“Tiger Team” Says... - 04/16/2008

“Tiger Team” Report

“We find that the Station Wagon Effect is produced, which we believe is more the rule rather than the exception, on all boats of the 'express cruiser' configuration.”

A typical express cruiser at the dock with cruising canvas.

There are a number of factors that contribute to that conclusion, probably the leading one being that most of the boats built in the size range that might employ cruising canvas that are also powered by gas engines are express cruisers. Further, two other aspects of their design have been noted by the “Tiger Team” of Augusto “Kiko” Villalon: the radar arch and the gap under the transom door which appears on most express cruisers, and increasingly on many small boats.

The Radar Arch & Transom Door

The “Tiger Team” report notes that the radar arch that most express cruisers have, with canvas in front of and abaft the arch, can possibly create angles that enhance the Station Wagon Effect.

“We determined that CO is coming into the boat largely through the 2-inch gap under the closed transom door, or the entire door space when opened,” says the “Tiger Team” report. Ironically, the 2” gap that many builders put under the transom door is a “toe kick” designed to make the boat safer for an individual who may be standing at the transom door when the boat is in motion (obviously never a good idea).

Old boats with carb engines and cruising canvas need special care.

The report says that boat builders are “…correct and well advised to install a label on both front and rear of all canvas tops, warning the operator about the dangers involved with use.” It goes on to acknowledge that “…owners ARE operating their boats with the canvas up.”

Low Pressure Areas

Tests done by the “Tiger Team” of a ski boat powered by a carbureted inboard V-8 gas engine under actual usage conditions measured the levels of CO both behind the boat and in the cockpit. (See next week’s newsletter for a full report on these tests). The sum and substance of this report is that there are powerful Station Wagon Effects and Venturi Effects at work.

While this boat is not an express cruiser, if it is powered by gas engines it may be susceptible to CO risk due to the cruising canvas being up.

Another “Tiger Team” report investigates the death of a man driving a small jet-powered boat with cruising canvas up, but with panels open both fore and aft. Possibly the driver thought that by opening the forward panel of canvas the air rushing inside the boat would push out any CO trying to enter from the stern.

Unfortunately, because of the running angle of the boat, the open panel just abaft the windshield was actually creating a Venturi Effect, pulling a vacuum, which was sucking CO gas from the transom into the cockpit of the boat. The man fell unconscious and died, and the boat subsequently ran up on a beach and stopped.

The report concludes the subject of cruising canvas by saying boats “…should NOT be operated with ANY of the isinglass panels installed. Indeed, no boat with this configuration should be operated under these conditions.”

CO Migration from Engine Room to Living Areas

When there is a leak in the exhaust system of a boat in the engine room it is possible for CO gas to migrate into the cabin or cockpit. The CO gas can get into the living areas several different ways, including migrating through the holes in the bulkhead for plumbing and wiring, as well as migrating over and around gaps between the bulkhead and the hull and overhead, or through limber holes. Currently, USCG regs (33CFR 183.410 Ignition Protection) limit an “annular clearance” to no more than .250 inches.

In another place the regs state that any opening connecting the engine room with any other part of the boat can not exceed 2% of the area of the bulkhead. But, that can be quite a large opening in some cases. Addressing this issue, a “Tiger Team” report says, “Lately, the USCG has formed a policy – not a regulation – that says they would like to see these bulkheads completely sealed from the boat’s interior.”

ABYC Rules

Indeed, ABYC (American Boat and Yacht Council) rules are more strict than those of the USCG. ABYC Section says in part “…compartment(s) that contain a gasoline engine shall be constructed to minimize the flow of gas or vapors from the machinery space by means such as, but not limited to, flexible compounds.” (Effective July 1, 2001).

ABYC’s NEW rules (effective July 31, 2008) require that in ALL boats with 1) a gasoline generator, or, 2) an inboard [or sterndrive] gasoline propulsion engine, shall have “A carbon monoxide detection system…” in every “Enclosed accommodation compartment – One contiguous space, surrounded by permanent structure that contains the following: a) designated sleeping accommodations, b) a galley area with sink, and c) a head compartment."

ABYC has two exemptions: “Note: A cuddy intended for gear storage and open passenger cockpits, with or without canvas enclosures, are not considered to be enclosed accommodation compartments.” To view the CO detectors displayed on the USCG Safe Boating site, click here.

The BoattestSTORE.com sells three of the USCG-cited alarms. Click here to access.

OSHA CO Levels

The levels of CO necessary to cause alarm are related to the degree of exposure ppm (parts per million) and the length of time exposed. So one can be exposed to a high concentration of CO, say 1000 ppm, and die in a few minutes, or inhale low doses, say 50 ppm, and be safe after 8 hours of exposure.

OSHA standards prohibit worker exposure to more than 50 ppm of CO gas over an eight hour period. For maritime workers, they must be removed from the hazard if the atmosphere exceeds 100 ppm. Peak CO level for employees in “roll on, roll off” activities of cargo loading and unloading is 200 ppm.


A “Tiger Team” report says, “We know that carbon monoxide is produced by ALL internal combustion engines and, consequently, until the industry finds a proper Catalytic Converter or other CO reducer system, an operator of a boat must deal with this situation. We know (and all boaters are warned of this today) that operation with a closed canvas configuration is a DANGEROUS and possibly LETHAL practice.”