Hour meters are off??

On diesel engines, hour meters are usually switched on by oil or fuel pressure.
Key on, engine not running usually does not enable the hour meter.
That is, unless somebody has Frankensteined it.

If your reading thousands of hours, a few hundred may not be to big of a deal of error.
Or if the meter(s) were replaced long ago.

Hours are just a guide, A complete survey and records tells more about the engine.

It woudl really help if you d tell us what kind of meters you re talking about. External Hobbs meters or electronic meters in the engine electronic displays ???

hobbs style meters aren’t the most reliable piece of equipment. I ve had many fail over the years. This likely explains the difference.

if electronic engines, a discrepancy that big needs to be explained.

Meters aren’t going to be running just with the keys on.

Do you have trolling valves or run one engine only for slow speed trolling? Not that uncommon if boat handles better for trolling on one side vs the other or if you only have power steering on one engine?

Mine had meters within the tach gauges. Couple days before she sold, noticed the digital hr read- out on one motor was jumping up by hours instead of minutes. Next day it was fine other then many more hours then the other.

I have to laugh as it reminded me of a time decades ago when I rented a truck in Atlanta and drove it home to Charlotte, approximately 250 miles. I noticed the odometer only added a mile about every ten. I go to check in with the rental company and try to explain to this scary woman that the mileage was incorrect as it only recorded 30 miles and I actually drove around 250. She was belligerent and made it clear they only went by the odometer. At her insistence, I was only able to pay for 30 miles. She also had no intention of having mechanics check it. A reminder that such devices as hour meters can sometimes have minds of their own and it's maddening when they choose to.