[Jessica11k]

Howdy all! I'd like to convert a gas-powered ski boat -- mostly because my family says I can't

That said, I'm worried this isn't practical!

I've read that I need 90 hp minimum to be a viable ski boat... does anyone know how I could achieve that? I'd like to spend less than $1,000 on the motor, because the rest of the project will inevitably be quite expensive.

I don't mind running several motors together, but I don't want to go over my motor budget.

Any advice at all is greatly appreciated, thanks!!

 

[rancid0076]

I’m going to be using a leaf motor, controller, and volt batteries. Will offer plenty above 90hp. I bought motor and controller off eBay about 800 for both.

 

[Duncan]

Howdy all! I'd like to convert a gas-powered ski boat -- mostly because my family says I can't

That said, I'm worried this isn't practical!

I've read that I need 90 hp minimum to be a viable ski boat... does anyone know how I could achieve that? I'd like to spend less than $1,000 on the motor, because the rest of the project will inevitably be quite expensive.

I don't mind running several motors together, but I don't want to go over my motor budget.

Any advice at all is greatly appreciated, thanks!!

The problem is not the motor - it's easy to get a ton of power

It's the batteries! -
With a car you use a lot of power accelerating but the power to maintain speed is a lot less
A ski boat needs that power all the time

Lets say you need 85 kw - (113 hp) - that means that an 85 kwh battery from a Tesla - 600 kg of battery! - will last less than an hour

 

[remy_martian]

To belabor Duncan's point even more - lithium and water really really don't get along very well. So your batteries just got even heavier.

 

[Wollysf]

Just as a data point, I converted my older 15hp evinrude outboard on a 14' aluminum skiff to 15 kW electric. Speed increased from 15 mph max to 21 mph. Removed the ICE powerhead and replaced with 15kW brushed motor onto same lower unit. Went 2X increase on rpm with belt drive. The earlier comments about battery capacity ring true to me. I am using this to cross a 1.5 mi lake in the Sierras. So I only need battery capacity to get me round trip across the lake once or twice, and then I charge from solar (cabin is off-grid). It take me about 4.3 kWh for one round trip. I started with lead-acid batts for early tests, then went to Nimh hybrid car packs, and now to Lipos. I have about 9.3 kWh under the center bench seat, @ 21S= 78vdc, 2P for 120Ah. Getting up on a plane takes about 150A, then I can stay on a plane at about 120A, or max speed at about 160-180A.
My guess is that you will use far less than 90 hp once boat is on a plane and skier is up. Maybe 40-50 hp. What duration are you looking for? Should be a fun project.