Steel boat bilge drying?

[Bmarler]

Hopefully the steps you’re taking will improve the issue. Please report back when you see the results.

 

[LeoKa]

Hopefully the steps you’re taking will improve the issue. Please report back when you see the results.

A short update.

The air exit duct was installed on Sunday and it has been running ever since. Today I installed a air blower into the bilge, too.
I did see some difference, but not complete success. At least, not yet.
I believe the air is drying inside for sure. Normally the PH windows are always moist when the heating is on and cold outside. The windows are clear now, although the temps are warmer during the day now, too.
I did some cooking yesterday and one side windows in the salon started to fog up. Once the propene oven was turned off, the fog disappeared in half an hour. This did not happen before.
In the cabin below around the floor area the surface is dry. However, when I finished installing the blower today I had to open the floor and I could see moisture there, still. I vacuumed out a small patch of accumulated water and I left the floor panel removed to let it dry.
My concern is, if the floor is closed up again the drying will occur very slowly, or not much. This is not what I wanted, because that is the area, which worries me.

 

[Mac2]

Get a better dehumidifier, one designed for a crawlspace. Heat will make it worse. Warm air holds a lot more water than cold air. You can get a commercial dehumidifier that pumps itself out and will remove about 12 gallons ( yes 12 gallons!) a day for under $ 800.00 that will work fantastic and last. I currently have 2, one with almost 4000hrs on it that works just as well as the new one we just got. When you get the relative humidity down around 40% that boat should dry up. You will need to move a little air into the inaccessible areas to assist those spots in drying.
Oh, get a get of ear plugs or get used to the sound of the units making your world dry. Do not confuse these units with those countertop things home depot sells, its like comparing hamburger to prime rib.

Hollywood

Spot on! Took me a couple of years to figure it out. Living aboard for 5 years now. Wife likes it 74 degrees. I use a residential heat/ac pump on the upper deck. Boat has insulating foam everywhere, but the bilge area. It used to absolutely drip water on the exposed metal from the condensation. I came to understand why steel boats rusted from the inside out. I started using two large home style dehumidifiers. One in the bow bedroom/head that drains directly to the shower, and a second one in the pilothouse. They will pull about a half gallon a day each before the boat dries up. They are set at 40% humidity until it gets really cold (upper 20s) then I drop them down to 35%. It might be to dry for some, but there is no more condensation on the windows, or dripping port light frames. There is no more water in the bilge because there is no moisture in the air. Problem solved.

 

[LeoKa]

Problem solved.

Lucky you. I tried the dehumidifier method, but no luck. Perhaps more Pro models do a better job.
I will continue experimenting with the dry air method. At one point, I will add the dehumidifiers, if needed.
Now I understand that heating the air is not very useful for condensation. Perhaps drying out and already wet bilge, but not on the long run.

 

[Portage_Bay]

Klee Wyck explained it well in post #24. Pull in outside air to heat. It's all about relative humidity. Pull in saturated air, heat it and the relative humidity drops. The incoming air will absorb the moisture of the indoor air. In other words don't seal the boat up tight to keep the heat in. Now move that air through the bilges like you are doing. Any heat source will work but a flame will work best because it draws in air for combustion.

I've lived and worked on steel boats for more years than I can recall. The only time we could not keep up is in heavy rain where everyone brings wet foul weather gear and clothing in.

Lucky you. I tried the dehumidifier method, but no luck. Perhaps more Pro models do a better job.
I will continue experimenting with the dry air method. At one point, I will add the dehumidifiers, if needed.
Now I understand that heating the air is not very useful for condensation. Perhaps drying out and already wet bilge, but not on the long run.

 

[portager]

You could mount the dehumidifier in the bilge or duct the outlet into the bilge and draw the return air from the bilge. You should be able to get a lower humidity in the bilge than in the house. By increasing or reducing the leakage between the bilge and the house, you should be able to increase the humidity difference between the bilge and the house to get a dry bilge and a comfortable house—just a Mechanical Engineer thinking out loud.

 

[LeoKa]

No progress, at least not much.
After two days, looking at the bottom of the bilge under the floor, there was about an inch water accumulated. Although, the air pull out was on all day, I did not run it at night, so I could sleep. The first day, running the air pull out fans/duct all night, I could not sleep much. I am not used to the fan noise. It seems the fans need to run 24/7 no matter what. I need to figure out the sleep problem. I do not like earplugs.
At this point, I still do not know, if the duct/fan system will be able to handle the water accumulation? An inch water in two nights, is significant.
I hooked up the dehumidifier again in this area. I could not see much water coming out of its hose, which drains into the grey tank, before. I will try to monitor it closely.
I think the problem is that I have turn on the heating for the night. If I don't have any heat, my cabin is 45-50F by morning, which is a bit cold even for me. With the heat on at night on min level, the cabin warms up to around 60-62F. This is still not very hot, though.
The battle continues....

 

[LeoKa]

You could mount the dehumidifier in the bilge or duct the outlet into the bilge and draw the return air from the bilge.

I think I understand what you are suggesting.
My duct/fan is going to the bottom of the bilge. It is pulling the air out from the lowest point. Right now, the floor is removed to expose the bilge area more, so the airflow should be free of blockage.
I have a large dehumidifier, but it is a household version. It does not have option to redirect the intake and the air exit. Only the drain hose is flexible.
Perhaps I need to search for a industrial dehumidifier, as it was suggested earlier.

 

[LeoKa]

I have a wood boat now and have bilge blowers running at very slow speed constantly drawing out bilge areas. I use a rheostat to slow the bilge blowers.

Lepke

What bilge blower do you have? What is a rheostat?

 

[klee wyck]

No progress, at least not much.
After two days, looking at the bottom of the bilge under the floor, there was about an inch water accumulated. Although, the air pull out was on all day, I did not run it at night, so I could sleep. The first day, running the air pull out fans/duct all night, I could not sleep much. I am not used to the fan noise. It seems the fans need to run 24/7 no matter what. I need to figure out the sleep problem. I do not like earplugs.
At this point, I still do not know, if the duct/fan system will be able to handle the water accumulation? An inch water in two nights, is significant.
I hooked up the dehumidifier again in this area. I could not see much water coming out of its hose, which drains into the grey tank, before. I will try to monitor it closely.
I think the problem is that I have turn on the heating for the night. If I don't have any heat, my cabin is 45-50F by morning, which is a bit cold even for me. With the heat on at night on min level, the cabin warms up to around 60-62F. This is still not very hot, though.
The battle continues....

Well, the battle continues but you remain out gunned by the laws of physics which cannot be violated. You need to up your game and you appear to be unwilling.
Remember? No free lunch.....you can either do what is necessary to have a dry boat or you can live with a wet boat and the inevitable consequences.

The laws physics that govern condensation or the reverse of condensation (evaporation) are found in this calculator linked here:

https://www.calculator.net/dew-poin...wpoint=44&dewpointunit=fahrenheit&x=Calculate

If accept the following stipulations, then I can understand what is necessary to avoid condensation.
1.) The outside air is 48 degrees and 85% relative humidity.
2.) The uninsulated hull is at the 48 degrees, the same as the water temperature of Puget Sound at this time of the year.
3.) There is a human(s) aboard respirating, adding moisture to the air, and cooking with propane, adding more moisture to the air.

This is a very big challenge to a dry boat.
You must get the temperature in the bilge above the dew point and keep it there with both warm air and enough circulation that the warm air cannot cool off significantly as it contacts that cold uninsulated hull. Dew point is the measure of temperature where moist air will give up moisture by raining or condensing on surfaces such as hulls and windows (or grass and sidewalks outside).

In my estimation, using the calculator above, you must keep the coldest part of the bilge above 66 degrees 100% of the time which will probably take over 20 total air exchanges per hour in that location.

You are either willing to do that or you are not, in which case you will remain wet until it warms up and dries out outside. No free lunch. This would be much easier if the hull was insulated but can be done if you make the necessary choices including learning to sleep under different ambient circumstances of temperature and sound.

 

[LeoKa]

I have ordered this unit. On sale for $419.50

https://www.alorair.com/product-details/alorair-sentinel-hd35p

I hope it fits into the limited crawl space I have in the cabin. If it does, it could drain directly into the grey water tank. Or, this has a pump, so it can push it up to the PH, where the water can exit, if the boat is on land storage.

I also discovered that the original builder was thinking ahead. The boat has a blower, which empties the shower area and the cabin head air. I removed the head from my cabin and connected the old duct to my bilge duct. This blower is very loud, so I only used it after showers. I turned it on now and I can feel the air move around my feet in the salon. It certainly suck the air out below. I can also sense a strong air flow coming out on the side of the boat, where the air outlets are. I think this could be very useful during the day. At night, it would be too loud.
The other air duct system I have built is a separate one, but that is quiet enough to run it 24/7, if I use ear plugs at night. Unfortunately the airflow is not very strong here. The duct and fan is 4" ID, but the air volume is possibly good for a cabinet only.

The dehumidifier will be here in couple weeks, so I have to deal with the noise until then. I really hope it will improve my drying capabilities. It can do up to 70 pint removal at a 1000 sqf area. I don't think my cabin is that big. I'll keep you updated.

 

[LeoKa]

1.) The outside air is 48 degrees and 85% relative humidity.
2.) The uninsulated hull is at the 48 degrees, the same as the water temperature of Puget Sound at this time of the year.
3.) There is a human(s) aboard respirating, adding moisture to the air, and cooking with propane, adding more moisture to the air.
/QUOTE]

Very good explanation, thank you!
Even I can understand it, lol.

I am doing my best to get there. I don't give up easily, but the budget is tight. I know, sometimes the budget cannot be considered, because on the long run, it will cost lot more.

 

[Snapdragon III]

I have a slightly different take from most of the posts here. My experience was with a 40' Aluminum trawler, that had condensation issues, although fortunately not corrosion issues as a result of it. I am in the Pacific NW as well. Since it sounds like you are at the dock and have shore power, I believe the dehumidifiers will be the most helpful thing to concentrate on. Bringing in lots of outside air, and adding heat will be ineffective and possibly counter productive in at least some weather conditions. I often had bilge condensation, but the time it was most extreme was in my engine room when running in warmer, rainy weather, while the water was cold. The large volume of air moving through the engine room would quickly condense on the cold aluminum hull and result in gallons of condensation in a few hours. This was despite the fact that it was 90 degrees plus in there, which huge vent fans blasting. The more air that moved through the more it condensed.
The better move to keep the boat dry is to run dehumidifiers in the boat, and try to limit air circulation in and out of the boat as much as you can without endangering your health. If you can keep the air inside the boat trapped there, and keep it at very low relative humidity, it will dry everything out quickly. To dry out the bilge you need to get this nice dry inside air down there, which can be challenging but it sounds like you have some plans in the works for that already. $150-200 home dehumidifiers work great for this, no need to buy super expensive commercial ones. They only work well above a certain temperature though. I think it's around 50? Under that they ice up and stop working. They work much better at 65+ if you are trying to dry things out.
Remember, if you don't have leaks, almost all the condensation is coming from you, and your activities. Cooking and breathing mostly. If you are getting condensation in the area you are sleeping the most effective way to stop it is to remove the moisture from the air before it touches a cold metal surface and condenses there. This means keeping the area a little warmer, and having the dehumidifiers running at night. If the boat is pretty well sealed it is likely enough to have it running in the next room over from your bedroom, with the door open. That way it's not so loud right were you are sleeping.
The small home style dehumidifier I run on my boat produces a couple gallons a day of water when we are onboard in the winter plugged into shore power. It makes it so much more comfortable onboard.

 

[LeoKa]

I have a slightly different take from most of the posts here.
The small home style dehumidifier I run on my boat produces a couple gallons a day of water when we are onboard in the winter plugged into shore power. It makes it so much more comfortable onboard.

Thank you for sharing your real life experience.
At this point, I am not very clear what could be the best solution in my situation? Here are few points:
1/ The ER has condensation. It is possible that it seeps over to the cabin area. I cannot tell exactly how, due to the boat's pitch, which changes as the water tank gets low (270g). The ER also has a watertight door, but there is an opening above the door, which will let outside air in. I do not know, if this can be an issue, or should I keep the door always closed and seal the opening above it? Although the ER is not heated, it is possible that the warm air comes through from the cabin area, which is on the other side of the bulkhead.
2/ I did run dehumidifiers before, but I could not see any significant change. If I cook and the windows fog up, the dehumidifier cannot clear the air enough and the moisture is there for hours even after the cooking finished. As I listed earlier, I bought a larger dehumidifier. It will be brand new and perhaps more effective. The other units are used.
3/ I do have air moving duct system installed. They are on 24/7 now, but the flow is not very strong. Steady slow air into the bilge and stronger air out from the bilge to outside. The distance between the IN and OUT point is the length of my cabin, which is about 10'. The floor covers up the bilge.
I am thinking about getting higher volume fans and see, if that makes any difference? The slow air down to the bilge collects the warm air from the salon ceiling right next to the diesel furnace. This goes to the bilge at the beginning of the cabin. The exit air is collected at the other end of my cabin directly from the bilge and pushed outside directly. So, this is a circulation there but I am not sure, if this is enough to dry the air enough in the bilge area.
4/ I also run the diesel heater more frequently. When I leave the boat, I turn it off for safety. Otherwise it is on all the time. This uses the inside air, but the exhaust pipe goes directly to the top. The open flame furnace takes the air in at the bottom from the salon.
My point is; I do have air circulation now, but I don't know if it is enough to dry the bilge. Once the new dehumidifier is in place, I will closely monitor the bilge area in question. I can live with lower temps inside the boat. I stopped using electrical heaters now. I think they did not help and more condensation was generated.
Now I put on an extra layer of clothes.... lol

 

[LeoKa]

I just checked the hull walls inside.
The ER does not have any, or just very little close to the bulkhead, where the cabin is on the other side.
The Cabin has very little what I can see. I did not open the floor to see the bilge, yet. I am sure it is not dry.
The rest of the boat is pretty dry everywhere.
As I mentioned, at this point only the diesel furnace is heating the boat at the salon level and below deck with the radiators.
The salon's temp is 58F and the RH is 60%.
The cabin temp is 53F and I turned on the older dehumidifier.

 

[Hippocampus]

Don’t know your boat but would suspect the ER has air movement via venting so even with a airsept and engine not running given ambient temp in er is different than outside there’s air movement. Put Saran Wrap +/or aluminum foil over vents. No air movement diminishes need for dehumidification.

������ remember to remove before running engine or genset.

 

[Bmarler]

Cooking is a big contributor to moisture inside the boat. On my old steel boat I installed a powered vent hood over the stove. That was a big help. Just having a propane burner lit releases moisture in the air, not to mention all the steam from whatever is on the burner.
I will do the same on the current boat when I have the time to make it up.

 

[LeoKa]

Cooking is a big contributor to moisture inside the boat.

Correct. When I cook (rare) I do have the windows moist. Lately, I just open the PH doors to make it go away faster.
Instead of propane, it would be nice to have a wood burning old style brick furnace, but it is not feasible for my boat....