Read an application note from the load dump protector
manufacturer (when still called SGS Thompson) about 1996.
It's more than just putting a suppressor diode on output or
using larger components. As they noted:
The protection at the alternator level is a quite new concept and
all the technical problems do not seem to be completely solved.

The problem has long been known and has long created
problems. Solutions have been installed for decades. Still an
adaquate design has not been perfected. My first experience
was in early 1960s when alternators used germanium diodes.
The problem has been understood that long. Thompson
Electronics does make load dump suppressors and are a major
electronic supplier to GM. However I don't know if GM uses
the parts (model numbers provided in the previous post) from
Thompson.

As Glenn Ashmore has so accurately noted, load dump is a
serious electrical threat even to powered electronics. Simply
look at the voltages that can exist on a 12 volts system
(which is why electronics whose specifications specifically
state load dump protection cost more). Especially susceptible
are boat power systems. Master battery switch must be
designed 'make before break'. IOW during battery switchover,
a battery must be always connected to alternator. Better
designs even transition the switchover to soften the 'change
of load'. Cars typically don't suffer as easily BUT will be
more susceptible as more functions become electrical (ie
steering) and voltage is raise from 12 volts to the new 42
volt standards.

Glenn Ashmore wrote:
GregS wrote:
Sounds like they need to make them properly, with higher voltage
diodes.

It is a matter of size and economics. Diodes capable of handling
high voltages and high amperages are large and expensive.
Leece-Neville makes such a rectifier for heavy EMT and construction
equipment but it is a box separate from the alternator and cost more
than any of us would want to pay.

99% of the alternator installations are automotive and do not have
master battery disconnects. Also automotive alternators seldom run
at a significant percentage of rated capacity for very long. The
major load last for only a few minutes to replenish the cranking
power.

Boats with house banks on the other hand usually do have master
switches and either the switch must have a capability to disconnect
the field current before opening the battery circuit or a bypass
diode of some kind on the alternator. To do otherwise is a pretty
good bet that eventually you will fry the rectifier diodes.
Unfortunately boats make up a microscopic percentage of the
alternator market so this type of protection is not provide for.
...