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Current system is passive ventilation system through single cowl vent intake on cabin top. I will be upgrading to active ventilation system, with in-line blower(s). There are several blowers on the market and I don't want to spend more the $150 for entire system, including switch, 2nd cowl vent, etc. I have adequate space near lazarette for 2nd cowl vent if needed.

Question 1: Any brand better than others? Rule makes affordable / quality products, but don't want to spend $30 every few years to replace a cheap blower. And don't want excessive noise.

Question 2: Should the passive cowl vent be converted to active for intake?

Question 3: Should I add a blower in the bilge to this system just in case? Normal bilge location under cabin sole, but easily accessible to potential blower system.

Question 4: What is the best way to vent the system? Cowl vent near lazarette? Or just vent into cockpit with low profile cowl?
 

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Boatbuilder's Handbook - Ventilation

I cant tell you every thing BUT there really SUCKERS that blow the air outside

The intake hose should go to the lowest part of the engine area and the outlet should be going overboard

The size and amount of blowers is based on the volume of the engine area
 

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Thanks. I have the setup / install pretty much nailed down, but main question is recommended brand and vent options. A blower in the area of 150CFM will suffice for the engine compartment.
 

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Vent off the side not the transom. Air can actually be sucked back into the cockpit causing carbon monoxide poisoning. I found this out during my last survey.
 

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A few points: Not having a blower with a marine gas inboard is illegal most places. In Canada, you have to run it for four minutes prior to ignition.

There are two types, "inline" (and I recommend Atwood) and "squirrel cage" (I have never heard the proper name for this, but they resemble an old-style, hand-held salon hairdryer).

Commonly, the larger "squirrel cage" is mounted close to the exit vent and drops the vent hose (typically the same wire and plastic type as is used in home dryers) down into the engine cave. You want this to go on the CARB side of the engine, because the A4 is typically "fume-y" in this area.

The "turbo/inline" type seems to be more common in the compartment itself, and the hose goes unimpeded to the external vent cowl.

Why this should be is another question, but it's what I've observed.

Make sure the blower switch contacts are clean and use a 10 amp (I am attempting to remember here) glass fuse and biggish wiring (12 ga. minimum). The blowers draw a fair bit of current and the last thing you want is hot wiring buried in the transom.

A final suggestion. Consider the PCV aftermarket kit from Indigo. It cuts down on the fumes. I found that when motorsailing in a following wind, I would get engine fumes in the cabin, and so I ran the blower in such conditions and cracked a forward hatch to clear out down below. Good luck.
 
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