Motorized rafting - Mountain Buzz

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Old 09-25-2018   #1's Avatar
lafayette or Grand Lake, Depends on mood, Colorado
Paddling Since: 1961
Join Date: May 2010
Posts: 1,140
Motorized rafting

I'm looking for a little or a lot of information on out board motors and rafts.
For a 16 foot cat with 25" tubes with the top of frame about 18" out of the water, what length shaft 20" or 25"? How many HP for same cat and dragging a couple more rafts on a windy low water Desolation trip. Four stroke or propane? Advantages/disadvantages of each? Best brands? Any info or suggestions would be appreciated very much.

I'm getting too old to row into the wind, but not to old to raft without wind

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Old 09-25-2018   #2
St. George, Utah
Paddling Since: 1974
Join Date: May 2011
Posts: 239
I use a 5 hp Tohatsu Sail Pro propane outboard with a 20" shaft. Previous to that I had a 6 hp Tohatsu gas motor. I really like the propane for a couple of reasons.

Much less exhaust odor and you never have to drain the gas to keep from clogging the carb jets like you do with a gas engine. It does use more fuel per mile than a gas motor but I can take the trade off.
In my opinion you don't need anything more than a 5 or 6 hp. You can't make much more speed due to hull speed limitations with a raft. A cataraft would likely be faster. Anything more and they get too heavy for one person to handle.

I have an adjustable mount that I can adjust for different water levels. I had a cheaper one leg mount but switched to a heavy duty dual leg mount that is much easier to adjust and takes the torque of the 4 stroke. Nice thing about the adjustable mount is you can adjust up for shallow water and down if you have a load in the front or for deeper water. I also run a prop guard.

I don't know if you would need a 25" shaft maybe if you have a fixed mount. You do need enough prop in the water to prevent cavitation.

I just pushed one boat down from Green River through Cataract to the Dirty Devil and used 2 - 5 gallon tanks in about 160 miles of motoring. I was running about 1/3 throttle and making about 6 mph into the headwinds with an 16' raft. I used the same set up last year to push out 8 rafts out to Pearce Ferry. 40 miles of motoring used about 4 gallons of propane. My gas motor did the same run the year previous with six boats and used less than 2 gallons of gasoline for a comparison.
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Old 09-25-2018   #3
La Grande, Oregon
Paddling Since: 1984
Join Date: Dec 2011
Posts: 107

I have a 7HP Honda 4 cycle. Use it on Snake, last day. Usually tie together 4 boats, have motor mounted on back of a seat on a 15' Sotar. I also have a adjustable mount so I can get it down in the water. I would agree with the 6-7HP as I can only run it about 3/4 throttle, or it cavitates no matter how low I have it in the water. Snake has a bad up river wind that this cures. Propane would probably be nice, but I had the Honda. Some exhaust but not bad. Long shank would be nice also but again I had the short shank so make it work. Does stick out a little less during the first 5 days when we don't us it. I always take extra gas, but have never used all the tank holds yet.
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Old 09-26-2018   #4
mowgli's Avatar
seattle, Washington
Paddling Since: 1983
Join Date: Feb 2010
Posts: 154
Here's my rig with Lehr 5hp propane
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Old 09-26-2018   #5
Salida, Colorado
Paddling Since: 1983
Join Date: Nov 2015
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We were motored out of the grand to Pearce Ferry this year by a guy that had the Lehr 5 HP propane motor, it was a cantankerous thing, built VERY cheaply, as one would expect from a POS made in China.

That being said, once it actually got started (10 min of bleeding, pulling and cursing), pushing an 8 boat barge, we averaged 4MPH (by GPS), sometimes got as much as 5MPH but no faster, I was impressed. Very glad to have it along when the breezes kicked in. The motorman never got past 1/2 throttle as he said in his experience more throttle only burned more propane, without providing more speed. We burned 4 gallons of propane on the motor out.

The big bonus to me is, you don't have to smell gas all the way down the river, AND you have propane along anyway. I'm going to buy a Tohatsu for 2 reasons. While I haven't actually seen one of the propane units, I've seen many of the gasoline ones, and their quality is much better than the Lehr, by leaps and bounds.

The second reason is the available shaft length of 25 inches. You can always get it out of the water using the trim adjustment if you have to, and I've had issues trying to get my current 20" long shaft gas motor INTO the water, especially on the back of my Avon pro using the standard Avon motor mount that slides into the motor becketts. I have a Cabellas adjustable mount on my 16 foot cat,

but it's spendy, and hangs the motor out from the back of the raft anywhere from 9 to 15 inches, making a tiller extension handle a necessity. I've NEVER seen one of these, usually homemade, like mine made from a busted cataract oar shaft, that was worth a damn, and makes it a WIDE swing to make a tight turn, usually in a critical time, hard to do while seated, and when you stand in a raft under motor, there's a chance you might be a sudden unintentional swimmer, not fun.

The pricing is comparable with the Tohatsu 100 bucks cheaper on sale, the warranty I think given the number of Tohatsu dealers and the comparatively few Lehr dealers would be easier to deal with should you need it. One more thing, the Tohatsu has a 5 year warranty, the Lehr 3 years...



A hundred bucks more for the Lehr, shorter shaft, shorter warranty and I can't find a stocking dealer anywhere near me, they all say buy online, which is fine I guess, but if they don't stock the motor, is there a chance they stock replacement parts?

Tohatsu dealers are all over CO and UT, which is pretty much where I primarily boat, and they stock the things, I'd still buy over the internet due to the pricing. Perhaps one could get a deal in the wintertime, but I'm lazy...

One more thing, no matter WHAT motor you purchase, get a spare metal prop or 2 especially if you're going to do Deso at low water, a couple spare shear pins is always a good idea as well. I've seen so many of the plastic props shear blades off faster than a fat chick tearing thru a bag of Cheetos, leaving the owner SOL without a spare prop, as recently as last weekend.

I've motored the entire length of Deso in bad weather with a metal prop (aluminum) and while hitting things here and there, usually sand bars, but occasionally rocks in places like 3 fords, and the daily section where it gets wide toward the end, that I wouldn't even think of doing it without a metal spare.

My 2, your mileage may vary.

Pray for snow this winter!! Hope this helps...
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Old 09-26-2018   #6
St. George, Utah
Paddling Since: 1974
Join Date: May 2011
Posts: 239
The Tohatsu Sail Pro comes standard with a high thrust prop and doesn't use shear pins, it has a clutch mechanism instead. I run a prop guard that mounts to the skeg and disable the reverse lock when doing shallow water. It does take a few cranks to get started, it has a flow valve that has to see rotation to open and allow gas to flow unlike gasoline that has pressure to a carb.

X2 on a spare prop.

That is a good price from Defender, I paid about $100 dollars more last year. The 20" can ship UPS but a 25" requires freight. A 25" would be nice on a fixed mount on a large tube Cat like the OP has. Like the other poster said you can always raise it up.

One thing to do every couple of years is to have the water pump impeller replaced as the gritty water and sand wears them out. I noticed that I was getting a reduced flow at the end of my Cataract trip but I was sucking a lot of sand and grit, the water was very low. I have around 250 miles on the motor all in gritty water.
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Old 09-27-2018   #7
Join Date: Jul 2006
Posts: 373
Save your lower unit with

Put an hour meter on the motor so you can do the maintenance as scheduled

If the motor has been anywhere other than on the transom pull the plug(s) and pull the start cord a few times to ensure that there is no oil above that piston. If there is, You can bend the cam shaft and the motor is then trash.
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Old 09-27-2018   #8
Salida, Colorado
Paddling Since: 1983
Join Date: Nov 2015
Posts: 619
[QUOTE=oarboatman;710373]Save your lower unit with

I used to use something very similar, but took it off as the increased width would catch rocks that the skeg would otherwise miss and beat the motor unnecessarily. Is a little overcomplicated from an engineering standpoint, as they say about engineers, if it's not broken, it doesn't have enough features !!

What I did was to take aluminum channel and form it like the shape of a paper airplane, if you would look at the airplane from the rear, .125 inch wall has been sufficient to date, and then thru bolt it to the skeg, making it approx .50" longer than the skeg on the forward (upstream) side of the skeg. If you can weld the front closed, that's an added bonus, but I'm a welder and didn't weld mine LOL

This affords the added strength to the skeg, and protects it from unintentional impact and adds side to side stability via the "wings" as it were resting on the lower unit. 6063 alloy is ideal for this as it's easily formed due to it's relative malleability and has a modicum of rigidity. Is the same alloy many big retailers use to make their raft frames out of.

Over the years I have seen many different designs, and came to the conclusion that none of them were perfect, each had a flaw including mine, but something is better than nothing in most instances and less is always more...

My 2, your mileage may vary
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