55inch fireboat mono deep V plywood hull

Hi I am a newbie to the forum and electric boats, need all the help I can get. My Fireboat is my own design mono deep V hull built with plywood without plans and it is 55 inches long 16 inches wide and weight is 25 lbs without any hardware. The end weight will probably about 30 lbs with all batteries motor and other parts needed. The speed I am looking for would be 15 to 18 mph, the prop I think will do is an octura X450/3. I used the Octura brushless speed prediction -RC boat calculator but it does not take the weight of the boat into the factor. What I would like to know is the seize of motor ,batteries and esc that is needed without over heating anything. Thank you for any help.
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Well, some sort of starting point would be ideal.

Like do already have something existing, batteries, or motor, or ESC you would like to use? What about driveline? Are you going to set it up like a racing boat with a stinger/strut hanging off the back, or place it underneath the hull like a real boat like that may have? Or are you thinking outboard?

Keeping the volts high will keep the amps low. You're not going to need much rpm to move it 18mph. I like the idea of high voltage, low amp, very low kv, swinging a big ol' prop.

That is hard to say, I would imagine the prop slip/hull efficiency is not great so maybe 35% for the prop slip data field.

To keep the speeds down and temps low I would imagine a lower KV motor is ideal. Maybe something like 800kv.
Larger motors will run cooler so you may want to look at the 56mm series motors.

TP Power tends to run around 89-90% efficient for the calculator uses.

https://www.offshoreelectrics.com/conversion.php

You should be able to use the calculator and plug in 6s or 4s for example to get to your ideal speed.

Like I said I am a newbie to electric boating and do not understand the terminology being used. I have no hardware except the ? in. flex shaft that is a spare from my gas-powered boat. So what I need to know is what seize motor, batteries, and esc that will give me a reverse and 15 to 18 mph. Thank you for any info.

If you want reverse I would recommend that you don't run a flex shaft assembly. They are wound to turn a specific direction and start to unwind when they are turned on the opposite direction. A straight shaft turning a submerged prop would be a better solution especially since you are not looking for a lot of speed. Look on the OSE store website for motors, there are several brands that manufacture 56 mm motors. That is the diameter of the motor and is the largest most common size which is what you want for a boat that size. You also want a low KV as suggested in the previous two post. The KV represents the rpm that the motor will turn for each volt of electricity supplied and is indicated when you are asked to choose when selecting which motor to purchase. As far as speed controls go I am of no help because most of us here on this forum run fast boats that don't use reverse. I am sure that if you were to e-mail Steve, the owner of OSE he would be more than happy to help you with recommendation to choose the right one.

Thank you very much Panchothedog now I have a better idea of what to look for.

Alright, I did a little bit of figuring.

This shouldn't be a bad setup:
Motor (540kv) https://www.offshoreelectrics.com/pr...?prod=leo-5692
Cooling Jacket https://www.offshoreelectrics.com/pr...eo-5675-jacket
Motor Mount https://www.offshoreelectrics.com/pr...prod=ose-83376
ESC https://www.offshoreelectrics.com/pr...200-6200200-v2
Prop https://www.offshoreelectrics.com/pr...d=oct-0955%2F3
2x-4x of these batteries https://chinahobbyline.com/shop/deta...wsize%E3%80%91
2x-4x of these connectors https://www.offshoreelectrics.com/pr...=ose-xt90-anti


Should play together well. The 4S batteries you'll want to wire in series to create 8S, and if you run four of them, then the other pair also wired in series, then paralleled to the first set to make 8S2P (this will give longer run time). The motor is capable of pulling 3000w continuous and 5000w peak, which translates to about 100-170A of current on 8S LiPo. That ESC is rated for 200A continuous, so it should live a long and happy life. Boat should go around the speed you're looking for.

They're right, straight shaft would be the way to go with this boat, so you can use reverse as much as you like. Since you're familiar with gas boats, I didn't look up the drive system.

As you are running a submerged drive, the speed calculator is pretty much irrelevant as it is for surface drive setups. Tbones suggestions on parts are good, however I do not think you will need to run 8s to get you speed goals, 4s will probably be close, but you will have to test it out. I ran the same motor in a 45" mono on 10s with a prather 235 at 63 kph max. This was testing for endurance running and surface drive. It will be finding out the best prop and battery.

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Originally Posted by Peter A

As you are running a submerged drive, the speed calculator is pretty much irrelevant as it is for surface drive setups. Tbones suggestions on parts are good, however I do not think you will need to run 8s to get you speed goals, 4s will probably be close, but you will have to test it out. I ran the same motor in a 45" mono on 10s with a prather 235 at 63 kph max. This was testing for endurance running and surface drive. It will be finding out the best prop and battery.

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My exact thoughts, 4s would be an ideal setup for speeds under 20mph. No need for 8s.
CNHL has some 9200 mAh 4s packs. Depending on the run time you want, running 2 of those in parallel would give some incredible run times.

I run a 42" mono on 4s with a 1700 kv motor and it runs pretty steadily in the 43-50 mph range with 4 different props I tried. Dropping the KV from my setup as already mentioned would be the only way to get down to sub 20 mph speeds.
I also think you could run a simple SeaKing 180a esc for this setup, or the lower cost flycolor 150a esc/OSE Raider 150a.

If y?all are dropping voltage, okay, especially easy to try two 4S wired in parallel, and okay with series as well.

But shouldn?t he drop the motor size as well? That motor can pull 100A continuous at 8S nominal voltage. Cut that in half, and if he tries to tow something he could be looking at over 200A continuous, 340A peak. Then ya?ll are talking about dropping to a 150A ESC as well?

I get it, not a speed boat. But no matter the boat, I always try to make sure my ESC is at least rated for what the motor is rated for. And we all know how easily those motor ratings can be exceeded.

I stand by the ZTW 200A recommendation. You can never have enough ESC, and it gives you the option of 8S. It is a 30lb hull.

I would like to thank you all for the help especially tbonemcniel for spending time looking up and setting me up with all that need to get started because I have no clue on electric but learning very quick :doh:

Here I am again I bought the OSE 56mm Angled Motor Mount and was wondering is there a special way to secure this mount to to the bottom of the boat ?

I did buy all that you suggested and now I need to program my ESC not sure how that is done , whatever recommendations you give and where to buy will be greatly appreciated

Quote:

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Originally Posted by Jalopy

Here I am again I bought the OSE 56mm Angled Motor Mount and was wondering is there a special way to secure this mount to to the bottom of the boat ?

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If it were me, I’d adhere the mount with JB weld, then lay some Kevlar cloth (more stretchy than carbon) with west systems epoxy.

And there does exist a programming box for that ESC. It is shown at the bottom of the ESC link above.