12V Systems
Motor Compartment Ventilation
Design
Air is circulated from inside the boat, into the motor compartment and out through an external vent by a blower and fan. These are always on when the key switch is on. It will not be obvious if one or both of these fail, so regular inspection is required if you live in a hot climate and want to maximize motor ventilation.
A fan on the front of the console above the motor compartment pulls air from the cabin into the motor compartment. A passive vent on the back of the console provides an additional source of cabin air.
A blower is attached to an external vent, which is on the bow of our boat. It pulls air from the bottom of the motor compartment, through a 3" duct in the bilge, and exhausts it out of the vent. The vent should be facing backwards to be most effective, but this more directly exhausts motor compartment fumes into the boat if the front window is open.
On newer Duffy boats, the external vent is located on the stern, which is an improvement. I assume that it operates in the same way.
Vent Blower
The original part is Jabsco 35115-0020, 3 inch Blower, 105 CFM, 12 Volt (spec. sheet). Jabsco states that this is intended for intermitent operation and, if used for longer periods, the maximum motor life is 1,000 hrs (about 2 hrs/week for 10 years).
Attach a cable clamp to one of the existing screws on the fan housing and loop the wires through it to prevent strain on the electrical connectors.
Jabsco offers the blower motor as a replacement part, but it costs as much or more than the entire assembly.
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Specifications
- Shaft Diameter: 1/4"
- Shaft Length: 1"
- Shaft Type: D Shaft
- Voltage: 12VDC
- Mounting Screw Distance: 2 5/16"
- RPM: Unknown
Fan
A standard 12V 90mm computer case fan is mounted under a cover on the front of the motor compartment.
Orient the fan so that it forces air from the cabin into the motor compartment.
The original fan has two wires (12V positive and negative), which was the standard for old computer fans. Modern computer fans have 3 or 4 wires, which provide fan speed feedback and allow for speed control. You can use these fans by leaving the third and fourth wires unconnected as shown in the table below.
Typical Three/Four Pin Fan Wiring
| Pin/Wire | Function | Wire Color |
|---|---|---|
| 1 | -12V | Black |
| 2 | +12V | Yellow |
| 3 | Sense | Green |
| 4 | Control | Blue |
External Vent
The vent is a standard 3" PVC Cowl Vent which is sold by several manufacturers. The size refers to the inside diameter of the vent base. The inside diameter of the deck plate it seats into is 3.25". The vent is pressure-fit to the deck plate, which is sealed and screwed into the deck.
The blower box below the vent has a flapper valve inside which is designed to cap the vent hose when the blower is off. Our flapper valve shown in the photo was broken near the hinge point.
