Fuel Tank / Bilge Ventilation
by, 04-05-2017 at 04:13 PM (201 Views)
Since doing the install of the fuel tank we remained concerned that there was not enough ventilation. If you go back and read that blog, you will see that we took pains to calculate the amount of vapor that would permeate through the hoses, and it appeared to be well within the limits of needing any active ventilation. We had planned on passive ventilation through clamshell vents in the lockers above, where air rising into the lockers from the area below the cockpit can flow out of the boat. However, we still felt the need for more ventilation just to be on the safe side.
After doing some research, we found that a simple bilge blower fan (spark proof), connected to some good quality hose, and routed up to an exit, would provide excellent positive ventilation. We also found that we could connect the bilge blower to a fume sensor, that would turn on the blower if the fumes reached something like 25% of the explosion level. The ones we looked at also provided a manual on/off as well. This sounded like a good safety measure, and made us feel better. And really, when you put 12 gallons of gasoline below the cockpit and next to your living space, isn't a little extra system protection and feeling safe what it is all about? We said yes.
So, we decided to route a 3" Rule Bilge blower which was rated at 135 cu ft / min. That would clear the bilge in just a couple minutes easily. We chose 3" Trident Polyduct Blower Hose for the hose. It was a bit more expensive, but the normal blower hose seemed so cheap and fragile, not much better than the aluminum foil dryer hose you can buy. This hose is really nicely made and sturdy, but very light. The whole system is only a couple pounds including the vent.
The wiring of course will be addressed later, but the fan is in place as is the hose and louvered vent. Our policy has been to go ahead and drill holes and mount hardware even though we will have to remove it later. We don't want to mess with drilling holes after the boat is final painted. Easy to remove a vent and set it aside and reinstall after painting.
The system starts with the hose just at the entrance to the bilge, where the fumes will collect. From there the hose runs up to the blower which is mounted well above the bilge, but in a place easy to access and change out if needed. Above that the hose goes up into the bottom of the cockpit locker. When turned on the blower will pull fumes from the bilge, and direct them up the hose and out of the boat.
Note that we had previously mounted wooden blocks to then inside of the hull. We simply mixed up some thickened epoxy, and pressed them onto a clean sanded spot where we wanted a block to screw into. Once dry we coated them with epoxy to seal them from water. The blower is screwed down using stainless steel screws, and the hose is connected to it with stainless steel hose clamps. The hose clamp over the wooden block is screwed into the block to lock the hose in the proper place. We really like this solution as it is easy to do, and inexpensive. Just drill a hole somwhere in the hose clamp band, and screw it down to the block. You can easily open it up, and insert the hose, then close it back. The red tabs on the end of the hose clamps are there to cover up the sharp end of the clamp.
Cockpit Locker and Louvered Vent
As the hose rises up into the cockpit it passes through a fiberglass tube that protects it. While the hose seems very well made, it could easily be torn by things rolling around in the cockpit locker. So the fiberglass tube is there to guide the hose up, and protect it at the base. Everywhere it passes through the floor is sealed with fiberglass to prevent any water ingress.
Important note here is that the hose goes all the way up to the bottom of the cockpit coamings, then turns down and out through the side. This is done to prevent water from easily flowing backwards from the vent and down into the bilge. Essentially the cockpit coamings would have to be under water before that happened.
To connect the hose to the vent, we used a plastic 3" hose elbow designed to interface with the outside vent. We just cut elbow portion off so it became a straight connection. A 3" hole drilled in the side provides the outlet, and is protected by a nice stainless steel louvered vent.
When I snapped this picture I had not yet put the stainless hose clamp on as I will have to remove the hose and assembly for painting. But rest assured they will be on there by launch time.
Ericson 25CB "Nordic Thunder"