Keel Bolt Question

[Rob Cohen "Soave" NS33 Westport, CT]

I was cleaning out the bilge of my NS 33 and discovered a heavy gauge insulated copper wire with a badly corroded end near one of my keel bolts.  the wire was led forward through the bulkhead. Removal of the owners cabin floorboard revealed it continued forward ( maybe to the anchor locker ? ) out of sight.

Inspection of the keel bolt revealed a stainless steel clamp and a handful of brittle corroded copper strands.  General cruising forums I see conflicting opinions ( not a surprise) about including keel bolts in a boats galvanic bonding circuit.  

Do other Nonsuch's have copper wire attached to a keel bolt ?  If so is there a better way to make the connection ?

Rob Cohen

s/v SOAVE

NS33 #009

Westport, CT

[Joe Valinoti]

It should go forward to the anchor locker and maybe the mast base.

 

Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA

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[Ward Woodruff]

The wire runs from the mast step ring to the forward keel bolt.  I believe its purpose is lighting protection. 

If you have enough wire length, reconnect both ends. You might want to run a new tinned wire. The existing wire does not have tinned strands. 

The stainless steel clamp is probably adequate to connect the wire to the keel bolt.  A crimped on lug should connect the wire to a bolt on the mast step ring. 

Ward Woodruff

N33 #8 Margery

Niantic Bay, CT

On Nov 6, 2023, at 7:11 PM, Rob Cohen "Soave" NS33 Westport, CT <rob....@gmail.com> wrote:



[Thor (26C Brentwood Bay BC)]

Most likely connected to the mast as a lightning ground.  

https://www.kp44.org/electric/MarineGroundingSystems.php

[Rob Cohen "Soave" NS33 Westport, CT]

Thanks Joe, Thor,  & Ward.

Sounds like the answer is : Yes, other Nonsuch boats do have a copper wire attached to their forward Keel Bolts.... so yes, I should restore the connection in my boat. 

I'll also add this to my seasonal checklist, I'll bet more than a few NonSuch have the same corrosion. 

On my boat the corrosion starting at the keel bolt shortened the wire enough that it no longer reaches.  The remedy will be to buy some wire, cut the old wire till I find sound copper splice in some new wire, tin the end near the keel bolt and reattach with the stainless clamp.  Sound right ?

I'm hoping the wire isn't for lightning protection, because the little I know about lighting protection is that if the conductor makes a right angle bend ( even if the conductor is heavy ) lighting is likely to keep going straight.  This I have seen firsthand ( my home has been struck twice).

Rob Cohen

s/v SOAVE

NS33 #009

Westport, CT

[Bill Wickett EX-22 #38 Makin' Time]

Hi Robb,

Glad you found the wire. I’m sure at the time the Nonsuch line was built, research on lightning strikes may not have been as advanced. Seems like a lot is still uncertain. 

Our 22 was struck in 2017. I was aboard in the cockpit.  The energy travelled down the mast and took 2 routes from the bottom of the mast. 

First was along that thick cable to the first keel bolt and dissipated out through the lead portion of the keel. This resulted in very fine pock marks in the bottom paint on the forward end of the sides of the lead portion of the keel. Like the bottom paint was blasted off in slightly larger than pin head sizes. None above the keel in the fibreglass

2nd area that the energy travelled to was along a slightly diameter smaller cable from the mast step to a bronze stud under the settee. This stud is one of the 2 fasteners for a Guest Dynaplate that a previous owner had installed on the hull. This is about a foot aft of the mast, forward of the keel. The damage there was scarring in the bottom paint. Looked like branches of a tree radiating out from the plate. There was no substrate damage. We did have the bottom stripped at the end of that season, and ran all new wiring to these 2 grounding points. (as well as all new mast wiring, light fixtures, etc)

https://www.marinco.com/search-results?q=Dynaplate

Good luck with your refit. Even though copper cable is expensive, I would suggest a full new run and not splicing to the old cable. 

Regards,

Bill Wickett

Hamilton , Ontario

[Brian M. Godfrey]

> Even though copper cable is expensive, I would suggest a full new run and not splicing to the old cable.

   I strongly agree.  At 30,000 to 120,000 amps for a fraction of a second, even one little Ohm of resistance in your connection could create an explosive heat buildup during a lightning strike.  And every connection can potentially be imperfect and add that resistance.  If you are touching it at all, you should consider replacing the whole run including the connectors on the ends.  Polish all contact surfaces.  And you should probably use Kopr-Shield within the crimps and between connectors and mast base or bolt or whatever.  You want tight connections, but you also do not want them to corrode. 
   Since the mast is the "lightning rod", it would be important to make sure there is no resistance between it and where your cable attaches to the mast base.  The butt of my mast has an aluminum plug to ensure that it remains round.  But my plug is pretty corroded where it rests on the mast base.  So there is probably a better path through the four retaining bolts.  But those are stainless steel, which is not the greatest conductor, so my electronics will provide the path of least resistance until they vaporize.  If I am struck.  Fortunately, my boat sits in a slip surrounded by at least a couple hundred other lightning rods.

   I became curious about how much power would be released by a big bolt of lightning passing through one Ohm of resistance.  A 120kA current across one Ohm of resistance will drop 120kV.  (I=E/R).  And since W(atts)=IE that would equal 14.4 Gigawatts of power - about 2000 Grand Coulee dams stuffed inside of that little brass connector, though for a very short duration.  So it's wise to eliminate every Ohm of resistance you can.

   Now I've got another thing to check on the boat next Friday...

--Brian M. Godfrey
  br...@wildbirdshop.com

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[Thor (26C Brentwood Bay BC)]

Lightning travels along the outside of a wire, this is why lightning rod cable is braided. A HF radio ground is the same and often copper foil is used.  All about surface area.

Unfortunately with corrosion you'll need jacketed wire, shrink wrapped connectors. Slather lots of lithium grease on the connector and you'll be fine.  Will it work..... no one knows.....

[Joe Valinoti]

West Marine and several other sites have great articles about lightning and grounding.

 

Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA

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[Ward Woodruff]

I’d buy a new length of wire and tinned crimp on connector. If the new wire is marine wire, the strands will be tinned. 

Pull the new wire in using the old wire as a pull wire.  Crimp a proper tinned connector onto the mast step end. I have a hydraulic crimper and dies if that helps. 

Ward Woodruff

N33 #8 Margery

Niantic Bay, CT

On Nov 6, 2023, at 10:29 PM, Bill Wickett EX-22 #38 Makin' Time <bill...@gmail.com> wrote:

Hi Robb,

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[Rob Cohen "Soave" NS33 Westport, CT]

Thank you all for the great advice....  I continue to learn and revise my plans.  I do have a couple questions :

1. As a shop for wire, it looks like "battery cable" is the term commonly used for the wire that is currently there.  Any other names or properties I should be searching for ?
2. Prices vary widely... links to sources others have used would be greatly appreciated.
3. I plan to be at the boat this weekend and will measure the gauge of the existing wire.  I'm probably going to replace the whole run so I could ( if it would make sense) update with any gauge wire.  Any suggestions on whether changing the gauge would offer any benefit ?
4. I'm still confused on physics behind the recommendation of not/never splicing.  Having worked for an electric utility as a capacity planner I rubbed elbows with power engineers who would dictate what we could and could not do ( to save a buck ) in our systems.  I seem to recall a splice used in lighting protection that would be inline, overlapped, and straight.  1 foot overlap, with multiple clamps, then 3 feet straight on either side of the splice.  I realize that in my case a new run is DEFINITELY easier and simpler, and POSSIBLY less expensive if I value my labor cost.  ( splices were VERY expensive in our project planning )....... Still curious about the physics behind the impact of a "fit-for-purpose" splice.  I also understand that the techs doing these splices had skills that I do not have ( yet ? )... which might be the strongest case for a full replacement.
5. Also, knowing the risks of a splice, it seems like the style of terminal ends would possibly be my weakest link.  In fact the hose clamp on the keel bolt sound superior to either a 1/4" tapped attachment or a large lug attached by an extra nut. When I see  how the cable is attached to the mast should I consider upgrade ?  General lighting protection standards say any change in direction needs to be minimized and that turning on anything less than an 8" radius is not acceptable.
6. If I have space, I will try and heed the 8" radius rule... likely going to be difficult n the mast end.

Sorry to belabor these points.... new owner / in the offseason / with way too much time to obsess about detail ..... AND my sailing season doesn't begin till April. 

Thanks,

Rob Cohen

s/v SOAVE

NS33 #009

Westport, CT

[Bruce Clark]

I have a bit of anecdotal evidence about the usefulness of this cable. I am on my second Nonsuch 30, 40 years apart. In 1982(ish) I was struck by lightning while on passage from NYC to Bermuda. The remarkable thing was how long it took to get hit in a very violent (rain, lightning, no wind) storm. We saw strikes with the water all around until we got ours. Damage was fairly minimal - all nav lights blew out, the voltage regulator on the alternator was fried (we were motoring since there was no wind and left over waves to deal with). I happened to be looking at the masthead when we were hit and watched the Windex blow off and fall to the ocean. We had a few tiny burn marks on deck where debris landed.

I assume the cable did its job and carried the current to the keel. There was no scorching either at the mast base connection or the keel connection.

BTW, I was holding the wheel when we struck and did not feel a thing.  Apparently there is a cone of protection under the masthead. After doing some research I did a magazine article about lightning for a long-defunct sailing magazine. What I discovered from about a dozen folks who had been hit was there was no clear pattern to the damage that occurred with the worst being one boat that sunk after the current exited through the hull (the boat was recovered from shallow water) so it could be examined).

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[JohnS]

Rob;

1. As a shop for wire, it looks like "battery cable" is the term commonly used for the wire that is currently there.  Any other names or properties I should be searching for ?

On my 26, the cable was (and still is...) #4 welding cable. Copper stranded, but not tinned. You may want to "up" the gauge to #2 or so - when I do mine, I likely will. (I want to find another nut to clamp cable to Keelbolt, rather than the SS clamp from the factory, but that's another story for another day)

1. I'm still confused on physics behind the recommendation of not/never splicing.  

Lightning, and electricity in general, is just a flow of electrons. Electrons (part of an Atom; protons and neutrons are in the centre, electrons fly around the outside. 

In wire, electrons flow around the surface of strands; not down the middle, simply because they try to keep away from each other. In the splice, one has to allow a path of "least" resistance to the electrons so that they can flow from one cable to the other, rather than exiting the cable bundle. 

Google "Faraday cage"; it's why airplanes tend not to get bothered by lightning (much! been on an A340 hit on final approach once... interesting...) and why stranded wire is better than solid.

 

On my 26C, the run is short; maybe 4 feet mast base to keel bolt. On your 33 a bit longer; the cost is not great either way.   

1. Also, knowing the risks of a splice, it seems like the style of terminal ends would possibly be my weakest link.  In fact the hose clamp on the keel bolt sound superior to either a 1/4" tapped attachment or a large lug attached by an extra nut. When I see  how the cable is attached to the mast should I consider upgrade ?  General lighting protection standards say any change in direction needs to be minimized and that turning on anything less than an 8" radius is not acceptable.

I expect to make a copper plate for keelbolt attachment; the mast base attachment will remain the same. I've got feelers out for a "spare" nut, maybe one will turn up in the spring. 

1. If I have space, I will try and heed the 8" radius rule... likely going to be difficult n the mast end.

I do think that, in my boat, the line is pretty straight, with one "kink" where the lightning rod goes through the floor by the mast base. I removed all floor panels to run other wiring there 2 years ago.

JohnS NS26C Bath ON

[Rob Cohen "Soave" NS33 Westport, CT]

Thanks JohnS ! 

"Welding Cable" brought up many options options to consider.

For those interested, the jump to heavier wire isn't as significant as I thought in small lengths.  ( HERE ) is a link to some options locally available ( for me ).  

Rob Cohen

s/v SOAVE

NS33 #009

Westport, CT

[Ward Woodruff]

Rob,

You don’t want to look at Home Depot. They have building wire. Building wire has larger diameter individual strand and the strands are not tinned. 

Don’t get welding wire. The strands are not tinned. 

You want boat wire. Try boatwireusa.com

$2.01 per foot for black #4

And terminal lugs like this for the mast step ring.  

 

These terminal lugs need to be crimped to the wire. An adhesive lined heat shrink tube is then applied to the wire/terminal to prevent water intrusion and subsequent corrosion. The hole in the ring end of the lug should match the bolt diameter you are attaching to. 

Ward Woodruff

N33 #8 Margery

Niantic Bay, CT

On Nov 8, 2023, at 5:00 PM, Rob Cohen "Soave" NS33 Westport, CT <rob....@gmail.com> wrote:

Thanks JohnS ! 

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[Brian M. Godfrey]

   Yes, and put some conductive/anti-corrosion grease inside, then borrow that hydraulic crimper and make sure it is done right.
   I think the trick is going to be how you make a really reliable and near zero ohm connection to the keel bolt.  I bet they don't make these lugs with a big enough hole, and is there enough bolt sticking up to put a nut on if they did?  I really need to look at my boat and see how it was done.  The clamp thing seems awfully iffy.

   About the zero ohms objective: if you measure it with a multi-meter with one or two AAA batteries inside, you may measure zero ohms.  You are putting very little current through it and just about any crimp is likely to have plenty of contact area within the  crimp to give that reading.  Lightning is going to try and push many thousands of amps of current through that crimp, so you want the absolute maximum contact area between the cable and the lug or it will look like more than zero ohms to the lightning bolt.  That's why the hydraulic crimper is best - IF it puts in a nice wide crimp.  Most hand crimpers make a fairly narrow crimp because that's all the strength most people have.  The hydraulic should be able to put in a wide crimp and crimp it really tight and uniform.

   About the lightning running up the outside of the wire thing.  It's kind of like that, but not exactly.  If the current ran only up the outside of a wire, then all larger capacity electrical wire/cable would have a large plastic core with copper foil around it.  That would be lighter, cheaper, less unwieldy, and much easier to pull. 
   Electrons repel other electrons in all directions.  So while there is the tendency to drive each other outwards, those electrons on the outside are also driving inwards.  What you are really going to see is close to zero current in the center, but the current increasing exponentially as you move outwards towards the edge of the cable. 

--Brian M. Godfrey
  br...@wildbirdshop.com

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[JohnS]

Ward - you are absolutely right - get the good stuff. The Admiral insists that things are done once, and done well, with cost not a deciding factor. The material cost for the proper items is nothing compared to your time. Thanks for bringing this important point up.

On a related note - when removing my 12v cables to go from welding wire (#4) to #2 boat wire, over half of the original crimps were loose. By loose, I mean, pull off the cables with your pinkie-loose. What an eye-opener.

The 12v #2 cables I used were done by the chandlery, and they do a very good job. The only remaining welding cable is the lightning cable mast to keel; that's on the "to-do" list.

JohnS NS26C 046 Bath ON

[Brian M. Godfrey]

   That foot long splice that the linemen make maximizes the contact area between the two cables.  That is much more important for the high current of a lightning strike than it is for the much lower current of a power line.

   I think adhering to the 8" radius rule is going to be difficult.  You'd need to do it where you connect to the mast and to the keel bolt, too.   I think the 90 degree jog from the cable entering the lug to the keel bolt is going to present a much greater problem than a tighter than 8" radius in the cable.  Plus, we've had anecdotal evidence that it might not be a problem, though I don't know if those were maximum, 120kA, strikes or "just" 30kA strikes.  :-)

   I'm curious if anyone knows what happens to the keel bolt during/after a lightning strike.  I can imagine the shock separating the bolt from the lead in the keel.  I doubt that the lightning current lasts long enough to melt and re-flow the lead, though I suppose it might.  It would probably happen too fast for the keel to drop, but might leave the nut a tad loose.

--Brian M. Godfrey
  br...@wildbirdshop.com

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[Steve Currier '86 N 36 #41 Caper TYC New London CT]

When I replaced the cable on my Nonsuch 36, I upsized the boat cable to a size 2, and used FTZ power lugs, which are heavier and longer than the standard.  These will take double crimps side by side, which I do with a FTZ  hand crimper which has been calibrated to size, I turn the lug 90* on the second crimp which gives you a cold welded bond.  Then use double wall adhesive heat shrink on the connections.  At the keel bolt end, I didn’t like the idea of the connections sitting in any bilge water so I used a length of 1” heavy wall copper pipe, flattened it, drilled holes for the appropriate size lugs and the keel bolt, then bent it in an “L” slid the end over the keel bolt, added a washer and nut to both ends and torqued the connections tight.  It was the best solution I could come up, still looks good after 5-6 years.  Hopefully a good solution.

Steve Currier

Nonsuch 36 #41 Caper

Old Lyme, CT.

Thames Yacht Club

[Joseph Carroll]

I have a heavy gauge wire that attaches to the mast step and connects to the keel area. It is not severely corroded, however, I believe that it grounds the mast should it be hit by lightning. I never had an issue with lightning, however, there have been storms where lightning came down into the cove where my boat is moored with another 100 + boats. Boat owners have reported damage to electronics due to lightning strikes.  Recommend that you revisit your problem, and replace the wire. 

Joe Carroll, Madaket, Nonsuch 30 #56

[Joel White]

My Boat US insurance mandated an updated Boat survey this year for renewal. The surveyor pointed out the mast grounding cable attached to the keel bolt was long and sagged into the bottom on the bilge, sometimes immersed in water. His report made a "recommendation" to lift this out of the bilge water. Of course the insurance underwriter is not insisting the grounding cable is repaired by a qualified boat yard and receipt provided before they will renew my policy.

Has anyone had this experience? More important, is grounding the mast to the keel bolt a risk? I expect most of our NS boats are grounded this way. Securing the grounding cable above any water in the bilge is an easy fix. Relocating the cable altogether is a task that seems unnecessary for overall safety and protection of the boat.

Opinions or recommendations appreciated.

Joel White

Rumaki

NS30U 303

[peter farley]

Be very careful with boat US. I had them for ten years no claims and then they wanted a survey. In the meant time they had significantly decreased the value of my boat and dramatically changed the prorating of replacements , the year they asked for the survey. Basically if it was older than four years you paid for it. My boat had been in Canada so the surveyor failed the fuel system for not having a US coast guard approved fuel lines. If he had cross referenced the numbers he would have found out they were approved. I had to replace all the fuel lines with type A1 and the filter because it had a glass bowl. After that they did not agree with the surveyors valuation. The surveyor they had me use! I had to appeal it to the underwriters who agreed to use the surveyors value for an extra $800 a year. I have American Modern now better coverage and half the price. I believe boat US only wants to insure newer boats and is trying to get rid of us old boats.

Peter Farley

Knot in a hurry u30 # 328

Keyport nj

[Brian]



Joel

Try Progressive, they have treated me well so far.

Brian Cayer

Spirit~Wind

N30U 419

Westbrook, CT

On Jun 21, 2025, at 11:55 AM, 'peter farley' via INA Nonsuch Discussion Group <INA-Nonsuch-Di...@googlegroups.com> wrote:

Be very careful with boat US. I had them for ten years no claims and then they wanted a survey. In the meant time they had significantly decreased the value of my boat and dramatically changed the prorating of replacements , the year they asked for the survey. Basically if it was older than four years you paid for it. My boat had been in Canada so the surveyor failed the fuel system for not having a US coast guard approved fuel lines. If he had cross referenced the numbers he would have found out they were approved. I had to replace all the fuel lines with type A1 and the filter because it had a glass bowl. After that they did not agree with the surveyors valuation. The surveyor they had me use! I had to appeal it to the underwriters who agreed to use the surveyors value for an extra $800 a year. I have American Modern now better coverage and half the price. I believe boat US only wants to insure newer boats and is trying to get rid of us old boats.

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