Will Webasto/Diesel Heater exhaust condensate damage gelcoat? Exhaust port installation on C34mkii- freeboard or transom

[Verano]

Anyone installed a diesel heater (of any brand) on a Catalina 34mkii? I would like to install the exhaust port on the transom, but the swept nature (about 45-60*) will cause even the bent elbow through-hull to catch rain and spray. I can run it out on a vertical area, but any condensate will drip on a step, is this condensate caustic and will it damage gelcoat? Or, once these heaters get going, is there no condensate to speak of because everything just turns to steam and blows away with the exhaust?

Other option for through hull exhaust fitting would be as far aft as possible on the port side, just about the height of the decal. This area seems unlikely to be in the water unless we have bigger problems. Could always install an expanding bung when not in use to seal it for sure(with a note reminding to remove permanently attached to the control of course)

Thanks for any suggestions, the Admiral is looking forward to being warm...

 

[Hollyberry]

I think you'll find most owners have installed the exhaust in the topsides, near the transom but also near or at stripe decal height.

 

[Stu Jackson]

Being warm is good!
You may obtain more C34MkII suggestions on the C34 forum, here: Main Message Board

 

[Verano]

Thanks for the reply, I must admit, I had to do a search for topsides vs freeboard and found a funny thread regarding this exact definition argument! Seems its all in which governmental authority or dictionary you consult =)

Topsides definition?

I'm just renewing my CG66 details and am puzzled as they ask for "Hull Colour (upper)", "Hull Colour (lower)", and "Topsides Colour". While I understand what they mean I have always understood topsides to refer to the hull above the waterline and thought coachroofs, wheelhouses etc. were...

forums.ybw.com

 

[dlochner]

You can also add a drain to the exhaust line. Sure Marine has them in different sizes and on an elbow.

 

[Head Sail]

I installed one on an mkI so the transom was not as angled. I put a piece of screen repair over the exhaust to keep bugs out. I also increased the diameter of exhaust to compensate. I think they make a little hood or you may be able to fashion one for your install. Some have placed the exhaust just below the aft end where it turns down to the water line. You will need the drain if there is not a direct path for condensate to drain. It won't be much if any depending on the length of the exhaust. Don't know if it will harm gelcoat.

 

[Tally Ho]

You can also add a drain to the exhaust line. Sure Marine has them in different sizes and on an elbow.
View attachment 211527

I though that was some sort of still!

 

[Head Sail]

Check out this YouTube video for an example.

 

[Verano]

Thank you all! Thought I'd watched every video on this install already but I missed this, excellent information

 

[Terry Cox]

Hi Verano, different model boat and diesel heater,, but installed our exhaust port on our transom step several years ago and we get no condensate or smoke; just warm air. No sign of any kind of discoloration or damage to the gelcoat.

 

[MikeHoncho]

They heat up and cool down so fast I thing condensate wouldn’t be a issue. I have a Wallis cooktop/heater that vents straight up and through the cabin and have never had a issue with condensation. I’d be a little concerned with sailing downwind and significant following seas with it installed on the transom.

 

[Captain Larry-DH]

No, condensate will not affect fiberglass. It’s pure water. If the skin fitting rusts you might get some rust stains, but those can easily be removed with the usual acid based chemicals.
Not sure what @Head Sail is referring to with a “hood” but I strongly advise against adding anything that might block the exhaust or be heated by a direct exhaust blast. The standard exhaust skin fitting is designed to keep the external parts cool that are in contact with fiberglass. The inner pipe is too hot and would damage FRP.
Also, assuming the boat is heading windward at anchor, putting the exhaust in the sides will be better for taking airflow aft. A transom exhaust is more likely to trap CO2 in an “eddy” of turbulence behind the boat that could draw CO2 into the cockpit and cabin from aft.

 

[jssailem]

When I installed my Wallas heater the ScanMarine tech was helpful in locating the exhaust thru-hull.

1. locate within 7ft of the unit
2. Preferably on the aft quarter behind the widest part of the boat
3. As high above the water line as feasible but beneath the deck enough to provide the 12” rise needed to stop water from flowing into the exhaust hose

They provide this image. Said that the transom is not preferred as backdraft from air movement can curl the exhaust smell back into the cockpit.

 

[Lee Hadjiosif]

You install the thru-hull about 10" below the deck measuring from the inside, about the same height as the fuel vent. You then use the 10" to loop the exhaust tube up and down again to create a loop so that no splash/rain water can get inside. Make sure that the thru-hull is double-wall and the tube has an insulation sleeve over it and not be in contact with anything. The exhaust air coming out is much hotter than the engine exhaust.

 

[thinwater]

You can also add a drain to the exhaust line. Sure Marine has them in different sizes and on an elbow.
View attachment 211527

That design won't work reliably as illustrated.

The water will fill the first loop. Then it will begin to dribble over into the second olp, but will leave a ~ 120 degree air pocket it will not have the velocity to purge through, and cannot go back. The air is trapped. This will happen 3 times, creating several times more back pressure than the static head available to push the water through. The solution is to eliminate one turn and place it about a foot lower in the line.

This is a common refinery problem. It is also the reason you lay a pump-out hose flat on the dock before you suck out your blackwater tank (it won't pump right if coiled on the stand).

 

[dlochner]

That design won't work reliably as illustrated.

The water will fill the first loop. Then it will begin to dribble over into the second olp, but will leave a ~ 120 degree air pocket it will not have the velocity to purge through, and cannot go back. The air is trapped. This will happen 3 times, creating several times more back pressure than the static head available to push the water through. The solution is to eliminate one turn and place it about a foot lower in the line.

This is a common refinery problem. It is also the reason you lay a pump-out hose flat on the dock before you suck out your blackwater tank (it won't pump right if coiled on the stand).

Sure Marine has been doing this for awhile. If it wasn't working, I would expect them to change the design.

The one factor you didn't consider is the heat from the exhaust. The drain goes between the muffler and the heater, with 800° exhaust blowing by the tube will likely reach a temperature above the boiling point and with the Venturi effect any vapor would be sucked up blown out the exhaust as steam. The installation instructions recommend the muffler be installed vertically, so condensation can drain out of the muffler. Short cycling the heater would be a problem as the system would not heat up enough to vaporize the water. The exhaust system is also insulated which would help reduce condensation.

 

[thinwater]

Sure Marine has been doing this for awhile. If it wasn't working, I would expect them to change the design.

The one factor you didn't consider is the heat from the exhaust. The drain goes between the muffler and the heater, with 800° exhaust blowing by the tube will likely reach a temperature above the boiling point and with the Venturi effect any vapor would be sucked up blown out the exhaust as steam. The installation instructions recommend the muffler be installed vertically, so condensation can drain out of the muffler. Short cycling the heater would be a problem as the system would not heat up enough to vaporize the water. The exhaust system is also insulated which would help reduce condensation.

So have I. Yes, I considered everything. Most failures would not be noticed, just a few drips.

First, this thread is about heaters, not engines. Much lower exhaust temp and velocity. That said, I stand by what I said for engines too. As illustrated it could not drain all of the water from an exhaust.

Second, it is very BAD if the loops dry out by any of the mechanisms mentioned, because then exaust will go into the cabin. Obviously. The loops must always remain wet to provide a gas seal.

Third, for there to be a venturi effect of that magnitude there would have to be a constriction, appreciable velocity (there is not for a heater, which is what the thread is about) and back pressure. This not advisable for a heater. Not overly smart for a motor--I would not want that.

Finally, if any of the heat or venturi effects you mention happen (they won't because of the loops--that is part of their function) then it would not be a condensate trap. See "second."

Yes, insulation helps. But the loop is designed to be cold so that it will function properly and it will not be even hot to the touch, let alone boiling by the last loop. This is the reason there are 3 loops instead of 1 or 2. Think on that.

But the cure is to make the tube from the heater exhaust to the loops 1-2 feet longer. Simple. Been there , done that, not guessing.

 

[dlochner]

So have I. Yes, I considered everything. Most failures would not be noticed, just a few drips.

First, this thread is about heaters, not engines. Much lower exhaust temp and velocity. That said, I stand by what I said for engines too. As illustrated it could not drain all of the water from an exhaust.

Second, it is very BAD if the loops dry out by any of the mechanisms mentioned, because then exaust will go into the cabin. Obviously. The loops must always remain wet to provide a gas seal.

Third, for there to be a venturi effect of that magnitude there would have to be a constriction, appreciable velocity (there is not for a heater, which is what the thread is about) and back pressure. This not advisable for a heater. Not overly smart for a motor--I would not want that.

Finally, if any of the heat or venturi effects you mention happen (they won't because of the loops--that is part of their function) then it would not be a condensate trap. See "second."

Yes, insulation helps. But the loop is designed to be cold so that it will function properly and it will not be even hot to the touch, let alone boiling by the last loop. This is the reason there are 3 loops instead of 1 or 2. Think on that.

But the cure is to make the tube from the heater exhaust to the loops 1-2 feet longer. Simple. Been there , done that, not guessing.

@thinwater you're the engineer, I'm not. I'm just a sailor who read the installation directions for the Webasto heater sitting in the basement waiting to be installed.

What you said makes sense for a naturally aspirated heater or an engine with relatively low exhaust pressure. However, we are talking about a small diesel heater with a fan to deliver combustion air. The installation manual gives several warnings about the amount of heat in the exhaust system and the amount of hot exhaust that exits the exhaust fitting. The manual also mentions the Venturi effect preventing exhaust gases from exiting through the drain. It also cautions that the copper drain tube can get very hot. If you'd like I can send a copy of the instructions to you.

The OP asked about the effects of condensation from heater exhaust on fiberglass. One solution to that question is to prevent condensation from reaching the outlet. A drain at the low point of the exhaust system will help as will insulating the exhaust pipe to keep the gases hot until they exit. Sure Marine thinks the drain works, I'm not going to challenge their experience and reputation.