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Author Topic:   Boat Heater Using Engine Cooling Water
number9 posted 11-24-2008 11:39 PM ET (US)   Profile for number9   Send Email to number9  
Does anybody here have knowledge of attempts made to recover heat from outboard cooling systems for cabin heating?

The thought came to me while in my "tech library" the other day. After looking through various maintenance manuals to get a better understanding of the water paths it seems one could rather easily come up with a workable system.

Along the same lines you would think the manufacturers would
develop raw water cooled closed systems for their high dollar motors to extend engine life.

Any thoughts?

fourdfish posted 11-24-2008 11:53 PM ET (US)     Profile for fourdfish  Send Email to fourdfish     
A guy in a boat moored next to me in Charlevous, MI had a heat pump in his boat that ran all night. He built it into the boat and told me it heated the cabin very well.
This was in June and the water was fairly cold in the harbor.
20dauntless posted 11-25-2008 12:52 AM ET (US)     Profile for 20dauntless    
I believe this is easily doable with a sterndrive or inboard engine. The system is essentially the same as the one that operates in your car. Common with outboards are diesel fired furnaces. I have a Wallas diesel stove/heater in my C-Dory that works wonders. I have seen Webasto units installed on other boats with vents all over. Espar and several other manufacturers also offer diesel fired heaters. All of these are expensive, I think the Wallas was about $2500 as a factory option.

Some people use propane, but that involves much more care in installation since propane is extremely flammable and is heavier than air and can collect in bilges and other low areas. Diesel has a very high flash point and is very efficient but it does not burn as cleanly as propane.

What boat are you looking to heat? How cold will it be where you are boating? There is a lot of discussion on the other boat forum I frequent, the C-Brats, about heaters and stoves. Here is a link:

http://www.c-brats.com/viewtopic.php?t=7499

Chuck Tribolet posted 11-25-2008 09:46 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
The problem is picking up the warm (not hot) water. On my
Evinrude 90, a little comes out the pee hole, most comes out
a bunch of small holes below the waterline, and around the
prop shaft.

The output water is maybe 80-90F, intake water is about 55F.

Raw water cooled outboards don't make sense. Most outboards
get pulled and flushed, or at least moored and tipped. And
outboards are usually aluminum, not cast iron, so don't need
the protection. Think about the outboard problems you read
about. They are "worn out" or "something broke", not "it got
corroded in salt water".

Chuck

swist posted 11-26-2008 07:12 AM ET (US)     Profile for swist  Send Email to swist     
The question is valid in the light of what the modern outboard has become - a heavy, complex, machine with all manner of "subsystems" aside from the basic engine.

A few years ago, the question would have been nonsensical as the whole concept of an outboard was simplicity and minimum moving parts to get the job done.

I don't see that much difference between an outboard and a sterndrive these days.

number9 posted 11-26-2008 07:15 AM ET (US)     Profile for number9  Send Email to number9     
Chuck,

Just wondering if you or someone you know of have pulled the zinc anodes from the powerhead and their condition after a lot of saltwater use. I don't really have enough experience to
know how much they get eaten up.

On the heater thought, looked at the cooling diagrams and the hot water could possibly be diverted at the thermostat housing. There's a temperature switch or sensor there on many engines. Run through the heater core and routed back to the exhaust. The water coming out the pilot hole is generally teed of prior to entering engine.

If I ever get around to trying it out will report back.

Bill

Chuck Tribolet posted 11-26-2008 07:53 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I've got 11 years and 900 running hours in saltwater on my
Evinrude. And a whole lot more hours at anchor while we dive.
The anode on the leg is still in good shape.


Chuck

westcoastwhaler posted 11-26-2008 11:19 AM ET (US)     Profile for westcoastwhaler  Send Email to westcoastwhaler     
Zinc anodes are for electrolysis protection, not saltwater protection.

I have similar results as Chuck with a number of outboards that live in the saltwater.

A2J15Sport posted 11-26-2008 01:19 PM ET (US)     Profile for A2J15Sport  Send Email to A2J15Sport     
I think it's doable. We have a heater in our 26' Crownline but that has a 454 cid. I/O.

On an outboard, it all depends on where the hot water is and where it exists the engine.

It would not be easy, but doable, IMHO.

A good idea.

fourdfish posted 11-26-2008 02:01 PM ET (US)     Profile for fourdfish  Send Email to fourdfish     
Although it could probably be done, I think hooking up a heat exchanger to an outboard would be very cumbersome and probably a bit ugly.
Blackduck posted 11-26-2008 02:41 PM ET (US)     Profile for Blackduck  Send Email to Blackduck     
The water is not hot enough. You would need water of about 175 degrees to be of any good. Even if the water was that hot exiting the engine, by the time it reached the cabin, it would loose a lot of that gain.
tomol posted 11-26-2008 03:05 PM ET (US)     Profile for tomol  Send Email to tomol     
I don't think it's doable. We had an extended discussion about it on another board. All we wanted was enough hot water to siphon off with a hose that we could stick into our wetsuits to warm up with. No dice.

Here's the thread:

http://www.spearboard.com/showthread.php?t=60584&highlight=hot+water

A2J15Sport posted 11-26-2008 03:45 PM ET (US)     Profile for A2J15Sport  Send Email to A2J15Sport     
I didn't say it would be simple, just doable.

Somewhere, on that O/B, is hot water leaving it at over 120 degrees F.

Having dived off many boats in 55 degree water, I would welcome 90 degree air. Assuming, heat loss to a heat unit.

I would look into the many "ski boat" units available. The pumbing would be custom and yes, UGLY.

deepwater posted 11-28-2008 06:11 PM ET (US)     Profile for deepwater  Send Email to deepwater     
i would think a boot like a huge trash can that covers the whole lower unit prop & skeg and be above the waterline (catch the pee) and run a pickup tube in and a return line to the boot using a bilge pump and the whole exhaust temp water would be used run it through a small car radiator and a 12v fan and you have heat,,fix a door and you can regulate the amount of cold water getting in and warm water escaping,,yes its doable
seabob4 posted 11-28-2008 07:31 PM ET (US)     Profile for seabob4  Send Email to seabob4     
Do yourself a favor. Get a 2000W inverter, get one of these
http://www.boatsafeheaters.com/products/cabin-heaters.aspx
and forget about the plumbing nightmares you may encounter.
deepwater posted 11-28-2008 08:35 PM ET (US)     Profile for deepwater  Send Email to deepwater     
now thats the ticket,,but how long is the extension cord,, ^@^ at dockside that would be great,,now way out on an overnight boondocks cove sleep out and i think the big bucket trick would work to heat the cabin until your all snug in the sleeping bags
seabob4 posted 11-28-2008 08:44 PM ET (US)     Profile for seabob4  Send Email to seabob4     
Deepwater,
An inverter, wired to your batteries...

Throw a serious deep cycle in the mix and you have your power.

20dauntless posted 11-28-2008 09:11 PM ET (US)     Profile for 20dauntless    
Bob, not so simple. The amount of battery power required to run that heater for 8 hours would be tremendous.

Assume for a moment that the heater you are using is rated at 750 watts. That will require 6.25 amps of 120VAC power. The inverter would require 62.5 amps of 12V power. Most batteries shouldn't be run down below 50% to maintain their health. A Group 27 battery offers about 90 amp hours of power and weighs about 65 pounds. So, not accounting for inefficiency's in the inverter, you could run a 750 watt heater off of a Group 27 battery for less than half an hour. So you'd need more than 16 Group 27 batteries to run a 750 watt heater overnight. That means an extra 1000+ lbs of weight, a whole lot of space, and lots of money.

Not to mention the power required to charge them. Most outboards would be overwhelmed, most Whaler's don't have generators, and shore power isn't always viable.

This is why most heating is done by diesel or propane. It is far more efficient and takes up less space.

seabob4 posted 11-28-2008 09:18 PM ET (US)     Profile for seabob4  Send Email to seabob4     
20Dauntless,
I believe you have your electrical equations a little mixed up. We install MarineAir's 12V AC unit, using 3 Group 27's dedicated to it, and it will run for 8 hours at 85% duty cycle.


20dauntless posted 11-28-2008 09:32 PM ET (US)     Profile for 20dauntless    
Seabob,

Can you point out where my math is wrong? It may be, I am not an electrical expert. Perhaps because the Marine Air units you use are 12V they require less power.

seabob4 posted 11-28-2008 09:49 PM ET (US)     Profile for seabob4  Send Email to seabob4     
20,
The MarineAir unit is a 120V AC unit powered by a 1000W inverter. There is something I'm missing here, (my fault, I know your math is correct!), but it is not a great stretch, such as 16 batteries! Hell, stick them all in the dinghy, right?

I'll get it figured out. I know that the A/C unit draws at least as many amps as the Boatsafe heater, especially down here in Florida in the summer.

Landlocked posted 11-28-2008 11:23 PM ET (US)     Profile for Landlocked  Send Email to Landlocked     
My standard little trolling motor deep cycle will power the blower in my propane furnace in my popup trailer for two days. I know propane has its risks but if you are careful, check your connections and make sure you have no leaks - I can think of no better alternative. The unit I have will keep the camper at a very comfortable 65 degrees. Battery = maybe 30 lbs. Propane cylinder is another 25.


LL.

seabob4 posted 11-29-2008 01:09 PM ET (US)     Profile for seabob4  Send Email to seabob4     
This is where I believe the energy consumption issue lies.

The conversion of Watts to Amps is governed by the equation Amps = Watts/Volts

Now, remember one would be running the Boatsafe heater through an inverter, thus changing 12V DC to 120V AC. Hence, the amperage usage, AT FULL POWER, would be 750/120, or 6.25 Amps. Now say, one warms up the cabin at full power, then turns the unit down to a setting that produces 375W, or halfway, which would probably be more than enough to maintain cabin temp, the amp draw decreases to 3.125 amps.

Does anyone see any fault in the math or my arrival at the calculated figures?

number9 posted 11-30-2008 05:27 PM ET (US)     Profile for number9  Send Email to number9     
FYI,

Water from the pee hole never makes into the engine. Only thing it tells you is that the water pump is pumping and your pee hole is not clogged.

Looked at a couple of service manuals and the thermostats on those engines open somewhere around 140 F.

jenkinsph posted 12-01-2008 12:00 AM ET (US)     Profile for jenkinsph  Send Email to jenkinsph     
Using batteries to convert to electric heat isn't practical but a very good compact and excellent unit was mentioned above, the Espar heater. Diesel operated in two types one being a hot air unit and the second being a hydronic water circulating unit. These units along with
the Wallas diesel stoves would be good choices. We are talking about tiny amounts of fuel per day here.

Steve

20dauntless posted 12-01-2008 11:57 AM ET (US)     Profile for 20dauntless    
Seabob,

Even if you could cut the power consumption in half (I don't know if you can), drawing 3.125 amps is still a rather large draw. Remember that the 3.125 amp draw is at 120V. AT 12V you would use 31.25 amps. This would allow an hour run time on a Group 27 battery, so you'd still need a very sizable battery bank. Depending on which Whaler you are trying to heat, you'd need a whole lot of output to stay warm anyway. Canvas enclosures don't insulate particularly well.

The Mr. Buddy heater has been used by C-Dory and Grady owners with fairly good results. It is inexpensive and runs on propane, but I'd be worried about CO poisoning. I still think diesel is the way to go.

As an example, I was out on Saturday in the San Juans. I got to the boat, turned on the motor, and switched on the stove/heater. Within 10 minutes I had hot air coming out of the heater and within 25 it was around 70 throughout the cabin. I ran the heater for 5 hours, used virtually no electricity (just for ignition, fuel pump, and fan), and very little diesel (less than a quarter gallon). The heater/stove exhausts overboard and you rarely smell diesel in the cabin. Combustion is contained so the risk of CO poisoning is extremely small, but I have a CO detector installed just in case. It really is too bad that Whaler doesn't make a pilothouse boat since they are unbeatable in cooler climates. It's a lot easier to justify owning a boat when it can be used 12 months a year...

pglein posted 12-01-2008 12:41 PM ET (US)     Profile for pglein  Send Email to pglein     
The water coming out of the pee hole DOES pass through the engine. At least on my engine (1985 Johnson 150), it exits from the Exhaust cover. This means that indicates that water is reaching and passing though the powerhead, but not necessarily that the thermostats are open and that water is pumping through the heads and cylinder passages. That means that the water is warm, but not hot, as it mixes both the water passing through the cylinder passages and the water that does not. Anyone can put their hand under this indicator stream and tell you that it is warm, but not hot.

I don't see any practical way to grab the hot water coming off the engine and divert it to a heat exchanger. The first problem is that the impeller is not designed to provide the extra pressure to push water through that extra length of hose. You could be putting your engine at risk of overheating. Systems like this are VERY common on diesel inboards. Every diesel boat I've ever owned had one. But they pumped coolant, not raw water, and typically the impeller pump is upgraded or reviewed by an engineer to ensure that it is up to the challenge. Diesel inboards are generally designed with this in mind as it is common to use the engine coolant to heat not just a cabin heater, but also a water heater and such things. Note that not only do you gain corrosion resistance by using the coolant, you also gain better heat transfer. Raw water will corrode out Red Dot heater in no time.

Cabin heating using electricity while underway strikes me as rediculously complicated and innefficient unless you are running a generator. I won't bother to do the math with regard to wattage and amp-hours, as it seems as though it's already been thoroughly discussed, but no matter how you slice it, the weight (extra batteries) and complexity (inverters) make it impractical on a small boat like a Boston Whaler.

Without a doubt, the best option for heating a cabin underway on an outboard powered boat is the use of some sort of fuel-burning furnace. Since I'm not aware of any commercially available gasoline burning furnaces, you will have to use some other fuel. Diesel furnaces are very efficient and effective. This is what you will find on most small boats and large yachts (including mine). Unfortunately, they are also very expensive. Propane is much more cost effective and reliable. Many people are afraid of propane on boats, but so long as you have a properly installed and designed system (including a contained and drainded storage compartment, a remote shutoff, and a sniffer), and use it properly (shutoff at tank when not in use), it is a perfectly safe fuel. People have been using it on recreational vessels for cooking and heating for decades and accidents are remarkably rare.

Tohsgib posted 12-01-2008 12:59 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Go to Walmart, buy a 12V ceramic car heater and plug it in. They are very frugal and produce some great heat quickly. If that is not enough, buy 2 of them or get the home version and an inverter. The home ones only burn less thsn $1 a day so it can't be that detrimental on the batteries over 6-8 hours.
20dauntless posted 12-01-2008 01:14 PM ET (US)     Profile for 20dauntless    
Bigshot (Tohsgib),

I don't know which electric heater you are talking about specifically, but it is easy to figure out how much power you need. Remember, Amps = watts x volts. It's that simple. Assume that you can't run your batteries below 50% and take into account how many amps your alternator outputs at various RPM's. The bottom line is that electricity is not a viable heating source for any length of time on small boats without generators. Propane and diesel are really the most viable options.

20dauntless posted 12-01-2008 01:16 PM ET (US)     Profile for 20dauntless    
I'm sorry, the equation is WATTS = VOLTS x AMPS. It can be expressed several other ways as well...
Tohsgib posted 12-01-2008 01:24 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
They can't draw too much if they plug into a cigartte lighter.
20dauntless posted 12-01-2008 01:36 PM ET (US)     Profile for 20dauntless    
That's true, but they probably don't provide much heat either. Can you provide a link so I can look? Heating a car which is fully enclosed is also a lot different from heating the open helm area of a Boston Whaler.
Tohsgib posted 12-01-2008 02:28 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
I thought we were talking cabins. Buddy has one in his dumptruck and it works great for like $13.
20dauntless posted 12-01-2008 02:57 PM ET (US)     Profile for 20dauntless    
It may work in the cabin effectively, but how often would someone be in the cabin of a small Whaler when underway? I'd guess that even a small electric heater would have sizable electrical demands that would preclude it's use for more than an hour with the engine shut down.
seabob4 posted 12-01-2008 08:32 PM ET (US)     Profile for seabob4  Send Email to seabob4     
The amp draw is based on AC voltage, not on DC. Remember, low voltage, high amps. High voltage, low amps. But do what you want.
20dauntless posted 12-01-2008 09:23 PM ET (US)     Profile for 20dauntless    
Yes, but you have to get the AC power from somewhere, either a generator, shorepower, or an inverter. If you are using an inverter, you are drawing 12V power from the boats 12V electrical system which is then converted to 120V power. So an appliance that uses 3.125 amps of 120V power also needs 31.25 amps of 12V power (not including for inefficiencies in the inverter).

So a 375W heater uses 31.25 amps of 12V power.

375 = 31.25 x 12

375 = 3.125 x 120

No?

deepwater posted 12-02-2008 05:48 PM ET (US)     Profile for deepwater  Send Email to deepwater     
i still think that recycling the heated water around the lower unit and exhaust pulling it up by bilge pump and running it through a small radiator and than back to the "bucket" is the simplest and few moving parts once you get 10 or 15 gal of hot water (you decide how big to make the bucket) turn off the motor and keep running the bilge pump
dfmcintyre posted 12-02-2008 07:57 PM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
I've been lurking with interest. An old friends 25 Outrage came from the factory with a Mercruiser with a closed cooling system. Since John liked to fish in the early spring, he had an optional heater installed in the superconsole. Was quite comfy. Ran both hoses in the tunnel up to the radiator / fan setup.

Couple of comments:

I think the btu output from a sterndrive is significantly larger then an outboard. Dunno if I'm correct or just passing hot water but when watching boats getting tuned up out of the water, sterndrive units seem to be passing quite a bit more water discharge.

Are we talking heating just the cabin, cockpit area or both? It seems to have changed. Thread creep?

And, are we talking while underway or stopped? Again, thread creep?

I think the easiest would be to purchase the smallest Honda generator:

http://www.hondapowerequipment.com/products/modeldetail. aspx?page=modeldetail§ion=P2GG&modelname=EU1000I&modelid=EU1000IAN

Plug one or two cube type heaters in, one below and one in the cockpit. Underway the outboard will probably overpower any noise from the generator. Moored it will give more then enough output to heat the cabin until ready to go to sleep.

The nice thing? It's got other uses around the home.

Regards - Don

sternorama posted 12-05-2008 12:41 PM ET (US)     Profile for sternorama  Send Email to sternorama     
http://www.zodi.com/web-content/

This company sells small portable propane powered heaters for camping. Not as much fun as the do it yourself thing, but prolly cost you less!

pglein posted 12-05-2008 03:05 PM ET (US)     Profile for pglein  Send Email to pglein     
Espar does make a few gasoline powered forced air heaters. The Aiortronic B5 is in their current line up, and although they don't recommend it for marine use, I don't see why it couldn't be adapted for it. It might be a little oversized.

Also, on eBay there is a B1LC for sale that they used to put in VW buses.

http:/ / cgi. ebay. com/ ebaymotors/ espar-heater-system_W0QQitemZ160301 120573QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item160 301120573& _trksid=p4506. c0. m245& _trkparms=72%3A543%7C65%3A12%7C39%3A 1%7C240%3A1318

This seems to me to be the way to go, but careful attention would need to be paid to keep it safe. Perhaps the unit would need to be mounted in a sealed box on deck, with insulated ducting running into the cabin for the heated air and the cold air return.

This would eliminate the need for carrying seperate fuel. But obviously, the safest thing would be to use a diesel heater and carry a very small tank of diesel for that purpose.

20dauntless posted 12-05-2008 05:11 PM ET (US)     Profile for 20dauntless    
If the gasoline model is cheaper it may make sense, otherwise I'd go with a diesel. These heaters use such a small amount of fuel that it really isn't a problem carrying a bit of diesel or kerosene. And since diesel is not particularly volatile you could easily carry a bit extra on deck if needed. This past summer I was on the C-Dory for over a month, ran the heater for about 10 nights, and cooked three meals on it most days. For the entire time I used about 3 gallons of diesel...not bad! Here is a link to what I have:

http://www.scanmarineusa.com/wallas_oven_85DU.pdf

It is set up with a 5L tank in the cabinet below and I get no odor from it and it will run for a very long time between fillups. Most fuel docks have both gas and diesel and you can always buy 1 gallon containers of kerosene to use if diesel is not easily available.

pglein posted 12-05-2008 06:23 PM ET (US)     Profile for pglein  Send Email to pglein     
I agree, diesel is definitely safer. But I'm always in favor of trying to keep the number of different fuels on a boat to a minimum, especially when carrying additional fuels means doing so on deck.

Ironically, on my trawler, I have the opposite problem. I'd like to find a diesel outboard with which to run a tender, or for trolling, since I've already got 420 gallons of it on board and no safe, convenient place to store even just a few gallons of gasoline.

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