the most common cause of boat problems is lack of proper maintaince.
if "just puttered out" means you started it, it ran fine, you got up to speed and it suddenly began losing power and turned off after maybe 5 minutes of running, wouldnt restart (possibly wouldnt even crank until 15+ minutes had gone by), thats what people describe when they didnt change the impeller and the motor got HOT and seized up with NO cooling water to keep it from overheating.....
and then there are all the other routine maintaince things, spark plugs and filters and......
if you dont keep them maintained they start having problems.
if you want to add what year, make and model, and a more informative description of what happened, perhaps we can be more help.
but at this point in time, check your maintaince records and figure out what you missed.