Join Date: Nov 2009
Thanked 26 Times in 25 Posts
Rep Power: 7
I've used 4, 6, and 10 hp motors on inflatables in the 9 to 10+ ft range over a number of years. The 4 and 6 were used on an Avon roll-up. The 6 hp could get up on a plane with one person and a tail wind, but that motor was awkward to lift onto the stern pulpit bracket (and that was a 2-stroke!) I downsized to the 4 hp, which--at 29 lbs--was half the weight of the 6, but had to deal with the slower speed. This wasn't a showstopper, but was inconvenient in some of the larger harbors and was marginal when you had to go through a cut against the current. I remember going into Menemsha at about 1/2 kt over the ground and being grateful the current hadn't peaked.
I got the 10 hp (4 stroke) motor when I stepped up to a larger RIB. That boat/motor combination weighed in at 250 lbs, dry and empty. I considered 6 hp to be marginal and, since the 8 and 10 hp motors were about the same weight, I went for the 10. I bought peace of mind for the tidal situation and consider that the dinghy can act as a tugboat for the mother ship, if necessary. The downside is that I tow it behind the sailboat, as I am reluctant to put davits on the sailboat.
Bottom line: The larger motor is more convenient for multiple trips in the larger harbors and provides reserve for bucking wind and current. I'd say the difference is measured in tens of minutes rather than tens of seconds.