Adding engine room blower - how do they prevent water from entering?

[chowdan]

Looking to add a engine room blower to our boat. The goal is primarily to reduce the compartment's heat build up during the summer months after the engine has shut down.

I've seen a lot of discussions about ventilation for the engine - i am strictly looking at extraction of the compartment - not looking at reducing engine temps or anything else.

I've seen some Moody 43 CC's that have grills in their transom which from the owners state that is where their blowers lead to. I can for the life of me understand how one can think its acceptable to route a 4" tube to this when a single wave off the stern could easily flood that tube.

I dont have the ability(space) to add a dorade box on the stern like some yachts have. I do have two screw lock plates on the side walls of the cockpit up high(we have a small T shaped cockpit) in line with the wheel, I was thinking I could just route the tube to face these plates and just open them up when i run the blower. Be quite noisy since engine compartment is open to this area so not sure thats the best choice.

Am curious how other sailboats have their compartment blower setup to exhaust out of the boat - in a way that prevents water intrusion

[s/v Jedi]

We have a large vent on the transom as well. The trick is only visible on the inside: there’s a big water separator there, with a drain. For us the drain comes out the transom as well, right under the vent.

[chowdan]

Originally Posted by s/v Jedi

We have a large vent on the transom as well. The trick is only visible on the inside: there’s a big water separator there, with a drain. For us the drain comes out the transom as well, right under the vent.

Interesting! Do you have any photos that you could share? I just stepped away to get some heads down time on work, but am very curious on this. I could very much fab up a GRP system if I hvae the motivation(or time), but might look to see if off the shelf units are not too expensive.

[Cheechako]

Originally Posted by chowdan

Looking to add a engine room blower to our boat. The goal is primarily to reduce the compartment's heat build up during the summer months after the engine has shut down.

I've seen a lot of discussions about ventilation for the engine - i am strictly looking at extraction of the compartment - not looking at reducing engine temps or anything else.

I've seen some Moody 43 CC's that have grills in their transom which from the owners state that is where their blowers lead to. I can for the life of me understand how one can think its acceptable to route a 4" tube to this when a single wave off the stern could easily flood that tube.

I dont have the ability(space) to add a dorade box on the stern like some yachts have. I do have two screw lock plates on the side walls of the cockpit up high(we have a small T shaped cockpit) in line with the wheel, I was thinking I could just route the tube to face these plates and just open them up when i run the blower. Be quite noisy since engine compartment is open to this area so not sure thats the best choice.

Am curious how other sailboats have their compartment blower setup to exhaust out of the boat - in a way that prevents water intrusion

With a large scoop cover, open side down it's probably not a big issue really, only so much could get in with each dousing. But sure, in a hurricane running down wind it could be an issue. I mounted one with the clamshell cover on the inner wall of the cockpit though for more security and with either, loop the big hose above the outlet and you wont have a problem.

Have decent fresh air inlet available though, at least as big as your outlet in area. I had one boat in the Caribe and I would run the fan while running then engine. At the end of the day the engine compartment was still very warm for hours soaking into the whole boat. That boat had limited air ingress to a fairly small engine room.

[chowdan]

Originally Posted by Cheechako

With a large scoop cover, open side down it's probably not a big issue really, only so much could get in with each dousing. But sure, in a hurricane running down wind it could be an issue. I mounted one with the clamshell cover on the inner wall of the cockpit though for more security and with either, loop the big hose above the outlet and you wont have a problem.

Have decent fresh air inlet available though, at least as big as your outlet in area. I had one boat in the Caribe and I would run the fan while running then engine. At the end of the day the engine compartment was still very warm for hours soaking into the whole boat. That boat had limited air ingress to a fairly small engine room.

I was just thinking about this - I was thinking one of the vents with a flange on it and then throwing a clamshell over top of that facing down(maybe they make one thats all in one?). When i posted this i also realized that I had ignored the idea of a loop in the system just as exhausts are - that would significantly reduce ingress haha.

That said, our compartment is fairly large - mainly because they decided to not enclose anything under the cockpit so its a giant void with electronics, engine, and a water heater. Intake i believe is fairly good to the area as theres a door(more like hatch) on either side of the aft cabin walls that allow access to the compartment. 80% of the engine itself protrudes into the aft cabin within its engine box as well and the face of the box has a 4" louvered vent.

[s/v Jedi]

Originally Posted by chowdan

Interesting! Do you have any photos that you could share? I just stepped away to get some heads down time on work, but am very curious on this. I could very much fab up a GRP system if I hvae the motivation(or time), but might look to see if off the shelf units are not too expensive.

I have a storm cover for it as well. For us this is the inlet where the diesels get their air from. I’ll see if I have pictures

[s/v Jedi]

Not much to see, just an aluminum thing bolted to the transom. The air opening is at the top, the drain at the bottom.

Left of it you see a copper grounding foil for the SSB and to the right is my rudder shaft.

[kavw]

Not sure the moody, but a decent slope downwards should suffice. Or, on the bottom of the duct, say pvc or fibreglass, just a drain hose to bilge. Since it should me a rarity that water will intrude to this vent on transom, rarely will water get into it and to the bilge. My tug, had a loop under the deck, I used 3” pvc from Home Depot to do the ducting from engine room.
My current sailboat, it routes into the mast and up. Air exists from wherever it wants, new air draws into the engine room. Keeps smells out etc… blower only turns on when engine battery is switched on, that’s also my reminder to shut off the engine battery.

[deblen]

Vent thru transom would be quieter.
Vent just above water line.

Put a high hump (anti siphon) loop in vent hose just inside transom
Use rugged hose or pipe from transom to hump.
Install exhaust flapper on external vent,


https://www.hardin-marine.com/c-469-...-flappers.aspx