Creating positive air pressure inside the boat

[cuthound]

12 hours ago, nb Innisfree said:

Instead of a bilge blower you could use a Ecofan positioned over a candle, make sure it's a very small candle or the power generated could blow your windows out, maybe an emergency snuffing arrangement just it case. 

 

To eliminate the risk of CO poisoning from the very small candle, couldn't you power the Ecofan from a battery powered LED flickering candle tealight? 

 

I'm sure the Ecofan would be just as effective... 🤣😂

[Slow and Steady]

19 hours ago, blackrose said:

 

Rats climbing up the tube! WTF? 😱 Perhaps I'll raise the end by a few inches!

 

Since I no longer have low level vents and have effectively halved the area of the mushroom vents I need to make up for the decrease in vent area somehow, so I don't think it would be very safe once my stove is going without the fan.

I must have missed the reason you no longer have low level vents. My own boat is such a carp fitout in practical terms it didn't have any low level vents and air absolutely did come in via the mushrooms along with anyone's smoke that happened to be wafting by. Adding just one vent about 500mm above the waterline, ducted down to floor level has made all the difference and air now  leaves via the mushrooms instead of coming in. Maybe your problem is similar? I'm sure you had good reason to dispense with low level vents but I can't think why you would?

[blackrose]

18 minutes ago, Slow and Steady said:

I must have missed the reason you no longer have low level vents. My own boat is such a carp fitout in practical terms it didn't have any low level vents and air absolutely did come in via the mushrooms along with anyone's smoke that happened to be wafting by. Adding just one vent about 500mm above the waterline, ducted down to floor level has made all the difference and air now  leaves via the mushrooms instead of coming in. Maybe your problem is similar? I'm sure you had good reason to dispense with low level vents but I can't think why you would?

 

Because smoke was coming into my boat through the low level vents. Some smoke was also coming in through the mushrooms before.

 

Now with the fan running bringing in fresh air through the ducting enough air is being brought in so that air inside the boat is forced out through the mushrooms and smoke can't come in. Forcing cold air into the boat means I have to burn a bit more coal myself but that's fine.

Edited January 15, 2022 by blackrose

[Slow and Steady]

15 minutes ago, blackrose said:

 

Because smoke was coming into my boat through the low level vents. Some smoke was also coming in through the mushrooms before.

 

Now with the fan running bringing in fresh air through the ducting enough air is being brought in so that air inside the boat is forced out through the mushrooms and smoke can't come in. Forcing cold air into the boat means I have to burn a bit more coal myself but that's fine.

Gotcha - so what you've done on balance is to lower and re-site your low level intake away from the smoke source. Makes perfect sense. Not unlike mine in broad terms, my inlet is just below pontoon level between rubbing strakes so not as low as yours, but in a place that doesn't have smoke wafting around like perhaps a cratch door vent might. I'd try it without the fan, you might not need it now air can get to low level and out at high.

Edited January 15, 2022 by Slow and Steady

[nb Innisfree]

51 minutes ago, cuthound said:

 

To eliminate the risk of CO poisoning from the very small candle, couldn't you power the Ecofan from a battery powered LED flickering candle tealight? 

 

I'm sure the Ecofan would be just as effective... 🤣😂

The heat from a small pet would prob suffice, a mouse perhaps. 

[blackrose]

35 minutes ago, Slow and Steady said:

Gotcha - so what you've done on balance is to lower and re-site your low level intake away from the smoke source. Makes perfect sense. Not unlike mine in broad terms, my inlet is just below pontoon level between rubbing strakes so not as low as yours, but in a place that doesn't have smoke wafting around like perhaps a cratch door vent might. I'd try it without the fan, you might not need it now air can get to low level and out at high.

 

It's only been a day but last night without the fan on it definitely didn't feel like there was enough air coming in. This morning I've let the stove die down and just got the Webasto on for heat and hot water so I haven't got the fan on and it's fine because the stove isn't burning oxygen. If the wind direction changes and I start smelling neighbour's smoke inside my boat then I'll just switch the fan on which will force air out of the mushrooms so smoke can't come in. 

 

Have you done a vent area calculation for your boat based on the kW input of all fuel burning appliances inside the boat? I think there's a formula in the BSS essential guide. I know mine so when I taped over the low level vents I knew that the vent pipe alone without the fan wouldn't be bringing in enough air with the stove running.

 

Edit: Just found the recommendations and formula for calculating minimum ventilation area from the BSS Essential Guide:

 

8.9 Ventilation:

The responsibility for the safety of anybody onboard your boat lies with the owner or skipper. We advise strongly that boats have enough fixed ventilation to feed all the appliances on board that use LPG, coal, wood, oil or other carbon-based fuels. Inadequate ventilation will starve the burners of vital oxygen resulting in poor burning and that can produce highly toxic carbon monoxide. Room-sealed appliances have their own external air supply built into the flue ductwork, but other appliances take their combustion air supply directly from the cabin space. The ventilation requirement can be calculated by using the formula from Annex B of PD 5482-3. It takes account of the number and type of appliances as well as the people on board. Minimum effective area (mm2) = [2200xU]+[650xP]+[440xF] U = total input rating (kW) for all appliances (including cookers) without flues P = number of people for which the compartment is designed F = input rating (kW) for all open or closed flue appliances The input rating for your appliances can normally be found on the manufacturer’s plate on the appliance and/or in the operating instructions. The ventilation requirement needs to be split as equally as practicable between: ■ high level (ideally cabin roof), and, ■ low level. Low-level venting can be achieved by letting in cold air from vents in doors and/or bulkheads, or by means of ducting from a higher level. Careful examination must be made of each ventilator to check for the presence of anything that would reduce the clear air opening e.g. filter, insect screen. Such filters or screens must also be in a clean and serviceable condition as partial or complete blockage of the clear air openings could make the ventilator totally ineffective and your calculations inaccurate. Louvered doors are a common form of providing permanent ventilation and the effective area needs to be carefully measured.

 

http://www.marinesurveys.net/BoatSafety/Guideline-chap8Equipment.pdf

 

I don't know if this is the latest version, but it will give you a good basis on which to calculate your ventilation requirements.

Edited January 15, 2022 by blackrose

[Slow and Steady]

1 hour ago, blackrose said:

Have you done a vent area calculation for your boat based on the kW output of all fuel burning appliances inside the boat? I think there's a formula in the BSS essential guide. I know mine so when I taped over the low level vents I knew that the vent pipe alone without the fan wouldn't be bringing in enough air with the stove running.

I haven't, but my low level inlet is ducted down to floor level about 2ft from the stove and I did site it there on purpose. There is also a big draughty side hatch opposite the stove and air has stopped coming in through the mushrooms so I'm heading in the right direction for sure! The other daft thing on the boat is that there are 2 vents in the rear doors but NO through vents in the internal doors! I don't have front doors or a cratch, I have an ugly bay window. What I do have is a ton of living space though (for a narrowboat). The stove is slap bang in the centre of the  living space which is also a good thing. I think every boat is a compromise somewhere. I'll be sorting out the ventilation AND installing another stove in my son's stern end bachelor pad when we do our massive re-insulation job - there seems little point doing it now when I'm going to rip the boat to pieces afterwards.

 

Thanks for the link. 2 people + 5kw stove =123 sq cm - not huge is it? I think one naturally needs more than that just to keep the condensation at bay and we never cook without opening a few windows. A lot of this is common sense (if you have any!) and that's why I started installing low level vents and ducted my trial one to floor level, it just seemed obvious and it HAS made a big difference despite it's quite small inlet size. I fitted a small one to be practical on the hull but also so I could have many small ones rather than a few big ones - again it seemed like common sense to spread them around for damp reasons.

Edited January 15, 2022 by Slow and Steady

[blackrose]

My new ventilation system definitely seems to be working. It's thick with smoke outside blowing in the direction of my boat but I can't smell it inside anymore. Sometimes I amaze myself with my own ingenuity. 😋