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Old 04-29-2015, 12:24 AM   #1
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Blowers

I have twin 270 Crusader engines and I usually run one at a time.
I do this for my own reasons and so I don't want this thread hijacked into the why of it all. I just do. Anyway, my question is two fold:

1). Can I run the blowers off my house batteries with the alternator from one engine keeping them charged? I'm not sure right now where they are powered from right now. I don't even know how much power they consume.

2). I usually leave the blowers on all the time I am running the boat. Some people think it is odd. I thought I was supposed to with gas engines. Am I?

Thanks in advance
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Old 04-29-2015, 12:39 AM   #2
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Don't see the need for running the blowers for diesel engines unless one wants to ventilate the engine compartment when occupying it or to help cool down the boat when stopped in hot weather. The engine sucks air from the relatively-hot engine department and then exhausts it. ... Got blower, but often don't use it.
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Old 04-29-2015, 12:52 AM   #3
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Well, with two engine setup and only one running at any given time ... why? Never mind... just kidding ...

1. Find out name and model of the blowers and check the specs. The Jabsco heavy duty models can draw as much as 12 amps each at 12vdc.

Other things to check/confirm/communicate ...
Are both engines' alts wired to charge both/all banks of batteries? Very unlikely.
Which battery, and indirectly which alt, powers the blowers?

2. Blowers ON at all times while a gasoline engine is running is a good rule of thumb, and prudent safety measure. The blowers should be ON for at least 4 minutes before engine start, and when idling or slow cruising since the natural ER ventilation might not be sufficient.

Hope this helps ...
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Old 04-29-2015, 01:02 AM   #4
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Twin FLs. The blower switch is beside the engine switches at the helm. The one day I did not run the blower the ER got very hot, I believe the blower is intended to be run with the engines. There should be heaps of amps, even with one engine, to feed the hungry blower.
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Old 04-29-2015, 01:17 AM   #5
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Is there a 4" to 6" suction hose on the blowers that goes to the bottom of the bilge? How is the air intake plumbed, remembering gas fumes are heavier than air.
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Old 04-29-2015, 03:38 AM   #6
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Out of interest, is it better to suck air out or blow air into an engine room? I've been contemplating setting up an extraction fan to suck out hot air from the ER (figuring the cooler the air in the er, the more dense, therefore better for the [turbo diesel] engines). Or am I crazy?
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Old 04-29-2015, 05:49 AM   #7
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I have some Delta T's on the forward engine room vents that bring air in at the front of the ER. Then some smaller squirrel cage blowers at the rear of the ER that suck air out of the rear ER vents. Of course the engine aspiration also takes air out. I use the blowers whenever the engines are running in order to keep ER temps lower than would otherwise be the case. I'm not sure what the blowers aggregate amperage draw is, but expect it is substantial and therefore shut the blowers off right after stopping the engines.
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Old 04-29-2015, 06:41 AM   #8
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I read a thread on the Defever Cruisers Forum recently citing someone who had run some pretty sophisticated thermodynamic calcs to show that (at least for Defevers with conventional in and out blowers) there is little to no benefit to running the blowers while underway. A frequent and very technically knowledgable poster cited the mass of the heat sink in the ER, calculated the volume of air that would need to be replaced under various outside temps and concluded it was futile to run the blowers while under way. He noted that with his setup, his engine room seldom got above 110 degrees while underway, with or without the blowers running. Once the engines are shut down and heat isn't being added, the bowers become effective. Haven't experimented myself; just passing along what I read and YMMV with a different boat. (Personally, I believe everything I read on the internet.).
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Old 04-29-2015, 07:01 AM   #9
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Out of interest, is it better to suck air out or blow air into an engine room?

Always better Gas or Diesel to suck the ER out and let the make up air come from unpowered vents.

The reason is engine rooms are not air tight to the vessel, so the heat and stench of the engine will be powered into the living spaces .

Much ungood with even a slight exhaust leak!

Even worse with a fire!
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Old 04-29-2015, 07:02 AM   #10
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Sucking is better than blowing. Pressurizing the engine room may force vapors (odors) to leak into the living spaces through small openings. Better to create a vacuum and have plenty of fresh air access for the engine room.

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Old 04-29-2015, 09:59 AM   #11
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Quote:
Originally Posted by angus99 View Post
I read a thread on the Defever Cruisers Forum recently citing someone who had run some pretty sophisticated thermodynamic calcs to show that (at least for Defevers with conventional in and out blowers) there is little to no benefit to running the blowers while underway. A frequent and very technically knowledgable poster cited the mass of the heat sink in the ER, calculated the volume of air that would need to be replaced under various outside temps and concluded it was futile to run the blowers while under way. He noted that with his setup, his engine room seldom got above 110 degrees while underway, with or without the blowers running. Once the engines are shut down and heat isn't being added, the bowers become effective. Haven't experimented myself; just passing along what I read and YMMV with a different boat. (Personally, I believe everything I read on the internet.).
Works this too in my DF. In the PNW the ER does not get hot when cruising, only, after a shutdown. Didn't need to do a thermodynamics evaluation to find this out. But hey, what are retired engineers to do when cruising?
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Old 04-29-2015, 10:50 AM   #12
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Like most discussion here...depends....


On my silverton where the engine room was 90% engines, 10 percent dead space...the blowers were extremely effective...on my Trawler where the percentages are reversed, they aren't much help.


Plus the amount of air the engines consume is huge also.


I don't believe blowers do much for eliminating gas fumes from the bilge when running...again the engines move a LOT of air and it is being stirred up by natural drafts and alternators, belts, etc.


Even for starting, the nose in the right spot is just as valuable as a blower.
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Old 04-29-2015, 11:43 AM   #13
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Our blowers -- which actually suck and expel -- run off our starboard all-purpose (~300 Ah, start, half the house, plus electronics) battery bank. On the analog ammeter, looks like they use about 9 amps when they're on. We mostly use 'em to cool down the engine room after a run.

FWIW, they we're really noisy when we got the boat. I eventually remounted them using short lengths of sanitation hose as stand-offs from the hard surfaces where they were originally attached. Made a world of difference!

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Old 04-29-2015, 11:52 AM   #14
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Gas engines dont really move a lot of air, especially at low throttle settings. Even a WOT the carb will only flow about 600 cfm. I'd run the blower.
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Old 04-29-2015, 12:00 PM   #15
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Depending on where blowers discharge, they can give you a way to do a sniff test on the engine room. Pretty important on the gas engines in case you get a fuel leak.

Blowers do virtually nothing to lower engine room temps while running, unless they are huge.

Only time I run mine is hot day after a run, with gennie on. Gennie elec end is air cooled and ER can get dang hot after a few hours.
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Old 04-29-2015, 12:02 PM   #16
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Quote:
Originally Posted by shufti View Post
Out of interest, is it better to suck air out or blow air into an engine room?
Here's what ABYC H-02says Ventilation of Boats Using Gas

(2) Installation of Powered Ventilation
(a) Blower(s) capacity shall be selected in accordance with the "blower capacity curve" in Figure 2. More than one blower may be used.

(b) As installed, the blower system(s) shall exhaust air from the boat at a rate in accordance with the "system performance curve" in Figure 2 when the engine is not operating and the blower is operating at the electrical system's nominal voltage.
(c) Blowers shall be mounted above the normal level of accumulated bilge water.
EXCEPTION: Submersible blower motors.
(d) Blowers shall be installed with ducts whose intake openings are:
- permanently fIxed,
- located in the lower one-third of the compartment.
- above the normal level of accumulated bilge water, and
- as nearly as practicable below the enginc(s) which it serves.


There is also a requirement for natural ventilation including ducting similar to the powered.

d. Natural Ventilation
(1) Each natural ventilation system shall be constructed with at least one intake opening. Each intake opening shall be on the boat's exterior surface.
(2) Each compartment requiring natural ventilation shall be equipped with exhaust duct(s) originating in the lower one third of the compartment, the duct opening permanently fIxed above the normal accumulation of the bilge water. If the compartment is an engine compartment, exhaust duct(s) shall be located as nearly as practicable below the engine(s).
NOTE: "Exhaust(s) and intake(s)" may not function as intended when wind
direction varies.
(3) Each exhaust opening shall terminate on the boat's exterior surface.
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Old 04-29-2015, 12:36 PM   #17
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I was actually thinking about putting a timer on my blower to run five minutes every hour while I am away from the boat just to circulate stagnant air. Thoughts?
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Old 04-29-2015, 12:43 PM   #18
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Greetings,
Thanks all you Murphy boys! I was just in the ER fiddling about, flipped on the blower and I've got a bad bearing. Squealing like a loser in a hog fight. Was just fine last week. AW SNAP!
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Old 04-29-2015, 12:47 PM   #19
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Greetings,
Thanks all you Murphy boys! I was just in the ER fiddling about, flipped on the blower and I've got a bad bearing. Squealing like a loser in a hog fight. Was just fine last week. AW SNAP!
Now you gotta fix something you never use.
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Old 04-29-2015, 12:53 PM   #20
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Greetings,
Mr. w. I do use it in the fashion of others. I flip it on to cool the ER after shutdown but last week I was painting my replacement tranny coolers (red) and had it on then to dissipate fumes. As much as I liked the 70's I can't remember much of them. Probably an excess of paint fumes....
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