diesel ventilation

gkny

Member
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The diesel in my boat is enclosed by cabinetry which is entirely enclosed within the cabin.  In other words there is no wall that is shared with the outside of the boat into which a vent can be installed.  The back of the cabinet is at the head of the aft quarterberth and a space has been left open.  This makes the aft berth somewhat smelly and very noisy when the engine is running.

  I have looked a bit at the issue of air sources for engines and most of what I have seen are systems for very large powerboats.  Does anyone have any experience with trying to increase airflow by adding a ventilation system.  Is a fan and ducting an option?  Is there a good way to wire such a fan so that it only runs when the engine is running.  The engine is a 28hp volvo diesel.

 

IStream

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Is there a way to vent through the bilge? On my last two boats I was able to improve engine breathing by having transom vent(s) communicate through the bilge to the engine compartment. 

I've yet to see a duct & fan system on a sailboat that didn't do more harm than good. You're better off with large, passive openings if at all possible. 

 

IStream

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Not to mention that it tends to sag and fold on itself unless very carefully installed. Throw an in-line fan in the mix that you either forget to turn on or that dies for one reason or another and you end up blocking half the clear opening and worse off than if you'd just cut some holes in the bulkheads and left it at that.

 

Bruno

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Is there a way to vent through the bilge? On my last two boats I was able to improve engine breathing by having transom vent(s) communicate through the bilge to the engine compartment. 

I've yet to see a duct & fan system on a sailboat that didn't do more harm than good. You're better off with large, passive openings if at all possible. 
That's an interesting idea, would you get enough airflow downward without mechanical assist for cooling, noise, odor control?

 

Diarmuid

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Not to mention that it tends to sag and fold on itself unless very carefully installed. Throw an in-line fan in the mix that you either forget to turn on or that dies for one reason or another and you end up blocking half the clear opening and worse off than if you'd just cut some holes in the bulkheads and left it at that.
Dust collection hose is rather sturdier; like dryer vent hose, tho, much of it relies on non-stainless spring steel coil. For a bit more coin, you can buy smooth(-ish) walled vacuum/blower hose with polymer coil that is really quite sturdy.

Our diesel engine compartment has two large (4") hoses running back to mushroom vents on the transom rail, one leg of which involved a blower), plus a third (aftermarket?) 3" duct out the side which teed to another line venting to low point of the cabin sole, with a blower wired for suction. Presumable to evacuate diesel smells or CO from indoors? If so, they dumped out in the cockpit, right next to the helm.

We still haven't figured out what parts of this to keep & what to pull out. We've added tons of additional ventilation to the cabin, so maybe we can dispense with some of the ductwork?

 

IStream

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That's an interesting idea, would you get enough airflow downward without mechanical assist for cooling, noise, odor control?
Your diesel is a great air pump so the air will be drawn to it, you just want the holes between the engine and the outside air to be large enough and numerous enough and along a direct enough path that the pressure differential along the way is minimal.

 

IStream

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Dust collection hose is rather sturdier; like dryer vent hose, tho, much of it relies on non-stainless spring steel coil. For a bit more coin, you can buy smooth(-ish) walled vacuum/blower hose with polymer coil that is really quite sturdy.

Our diesel engine compartment has two large (4") hoses running back to mushroom vents on the transom rail, one leg of which involved a blower), plus a third (aftermarket?) 3" duct out the side which teed to another line venting to low point of the cabin sole, with a blower wired for suction. Presumable to evacuate diesel smells or CO from indoors? If so, they dumped out in the cockpit, right next to the helm.

We still haven't figured out what parts of this to keep & what to pull out. We've added tons of additional ventilation to the cabin, so maybe we can dispense with some of the ductwork?
That vacuum/blower hose looks far, far better than any dryer hose I've ever seen.

 

justsomeguy!

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That vacuum/blower hose looks far, far better than any dryer hose I've ever seen.
Certainly better than lightweight dryer hose, but if it's anything like the stuff I recently bought (and it sure looks like it), it also

tends to sag and fold on itself unless very carefully installed. 
Meaning lots of supporting plastic zip ties. 

 

Zonker

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For a 28 HP diesel, 2 x 3" hose will work or 1 x 4". Almost the same cross sectional area. The diesel will happily suck in enough air to run.

If you enclose it in a box, consider sound insulation on the inside of the box.

An exhaust fan to cool off the space AFTER the engine is shut off will help cool the berth.

On one of our previous the boat the clamshell vent was in the cockpit footwell. Dumb place to put it, but there was an exhaust fan. On a cold night you would sit near it and have warm feet or hands by leaning forward. :)

 

Charlatan

Member
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Kiwiland
  I have looked a bit at the issue of air sources for engines and most of what I have seen are systems for very large powerboats.  Does anyone have any experience with trying to increase airflow by adding a ventilation system.  Is a fan and ducting an option?  Is there a good way to wire such a fan so that it only runs when the engine is running.  The engine is a 28hp volvo diesel.
Yes, I have done this and have the experience.

On older boats it is normal to ventilate the engine box to the bilge. This is noisy. If you look at any of the modern European production boats they have force ventilated engine boxes (a centrifugal fan). The boxes are also fully sealed, so are quiet. So quiet you can't hear the engine in the cockpit, and actually need to look at the rev counter to see what it is doing. My engine is so quiet now I have to look at the rev counter, and this is an old boat. Look at either boat review photos in sailing mags, or go to a boat show on a quiet day and lift up the engine cover, you will see a centrifugal fan high up in the engine box.

My boat is 35 yrs old and wooden, initially I had a 37 Hp Izuzu, but now have a 35 Hp Beta, so not too dismililar to you in basic size (for the purposes of ventilation). My objective was sound proofing.

I used a Gianneschi centrifugal blower fan, the C202. It is rated for continuous running. Be warry of axial fans, esp if you are in America. They are noisy, but they are generally used as bilge blowers for gasoline engines (which are common in the US, cause you guys love to burn gasoline and fuck the environment), and are not rated to continuous running. The C202 was about $400nz, compared with about $65nz for a piece of shit bilge blower, so expensive, but they have a noise rating (i.e they are quiet and certified to it), are well built and spec'ed for continuous running. You can also get them made in any configuration to suite your space, i.e. motor on the left or right, discharge on the top, side etc. The bilge blower fan at $65 was noisier than my old noisy diesel engine...

Refer attached spec sheet for the C202 blower. (bottom of post)

Most good chandlers should have ventilation pipe. I used 3 inch, which was smooth inside and with a stiff nylon hoop on the outside, from the local chandler:

https://www.burnsco.co.nz/shop/rv/plumbing-pumps-toilets/hose-hose-clamps/ducting-hose

Note, I'm in NZ, my apologies if you are not.

The ventilation fan blows into the engine box. My inlet was from a vented cupboard under the stove, so low down to get the cool air from near the bilge. I sealed the engine box with sound proofing, and made a baffle box on the inlet to prevent sound break out. Other than the regular foam sandwhich stuff, you can get a heavy vinyl that is ideal for tight spaces and for making gaskets to go around protrusions and ducting. If you have an older boat, you'll have loads of wires and pipes to seal around. I used Wavebar from Pyrotek:

https://www.pyroteknc.com/products/wavebar/wavebar/

Obviously the engine consumes air, so you need to get more air into the engine box than you take out.

For cooling of the engine box, I ran a duct (with ducting as above) from near the top of the box, out the back of the boat beside the exhaust pipe. Mine is vented to the Lazzarate locker, which is open to the air into the cockpit via a hole for the autopilot arm. Initial I just relied on the air pressure from the input blower fan, and we did get hot air out of the exhaust ducting, but it was a fairly long run.

So I got a 12 v DC axial fan, which is basically a computer fan, and rigged that up on the exhaust duct in the engine box. These PC fans are cheap (very cheap $12 nz plus delivery) but they are spec'ed for continuous running.

Both fans are wired to the engine ignition key so they run when the engine is on and stop when the engine stops.

To make sure this all works, and to raise an alarm if one fan dies, I use a regular little digital weather station thingee with an 'outside temp' on a probe, which is inserted inside the engine box. At full revs and continuous running the engine box (at the top) gets to around 40 deg C and stays there. When the engine stops, the box heats up to 50-55 deg C. We tend to run the engine at low revs or idle for a bit before shutting down. This is a natural part of coming into the berth / marina slowly, or anchoring, but it allows the engine to cool down via the cooling water before shutting down. Obviously its not good for engines to go from max revs to turned off strait away, without dissipating some heat.

We don't see a need for a timer to run on the fans after the engine shuts down.

If you want to get techo, new engine installation manuals have the required air input and output for certain sized diesels. This should be available for your engine, but the brand and model of engine doesn't matter, just the size. Nanni had the easiest to find and in a volumetric flow rate (needed for sizing fans), but it is also in the Beta installation manual, which is download-able from their website here, page 18:

https://issuu.com/betamarine/docs/om-221-20031_he_rev-13_-_1219?fr=sM2MyMDM3MDg0

Note that the beta manual only gives square area of openings, which is not much help if you want to duct the ventilation out of the cabin space. This shows an inlet opening and a outlet blower fan. You can do this and make a baffle box on the inlet for noise deadening. I had the big fan on the inlet to ensure good air supply for the engine combustion requirements. Possibly over the top, but it works really well on my set up.

View attachment Gianneschi 2015-43-C Blowers.pdf

 
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El Borracho

Sam’s friend
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Your diesel is a great air pump so the air will be drawn to it, you just want the holes between the engine and the outside air to be large enough and numerous enough and along a direct enough path that the pressure differential along the way is minimal.
This is the best answer. That 28 hp diesel pumps about 200 cfm for free. To the outside, too! So you only need an inlet. Size it several times larger than the air filter intake. For a bonus aim the cool inlet air at the intake side of the alternator...the only air cooled component of the engine.

 

SloopJonB

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For a bonus aim the cool inlet air at the intake side of the alternator...the only air cooled component of the engine.
Very good advice.

I've noticed that alternators that are packed into the back of FWD automobile engine compartments have a much shorter life than BITD of "sit in" engine compartments.

 

Charlatan

Member
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Kiwiland
I've got my inlet blower fan pointing straight at the alternator. Alternators really do benefit from being kept cool when they are working hard.

 
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Ishmael

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My alternator lies at the very outboard front side of the engine, to the extent that it has its own little engine box extension under the galley sink. I would love to get air to it, but it's not going to happen in my lifetime.

 

gkny

Member
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Thanks for all of the good advice.  I was worried about closing the gap but there are a number of holes in the stringers that are at the front and back of the engine compartment that are from 2" to 3.5 inches so it sounds like I will be o.k.

 
Depending on where you are it's nice to have a exhaust blower setup to knock down the heat in the space.  As above it will draw air itself ok as long as the space is not restricted.  It's not super healthy for a diesel to be starved of air but on a small auxillary positive pressure via intake blower in the space is a little overkill.  In a extreme case over time you will end up with a pretty dirty engine by starving air with poor combustion.  Lots of carbon leading to blow by.  Simply running a duct from the space by the intake out is a good idea.

 

yllek

New member
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2
I was curious as to how much air we're talking about. I calculate for my 35 hp engine about 52 cf/m. Still not meaning much to me, with a 4" vent hose (assuming, unrealistically, no air is leaking into the engine compartment) air flow in the hose is about 6.8 mph or just under 6 knots. I'll be looking at getting that air at least in the vicinity of the alternator. I hadn't thought about that but a gentle cooling breeze would be nice in there.

 

SloopJonB

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As long as there is an opening a little bigger than the intake port of the engine there won't be any breathing problems.

Anything bigger will help with the aforementioned cooling of the alternator. Having the opening in the vicinity of the alternator so the intake air is drawn past it should be good enough.

 
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