Tabernacle, balustrades and fixings onto an aluminium deck

[Spanjaard]

First of all, I would like to wish you all a Happy New Year.

As part of the maintenance works for this year, I decided to strip out the old treadmaster that must be about 45 year old and that has bubbled up on multiples areas of the deck which is aluminium.

But as I started chipping away the treadmaster, I found that all fittings, including the tabernacle, the balustrades and the cleats have been mounted over the old treadmaster.

I am planning to repaint the deck with kiwi grip or similar non-skid paint. However I have the dilemma of reinstalling all fittings including the tabernacle, metal against metal, or if I should install rubber gaskets in between the fittings and the deck for better grip and to prevent any leaks.

At the moment I am cutting the old treadmaster around all fittings and probably I could paint the deck without removing all balustrades, cleats and tabernacle, with little or no difference...

I don't know if I could bear knowing that the old treadmaster still remains on some places as I hate bodge jobs, even though, removing all fittings is going to be a pain and will require a good dose of testicular fortitude and determination.

Any advise will be appreciated.

 

[rogerthebodger]

I have a steel deck boat that I had treadmaster fitted around the deck fittings. These deck fittings had tapped plated welded to the deck so easy to replace when necessary.

In your case how are the fittings fitted to the deck if they are bolted through the deck I would remove then from underneath and fit then back on using tapped plated underneath. This would allow removal for repair or resealing .

In bolting through I would use a sealant like sikaflex under the fittings.

I have used hard rubber on my bow fittings and under my mast step just as I had some hard rubber belting available

If the fittings are aluminium you could get them welded to the aluminium deck

Most of my deck fittings, including my aluminium toe rails, has tapped steel pads welded to deck and the fitting bolted into these tapped pads

Mid deck cleat

https://flic.kr/p/WVhB4G

Leg support slides

https://flic.kr/p/WYNnEt

Winch mounting pads

https://flic.kr/p/WVi6c5

For deck mast step, hatch frames and mast pulpit

https://flic.kr/p/WHUwrm

 

[AntarcticPilot]

I presume you'll need to use something such as Duralac to isolate the deck fittings from the aluminium? Otherwise, I can imagine severe problems with galvanic corrosion down the line. Maybe that's why the Treadmaster is underneath the fittings - to provide extra isolation.

 

[Spanjaard]

I have a steel deck boat that I had treadmaster fitted around the deck fittings. These deck fittings had tapped plated welded to the deck so easy to replace when necessary.

In your case how are the fittings fitted to the deck if they are bolted through the deck I would remove then from underneath and fit then back on using tapped plated underneath. This would allow removal for repair or resealing .

In bolting through I would use a sealant like sikaflex under the fittings.

I have used hard rubber on my bow fittings and under my mast step just as I had some hard rubber belting available

If the fittings are aluminium you could get them welded to the aluminium deck

Most of my deck fittings, including my aluminium toe rails, has tapped steel pads welded to deck and the fitting bolted into these tapped pads

Thank you very much Roger.

Very impressive the catalogue of photographs with all the works to be carried out. Worth considering the welding of the balustrade poles onto the deck as the supports and poles are aluminium. Perhaps would be a a better idea to get some pre tapped aluminium plates welded onto desk for ease removal of the balustrade poles as you suggested.

In regards of the rubber matting, I can get some gasket (3/4mm) same one as the ones used on the inspection plates in manholes which are specially designed for water. Would you recommend to use sikaflex between the rubber matt and the deck? Or this would degrade the rubber?

And the last question, these horrible scratches on the hull, how did you repair them? Welding?

 

[Spanjaard]

I presume you'll need to use something such as Duralac to isolate the deck fittings from the aluminium? Otherwise, I can imagine severe problems with galvanic corrosion down the line. Maybe that's why the Treadmaster is underneath the fittings - to provide extra isolation.

Thank you for your reply.

I will research about duralac to see if it is more suitable than sikaflex.

In regards of the galvanic corrosion, I am not expert but the boat has two cast iron bilge keels which are bolted to the hull. The pulpit, which is stainless steel, is also bolted to the aluminium toe rail, metal to metal. And most of the fittings are bolted onto deck with stainless steel bolts, nuts and washers...

Before I bought the boat, which is 45 years old, I had a proper survey of the hull to measure the thickness of the whole hull, with no signs of galvanic corrosion. The anodes are alright.

I haven't got installed neither a galvanic isolator, nor a isolation transformer (which I don't know where would it fit in my 28" boat). But since I am on a mooring buoy by the Crouch most of the time, for the sake of not getting paranoid, I may install one of those galvanic isolators for when I visit marinas, rather than dropping a 5 pound anode connected by a cable to my toe rail, which is the method I have followed so far.

 

[AntarcticPilot]

Thank you for your reply.

I will research about duralac to see if it is more suitable than sikaflex.

Duralac (there are other things that do the same thing, such as TefGel) is not a replacement for Sikaflex; it does a different job. Aluminium and ferrous metals in direct contact will set up an electrolytic cell between the aluminium and the iron; the aluminium will preferentially erode. To avoid this, the two metals must be insulated from each other. Duralac and similar products act to insulate the two metals from each other. Of course, Sikaflex may have the same result if the film is thick enough, but it isn't certain to. As the metals aren't immersed in sea water, your anodes will have no effect on deck fittings; they aren't in the same electrochemical circuit.

 

[Spanjaard]

Thank you. I really would like to understand these issues regarding the electrochemical issues that might affect the boat.

How did you get this info? Do I need an electrician to explain it to me, are there any books or websites that deal with this issues?

Thanks.

 

[vyv_cox]

An elastomeric gasket, nitrile or neoprene, would be the best means of isolating fittings from your deck. I would use gaskets in conjunction with Sikaflex.

My website covers many of the corrosion questions you are asking. The fundamental answer to corrosion is 'keep the water out'. Anything you can do to achieve this will benefit. Duralac is of benefit where gaskets cannot be used, e.g pop rivets, mast fittings etc but a gasket will always be superior
Cox Engineering

 

[NormanS]

If the fittings at present are soundly attached, and are not giving any problems, I would leave them alone. Leave the treadmaster under them, as it's already doing a good job of isolating.

 

[rogerthebodger]

Thank you very much Roger.

In regards of the rubber matting, I can get some gasket (3/4mm) same one as the ones used on the inspection plates in manholes which are specially designed for water. Would you recommend to use sikaflex between the rubber matt and the deck? Or this would degrade the rubber?

And the last question, these horrible scratches on the hull, how did you repair them? Welding?

As Vyv says rubber will insulate stainless steel from aluminium.

My aluminium toe rail has strips of foam rubber between the toe rail and the steel tapped plate that is welded to the deck

The scratches happened when the marina in was moord in broke up some years ago. Several GRP boats were holes and sunk and all i had was those scratches that I pilled with epoxy filler sanded and repainted. hull was not holed so no welding necessary

 

[vyv_cox]

If the fittings at present are soundly attached, and are not giving any problems, I would leave them alone. Leave the treadmaster under them, as it's already doing a good job of isolating.

True enough but after 45 years I think it is time to have a look.

 

[AntarcticPilot]

Thank you. I really would like to understand these issues regarding the electrochemical issues that might affect the boat.

How did you get this info? Do I need an electrician to explain it to me, are there any books or websites that deal with this issues?

Thanks.

I thoroughly recommend @vyv_cox book. I happen a) to have some university chemistry behind me and b) my late wife's doctorate was in electro-chemistry. But the basics are very simple - you need a circuit containing two different metals and an electrolyte (sea water). Break the circuit and no electrolysis.

 

[Rappey]

The fundamental answer to corrosion is 'keep the water out'.

From my own experience having owned an aluminium centre consol type boat for 18 years the statement above is by far the most important.
I had parts bolted with stainless and most fared well. Verticle surfaces were fine but horizontal ones suffered.
I stuck down the green sandpaper like anti slip pads (self adhesive) on the floor and over time they caused a lot of corrosion underneath consisting of a jelly like substance and white dust. Cleats were the worst offenders.
Marina cleats bolted on decking suffer terrible corrosion under the base plate where you cant see it producing a jelly like substance.
Pin holes in the hull and many stress fractures finally made me sell the boat.

 

[Spanjaard]

I thoroughly recommend @vyv_cox book. I happen a) to have some university chemistry behind me and b) my late wife's doctorate was in electro-chemistry. But the basics are very simple - you need a circuit containing two different metals and an electrolyte (sea water). Break the circuit and no electrolysis.

Which book? Metals in boats?
Just to make sure before I buy it in amazon

 

[Spanjaard]

From my own experience having owned an aluminium centre consol type boat for 18 years the statement above is by far the most important.
I had parts bolted with stainless and most fared well. Verticle surfaces were fine but horizontal ones suffered.
I stuck down the green sandpaper like anti slip pads (self adhesive) on the floor and over time they caused a lot of corrosion underneath consisting of a jelly like substance and white dust. Cleats were the worst offenders.
Marina cleats bolted on decking suffer terrible corrosion under the base plate where you cant see it producing a jelly like substance.
Pin holes in the hull and many stress fractures finally made me sell the boat.

Thank you Rappey.

Where did you kept your boat most of the time? at marinas?

 

[AntarcticPilot]

Which book? Metals in boats?
Just to make sure before I buy it in amazon

That's the one.

 

[Spanjaard]

That's the one.

Ordered. Coming on Monday. That's fast, printed and delivered (Post Office will be out of business very soon).

 

[vyv_cox]

Ordered. Coming on Monday. That's fast, printed and delivered (Post Office will be out of business very soon).

I also answer specific questions via my website.

 

[rogerthebodger]

Which book? Metals in boats?
Just to make sure before I buy it in amazon

Written by our very own Vyv_cox so it must be good

 

[AntarcticPilot]

Just for reference, here's my review of the book on Amazon: Check out this Amazon review of Metals in Boats