Mercruiser Parts and Service Customer Service Issues

We own a [redacted] V8 Mercruiser engine installed on our 24 ft. Crown Line boat. It was functioning well a week ago. Yesterday, when attempting to start the boat, we noticed that it turns over but the spark plugs are not firing. As it's a holiday weekend, finding a mechanic is proving impossible. We have a friend with a diagnostic tool for cars but unsure if it's suitable for a boat. Any advice on troubleshooting while waiting for a Mercruiser Mechanic would be greatly appreciated. Thank you for any assistance. Unfortunately stuck at home on a lovely weekend here at Norris Lake. - A. K.