Electric propulsion for small fantail launch

Have you seen some of the bass boats they push along? And, they do it all day long too.

 

We want to stick wi the existing conventional running gear.

There’s an electric golf cart available nearby. Any thoughts in repurposing its components?

 

A golf cart will have all needed components, if you are lucky even the charger. The wiring harness will have to be adapted in lenght, so it fits the boat. Most motors do not have a front plate and bearing, those are integral to the differential and will have to be fabricated. The motor axle has an internal spline, you need the matching shaft from the differential. If you need the gear reduction you can use the entire differential, the ratio varies between 8-12:1.
For you it does not matter if the motor is series, shunt or AC, just make sure all components come from the same model of cart.

 

I suggest you look at the electric Duffy boats for inspiration. They have a similar vibe: Duffy Electric Boats | World's Premiere Electric Boat Company Since 1970. (duffyboats.com)

You could replace the one lunger with an elco inboard motor nicely as a drop in: Electric Inboard Motors - Elco Motor Yachts

If you are limited by funds a Haswing or Caroute trolling motor could be used that would easily push that along at 4 mph +.

 

Elco is great, and they've been around a long time, and yes, Duffy for inspiration. But as @gonzo points out, 2 kW will match the rated power of the current engine, and as @Rumars says, a golf cart has all the components. The only thing I can add is that there are some LiFePo marine-grade batteries available for a bit over $300 per kW. They appear to have a 200-amp discharge limit, which would put you just over your 2 kW requirement. They have a built-in BMS, so an integrated package. The charger from the golf cart might not work, but the rest of the components should so long as you limit your controller to 2 kW. With one of these batteries, you could have ~2 hrs of runtime near flat out.

 

Read through these pages they may give you some idea..
The Electric Boat Association (EBA)

 

What is the diameter and pitch of the boat's propeller? My electric boat used a 1750RPM 24 VDC PM motor, belt driven for 400 RPM at the prop, and has two speeds forward and 2 speeds astern, all with a couple of double pole double throw relays, each costing $25 from Graingers. With two large 12 volt lead-acid batteries I could cruise at 4 knots for a few hours. I found the two speed setup entirely satisfactory, avoiding the expense of typical variable speed controllers.