Are these vents essential?

[Neil2]

As I suggested earlier, builders will have to do a number of things in order to comply with the Recreational Craft Directive that they themselves might not consider necessary.

 

I can't find the reference to it but I'm sure it was in an account of a new build where this issue cropped up. The person who commissioned the boat didn't want the engine compartment vented because they intended taking the boat on tidal waters but the builder insisted because of the RCD requirement. IIRC the builder made blanking plates to be fitted over the vents for when the boat was taken into choppy waters which does make you wonder what the point of the vents is.

 

If I have this correct, what puzzles me is why the RCD regs require it but the BSS doesn't.

[Kantara]

Many thanks to all of you. I thought I'd got no replies, since the email notifications didn't happen! I'm so glad I logged in this morning. Very helpful, all of you.

 

...and I'll post a photo of the vents later today, if that's going to help.

Edited February 12, 2015 by Kantara

[Kantara]

Give alexanders a ring they might give you a reason why they fitted them.

 

Neil

Thanks, yes, I've contacted Alexanders, and they said I should contact Riverview - who turn out to be no more.

[Guest]

It's a surprising amount of air by volume.

 

I think the maths is right for this- A 1.8 litre engine, doing 1,000 RPM, will draw in (1.8 x 1000) /2 = 900 litres of air per minute.

 

(Divided by two because it's a four stroke engine, so each cylinder only draws air in once per two revolutions).

It is a surprising amount of air when calculated, but the engine I have manages to suck that much air through a pipe of about 2 inches dia, so I have never understood the need for the comparatively huge vents in some hulls ( unless air cooled of course.)

[Kantara]

I attach the photos of the vents in question. The one with the taped-on grille is the port one, the other side of which are the batteries. The other photos shows the other side, and it's the right-hand vent in question. Note the other two vents on that side. The smaller one is right next to the engine air intake.

 

[Guest]

Does seem a lot of ventilation to me. My boat has the two similar to the smaller sized ones with which it got RCD to sailaway standard, and has passed numerous Boat Safety tests. My previous boat had two smaller ones too. Difficult t say though without seeing the inside of the vents.

Edited February 12, 2015 by Guest

[Alan Saunders]

The installation instructions from the engine manufacturer should specify the required ventilation area. When I renewed my deckboards and added seals I incorporated two small brass 6" x 3" louvered (Mapp?) vents. I am certain that I sized them as more than adequate for my Vetus M3.10 (850cc, 3K rpm?).

 

Both vents are within the cockpit area, above the boards and therefore way above water level. One is high up in the trunking to the controls and the other low down in a cover over an ehaust 'swan neck'. Even when the engine is not running, the compartment is adequately ventilated.

 

Air for a water cooled engine can be ducted from above the cabin roof - see all those 'fishing boats' with high level ducts to avoid ingesting waves. Hydrogen from the battery will diperse better from a high level vent but the engine will do a good job of sucking it in. Air vents in the hull are undesirable but a cheaper solution than ducting for a boat builder.

 

Alan

Edited February 13, 2015 by Alan Saunders

[Scholar Gypsy]

As I suggested earlier, builders will have to do a number of things in order to comply with the Recreational Craft Directive that they themselves might not consider necessary.

 

I can't find the reference to it but I'm sure it was in an account of a new build where this issue cropped up. The person who commissioned the boat didn't want the engine compartment vented because they intended taking the boat on tidal waters but the builder insisted because of the RCD requirement. IIRC the builder made blanking plates to be fitted over the vents for when the boat was taken into choppy waters which does make you wonder what the point of the vents is.

 

If I have this correct, what puzzles me is why the RCD regs require it but the BSS doesn't.

 

A cautionary tale...

[Neil2]

 

A cautionary tale...

I remember that incident at the time it happened and I wondered what the boat had been overplated with...

 

When you see where the "new" waterline is, unless they used lead plating the boat must have been way over ballasted to begin with. It should have been obvious that it was sitting way too low even to be safe on a canal.

[MtB]

Thanks for the photos. Those look ridiculously large holes to have cut in the hull.

 

I'd have them removed and securely welded over if it was my boat. The represent a significant sinking risk in my opinion.

 

If the engine really needs that much ventilation there is no reason I can think of not to have the vents through the cabin sides.

 

 

MtB

[Kantara]

The vents may be there to allow air into the engine air filter. Do you have any other air inlets in to the engine compartment? All engines need to breathe & to to help cool the alternator.

 

Edited....Just read your post properly & you said you have other vents,so you should be ok to blank off the grills. Perhaps your boat had an air cooled engine in the past.

No, it's the original, water-cooled engine.

If they come off accidentally can't you screw them on more firmly? (preferably with the grille inside the hull, not outside it).

It's a solution, but I'd rather get rid of them altogether if they're not essential.

It’s interesting that one of the vents is by the batteries. If you have open-vented batteries you will need ventilation.

 

On Electrical installations the BSS essential guide says:

All battery compartments containing unsealed or open-vented batteries must be adequately ventilated to prevent a build up of flammable mix of gasses.

 

Spelling it out in more detail, the Boat Safety Scheme says:

All unsealed or open-vented batteries must be stored within a ventilated space.

Dedicated battery spaces or boxes for unsealed or open-vented batteries must be ventilated at the top or the highest point of the sides of the space or box and any ductwork used must run horizontally or upwards.

The ventilation pathway from all battery storage locations must lead to the outside of the hull or superstructure.

Thanks for that. I have sealed batteries, so venting isn't required for them.

[by'eck]

Any comments about the buider knowing what he was doing (assuming they are original) go out of the window after seeing those pictures.

[Kantara]

 

On the other hand, the boat may have been re-engined since then, so at least some of the vents may appear redundant (eg on our boat)

Nope, it's the original engine, water-cooled.

My boat has no apparent external vents. Good thing if you the back end gets lowered as it seems many sinkings occur when the engine vents reach water level. On the semi-trad stern there is a single vent on the inside, above the batteries and near the alternator, covered with a six inch grill. I've had no problem with overheating of the alternator and there is adequate air for the engine intake - just look at how small the intake is on the air filter box, you don't really need much.

I take your point about the air filter intake. Thanks for that.

 

Liverpool Boats used to have two huge vents with angled bar welded across them - very solid! By contrast, Northwich Boats (based near Sandbach) used to have two holes in the hull with standard brass 6" x 6" ventilator grills screwed over them. They always looked very vulnerable to me.

Indeed! If I have to keep the vents, then I'll get something much more durable welded across the vents. But I'd rather lose them altogether if that's feasible.

 

Liverpool Boats used to have two huge vents with angled bar welded across them - very solid! By contrast, Northwich Boats (based near Sandbach) used to have two holes in the hull with standard brass 6" x 6" ventilator grills screwed over them. They always looked very vulnerable to me.

Indeed! If I have to keep the vents, then I'll get something much more durable welded across the vents. But I'd rather lose them altogether if that's feasible.

 

I'm sure I read somewhere recently that the RCD requires engine room vents and has done for some years. I'm guessing the regulation came in around 2000-ish. But it's irrelevant with a secondhand boat and I don't think there's any BSS requirement so you only have to have them if the batteries are in the engine compartment.

 

There are other ways you could achieve battery venting of course

I have sealed batteries, so venting them's not an issue - thanks.

Any comments about the buider knowing what he was doing (assuming they are original) go out of the window after seeing those pictures.

That thought had crossed my mind, too! :-)

[MtB]

Indeed! If I have to keep the vents, then I'll get something much more durable welded across the vents. But I'd rather lose them altogether if that's feasible.

 

 

With a water cooled engine you absolutely don't need those vents there. You don't really need any vents at all as combustion air will happily find it's way to the engine through all the gaps and cracks in doors and hatches unless your engine bay is exceptionally well sealed up, which I doubt!

 

The sinking risk is that if the boat is in a bad way and taking on water, people seeing the boat low in the water will not perceive any immediate risk of sinking while the gunwales are well above water, and may not notice the vents close to or below the waterline, so will see no urgency in assisting.

 

Once the vents are underwater the boat will go down in minutes.

 

MtB

[Kantara]

The installation instructions from the engine manufacturer should specify the required ventilation area. When I renewed my deckboards and added seals I incorporated two small brass 6" x 3" louvered (Mapp?) vents. I am certain that I sized them as more than adequate for my Vetus M3.10 (850cc, 3K rpm?).

 

Both vents are within the cockpit area, above the boards and therefore way above water level. One is high up in the trunking to the controls and the other low down in a cover over an ehaust 'swan neck'. Even when the engine is not running, the compartment is adequately ventilated.

 

Air for a water cooled engine can be ducted from above the cabin roof - see all those 'fishing boats' with high level ducts to avoid ingesting waves. Hydrogen from the battery will diperse better from a high level vent but the engine will do a good job of sucking it in. Air vents in the hull are undesirable but a cheaper solution than ducting for a boat builder.

 

Alan

Helpful, thanks! I'll look into the manufacturer's requirements. Their website's not helpful, but I have the manual - not sure it covers installation, but we'll see.

 

 

With a water cooled engine you absolutely don't need those vents there. You don't really need any vents at all as combustion air will happily find it's way to the engine through all the gaps and cracks in doors and hatches unless your engine bay is exceptionally well sealed up, which I doubt!

 

The sinking risk is that if the boat is in a bad way and taking on water, people seeing the boat low in the water will not perceive any immediate risk of sinking while the gunwales are well above water, and may not notice the vents close to or below the waterline, so will see no urgency in assisting.

 

Once the vents are underwater the boat will go down in minutes.

 

MtB

Thanks for that. My gut feeling has been all along that the vents are overkill at best. I think the problem pair at least will get sealed.

[Naughty Cal]

Are they original fit from when the boat was built?

 

They don't look like it to me. They look like they have been added for whatever reason.

 

Not sure why a previous owner would feel the need to add quite so many though.

[Neil2]

Found it - this is an extract from the TNC website describing the commissioning of their boat built by R&D fabrications. I believe the "he" referred to is former(?) owner of the company Ray Denton

 

"These were vents for the battery box and for fire fighting in the engine compartment. He said that these have to be fitted for CE certification, but he could make some plates with some threads welded to the back. These could be sealed with a rubber gasket and held on with some washers and wing nuts. These of course could only be fitted at our own risk, for tidal crossings".

 

I was struggling to understand this at first but I suppose in the event of a fire in the engine compartment there should be a means of extinguishing the fire without having to remove the deck boards/hatch.

 

I think boats in categories C to A must have an extinguisher in the engine room capable of being operated remotely, or that operates automatically. Cat D (inland) boats don't have this requirement, hence the need for an "external" compartment access.

Edited February 13, 2015 by Neil2

[Naughty Cal]

Our insurance also states that we have to have an automatic fire extinguisher in the engine bay.

[blackrose]

 

Agreed - the gaps around the deck boards will account for that area!

I don't have gaps around my deck boards.

 

It is a surprising amount of air when calculated, but the engine I have manages to suck that much air through a pipe of about 2 inches dia, so I have never understood the need for the comparatively huge vents in some hulls ( unless air cooled of course.)

To prevent a build up of flammable battery gases perhaps? (On boats with wet lead-acid batteries). Hydrogen may not escape through a 2" hole.

Edited February 15, 2015 by blackrose

[blackrose]

Air for a water cooled engine can be ducted from above the cabin roof

Assuming it's a trad stern?

 

More difficult with a cruiser stern, but I don't know why we don't see more cruisers with higher vents in the control pedestal for example. I guess builders don't think that we might be talking our boats onto tidal waters.