Originally Posted by Northern Spy
That appears to be a fairly standard end loaded full port ball valve. It will have a chromed brass or 316 ball. The seats and stem packing are PTFE (aka Teflon). There really is nothing to lubricate there. Most effective maintenance you can do for them is cycle them once a month to keep growth off.
I agree with Northern Spy but so many people want to grease ball valves that Groco added a zerk fitting to their ball valves. If you still feel the need to lubricate your valves, and they are equipped with drain plugs, you can install your own zerk fittings.
If they are not equipped with drain plugs, they are not really Marine valves and you should go ahead and replace them with Groco valves.
Are the valves all above the waterline?