I have a 47" classic Fireboat which I would like to use my G-60 500kv electric motor with a 6s Lipo battery and a 120 amp watercooled esc. I wondered if anyone could give me anyone idea of what prop size to start with experimenting to give best power anyone and endurance ? I am told the G-60 is the electric equivalent of a 10cc glow engine, so what size would go on that might be a start. Thanks in anticipation, Dave W 😊
Just a word of caution - I fitted my 47 inch fireboat with a JP Energ I.C. 60 O/R 670 (C50-20) Brushless Motor which is similar to the one you are considering fitting. I use it with a Fusion hawk 120 amp electronic speed controller and it is powered by two 4s LiPo batteries. The performance is exciting to say the least and I find that once it is on the plane it becomes unstable and prone to capsizing.
Thanks Shaun, I intend being careful with it. The boats were originally fitted with 10cc glow engines, so an equivalent electric motor should be ok. But I can always reign it in on the throttle side of the esc curve. Are your 2 LiPo's in series of parallel ? I expect parallel, as series would give 8s which would be crazy. You still didn't say what size prop you were using. Best wishes, and good sailing, Dave W 😊
Hi Shaun, This design of hull forces the craft higher and higher the faster it goes. When it is high on the plane and almost hanging on the last few inches of propshaft it can fall off the plane either way, usually to the right (Starboard) side because of engine torque. The full size boats were fitted with 2 or 3 engines to help counteract this.
The British Powerboat Company, who originally designed the hull that Vospers copied back in the 1930s/40s also noticed this which led to double skinning the hull with 1 inch thick mahogany for extra strength against pounding and falling on the waves. Lowering the drive angle of the propellor shafts and adding more weight from the C of G back to near the stern.
We build this 3 screwed designed hull with one mainshaft usually so do not have the benefit of shaft rotation to stabilise the boat at speed. It was in the 1960's that Fairey engineers had the same problems (Swordsman,Huntsman etc) They came up with large transom mounted powered Trim Tabs. Their boats had similar problems and only one shaft in the main.
I suggest you try fitting 2 x 2 inch wide by 1 inch deep trim tabs at the very bottom of your transom midway between the keel and the chine as well as move your battery packs forward a bit initially. Try some fast tests with this, you only need 2 to 4 degrees of down on the tabs initially. Add removeable weights near the CG as needed, a bit at a time but don't stop the bow lifting up onto the plane.
This one is for you.....I wouldn't fit a 6 cell Li-Po to run your 47 inch fireboat!..It would be uncontrollable almost, even if you throttled back. That relates to an output speed in excess of 11,000 rpm at the prop. Safer to try a 5 cell (9,250rpm) or even a 4 cell (7,400) initially. Also see my message to Shaun. I use a G60 in mine with 4 cells which is ample, the extra battery pack in Shauns will double the running time. I only use 1 cell. I use a 50mm two blade Hydro Graupner prop (From Gliders UK), it could handle a bigger one but everything starts to get a bit warm!!
Thanks Ron. I always though the I'v times the voltage gave the prop revs. As my G-60 is only a 500kv, then my 4s at 14volts should be sufficient, but a 3s might be a bit short at 11.1v. But I will give the Graupner 50mm hydro a try, which at the least is a place to start from. Once again, thanks for the advice Ron. Happy sailing, Dave W😊