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Old 2 Weeks Ago   #1
Salt Lake City, Utah
Paddling Since: 2008
Join Date: Mar 2010
Posts: 337
Out Board Motor

I saw a video from another thread of a person pushing a tons of boats and people with a 3.5 hp motor. I couldn't find the thread again therefore I'm starting this one. Is this for real? Does anybody have experience with a 3.5 hp 4 stroke motor? Can it really push that much? I really like the cost and especially the weight. I will likely not be pushing more than three rigs. More than likely, I will be using it on single boat missions.

What brands are you die hards using?

Ode to the black oar!


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Old 2 Weeks Ago   #2
dirtbagkayaker's Avatar
Bazzaro, World
Paddling Since: 2020
Join Date: Oct 2008
Posts: 1,323
I once did the lake out on the owhyee. 16' Cat pushing a 16' willy loaded with a 13' maravia and 14' willy all loaded and powered by a 6hp on the cat. Wont do it again. Very, very slow.

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Old 2 Weeks Ago   #3
Missoula, Montana
Paddling Since: 2012
Join Date: Mar 2015
Posts: 261
I pushed two rafts and an IK down the Snake with a ~3hp 2 stroke British Seagull this summer. It wasn't breaking any speed records, but it pushed through the wind and crazy eddies without a problem.
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Old 2 Weeks Ago   #4
breckenridge, Colorado
Paddling Since: 1991
Join Date: Mar 2009
Posts: 4
I use a 4 stroke 4 horse to push my 16' cat and 2 other 14' rafts all the time. I also own an 8 horse but it is heavier and really not necessary.

Going down Ruby to Cisco this weekend with the same setup. I started using them after a 10 hour row out of Westwater.

It allows you to cover a lot more river in less time not to mention cutting through the dreaded W!
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Old 2 Weeks Ago   #5
Salt Lake City, Utah
Paddling Since: 2008
Join Date: Mar 2010
Posts: 337
What kind of 4 hp motor do you have? How long have you been using it? How long is the shaft?
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Old 2 Weeks Ago   #6
breckenridge, Colorado
Paddling Since: 1991
Join Date: Mar 2009
Posts: 4
I am running a Mercury with a long shaft (i think its like 23") but if i were to by a new one i think that Hondas are the best.

You will also need a jack plate that adjusts the motor up and down due to different weight loads. They are available all over the internet.

You also will be required to register your boat in the state you live every year and make a placard with your numbers and yearly sticker.
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Old 2 Weeks Ago   #7
eddy hopper's Avatar
DURANGO, Colorado
Paddling Since: 1977
Join Date: Sep 2007
Posts: 79
I have the Honda four stroke 2 horse and have used it on my Cataraft and Dory. 35lbs. 1/4 gal. tank runs for about an hour. I'd say we travel about 4.5 mph in flat water. Really like the weight and that it's air cooled.
"Eddies are our friends"
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Old 2 Weeks Ago   #8
Custom Whitewater Equipme
Central Point, Oregon
Join Date: Dec 2013
Posts: 88
We use a 6Hp Tohatsu and it works great. Tohatsu 6hp outboard

If you motoring on Cat or long trips the Sail Pro version has a charging coil which is great but not needed if your just pushing out from westwater. A long shaft (20") is a must.

If your only using it on flat water you can adjust the motor height by changing the air pressure in your boat.

Save your self a lot of money and heart ache and get one of these BEFORE you use your new toy.

Rock Hopper Motor Guard : Cabela's
May the water be under your boat and the wind at your back.
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Old 2 Weeks Ago   #9
Electric-Mayhem's Avatar
Lakewood, Colorado
Paddling Since: 1993
Join Date: Jan 2004
Posts: 435
I started this thread looking to rent one from someone and it turned into a seven page thread about the ups and downs of using a motor....

Anyone have a Outboard motor I can rent for a Deso trip next month?

At the end of the day I ended up buying a 5hp 4 stroke Honda motor from a fellow mountainbuzz member and have used it on two Desolation Canyon trips.

Both trips I only had to get myself and another raft down. It definitely makes a difference speed wise. I could get 4-7 mph on flatwater sections and upwards of 10mph with swift current (using a GPS to check speed). You can get close to 4mph rowing, but by the end of the day you'll certainly be worn out. With the motor, you can kinda lounge back and chill and get to camp with some energy. I'm sure adding more boats to the mix will slow it down, but I think it will still push through wind and save everybody wear and tear on their limbs.

I will say that on my grand trip this year we did some LONG days of rowing and I actually really enjoyed that too. If the wind had been worse I would definitely have changed my tone. We did have one pretty bad wind day earlier in the trip and it doubled the effort taken to get down the river and that is the time when lashing boats together and letting a motor do the work is nice.
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Old 2 Weeks Ago   #10
Western Slope, CO, Colorado
Paddling Since: 2009
Join Date: Jun 2010
Posts: 45
This is an age old quandary that took me a while, some old salty sailors, and quite a few pints of grog to finally wrap my head around. Why a 100' ocean going sailboat only needs a small outboard to make the same speed as under all the force of her sails. Or also, why 100' sailboats go faster than 50' sailboats. AKA why a 50' sailboat will never beat a 100' sailboat in a race.
Displacement hulls, one's that sit in and displace water, like sailboats or rafts, need very little power to move through the water up to a limit. That limit is a function of their hull length. Any more speed than that will require logarithmically more power as the engine will need to start lifting the hulls weight and begin rising out of the water, AKA planing like a speedboat. AKA Why it takes 250 HP to push a boat not much heavier than a raft at 50 MPH when that's only 10X the speed you can row it. You're not supplying 250 divided by 10 = 25 horsepower rowing energy, right ? Maybe 1, tops.
There is a formula that takes in hull length and will produce the maximum speed. Surprisingly, there is only 1 variable. Maximum Hull Speed in knots equals 1.34 times the square root of the waterline length in feet (HS = 1.34 x √LWL). Hull length is the amount of the boat actually under water. Knots converts into MPH with : 1 Knot = 1.15077945 mph. So, for a 14' raft, the maximum speed to efficiently move would be 5.76 MPH assuming all 14' is in the water. Notice there is no weight parameter in that equation. More or less weight will require more or less power and fuel to get to or reach that maximum efficient speed.
Any more speed than that is at the expense of quickly increasingly HP needs and fuel consumed as the hull starts lift out of the water and plane. A 10,000 HP motor will not move a sailboat or raft any faster than that hull speed if enough weight is added to prevent it from rising out of the water and becoming a planing hull vs. a displacement one. Lifting out of the water.
With a planing hull, the vessel starts becoming more and more inefficient, requiring more and more power and fuel on a quickly escalating curve as the speed increases.
The rough rule of thumb for determining Horsepower Required for a Sailboat is one horsepower per 500 pounds ( 50lbs ) loaded. No hull speed required for this calculation. Strictly weight. Why ? Because any more power will begin moving the hull up and out of the water, planing, and becoming inefficient. Weight of the boat vs. weight of water. That simple.
I would wager a 2 HP motor would have moved you very nearly as fast as the 5HP on perhaps half the fuel and a fraction of the weight if you could have found a smaller form factor motor.
There are some smaller form factor motors already around that scale to maybe 15 # and fitting in a 8" X 8" X 36 " box. They may move a raft at about 2 - 3 MPH or more, but to my knowledge haven't been tested yet.
I have one I'd be willing to test on a raft if anyone has time and is in the Montrose area. Maybe at Ridgeway or Sweitzer if you have a registration number on your raft.
PM me if interested.

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