I have two problems that are compounding each other. I have always had trouble with zincs going away fast. I am down to 50 hours and still they just crumble when I pull them. Had a big overheat while trying to power through a Papagayo in Costa Rica. Cause was crumbled zinc residue blocking the tube stack. I got it cleaned out OK, but the tube stack will not come out for anything. After removing both bolts, I can get the rear end off, but the front cap and the stack will not move. I am afraid of a "bigger hammer". For now, I cleaned out the tubes from the rear end only, and put it all back. How do I get the tube stack out? Why are my zincs going away so fast, and blocking the cooler?
My procedure for removing the front tubestack cover is as follows:
1) remove the rear cap first. This will drain the raw water from the tube stack so that it doesn't leak from the front one on to the alternator.
2) remove the bolt and bonded seal from the front cap, insert a longer 8mm bolt or a thick phillips screwdriver into the hole and just lever the bolt or screw driver sideways. This will free the cap and then it will come out.
3) Then you must prise out the O ring from both the front and the rear of the tube stack. This will likely damage the O rings so make sure that you have spares.
4) drain the coolant to below the level of the tube stack so that you dont have too much mess to clean up.
5) Now take a piece of wood and put it across the top of the alternator on to the front of the tube stack. Hit the wood with a decent blow from a hammer and this should shock the tubestack loose. Then you can slide the tubestack out towards the rear.
You may be able to re use the M8 bonded seals and the exhaust flange gasket but it is always wise to have replacements on hand for in case.
As far as your zincs are concerned, this is almost definately an electrical issue. I don't know how the boat is wired but sometimes grounding and bonding get confused and this leads to problems. You certainly need to attend to this.
Thanks for the info on the tube stack. I do have spare O-rings, but no new bolt seals. I took them out once before, and never noticed they were there, but they are still OK. The first time, everything just slid apart. I tried the Phillips screwdriver--maybe I'll just get a very log M8 bolt to keep for that purpose. I wondered if I could create a puller to move it from the back, but not sure how robust the tube stack is. I am OK with the wood and a light tapping, but when in Central America, the general rule is never hit anything with a hammer unless you already have another one!
Re: Wiring, I do have a question on that score. I am certain that the bonding and ground systems are OK, (Both are connected to the block--ground by the starter, bond to the main bond bus at the prop strut I believe this bond is needed so the gear train doesn't carry stray current to the prop). I have the 100A alternator, and was surprised to note that it does not have a dedicated ground. I remember asking Ethan about it, but I thought he said it was not needed. Certainly everything works, but it means the block is carrying full charging current. Should I run a separate ground to the alternator frame? Is there a terminal for that, or do I just use a case bolt?
Do not make a puller for the tube stack. You are likely to cause some damage. The tube stack has a little corrosion holding it to the manifold and by using a piece of soft wood and hitting the wood, you will shock it loose and not hurt anything.
The 100 amp alternator is grounded through its case. As far as your wiring is concerned, from your description, is appears that the small zinc anode in the heat exchanger is looking after the entire boats electrical system as well as all the under water metal work. Adding more wires will only cause more trouble.
The bonding wires should connect all underwater metal work to a zinc anode and possibly a ground plate. If you have the rig connected to the ground plate for lightening protection, that is fine but this lot should not be connected to the engine at all. I know that there are some who say that everything should be connected for one reason or another and there are many books written by "experts" but my experience definately shows that connecting the bonding system to the electrical system is extremely good for our sales of zincs and other spare parts but not much more.
I will pull the wire from the bonding bus off the engine. It was there when I bought the boat, but my old Universal had a huge zinc. There, I said something nice about that engine. There is a zinc on the prop strut (largest chunk of underwater metal on the boat). Also one on the shaft, and one on the prop. They all last a good long time. Maybe this is why... I am about to make a 50 hour passage, expecting no wind. I may be able to tell by then.
I have read enough expert opinions that I'm open to at least half of them being wrong. They can't all be right!
Last post on this subject (for me, anyway) Score one for Stanley. After disconnecting my bonding wire from the engine, my zinc was down about 50% at 100 hours. More important, this is the first time I have been able to remove the zinc with the "pencil" still attached to the plug.
It looks like this has fixed the problem with crumbling zincs--so I won't have to pull the tube stack every 200 hours or so! That means it will be even more stuck, but I know how to fix that, too.
There is a zinc on the prop strut (largest chunk of underwater metal on the boat). Also one on the shaft, and one on the prop. They all last a good long time. Maybe this is why... I am about to make a 50 hour passage, expecting no wind. I may be able to tell by then. 
