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Bilge ventilation


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Reading up on the pros and cons of bilge ventilation and not the comment "The important thing is to try to do your best to ventilate the bilge area as well as you can - which will be not very well unless external bilge vents were built into the boat from new, very few have them." How are these installed please. Am I to assume that a duct is used leading from the bilge to the exterior above the waterline. Like wise the computer fans used for the cooling of fridges and inverters etc. Are the ducted to the cabin area or again outside the hull? I am planning to install louvered vents in the electric cupboard - one high up to the outside and one low down in the cupboard door your views please. Sorry if I`ve listed a number of questions but my head is currently tuned to ventilation requirements. Thanks in anticipation.

 
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My low level vents are ducted to bilge , behind the linings, from the front cabin bulkhead (approx 8 inches above the front deck) instead of being in the front doors.

All my ballast sits on blocks and there is a two inch air gap above the ballast with all the floor bearers running down the boat.Appliances like cookers/ fridges have air holes cut directly below them into the floor so constantly draw up the cooler air. Copper central heating pipes are run at floor level (but open to the bilges) and also draw air from the bilges when the heating is on. Been like that for some twenty odd years now and I have to say the bilges are probably the best bit of my boat and the only bit thats better than younger ones!

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Any type of ventilation may be a waste of time if the 'limber holes', which are the chopped off corners of the ends of the baseplate stiffeners, are insufficiently large and/or are blocked by trash (for example stuff left over and swept 'under the carpet' by the shell builder or the fitter-out.  

When the floor is in place leaving a gap at each side will provide some ventilation, but will also allow trash to collect and block the limber holes, and will be unseen.

Are you fitting-out?  I would ensure the limber holes are clear before starting, and stuff something in the gap at either side of the (18mm plywood?) floor boarding and only clear it out when panelling the hull sides.

You should certainly fit an inspection panel or proprietary hatch in the floor at the aft end, to allow inspection for any water, and to allow a wet and dry vacuum to be used if necessary.

Edited by Murflynn
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I wouldn't vent my electrical cupboard if I had one outside but vent top and bottom into the boat. My fridge has a couple of computer fans in the floor sucking up from the bilge and over the condenser and just exhaust into the galley over top of the fridge. 

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The reasoning behind my exterior and interior vents in the electric cupboard is because I`ve a Vetus 3000 inverter and separate large Vetus battery charger. 240 volt fridge, washing machine etc etc. and am concerned about how to dissipate the heat the the Vetus items produce.

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Regarding the limber holes the boat arrived with the flooring laid and whilst there is a gap around the edge to aid ventilation and a hatch provided at the stern bulkhead with out lifting the floor I`m unable to confirm the state of the limber holes without lifting the floor. Perhaps a job for my Snap-on camera.

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31 minutes ago, jddevel said:

The reasoning behind my exterior and interior vents in the electric cupboard is because I`ve a Vetus 3000 inverter and separate large Vetus battery charger. 240 volt fridge, washing machine etc etc. and am concerned about how to dissipate the heat the the Vetus items produce.

I would be worried about damp air in the electrics cupboard.

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8 minutes ago, jddevel said:

Ditchcrawler. I was assuming that on the principle of hot air rising that cooler air via a low internal vent would then leave via the external higher up. Are you suggesting that damp air may be drawn in?

Honest truth I don't know, but not something I would take a chance with.

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As the air warms up it expands and becomes less dense (lighter) and so will rise up, as it rises it will draw cool air in at the bottom to replace the warm air that has gone out the top vent.  Same principle as your stove, hot flue gasses out the top, drawing cool air in at the bottom.

The cold air will warm up as it passes over the hot parts of your electronics, as the air warms up it's relative humidity gets lower, so the air appears drier.

An Inverter outputting 3kW at say 95% efficient will generate about 150W of heat within the inverter.  Keep that in a closed box and it is going to overheat.  It must have ventilation otherwise the hot air will be circulated round and round by the inverter fan.  A less efficient inverter inverter could easily have over 200W of heat to get rid of.

Edited by Chewbacka
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