Blower or no blower?

Windjammer said:
S.O.P for me:
Raise hatch/smell test
Blowers on for a full 4 to 5 minutes.
Start genset.
Start Engines.
Lower Hatch.
Blowers stay on until we return to the dock and are the last things off.
The fumes from 1/4 cup of gasoline are equal to 15 sticks of dynamite...
Click to expand...

This is my routine EVERY time I leave the dock and EVERY time after I refuel.
Leave them running till back at the dock or anchored.
If I shutdown the engines, I'll leave the blowers running for a few minutes for cool down.

@Waterlife,
Intake should be high in compartment, cool air in.
Exhaust hoses as low as possible fumes out, (gas is heavier than air)
 
On my 380 the manual says to only run them before starting the engines or when moving at idle. No idea how it gets better ventilation when underway. Good points.
 
Some older blowers weren’t rated for continuous duty.
Above idle the engine(s) draws enough air volume in and goes out thru the exhausts to provide sufficient air flow within the engine room

but remembering to turn them on snd off is iffy
 
In addition to the above, often one side of the vent box on the hull will not have a hose attached to it. That is the "outlet". As mentioned, hot air rises. In this case, the increased airflow over the vent also creates a negative pressure which in turn helps draw out the air.

'Course, the "easy" answer is that thousands of boats like yours have been running like this for decades with no ill effects from heat. Meaning, the engineers at Sea Ray know what they are doing. Don't confuse what YOU think is hot to what the ENGINE "thinks". :)

Although you've stated you've been doing this for a while, I don't think it's good practice to run with the engine hatch open. It just puts more stress on the hatch and the hyd rams with the flexing the hatch would endure from being propped open.
 
A little of history and engineering reasoning. I spent over 20 years as an engineer in the Coast Guard Office of Boating Safety and sat on the ABYC committee that deals with engine room ventilation. The point with a blower is to prevent explosions. But how do they do that. Many of you may be familiar with the fire triangle. You need three things to start a fire, fuel, air, and a source of ignition. The fuel system regulations deal with preventing leaks and fuel fumes inside the boat. The electrical regulations deal with sources of ignition. And the ventilation regulations provide the air? Why provide?

Explosions due to gas fumes only occur within a short range of air/fumes mixtures. There is a lower explosive limit (LEL) usually 7 parts air to 1 part fuel. and an upper explosive limit: 14 to 1. Below the LEL the mixture is too rich and above the Upper limit it's too lean. What the blower does is introduce more air to keep the air/fuel mix too lean to ignite. So if you do have fumes in the engine compartment, it doesn't go boom. Why then do you turn on the blower for 4 minutes? Time to get the fumes out and air in and make the mixture too rich. The blowers are required to be ignition protected, that is not be the source of ignition.

And as for the vents. Research has shown that even when the blower isn't on (and the engine is not running) air moves in and out through the vents. On most boats there is an exhaust and an intake, but research has shown they can switch depending on lots of factors, outside temp, temp in the engine room, the direction of the wind relative to the boat. So when the boat is standing still, your intake may be the exhaust and exhaust the intake. But when you switch on the blower, it is on the exhaust ( the one that goes down to about 4 inches above the bilge) and the other the intake, which doesn't have that long a hose on it, just long enough to bring air into the engine room.

If you are underway and you switch off the blower, then it depends on the wind. if you're going slow and the wind is from astern, the exhaust may be the intake and vice versa.

Those of you who use the blower to reduce heat in the engine room after shut down, there is also some research (done by the EPA of all things) that shows that engine room temps don't get up much more than about 118 F even when the boat is standing still and the blower is not running.

And for those who think that fuel injection has solved this problem; the fumes can come from multiple sources. Bad fittings, bad gaskets, leaky hoses, leaky fuel pumps. Most fuel leaks are at fuel system fittings.

Any way my apologies for the long post: Just follow the instructions. Run your blower for four minutes before firing up. After you're underway you can shut it off if you like. Definitely check the bilge and run the blower after refueling before starting the engine. A typical scenario with fueling related boat explosions is the operator gets fuel, gets underway, and about 100 feet later it goes up. That's how long it takes to get into the range between the LEL and the Upper limit.
 
Thanks for the replies, I think i will run an air temp gauge at Air intakes to see what differences there are at idle and up and out, very curious. As i said there is a noticeable difference when plenty of clean air is entering. I actually sit door on 2 pieces of cut Noodle at either corner for support, (but understand your point) This is a 30nm run. each way.
Also another point, Lazy Daze, you mentioned a hose connected to the front (intake side i gather). Mine has no hose except for blower hose exit. Is this what you referring too? I have thought about running an air hose from intake (side of boat) to just in front of Air intake but worried i would be restricting air flow even more.
 
I ended up replacing both to the squirrel cage blowers. They are quieter and def move more air. I still have a hard time running them constantly, when I first had them installed the existing wiring setup couldn't handle the draw for more than a couple of minutes so I had to have them wired direct to the batteries with a separate fuse.
 
Ike said:
A little of history and engineering reasoning. I spent over 20 years as an engineer in the Coast Guard Office of Boating Safety and sat on the ABYC committee that deals with engine room ventilation. The point with a blower is to prevent explosions. But how do they do that. Many of you may be familiar with the fire triangle. You need three things to start a fire, fuel, air, and a source of ignition. The fuel system regulations deal with preventing leaks and fuel fumes inside the boat. The electrical regulations deal with sources of ignition. And the ventilation regulations provide the air? Why provide?

Explosions due to gas fumes only occur within a short range of air/fumes mixtures. There is a lower explosive limit (LEL) usually 7 parts air to 1 part fuel. and an upper explosive limit: 14 to 1. Below the LEL the mixture is too rich and above the Upper limit it's too lean. What the blower does is introduce more air to keep the air/fuel mix too lean to ignite. So if you do have fumes in the engine compartment, it doesn't go boom. Why then do you turn on the blower for 4 minutes? Time to get the fumes out and air in and make the mixture too rich. The blowers are required to be ignition protected, that is not be the source of ignition.

And as for the vents. Research has shown that even when the blower isn't on (and the engine is not running) air moves in and out through the vents. On most boats there is an exhaust and an intake, but research has shown they can switch depending on lots of factors, outside temp, temp in the engine room, the direction of the wind relative to the boat. So when the boat is standing still, your intake may be the exhaust and exhaust the intake. But when you switch on the blower, it is on the exhaust ( the one that goes down to about 4 inches above the bilge) and the other the intake, which doesn't have that long a hose on it, just long enough to bring air into the engine room.

If you are underway and you switch off the blower, then it depends on the wind. if your going slow and the wind is from astern, the exhaust may be the intake and vice versa.

Those of you who use the blower to reduce heat in the engine room after shut down, there is also some research (done by the EPA of all things) that shows that engine room temps don't get up much more than about 118 F even when the boat is standing still and the blower is not running.

And for those who think that fuel injection has solved this problem; the fumes can come from multiple sources. Bad fittings, bad gaskets, leaky hoses, leaky fuel pumps. Most fuel leaks are at fuel system fittings.

Any way my apologies for the long post: Just follow the instructions. Run your blower for four minutes before firing up. After you're underway you can shut it off if you like. Definitely check the bilge and run the blower after refueling before starting the engine. A typical scenario with fueling related boat explosions is they fuel, get underway, and about 100 feet and it goes up. That's how long it takes to get into the range between the LEL and the Upper limit.
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I have been a fireman for over 40 years and knew and agree 100% with your post. I just couldn't put it into a coherant post for others to understand. It's hard to explain why more air isn't always better!
 
Thanks Ike, Very good info.
 
Thanks. about 90% of my job was explaining the regulations to the public. I've been retired for 15 years but I find I'm still doing it.
 
Groucho said:
I ended up replacing both to the squirrel cage blowers. They are quieter and def move more air. I still have a hard time running them constantly, when I first had them installed the existing wiring setup couldn't handle the draw for more than a couple of minutes so I had to have them wired direct to the batteries with a separate fuse.
Click to expand...
Excuse my ignorance but what is a squirrel cage blower????
 
ok GOT IT
Centrifugal.
 
Ever bought your kids a hamster or guinea pig? That little wheel they run in and make it go round and round is a squirrel cage. A squirrel cage blower has a fan that looks similar. This is as a opposed to a blower that simply has a bladed fan in it. (an axial blower)
 
This all makes me think about a camera for the engine room. I’m always worried that it will get too hot in there. Maybe if mounted fairly low in the space?
 
superwa said:
This all makes me think about a camera for the engine room. I’m always worried that it will get too hot in there. Maybe if mounted fairly low in the space?
Click to expand...

I think thats overkill....Some things as long as they are designed by the factory are better off not looking at all the time.
 
I always run my blows when I'm at the gas dock for pump out and gassing up. I always run the blowers before starting up the motor and I always leave them on when I forget to turn them off once I'm out of the channel . I kick them on once I'm back off plane and let on for a while once when I'm back at the dock. The key is forgetting to turn them off so you don't have to remember to turn them on again.
 
C3B49088-512B-4AB9-94F5-014A419D1003_sRGB.JPG
dvx216 said:
I always run my blows when I'm at the gas dock for pump out and gassing up. I always run the blowers before starting up the motor and I always leave them on when I forget to turn them off once I'm out of the channel . I kick them on once I'm back off plane and let on for a while once when I'm back at the dock. The key is forgetting to turn them off so you don't have to remember to turn them on again.
Click to expand...
You should shut down your blowers when you are at the gas dock receiving fuel. After the tank cap is secured, run the blowers for 4 minutes and do a sniff test before turning the keys. Running blowers while taking on fuel can draw fumes into the engine room.
 
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