It should be a Marine Starter in order to be certified as "ignition proof" (protecting from sparks in your bilge area).  Here is one of the many threads about starters:
http://www.smwebhead.com/phpBB3/viewtopic.php?f=11&t=14136&hilit=starterIf you had to 
temporarily use a non-marine starter, you would want to be extra careful about ventilation and checking for fumes before each start.
 
					
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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
  tow: 2017 Honda PILOT EXL-AWD
  prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings