Engine Compartment Construction; Engine Compartment Ventilation; Engine Compartment Seams; Clearance - Mercury MerCruiser Product Applications Manual

Engine

Engine Compartment Construction

Avoid serious injury or death and property damage due to improper boat design and
construction. Always adhere to all applicable Marine Regulations (United States Coast
Guard [USCG], European Union - Recreational Craft Directive [EU-RCD], and so on) and
the standards they reference (American Boat and Yacht Council [ABYC], Society of
Automotive Engineers [SAE], International Standards Organization [ISO], and so on)
when designing and constructing the boat and the boat components, such as the engine
compartment, fuel delivery system and exhaust system.

Engine Compartment Ventilation

See Section 4—Air Intake System.

Engine Compartment Seams

Avoid engine damage. Water, that runs onto the air intake, may enter the engine and
cause serious damage to internal engine and/or turbocharger parts. Engine compartment
design must not allow water to run onto the air intake or air filter.
Exercise care in the design and construction of the engine compartment. Seams must be
located so that rain water is directed away from the air intake system and electrical system.

Clearance

IMPORTANT: The engine compartment must provide a minimum of 13 mm (½ in.)
clearance between the boat and any component on the engine (i.e. exhaust manifold,
elbow, oil pan, transmission case, etc.). This allows for engine mount deflection during
operation.

Engine Bed Requirements

The engine bed (i.e. stringers) must be designed to support the G-forces imposed by the
engine during the most severe duty. The bed must also handle the torque produced by the
engine and the thrust generated by the propeller. Deflection of the engine bed could stress
the engine components, causing possible engine misalignment and transmission failure.
The proper design of the engine bed varies considerably from one boat design to the next.
Therefore, Mercury MerCruiser makes no attempt to provide detailed engine bed design
requirements to cover all possible applications. The proper design of the engine bed is left
to the boat manufacturer. The following general guidelines are provided:
• The engine bed must be firmly affixed to the boat and should be made as large as
possible to distribute the load evenly. Reinforcements should be used where
necessary. Mount pad locations should be as large as possible.
• The engine mounts are designed for the industry standard 572 mm (22½ in.) stringer
widths (center to center), but can accommodate widths up to 610 mm (24 in.).
• The engine bed must position the engine so that a minimum 6 mm (¼ in.) of up and
down adjustment exists on all four mounts after performing the final engine alignment.
This is necessary to allow for realignment in the future. Engine mount isolators will
compress slightly over time.
• The front and rear mount locations on the engine bed should be in parallel planes. This
can be checked by tying a string from the left front mount location to the right rear mount
location and another string from the right front to the left rear. The strings should just
touch were they cross.
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CAUTION
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90-863758060 AUGUST 2006