The needle on your boat's temperature gauge is rising. This almost always means you have a lack of water flow in the cooling loop. Outboards, most small inboards and I/Os don't have radiators like your car, and instead use the water they are floating on to cool the engine. If that water stops flowing, the engine heats up and can ultimately fail.
Solution: Trace the source. In a vast majority of cases, the problem is an obstruction in the raw water intake - like weeds, mud or a plastic bag. Locate the intake and clean it out.
A loose hose clamp or a split or burst hose can also slow water flow, and it can spray damaging moisture around the engine.
Prevention: You also need to regularly service and replace the water pump impeller. Also look at the condition of its housing. Scarring or pitting of the metal housing can cause even a good impeller to lose pumping power.
Carry Onboard: Soft wire or rod to snake intake clogs, spare impeller.