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Q&A Flat bottom boat trolling motor power

I found a couple of references. This one has a chart that says the minimum thrust for a 12 foot boat is 30lb, it says 50lb for 17 foot boat, and 101lb for a 22 foot boat. This speedboat artcle...

posted 5y ago by James Jenkins‭ · edited 4y ago by James Jenkins‭

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James Jenkins‭ · 2020-05-01T15:25:57Z (almost 4 years ago)

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~~I found a couple of references. ~~
<a href="https://1source.basspro.com/index.php/component/k2/195-boat-rigging/476-how-to-choose-the-right-trolling-motor-for-your-boat" rel="nofollow noreferrer">This one</a> has a chart that says the minimum thrust for a 12 foot boat is 30lb, it says 50lb for 17 foot boat, and 101lb for a 22 foot boat.
<a href="https://www.formulaboats.com/blog/much-horsepower-need-boat/" rel="nofollow noreferrer">This speedboat artcle</a> says, you should have <s>at least</s> 20 Horse Power for your 800 pound boat.
~~<blockquote>~~
~~The rule of thumb is based on weight alone, and says you should have between 40 and 25 pounds of weight for each horsepower.~~
~~</blockquote>~~
~~From experience I can tell you that I can paddle both a Canoes and Row Boat faster then most trolling motors can move a similar boat. ~~
I would never "rely" on a trolling motor for movement, particularly on a river where either/both current and wind can easily overcome small motors. Even with a gas motor, you should have oars or a paddle as backup and not go out in conditions where you are not able to safely return by manual power (row/paddle).
~~An additional consideration, is judging remaining power. It is relatively easy to gage liquid fuel, batter power less so.~~
~~<h2>River Specific Rule of Thumb</h2>~~
~~There is not one, and if you find something don't rely on it. ~~
~~You clarified that you will have a generator and batteries present, even if you don't have an electric motor. So the electric motor seems like an optimal plan. ~~
On a lake the only variable to account for is wind. On a river you have a current, and you either have a dam or you don't have a dam. The lake is broad open body of water where the wind is relatively predictable. A river is a narrow winding body of water in a valley where the wind changes drastically in moments.
The current can change without warning. If there is a dam upstream, the operator can open the spillway at anytime increasing the current significantly. If there is no dam, then a flash flood anyplace upstream can alter increase the current where you are. Combined with wind considerations, make for a risky venture.
~~Additionally If there are any bridges across the river, you are unlikely to be able to motor under them with a trolling motor. Terrain changes can cause similar issues. ~~
~~See related, attempts to overcome river challenges. ~~
~~<ul>~~
~~<li><a href="https://outdoors.stackexchange.com/q/7101/4079">What is the most effective means of paddling a canoe, against the current, under a bridge?</a></li>~~
~~<li><a href="https://outdoors.stackexchange.com/q/16937/4079">How to manage the sail of a sunfish when paddling?</a></li>~~
~~</ul>~~
~~Note that I looked for an outboard motor with an integrated generator and there are a couple of DIY projects, but no off the shelf solution. ~~

I found a couple of references.
<a href="https://1source.basspro.com/index.php/component/k2/195-boat-rigging/476-how-to-choose-the-right-trolling-motor-for-your-boat" rel="nofollow noreferrer">This one</a> has a chart that says the minimum thrust for a 12 foot boat is 30lb, it says 50lb for 17 foot boat, and 101lb for a 22 foot boat.
<a href="https://www.formulaboats.com/blog/much-horsepower-need-boat/" rel="nofollow noreferrer">This speedboat artcle</a> says, you should have <s>at least</s> 20 Horse Power for your 800 pound boat.
<blockquote>
The rule of thumb is based on weight alone, and says you should have between 40 and 25 pounds of weight for each horsepower.
</blockquote>
From experience I can tell you that I can paddle both a Canoes and Row Boat faster then most trolling motors can move a similar boat.
I would never "rely" on a trolling motor for movement, particularly on a river where either/both current and wind can easily overcome small motors. Even with a gas motor, you should have oars or a paddle as backup and not go out in conditions where you are not able to safely return by manual power (row/paddle).
An additional consideration, is judging remaining power. It is relatively easy to gage liquid fuel, batter power less so.
<h2>River Specific Rule of Thumb</h2>
There is not one, and if you find something don't rely on it.
You clarified that you will have a generator and batteries present, even if you don't have an electric motor. So the electric motor seems like an optimal plan.
On a lake the only variable to account for is wind. On a river you have a current, and you either have a dam or you don't have a dam. The lake is broad open body of water where the wind is relatively predictable. A river is a narrow winding body of water in a valley where the wind changes drastically in moments.
The current can change without warning. If there is a dam upstream, the operator can open the spillway at anytime increasing the current significantly. If there is no dam, then a flash flood anyplace upstream can alter increase the current where you are. Combined with wind considerations, make for a risky venture.
Additionally If there are any bridges across the river, you are unlikely to be able to motor under them with a trolling motor. Terrain changes can cause similar issues.
See related, attempts to overcome river challenges.
<ul>
<li><a href="https://outdoors.codidact.com/questions/47310">What is the most effective means of paddling a canoe, against the current, under a bridge?</a></li>
<li><a href="https://outdoors.codidact.com/questions/54827">How to manage the sail of a sunfish when paddling?</a></li>
</ul>
Note that I looked for an outboard motor with an integrated generator and there are a couple of DIY projects, but no off the shelf solution.

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