Aluminum Boat

[surfmachine]

Ahoy shipmates.
Well, after three years of ownership of the aluminium felt sloop I can update you on some of my experiences!
1. Rebored the engine and fitted new pistons and liners and all new bearings. also recon the diesel fuel pump and injectors.
2. Welded some small aluminium plates over two pinholes that were weeping from the sealed void above the lead inserts in keel, below the welded floor. The weeps were evident when she was lifted onto the hardstand, no water ingress to the cabin, but into a void in the keel. Now a good.
3. Cleaned and welded some deep pits inside the hull at the front of the keel to hull welds.
4. Detected earth leakage onto the hull and eliminated them by a process of trial and error. Removed all electrical water pumps for the galley, now use footpumps. Have a permanent earth leakage detector on the fuse panel.
5. No other issues.
6. Have added lots of stainless steel work to the davits and safety rails, all new solar panels and two wind gennies.

Off sailing in thailand and then back to Sumatra surfing, in 13 days with my wife!

I am very happy with the boat!

Fair winds from Keith.

[Steve Pope]

Sounds great, my only concern is if there is any salt water still in contact with the lead and the alluminium where you welded the patches over the weep holes, not a good recipe

[surfmachine]

Ahoy Steve.
No, not at present, I enlarged the holes and cleaned out the void, maybe only 4 litres size?
Dried it out, washed it with fresh water, dried it again with heat gun and air compressor, then welded oversize patches over the holes.
Out on the hard now, and no weeping!
Fair winds from Keith.

[Steve Pope]

Hello Keith, that is what I hoped you would say, Enjoy the surfing, where to after that?
Steve.

[Eric50]

As you well explained Surfmachine, provide you have ability to weld aluminium, repairs can be done easily and with a long lasting result on the pinholes that are appearing after decades, this is one of the aluminium diseases that cannot be avoided along time, but we are usually talking about decades before it has to be treated...

Our boat was made in 1990 and we still not have signs of pinholes in "critical" areas, we recently installed a galvanic isolator (just in case) and noted a significant reduction of the anodes consumption.

Don't make me wrong, the anodes were having a normal consumption each year (about 30% of their volume), but now it is much less, we estimate the consumption reduced by 50% of what it use to be.

Of course, we keep replacing them each year anyway, as a routine.

We recently renew the paint, but we could have kept it in its condition without any problem, the goal was purely aesthetic, some blisters are still there at 2/3 different location, as they have always been there, without visible extension, few square centimeters overall...nothing critical.

As already explained in previous post, our 11 years of aluminium boat ownership gave us following feedback:

Aluminium corrosion : no sign or evidence of corrosion, regular visual inspection and electrical leakage monitoring in association with proper installation, anode management and limited shore connection (as much as possible and compatible with life aboard during cruisng and maintenance works) gave excellent results.

The boat has 4 pendular anodes (2 on the hull, 2 on the rigging) installed for long term mooring, 2 fixed ones on the keel and 2 on the propeller shaft (Maxprop propeller has one as well).

Most of the maintenance (99%) is not related to aluminium, but to wearing, electrical, wood and varnish, Equipment out of order or out of validity date and engine of course.

I consider that this result is coming firstly, and for most of it, from the fact that the aluminium construction and the electrical installation were properly managed, in second that we do perform regular maintenance and inspection as on any other boat.

We sailed in almost all kind of condition (up to well established force 9) and never had any concern about the boat integrity, nor about potential collision issue, in one of the busiest area in the world on water.

And 8 tons when fully empty...

[gjordan]

Please correct me if I am wrong, but assuming your boats electrics are correct and you dont have dissimiler metal problems, isnt the biggest threat to a metal boat the stray currents from bad dock wiring or bad wiring on the boat in the next slip. It is something that you have very limited control over, and can change at any time. Just something to think about._____Grant.

[David M]

If you do everything right regarding an aluminum boats electrical system and anodes, you will not have a corrosion problem, including being in an electrically hot marina. Been there, done that.

Stray electrical currents want to follow a pathway back to Earth. If your hull is not part of that pathway then you will be fine.

[Eric50]

GJorda, we fully agree, that was the main reason to have a galvanic isolator installed, in order to minimize as much as possible this (external) risk.

[David M]

A galvanic isolator prevents stray DC currents at your shore power connection from using your aluminum hull as that pathway.

[goboatingnow]

An aluminium boat with an AC system should have an isolating trsnsformer not a galvanic isolator.


Dave

[David M]

Both are acceptable. I don't have the transformer but have an isolator, (which goes in the boats AC ground). Yes, it is ok to have an isolator. I have no corrosion problems.

I understand the benefits of the transformer but don't need it. I have a floating AC sytem meaning nothing AC is bonded to the hull, as an aluminum boats AC system should be.

[goboatingnow]

Originally Posted by David M

Both are acceptable. I don't have the transformer but have an isolator, (which goes in the boats AC ground). Yes, it is ok to have an isolator. I have no corrosion problems.

I understand the benefits of the transformer but don't need it. I have a floating AC sytem meaning nothing AC is bonded to the hull, as an aluminum boats AC system should be.

Your AC system without an isolating transformer cannot by definition be floating , since ground ( and seawater) are valid return paths for such AC , any undetected fault currents can flow back to source via your hull and seawater. The galvanic isolator only protects your boat from "other" external impressed fault currents. It can not protect you from fault currents that inadvertently generated on board your boat. ( whether your hull is knowingly in circuit or not )

The purpose of an isolating transformer is to create exactly what you mentioned a proper floating AC supply, in this case whether the hull becomes connected or not , it and the seawater its in, can never provide a fault path , hence they cannot carry any leakage or fault current.

A galvanic isolator is not sufficient for an aluminium boat with any significant AC infrastructure onboard IMHO

Dave

[SV Maclas]

On our aluminum boat we have found that an epoxy barrier coat followed by a yearly change in zincs is all that needed to keep things looking great. We are fortunate that we have threaded posts we can simply spin half of a 5" rudder zinc onto. A quick dive and all of the zincs are changed.

[goboatingnow]

Originally Posted by SV Maclas

On our aluminum boat we have found that an epoxy barrier coat followed by a yearly change in zincs is all that needed to keep things looking great. We are fortunate that we have threaded posts we can simply spin half of a 5" rudder zinc onto. A quick dive and all of the zincs are changed.

That's great , but Zincs will not protect you from impressed current faults, I've seen quite extensive damage done to aluminium boats in circumstances of such fault currents. Like most things , if it doesn't happen to you it doesn't necessarily mean you are correct .

Dave

[s/v Jedi]

Yes, Dave is right... you need to have an isolation transformer on an aluminium boat, plus a "corrosion detector" or whatever they call them these days.

I wrote my butt off on isolation transformers a couple of years ago, waking up a lot of people on the issue; may be I should do that again or better... it's Dave's turn