Proper ventilation of engine spaces on boats is an often-misunderstood topic and can cause some grief for boat owners when it’s time for a survey. The reasons for having powered ventilation of an engine space are many, but they vary depending on the type of engine installed in the vessel. Powered engine space ventilation is of paramount importance to safety for gasoline powered vessels, as blowers are designed to remove highly flammable gasoline vapours from an enclosed engine space. Of course, this is only important if gasoline fumes are present, either from significant permeation of plastic fuel tanks or fuel hoses.
Unfortunately, fumes may not be detectable by those onboard when the engine hatch is closed. Small Vessel Regulations therefore require powered ventilation for enclosed gasoline engine spaces. This law is part of what the Small Vessel Regulations define as a critical safety requirement, meaning it applies to all gasoline inboard and gasoline stern drive powered vessels regardless of the date that the vessel was manufactured. Boat builders have been largely compliant with the powered ventilation requirement for decades. What has changed over the years is how this is achieved.
As construction standards have improved in North America, newer boats are manufactured to a more stringent standard. As a rule of thumb, blowers in gasoline engine spaces are to be operated for a minimum of four (4) minutes prior to starting the engine(s). The expectation is that the entire volume of air inside the engine space must be exhausted through a vent in that four (4) minute time frame. This may be achieved using a single bower or multiple blowers, depending on the volume of the engine space. As such, manufacturers must calculate the volume of the space and ensure the capacities of the blower motors are sufficient to meet the four-minute criteria. Current construction standards specify the types of blower motors, including compliance with ignition protection requirements (the electric blower motor must be designed so that it will not generate sparks that will ignite gasoline fumes). Thankfully, these calculations are completed by the boat manufacturers and suitable blowers are usually installed at the factory.
Construction standards also identify proper installation for blowers on diesel powered vessels. The flash point of diesel fuel is much lower than that of gasoline, so the risk of igniting fumes in the engine space is significantly lower. Small Vessel Regulations do not require powered ventilation of diesel engine spaces. It is, however, still considered to be best practice. Powered ventilation in diesel engine spaces helps keep compartment temperatures down, particularly for turbocharged diesel engines that have very high component temperatures. Powered ventilation system components are much the same for both diesel and gasoline powered vessels.
Over time, however, the components of the powered ventilation system will deteriorate, resulting decreased effectiveness or a complete failure of the system. When this occurs, boat owners are often completely unaware that they are not getting proper discharge of the air in the engine space. In many instances we have found a blower that sounds like it works but is really not doing its job. This, of course, is a significant safety risk for anyone onboard (or within a stone’s throw of the vessel). The following partial list of common survey findings demonstrates how easy it is to have a situation arise where gasoline fumes can be ignited, potentially causing a catastrophic fire or explosion. In all of the cases listed below, proper airflow is found to be either reduced or absent:
- Torn, damaged or blocked ducting
- Equipment occluding the inlet ducting
- Howling or noisy blower motor
- Inoperable blower motor
- Ducting disconnected from the exhaust vent (often very difficult to see)
- Blower or DC wiring installed backwards (resulting in the blower sucking air in, instead of blowing it out)
- No airflow from one of the blowers, even though they both sound like they are working
- Insufficient blower capacity (undersized, or one blower where there should be two or more)
Some of the causes can be difficult to diagnose, but many are very simple to sort out and fix. The good news is that blower motors and ducting are relatively inexpensive. Most of the issues can be avoided if boat owners take the time necessary to familiarize themselves with their powered ventilation system and makes sure that the blower not only comes on when the switch is activated, but that they can also feel airflow at the exhaust vents of all blowers fitted to the engine space.
A good marine surveyor should be able to identify deficiencies with blower systems, as well as construction requirements relevant to their installation. A good marine surveyor should also be able to accurately identify in the survey report exactly what regulation or standard applies, and whether the deficiencies found are required by law or simply considered best practice.
By Timothy J. S. Martin,
AMS® #1360 Society of Accredited Marine Surveyors
MIIMS, International Institute of Marine Surveying
Transport Canada Approved Tonnage Measurer <24m
Director, Eastern Operations