corrosion on outdrives

[Brent]

My outdrives have some corrosion spots on them and I'm looking for a effective treatment to stop it returning as this is the first time I've had to tackle this problem. Has anyone got some tried and tested effective treatments they'd like to pass on.

I've posted this same question on the YBW main forum site (Practical boat...) and got one reply (perhaps they don't get their hands dirty so don't know)!!!. Come on MBM readers come to my aid and give me some tips on drive corrosion repair, someone must have a "sure thing repair". Show me that the other ybw forums aren't worth surfing and that this is the forum to view. If it helps I'm a monthly reader of MBM and enjoy it. I hope this helps bring me into the fold.



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[Dave1258]

Hi Brent welcome to the madhouse!
Have you checked on your zincs lately, finding out the cause of your corrosion problems will help with an effective repair procedure to be carried out

<hr width=100% size=1>Someday my ship will come in, and with my luck I'll be at the airport!!

 

[stamfordian]

Mmmm,the Medway salty stuff...so assuming as other post your anodes are up to scatch ,weeare talking about a failure of the paint on the the drives...follows is a step by step guide as to how to tackle...assume non drying mooring....get lifted out....wash off fouling from drives...be brutal...rotory wire brush.....allow to dry off completly and rub the whole thing down (soorry both) until all antifoul in particular is history,use a good qulity etch primer and spray after masking rubbers to a good finish....may take several rub downs and coats....then if your going to antifoul the leg go for Teflon and apply two coats of recommended anti foul primer then top coat twice...after all this you should have pristine out drives tha t have the finish of a frying pan......allow to cure and dump back in water with new anodes(the boats out anyway).You asked for it!!!/forums/images/icons/smile.gif

<hr width=100% size=1><A target="_blank" HREF=http://www.arweb.co.uk/argallery/stamfordian>http://www.arweb.co.uk/argallery/stamfordian</A>

 

[Dave_Knowles]

Hi Brent,

Two things to look at before you do repairs are:

1 Do you have fresh water anodes or seawater ones. I only found out the other day the difference after our local Volvo agent offered me either and did not know why there were two types.

2. If the boat is antifouled it is important that you leave a gap around the outdrive because the antifoul touching the outdrive can create corrosion.

Whe I had my boat out last summer I painted my outdrive with International outdrive paint and so far all looks fine so maybe it would be worth vcleaning off the spots with a wire brush and then painting them. You mayneed to prime first. Check the instructions or speak to International for advice. But the important thing is to get to the cause.

<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[oldgit]

Re:Why outdrives are a pain(Lesson 1)

Hello Brent.Presume you are also getting small pits in drive leg casings apart from normal growth of gunge,had similer probs with my Mercruiser legs.As with previous posters comments you will need to throughly clean and de-barnical/forums/images/icons/laugh.gif everything,including all those difficult to get at nooks and crannies.Gouge out any muck from any pitting and fill.A real piggy of a job.A proper industrial jet wash will be a great help and i do not mean one of those toy things they sell in Halfords etc.I have read several warnings not to use steel wire brushes as they leave microscopic steel particals embedded in the aluminium.Which then rust and cause some sort of future problems.
Was told to give light sand down which gives key for primer and then x 2 topcoats of mega expensive antifoul in the colour of choice.
My present boat which has two volvo legs was treated to this palaver last year and although in the water for 12 months(on Medway in Rochester) does not have any significant amount of weed.
Pirates Cave on Medway City Est seemed to be cheapest for anti foul and primer last year.You could also try Ray Stapley Marine in same area.

<hr width=100% size=1>If it aint broke fix it till it is.

 

[duncan]

You are going to have 3 main forms of damage to an outdrive -
Barnacle growth etc
Galvanic corrosion when your anodes have given up
Dings and grazes from hitting things

The first requires you to remove back to your drive surface - as other posts have said high pressure jet wash does well. I would also recommend a wooden spatula (nick an old one from the kitchen). This won't damage the paint/drive but will scrape off barnacles and deposits well.

After ensureing that the corrosion won't reoccur treatment is just as for a rust spot on a car. The main reason for being brutal is that the alloy around the corrison will be weakened but you don't ned to get to carried away! Avoid wire brushes for the reasons gived - you can get some excellent fibre based ones if you really need to. Fill with an epoxy filler, car ones are excellent, and finish smooth. Critically you must now dela with both paint and antifoul seperately!. For a mercury drive you might as well use their 'cans' of primer and finish. For antifoul you have 2 main choices - Trilux or equivalent biocide based or a teflon based system like Internationals Veridian. In the latters case you still get fouling growth but it 'slides off' once you get going. It's certainly better if you want to avoid drag but Trilux is a hell of a lot easier and can be topped up better as well.





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[oldgit]

Re:And do not forget

Those silly rubber concertina things that keep the water out of the boat.Def. good idea to check and if any doubt change them now boat is ashore.Not that big a job about a day to do both with cups of tea included.You can source your replacement bits more cheaply from somebody like <A target="_blank" HREF=http://www.keypart.co.uk>http://www.keypart.co.uk</A>.a phone call to them will result in your parts arriving faster.Got to do mine at end of month.........Enjoy.

<hr width=100% size=1>If it aint broke fix it till it is.

 

[adarcy]

Re: corrosion on Merc drives

Brent

Do Mercruiser outdrives still have their own electrical anti-corrosion thingumyjig?
We certainly had it on our v old 165hp sterndrive which worked well and when we changed to a Volvo sterndrive boat which didn't it ate anodes ++

Ah I've remembered "Mercathode"

If it does and you have corrosion, perhaps it ain't working!

BTW Welcome

Anthony

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[oldgit]

Re: corrosion on Merc drives

Was this not some sort of constant current device that needed perm battery connection.Seem to remember you could check efficacy of thing with multimeter.

<hr width=100% size=1>If it aint broke fix it till it is.

 

[duncan]

Re: corrosion on Merc drives

I believe only the BIII unit is currently fitted with a mercathode.
It is permenantly connected to the battery but doesn't constantly draw power apparantly. To test if it's working requires a very sensitive meter to the water around the drive. First sign of it not working is anodes go quicker (before the drive).
The other possible reason (and 1 I had on a BIII) was the fitting of Keypart anodes - they weighed twice the normal ones and hadn't a mark on them in a couple of months after fitting - the drive however fared badly!!!!!!!!!!!!

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[Brent]

Re: corrosion on Merc drives

Thanks to all who have replied, you made the other bunch on the MBY forum look dim. I have only had this boat a few months so care of the drives in the past is unknown.

To answer Anthony, yes it has the "Mercathode" system but I don't think they ever got used as the battery switches need to be on for them to work. I know the switches were always off when the boat was not in use by the previous ower who had it from new. My quest this year is to make sure they work.

Thanks again to all who replied and to those who may continue.

Brent

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by Brent on 26/01/2004 19:11 (server time).</FONT></P>

 

[BarryH]

Re: corrosion on Merc drives

"plink, plink....fizzz"..................think about it!

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[duncan]

Re: corrosion on Merc drives

I would be amazed if the battery swithes need to be on - they should be wired direct along with the bilge pump.
I should have poped over at the weekend as you are only a few minutes away but only thought about when the sun was going down on Sunday.
If you want to see some pictures of real Mercruiser corrosion let me know your eMail and I will send them over! Sad eh?

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[oldgit]

Re:Oi no PMs.Lets see the piccies on here.NM

/forums/images/icons/laugh.gif

<hr width=100% size=1>If it aint broke fix it till it is.

 

[duncan]

Re:Oi no PMs.Lets see the piccies on here.NM

hmmmm I don't know............
http://arweb.co.uk/argallery/Boaters2/I_000066
<A target="_blank" HREF=http://arweb.co.uk/argallery/Boaters2/I_000065>http://arweb.co.uk/argallery/Boaters2/I_000065</A>
enough I hope!

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[adarcy]

Re: corrosion on Merc drives

Agreed Duncan

they should surely be wired in permanently live else not working >90% of the time.
It may only put out a few millivot field but it should surely be measurable whilst in the water. Fairly obviously, no current if out of the water.
As long as it doesn't flatten the battery (inadequate boat use) then the Mercathode seems a smart idea to save on anode wear but the anodes are present as a fail-safe. Certainly cheaper than buying anodes more frequently as one doesn't cost any extra petrol to recharge the battery.

I don't know why Volvo etc don't do the same ?patents ? some other prob I/we don't know about.

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[oldgit]

Re:Oi no PMs.Lets see the piccies on here.NM

eek see wot you mean.............

<hr width=100% size=1>If it aint broke fix it till it is.

 

[bbilly]

Have a look here: http://marinesurvey.com/yacht/SternDrive.htm


<hr width=100% size=1>"Life is too important to take seriously."