How often do you change Spark Plugs in your boat?

I have a 2003 Ebbtide Campoine 18.5' Mercruiser 4.3 V6 Alpha one. I just pulled it out of storage started doing the normal routine of cleaning and mechanical upkeep. Gear lube and Oil has been changed before storage (everything up to par) my question is regarding the spark plugs...



When should you change them? Is 3 years too soon? (I'll pull one out tonight and look for corrosion, etc).



Also any other spring time engine recommendations for a 4 year old boat?How often do you change Spark Plugs in your boat?
When is the last time you changed your water pump impeller . if you cant remember you maybe due. Real important they get weak with age and take a set when sittng to long and become weak.

If you pull your plugs and the white insulator around the center electrode is light brown they are good . A correct burning plug thats what color it should be Be sure to check all the bellows behind the drives bellhousing and look for drycracking between the webs. if you see any you need it changed.How often do you change Spark Plugs in your boat?
As you mentioned, just inspect them. If, the Anode/Electrode not look badly worn they probably OK for another season.

I not have a boat now and am looking, but, the last I had, I kept year round in a slip. Summer it was beached at the camp area and used most everyday. I usually changed plugs in it every summer. It probably got more use than a car.

I tried to find some pictures, many manuals show different plug wear. It a personal preference, but, I do use a little Anti-Seize on my Plugs.
You fire up on the old spark plugs from the season before, the motor should have been ';fogged'; before it was winterized, burn the old oil out of the motor at start up (IT SMOKES), THEN replace the spark plugs, why foul up ';NEW'; plugs ? they should be changed every spring, changing over to ';NEW'; spark plugs makes a world of difference on an outboard motor, don't forget, it burns ';MIX';, not straight gasoline like a car (if it's a 2 stroke outboard), so they get dirtier faster than a car's spark plugs.
I change them at least every 100 hours and clean them at least once a year.
Just do it every year when it comes out of storage, they are cheap.