Trolling motors for catamaran

[Afilimon]

Hello guys,
I'm new on this forum, and saw lot of great articles here, hope you can help me to.
The problem is related with power of trolling motors. I have catamaran type boat, with two 4m long and about 0.7m width pontoons. The weight of fully loaded boat with passengers is about 1500lbs. For this boat I use two 86lbs 24V motors. Maximum speed of boat measured with GPS was about 4.349598mph(7km/h) with total current draw about 80amp.
But I'm not sure how effective I'm using this motors. Because I read lot of articles about trolling motors and rule for choosing motors is same: 2 lbs of thrust for every 100lbs.
For example here:
https://www.trollingmotors.net/blogs...r-thrust-guide
is given same formula- 2 lbs of thrust for every 100lbs. So in my case 1500/100*2=30lbs. Even if I take 55lbs motor, this is far away from 2*86lbs. Also I know, that speed of the boat depends of rpm of motor and pitch of prop, not only lbs. Motors with different lbs can go in same speed.
So my questions:
1. how many lbs I need for my boat to achieve about 4mph?
2. If boat goes lets say 3 miles per hour with one 86lbs motor and uses for example 30A current. What happens if I turn on another identical 86lbs motor? Did total current must be 30A or 60A for same speed at same conditions?
sorry for english.
Greately thank you.

[makomark]

that's a lot of weight in a 'small' boat, especially for the batteries.....is it a pontoon?

guess the first question is how fast do you need/want to go, using just the electric motors?

As a general rule around here, most people only use their trolling motors for fishing....so speed isn't an issue.

[Afilimon]

Hello,
thank you for reply.
It's difficult to describe what kind of water vehicle this is, we call its just POPA BOAT.
https://www.facebook.com/16794303356...1292296846387/
But basically this is catamaran with two electric motors. The goal is to have vehicle with mean speed 3 or 4 miles per hour for about 5h. Now the best result is about 2h with about 2.5mph speed. I'm looking for how to prolong battery working time. So questions is: How to find optimum lbs value for the motors? I not found on internet how to calculate required lbs for catamaran with two motors. So I think maybe here you guys with your experience can help me to understand what is what.
I hope, that somebody knows methodology how to choose motors for catamaran.
Or if not, then how to understand behavior of two motors on the same boat: If lets say boat with usual shape is driven with one 86lbs motor with max speed. And current for example wit 24V system is 40A. What happens if I turn on another motor with same parameters? Did total current per two motors must be 80A or 40A? Did motors must share load or not? Because measured current on my boat with max speed is about 80A.

Thank you

[TipDS]

Hello,
thank you for reply.
It's difficult to describe what kind of water vehicle this is, we call its just POPA BOAT.
https://www.facebook.com/16794303356...1292296846387/
But basically this is catamaran with two electric motors. The goal is to have vehicle with mean speed 3 or 4 miles per hour for about 5h. Now the best result is about 2h with about 2.5mph speed. I'm looking for how to prolong battery working time. So questions is: How to find optimum lbs value for the motors? I not found on internet how to calculate required lbs for catamaran with two motors. So I think maybe here you guys with your experience can help me to understand what is what.
I hope, that somebody knows methodology how to choose motors for catamaran.
Or if not, then how to understand behavior of two motors on the same boat: If lets say boat with usual shape is driven with one 86lbs motor with max speed. And current for example wit 24V system is 40A. What happens if I turn on another motor with same parameters? Did total current per two motors must be 80A or 40A? Did motors must share load or not? Because measured current on my boat with max speed is about 80A.

Thank you

The "hull speed" for your boat should be approximately 4.6 knots, so I wouldn't plan to ever get above that on trolling motors. If you try, the power requirements go up at a nearly exponential rate, until the boat planes out.

If you're trying to maximize battery life, you should consider digital motors. They waste far less energy as heat than traditional electric motors.

In the end, you're probably best contacting the support department for the brand motor you will likely purchase. They can help you determine what size motors you need for your application AND what kind of battery system you need. Some motors only need 12V, some 24V or even 36V. Also, the type of battery (or batteries) you use will have a big impact on loiter time.