Are these vents essential?

[Kantara]

Our Alexander/Riverview semi-trad has two grilled vents into the engine compartment, one on either side of the hull. The grilles of both of these are subject to regular accidental removal, mostly from catching against the armco at moorings. One of them is directly next to the battery bank, the other opens into an empty space. There are two other vents into the engine space as well. Do you think they're likely to be essential for the cooling of the Barrus 2000 engine, or would the other two vents be enough? I've seen numerous boats with apparently no vents to the engine space.

 

Any thoughts, please?

Edited February 10, 2015 by Kantara

[Boat&Bikes]

Probably not essential. I would block them off for a while and see if it effects anything.

 

Ian.

[Flyboy]

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.

Edited February 10, 2015 by Flyboy

[Machpoint005]

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

[arbutus]

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.

[Naughty Cal]

The builder of the boat obviously put them there for a reason.

[Machpoint005]

The builder of the boat obviously put them there for a reason.

 

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)

[Alan de Enfield]

The builder of the boat obviously put them there for a reason.

 

Agreed - they are not going to make work unless they need to.

[dor]

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.

[Machpoint005]

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.

 

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

[Neil Smith]

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

 

Neil

[Guest]

Any chance of a pic of these vents?

[cuthound]

I have a boat with an Alexandra shell. It has a single vent, just below gunnel level on the starboard side only. The hole is covered with 2 welded strips, flush with the hull so cannot be knocked off. I have seen lots of boats with engine ventilation like this, but never vents which can be knocked off.

 

As others have said, can you post a picture of the vents?

[dor]

I have a boat with an Alexandra shell. It has a single vent, just below gunnel level on the starboard side only. The hole is covered with 2 welded strips, flush with the hull so cannot be knocked off. I have seen lots of boats with engine ventilation like this, but never vents which can be knocked off.

 

As others have said, can you post a picture of the vents?

 

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.

[Neil2]

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

[Neil Smith]

My new shell was only built last year by Paul Widdowson and has one vent about 10"x 6" with welded flat bars at 45% flush with the hull side.

 

Neil

[zenataomm]

[FadeToScarlet]

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.

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).

[Naughty Cal]

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).

Blimey, that means at full chat ours needs 4560 litres of air per minute!

[system 4-50]

I remember visiting a Harrier at Yeovil that had a placard that said it swallowed 2 tons of air every 5 seconds...

[MtB]

The builder of the boat obviously put them there for a reason.

 

 

Pointless post of the month.

 

Until we find out what the reason is, we won't know if it is a good reason or a stupid one.

 

 

MtB

[Naughty Cal]

 

 

Pointless post of the month.

 

Until we find out what the reason is, we won't know if it is a good reason or a stupid one.

 

 

MtB

Boat builders don't tend to make more work for themselves than is absolutely necessary.

[dave moore]

Most of the builders I work with do rather more than the bare minimum to ensure that their products reflect their skills, some going to way beyond what is necessary to produce top end quality. Just a balancing thought.....

 

Dave

[Naughty Cal]

Most of the builders I work with do rather more than the bare minimum to ensure that their products reflect their skills, some going to way beyond what is necessary to produce top end quality. Just a balancing thought.....

 

Dave

And judging by posts on this forum some dont even do what would be classed as the bare minimum

 

It is highly unlikely that a boat builder would spend time putting in extra vents just for the laugh.

[dave moore]

I've seen plenty of boats matching your description over many years but I thought I'd add a comment based on my experience within the industry rather than echoing the bleats of others. There are folk building who care about both their product and customers and I'm happy to work with them.

 

Dave