[RC232] Should RC1140 be better than RC1180for this application because attenuation on water will be lower a at 433 ?

Yes, generally the lower frequencies are best range-wise in all matters. A RC1140 with max output power, 10 dBm, will have double range compared to RC1180 at 868 MHz and 10 mW (around 1.2 km vs 600m, line of sight).
However, the RC1180HP (High Power) has 500mW, and this will overcome the slight drawback of the higher frequency.
So for max range (if required), the RC1180HP will be the best solution. It depends if this is a strict requirement for the customer.

Last Update: September 22, 2017  

September 22, 2017   927    RC232 Q&A