Originally Posted by PeterM
seriously - with 40hp it may still take some time to get going ....
No way. That package sounds very similar in weight and power to mine. 2 Adults, 2 kids probably similar total load to mine gets on the plane fine. 4 adults gets there without two much difficulty. All with 20HP. The only way a 40 could struggle is if you massively over-propped it in the hope of achieving ridiculous speeds on a flat calm day: speeds that you'd probably never attain because a wee boat at silly speed is terrifying.
Northsearibber - you need to give us more info -->
- engine make/model (and recommended rev range)
- current prop size
- speed (take a smartphone in a waterproof bag) with you and with you and the family
- picture of the engine height
- details of the engine trim
- an idea how much experience you have
- ideally a picture of it "not quite on the plane"
People will then be able to give you a better idea. In terms of prop selection without a tacho you'll be stabbing in the dark.