Gas prop to electric jet conversion?

[Christopher Pohle]

This might be a completely silly idea, and feel free to let me know if it is. I have an old Prather 46" deep vee that I built in high school almost 20 years ago, and getting it running again would require new electronics, hoses, and a complete rebuild of the 25cc Homelite Special engine. Since that's already quite a bit of work, I recently had the idea to convert it to an electric jet drive (maybe even dual jet?) and I'm wondering if anyone here has the experience to tell me if I'm just bat-**** crazy, or if that's actually workable. Any and all input is appreciated!

Edit: my other thought is to electrify it but keep the prop drive and make it an ocean basher

 

[LohringMiller]

I converted a Calcraft 3.5 size mono to P limited electric jet. The boat was a little big for that power but ran well. It is slower than the same hull with a propeller drive, but was very manoverable. I built a smaller and lighter boat for the drive and that worked even better. See my article on jet boats at namba.com/content/library/propwash/2021/October/8/

Lohring Miller

 

[Christopher Pohle]

Interesting, thanks! At 46" mine is significantly bigger though (assuming my search result for your boat was accurate), and has a heavy glass hull. What size motor do you run? Assuming I keep the existing running gear, I figure I'll need to be running a 56mm can on low Kv 10-12s, or a higher (900ish) Kv on 8s. Though I'd definitely go for a less aggressive prop because if I'm ocean bashing I don't think I want it to be prop riding. Which it absolutely did with the 25cc Homelite Special.

As an aside, I thought I might use the existing through-hole from the tuned pipe for a sealed self-righting ballast tank.

Thanks for your input!

 

[LohringMiller]

I consider P limited size electric power plants to be similar to 3.5 size nitro engines. We ran 6S power plants on 7.5 size boats including a Leecraft XT-460 and a Mutt II sport 40. I run an 8S power plant in my electric 1/8 scale boats to replace 11 cc nitro engines. The Castle ESCs are very suitable for any of these sizes. Pick a motor with a KV that gives 20 to 25,000 rpm loades. That will be something like 80% of the rated KV. This is a vidio of a 6S pump that should work. It uses a 100 KV motor that can pull 100 amps at 6S.

Lohring Miller

 

[Christopher Pohle]

Oooh you were talking about glow engine size. Thanks the clarification, your first post makes a lot more sense now. 1/8th scale sounds like the size range mine would classify as. Regarding the pump in the video, did you mean 1000Kv motor? 100Kv at 6s is only 2200 rpm. Also, the video creator said he was running it with a 360kv SSS 56114 motor (the very same motor I'd already picked as a good candidate, actually). Even on 10s though, 360Kv only gets you to about 13.5k rpm. The 960Kv version on 8s comes out to 28.5k rpm, though, so maybe that's the ticket (and I already have an 8s capable charger). No idea how many amps it would pull. I do want a setup that gives me good low-speed punch, as I doubt I'd be spending much time at high throttle beyond quick bursts for my use case. And like I said, it's a heavy fiberglass hull. Unfueled, the all up weight with the gas engine is 16lbs and I doubt it'll get any lighter by swapping to motor, pump, and batteries. Speaking of batteries, what capacity do you like to use on your 1/8th scales, and how many amps are you pulling from them? I can't imagine an XT-90 being anywhere near sufficient as a connector.

 

[HTV Boats]

I would go with the Castle XL2 which is a proven ESC on 8S. 4S batteries in parallel are plentiful and reasonably inexpensive. A 4070 TP from 900 to 1100kv and you should make 60-70 mph and decent FE run time. 200-300 amps. Props from 52mm-62mm diameter. Stay with the 1/4 drive and get a step down to .187 flex shaft. If you need .250 props a simple adapter is easier than drilling .187's to .250
Mic