BPZ8H-N

The Z means it is a radio suppression plug. If you are not getting a
buzz in your radio, don't worry about it.

Thanks for the info. This makes sense. I will not worry about this
and start stocking up with spare spark plugs with BP8H-N-10 marking.
That version is easily available in local stores and is quite cheap.

I will add a VHF radio into the boat, and I will see how it goes.

Jay Chan