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(Matt Lang) wrote in message . com...
(Lee Jones) wrote in message . com...
(Matt Lang) wrote in message . com...
"Calif Bill" wrote in message hlink.net...
"Matt Lang" wrote in message
om...
Folks,

I will be getting such boat (19') and will be using it in salt and
freshwater. Power comes from a merc sportjet.

I have been looking into corrosion protection and learned that you
should have magnesium in fresh and alumium or zinc in sal****er ...

Seems there isnt a good all around thing?

Since the hull of this boat will disintegrate if protection isnt done
right I was hopeing to gather good advise from here.

Merc makes a mercathode to protect their sterndrives. I am not sure if
this would be useable on an aluminum hull as it would ground the hull
to the battery, which I think isnt good for this type hull.

There is also electroguard which makes such devices for large boats..

Does anybody know what is best for my fututre hull & drive? The hull
will last forever therfore a few hundred bucks for the right
protection is no issue.

Thanks for all advise !!
Matt

Zinc also works in freshwater, just not as good as magnesium. Sounds like a
Willy Predator. Since it will be a trailer boat, just add a couple of
decent size zinc's to the hull at the transom and make sure there is one on
the bottom of the jet nozzle. My 1991 Jetcraft Bluewater is still going
strong. Only corrosion hole is going to be welded Friday morning, and that
was from something, probably copper, getting in the anchor locker and the
back of the locker collecting a lot of dirt against the bulkhead. Is a 1/8"
hole outside and maybe 1/2" at the inside of 0.190 thick aluminum. I run
mine in both fresh and salt water.

Hi Bill,

thanks for your advice! I will definately add some zincs, but will
also look into the cathodic protection.

The sportjet uses a SS impeller which accelerates corrosion. On their
sterndrives Merc recommends using the Mercathode if a SS prop is
used...

Matt

Hi,
If I can offer some advice on cathodic protection, never use a
magnesium anode on an aluminium hull. Aluminium will corrode much more
quickly at high pH and cathodic protection over a certain level will
cause this. Aluminium or Zinc anodes are ok, but magnesium has a much
more negative potential, which would take the aluminium into the
danger zone.

Same goes for any sort of impressed current device (connected to
battery or other power supply). You would need to be very careful that
you don't depress the potential of the aluminium too much. On large
craft, ferries and so on, an automatically controlled system is used.

Hope this helps

lee

Thanks Lee!

Yeah I suspected this isnt an easy one ... do it wrong and the hull is
gone in no time

I contacted a manufacturer that makes these things for large vessels
.. lets see what they have to offer

Mayy

As it happens, I work for a company who makes systems for large
vessels, we have a number of units on large aluminium ferries. Don't
worry I'm not trying to sell you something, because the cost would be
too prohibitive. A large ferry company has a huge benefit in reduced
dry dockings, maintenance etc, but for a small boat it just isn't
worth it.

There may be someone making small units suitable for your boat, but to
be honest, I'd stick with sacrificial anodes, aluminium or zinc.
Probably zinc.

If you do decide to buy a self powered system, be very careful they
know what they are doing and have plenty of experience of aluminium
cp. I know of aluminium ships that have had a hole in the hole in a
matter of months.

Take care
Lee

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