Need help with an Aluminium boat

[Fidu666]

Originally Posted by hellosailor

You may have heard of this place called Greece? Full of people calling themselves Greek and claiming to have been master mariners and founders of Western Civilization?

Well, before they got deluded in following the carpenter god, the Greeks knew an awful lot about the Gods, including a sea god named Poseidon. Boats, all boats, are Poseidon's daughters and they are under HIS CARE. This is why a captain asks Poseidon's blessing to marry and care for one of his daughters, and to this day a wise caption will place a gold coin, his boat's bridal dowry, under the mast when it is stepped. (No, you don't CHRISTEN a boat, you have a proper pagan priest BETROTH you to it.)

Poseidon's color happens to be BLUE. And as any Greek can still tell you, NEVER GO TO SEA IN A BLUE BOAT. It is Poseidon's color, and he might get jealous and TAKE THE BOAT.

Very very bad juju to paint a boat blue. Perhaps in Italy they no longer have the story straight, aluminum doesn't matter. The only way that you could have worse luck would be by having another female about the boat. Poseidon might not like that either.

As to leaving ports on Friday...That's a Moslem Holy Day. *Poseidon* doesn't give a damn about Fridays. But unless you've got a mosque on your boat...that's another whole set of rules you might be breaking.

Sanding and scraping already!

[Norbert1]

I build my aluminium Reinke complete allone 2000.
Since that we are once around the world.

Aluminium have the same advantage and disadvantage like every other material.
Thats for the haters and for the fanatics.

So first. Your concerns for the outside hull, as longe there are no holes deeper then 1 mm
are not reasoening.
All your concerns have to be directed to inside the boat.
You have to fight yourself to the deepest points inside.
Thats where you get a dangerous mix from
moist, dirt, copper pices and oxygen.

Somtimes it looks like ok, but if you put sodiumhydroclorid on it, suddenly you get black spots. You have to clean with fresh water after and repeat.
The black spots are alluminium oxide which is stuck inside.
So if you use the sodiumhydrochloride and the material get white without black spots, that is good sign.
Be carful and use only in small spots, than rinse with fresh water.
If you start doing that you will get a expert soon for yourself.
Remember, the problem are only surfaces which are horizontal, and the dirt can collect.

The other problems are direct connection from stainless to aluminium.

Also, Epoxypaint can be a problem at it self.
Because the paint cracks, salt get under, the bad process starts.

Still I would build my next boat with aluminium because I know how to deal with.

Good luck

[paul2884]

Speaking from experience - paint falls off aluminium boats!

Only paint the minimum, just below the water line and have all the topsides/decks bare it will look much tidier than a painted boat in 2 years’ time.

The blue top sides are unusual and I would expect the paint to be flaky in places, the marks from (as said before) lifting straps? are also to be expected.

Get all the paint blasted off and the underside re-painted/antifouled (must be copper free antifouling!), fit an isolating transformer if there isn’t one fitted already.

Nothing looks too bad at the moment and at least you won’t get osmosis

[Erik de Jong]

Originally Posted by paul2884

Speaking from experience - paint falls off aluminium boats!

It only falls of off poorly built aluminium boats.
But I agree, an alu boat should not be painted to start with.

[nmccubbin]

We have an aluminum 47 footer. Unpainted topsides but of course antifouled below waterline
Been cruising since 2004
We pay extra attention to aluminium boats, and would guess that about 3/4 have painted topsides and 95% have painted decks and cabins
Paint is good for about 8 15years
Our bottom paint undercoat is still good after 15
I am inclined to agree that your Italian boat has paint issues. Sandblasting off is best answer

[Redreuben]

Maybe the blue pigment is a metal ?
Anyway, around here aluminium yachts are called aspirins.

[LargeMarge]

re:
"...electrolysis..."

Are you certain of your terms?

Based on your information, you appear to be describing galvanic corrosion.

The difference is significant. An experienced surveyor will know the difference.

[bluenomads]

Originally Posted by nmccubbin

...Sandblasting off is best answer

We're contemplating soda blasting our superstructure, deck and hull sides above water. Has anyone done this? DIY or pay a company?

[a64pilot]

Originally Posted by Erik de Jong

It only falls of off poorly built aluminium boats.
But I agree, an alu boat should not be painted to start with.

It seems that almost anything other than anodizing is temporary on aluminum, paint, powder coat etc all seem to fail eventually and then it seems that salt water gets in, a little corrosion spreads and pops off the covering.
You see it on powered coated aluminum dinghies, masts etc.
Anodized seems to last a long time however.

[jmorrison146]

[Erik de Jong]

Originally Posted by a64pilot

It seems that almost anything other than anodizing is temporary on aluminum, paint, powder coat etc all seem to fail eventually and then it seems that salt water gets in, a little corrosion spreads and pops off the covering.

Of course everything is temporary, but there is absolutely no problem with keeping paint on an aluminum boat for 20 to 30 years without having to redo it. Main condition for a long paint life is that your electrical system is perfect, not good, but perfect. Paint adhering problems on steel and aluminium boats is in 99% of the cases caused by an error in the DC system on a boat.

[Norbert1]

Originally Posted by Erik de Jong

Of course everything is temporary, but there is absolutely no problem with keeping paint on an aluminum boat for 20 to 30 years without having to redo it. Main condition for a long paint life is that your electrical system is perfect, not good, but perfect. Paint adhering problems on steel and aluminium boats is in 99% of the cases caused by an error in the DC system on a boat.

Of course electrical system have to good.
But how can you avoid having ground on your boat. I have tried a lot but still a problem.
For example the engine.

Than I have Alluminium things on my boat, not connected to the hull at all and still the paint peels of after same years.

In my eyes sandblasting is a key. The other is the choise of paint. I have bad expirence with 2 k systems above the waterline ( without andblasting). But good experience with waterbased paint or 1 k systems.

If the hull is new it should sandblasted than the right epoxy an than poleurethan.
But inside is at least important the same like outside.

[Erik de Jong]

Originally Posted by Norbert1

Of course electrical system have to good.
But how can you avoid having ground on your boat. I have tried a lot but still a problem.
For example the engine.

Than I have Alluminium things on my boat, not connected to the hull at all and still the paint peels of after same years.

In my eyes sandblasting is a key. The other is the choise of paint. I have bad expirence with 2 k systems above the waterline ( without andblasting). But good experience with waterbased paint or 1 k systems.

If the hull is new it should sandblasted than the right epoxy an than poleurethan.
But inside is at least important the same like outside.

On alu you always have to use an etch primer before any other paint is used.

You can't just put a random engine in an alu boat, it needs to be fully isolated (block is in that case not used as ground for the engine's electrical system).

Rudder is probably what you are refering to for lose aluminium object that is isolated under water? You say that you have issues with the hull and mainly the engine, so you have a hull that is causing problems and that might give enough potential difference between rudder and hull to get such problems.

In basic, solve the problems on your hull, and your rudder is most likely going to be fine.

[Norbert1]

Originally Posted by Erik de Jong

On alu you always have to use an etch primer before any other paint is used.

You can't just put a random engine in an alu boat, it needs to be fully isolated (block is in that case not used as ground for the engine's electrical system).

Rudder is probably what you are refering to for lose aluminium object that is isolated under water? You say that you have issues with the hull and mainly the engine, so you have a hull that is causing problems and that might give enough potential difference between rudder and hull to get such problems.

In basic, solve the problems on your hull, and your rudder is most likely going to be fine.

I have a Outboard Engine 25 hp 85 kg. Not easy to isolate the bracket from hull.
Its allways not easy to put nylon washers etc, than using a big wrench, the whashers will break.
So I put two switches on plus and minus and the engine is only connected if running. Still I can not find where the ground is coming from. Even I have build the boat from scratch.
On the other hand, everything have of course plus and minus wire, and i have tested the mAmp on the hull, between minus battery and the hull and messure only 0.4 mAmp
So I dont think thats a deal.
Static loading is probably a bigger issue.

Then I have the Hamradio antenna ground on the hull.( using pactor every day) So that keeps me thinking.

I did not refer to the rudder, as I have no issus at all under water. Problems are allways inside the boat, on places where dirt and moist come together.

I was refering to alluminium items, nothing to do with the boat at self. But still the paint peeling.

[Erik de Jong]

What alloy did you use when you built the boat?