Bilge blowers

[Lady Campanula]

I'm aware that 'best practice' is to utilise a bilge blower to vent any heavier-than-air combustible/explosive gases prior to engine start. It's also optimum to have 'flame proof' switches on such gear.

Does anyone have knowledge to share about retrofitting such a device on an elderly boat?

 

[Plomong]

Mine is so noisy (ear-shatteringly noisy) that I'm preparing to make it switchable so that it would be run prior to engine start, but only when starting from cold. At all other times it would be off.

Why only from cold ?? Well, the batteries are in the engine compartment, so they may generate hydrogen gas while being charged. However, when running the motor the engine draws air from inside the compartment, so there is no risk of gas buildup. When hooked up to pontoon supply, the battery charger is on line. Thus the compartment might have some gas buildup. To clear it, and not risk a hydrogen gas explosion, I plan to turn on the blower before switching on the batteries (no spark possible), then turn the ignition key to ON to run the blower for a minute or two before starting the engine.

Some hours of tests out through the harbour (using a digital thermometer) have shown that the temperature rise in the engine compartment is negligible or non-existent when the blower is switched off. In fact, very difficult to find any rise at all. It would, however, be advisable to run the blower again once the engine has been turned off, as there was a 4-5 degree increase in temperature at that point.

Plomong

 

[Bilgediver]

I'm aware that 'best practice' is to utilise a bilge blower to vent any heavier-than-air combustible/explosive gases prior to engine start. It's also optimum to have 'flame proof' switches on such gear.

Does anyone have knowledge to share about retrofitting such a device on an elderly boat?

The blowers are blowing into the bilge and not sucking and so the internal motor sees unpolluted air so there is a minimum risk moreover the better ones are described as ignition protected which is probably uncle Sams way of saying they are less risky then the el cheepo ones though not really flameproof.

The switches are in the cockpit or helm position so no need to be flameproof.

These are normally fitted to petrol engined boats to remove fumes which might accumulate in the event of petrol leakage Definitely a good idea..

These are normally run for about 5 minutes before engine start.

 

[VicS]

The blowers are blowing into the bilge and not sucking and so the internal motor sees unpolluted air so there is a minimum risk moreover the better ones are described as ignition protected which is probably uncle Sams way of saying they are less risky then the el cheepo ones though not really flameproof.

I was looking at the Rule website a couple of days ago following a question about Rule bilge blowers.

They actually show them as extractors with the suction ducting starting low down in the compartment!

If you use them as blowers you would have to be sure they are not blowing any gases or vapours somewhere else you would not want them!

 

[Marsupial]

Vics is quite correct, but the OP is concerned with a build up of combustible gasses. However an extractor is still the best way to go. Batteries produce hydrogen gas which wont be a problem as its lighter than air and it will find its own way out of the boat. The problem is with petrol vapour and methane/propane gas which is heavier than air and will collect in the bilges.

Back in the old days before overboard venting gas lockers it was thought to be good practise to cycle the MANUAL bilge pump for 30 seconds before starting the engine to clear the bilge of any unwanted gasses, we think it worked, not sure I would have employed an electric device for this job.

Ventilating the engine has been covered extensively on the forum and regardless of combustible gases engines should be positively ventilated with a temperature-controlled system. These systems have the "blower" extracting ie blowing air off the boat.

 

[Deleted member 36384]

..... and regardless of combustible gases engines should be positively ventilated .....

Its called negatively pressured ventilation. You are extracting air from a compartment which has to be replaced with air from out side the compartment. Positively pressured ventilation is when air is forced into a compartment and it vents out to other compartments.

Positive pressure prevents the ingress of explosive gasses, negative pressure removes them.

Lady Campanula - Some vents are installed into the coming around the cockpits such that the air strikes the deck, others are vented via the stern. Both exits are obviously high up. You need a decent grill and / or cowl to keep the rain out. Fit the hose high and drop down if possible to the vent. The ducting is very flexible and pretty easy to run.

On my own boat it extracts quite high up in the engine room as its for sucking out hot air (from the engine, not just me) so I guess its not really suitable for gas extraction.

I have a deep bilge and pump 75 strokes on the manual pump and always turn off the gas at the bottle, in my case. If you have a concern about explosive gas / vapour build up which will be extracted by fan then it does have to be explosion proof if mounted inside the compartment. If the fan is mounted outside the compartment it does not provided that the fan is designed for that purpose i.e. non static and fan shaft sealed from the motor.

On a diesel boat with outboard fuel stored in the vented gas locker and a gas alarm I dont see a need for an electrical fan to vent the bilge. The manual pump is good enough as is a good airing.

 

[Lady Campanula]

I'm considering again the recommendations of the MAIB report on the 'Lord Trenchard' explosion in Poole Harbour, 1999.

In the interests of learning from others' incidents:

Four people were on board 'Lord Trenchard' at her berth in Poole Harbour on the morning of 30 June 1999. When the skipper tried to start the diesel generator at 0710, an accumulation of liquefied petroleum gas (LPG) ignited, resulting in an explosion which seriously damaged the vessel. The skipper lost his left leg above the knee. LPG had leaked from a slack connector on one of the pair of gas bottles in the ready-use locker and migrated into the hold space accommodating the generator, through various non gas-tight penetrations in the locker. The attempt to start the generator ignited the gas in the hold. The leakage was not detected by the vessel’s gas alarm system.

'Lord Trenchard' was a sailing vessel of 13.54m registered length, constructed of glass reinforced plastic (GRP) and operated by the Joint Services Adventure Sail Training Centre (JSASTC), Gosport. She was owned by The Crown. The vessel was modified during 1995/6 in order to comply with the requirements of The Safety of Small Commercial SaiIing Vessels - The Code of Practice (the Code), She was then surveyed by the chosen certifying authority, Lloyds Register of Shipping (LR) who issued an interim certificate provisional on 29 October 1997

( glitch with Foxit Reader now sorted... )

I spent several separate weeks on that vessel many years before, and I well remember the then skipper, John Reed, briefing me in detail about the gas safety systems on board and why they were there. I'm thinking the 'not-so-fail-safe' circumstances could occur again.

 

[markdj]

To be clear...

A gas locker should be sealed with drain to outside. Gas alarm then takes care of the bilges.

Battery box should have a vent to outside, doesn't require fan.

For petrol engines an extractor should be used for 2 minutes before running then turned off. A fan for blowing air in is not normally fitted, natural ventilation its used.

On diesel engines an incoming fan can be run to force cool air into the engine space but a running engine will draw in so much air, the cooler the better and can be set to run after the engine stops to cool the engine compartment.

For fans, we had a 20 quid jobby but it was so noisy, was terrible. Got a decent one from asap and never looked back.

 

[Bilgediver]

I was looking at the Rule website a couple of days ago following a question about Rule bilge blowers.

They actually show them as extractors with the suction ducting starting low down in the compartment!

If you use them as blowers you would have to be sure they are not blowing any gases or vapours somewhere else you would not want them!

I am always a little concerned about sucking as some bilge blower motors are not exactly explosion proof I often wonder what might happen if the brush sparks met the wrong mixture. The ones which meet the ISO rules etc are probably safe for extracting explosive mixtures however I would beware using the cheepies advertised as blowers as extractors where explosive mixtures might be expected.


I believe these things are mandatory on USA boats fitted with petrol engines .

 

[Marsupial]

Its called negatively pressured ventilation. You are extracting air from a compartment which has to be replaced with air from out side the compartment. Positively pressured ventilation is when air is forced into a compartment and it vents out to other compartments.

QUOTE]

sorry its was a long night, I mean mechanically ventilated as you describe, the blower "sucks". but a "good airing" wont get rid of heavier than air gas - you need to help it out.

but please quote me correctly "...with a temperature-controlled system. These systems have the "blower" extracting ie blowing air off the boat." which is what you said I didn't say.

 

[electrosys]

I am always a little concerned about sucking as some bilge blower motors are not exactly explosion proof I often wonder what might happen if the brush sparks met the wrong mixture. The ones which meet the ISO rules etc are probably safe for extracting explosive mixtures however I would beware using the cheepies advertised as blowers as extractors where explosive mixtures might be expected.

If you're concerned (rightly so), then I'd fit some fine wire gauze to the input - as near to the fan as possible. That's how miner's safety lamps could allow a naked flame to be used in a methane-rich environment.

 

[Bilgediver]

If you're concerned (rightly so), then I'd fit some fine wire gauze to the input - as near to the fan as possible. That's how miner's safety lamps could allow a naked flame to be used in a methane-rich environment.

Good bit of lateral thinking but I think it would play havoc with the performance.

I would certainly look carefully at some of these blowers before using them as extractors. SParky bilge pump motors have have caused the singing of a few folk in recent years and one of these fans could do likewise if not made to the correct standard and happened to meet an explosive mixture.

The Attwood ones do specifically refer to an ISO standard. The Rule ones were described as blowers and did not mention this matter on the site I visited, maybe they do a different range for extracting explosive mixtures.

 

[pvb]

I'm considering again the recommendations of the MAIB report on the 'Lord Trenchard' explosion in Poole Harbour, 1999.
I spent several separate weeks on that vessel many years before, and I well remember the then skipper, John Reed, briefing me in detail about the gas safety systems on board and why they were there. I'm thinking the 'not-so-fail-safe' circumstances could occur again.

If you're that concerned about a gas leak, then an extractor from the bilge would give you some reassurance. However, you must get an "ignition protected" fan, and bear in mind that you also need to ensure that your main battery switch is ignition protected!

I'm not sure whether you've thought this through though. As I recall, the explosion on the Lord Trenchard happened when the boat was in normal use, not when it was first entered. On this basis, to be sure of being safe, you'd need to turn the fan on when you arrive at the boat and leave it on continuously all the time you're using the boat, which isn't exactly practical. A better solution for peace of mind might be a gas detector (although the Lord Trenchard had one of those too).

 

[electrosys]

Computer CPU and power supply fans are brushless, but you'd need to ensure that the switch is well away from the target area.

 

[Lady Campanula]

If you're that concerned about a gas leak, then an extractor from the bilge would give you some reassurance. However, you must get an "ignition protected" fan, and bear in mind that you also need to ensure that your main battery switch is ignition protected!

I'm not sure whether you've thought this through though. As I recall, the explosion on the Lord Trenchard happened when the boat was in normal use, not when it was first entered. On this basis, to be sure of being safe, you'd need to turn the fan on when you arrive at the boat and leave it on continuously all the time you're using the boat, which isn't exactly practical. A better solution for peace of mind might be a gas detector (although the Lord Trenchard had one of those too).

I am thinking it through, and working towards a suitable solution. It's an elderly boat, fitted out by the first owner, and we've experienced fatigue failure in a diesel return pipe that dumped most of a tankful into the bilges. Of course, the split was almost inaccessible and well-nigh impossible to inspect.

That has me thinking about the gas supply pipework, which runs from a gas locker right at the stern, about 4 metres or more forward to a simple shut-off tap, then to the cooker. It occurs that, should a fatigue crack open in this pipe, then gas may/will pool in the bilgewell whenever the shutoff at the bottle/regulator is open.

As one idea, there's a couple of battery-powered hand vacuum cleaners available, and I'm considering running a length of plastic hose down into the bilgewell, the end of which can be shoved/taped into the intake nozzle of a 'vac', and running that for a minute before switching on any other electrics.

Then there's the use of a self-contained solar-panel extractor vent ( SL? ) attached permanently to a similar flexible hose, which would operate permanently/continuously.

And of course I'm going to fit a bubble tester, and replace anything I can that's even slightly suspect.

...All this for a cup of tea!

 

[GrahamHR]

Oh dear, seems to be traces of the "petrol boats always explode" mentality here. American "Bilge blowers" such as made by Attwood, Rule etc are designed to be sparkproof and to extract potentially explosive fuel/ air mixtures safely. The USCG regulations ae pretty severe. My (American) boat has one, it did get very noisy due to corrosion, (actually like all domestic extractor fans do!) but the new one is very quiet. There are actually 2 x 3" and a 4" air inlet to the engine compartment, on my boat with a 4" extractor.

Graham

 

[VicS]

All this for a cup of tea!

I reckon you be lucky to survive long enough to enjoy it You are having a laugh aren't you

The vacuum cleaners may well be the least suitable thing to use as extractors and the most likely thing to ignite any flammable gases passing through them.

The gas pipe should be supported so that fatigue failure is just not likely to occur. If it flaps about then support it at what ever intervals are necessary to stop it and at no greater intervals than recommended by the Boat Safety Scheme.

I think you will find that a gas pipe passing through an engine compartment should do so in a sealed duct/conduit ( may only apply to petrol engines ????)

The bottle shut off valve should be shut except when gas is in use.

I doubt if a solar powered ventillator shifts enough air to make it worthwhile rigging it up.

 

[Lady Campanula]

OK, OK, you win! I'll just go on betting on the statistics to get me by....

Now, another leetl question. What about the highly flammable, volatile, almost explosive, vapours that constitute those 'Easy Start' sprays one sometimes uses to start the donk?

Much of that stuff is not drawn into the air filter, then the pre-chamber, and combusted, but misses and is squirted down alongside the engine block. What happens to it? Is it lighter than air, and so dissipates like hydrogen? Or otherwise....?

I'm beginning to think I should do something safer - like EOD!

 

[electrosys]

Computer CPU and power supply fans are brushless, but you'd need to ensure that the switch is well away from the target area.

... and as they say on some TV shows .... "here's one I made earlier".

'tis an ex-SCSI enclosure fan (brushless !) epoxied between a couple of plastic pipe sockets. This portable 'blower' - actually a 'sucker' - has been in intermittent service for a couple of years now, without problems.

 

[prv]

As one idea, there's a couple of battery-powered hand vacuum cleaners available, and I'm considering running a length of plastic hose down into the bilgewell, the end of which can be shoved/taped into the intake nozzle of a 'vac', and running that for a minute before switching on any other electrics.

I would expect vacuum cleaner motors to generate plenty of sparks even without any fault, just like my 12v drill does. This sounds like a terrible way to extract potentially-explosive gas.

Pete