Unexposed keelbolts

[Dougal]

About to use a keel bolt for ground on SSB antena, only to realize that all my keelbolts are fully encased (Evasion 32).

They're all completely glassed over! Is it ok to grind down one of these bulges to expose the bolt?

 

[noswellplease]

That appears to be a rather drastic action and I would guess counter productive. For keelbolts to provide earth there would need to be conductivity from the bolts throught the GRP the Gellcoat the Antifoulant to the water. GRP is a insulator as far as I know. I would think your earth could be your engine casing which is proably connected to your sacrificial anode and to the seawater and earth. Now what is very important is the insulators on your aerial being clean and free of salt deposits. Also tuning your aerial once you have it set- up for the frequency you will be using most of the time. Hope this helps. Russell

 

[Dougal]

No, the bolts are holding on a massive cast iron keel. That's the ground, not the GRP. Most experts and manufactures state the engine should ONLY be used as a last resort.

 

[William_H]

One thought is that if you know where the bolts are you could simply drill a small hole down hopefully into the bolt head (until you get iron filings come out) them tap a thread into the bolt head. Then fit a bolt with lug and wire under the head. Use a steel bolt and give it plenty of grease and paint when finished to reduce corrosion. Be very carefull with the thread tap as they snap off very easily. I imagine like 3/16 or 4mm but get the correct drilling size for the tap and bolt.
You may have to partly expose the bolt head but even this would be better than exposing all of the bolt head to remove the keel bolt.

You might consider just drilling down into the centre of the keel until you hit iron.Then tap a thread into the cast iron, But it could be a long way down requiring very long tap and bolt.
Good luck with the SSB olewill

 

[Dougal]

Great idea - many thanks.

 

[Billjratt]

For the SSB (I assume xmit as well as rec) you really should have a flat copper band as the Gnd connection.. how many different metals are you prepared to connect together in the bilge? If you can possibly afford it, a dynaplate works well, does not compromise any other bits, and will still be connected when you really need it for that offshore stuff - unlike the fizzing keelbolt...