Why so much ventilation on boats?

[MtB]

Oops, forgot one.

 

4) The reduced air volume in sleeping accommodation in a bote cabin means the oxygen depletes faster as you breathe it, so better ventilation is necessary.

 

I know you have a wide beam and can probably get agoraphobia in your bedroom, but most boats have tiny cabin spaces compared to houses.

[blackrose]

Two reasons:

 

1) The greatly reduced volume of air inside a boat cabin amplifies the effect of gas leaks, combustion products leaking into the atmosphere etc

 

 

While I'm sure some people's boats represent a reduction in volume from what they were used to on land, my boat is the largest space I've ever lived in - it's about 6 times the size of the rented room in my new slum.

 

Oops, forgot one.

 

4) The reduced air volume in sleeping accommodation in a bote cabin means the oxygen depletes faster as you breathe it, so better ventilation is necessary.

 

I know you have a wide beam and can probably get agoraphobia in your bedroom, but most boats have tiny cabin spaces compared to houses.

 

Yes, exactly.

Edited January 16, 2013 by blackrose

[MtB]

While I'm sure some people's boats represent a reduction in volume from what they were used to on land, my boat is the largest space I've ever lived in - it's about 6 times the size of the rented room in my new slum.

 

 

 

Yes, exactly.

 

You are a victim of the 'one size fits all' philosophy of rule creation - a vain attempt to make the rules simple and easy to check for compliance.

 

OTOH ventilation calcs on botes are complex enough already without having to incorporate a 'room volume factor' into the arithmetic!

[nicknorman]

True - but is that the only reason boats and caravans are so well provided for in terms of ventilation?

 

I don't know for sure but thought it was in relation to CO too.....

Having a combination of high and low level vents helps them to work better if the space is heated - the warmer (lighter) air will tend to flow out of the upper vents and be replaced by colder (heavier) air coming in via the lower vents. If the vents were all at the same hight, the through flow would be less.

[Ally]

i was wondering about this as the vents in the stern door drive me mad because of the noise that they let enter when i am in bed.would the mushroom vent over the bed not suffice as the solid fuel stove is at the far end of the boat beside two door vents then three mushroom vents down the length of the boat and the cooker is in the middle.oh! yes there is allso a bulk head vent at the rear that vents into the cupboards at the back and under the stairs where the invertor is and through to the bedroom.surely it would be ok to block the two vents in the rear door or am i a suicidal maniac?

I would have to assume that your boat has been given the correct amount of ventilation. It's worked out by sq inch, according to what your appliances are, ie stove max output, cooker hob/oven, other heating appliances, people on board, etc, so I would NOT say block any up. If you can work out what your requirements should be, and then find you have more low level than required, then you have a choice, but I would assume it is correct...though many do over vent...just as some under vent.

 

The requirement if for low and high ventilation. It must indeed be 'open' not closeable, but they can be fitted in much less obtrusive ways than filling bow and stern doors with huge vents.

Edited January 16, 2013 by Ally

[David Schweizer]

The modern windows in my room don't have any built-in vents.

The Building Regulatiions regarding ventilation are not straightforward, as I found out when applying for Building Regulation approval for the extension on our house. However my experience would suggest that if yo are replacing an existing window in a building built before the ventilation requirements were introduced, you do not need to fit ventilated windows, but if you are putting windows (or french doors) into a new build they must be ventilated.

 

I am not sure about Mike's observation regarding open flues etc. The extension in our house had no open flue in it and the Building Regulation Officers had no details of the rest of our house, but they insisted upon slot vents in the top rails of the french doors.

 

We recently had new windows fitted throughout our house (except for the new extension) and none of them have ventilation, but the newbuild coservatory built by the same company does.

Edited January 16, 2013 by David Schweizer

[Ray T]

Paul C, on 16 January 2013 - 12:32 PM, said:

 

Gases don't collect in the bottom of a container, they disperse readily with other gases eg the atmosphere.

 

 

That is wrong and dangerous. Gases heavier than air do collect in the bottom of containers.

 

As a matter of academic interest, when I joined what was The GPO in 1967 part of my apprentice ship was with out door gangs installing cables.

This involved going down into surface level manholes. One of the gas tests we had to do was with a Davey Lamp to test for heavier than air foul gas. We did find this on one occasion and the remedy at the time was to bail out the gas with a bucket on a rope. I was given this task and felt a right pillock apparently bailing "nothing" down the gutter.

 

As well as heavier than air foul gasses there are explosive gasses which collect in manholes as well.

 

BT/Openreach now has specialist venting equipment and electronic gas detectors.

 

ETA Heavier than air gasses are a "fluid" you often cannot see.

Edited January 16, 2013 by Ray T

[n.b.Goldie]

LPG is heavier than air and sinks to the bottom. It also, from posts above, seems to be able to find its way through very small gaps. I doubt most floors are gas-tight and therefore any spilled gas will find its way int to the bilge. Eventually, if the rate of gas going into the bilge is greater than the rate at which the gas degrades, if it does, the bilge will be full of gas. There is no outlet for the gas it being at the lowest level and once full the bilge-gas will overflow the floor. At this point any floor level ignition source will ignite it. Sop what is the point of low level ventilation as it cannot disperse any gas. Low level ventilation is usually the bottom of front and/or rear doors which are way higher than the bilge or floor.

 

Or have I missed something?

 

Regards

Ditchdabbler

 

p.s. I understand that carbon monoxide is lighter than air and therefore low level ventilation will help disperse it but we are discussing heavier than air LPG

 

 

 

[Timleech]

LPG is heavier than air and sinks to the bottom. It also, from posts above, seems to be able to find its way through very small gaps. I doubt most floors are gas-tight and therefore any spilled gas will find its way int to the bilge. Eventually, if the rate of gas going into the bilge is greater than the rate at which the gas degrades, if it does, the bilge will be full of gas. There is no outlet for the gas it being at the lowest level and once full the bilge-gas will overflow the floor. At this point any floor level ignition source will ignite it. Sop what is the point of low level ventilation as it cannot disperse any gas. Low level ventilation is usually the bottom of front and/or rear doors which are way higher than the bilge or floor.

 

Or have I missed something?

 

Regards

Ditchdabbler

 

LPG will slowly disperse/diffuse into the surrounding air, and the more air movement there is at low level the better for getting rid of it.

 

Tim

 

I suppose we shouldn't refer to it as LPG once it's out of the bottle, but ...

Edited January 16, 2013 by Timleech

[n.b.Goldie]

LPG will slowly disperse/diffuse into the surrounding air, and the more air movement there is at low level the better for getting rid of it.

 

Tim

 

I suppose we shouldn't refer to it as LPG once it's out of the bottle, but ...

 

A good argument for making sure the floor also has adequate ventilation methinks. I doubt many boats do though.

 

Regards

Ditchdabbler

[nb Innisfree]

I suppose we shouldn't refer to it as LPG once it's out of the bottle, but ...

 

Actually, when in the bottle, it's both a liquid and a gas.

[Rich]

The modern windows in my room don't have any built-in vents.

 

I would suspect that either they aren't very modern, aren't very well made, i.e. draughtproofed, or whoever fitted them didn't do so in accordance with building regulations.

[Timleech]

Actually, when in the bottle, it's both a liquid and a gas.

 

Well yes, but much much more liquid than gas (by weight) until the bottle is empty.

 

Tim

[ditchcrawler]

Whilst I would not advocate covering them all up, I believe that in the latest version of the Boat safety scheme, ventilation requirements are "advisory only"

And has been for several years. I think if they were building your flat today building regs may require a level of ventilation. I don't know what regulations cover ventilation in caravans and of course they are not subject to a 4 yearly inspection.

 

...yet by regulation I must have big non-closeable vents in the doors (or some other low level area)

No you don't. its advisory to have a certain level of ventilation, its just an easy option to put a big hole in the door to let the northeasterly blow in one end and out the other.

 

Two reasons:

 

1) The greatly reduced volume of air inside a boat cabin amplifies the effect of gas leaks, combustion products leaking into the atmosphere etc

 

2) Your rented room probably has no open-flue appliances. if it did, then large vents would be installed too.

 

3) There is no restraint discouraging the desk jockeys who write the rules from over-egging the requirements. They don't have to sit in the draught.

 

Ok I can't count.

 

 

MtB

I think the last one is probably the main reason. If you employ someone to come up with a standard, if they want paying that's what they will do.

[Rob@BSSOffice]

...yet by regulation I must have big non-closeable vents in the doors (or some other low level area)

 

Still in pedant mode, as David wrote earlier, you are advised (since Jan 2002) that ventilation is required for (paraphrase)breathing humans and oxygen consuming fuel burning appliances.

 

I lay myself open to be corrected but in buildings ventilation used to be required in the heads or toilets as we building dwellers know them and if we have a stove rated above 5kw open ventilation to the outside is required.

 

The ventilation calculation was originally based on BS5842:3, but recently the new calculation based on the one in BS8511 has been adopted.

 

Rob

[Radiomariner]

Thanks Rob.

A few further points.

The prime way of keeping LPG out of the boat interior is to have a gas locker that drains safely and have no leaks in the system, and flame failure devices. Very little to do with ventilation.

Oxygen burning appliances do just that. If burning efficiently they produce, in the main Carbon Dioxide, CO_2. but use up oxygen. With insufficient ventilation the oxygen in the air becomes depleted, which is bad enough, but in addition, the depleted level of oxygen results in the appliance burning less efficiently and exhausting Carbon Monoxide, CO, which is toxic and will kill you. Even low levels of CO build up in the blood stream over time.

OK, sometimes it may seem that the ventilation requirements are a bit drastic, as somebody said, how often do you have four burners going on the hob, the grill and the oven on at the same time. However the regulations must allow for the worst possible scenario. Also remember that one of the effects of oxygen deplation and CO poisoning is first drowsiness then unconciousness, which in a poorly ventilated space can happen before you think "its bloody hot in here, must open a window" especially if you have had a few drinks or some other medication!

There is no requirement for the low level ventilation to be in the doors, That is usually most convienientt and easiest to install. Air from a higher location for instance could be ducted to a low level.

The ventilation requirement calculations used by BSS have been generalised and simplified and do not consider forced ventilation. (Forced ventilation ie fan assisted ventilators, can for instance be shut off). They are based on the Kilowatt rating of the appliance multiplied by a factor that depends on whether the appliance has a flue or not. Until January 2013 the requirement for solid fuel stoves was calculated using the same as gas flued devices. A new calculation has been introduced for solid fuel stoves.

Calculation is as follows: -

 

Unflued appliances - ie cookers, ovens, catalytic heaters etc. Kw rating multiplied by 2200

Flued appliances - ie flued Paloma water heater Kw rating multiplied bt 440

Flued solid fuel stove (New from Jan 2013) Kw rating multiplied by 550

Persons on board Number of berths multiplied by 650

The total of the results added is the total ventilation requirement in sq. millimeters (Yes some older examiners still calculate in inches. 1"² = 645.16mm^{2 )}

This should be divided equally high and low

 

edited to add : - Most homes in UK use Natural Gas, which unlike LPG is lighter than air and disperses rather than gather in the basement! (but can still gather in pockets)

 

 

 

Edited January 17, 2013 by Radiomariner

[BEngo]

Still in pedant mode, as David wrote earlier, you are advised (since Jan 2002) that ventilation is required for (paraphrase)breathing humans and oxygen consuming fuel burning appliances.

 

I lay myself open to be corrected but in buildings ventilation used to be required in the heads or toilets as we building dwellers know them and if we have a stove rated above 5kw open ventilation to the outside is required.

 

The ventilation calculation was originally based on BS5842:3, but recently the new calculation based on the one in BS8511 has been adopted.

 

Rob

 

The other thing about buildings is that the ventilation calculations for these, way back, included an expectation of adventitious ventilation- a fancy term for the, then inevitable, gaps round doors and windows. Any one else remember draught excluders under doors? As doors and windows came to be made to seal better so Building Regs came to require trickle vents and external ventilation for rooms with an open fire for example.

 

At the time of the inception of the BSS I asked for, but was flatly refused, a similar allowance for boats, despite support from some of the surveyors involved. I also asked for a diversity allowance so that the requirement was not for enough ventilation for the cooker to be permanently fully on, plus everything else flat out, but again was flatly refused. The result was that existing boats had big holes cut in doors front and back as the simplest and cheapest way to comply and draughts resulted. Some, if not many, boats then blocked the ventilators between BSS examinations to eliminate the draughts. I am told cling-film was effective and hard to detect.

 

Then BW realised that they didn't have a logical basis for requiring ventilation in private craft and ventilation became optional.

 

Ventilation is still a Good Thing and if it is designed in from the start it's quite easy to achieve the requirements without draughts. Excess ventilation may raise your heating bills but it goes a long way towards dealing with condensation, mildew and other damp-related problems.

 

N

[David Mack]

As doors and windows came to be made to seal better so Building Regs came to require trickle vents and external ventilation for rooms with an open fire for example.

 

Building Regs now specify the level of airtightness required in a new building, so we have the rather ridiculous situation that a building must be effectively airtight, but then needs trickle ventilation to provide fresh air for the occupants!

[Radiomariner]

 

The other thing about buildings is that the ventilation calculations for these, way back, included an expectation of adventitious ventilation- a fancy term for the, then inevitable, gaps round doors and windows. Any one else remember draught excluders under doors? As doors and windows came to be made to seal better so Building Regs came to require trickle vents and external ventilation for rooms with an open fire for example.

 

At the time of the inception of the BSS I asked for, but was flatly refused, a similar allowance for boats, despite support from some of the surveyors involved. I also asked for a diversity allowance so that the requirement was not for enough ventilation for the cooker to be permanently fully on, plus everything else flat out, but again was flatly refused. The result was that existing boats had big holes cut in doors front and back as the simplest and cheapest way to comply and draughts resulted. Some, if not many, boats then blocked the ventilators between BSS examinations to eliminate the draughts. I am told cling-film was effective and hard to detect.

 

Then BW realised that they didn't have a logical basis for requiring ventilation in private craft and ventilation became optional.

 

Ventilation is still a Good Thing and if it is designed in from the start it's quite easy to achieve the requirements without draughts. Excess ventilation may raise your heating bills but it goes a long way towards dealing with condensation, mildew and other damp-related problems.

 

N

 

The BSS guide advises that gaps round doors and windows etc can be taken into account when calculating ventilation. Is mostly un-necessary as there is either already sufficient vetilation, or there is so little that these gaps would not reach the minimum. I quite often find myself seeking out such gaps when the ventilation requirement is not met by a very small figure.

[ditchcrawler]

The BSS guide advises that gaps round doors and windows etc can be taken into account when calculating ventilation. Is mostly un-necessary as there is either already sufficient vetilation, or there is so little that these gaps would not reach the minimum. I quite often find myself seeking out such gaps when the ventilation requirement is not met by a very small figure.

On our boat I actually built some in. We have a dog box over the galley and the glass overshoots the frame so that any condensation drips outside. It adds about 80 square centimeters of fixed ventilation from memory.

[Radiomariner]

On our boat I actually built some in. We have a dog box over the galley and the glass overshoots the frame so that any condensation drips outside. It adds about 80 square centimeters of fixed ventilation from memory.

 

Thats a good idea. I like it. BSS examiner might not spot it, be sure to point it out to him(her).

8000 mm² (80cm²)is more than a standard 4 inch mushroom with a 1 inch gap between shoulder and cowl, or two mushroom vents with half inch gap. Quite a lot!