briandrew":36vi2k8c said:
We have just purchase a 2009 R25 which is kept in saltwater at a Marina. When we hauled it out of the water to replace a broken actuator we noticed the large zinc on the end of the prop was entirely gone. I am pretty sure there was a new one installed 3 months earlier by the previous owners. This obviously has us concerned and led me to look into the bonding system of our boat. While it appears that there is some sort of bonding system in place, my understanding is that all this bonding should lead to a sacrificial zinc I can not trace the wires. The only zincs we have are 2 small thruster zincs, 2 trim tab zincs and the prop zinc. Is it possible that the bonding is led to one of these points?
Hello Brian,
CONGRATULATIONS on your new tug and WELCOME to Tugnuts!
The bonding system on the Ranger Tugs uses a GREEN wire which connects all under water metal to EACH OTHER and the DC GROUND buss. There is galvanic current flow between dissimilar metals when under water (or, an "electrolyte" solution)...hence the stainless steel prop shaft with a BRONZE prop attached results in galvanic action whereby the Stainless will deteriorate due to anodic (galvanic) action (since the bronze is MORE CATHODIC or STABLE or PASSIVE). Consider your prop nut zinc a WEAR item which requires REGULAR replacement. Don't wait till it is falling off (or GONE) to replace it. They cost something but are DIRT CHEAP compared to the cost of a new prop shaft. Note that, since the BRONZE propeller and SS Prop shaft are touching each other, the BONDING system is not in play here. The galvanic action from dissimilar metals is going to happen whether the green wire is connected to the engine block (electrical continuity remains through engine block to transmission to prop shaft).
Also, realize that the prop zinc may look "OK" on the outside but have enough deterioration on the INSIDE that it no longer makes ELECTRICAL contact with the prop shaft...and, thus becomes USELESS. If it 'wiggles' when you grab it...it's probably not longer a "low resistance" electrical connection and therefore can't do it's ANODIC thing...which means your lovely SS prop shaft is getting eaten instead...YIKES :!:
The green bonding wire DOES connect to the prop and rudder (you DO have a rudder zinc, right?) zincs. This results in protection from galvanic (dissimilar metals) corrosion discussed above, and
-Serves as the AC grounding circuit on the AC side
-Provides a path to ground for the high voltages and currents associated with lightening strikes (NOTE: need AWG 6 wire size as MINIMUM for lightening protection)
-Prevent damage to underwater hardware from STRAY CURRENTS originating WITHIN your boat by providing a path for stray current directly to battery negative which precludes their passing through any underwater hardware. STRAY CURRENTS commonly happen, for example, with a bilge pump float switch which has a leaking seal...stray current corrosion sets up at the positive terminal thus disabling the switch and your bilge pump. Now, the puddle of bilge water would be slightly electrified and become the source of stray current which will be safely and harmlessly conducted back to your battery's neg post by the bonding system.
Bonding is a HUGE topic with numerous advantages and disadvantages. All I know about it is from reading and limited boat ownership experience in salt environments. Rapid zinc loss in a marina environment where you and your neighbors are connected to dockside AC introduces all kinds of other hazards. For example, stray current leak from another boat could...oh, boy you better get out your Volt/Ohm meter and do some testing. See the source below...Nigel describes several simple test to run on YOUR boat/CORD and the shore-side AC receptacle.
Get the book by NIGEL CALDER titled
Boat Owner's Mechanical and Electrical Manual it is OUTSTANDING in explaining all this and more. NOTE: this is not my book or a friend of mine's book; I have no financial or other interest in making this recommendation. It's simply an excellent resource!
Fair Winds,
/david
