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  #61  
Old 11-10-2012
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Re: Winter Moisture Control

This might be an interesting graph. You can see the temperatures we live within and the large difference in which these temperatures can suspend water vapor. Literally twice as much between 10c and 20c (50f and 68f). It looks to me like when you get above 80c or 90c, its capacity become infinite, so I'm still interested in the scorched air concept that Maine suggested.

Also look at the green line with the amount of water suspended at 50% relative humidity (which would feel dry and comfortable) in a nice warm 20c/68f cabin, then keep that water content constant and move the temperature to the left to see what it would have to decline to until it would begin to condensate out. 10c/50f isn't much of a temperature drop, considering how cold the hull is going to be in the winter. While the entire cabin doesn't condensate, its easy to see why bilges, the back of lockers or the spaces behind interior trim do.

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Re: Winter Moisture Control

Quote:
Originally Posted by TheTardis View Post
Thanks all! I appreciate you all taking the time to answer my questions!
It's good that your shore power system is new, or at least in good condition.
Just remember that while running heaters and appliances, you should try not to exceed 80% of the maximum rating for an extended period of time.

Otherwise you get a syndrome called "boiling the frog". The wiring could get hot, and have a meltdown without ever tripping the breaker. If you're running two heaters, you'll need to shut off a heater momentarily to run your microwave oven or other appliance.

I'm not trying to turn you into an electrical engineer, just do a little simple math in your head:

You have a bucket of 30 amps to work with:
80% of 30= 24 amps safe, indefinite working load.

1500w heater. How many amps? 1500 / 120= 12.5 amps.
2nd heater set to 900w. How many amps? 900 / 120= 7.5 amps

12.5 + 7.5= 20 amps.

Mini Fridge: 6 amp start-up surge, 1.5 amps normal running load.

So, you can safely run one heater full-blast, another heater on 1/2 power, run your mini-fridge, and still be safely within your limits, and not experience any "nuisance tripping" of your circuit breakers.

You can always figure out your electrical loads by reading the labels on the backs of your appliances. They'll always give you something to work with: amps or watts. A casual manipulation with Ohm's Law, and you'll know if you're going to overload your wiring or not.
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  #63  
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Re: Winter Moisture Control

Quote:
Originally Posted by BubbleheadMd View Post
It's good that your shore power system is new, or at least in good condition.
Just remember that while running heaters and appliances, you should try not to exceed 80% of the maximum rating for an extended period of time.

Otherwise you get a syndrome called "boiling the frog". The wiring could get hot, and have a meltdown without ever tripping the breaker. If you're running two heaters, you'll need to shut off a heater momentarily to run your microwave oven or other appliance.

I'm not trying to turn you into an electrical engineer, just do a little simple math in your head:

You have a bucket of 30 amps to work with:
80% of 30= 24 amps safe, indefinite working load.

1500w heater. How many amps? 1500 / 120= 12.5 amps.
2nd heater set to 900w. How many amps? 900 / 120= 7.5 amps

12.5 + 7.5= 20 amps.

Mini Fridge: 6 amp start-up surge, 1.5 amps normal running load.

So, you can safely run one heater full-blast, another heater on 1/2 power, run your mini-fridge, and still be safely within your limits, and not experience any "nuisance tripping" of your circuit breakers.

You can always figure out your electrical loads by reading the labels on the backs of your appliances. They'll always give you something to work with: amps or watts. A casual manipulation with Ohm's Law, and you'll know if you're going to overload your wiring or not.

I recommend a max of 80% to all my customers. 24A for 30A service and 40A for 50A service, but do you think they listen...? I think they do, but then have no idea when, why or how they exceed the 80% suggestion...


Personally I don't like to see any marine shore power cord loaded to more than 80% of its rated capacity. I still hold to these values even with the new Smart Plugs because the dock pedestal still uses the old crappy twist lock which has MINIMAL contact area, especially for the corrosive environment they live in.. When I do, see them loaded this way, I see them fail at very high rates. The off the shelf, when new, laboratory rating bears little meaning in "real world" of the destructive marine environment. This is why I feel a much safer way to handle on-board AC is to not overload the cord sets to any more than 80% of its rating...

This is what happened to one customer who thought running multiple electric portable electric heaters on-board was a good idea. Oh, and this was 50A service.


I just posted this same math on the C-36 boards and to a guy I am consulting with. We also CAN NOT forget the water heater, also 1500W, the coffee maker, the battery charger, hair dryers etc. etc....

Most any boat wanting to use electric heat as the sole source should have at a minimum a second new 30A service added for the heaters...
Still despite listening:


And another:
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Last edited by Maine Sail; 11-10-2012 at 08:52 AM.
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  #64  
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Re: Winter Moisture Control

Well...glad to see that we're in agreement then.

Luckily, Tardis and I are not using a hot water heater, and I have no plans to install one. I'll use an electric kettle to make hot water for washing dishes this winter, but that's my limit. I'm comfortable being a minimalist.

Tardis' boat is 25', mine is 30' which is a small cabin volume, so hopefully running at 80% capacity will be adequate. That's why I have the propane heater as an emergency supplemental for those low-teen/single-digit days.

She just needs to understand that she might have to suspend a heater while she runs the microwave, toaster, electric kettle or whatever hair-care appliance she might be partial to.

I frequently touch cords and outlets to feel the temperature, and make sure everything's ok.

Your pictures are very good reinforcement, but at the same time, I don't want to come across as one of those old, dire Sailnetters that make it seem like sailing and liveaboard life are a "deathwatch" (credit to Smackdaddy's faux news article).

It's perfectly safe and enjoyable as long as you're a little more self-aware than the average home owner.
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Re: Winter Moisture Control

Quote:
Originally Posted by Minnewaska View Post
This might be an interesting graph. You can see the temperatures we live within and the large difference in which these temperatures can suspend water vapor. Literally twice as much between 10c and 20c (50f and 68f). It looks to me like when you get above 80c or 90c, its capacity become infinite, so I'm still interested in the scorched air concept that Maine suggested.

Also look at the green line with the amount of water suspended at 50% relative humidity (which would feel dry and comfortable) in a nice warm 20c/68f cabin, then keep that water content constant and move the temperature to the left to see what it would have to decline to until it would begin to condensate out. 10c/50f isn't much of a temperature drop, considering how cold the hull is going to be in the winter. While the entire cabin doesn't condensate, its easy to see why bilges, the back of lockers or the spaces behind interior trim do.

The long version can be found on a psychometric chart, go for any humidity or temperature.
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Re: Winter Moisture Control

Amen to Mainsail's shore power post.

Sail Delmarva: Shore Power Melt-Down

While I do use a 1500W heater, if I need more I use my installed propane heater rather than run 2 x 1500W. In fact, I'm much more comfortable now that I have solar and don't leave the boat plugged in. A shore power connection is always a question mark, compared to solid dry connections.
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  #67  
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Re: Winter Moisture Control

Quote:
Originally Posted by BubbleheadMd View Post

Tardis' boat is 25', mine is 30' which is a small cabin volume, so hopefully running at 80% capacity will be adequate. That's why I have the propane heater as an emergency supplemental for those low-teen/single-digit days.

She just needs to understand that she might have to suspend a heater while she runs the microwave, toaster, electric kettle or whatever hair-care appliance she might be partial to.
Thanks for posting this. I was actually just making a list of what I'm planing on taking aboard and how many amps each draws. Good to know about the 80% as well... But the real question is; how ever am I going to straighten my hair, microwave the wax for my legs, and run the disco ball at the same time while staying warm?!
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Re: Winter Moisture Control

Quote:
Originally Posted by TheTardis View Post
Thanks for posting this. I was actually just making a list of what I'm planing on taking aboard and how many amps each draws. Good to know about the 80% as well... But the real question is; how ever am I going to straighten my hair, microwave the wax for my legs, and run the disco ball at the same time while staying warm?!
I know, except for me it's the electric stripper pole. That thing draws 11 amps so I can't run it when the heater's on!

On a related note, I may have saved a guy's boat from burning down today:

I was eating dinner in the cockpit when these two fellows approached. They were interested in my spreader lights and the conversation turned to shore power. The owner described a very odd wiring situation in his cockpit from the previous owner, so I volunteered to look at it.

It seems that wherever the P.O. kept the boat, they only had 50 amp shore power available. A 50 amp plug is different from a 30 amp plug. The guy installed a 50 amp plug, jumper'd it to a 15 amp, household outlet, cobbled together a pigtail out of scrap and electrical tape, and ran that to the boat's 30 amp shore power inlet!

This pigtail wire was total crap and very warm in my hands. I explained what had been done, and told the owner to junk the 50 amp shore power cable, stop using the 50 amp outlet, and just get a 30 amp cable and plug into the factory installed 30 amp inlet.

Unreal.
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Re: Winter Moisture Control

Quote:
Originally Posted by BubbleheadMd View Post
I know, except for me it's the electric stripper pole. That thing draws 11 amps so I can't run it when the heater's on!
Might want to watch out with that pole, I hear friction fires are quite common!

Good on you for helping that guy. IT is insane what people will do, but at least the new owner had the smarts to think something was fishy.

Also, if anyone is at all curious as to what I've been up to in my little boat, I'm keeping a photo log :
TheTardis Gallery - My Photo Gallery
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Re: Winter Moisture Control

Um...it's empty!
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