Bilge/Motor Room Blower Exhaust Port?

[Extemporaneous]

Hi all,
I'm installing a 4" blower (continuous duty) in my motor room in order to keep it cooler while I'm under way.
My question is what is the best (or some examples of) setup for the exhaust port?
I'd hate to have a 4" hole in my boat with no way to stop water from coming in. Pic's would be great.

Thanks,
Extemp.

[sabray]

you could use a mushroom vent which screws shut. Mine vents in inside the cockpit coaming so is not exposed to rain and deck washing.
Vetus Mushroom Ventilators

[Evan]

A dorade box like a dorade vent can work. A means of positive closure is nice too.

[GordMay]

Intake vent facing forward and exhaust facing aft, with 6 ft. min. sepration.
As sabry notes, many mushroom vents are closeable from inside (screw down), but engine compartment vents aren't always easily accessable from inside; in which case a Dorade (water trap), or an outside closure may be preferable.

Some cowl vents have drop in closure plates. Don't forget to remove the closure prior to operating the fan.

[Hud3]

I installed an in-line exhaust fan with 4" flexible ducting to cool my boat's engine compartment, and used a SS clamshell for the discharge, mounted high on the transom. Also included a piece of SS insect screen behind the clamshell to keep the bugs from using it as an access hatch. Have had no problems at all with water getting in.

[GordMay]

I too used a 4" in-line fan, but c/w (2) PVC Low-Profile Cowl Vents on the after quarters.
I never felt the need to use the snap-in closure plate, even on the aft-facing exhaust.

Nicro Low Profile PVC Cowl Vent:
4 Inch Snap-in Deluxe Low Profile PVC Cowl Vent | Marinco
And:
4 Inch Black Snap-in Deck Plate | Marinco

Attwood Marine Turbo 4000 4" Inline Blower:
Attwood 4" Air Hose Categories

[Tempest245]

Gord, Hud, et al.. What was your motivation for doing this? Keeping the heat out of the cabin? Is this a lower latitude issue? Or does it improve engine performance?

[GordMay]

Originally Posted by Tempest245

Gord, Hud, et al.. What was your motivation for doing this? Keeping the heat out of the cabin? Is this a lower latitude issue? Or does it improve engine performance?

Yes, yes, and yes.

From (2) earlier posts:

Engine Room/Compartment Ventilation:

The maximum temperature of the engine room should never exceed 140 degrees F, within 3/4" of any electrical equipment (Alternator), and should never exceed 115 deg. F anywhere in the engine compartment.

The approximate cooling ventilation (this is in addition to combustion air requirements) rate may be determined by the following formula:
CFM = (1000 x H.P.) ÷ T
where:
HP = maximum engine horsepower
T = allowable temperature rise, ‘F. (often specified at 15 degrees)

Hence, for a 22 H.P. engine:
CFM = (1,000 x 22) ÷ 15 = about 1,500 CFM Cooling Air (1,466.66),

which (@ ± 1,000 FPM velocity) would utilize (2) 224 square inch ducts - both make-up air & exhaust (2 @ 16" x 14", etc)

***

Engine room Ventilation:

The maximum temperature of the engine room should never exceed 60 degrees C (140 F) within 20mm (3/4") of any electrical equipment, and 45 C (113 F) at the air intake.

Ventilation Requirements for Yanmar Diesel Engines:
Duct Sizes (2 Required - 1 Supply In & 1 Exhaust Out)
Engine Square inch = Diameter
1GM10 3.02 sq. in = 50mm = 2" dia.
2GM20 6.0 sq. in. = 75mm = 3" dia.

100mm inside diameter tube duct area is 78.54 cm2
50mm inside diameter tube duct area is 19.7 cm2
4 inch inside diameter tube duct area is 12.57 inches2
2 inch inside diameter tube duct area is 3.15 inches2

Note: TWO ducts the same size are required, one inlet and one outlet.

[seacap]

Batteries don't like heat for one reason. Also to much heat cooks everything in your engine room. Deteriorating rubber and other parts in your engine room more rapidly.

[Hud3]

I was fine until I installed a large case alternator. Those suckers put out a lot of heat. I located the fan intake right over the alternator. I made a big difference in engine compartment temperature.

[Extemporaneous]

Thanks.
They all look like good ideas.
I'm going to have to see where I could mount something. All the combings seam to be fairly narrow on my boat. I'll need to take measurements.
If I can't find the horizontal space to fit a low profile, could the clam shell be put high on the outside of the hull facing downwards?
I also came across this (see attached). It would also mount on the outside of the hull.
What do you think?
My concern with this is that because of the shape of my hull (curved), it would be tilted slightly upward and if water was to get into it, it would not flow out.

[Extemporaneous]

Originally Posted by GordMay

Hence, for a 22 H.P. engine:
CFM = (1,000 x 22) ÷ 15 = about 1,500 CFM Cooling Air (1,466.66),

Ventilation Requirements for Yanmar Diesel Engines:
Duct Sizes (2 Required - 1 Supply In & 1 Exhaust Out)
Engine Square inch = Diameter
1GM10 3.02 sq. in = 50mm = 2" dia.
2GM20 6.0 sq. in. = 75mm = 3" dia.

Gord,
Is this right?
I've got one of the most powerful 4" continuous duty blowers and it is only 250 CFM. Could your first statement be CFH? I can't imagine pulling 1500 CFM through a 4" tube, even pushing and pulling (supply & exhaust). I bet it would be incredibly noisy.
If I've misunderstood something, please straighten me out.

Regards,
Extemp.

[GordMay]

Extemp.
I believe you're right - this is wrong.
Now that I think about it, I suspect my source (Mech Eng I worked with) was calculating for an air-cooled engine. He's out of town today, but I'll try to confirm tomorrow.

Also note that most blowers available at 12VDC will be rated fre-air flow (with 0 static pressure) which must be significantly derated for "as installed" condition. Your 250cfm fan might actually deliver only about 125 cfm under 1" S.P.

[Hud3]

Extemp,

I'd advise against mounting the vent on the side of the boat. A wave on the beam will run right up the side and into your ducting. I've never had that problem with my transom mounted clamshell vent.

[Extemporaneous]

Originally Posted by Hud3

Extemp,

I'd advise against mounting the vent on the side of the boat. A wave on the beam will run right up the side and into your ducting. I've never had that problem with my transom mounted clamshell vent.

Ya, I'm sure your right. How about clamshell mounted at 90 degrees (facing forward or aft)? My problem is that I have a canoe stern and don't have much for horizontal surface back there.
I'll have to figure something out.

Thanks,
Extemp.