I plan to install a 12-Volt 55-lbs-thrust trolling motor on a [MONTAUK 17].
What will be the boat speed [of a MONTAUK 17 at full thrust of 55-lbs]?
Predict Speed of MONTAUK 17 with Trolling Motor
Re: Predict Speed of MONTAUK 17 with Trolling Motor
You can calculate the horsepower of an electric motor by knowing its voltage and current. See
https://electricboatingtips.com/thrust-to-horsepower/
In an example given at the above resource, a 55-lbs-thrust motor is said to consume 12-Volts at 50-Amperes. This is 600-Watts. Assuming an efficiency of 0.85 to actual power output gives 510-Watts, and converting to HP gives 0.68-HP.
Predicting velocity at displacement speeds is highly dependent on hull form. I can't suggest a formula to convert 0.68-HP into a boat speed.
Another source will be from anecdotal first-hand reports, which I cannot offer.
My guess is an easily driven boat like a MONTAUK 17 with minimal load, with the outboard engine tilted up to reduce drag, and not going upstream into wind and waves could perhaps go 5-MPH—but just a guess. If you really worked at it, you could probably row a MONTAUK 17 at 5-MPH. I am sure one horse could pull a MONTAUK 17 at 5-MPH through the water.
Note: I deleted an earlier analysis using a formula that claimed to be able to predict HP from Thrust and Velocity. I didn't see the underlying relationship between the factors explained sufficiently, so I didn't have faith in the formula. In order for a formula to be useful, there must be some fundamental understanding of how the factors are related. In the case of relating velocity to power and thrust, there would have to be an assumption about the resistance of the body being accelerated. There is a very big difference among hull shapes in how easily they can be accelerated, but there was no consideration in that formula for any influence of hull shape. That's why I discarded it.
https://electricboatingtips.com/thrust-to-horsepower/
In an example given at the above resource, a 55-lbs-thrust motor is said to consume 12-Volts at 50-Amperes. This is 600-Watts. Assuming an efficiency of 0.85 to actual power output gives 510-Watts, and converting to HP gives 0.68-HP.
Predicting velocity at displacement speeds is highly dependent on hull form. I can't suggest a formula to convert 0.68-HP into a boat speed.
Another source will be from anecdotal first-hand reports, which I cannot offer.
My guess is an easily driven boat like a MONTAUK 17 with minimal load, with the outboard engine tilted up to reduce drag, and not going upstream into wind and waves could perhaps go 5-MPH—but just a guess. If you really worked at it, you could probably row a MONTAUK 17 at 5-MPH. I am sure one horse could pull a MONTAUK 17 at 5-MPH through the water.
Note: I deleted an earlier analysis using a formula that claimed to be able to predict HP from Thrust and Velocity. I didn't see the underlying relationship between the factors explained sufficiently, so I didn't have faith in the formula. In order for a formula to be useful, there must be some fundamental understanding of how the factors are related. In the case of relating velocity to power and thrust, there would have to be an assumption about the resistance of the body being accelerated. There is a very big difference among hull shapes in how easily they can be accelerated, but there was no consideration in that formula for any influence of hull shape. That's why I discarded it.
Re: Predict Speed of MONTAUK 17 with Trolling Motor
Wow, thanks for all that. Looks like [a 55-lbs-thrust trolling motor] will be exactly what I am looking for.
Re: Predict Speed of MONTAUK 17 with Trolling Motor
Better get a real-world first-hand observation to be sure. There are probably some examples in the archives. Here is one I found with a search term:
170 MONTAUK: 12-Volt or 24-Volt Trolling Motor
https://continuouswave.com/ubb/Forum8/HTML/004130.html
As noted, with a limit of one 12-Volt battery the biggest thrust motor is probably going to be a 55-lbs model. If you can tolerate the greater weight and complexity of 24-Volt power you can get a more powerful trolling motor.
Your needs will depend on what sort of conditions for use. Foul currents and headwinds are going to need power to push the boat.
170 MONTAUK: 12-Volt or 24-Volt Trolling Motor
https://continuouswave.com/ubb/Forum8/HTML/004130.html
As noted, with a limit of one 12-Volt battery the biggest thrust motor is probably going to be a 55-lbs model. If you can tolerate the greater weight and complexity of 24-Volt power you can get a more powerful trolling motor.
Your needs will depend on what sort of conditions for use. Foul currents and headwinds are going to need power to push the boat.
Re: Predict Speed of MONTAUK 17 with Trolling Motor
Thanks Jim H