Why close hatches while fueling

[glennd3]

The manual says to close all hatches when fueling our boats. The only reason I can think to do this is it would allow you to smell a leak. Any other reason?

[Noah]

Pretty much standard operating procedure in manuals, boating classes and insurance recommendations. Although many with diesel engines do not bother. The reason to shut hatches and ports is to prevent fumes from wafting into cabin where they could be a fire and/or explosive hazard. While diesel is less explosive than gas, it will ignite. Another fueling "rule" that is often not followed by many recreational boaters  is to have all passengers disembark.

[KWKloeber]

Another point in addition to Noah's is that it's S.O.P. on boats generally because gasoline vapor is 3-4 times heavier than air and can flow along the surface to an open hatch.

However, diesel vapor is lighter than air so it wafts away rather than settling into the cockpit or a hatch.

Additionally, diesel fuel has a MUCH lower evaporation potential vs. gasoline and at standard conditions (ie, STP standard temp & pressure) the vapor won't even ignite (as we all know nor will diesel fuel explode at STP.)

A "good" fuel dock will follow the insurance rules and ask gassers to close hatches and disembark but most just hand you the nozzle. 

[Ron Hill]

Guys : To add to Ken and Noah's comments.  If you have a gasoline engined boat you have to run the blower for 3 minutes before starting, to insure that all gasoline fumes are sucked out of the bilge areas before starting.  As Ken mentioned gasoline vapors are heavier than air and boats have been known to explode when starting the engine - if those fumes are not evacuated !!!

A thought

[KWKloeber]

And don't think what Ron said about evacuating fumes is pie in the sky.

People were blown off these boats on Lake Norman sine we're able to jump overboard.
If you're on a powerboat that doesn't refuel safety, say "Bye."