Can anyone help me with this issue please.
Cabin cruiser 1m long; 4240 x 740 brushless motor; 5S lipo; 55mm prop.
Cruised happily for 15 mins, then made noise (not dissimilar to slipping coupling) and powered down to a stop. Would then only creep along. On inspection found all three fuse holders and 25A fuses had melted, but fuses not blown. The motor was not hot, nor was the ESC. Out of water seemed to operate OK. It was suggested that the prop might be too large, and caused the motor to go out of sync after a while.
So, what do you think might be happening ?
😉

Some weeks have passed and I have had one or two opportunities to further test and experiment with the power train set-up.
With the three fuses between motor and ESC removed I carried out trials using a watt meter, and different size props. The motor is rated at 50 amps max. and 870 watts max.power. The ESC is rated at 90 amps.
X40 prop pulled 25amps and 492 watts.
S45 prop pulled 21 amps and 419 watts.
X45 prop pulled 31 amps and 594 watts.
S50 prop pulled 27 amps and 505 watts.

All these values are safely within the parameters of the motor and ESC. I did not have the X50 or 55 sizes with me, but they should be next to test. In the original set up I was using an X55, and fuses between motor and ESC when they melted and the motor went out of sync.

In all the above cases I checked every component after fast running to see how cool or hot they had become, and the only heat detected was very slight warmth in the cables between motor and ESC, and a hint of warmth in the ESC. No problems arose.

I am pleased that the early issues have been resolved, and thank you one and all for your input without which I would have been floundering !
I can now look forward to years of enjoyment on the water. 😉