Converting from gas to electric

[Jdupay]

I am relatively inexperienced in the world of RC boats and I am looking for advice. 5 years ago I built a wood v-hull rc boat. It is 4 feet in length 15 inches wide and weighs 15 pounds with the gas motor that is currently in it. The motor is currently a 26cc two stroke. I am looking for suggestions on what kind of motor and ESC set up I should be looking at to be able to power this boat.

[Bande1]

a gas system is quite a bit less weight of an electric setup if that is your primary concern. a 26cc engine weighs about the same as medium 8s battery pack. not counting the motor and ESC which makes electric easily double the weight. Ive been converting my electric hulls back to gas, personally. its so much cheaper and more fun than waiting around for hours for large, multi-hundred dollars battery packs to cool down and then recharge.

[fweasel]

A boat that large will work best with a single 56mm motor, lower kV , and a larger prop diameter similar to what you were running on gas. Assuming you're looking for similar performance as your gas setup, something in the 600-800kV range depending on voltage is a place to start. As for batteries, you're run time is going to be significantly less. If something in the 4-5min range is acceptable, 2x5S 5000mAh or 2x6S 5000mAh lipos in series to give you 10S or 12S respectively is a good start leaving room to move the weight around to adjust center of gravity.

[Bande1]

A boat that large will work best with a single 56mm motor, lower kV , and a larger prop diameter similar to what you were running on gas. Assuming you're looking for similar performance as your gas setup, something in the 600-800kV range depending on voltage is a place to start. As for batteries, you're run time is going to be significantly less. If something in the 4-5min range is acceptable, 2x5S 5000mAh or 2x6S 5000mAh lipos in series to give you 10S or 12S respectively is a good start leaving room to move the weight around to adjust center of gravity.

on my gas conversion with a single 56mm running 6500mah and 7600mah budget packs I get about 90-110 seconds at a 55mph pace. about 45 seconds if propped up to go over 60mph. I would highly advise bare minimum of 10,000mah for approximately 3 minutes of run time. a stock 26cc, which I own and run, is approximately equal to about 4500w or so. about 165A load on 8s.

[fweasel]

We're talking about very different setups if you're only able to run 90seconds. On my last Zelos 48G conversion, I ran 2x6S 5000mAh packs and got about 4min when propped for 70mph top speeds, which was significantly faster than the 30cc gas setup I replaced.

[Bande1]

We're talking about very different setups if you're only able to run 90seconds. On my last Zelos 48G conversion, I ran 2x6S 5000mAh packs and got about 4min when propped for 70mph top speeds, which was significantly faster than the 30cc gas setup I replaced.

you went 70mph for 4 minutes on 5,000mah in a 4ft long boat? that would be about 7kw at least. the calculator has that at 103 seconds. which is almost always way over blown for runtime.

Screenshot 2023-09-14 7.08.12 PM.jpg

you would have to pull 75a to run 4 minutes. which is about 25mph.

[fweasel]

The run was bashing, peak speeds were 70mph, not continuous.

[Jdupay]

If that is the case, do you have any suggestions on a better gas set up? I currently have a cheap medium quality motor in it and I have never gotten it to run right.

[Bande1]

If that is the case, do you have any suggestions on a better gas set up? I currently have a cheap medium quality motor in it and I have never gotten it to run right.

start with the basics. is the carb adjusted right? 2 1/18 turns out on the low needle. 1-1 1/8 out on the high needle. the carbs need to be drained after use by pinching the line and letting the engine idle until the fuel runs out. after some time the carbs need rebuild kit. easy and cheap. the tuned pipe. when you move the pipe fore and aft on the exhaust manifold it adjusts the power band RPM. generally 13.5 inches from the mufflers ridge to the manifold face.

next, gizmo motors sells racing mods for about $200-250. with a stroker crank, ported head, etc. it will get you into the 60mph+ range. There are people that will build the motor for you such as Huff racing. Intlwaters forum is the place to go for gas boat knowledge.

if you are just not a gas person then fine, go electric. get those rail mounts OSE sells and an electric motor should bolt right up to the engine mounts. You can get a budget motor like the rocket RC 56102 for $120 on amazon. a set of SMC HCL_HC (hc = high capacity) 8800mah for $160. Run 8s via two 4a packs in series with a super low KV motor like 600-700kv. that will allow you to use your gas props. you will need a charger, spend another $100 for that. The ovonic chargers on amazon are pretty nice for $100 and charge 4s packs at 12a per channel on your vehicles starting battery.

[Peter A]

a stock 26cc, which I own and run, is approximately equal to about 4500w or so. about 165A load on 8s.

Sorry Bande your math is wrong. A stock 26 zenoah is 3.5 hp or 2625W equivalent.

4500W on 8s is 155A - 4500/29 = 155.

I have a stock 26cc Thunderboat and I am giving serious thought to converting it to electric. The big advantages I have with this are that I have a spare painted hatch, motor (TP4070 440kv) esc etc. I can fit the motor in the existing gas mounts and batt trays outside the rails, so it can easily be converted back. This motor on 12s in a 45"mono turning a ABC 2314 /4 chopper prop ran at 90 kph and drew around 60A, I could do two heat races on 6000mah. With a bigger prop on the Thunder boat it would be faster than it is now and easy on batts for heat racing.

One of the guys in our club converted his Slingshot gas rigger to electric. It runs a TP5670 650 kv, ZTW300 G2 esc, 12s (2x6s) 5000 mah, detongued X470 at 130 kph and does heat races without cooking batts.

To the op, the extra weight of electrics in a mono does not effect the top speed, and it can be of advantage in rough or race water. It all depends on what you want to achieve with your boat at the end of the day.

[Bande1]

Ive ran them back to back with a tp 4070 pulling 4387w on the data log went the same speed as a zenoah 26cc in the same boat. about 53mph.

in regards to the slingshot rigger the guys in my club developed and build that hull. Running pro mod 29.5cc they run 9 second laps. 10 second laps are 90mph sustained. Their 8hp engine, which should be equal to 6,000w, literally laps my 7000w, 12s sprintcat once a lap. Its not even in the same universe.

[Bande1]

I should say not back to back ive ran electric and the 26cc, it was a month apart but nothing had changed with the hull.

[lohring]

Everyone I know runs tuned pipes on their stock Zenoahs. Our testing shows a little over 4 hp with the right pipe. That's a little under 3,000 watts. On 6S that needs around 120 amps.

Lohring Miller

[Bande1]

Everyone I know runs tuned pipes on their stock Zenoahs. Our testing shows a little over 4 hp with the right pipe. That's a little under 3,000 watts. On 6S that needs around 120 amps.

Lohring Miller

IF you believe 750w = 1hp
seems more like 1000w = 1hp in real life to me (maybe its the extra weight of electric)

[Xrayted]

Science and facts are great like that. They dont change or become invalid based on what anyone "believes" or lacks in understanding of them

[Bande1]

2 weeks to slow the spread. remember to double mask. Trust the science!!!

you put a 45" hull on 6s up against a 4hp gas boat?

[lohring]

The difference is that our dyno measured power at the engine output. We measure electric motor power at the battery output. If you allow around 80% ESC/motor efficiency, you get 932 watts per hp. That means to get 4 hp at the motor output you need 5 hp or 3700 watts at the motor input. That's a little over 150 amps.

Lohring Miller

[Bande1]

Interesting. So it is kinda close to 1000w per HP.

[Xrayted]

No, not really. Electrical and mechanical HP conversions to watts are 745 and 746 for 1 HP, so essentially the same. Those values dont change and are what they are. What's being talked about here now is the difference in how or where those values are being measured, not the values themselves.

Sort of like having 500HP measured that the crank in car like all automakers publish, vs doing a dyno which measures at the wheels after the losses are factored in, so its lower. The definition of measured HP doesnt change, and if you want 500HP at the wheels then the crank power will need to be higher. A gas motor also has driveline losses no differently than our electrical systems do

The fact that a rigger can easily lap your higher powered cat design hull doesnt mean much either. Of course it will because it's not just about the raw power numbers. Weight and hull design matter even more, and riggers are some of the lightests with least water contact designs, so of course they will whip you every time, even with way less power.

It reminds me of the guys that constantly try and challenge me with their big 600+HP V8 Camaros and Dodge Chargers. Loud heavy "boats" and they all look stunned when I destroy them with my 500HP 6 cylinder car because they never consider that I weigh 900 lbs less than they do in a much more agile car, so I have the advantage despite having 100HP less

[vvviivvv]

Also consider a outrunner... perfect for bridging the gap between Gas and electric.

[Bande1]

No, not really. Electrical and mechanical HP conversions to watts are 745 and 746 for 1 HP, so essentially the same. Those values dont change and are what they are. What's being talked about here now is the difference in how or where those values are being measured, not the values themselves.

Sort of like having 500HP measured that the crank in car like all automakers publish, vs doing a dyno which measures at the wheels after the losses are factored in, so its lower. The definition of measured HP doesnt change, and if you want 500HP at the wheels then the crank power will need to be higher. A gas motor also has driveline losses no differently than our electrical systems do

The fact that a rigger can easily lap your higher powered cat design hull doesnt mean much either. Of course it will because it's not just about the raw power numbers. Weight and hull design matter even more, and riggers are some of the lightests with least water contact designs, so of course they will whip you every time, even with way less power.

It reminds me of the guys that constantly try and challenge me with their big 600+HP V8 Camaros and Dodge Chargers. Loud heavy "boats" and they all look stunned when I destroy them with my 500HP 6 cylinder car because they never consider that I weigh 900 lbs less than they do in a much more agile car, so I have the advantage despite having 100HP less

all you girls are adorable when I pull up on my R1. Here's another bit of science - gasoline has 33.7kwh per gallon. You average 6s lipo has about .133kwh

[Xrayted]

Yes, it’s not news to anyone that gasoline has a higher energy density than any current battery technology. That’s why we still use fossil fuels for almost everything.

It has nothing to do with available power, but you can run the same speed or slower for longer

[Bande1]

Yes, it’s not news to anyone that gasoline has a higher energy density than any current battery technology. That’s why we still use fossil fuels for almost everything.

It has nothing to do with available power, but you can run the same speed or slower for longer

You can keep up with some basic gas boats for 40 seconds! wow

now wait another 1hr for a re-charge to do 5 laps...

[Peter A]

Well this thread has derailed!

[lohring]

Electric model boats can easily run flat out for a full race including penalty laps. If you have a high power charger, modern batteries can easily be charged at 2C. That means 20 to 30 minutes between heats. These days the fastest RC model boat is electric powered. http://www.ne-stuff.net/2016/10/2853...ld-record.html IC engines are rpm limited so existing props don't have enough pitch for the highest speeds. They can be pitched up, but the maximum is still limited.

Lohring Miller

[Bande1]

you're charging lipos without a cool down period? thats dangerous.

[LibertyMKiii]

I am relatively new to RC boats.
What are the fastest SAW runs with petrol/nitro setups?

It seems like electric motors dominate that area.
RPMs are not really a good excuse as you can use a gear drive to up the prop RPMs.

[Bande1]

I am relatively new to RC boats.
What are the fastest SAW runs with petrol/nitro setups?

It seems like electric motors dominate that area.
RPMs are not really a good excuse as you can use a gear drive to up the prop RPMs.

I think theyre around 10-15mph slower than electric. around 130mph range. electric can go very fast for short periods. 10 seconds, 60 seconds, maybe even 90 seconds with extremely expensive premium batteries.

put it this way, racing orgs have to lower the electric lap counts so the boats can make a whole race.

[LibertyMKiii]

I think theyre around 10-15mph slower than electric. around 130mph range. electric can go very fast for short periods. 10 seconds, 60 seconds, maybe even 90 seconds with extremely expensive premium batteries.

I think each has its place. If I wanted long run times and cool running temps then absolutely gas/nitro setups make the most sense.
If you only need to run for 1-2 mins tops then electric has its place.

I have output 10kW on 6-cell electric and know people have gone north of 18kW on 8-cell setup. I don't think you can get that sort of power out of the small engines... short of putting a dirtbike motor in your boat.

[lohring]

The charging range is 0 to 45 C or 32 to 113 F. That's pretty warm. It doesn't take long to cool enough. Often warming the battery before charging is needed. We used 6 hair dryers in our electric hydro to warm the batteries before running.

Lohring Miller

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https://batteryuniversity.com/articl...w-temperatures