in it..
I would have an aluminium dingy but never a full sized boat again, unless it was brand new. Its not like its easy to weld/repair either.. but on the other hand it is so light and strong..

Yeah ally boats seem very popular in the states and Auz as bass boats. Mostly fresh water use. Never really seen one used in salt water much, what you've just described is probably the reason why.

 

[Rappey]

It's more likely a rare boat in the uk because aluminium boats cost so much.
You can get cheap stamped out ones but welded ones are very expensive.
As a dingy they are brilliant as a lot lighter than grp and usually one does not leave their dingy in the water when not in use.

 

[rotrax]

Yeah ally boats seem very popular in the states and Auz as bass boats. Mostly fresh water use. Never really seen one used in salt water much, what you've just described is probably the reason why.

Probably 50% of NZ new trailer boat sales are Aluminium. NZ and Finland are fighting it out for the highest per capita boat ownership in the world.

Worth looking them up - some are fabulous.

A friend in Wellington has a twenty two year old Stabicraft, a pointed nose pontoon type twenty footer.

It looks great bar the once bright red paint which has faded to pink..................................

 

[MystyBlue2]

Probably 50% of NZ new trailer boat sales are Aluminium. NZ and Finland are fighting it out for the highest per capita boat ownership in the world.

Worth looking them up - some are fabulous.

A friend in Wellington has a twenty two year old Stabicraft, a pointed nose pontoon type twenty footer.

It looks great bar the once bright red paint which has faded to pink..................................

Yeah they are beautiful, a friend of mine that i bought my new motor from had a 19ft flat deck aluminium USA bass boat (not sure make and model), all carpeted and electric trolling motor on the bow, registration numbers on from New york and same on the twin axle trailer, funny enough he wanted to keep the mercury outboard i bought off him to mount it on the back of the tinny and sell it as an American set up. But i ended up getting the motor lol.

Really nice boats and the welding is beautiful to look at too. Shame we haven't got the lakes like the Americans have or i would have one.

 

[Bouba]

There are plenty of unpainted aluminum sailing yachts in the sea

 

[rotrax]

Yeah they are beautiful, a friend of mine that i bought my new motor from had a 19ft flat deck aluminium USA bass boat (not sure make and model), all carpeted and electric trolling motor on the bow, registration numbers on from New york and same on the twin axle trailer, funny enough he wanted to keep the mercury outboard i bought off him to mount it on the back of the tinny and sell it as an American set up. But i ended up getting the motor lol.

Really nice boats and the welding is beautiful to look at too. Shame we haven't got the lakes like the Americans have or i would have one.

Most NZ aluminium boats are used on the sea. And dont seem to suffer for that use.