Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

Venting of Gasoline Boats

In general, the previous engine vent recom-

mendations will serve properly on a gasoline-

engine boat. Gasoline vessels, however, must

additionally meet specific legal requirements

under the Code of Federal Regulations

(CFR). Be sure to study and follow ABYC

standards H-2, Ventilation of Boats Using

Gasoline, and H-24, Gasoline Fuel Systems.

Refer to Chapters 4 through 6 on fuel sys-

tems. Ensuring a proper installation mini-

mizes leaks and spills, which is critical with

regard to safety and to reducing the loads on

the ventilation system. Also see pages 87

through 89 concerning ethanol-gasoline prob-

lems in fiberglass fuel tanks.

Note that the requirements for ventila-

tion regarding gasoline apply to any blend of

gasoline, including ethanol gasoline such as

E-10, E-15, or even E-85 (10%, 15%, or 85%

ethyl alcohol by volume).

Basics for Gasoline

Ventilation

In the United States, the law requires that

every boat with a permanently installed

gasoline engine must comply with Subpart

K—Ventilation, 33 CFR, sections 183.601

through 183.630. There are no exceptions:

main engine, generator, or any other

gasoline-driven device that is permanently

mounted in the boat. Note that these regu-

lations do not require powered ventilation of

engines or tanks that are not permanently

mounted. So a small sailboat set up to

remove its outboard engine from a bracket

and stow it in a locker with a standard

6-gallon (23 L) portable fuel tank stowed in

another locker would have to install only

passive or natural ventilation for these

locker spaces, as we’ll discuss later.

In any case, allgasoline-engine boats

must comply with the CFR and be ventilated

accordingly, unless—under the CFR—the

engine is installed out in the open—“open to

the atmosphere.” This is specifically defined

as a compartment or space that has 15

square inches directly exposed to the open

outside air for every net cubic foot of com-

partment space (1,041 cm^2 exposed to the

open outside air for every net m^3 of compart-

ment space). A small cuddy-cabin boat with

a gas engine under the cuddy would likely

qualify as “open to the atmosphere” if the

cuddy was wide open along its after wall,

with no bulkhead closing it off. Critically, if

any provision at all is made to seal this open

after face of the cuddy with even a canvas

cover, it is no longer “open to the atmos-

phere” and will have to be ventilated accord-

ing to the CFR.

Net Compartment Volume for

Gasoline Ventilation

The net compartment volume is calculated in

exactly the same way we calculated the net

compartment volume of After Burnerear-

lier. To work out the ventilation require-

ments, you need to calculate the gross and

then net compartment volumes for any area

containing gasoline engines. As we did for

our example After Burner, you subtract all

permanently installed, built-in machinery or

equipment such as

engines

tanks: fuel, water, and so on

generators

batteries

accessory equipment and machinery

such as water systems, air-conditioning

units, compressors, and so on

You cannotsubtract items that may be

stowed in the space but removed, such as

docking gear: fenders, line, and so on

anchors and line

stowed furniture or food

anything else that may be removed from

the compartment

Powered Ventilation Is

Required

Every gasoline-engine boat mustbe venti-

lated by a powered exhaust blower. These

mustbe ignition-protected, (nonsparking)

exhaust vent blowers. The rate of flow in cfm

or m^3 /min. is determined based on net com-

partment volume using the Table 16-2.

PART FIVE:VENTILATION, AIR-CONDITIONING, AND HEATING