Anodes - gh26

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JFJ
Posts: 31
Joined: Tue September 6th, 2016, 12:07 am

Anodes - gh26

Post by JFJ »

Hi all

I had the steel keels of Iris shot blasted, and refinished in 3 coats of 'Jutonmastic 90' - an epoxy 2 pack marine primer. Looks a great job - havent antifouled yet.
The previous zinc anodes did a great job on these wings - there were 2 bolted through each, with the metal cleaned in direct contact and I didnt have much pitting - indeed, most of the original galvanization was still in place.

However, now I have epoxied the surface, I am not so keen on cutting it back round the anode.

I have some old 'Arc' copper multiply welding wires from a heavy duty machine - heavily lugged and each about 15 ft log, and perhaps 8mm thick. I was thinking of bolting these to the keels on the inside, and running them back to a large anode fitted in the stern. Good idea - or should I grind the epoxy?

On a second note. The aft anode (a double bolted affair) had 2 wires comming off it. One is attached to the engine bell housing (and looks like a diy job fitted later), while the other had broken off completely and I dont know where it went! The whole wire was in the bilge. Now, the engine is a volvo penta MD 2020, in good shape. According to my reading of the workshop manual, the engine should be 'galvanically isolated - they are not to be connected to an anode. The drive shaft has a plastic thrust coupling, and the alternator and starter have direct negative connections - so I can see that it could be so. The stern gland was replaced before I bought the boat. The question would be then - should the anode be connected to the stern bronze drive flange - and then - what about the prop - it would usually be isolated with the rubber in the cutlass bearing. There is no anode on the driveshaft....
JFJ
Posts: 31
Joined: Tue September 6th, 2016, 12:07 am

Re: Anodes - gh26

Post by JFJ »

Well,
I got my hands on a copy of 'boat owner's Mechanical and Electrical Manual' by Calder.

Seems I went overboard on the cables - only need AWG 8. so important because the wire I have is expensive stuff and would be better off with other projects - pain to re-crimp too!

As to the bilgteplate anodes - I think I will grind a patch through the epoxy - it is the best protection in the event of a grounding affecting the bottom edge.

As to the 'main' anode. It appears that it was 'oversizesd' - this is a bad thing - as it seems to have affected the surfacce of the gelcoat through alkali damage... I had wondered about that when I recoated with barrier coat. It appears that at some time, the zinc basically disolved in place, and released its hydrogen into the gelcoat - blistering it a bit. Seems (according to Calder) to be due to either an oversized anode or an anode which isnt bonding. (which would explain the original wire which is broken and I dont know where it went.) I think that going forward (I will refit the existing anode - still a KG left at least) I will connect the wire to the sterngland -but will assess at the weekend.No way I think that can protect the prop though.
JFJ
Posts: 31
Joined: Tue September 6th, 2016, 12:07 am

Re: Anodes - gh26

Post by JFJ »

Well, I did manage to get the prop & driveshaft protected.
Problem - the engine is an MD2020 - which means a eath break on the drive shaft (the coupling has some very important plastic washers to provide earth separation).

So, plan B (this is more of a tip than a help)

1get a carbon brush assembly out of an old appliance - in my case a washingmachine. Replace the actual brush if necessary.

Screw the brush assembly to a small stick (Hardwood)
Align the brush aganst the shaft, and epoxy the stick in place to the hull - perpendicular in all the planes you can manage and close to the stuffing gland you can comfortably reach... (dont go right against it as you need to monitor it occasionally - in my case I add chainsaw oil once a year.)

Run a heavy earth cable to the anode from the pin of the brush assembly.
Measure resistance with a multimeter after the brush has had a chance to bed in - in my case, about an hour motoring after launch. You need almost no resistance.
there should not be much vibration on the shaft near the stuffing box. My prop and ss shaft gets anode protection as I cannot get an anode between prop and cutlass bearing....

Tested after a year in the water just now, and resistance is still only 4 ohms, and there was no sign of corrosion on the prop and rings 'true' when tapped with a screwdriver (ie rings, to prove the bronze isnt dezincing).
It simmilar to https://www.force4.co.uk/item/M-G-Duff/ ... XaEALw_wcB but cost (me) the price of some 5 minute epoxy....


Regards
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