On a 40-foot boat, I think there are some great alternatives, all of which could be done with or without the cameras. First, before leaving on any long-term cruise, Clean the engine-room bilges and lay down new marine oil-absorbent pads under the engines and gears, which makes it easy to see if any oil is leaking.
If you are keeping an eye on your exhaust smoke while you are running and don’t see evidence of lost oil, where else can you look? The most likely place is in the bilge. Theoretically, oil could also escape into the coolant water. The most likely place to lose oil would be through very smoky exhaust. If there is a serious loss of oil, gauges and alarms will let you know.
A change in engine temperature should be your indicator of lost coolant water. Again, if it’s not steaming out the exhaust, it will most likely spill into that clean and dry bilge.
We have a gear temperature gauge. If there is a loss of gear fluid, it will usually be in the bilge.
Listen, listen, listen. Don’t use the stereo while running, because you may not hear important changes in the engine.
Always take a close look at the engine room before you leave. Inspect belts, hoses, seawater strainers, fuel filters and oil levels.
Occasional inspections of the engine room are good. A great time to do this is right after you start the engines. Any time I have had a problem with my engines while they were running, it happened quickly. One last thing to look at while running is the shaft logs, to make sure there is little water leaking and they are turning smoothly.