I have seen situations where there is little underwater metal, boat not kept in a high current marina, and small electric not bonding their through hull metals.
Any serious system needs to be bonded.
http://www.powerandmotoryacht.com/video/maintenance/boat-bonding-system-multimeter-checks
Not sure why we are even questioning this.
No, any
serious system does not always
"need" to be bonded. A well designed system can survive just fine without bonding underwater metals and in many cases will do better than a bonded system.. The key words there are
well-designed system..
Please read Stan Honey's excellent article on this...
Marine Grounding & Bonding
Stan Honey for Practical Sailor & West Marine:
"Bonding and Electrolytic Corrosion Due to Hot Marinas
Do not bond any thru-hulls or other immersed metal that can be electrically isolated. Specifically, keep your metal keel/ballast, your metal rudder shaft, your engine/prop, and all thru-hulls electrically isolated, from each other, and from the engine.
It's worth understanding the reason.
In an increasing number of marinas, there are substantial DC electric currents running through the water. If your bits of immersed metal are bonded, the electric current will take the lower resistance path offered by your boat in preference to the water near your boat, and the current will flow into one of your bits of metal, through your bonding wires, and then out another bit of metal. The anodic bit of metal or thru-hull that has the misfortune to be on the "out current" side of the current running through your bonding system will also become "out metal" and will disappear, sometimes rapidly.
Your zinc is only intended to protect against the modest galvanic potentials and therefore currents that are caused by the dissimilar metals that are immersed and electrically connected together on your own boat.
Your zinc is incapable of supplying enough galvanic potential to protect against substantial DC currents that may be flowing in the water. These DC currents in the water will cause electrolytic corrosion to your bonded thru-hulls or metal parts."
Nigel Calder:
"Unbond & Isolate
The opposite approach to bonding and cathodic protection, which is more prevalent in Europe than in the USA, is to unbond all underwater fittings, isolate them electrically, and allow them to reach equilibrium at their own voltage....
We had an unbonded boat in the warm tropical and semitropical waters for 12 years and no signs of corrosion"
Nigel's own boat unbonded.....
It is always interesting when we paint or assume marine corrosion/bonding as a black & white issue. It is far more complex and each vessel needs to be considered on its own merits, use and installed systems or lack there of. It sure would be nice if it was just as simple as always bond or never bond. My job would be sooo much easier.........
There are many well respected industry
experts in this field who don't necessarily believe in bonding or who physically don't do it on their own vessels. Nigel Calder & Stan Honey come to mind, and two who do not
always believe in bonding. It is hardly black & white issue and certainly not mandatory or a must do.
As a marine electrician I get to do this stuff every day. I specialize in corrosion as just one of the many electrical systems areas I work with. I don't paint each vessel with the same brush, you just can't do that.
My own vessel is
not bonded, never will be, except for lightning and the AC / DC grounding bond. Many of my customers boats are bonded because they have suspect wiring issues they don't want to spend the money on to address. Even more, most bonding systems are so corroded they are really doing nothing and on many boats one can't even measure continuity between fittings. This can actually serve to create issues rather than solve them.
I have some 40+ year old boats I work on that are unbonded with perfectly operating 40 year old tapered cone bronze seacocks. Not all builders bonded underwater fittings yet even at 40 years + these unbonded fiberglass vessels exhibit zero issues and show no signs no de-alloying of the below water metals...
This is not just a black and white answer and on many boats, with unknown wiring condition, wet bilges etc. bonding
can be beneficial (certainly might buy you some time in an on-board DC leak).
On a boat that is perfectly wired I personally prefer unbonded, as my own boat is. I don't suggest everyone unbond however but organizations such as Practical Sailor, The West Marine Advisor, Stan Honey, Nigel Calder and other well respected individuals have and do.
