Lehr Propane Outboards

[s/v 'Faith']

Loki,

Welcome! I have Norse history and know what Loki means, but your user name is funny to me since I have neighbor with a dog named Loki also.

Contributes nothing to the thread, but hey... You get what you pay for.

[s/v 'Faith']

Originally Posted by lokidog

I wish Consumer Reports or someone would do a test of engine economy for small boat engines. You would think Lehr would do some comparisons so they could say "Our engine gets 1.7 times the economy of Brand X gas engine.", or something to that effect. Especially with a new product that many people seem to have confusion about on the web, eg. gallons vs pounds.

Just based on what has been posted here.... If a Lehr does indeed burn ~1# per hour at full throttle, you can compare that to ~1/2 gallon in your Johnson (well, maybe not yours since it is seized)

Propane varies quite a bit, I suppose the high might be using new 1# bottles at $4 or so each. So if the numbers are close, fuel costs per time can run approximately 2x what you are paying now.... But if you use a larger tank (like a 20# exchange cyl) you might find you can get down to something like a $1 an hour....

Of course, a 4 stroke of equivalent HP might be even cheaper to run.

Maybe someone with direct experience has some good numbers.

[HopCar]

"You would think Lehr would do some comparisons so they could say "Our engine gets 1.7 times the economy of Brand X gas engine.", or something to that effect."

It probably wouldn't look especially good. A gallon of propane doesn't have as much energy as a gallon of gasoline so in theory it takes more propane to do the same work. It's not too bad because the propane engines run at a higher compression ratio and are better at converting the propane into useful power. None the less, a good gasoline engine will probably run a little longer on a gallon of gasoline than the Lehr will on a gallon of propane.

In my neighborhood propane costs about $4.00 per gallon when put into tanks at the local U-Haul store. I think that's about what high test gasoline is going for around here. For some reason they charge a lot less to put it into a propane powered vehicle. Not sure why.

At that rate I figure it would cost me about $4.oo per hour in fuel to run a 9.9 Lehr.

I think there is a very large mark up on propane in small quantities. I know it gets very cheap if you have a big tank at your house to cook with and they deliver a couple of hundred pounds at a time. Another thing that affects the price of propane, no self serve. They have to pay someone to pump it.

S/V Faith, It's really expensive to run the Lehrs on those 1 pound cans, A lot of people are doing it anyway because it's so convenient. If you refill the little bottles from a bigger tank that you filled for $4.00 per gallon, that's only $1.00 per refill.

The 2.5 burns 1 pound or about 1/4 gallon per hour at WOT.
The 5.0 burns 2 pounds or about 1/2 gallon per hour at WOT.
The 9.9 burns 4 pounds or about 1 gallon per hour at WOT.
Fuel consumption drops a lot if you run these at about 3/4 throttle.

The 9.9's will not accept the little 1 pound bottles. It's just not practical to run them on the small bottles.

I know it's confusing going back and forth between pounds and gallons. Just remember that a gallon of liquid propane weighs a little more than 4 pounds.

[pbiJim]

Originally Posted by HopCar

The 9.9's will not accept the little 1 pound bottles. It's just not practical to run them on the small bottles.

I was wondering about that. I was surprised that even the 5hp was able to run off of the little 1 pounders.

1 pound tanks, 20 pound gas grill tanks & most any other propane tank that you are going to find on a pleasure boat is most likely a vapor service tank. In those tanks, the liquid propane boils off inside the tank & the resulting gas is piped out to be used. The amount of head area in the tank limits the rate at which the gas can be harvested for use. Because of this, the smaller tanks have less flow capacity than the bigger ones do.

Larger propane motors, like the ones on forklifts, use liquid service tanks. They take the propane into the motor in liquid form. It first passes through a vaporizer, which is basically a heat exchanger that uses radiator coolant as a heat source. After that, the propane gas goes through basically the same kind of "carburetor" that a vapor service motor would use.

The performance of a vapor service tanks usually drops off when the temperature drops too far. Has anyone tried using one of these propane outboards in cold weather?

Also, does the manufacturer specify what grade of propane should be used?

[Jd1]

Originally Posted by HopCar

The 9.9's will not accept the little 1 pound bottles. It's just not practical to run them on the small bottles.

I think the small bottles are an essential safety feature. Unless one has a fiberglass tank, one can not verify the amount of propane left in the tank and it would be silly to carry two big tanks wherever you go.
I was told that the 9.9 would accept the little bottles but that was some time ago and looking at the Lehr site it confirms that the 9.9 will not run on little bottles.
This is a real predicament for me. The small emergency tank was a big deal! Also, if you pull the engine off your dinghy a lot then the little self contained bottle was a real bonus.
Too bad!

[HopCar]

" The amount of head area in the tank limits the rate at which the gas can be harvested for use. Because of this, the smaller tanks have less flow capacity than the bigger ones do."

Exactly right. It doesn't seem to be an issue in the 9.9 and smaller motors but I expect when they come out with a 15 it will want to be fed a liquid diet.

In fact you can feed all of the Lehr outboards liquid propane. Both the 5.0 and 9.9 are equipped with vaporizers and the 2.5 uses so little vapor that it can vaporize the liquid in it's fuel lines.

If you think about it, the 2.5 and 5.0 are fed liquid propane from the 1 pound cans until the cans are half empty. They are mounted on their side. The support for the can is made of aluminum that is meant to transfer engine heat to the can and help vaporize it when the level drops low enough that it is feeding vapor.

"The performance of vapor service tanks usually drops off when the temperature drops too far. Has anyone tried using one of these propane outboards in cold weather?"

Yes, on another forum I heard from someone who lost power after running a 5.0 for some time on the small can in cool weather. I spoke to an engineer at Lehr about it and he said that when the small can gets low in cold weather the last small amount of liquid might not evaporate fast enough to sustain full power. It seems to me that the bigger the engine and the smaller the tank, the more likely you are to have trouble getting enough vapor to run the engine at full power. In really cold weather you'd probably want to feed the engines liquid and let the evaporator do it's thing. Who wants to be that cold on a boat anyway?

"Also, does the manufacturer specify what grade of propane should be used?"
In the US I haven't seen different grades of propane but I'm told that in other countries butane is often mixed with propane. Is this what you're concerned with or are there different grades of propane that I'm not aware of?

[HopCar]

JD1, there are adapters that would allow you to connect the little 1 pound cans to the hose so that you could run the 9.9 on the small can in an emergency. That would get you another 15 minutes at WOT, maybe 1/2 hour at 3/4 throttle.

[Jd1]

Originally Posted by HopCar

JD1, there are adapters that would allow you to connect the little 1 pound cans to the hose so that you could run the 9.9 on the small can in an emergency. That would get you another 15 minutes at WOT, maybe 1/2 hour at 3/4 throttle.

Thanks! Good to know.
Now if I could only make up my mind about a dinghy .... <sigh>

[pbiJim]

Originally Posted by HopCar

In the US I haven't seen different grades of propane but I'm told that in other countries butane is often mixed with propane. Is this what you're concerned with or are there different grades of propane that I'm not aware of?

In the US, 3 grades of propane are present. They are 5, 10, & industrial. The general public never sees the industrial stuff. It is normally only used as a feed stock for chemical reactions. Grade 5 is the clean stuff. Grade 10 is what is specified for use in a gas grill.

The different grades represent the quantity of a particular impurity that is present in the propane. I don't remember what that impurity is, but I can go look it up if someone wants to know. The issue with that impurity is that it gives off some sort of plastic molecule as a byproduct of combustion.

When using propane as a chemical feed stock, this impurity is desirable as it boosts production yield & that is why it exists in very high concentrations in the industrial grade.

Some propane motors specify that only grade 5 should be used for fear of plastic residue fouling the innards of the motor. I am not sure if this is an old wives tale or not. A local equipment dealer in my area sells grade 10 to all of his customers. He claims to know of no problems with the equipment running on his fuel. I've been refilling my forklift tanks at a gas station for the last 2 years without any issues & they don't even know what grade they carry. For that matter, most propane retailers in my area don't seem to know what grade they have. I'm curious if most places now carry grade 5 without knowing it or if a motor really doesn't care if it gets fed grade 10.

In general, propane is a wonderful motor fuel in warm environments. Propane is much more friendly to the motor than gasoline is. I've gone to do an oil change on a propane motor after 1,000 hours of service & still found the old oil to be clean & honey color. When the mixing valve (carburetor) is tuned correctly, they burn clean enough to be used indoors.

[pbiJim]

Originally Posted by HopCar

"You would think Lehr would do some comparisons so they could say "Our engine gets 1.7 times the economy of Brand X gas engine.", or something to that effect."

Actually, no I would not expect that. A buddy of mine in Arizona has a duel fuel truck that can run on propane or gas. He got it because, in that state, alternative fuel vehicles are allowed to use the HOV lanes on the highway with only 1 person in them. He tells me that it is more expensive for him to run on propane than gas because the motor chews through the propane faster. Apparently, with today's high gas prices, the cost differential has shrunk, but not disappeared. I don't know how much the current cost difference is.

[pbiJim]

Originally Posted by Jd1

I think the small bottles are an essential safety feature. Unless one has a fiberglass tank, one can not verify the amount of propane left in the tank and it would be silly to carry two big tanks wherever you go.

There are 4 methods of measuring the amount of propane in a gas grill tank that I am aware of. 3 can be used on any standard tank.

The most reliable method is to weigh the tank. I usually just pick up the tank & slosh it around a little. That gives me a pretty good idea (+/- 15%) of what is left. Spring loaded hang scales also exist that monitor how much is left in the tank. My webber grill came with one of these built in.

You can buy a gauge that goes inline with the feed hose, but those are notoriously inaccurate due to the way that propane expands & changes pressure with changes in temperature.

When I was a kid, I used to see check strips that one would stick to the side of the tank. I found these to be a bit impractical. You had to pour hot water on them to take a reading. The hot water would make the strip change color. The full portion of the tank would change to a different color than the empty portion.

The 4th method is to get a tank with a built in float gauge. I don't see these often, but they are out there & they do work reliably. I have most often seen these float gizmos mounted in special tanks that have a second bung for the gauge.

[HopCar]

pbiJim, Thanks for the lesson on propane grades. I had no idea. I haven't seen anything from Lehr that addresses that issue. I guess that any propane that is normally sold to consumers will work. Next time I talk to Lehr I'll ask about it.

I agree with you in regard to engines needing more propane than gasoline to do the same work, see my post #33. The Lehr outboards are probably a little better about that than your friends dual fuel truck. The truck is probably set up to run on regular 87 octane gasoline. Propane has an octane rating of about 110 and can be run at a higher compression ratio. The Lehr outboards take advantage of this by running at a high compression ratio to squeeze a few more BTUs out of a gallon of propane than a dual fuel engine can. Still, you can't beat the fact that gasoline is more energy dense than propane.

[pbiJim]

Do you happen to know what compression they are running at?

Thanks,
Jim

[Jd1]

Originally Posted by pbiJim

The most reliable method is to weigh the tank. I usually just pick up the tank & slosh it around a little. That gives me a pretty good idea (+/- 15%) of what is left. Spring loaded hang scales also exist that monitor how much is left in the tank. My webber grill came with one of these built in.

You can buy a gauge that goes inline with the feed hose, but those are notoriously inaccurate due to the way that propane expands & changes pressure with changes in temperature.

When I was a kid, I used to see check strips that one would stick to the side of the tank. I found these to be a bit impractical. You had to pour hot water on them to take a reading. The hot water would make the strip change color. The full portion of the tank would change to a different color than the empty portion.

The 4th method is to get a tank with a built in float gauge. I don't see these often, but they are out there & they do work reliably. I have most often seen these float gizmos mounted in special tanks that have a second bung for the gauge.

The only method that I would find usable is #4. I did not know that float gauges existed for small tanks. They are of course standard fare for larger tanks.
The in-line gauge is useless as the pressure reading is mostly a result of temperature. You only see a drop when you are starting to run out of liquid propane and then it's too late.
Having to boil a pot of water before you take a dinghy ride to shore kinda takes spontaneity out of the picture and weighing also doesn't strike me as something that would get done consistently before departure. IMHO it has to be easy to quickly check levels in order for it to get done consistently.

Thanks for the heads-up on the float gauge tanks!

[DWJ]

For what its worth I've been buying the 1lb cans from target for $2.75 each. I get about 45 min of run time out of 1lb can. that's running at half throttle. which is about 80% of the speed at full throttle. I have a Lehr 5hp which I bought from Hopcar.