Engine blower motor

[Dockhead]

Originally Posted by jimbunyard

. .. .
"Second - positive displacement is neither here nor there."

I suggest you put a board over the intake of your engine and then one over the intake of you blower and see what happens.

What does that have to do with anything at all?

Originally Posted by jimbunyard

Again, the selection of a blower motor should be made based on the specific application's dynamics.

I think everyone would agree with that

[JohnB40]

Thanks for comments.
Yes there are cheaper blowers but I was trying to use the same blower casing as it's directly bolted on to the transom. The motor does seem to cost about $50 as I see a fairly similar one on AC Truckers website. But it is a bit different, two speed, part number 2807-506-032 whereas I'm looking for 2807-506-006. I guess that goes in a Plastimo casing and the price goes to about $300.
Also the air hose is 70 mm (good old Beneteau) so I would have to replace some of the hose with say 3 inch and it's all cable tied in a hard to get at way.
I can get a $40 inline 3 inch blower at local marine place but again I'd have to attach the hose to the transom in a really hard to get at place and it would be 3 inch, so again need to connect to 70 mm (2 3/4 inch) unless replacing much hose. There are 3 to 4 inch plastic reducers but not 3 to 2 3/4 ... though imagine I could solve.
It's really just so easy to replace the motor for about $50 (if I can find it) rather than change to an inline blower with a different size air hose.
Thanks again.
JohnB40

[Jim Cate]

What does that have to do with anything at all?

Well, it is an extreme example of what happens when you obstruct the air flow for two different types of pumps.

DH, what sort of blower is yours? They are typically "squirrel cage" types, and if my memory isn't totally shot, this type's throughput drops dramatically with back pressure, where a positive displacement pump's does not. I think this is what Jim B was trying to demonstrate.

You haven't told us what marque your pump is, and I dunno if they publish flow curves relative to back pressure, but I strongly suspect that your fine pump does not reach the 7 m^3 per minute figure as installed. Likely is a LOT less, where the engine's flow will in fact be just about what it's displacement and RPM calculates to.

At any rate, adding air flow through the engine room is always a good thing... I'm just picking nits here!

Jim

[deluxe68]

Originally Posted by JohnB40

Thanks for comments.
Yes there are cheaper blowers but I was trying to use the same blower casing as it's directly bolted on to the transom. The motor does seem to cost about $50 as I see a fairly similar one on AC Truckers website. But it is a bit different, two speed, part number 2807-506-032 whereas I'm looking for 2807-506-006. I guess that goes in a Plastimo casing and the price goes to about $300.
Also the air hose is 70 mm (good old Beneteau) so I would have to replace some of the hose with say 3 inch and it's all cable tied in a hard to get at way.
I can get a $40 inline 3 inch blower at local marine place but again I'd have to attach the hose to the transom in a really hard to get at place and it would be 3 inch, so again need to connect to 70 mm (2 3/4 inch) unless replacing much hose. There are 3 to 4 inch plastic reducers but not 3 to 2 3/4 ... though imagine I could solve.
It's really just so easy to replace the motor for about $50 (if I can find it) rather than change to an inline blower with a different size air hose.
Thanks again.
JohnB40

I looked at the Kysor motor online and it is two speed but only uses two wires. Normally that means you select the fan speed by moving a jumper wire on the motor. I could not find any diagrams online or specs for comparing motor rpm’s. If the 2 speed fits then I would use it.

[Dockhead]

Originally Posted by Jim Cate

Well, it is an extreme example of what happens when you obstruct the air flow for two different types of pumps.

DH, what sort of blower is yours? They are typically "squirrel cage" types, and if my memory isn't totally shot, this type's throughput drops dramatically with back pressure, where a positive displacement pump's does not. I think this is what Jim B was trying to demonstrate.

You haven't told us what marque your pump is, and I dunno if they publish flow curves relative to back pressure, but I strongly suspect that your fine pump does not reach the 7 m^3 per minute figure as installed. Likely is a LOT less, where the engine's flow will in fact be just about what it's displacement and RPM calculates to.

At any rate, adding air flow through the engine room is always a good thing... I'm just picking nits here!

Jim

I linked to my blower above -- it's a Jabsco one. https://www.jabscoshop.com/marine/bl...24-volt-dc.htm



Sure, I understood that this type of blower is more sensitive to back pressure, but how does that move the needle? That was my point.

7.1m3 per minute even if cut in half -- which it certainly won't be, blowing through a short, almost completely straight 4" duct through the transom -- will still move more air than 7 liter diesel at 1000 RPM and will move more than double what my engine will move at redline. This issue is a red herring.


The point is -- don't blow air into engine compartments.

[Jim Cate]

The point is -- don't blow air into engine compartments.

Agreed!

My comments were relative to keeping the ngine compartment at lower pressure than to rest of the boat, and IMO the engine itself will do this. Additional air flow can't hurt, but may not really be necessary. Depends on the individual installation, I think.

Jim

[Bean Counter]

Originally Posted by Zai

Here are the specs. right from Defenders web page, of the Shurflo 30 dollar model.

Note it is continuous duty.

Attachment 178184

Seems a great price and 3 year warranty too. I'll try one if/when one of the three Johnson blowers we run ( about 2000 hrs at the moment) gives up the ghost (although they are on special at $50) but move air at 163 CFM vs 120 for the yellow tail.


https://www.marineengineparts.com/jo...3-flange-mount

[Lepke]

Originally Posted by steve77

A related question - Our blower is very noisy, meaning I can hear it easily even over the noise of the engine. Are the high dollar units appreciably quieter? Ours is a three inch in-line blower similar to the yellowtail from Defender. It's very old, probably 20 years or so.

Probably bearing noise. When the usually sealed bearings run out of lube, the bearings make more noise. When the bearings get real bad the blades or squirrel cage rubs. Sometimes before the bearings go bad you can add grease or oil and extend the life.

[jimbunyard]

Originally Posted by Dockhead

I linked to my blower above -- it's a Jabsco one. https://www.jabscoshop.com/marine/bl...24-volt-dc.htm



Sure, I understood that this type of blower is more sensitive to back pressure, but how does that move the needle? That was my point.

7.1m3 per minute even if cut in half -- which it certainly won't be, blowing through a short, almost completely straight 4" duct through the transom -- will still move more air than 7 liter diesel at 1000 RPM and will move more than double what my engine will move at redline. This issue is a red herring.


The point is -- don't blow air into engine compartments.

It is interesting that you make a distinction between blowing air into engine compartments and sucking air into them...

I assume, in a boat with as high a pedigree as a Moody 54, that the engine room or compartment is isolated and sealed from any living spaces within the boat, which should mean that there is at minimum a 5.5 (20 in2) duct allowing external air into the engine space (4" blower outlet [12.56 in2] + 3" exhaust outlet [7.065 in2]).

If you have such a minimally sized inlet, then I'd guess that your (undefinedly) short, almost straight (hopefully with a smooth ID) duct is almost certainly reducing the 'nominal' output of the blower when the engine is running (and for that case, even when it's not). The turbulence caused by the squirrel cage at over 1000 rpm, as well as the velocity of the airflow directly from the outlet, and the friction of the duct, all conspire against this nominal output, and could even combine to contribute to some sort of 'resonant restriction'. Who knows without actual flow tests?

If you indeed have an isolated-from-living-spaces engine room, it is imaginable that 'blowing air into (your) engine room' might actually be a more efficient way of circulating air through it...

Compare this to my raggedy-ass engine compartment, where in what- passes-for-winter around here the radiant heat from the engine warms the cabin a bit, if I had a blower, I'd set it up to blow overboard, even though I'm confident that there are no exhaust leaks...


Perhaps a more direct example of the 'board over the respective inlet' comparison would be "plumb the two inlets together, turn the 'pumps' on simultaneously, and see what happens..." Since the blower is a non-positive displacement pump, and the engine is, my prediction is that the blower motor burns up or pops the breaker or fuse within 30 seconds.

Of course, since the blower probably has a switch, it is a red herring; the blower can always be turned off and instantly turned into an inlet (albeit a rather restrictive one) instead of an exhaust...

[malbert73]

Remember diesels have a crankcase breather for blow by gases which typically is routed back into air intake but probably can contribute diesel small even with perfect exhaust system

[Dockhead]

Originally Posted by jimbunyard

It is interesting that you make a distinction between blowing air into engine compartments and sucking air into them...

I assume, in a boat with as high a pedigree as a Moody 54, that the engine room or compartment is isolated and sealed from any living spaces within the boat, which should mean that there is at minimum a 5.5 (20 in2) duct allowing external air into the engine space (4" blower outlet [12.56 in2] + 3" exhaust outlet [7.065 in2]).

If you have such a minimally sized inlet, then I'd guess that your (undefinedly) short, almost straight (hopefully with a smooth ID) duct is almost certainly reducing the 'nominal' output of the blower when the engine is running (and for that case, even when it's not). The turbulence caused by the squirrel cage at over 1000 rpm, as well as the velocity of the airflow directly from the outlet, and the friction of the duct, all conspire against this nominal output, and could even combine to contribute to some sort of 'resonant restriction'. Who knows without actual flow tests?

If you indeed have an isolated-from-living-spaces engine room, it is imaginable that 'blowing air into (your) engine room' might actually be a more efficient way of circulating air through it...

Compare this to my raggedy-ass engine compartment, where in what- passes-for-winter around here the radiant heat from the engine warms the cabin a bit, if I had a blower, I'd set it up to blow overboard, even though I'm confident that there are no exhaust leaks...


Perhaps a more direct example of the 'board over the respective inlet' comparison would be "plumb the two inlets together, turn the 'pumps' on simultaneously, and see what happens..." Since the blower is a non-positive displacement pump, and the engine is, my prediction is that the blower motor burns up or pops the breaker or fuse within 30 seconds.

Of course, since the blower probably has a switch, it is a red herring; the blower can always be turned off and instantly turned into an inlet (albeit a rather restrictive one) instead of an exhaust...

This is an awful lot of convolutions to try to get at -- what?


The proposition of not blowing air into engine rooms is a much simpler concept. You want to move air through the ER in order to keep temps down. Right? How do you want to move it? If you suck it, you keep pressure down, enhancing the engine's effect, keeping fumes, heat, etc. inside the ER rather than getting it into the passenger space. If you blow air in, rather than sucking it, you will be working against the engine and reducing the beneficial effect of keeping pressure down, in the best case (in the worst, you will overcome this effect and create overpressure). This is a very simple concept, and the reason why no actual engineer in the world would blow air into a sailboat engine room. All this business about positive displacement and squirrel cages is noise -- whatever the efficiency loss in the blower, 10%, 20%, 50%, even 90% -- every cubic meter of air blown in, will be creating an undesirable effect of one degree or another, and for what? What's the point?


As to concrete cases -- every sailboat I've ever seen, from a Catalina 27 to a Swan 90, other than those with ER in a separate watertight compartment (Sundeer 64, Amel 53), drew air into the ER through the bilges, not through separate ducts from the outside. If you end up with overpressure in the ER, it is a very not good thing. Fumes and heat will come out through the bilges, and also I've never seen an ER which was perfectly air tight, so there will be leakage from other places as well.


Why all this? Just suck, don't blow. I don't know what's so hard to understand about this.

[transmitterdan]

Dockhead and others are right. Never ever force air into an engine space. If you want to force air onto something like an alternator to cool it make sure the air source is taken from inside the engine compartment. If you want to get more fresh air into an engine compartment suck harder and/or increase the size of the fresh air inlet. But do not ever force air into the compartment.

Another detail involves fire suppression. All blowers and engines should be automatically cut off in the event of fire.

Frankly I think a lot of worry about heat in a diesel engine compartment is unnecessary. Combustion computations use degrees Kelvin not Centigrade. So going from 25C (298K) to 55C (328K) is not a huge increase (~10%) to the engine intake air. Lowering it a few % at the risk of crew death isn't worth it. If you truly need a cooler alternator use an external diode kit and put the diodes somewhere outside the engine compartment. But what is unlivable for people is not that bad for a diesel engine.

[Dockhead]

Originally Posted by transmitterdan

. . . .If you want to force air onto something like an alternator to cool it make sure the air source is taken from inside the engine compartment.

Indeed -- a small blower taking air from near where the air enters the ER from the bilge, directing a stream of this cool air onto the alternator, is harmless. But shouldn't really be needed if you're using a hot rated alternator. A typical school bus alternator is rate to produce full output 24/7/365 in an ambient temperature of 120C.

Originally Posted by transmitterdan

Another detail involves fire suppression. All blowers and engines should be automatically cut off in the event of fire.

Frankly I think a lot of worry about heat in a diesel engine compartment is unnecessary. Combustion computations use degrees Kelvin not Centigrade. So going from 25C (298K) to 55C (328K) is not a huge increase (~10%) to the engine intake air. Lowering it a few % at the risk of crew death isn't worth it. If you truly need a cooler alternator use an external diode kit and put the diodes somewhere outside the engine compartment. But what is unlivable for people is not that bad for a diesel engine.

I agree with you in general, and it's a good point, but it depends on what you have in your ER, doesn't it? Some people have batteries -- heat is death for those (they probably don't belong there under any circumstances). Electronics?


In any case, though, your other point hasn't been made previously, and it's important -- blowers absolutely should shut down in case of fire. Mine are controlled by a SeaFire system and go off automatically.

[transmitterdan]

Well it's a poor idea to put heat sensitive gear in the ER in my experience. I know a lot of us do it but it's still a bad idea. In our boat we put some electrical gear in the ER but it only runs when we are not motoring. Even so it's not the best idea. I think house batteries should never be in the ER as a matter of safety to the boat.

[Dockhead]

Originally Posted by transmitterdan

Well it's a poor idea to put heat sensitive gear in the ER in my experience. I know a lot of us do it but it's still a bad idea. In our boat we put some electrical gear in the ER but it only runs when we are not motoring. Even so it's not the best idea. I think house batteries should never be in the ER as a matter of safety to the boat.

I agree completely, but in many cases there is no practical alternative.



Batteries definitely not, but cruising boats, basically all of them -- warning, pet peeve ahead -- are so disastrously short of technical space, squeezed out to maximize accommodation space which sells boats at boat shows -- that you simply can't find room.


I have battery chargers, and charger/inverter in mine, which are pretty heat sensitive, but flowing 7m3 per minute through my ER keeps it below 30C in my climate (I monitor ER temp, at the top of the space). This gear was put there by original design and I simply don't know where I would move them to, if I had to move them.