Location of blower exhaust vents

[joliette]

I'm looking to hook up my 4" blowers in the engine compartment to a pair of vents that I have to install. Are there any rules or guidelines concerning the location of engine compartment exhaust vents? I could locate the vents on the transom or the sides but, in both cases, they would be close to the waterline - at around 12"- 15" - and that just doesn't feel right to me (when through hulls fitted under 12" above the waterline should be fitted with seacocks).

Another possibility (although more problematic to execute) would be to fit them on the aft deck with some kind of cover plate to prevent water ingress.

Any thoughts or advice would be much appreciated.

 

[jfm]

I'm looking to hook up my 4" blowers in the engine compartment to a pair of vents that I have to install. Are there any rules or guidelines concerning the location of engine compartment exhaust vents? I could locate the vents on the transom or the sides but, in both cases, they would be close to the waterline - at around 12"- 15" - and that just doesn't feel right to me (when through hulls fitted under 12" above the waterline should be fitted with seacocks).

Another possibility (although more problematic to execute) would be to fit them on the aft deck with some kind of cover plate to prevent water ingress.

Any thoughts or advice would be much appreciated.

Need pics really. What is the flow direction? Do these vents feed air into the e/r or does air from the e/r come out of the vents? If the former you could fit them in the cockpit?

You could imake a water catcher tray/tub, to catch green water that gets in thru the vents and drain it away, rather than have it slop into the e/r

 

[MapisM]

Didn't the boat have any, originally? That's very surprising, for a petrol boat.
Regulations aside , surely Levi knew the danger of petrol vapour well before RCD...
Anyway, the only STRICT rules are that:
1) you must fit proper fireproof blowers, with well insulated electric connection;
2) they should extract air from the very bottom of the e/r. There are 4" flexible hoses available for this specific purpose.
I don't think you'll ever need to use them while cruising, only before turning on the engines. Some builders recommend to turn them on also when cruising at very slow speed dor some time.

 

[MapisM]

To better explain what I meant, just look at this installation:
The two white inline blowers are visible at the bottom of the pic, attached to the transom. The one on stbd side is more visible, whilst the other one is partially hidden by the hatch actuator.
The flexible hose goes from the blowers, up to two grilled plates on the transom. But for the "out" section, any other placement will do, as long as high enough on the w/l and protected by water ingress.
What's more important (and not obvious), as you can see in the mirrors under the engine hatch, is to fit another piece of hose in the "in" section, from the blowers to under the engine, to suck air as close as possible to the bottom of the hull. I've seen that missing in various installations, but this is the proper way to do it.

 

[joliette]

Didn't the boat have any, originally? That's very surprising, for a petrol boat.
Regulations aside , surely Levi knew the danger of petrol vapour well before RCD...
Anyway, the only STRICT rules are that:
1) you must fit proper fireproof blowers, with well insulated electric connection;
2) they should extract air from the very bottom of the e/r. There are 4" flexible hoses available for this specific purpose.
I don't think you'll ever need to use them while cruising, only before turning on the engines. Some builders recommend to turn them on also when cruising at very slow speed dor some time.

I think the original boat was well engineered for the time, but things have changed since the 1960's and I had to replace the integral grp fuel tanks as they are no longer suitable for modern petrol containing ethanol. The only natural engine ventilation that I have been able to find is at the back of the engine compartment under the short aft deck. There was no sign of any blowers being fitted apart from a possible vent location on the aft deck.

I don't like the idea of taking air in through the aft engine compartment and then having the exhaust at the front, into the cockpit. I'd rather work it the other way round, so have calculated vent sizes and designed baffle boxes (to keep water out) and fitted these to the front of the engine compartment. Engine compartment volume and two engines demand two 4" blowers, which I will fit with intake ducting reaching down under each engine, but at least 24" from the intakes ... no problem!

I guess I need to consider carbon monoxide risks? That being the case an external location for the blower exhausts is needed ... so I guess it will have to be on the aft deck.

 

[MapisM]

Mmmm... I'm a bit confused.
I assumed that you were fitting the blowers only for safety, i.e. extracting petrol vapours (if any) from the engine compartment before turning the engines on.
That's normally the only reason to fit blowers in this kind of boats, because while cruising the ventilation needed by the engines is provided by some intakes where the air can naturally flow in, according to what the engines require.
And this kind of ventilation neither requires blowers nor outlets, because the air flowing in is "eated" by the engines, and expelled through their exhausts.
Which in turn grants also a constant ventilation of the engine compartment.
Are you fitting the blowers also for ventilation while cruising, instead? And if so, why?

 

[Scarron]

My Triana 25 has two of these http://www.vetus-shop.com/vetus-cowl-ventilator-donalds-and21675mm-fixed-plastic-ring-p-1271.html type things on the aft deck facing backwards. Both fed by 3" extractor fans and flexible ducting, one extracts from about 4" above the bottom of the engine compartment to pick up any petrol vapour from the carbs etc. and the other runs through the bulkhead to extract from the tank compartment / main bilge to pick up any leaks or spillage whils fuelling also any gas from the portable cooker. I just run them for a few minutes before starting and whilst refuelling.

As MapisM says the induction air for the engines comes form another pair of vents into the engine compartment, mine were plumbed to the air scoops on the cabin sides but I don't like the idea of damp salt spray being brought directly into the compartment so instead I feed from some open lockers within the cockpit sides. It's usually a fair bit drier in there [not always though].

Paul.

 

[joliette]

My Triana 25 has two of these http://www.vetus-shop.com/vetus-cowl-ventilator-donalds-and21675mm-fixed-plastic-ring-p-1271.html type things on the aft deck facing backwards. Both fed by 3" extractor fans and flexible ducting, one extracts from about 4" above the bottom of the engine compartment to pick up any petrol vapour from the carbs etc. and the other runs through the bulkhead to extract from the tank compartment / main bilge to pick up any leaks or spillage whils fuelling also any gas from the portable cooker. I just run them for a few minutes before starting and whilst refuelling.

As MapisM says the induction air for the engines comes form another pair of vents into the engine compartment, mine were plumbed to the air scoops on the cabin sides but I don't like the idea of damp salt spray being brought directly into the compartment so instead I feed from some open lockers within the cockpit sides. It's usually a fair bit drier in there [not always though].

Paul.

I think I'm on the right track then, as my set up sounds similar to the Triana. However, I have one blower per engine, with the inlet ducts reaching down under each engine. My inlet vents to the engine comparment are also in the cockpit on the front of the engine compartment with custom built 90 degree baffle boxes and water drainage back out into the cockpit.

As I see it the main function of the blowers is to get rid of any dangerous fumes before engine ignition. However, I gather there is also the possibility to run them continuously to improve air flow and to help manage engine compartment temperature if necessary?

My fuel tanks (are now) in a completely separate compartment with no sources of spark ignition in it, so I was just going to naturally ventilate it with air flow through the boat, rather than dedicating a blower to it. The Settimo Velo has an inlet vent high on the stem, so I was thinking of directing the airflow from this through the blige and lockers, into the fuel tank compartment and then into the engine compartment and out through and additional vent on the aft deck ... My only slight concern with this idea of naturally ventilating the fuel tank space is that the helm console - containing all the electrics (ignition switches, gauges, instrument, switch panel etc.) - sits on top of this space and has some airflow to it ...

 

[Scarron]

Yes you are definitely on the right track, I like the sound of your inlet vents from the cockpit with built in drains.

A general note on fuel/LPG safety;- you are right that the main function of the blowers [suckers really] is to extract flammable vapours from anywhere in the boat that they may gather, the key thing is that both petrol and LPG vapours are heavier than air so you really need an extract hose from everywhere low down in the hull that they could gather.

A really scary thing to do is watch carefully when refuelling on a cold day, you can see the vapours being displaced from the tank absolutely flooding back out of the filler tube, usually these just drop to the surface of the water and get blown away however if you are unlucky, with a little breeze these can easily get over the cockpit coamings and gather in the cockpit/tank compartment and bilges. The same is true of LPG leaks when changing bottles/canisters etc. the thing is, being significantly heavier than air it'll sit in your bilges for ages and natural ventilation just won't get rid of it.

If you have a well maintained fuel system then actually the risks in the main boat are far higher than the engine compartment. People are generally afraid of petrol boats blowing up, but with a good fuel system and properly functioning blower/extractors they are very safe, in my opinion LPG gathering in the bilges of all boats and especially yachts is a much bigger problem: as blowers are not generally fitted - a pretty dangerous oversight in my view..

As a secondary function the engine room blowers can help to dissipate excess heat, I run mine occasionally, usually for a bit when running at displacement speed after slowing down from a run out.

Sounds like you are getting to the secondary rigging stage - making good progress, are you coming to our rally in August? http://www.powerboatrally.com/

 

[MapisM]

As I see it the main function of the blowers is to get rid of any dangerous fumes before engine ignition. However, I gather there is also the possibility to run them continuously to improve air flow and to help manage engine compartment temperature if necessary?

Nope. That requires a different setup, usually with a couple of blowers on each side of the e/r. The two in front blow air inside the e/r, whilst the two astern suck air.
This is strictly meant to keep the e/r properly ventilated, but I've never seen such arrangement on any small(ish) boat, where there's actually an engine compartment, rather than an e/r.
By keeping your blowers running while cruising, in theory you might have a negative effect on the engines, because since they extract air, they actually work "in competition" (for lack of better wording) with the engines in sucking air, hence reducing the air pressure - not a good thing, for a naturally aspirated engine.
Coming to think of it, if the blowers could be reversed, it might make sense to keep them running while cruising. Or maybe just one of them, to improve the air circulation. But I've never seen such arrangement.

 

[mil1194]

SOrry to take this OT - but are they actually mirrors or polished stainless (or something?) Whatever they are - is there a practical reason for this or just for looks?

 

[MapisM]

Polished s/s, I guess (not my boat). Just a matter of making it look cool, anyhow.
That's one of those "only in America" things...
...they're also mad about custom painting on performance boat, btw.
Feast your eyes on this one, frinstance!
Gorgeous boat btw, gimme one of them in solid white and I'd rather save on wine to pay the fuel bills...!

 

[mil1194]

Polished s/s, I guess (not my boat). Just a matter of making it look cool, anyhow.
That's one of those "only in America" things...
...they're also mad about custom painting on performance boat, btw.
Feast your eyes on this one, frinstance!
Gorgeous boat btw, gimme one of them in solid white and I'd rather save on wine to pay the fuel bills...!

OOooooooooooooooooooo............I've come over all funny.........

 

[MapisM]

Yeah, I see what you mean.
Did you see those #6 outdrives painted to match the hull, at the bottom of that page?
Boating porn at its best!

 

[mil1194]

Yeah, I see what you mean.
Did you see those #6 outdrives painted to match the hull, at the bottom of that page?
Boating porn at its best!

Just cancelled SWMBO'd 40th b'day party to (part!!!!) finance one.......bet it's dear mind........

Stunning finish even if it isn't your fancy.

 

[joliette]

Yes you are definitely on the right track, I like the sound of your inlet vents from the cockpit with built in drains.

A general note on fuel/LPG safety;- you are right that the main function of the blowers [suckers really] is to extract flammable vapours from anywhere in the boat that they may gather, the key thing is that both petrol and LPG vapours are heavier than air so you really need an extract hose from everywhere low down in the hull that they could gather.

A really scary thing to do is watch carefully when refuelling on a cold day, you can see the vapours being displaced from the tank absolutely flooding back out of the filler tube, usually these just drop to the surface of the water and get blown away however if you are unlucky, with a little breeze these can easily get over the cockpit coamings and gather in the cockpit/tank compartment and bilges. The same is true of LPG leaks when changing bottles/canisters etc. the thing is, being significantly heavier than air it'll sit in your bilges for ages and natural ventilation just won't get rid of it.

If you have a well maintained fuel system then actually the risks in the main boat are far higher than the engine compartment. People are generally afraid of petrol boats blowing up, but with a good fuel system and properly functioning blower/extractors they are very safe, in my opinion LPG gathering in the bilges of all boats and especially yachts is a much bigger problem: as blowers are not generally fitted - a pretty dangerous oversight in my view..

As a secondary function the engine room blowers can help to dissipate excess heat, I run mine occasionally, usually for a bit when running at displacement speed after slowing down from a run out.

Sounds like you are getting to the secondary rigging stage - making good progress, are you coming to our rally in August? http://www.powerboatrally.com/

Ah, I didn't think about that! ... I was assuming the tank breathers would send any vapour away. So, I think I will put another blower in the tank space beneath the cockpit. That will suck air through the whole of the bilge and I can vent it through the engine compartment blowers ... I was going to install gas on the boat for cooking but I already have one of those Origo meths things so will probably give that I try to begin with. For gas I'll have to build a locker in the cockpit for the bottles and vent that overboard, so I will hold back on the additional work for the moment or I'll never get her on the water ... in time for August?!?