Old tar. What sort of props are you looking for?? brass three blade or something more exotic?? Brass props available anywhere, Cornwall model boats for instance. The 850 will take an X50 prop easy and you need all the go you can get. Do we take it the outer props are driven by leeser motors, for effect?? MAkes no practical difference which way the twin props rotate.

i hate to say it but you should really ditch the SLA batteries. With this sort of boat you do not need to ballast to any waterline, and so the less weight the better. Performance will improve by probably a factor of two with a 5ooo mAhr NiMh pack. Get two and the total running time will easily be the equal of your two SLA`s, as you would not run them flat to get the full 7Ahr capacity

Ashley

Old…sailor.

What size motors are on the outer shafts?? this would determine the size needed. As to avaialbility, two blade "P" or "X" pitch props are available from a number of suppliers.. Howes, Cornwall model boats..etc. BUT you MAY struggle to get them handed…

P or Standard pitch is finer than the X pitch, and may be more suitable for the outer shafts, allowing the motors to spin more freely, it would also allow a closer sizing match with the centre prop for uniformity`s sake.

Effectively, a 5000mAhr nimh battery would be the equal of a 7Ahr SLA as you would not use all the 7Ahr of an SLA as you may damage it and it would not hold full charge again, whereas you can drain a Nimh battery almost flat (if using a BEc obviously not TOOO flat)

Ashley