Shafts, struts, zincs and rudders

[DOUGNASH]

Hi Folks,

Spent the afternoon under the boat today.

Got some simple questions and some pics of course

So I cleaned up the shafts and now they are very shiny.



The zinc on the shaft was basically gone, then I noticed a lot of other boats have 2 on each shaft. Since the 1 was eaten away from a short last season (july-November) I figure I should probably double up too. Any input on good/bad idea? what about placement of each?



So the struts and rudders were painted I guess years ago, I would love to strip all the old paint off to get the brass showing again. Who's got the easiest and fastest solution for this?



This is a close up of one of the props. What do you think about the pitting? I spent $900 last year to get them re-done. What do you think caused this?



Here is the zinc on the stern, this one looks pretty good with a lot of it still there. Do you think I can squeeze in another season?



Here's a shot of the stern...



As always, thank for your helP!!!

[Big D]

I'd put a couple of anodes on each shaft, can't hurt. I'd get one close to the main strut and another by the intermediate strut. The one on the transom looks fine to me, plenty of anode left from what I can see. The mounts look OK, they sometimes rot away before the anode is done.

Does the prop have pitting on all the blades or just one. Cavitation could cause this due to prop defects (chipping etc), excessive cupping, bad blade design, high speed etc. It may also be that the previous repairs involved welding and the welds were dirty or contaminated and is now resulting in loss of material.

Do you guys get really cold winters where you are? The reason I ask is that it's a no no where I'm from to use concrete blocks for blocking. They can shatter with temp changes. Having said that, I see them used here too but I've seen even marinas use the strangest things to block boats....until of course there's an accident.

[kallen]

My opinon. If you are chewing up zinc that fast I would be checking for stray electrical currents in the water (forget the name of it). Check your neighbors boats for zinc problems. Also have someone check your own boat for a grounding problems (bonding system).

[Big D]

I agree kallen. They are salties down there though so it may be the norm, but certainly you brought up valid points.

[Struts and Rudders]

Is that red paint or is the metal taken a red hue?

If metal has taken a red hue your running gear suffer from de-zincification.

Inspect the bonding system very well...if you are in a cement walled marina it could be the marina itself. Could be your neighbors boat as well, though your zinc looks good. Drop a meter in the water and see what kind of current you are seeing.

Look into it...the metal strength is lost during de-zincification.

SRD

[prowlersfish]

I would Check most the above . use 2 shaft zincs per shaft and check to make sure that plate zinc is connected to the rest of the system ,I bet its lost connection somewhere . would not hurt to put zincs on the rudders too
your shaft zincs are doing all the work .

[koviak]

Do all the above but also add a galvanic isolater to your shore power system. Your boat with all its metal gear in the water is a natural battery. Add additional boats around the marina with ac voltage and stray current becomes a big issue. Isolate the shore power ground and you no longer attract the stray current, ie: saves your zincs and metal gear.

[alexander38]

When you do put the 2nd zinc on measure the distance from the prop to rudder then subtract and 1" or 2 from it then use that number to place the zinc in front of the main strut . That water flow won't be cut off from the cutlass and help keep the prop and shaft off the rudder if you ever drop it.
And what the other guys have said about you pinkish looking gear is true if that's not faded red paint you need stuff checked out ASAP

[DOUGNASH]

Thank you for all of the replys!

So I will add a 2nd zinc on each shaft, I like the idea to put one on the shaft to hold the prop away from the rudder if it drops.

The prop only has that one area that is pitted, so let's see what it looks like at the end of this season.

The redish tint on the struts and rudders is actually really old paint, I do see the bronze coming through in small parts where I wire-wheeled it last year. Believe it or not that red paint was all over the shafts too when I bought it last year, that was a nice project last June, at least I was in the shade!!

Prowlersfish I think you are on to something about the back zinc not being connected somewhere. I have been wanting to remove the lower cockpit deck, so this will be a great reason to do it now. I can crawl around through the cockpit hatches, but it will be more fun just to take off the entire deck.


I also like the idea about adding an isolator to the boat. I understand it gets installed on the "earth line" from the shore power, I am just not sure where on the line. I guess I have to follow the line coming in from the shore plug.

Here is a pic I took off the internet of one installed.

The galvonic isolator is the black box, what is the other "box" where the line is connected.




As always, I will keep you guys posted on my progress...

[Big D]

Looks like main breakers to me. The isolator is also the simplest form of one. The more sophisticayed units display in one form or another the existing conditions and will advise if there is a fault.

[risctaker]

If you install the Galvanic Isolator (really good idea to do!) you can dispense with all the extra zincs. The isolator will do all the work.

[prowlersfish]

I would still keep the zincs cheap insurance ,

[Sea Play'n]

I have an 11M that the shaft zincs would go in a couple of months, and the transom zinc was relatively untouched. This happens when there is corrosion in the bonding system. The first place to check is where the bonding system joins the ss bolt inside the transom that the zinc bolts to on the outside. Get a friend to help and extend the leads on your multimeter. Place one lead on the copper bonding wire inside the transom and the other on the zinc anode on the outside. Using the Ohms scale there should be almost NO resistance. If there is a few thousand ohms resistance check for and remove any corrosion on the mounting washers on the anode. You might have to replace the terminal on the end of the bonding wire.
Once the bonding system is fully functioning, you shouldn't need shaft zincs.
Another insidious place for electrolysis problems on these boats is stray currents originating from bilge pump/ high water alarm wiring on any of the 3 bilge pumps.
Carefully check for any wiring immersed in bilge water and don't pass over an old automatic bilge pump switch! They can leak current and as the bronze bilge drains are bonded to the whole system you are now electrifying all your expensive props, struts and rudders and they will suffer! If you can't solve this on your own, get a professional to analyze you vessel.
Installing an galvanic isolation transformer does not solve any bonding problems, it only solves stray currents coming from the shore power ground.

Hugh