Originally Posted by BlueFlyer
The OEM units are spark shielded and will not cause vapour or gas explosions. Non marine
units for autos, etc create fat sparks when used. Not a problem for autos, but not too good on boats! This applies to both starters and alternators.
This only applies to gas powered vessels. The spark arresters are usually just a screen
on the back half of the case. Still, if that is important to you, you can have an alternator
shop build one with the spark arester for around $100. Whatcom Electric
will build an alternator
with the same internal components and a spark arester as a Balmar
in an AC Delco case.
It is something to be aware of, but on a diesel
boat it really is less of a concern in the same way many diesel
powered boats are not fitted with blowers but gasoline boats are.