"If it works on your car it should be fine on a boat."
Those inept, self-serving, untrustworthy technical employees at places like Westinghouse, GE, Delco, Raytheon
...pretty much everyone in the "electrical gizmo" businesses says that spikes ARE normal. Batteries WON'T absorb them all. And that they all get many devices back for repair after spike damage, from routine installations.
They do not install spike protection devices in their equipment
(usually) because all spike protection devices cost money
, and eventually they wear out and fail from repeated spikes, making internal protection a futile venture that only makes their product economically uncompetitive.
Case in point, Delco made a car alternator
series with added internal spike protection, to protect the "new" computers
in GM cars. The new alternators had higher failure rates because of the spike protectors eventually failing (i.e. at 100k miles) and shops didn't want to deal with them. So, they stopped making them that way.
If your electronics
are running off one breaker, it is also pretty simple to put a protection device on that breaker--and protect them all at once, inexpensively. Last time I did a major rewire, I put a couple of spike protectors (transzorb, zener diode) in a small box, added a piezo buzzer that will go off if any of them fails open, and an extra crowbar fuse, so if the protection fails shorted, it will also immediately blow a fast-acting fuse in the box. Maybe $25 in parts
in a silver "cigarette box" next to the breaker panel. No icebox
or big things like that on it--but all the instruments are protected.
Adding a simple diode or transzorb across the power line AT each device would work almost as well, very simple and cheap
, while it lasts.