Old Prather 46" Deep Vee electric conversion

[GeckoDragon]

Hi all, new here and have a question or two:
I've been noodling an electric conversion for my old gas powered Prather 46" deep vee for a while now, and I think I have the basics worked out but want feedback from people with actual electric boat experience. I'm currently looking at pairing a 780Kv Leopard 56110 with a Castle Hydra XLX2 esc, and running on 8s. Is this combination sufficient, and will it handle the loads? It's a heavy fiberglass deep vee hull. My other question is do I need a pump for the water cooling system?
Thanks!

[Bande1]

No you don't need a pump. RC boats are cooled through water pickups in the rudder.

[fweasel]

Your setup will be very mild and you'll be able to run similar gas sized props from your old setup. Water pumps in electric boats are really only needed in very extreme SAW setups that generate a lot of heat in a very short amount of time and need the cooling to continue while the boat sits idle between passes. You'll be fine with a properly sized rudder with a single or dual water pickup.

[Peter A]

That setup will handle it easily. Those older hulls don't always handle so well at higher speeds so a "mild" setup will work well. Bearing in mind the faster you go the less runtime you get.
Are you running a submerged or surface drive?

[GeckoDragon]

Thanks for the replies!. It's a surface drive, and I intend to use the old running gear so I won't have to worry about fabricating a new steering servo mount. Water pickup is actually a through-hull just forward of the transom. If I want it to be less "mild" should I up the voltage to 10s? The Castle ESC is only rated for 8s, so what do y'all recommend instead? (edit: or maybe I could up the motor Kv from 780 to 950?)
A few pics so y'all can see what I'm working with (please ignore the mess, I'm trying to fit the contents of a 3 bedroom house into a 1 bedroom apartment...)
20231117_162436.jpg20231117_162555.jpg20231117_162609.jpg20231117_162623.jpg

[Bande1]

DDM racing has G260 promod kits on sale right now for $120. I replaced my TP 5670 12s electric system with it and the gas engine is faster.

[GeckoDragon]

Neat, but this is an electric conversion. I've no interest in fitting a new combustion engine. Thanks for the suggestion though

[koen]

the only thing is change the prop shaft in a surface drive it's a lot easier on the motor and esc and you can use bigger props (but start small and take temps every 1 or 2 min)

[Peter A]

Ok so that is a subsurface drive.
Stick with 8s but start with smaller props. Is the prop shaft 3/16"or 1/4"? If it is 1/4"you will need to get a new flex with a 3/16"step down for smaller props. I would suggest starting in the 55-57 mm x 1.4 pitch range.
Run, test, check temps, and current. you have plenty of room for parallel 8s 2P, the weight will not be an issue.
Start mild and work up to where you have it running as you want it. You may want to swap out the subsurface drive for a new stinger, rudder, trim tabs etc later.

[GeckoDragon]

There's no way this is a subsurface drive. It's an aerated prop that kicked a 7ft tall roost with the gas engine, and was visibly prop riding above 75% throttle. This isn't something I bought used and am trying to figure out- I built it new back in high school. I definitely appreciate the prop suggestions, but if those are subsurface they aren't relevant.
On edit- do y'all only consider surface drives to be where the shaft exits through the transom? Because it could be me just misunderstanding the common nomenclature. But the current setup is with a surface-piercing aerated prop, which to me says "surface drive." If I'm wrong on that, I'd love some clarification.

[Peter A]

Yeah I think you night be confused. There is submerged drive, where the prop sits completely submerged under the keel, surface drive where the prop sits with the prop hub above the keel, and what you have, which is sub surface wher the prop hub sits below the keel but the blades pierce the surface. This is what gives you a rooster tail.
You can disregard the advice if you like, but I have built and run boats this size, so suit yourself. I was just trying to be helpful.

[GeckoDragon]

Thanks for clarifying! Guess I need to brush up on terminology. Peter A, your advice is definitely helpful and appreciated- if I came off as combative, that wasn't my intent and I apologize.

[srislash]

There's no way this is a subsurface drive. It's an aerated prop that kicked a 7ft tall roost with the gas engine, and was visibly prop riding above 75% throttle. This isn't something I bought used and am trying to figure out- I built it new back in high school. I definitely appreciate the prop suggestions, but if those are subsurface they aren't relevant.
On edit- do y'all only consider surface drives to be where the shaft exits through the transom? Because it could be me just misunderstanding the common nomenclature. But the current setup is with a surface-piercing aerated prop, which to me says "surface drive." If I'm wrong on that, I'd love some clarification.

So having tried one of these old setups myself converted to FE, what happened with mine was the boat would ride up on the prop getting basically the entire hull out of the water which made it rock side to side violently. With the power of brushless motors and spinning at a greater rpm we aim for the bottom 1/3 of the prop piercing the water.
How did it run on the gas motor? Smooth and strait or rocking back and forth(chinewalk). If it ran ok then match the battery voltage up to what the gas motor used to run. Likely 15k rpm. A smooth running boat has a better lifespan although running loose on the ragged edge is entertaining
Shawn

[Bande1]

its going to be an awesome 90-120 second run on batteries. wait an hour, run for another minute.

[Peter A]

its going to be an awesome 90-120 second run on batteries. wait an hour, run for another minute.

I had a 45" mono that I could get up to 8 min runtime from 6000mah, speed was low at around 55 kph though. At 90 kph it could do two heat races on the same batts. The faster you go the shorter the runtime. You can be sure that this boats original gas setup would have been lucky to crack much more than 40 mph. To achieve the same or even better speeds would give a reasonable runtime it set up well. On 8s 2P you may well get 5 mins or more at 50 mph.

[Bande1]

ironclad RC took me up on that challenge. he put a 11,800mah pack in the boat and went around at 40mph for 7 minutes. Then I said "now go race pace." he managed 52mph and blew the ESC from all the weight. Its about 90-120 seconds unless you putt-putt or something. the length of a race. plain boring old mathematics energy in-energy out.

[GeckoDragon]

its going to be an awesome 90-120 second run on batteries. wait an hour, run for another minute.

Or just use a parallel balancing board... I fly FPV freestyle multirotors, so I'm quite familiar with charging lots of batteries simultaneously and have the equipment for it.
@srislash, the boat ran very well previously (on flat water). Didn't get the front/rear balance dialed in, but that won't matter now since I'm changing the setup. I feel like 70km/h would be a good speed to aim for. I won't be doing any racing, just bashing around at the lake, and using it to introduce my young nephews to hobby-grade rc. Probably run a pair of 4s in series, 7.5-10Ah range. What C rating should I look for?
Loving the feedback, thanks y'all!

[srislash]

Or just use a parallel balancing board... I fly FPV freestyle multirotors, so I'm quite familiar with charging lots of batteries simultaneously and have the equipment for it.
@srislash, the boat ran very well previously (on flat water). Didn't get the front/rear balance dialed in, but that won't matter now since I'm changing the setup. I feel like 70km/h would be a good speed to aim for. I won't be doing any racing, just bashing around at the lake, and using it to introduce my young nephews to hobby-grade rc. Probably run a pair of 4s in series, 7.5-10Ah range. What C rating should I look for?
Loving the feedback, thanks y'all!

At least 40c. Actually I feel that is all there realistically is, lots of claims of higher but most testing that I have read proves otherwise. The hobbyking Panther grapheme packs are good, Dinogy always good, I believe CNHL is still good.

Shawn

[srislash]

Oh and here was my 45” Dumas conversion

[fweasel]

At least 40c. Actually I feel that is all there realistically is, lots of claims of higher but most testing that I have read proves otherwise. The hobbyking Panther grapheme packs are good, Dinogy always good, I believe CNHL is still good.

Shawn

FYI, the panthers are crap now, as are most of hobbyking's offerings. I was shocked when I saw their rating drop in the testing thread as they had always been one of my best performers. My 4yr old 6S packs are still performing like new.

[Peter A]

Or just use a parallel balancing board... I fly FPV freestyle multirotors, so I'm quite familiar with charging lots of batteries simultaneously and have the equipment for it.
@srislash, the boat ran very well previously (on flat water). Didn't get the front/rear balance dialed in, but that won't matter now since I'm changing the setup. I feel like 70km/h would be a good speed to aim for. I won't be doing any racing, just bashing around at the lake, and using it to introduce my young nephews to hobby-grade rc. Probably run a pair of 4s in series, 7.5-10Ah range. What C rating should I look for?
Loving the feedback, thanks y'all!

Ok so if 70 kph is your goal speed then I can set you in the right direction. I have previously built and run electric offshore endurance boats so have some experience here. 70 kph was the speed range I was running, and doing 20 minute races on 20,000 mah packs.
I would recommend changing the driveline to surface drive. Whether you use the existing strut and rudder or get a new stinger and rudder.

Props for the 70 kph range are X455-457, Prather 240-245. These will put you between 70-80 kph. You should be able to see an average current draw at around 70A, but don't skimp on the esc. A ZTW 200 or Castle for 8s, something bigger if you want the ability to go to 10s, but you don't really need to.
If you run 10,000 mah capacity then you should get runtimes as long as 7-8 minutes, but test and check. Set your esc lvc higher at 3.2v to reduce the risk of over discharge.

[LibertyMKiii]

Or just use a parallel balancing board... I fly FPV freestyle multirotors, so I'm quite familiar with charging lots of batteries simultaneously and have the equipment for it.
@srislash, the boat ran very well previously (on flat water). Didn't get the front/rear balance dialed in, but that won't matter now since I'm changing the setup. I feel like 70km/h would be a good speed to aim for. I won't be doing any racing, just bashing around at the lake, and using it to introduce my young nephews to hobby-grade rc. Probably run a pair of 4s in series, 7.5-10Ah range. What C rating should I look for?
Loving the feedback, thanks y'all!

C Ratings are completely bogus and made up values. There is no regulating body on the battery industry so they put a made up value in there to sell more products. One great example is CNHL and their 70c G+ lipo is their highest output lipo, but they also sell a 90c and 120c that output less power.

I would go with tried and true/trusted brands. The CNHL G+70c is a good pack that ranks high in the mid-grade list.
Or if you want to go top shelf go with something from SMC.
They happen to be running a great sale this week for thanksgiving/black Friday.

I'd also recommend going with any battery that has a minimum of 10awg or 8awg wire. QS8 battery connectors are also great for handling the heat these fast electric setups produce.

I'd go with the Castle XLX2 hydra for the ESC. It runs cool and has all the power handling you could want (better suited for a big heavy boat also)
Should you want to explore going faster it has data logs and you can get into the data for helping you make prop change decisions.

[GeckoDragon]

@Peter A - yep, I'd say it was in the 30-35mph range with the gas engine
@srislash - that's a 45"? Daaaaang. That kind of performance is badass, but I don't think I need mine to be quite that level...

Sounds like the Leopard 56110 w/ Castle XLX2 Hydra is a solid combination, so I think I'll go with that. As far as batteries, how do y'all feel about Tattu? They're pretty well regarded in the FPV community. Although we do prioritize low mass & high rate discharge (my favorite batteries [not Tattu] are 6s 1050mAh, and they handle 120A draw without breaking a sweat). CNHL doesn't have a bad rep, solidly midgrade, so I'll definitely look at those