Matt....
You probably don't need any kind of blower with an outboard, but it wiil
depend on your fuel tank installation. Requirements are in CFR, Title 33,
Parts 175 and 183, as shown below.


Ref:
http://www.access.gpo.gov/nara/cfr/c...rch.html#page1

Title 33, CFR.....

Sec. 175.201 Ventilation.
No person may operate a boat....

Sec. 183.610 Powered ventilation system.
(a) Each compartment in a boat that has a permanently installed
gasoline engine with a cranking motor must:
(1) Be open to the atmosphere, or
(2) Be ventilated by an exhaust blower system.
(b) Each exhaust blower or combination of blowers must be rated at
an air flow ... etc....


Sec. 183.620 Natural ventilation system.
(a) Except for compartments open to the atmosphere, a natural
ventilation system that meets the requirements of Sec. 183.630 must be
provided for each compartment in a boat that:
(1) Contains a permanently installed gasoline engine;
(2) Has openings between it and a compartment that requires
ventilation, etc......
(3) Contains a permanently installed fuel tank and an electrical
component that is not ignition protected......
(4) Contains a fuel tank that vents into that compartment; or
(5) Contains a non-metallic fuel tank:
(i) With an aggregate permeability rate etc......
(b) Each supply opening required in Sec. 183.630 must be located on
the exterior surface of the boat.