[boudreaux504]

I have looked through the forum and not seen many posts re: boat conversions. I'm not surprised, electricity and water usually don't mix well. The electric outboard motors on the market may be more cost effective than what I'm considering; if that's the case, I'll call it quits on the DIY.

Here's the facts, I have a 25Hp Evinrude from 1973 on a 14' flat boat. These are not meant to go fast or travel for days at a time. It's just a hobby boat. The longest run I've made yet is 2.5hrs with the existing set up.

From what I can find, the existing 2 stroke motor operates between 4k to 5k RPM. I am not trying to break speed records with a conversion, but I do want to at least get the boat up out of the water (aka on step). So, based on gear ratio and some voodoo math, I figure I need 2500RPM of a 25hp equivalent to get on step... Unless there is 300# of batteries in the boat.

Now I'd like to hear the voice of experience chime in... Am I taking on a $7000 project to meet the goals above? Is it realistic to think I can find motors and batteries at local auto salvage yards to meet my needs?

There are several videos on teh interwebs showing some outboard conversions. Many of them targeting a much different objective. I do not want to build a diy trolling motor... I can buy one of those for a few hundred bucks. The video done by Myth Buster's for their our board is what I am aiming for (minus the jet drive.) https://youtu.be/_EV2qq2-Lck

I look forward to your responses (even non-boat folks).

 

[piotrsko]

Not auto salvage but electric forklift salvage for motor & controller. Batteries: everywhere depending what you end up doing. 25 hp is 19 Kw . Watts=E x I. You could even use a pump motor. Mounting to the outboard might be difficult.

 

[boudreaux504]

Forklift motors have comparable RPM? If the range of RPM is significantly higher/lower, I could link to the lower unit with belt drive. Using different pulley sizes would allow for some mechanical advantage to make up the difference. Even if it's just 1:1, may help with vibrations etc.

My other idea for matching up the electric motor to the lower unit would be making a coupling with some 3D printed options. However, I'd need to have better understanding of the kinds of stress (ft/#?) involved. It may be more cost effective to have something made with a CNC milling machine. There are companies not far away that specialize in fabrication for the local oil & gas companies.

Do forklift motors require a cooling system? There is an impeller in the lower unit already... Part of the combustion engine cooling and exhaust.

 

[Duncan]

hi
re- rpm
a larger slower prop will give more thrust for less power,
the reason that the revs are so high is the 2 stroke engine needs that

 

[boudreaux504]

Now, I need to do the real math on this one. Calculating my MPH with current setup (thereby legitimizing the previously mentioned voodoo math estimates) would give me an actual target to shoot for. I know ~4500 RPM is what my motor does now, all I need is prop pitch and then the actual gear ratio... Let's say I come up with 20mph at 4500 rpm, ideally, I'd want to recreate the same speed at whatever rpm the electric motor is by buying the appropriate pitched prop.

The downside is that I would have to spend a nice chunk of change on a new prop when the one I have is perfectly good. Is the 5k rpm electric motor hard to find? Is it more expensive than finding a slower motor and buying a new prop (~$250)?

 

[Duncan]

Hi
Most forklift motors run about 1500 rpm - they can run faster - but if you want the motor to run faster you need a higher voltage - which means that you can't use the Forklift controller

 

[aeroscott]

For a 2 hour run you need a long narrow boat , like they use for cargo carrying in the 3ed world or live with a speed loss of 30=50% for 400lbs or more of batteries . Get a ac motor

 

[boudreaux504]

2hrs is more than I usually need. If I keep the same speed, the longest run I make is 35 minutes there then about the same to come back (depending on wind). My most frequent run is less than 30 min round trip.

Flat boats are not made to go all that fast, but I don't want to cut the speed in half.

 

[boudreaux504]

@duncan I'm trying to price some forklift motors from local shops. Hopefully they will be able to provide enough info so that I can match specs to price.

Are there DC and AC forklift motors? Or do I need to look in a different direction for AC motors?

 

[brian_]

Are there DC and AC forklift motors? Or do I need to look in a different direction for AC motors?

When people in this forum (and others) say "forklift motor", I believe that they always mean a brushed (and normally series) DC motor; they are only called "forklift" motors because old forklift trucks are the most common source of motors of a suitable size powered from a DC source.

Many newer forklifts use AC motors (for instance, it looks like the entire Toyota line is AC), but those motors are unlikely to cheap and readily available, so I haven't heard of anyone using them (but maybe lots have been used - I wouldn't necessarily have noticed).

For AC motors, people are buying induction and PM motors sold specifically for EV conversions (many of them from failed conversion companies), running used industrial induction motors (typically faster and at higher power than their normal operating conditions), and salvaging motors from wrecked commercially-produced EVs (e.g. Leaf, occasionally a Tesla).

 

[aeroscott]

Flat bottoms are fast on flat water. v bottoms cats are are displacement hulls
that don't have a hull speed . Any narrow 10 to 1 or more length to width ratio will not push a bow wave in front of the bow , it will move back along the hull supporting it..The water length formula is a empirical formula (observed) on vessels that were that here no more then 7 to1 . Planing vessels avoid this by lifting the hull at the expense of more power.Pick up a old Hobbie Cat, cheep add spray shields, needed very wet boats.

 

[boudreaux504]

Thank you all for your input. Work has picked up a bit this week. I'll do more research based on the suggestions provided here. I'll come back to this thread when I have made progress.

 

[aeroscott]

Good luck, if you need more information on planing verses displacement hulls, try jim brown, dick neweck, james wharram. they are a big part of the multi hull design world.