With my new Suzuki 20 4-stroke I've carefully logged the fuel use vs distance. Overall in a mixture of conditions the average equates to getting around 75Nm from a 25l tank. So using the old rule of thirds (third out, third back and third for emergencies) you have a safe 50Nm range.
For me that would be plenty far enough for a day in a SIB.
IMO i go for max hp giving redundancy not flogging the engine then mine will perform with 4 in ok but there's no room for more so there's the limitation [yes the boat can carry 6 but not safe IMO].
I'd go with the most HP that the boats rated for and certainly go for 5 more HP for £50.
I had a 15 hp 2 stroke Mercury on my Honwave 3.5 AE but it's a better craft all round with the 20 hp Tohatsu 4 stroke. Quieter, more economical, no pre-mixing and a lot more powerful. Seems as guick on acceleration too but that;s tough to judge accurately.
Obviously heavier but as the boat will live on a trailer no issues.
Rarely will anyone here suggest anything except going for the maximum manufacturer recommended size or maximum you can afford.
I'd say the exception to that could be (a) if you have to lift it off / manhandled it at all (or manoeuvre on transom wheels) OR (b) if the engine is much heavier and in a sib you will mostly use alone with your own weight at the back.
Well the sib will mostly be on a trailer and also will be dismantled for hols, I am also changing the sib a bit and have a seating arrangement like a zodiac
spy-sea-one
