Propane outboard in cold weather question

GSBNY

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May 9, 2019
138
O’Day 192 New York
I’m planning on taking my boat out of the water tomorrow and have about a 30 minute motor to where I need to go (my mast is down already). I have a Tohatsu Propane SailPro with a 4lb tank (not sure what’s left in it, maybe half) and 2 1lb back up tanks (both new and full). Temperatures will be about 45 at the peak tomorrow.

Should I worry about anything due to the cold temperature?

I seem to remember that Propane acts differently in the cold but this is my first cold weather motor with the Tohatsu and don’t know what to expect. I had planned to get the boat out sooner but some family issues prevented me from getting to it.
 
Dec 28, 2015
1,837
Laser, Hunter H30 Cherubini Tacoma
Shouldnt be a problem. If you find a performence issue while using it after a while with frost building up on the tank, swirl the tank around to get the liquid up to the upper part of the tank to warm it up. Worst case is pouring water on it to also warm the tank up.
 

GSBNY

.
May 9, 2019
138
O’Day 192 New York
Shouldnt be a problem. If you find a performence issue while using it after a while with frost building up on the tank, swirl the tank around to get the liquid up to the upper part of the tank to warm it up. Worst case is pouring water on it to also warm the tank up.
Thanks for the info.

I have the 1lb tanks in a warm place tonight and I’m planning on insulating them before I put them on the boat tomorrow.

I also have a bunch of hot hands packets at home so I was considering wrapping the 4lb tank and putting 2 of the packets in the wrapping to provide some sort of heat source if need be. That would only be if I had trouble from the start.
 
Dec 28, 2015
1,837
Laser, Hunter H30 Cherubini Tacoma
Unnecessary. You wont be pulling enough propane out of the tanks and it wont be cold enough for them to auto refrigerate.
 
Dec 28, 2015
1,837
Laser, Hunter H30 Cherubini Tacoma
No problem. I enjoy propane physics and on occasion, propane accessories.
 
Feb 8, 2014
1,300
Columbia 36 Muskegon
Propane devices work by burning the evaporated gas from the tank. The colder the temp, the slower the liquid propane evaporates and the less gas is available for use. In sub zero temperatures that can be a problem, on occasion I've had my barbecue grill refuse to light with a full tank in winter. But 45 degrees F isn't cold enough to cause that problem and the lower the liquid level in the tank the more room there is for evaporated gas. So at that temp and with a half tank of propane you should be fine.
 
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May 24, 2004
7,129
CC 30 South Florida
Raising and then lowering the mast on the O192 should not be too much of a hassle. Either that or tow boat insurance should guarantee your safe arrival. Engines can fail for a variety of different reasons so it is always good to have a plan "B".
 
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GSBNY

.
May 9, 2019
138
O’Day 192 New York
Well, lesson learned and I’m fully admitting fault here.

Kept the tanks indoors last night to keep some heat in them. Hooked up my main 4lb tank for the trip around and motor started perfectly. I let it warm up a bit and off we went. I only got about 1000’ down my canal when I realized the rpm’s were falling so I broke out my nice and warm 1lb tank and guess what, the adapter fitting didn’t fit properly. Right as I figured that out, the motor cut out. Luckily the 20mph winds on my tail kept the boat moving forwards enough that I had steerage to get to a dock about 50’ ahead of me. Unfortunately, when I got to the dock I had no way of slowing down so my girlfriend and I grabbed the dock and held on as tight as we could. If we missed the dock we were going straight into another boat, but we were just able to stop in time and tie off.

Fortunately my back up plan worked and I had a tow boat on stand by who was able to get over to me in about 10 min. Got towed to the boatyard for haul out tomorrow morning.

Obviously, I had some oversight here. I should have checked the adapter fitting beforehand and my math trying to figuring out how much propane was left in the main tank (obviously not enough) was definitely off. Next season the plan is to top off the tank every 4th trip and find the right adapter for the 1lb tank (or buy another 4lb tank for standby).
 

GSBNY

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May 9, 2019
138
O’Day 192 New York
Glad that worked out ok in the end! These composite tanks are translucent, and have other advantages too. Wish they made them smaller than 11lb though. Have asked...
I had originally looked at those but my fuel locker is quite shallow. The 4lb tank just fits in there (vertical clearance) and there’s space for 2 of them side by side. I would need a horizontal tank to use anything bigger than my 4lb.
 
Jul 28, 2018
57
Catalina 22 TX
Yeah, hopefully propane outboards will be common enough someday and someone will make a suitable tank.
 
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GSBNY

.
May 9, 2019
138
O’Day 192 New York
So you ran out?
I think that’s what happened. I know it was low but the tank felt like there was enough left for the short trip. Guess it was lower than I thought.

Got any recommendations on tank gauges?
 
Jul 28, 2018
57
Catalina 22 TX
My thought has been that weight is better than a pressure gauge.

In practice though, when the engine rpms start to drop steadily at constant throttle I know I have limited time left. It sounds like you do the same. I put a cheap tach on the engine cowl, which counts total run time too.

For a longer trip with larger tank, I'd measure (and log) time at WOT as the limiting factor.
 

GSBNY

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May 9, 2019
138
O’Day 192 New York
I had thought about keeping a log of run times so I could keep track throughout the season but I forgot. That hour meter is a good idea for sure.

I heard that weight is the only accurate way to do it. Now that the tank is empty (I think) I can take a baseline weight and go from there.

First season with the boat and new outboard, it’s all a learning curve.
 
Dec 28, 2015
1,837
Laser, Hunter H30 Cherubini Tacoma
My thought has been that weight is better than a pressure gauge.

In practice though, when the engine rpms start to drop steadily at constant throttle I know I have limited time left. It sounds like you do the same. I put a cheap tach on the engine cowl, which counts total run time too.

For a longer trip with larger tank, I'd measure (and log) time at WOT as the limiting factor.
Pressure gauges do not work with liquified (compressed) gas. Only thing I know of is a float type gauge or weighing it. The ones you see on Amazon that you put inline with the hose are BS. Laws of Vapor Pressure dictate it.
 
May 24, 2004
7,129
CC 30 South Florida
Just weigh your tank when empty and after filling up. The difference will be the weight of the fuel; divide the weight into 4 equal parts and assign Full, 3/4, 1/2, 1/4, Empty. The reason gauges do not work is because propane maintains a constant gas pressure until there is none.
 
Mar 26, 2011
3,399
Corsair F-24 MK I Deale, MD
S
Just weigh your tank when empty and after filling up. The difference will be the weight of the fuel; divide the weight into 4 equal parts and assign Full, 3/4, 1/2, 1/4, Empty. The reason gauges do not work is because propane maintains a constant gas pressure until there is none.
Specifically, how do you do this on-board? (Not "how is it done?") Bathroom scale?
 

GSBNY

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May 9, 2019
138
O’Day 192 New York
I’ve been thinking a bathroom scale onboard (at the dock) would do the trick. I could also easily remove it from the boat once in a while to weigh on the dock.

When I have the pound per hour burn rate figured out it won’t be too much of an issue.

The Tohatsu website claims the motor will run for 5 hours at WOT on an 11lb tank. So my 4.25lb tank should run 1 hour and 55 minutes at WOT. Over the 20 times I’ve used the motor (out and back), I’ve never used more than 1/4 throttle.

So I think at 1/4 throttle max I should be able to get at least 3 hours of run time under my normal circumstances not including any extended motoring.