Watertight air ventilators

[jssailem]

Anyone have any experience with a "Air-Only ventilator"? I am looking for a way to get air into my Wallas heater but minimize/stop water ingress. Currently I am using a PVC soft cowling off the stern of the boat. The 3" air tube has an 12 inch air loop in it to limit water from reaching the heater. But if I take a wave over the stern I can foresee the loop being filled. This item from Modus Maris Ltd looks interesting in theory.

Ideas?

 

[centerline]

I have thought about the water ingress when I installed my Wallas..... wallas does make a closable vent for the purpose, but you cant use the heater with it closed, but I didnt go with that option, but instead have the regular vent...

I think the only other way is to build a modified Dorade box for the vent, but without some thoughtful modification, one may have trouble with using the heater due to the exhaust venting out the middle tube, with the fresh combustion air being brought in thru the outer tube.... with too much restriction, the outlet and inlet might not have enough separation, and so the unit may ingest too much exhaust with its combustion air.... and so become very inefficient in its fuel burn... its just something to think about.

when I did my installation, I used extra vent tubing, and from the heater I routed it down and below the elevation of the heater, then turned and went up as high as possible into the gunnel area, then back down to the vent outlet/inlet..... then I made a 1/4" hole in the bottom of the outer tube at the low point.

the theory is, that any water that goes in the vent will be metered due to the size of the vent opening, so it wont be much, and then it will have to make its way upwards about 12inchs thru a tube that has an obstruction from another tube inside of it (the exhaust), and if any water makes it completely over the top of the loop, it will run down in to the sag and drain out the hole I made in it..... and hopefully never make it up to the heater unit.

I am not sure how yours is installed, but I think I have a good thoughtful installation, and the only thing I can think of that would make it more secure and still always be available for use, is to have an open shield over the vent (but open on all sides) so that a direct shot of water from a wave (or fire hose) could not force its "pressure" directly into the vent opening.... and a glancing shot of water wont allow much into the opening to do any harm if it was installed according to the instructions with the heater.....

I have my vent installed on the rear quarter about 5" below the rubrail, which is highly recommended by wallas, rather than out the stern of the vessel.

 

[Maine Sail]

Anyone have any experience with a "Air-Only ventilator"? I am looking for a way to get air into my Wallas heater but minimize/stop water ingress. Currently I am using a PVC soft cowling off the stern of the boat. The 3" air tube has an 12 inch air loop in it to limit water from reaching the heater. But if I take a wave over the stern I can foresee the loop being filled. This item from Modus Maris Ltd looks interesting in theory.
View attachment 123929 View attachment 123930
Ideas?

Wallas makes an exhaust outlet called, IIRC, a 5400 that works perfectly on the transoms of sailboats. It is self draining..

 

[Ken Cross]

My Wallas uses fresh air from inside a cockpit lazarette. Exhaust is out the back. It seems to work.
Ken

 

[jssailem]

Thank you for the info.
My exhaust is on the Starboard rear quarter about 10 in below the rub-rail and 20 in above the water line. I have a 15in loop in the exhaust line between the heater and the exhaust outlet.
That is not my concern. The fresh air inlet is currently attached to a Cowl Vent on the stern deck. There is a 15in loop in the inlet tube. But it is a 3in diameter tube. My concern is how to seal the vent in foul weather and a following sea. At present a boarding sea could reach the Cowl vent.

So I'm looking for a resolution.

The Wallas uses two sources of inlet air. 50% comes from the cabin as recycled air. 50% is coming from this fresh air source. Main reason is to have an air exchange that brings in dry outside air. (At least that is the way it was explained by the Wallas dealer.) As I am led to understand the heater can run by recycling the cabin air. Only liability is it contributes to a moister cabin environment without the fresh air exchange. It is not like my boat is a well sealed compartment, but reducing water ingress is important even is small proportions.

 

[centerline]

My Wallas uses fresh air from inside a cockpit lazarette. Exhaust is out the back. It seems to work.
Ken

the wallas heaters can use their fresh air for the heat from any place the fresh air tube opening is placed, but the fresh combustion air is collected thru the outer part of a double wall tube... the exhause is vented out the inner part of the double walled tube...
this arraingment allows for the incoming air to insulate the exhaust tube from becoming too hot, and to cool the exhaust gasses, and at the same time heat the incoming air a bit so combustion is cleaner/hotter...

 

[jssailem]

I understand that is true on some models. I have a DT40 from early 2000's. One of the previous owner purchases never installed. Had it to the distributor for a checkup where was told combustion air comes from surrounding space air. In my case the area under the aft seats behind the engine bulkhead. It is an area of about 7x4x5 with a cowl vent and opens to the port cockpit lazarett. I call it the hole.

So how do you seal up cowlings when the sea waves rise and break over the deck?

 

[Ken Cross]

the wallas heaters can use their fresh air for the heat from any place the fresh air tube opening is placed, but the fresh combustion air is collected thru the outer part of a double wall tube... the exhause is vented out the inner part of the double walled tube...
this arraingment allows for the incoming air to insulate the exhaust tube from becoming too hot, and to cool the exhaust gasses, and at the same time heat the incoming air a bit so combustion is cleaner/hotter...

Thanks Centerline. I hadn't noticed the combustion air path but now I need to go look. . I was referring to the fresh part of the cabin air.
Ken

 

[jssailem]

Hey guys. We have drifted from the focus of a vent design that can limit water ingress and yet provide fresh air to the system. This is not combustion air but outside air to be heated and circulated in the cabin.

 

[Ken Cross]

Hey guys. We have drifted from the focus of a vent design that can limit water ingress and yet provide fresh air to the system. This is not combustion air but outside air to be heated and circulated in the cabin.

Yup. Ours comes from inside the lazarette. It seems to work well. No chance of water ingress.
Ken

 

[Maine Sail]

My Wallas uses fresh air from inside a cockpit lazarette. Exhaust is out the back. It seems to work.
Ken

ken

You probably have a DT-40 the DT-30 & smaller use a dual pipe (pipe within a pipe) air intake / exhaust hose to increase intake air temps and aid in clean combustion..

 

[jssailem]

Maine Sail Thanks for you observation. The thread was started looking for an idea to vent intake air. I am looking for a good way to vent outside air into the furnace not for combustion but to heat for circulation. The unit is a 40DT. The Air-Only vent looks like an option that would help to limit water intrusion in to the air intake ducting. Thoughts?