PS Advisor September 2002 Issue

PS Advisor: 09/02

CO Detector Placement
While I found your article on CO detectors (July 1) quite useful, I am having difficulty getting information on where to place a detector in the small confines of a boat.  We generally sleep in the V-berth of our 30-foot sailboat, and have a small Cole woodstove in the main cabin. 

Two questions: First, is CO heavier or lighter than normal air; hence, should the detector be placed high like a smoke detector, or low near the sole? Second, is placing the detector in the V-berth too near our sleeping location to be effective?

-Scot Hunter
Vashon Island, WA


Good questions. According to the Kidde Safety website, "CO is slightly lighter than air and as it begins to rise, it mixes with surrounding air and diffuses throughout the house."

It's normally recommended that you install a detector in each sleeping area that's separated either by some distance or a partition. They can be mounted near sleeping areas, but this results in slightly less protection. They shouldn't be installed within 12 inches of opening windows, exterior doors, heating or return air vents or other drafty areas. They should also be at least 5 feet away from cooking areas. They should not be located behind curtains, furniture or other areas that will block air flow to the detector.

They're normally installed about eye level for easy viewing and should not be placed in areas that are wet, get direct sunlight, or areas where temperatures may go below 40F or above 100F.

That's the chapter and verse. Obviously, there will have to be some compromises aboard a boat. One good bet would be to mount the detector high and outboard on the bulkhead on the main cabin side. If it goes off, you'll certainly hear it in the V-berth. Alternatively, you could mount it on the other side of the same bulkhead, in your sleeping area. Or, you could do both.

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Outboard Issues
I currently own a Evinrude 9.9, 1989 two-stroke outboard for my C&C 25 sailboat.  When I am done sailing for the day, is it better to pull the fuel line and let the gas/oil mixture drain with the engine running until it runs out, or should I simply kill the engine and let the fuel/oil mixture remain inside the engine?

Also when measuring shaft length, do you measure from the bottom of the engine to the absolute top or from the bottom to the engine block? I am looking for a new engine and want to make sure I get the same depth for the prop.

Are there any ultra-light 4-stroke engines that you would recommend?  I race the boat and weight is an issue.

Thanks for your help.  I look forward to your publications every month!

-David Caporale
Via e-mail


Years ago, carburetors in some outboards would allow the fuel/oil mix to spill inside the engine if you tilted the engine up without draining the carb first. Those days are over. Even your '89 9.9 has a gasketed air-box that should allow you to tilt with impunity. If in doubt, check for fuel spills inside the engine cover when it's tilted up. Another argument against the draining practice is that some modern engines don't like to have their fuel pumps run dry.

The guys at Powerboat Reports say that it would be a good idea to unplug the fuel line at the engine if you live in a blazing-hot place. Pressure in the fuel tank, if it has the vent screwed down, can push the mix beyond the carb and lead to flooding.

Measure the outboard shaft from the mounting bracket (right where it will sit on the mount) down to the horizontal ventilation (cavitation) plate above the prop. It will help to remember that shaft lengths are defined in five-inch increments.

As far as we know, there are no ultra-light four-strokes in the 9.9-hp range (or any range, for that matter). They range from the 91 lbs (Yamaha) to about 114 (Nissan/Tohatsu). It'll be nice when someone makes a four-stroke that weighs the equivalent of its two-stroke cousin.

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