One thing remains constant with marine electronics: When you buy any unit, the very next year you will be able to buy a model with more features and better performance for the same money, or a model with the same features and performance for considerably less.

It's kind of a catch-22: If you don't upgrade, you miss out on the use of a new unit for a whole fishing season. If you buy a new unit, you face the same dilemma a year later.

I'm convinced that the best strategy is to upgrade only when new units appear with enough real-world improvements for your fishing style to be worth the extra bucks.

If your present unit develops a terminal problem or just outright dies, a potential replacement won't have to show you much new technology to look better than what you've got.

Still, getting one fixed sometimes takes less time and money than rigging a new unit on your boat. A call to your ailing unit's factory customer service center is worthwhile, and might even surprise you.

Marine electronics evolution happens at a rate as fast as that of computers because, like almost everything electronic these days, they are computerized.

On the down side, this includes them in the growing family of disposable electronic products, so repairing a unit that's more than a few years old is often not an option.

The amount of time that an LCD screen or computer component exists before it becomes obsolete and unavailable can be less than a year. This means that if a fish-finder or GPS unit breaks down after just 18 months, the component needed to repair it may no longer be manufactured.

To combat this problem, some electronics manufacturers offer trade-in allowances on recent models that can no longer be repaired. You send in your old unit and get a discounted price on a more recent model that is new or factory-reconditioned. The replacement may be able to use your old transducer, GPS antenna and power cable, saving you some rigging time.

Replacing a unit that works great for you now, just for the sake of a few extra bells and whistles, doesn't always make good economic sense. Your old unit will continue to find fish or help you navigate just fine.

If your fishing changes and you need display detail or functions that your old unit doesn't have, then it's time to consider an upgrade. A typical situation might be discovering how good a sonar picture or some of the newest GPS mapping software looks in color and then deciding to upgrade to a color unit.

Don't try this at home without being prepared for a budget hit, but spending just one day in somebody else's boat watching a color unit can lead to an upgrade.

When you approach the half-century-old mark, another possibility pops up. If you'd like to be able to see small screen details without digging out your reading glasses, a new unit with a larger screen can make it happen.

My bottom line recommendation is to stick with what works until it no longer works, then upgrade and don't look back.