I'm learning more each week that I get out on the water in my 3.3M SIB. My boat has a soft inflatable floor. My boating buddy has a rigid aluminum floor. His SIB is also 3.3M. Both boats are rated for max 15 hp.
It seems to me 15 hp and its relative top speed can't be fully utilized unless you are on smooth water conditions. On rough water these sibs bounce around a fair bit and beat you up. You likely can't rip a 7.5 hp outboard wide open in rough conditions, let alone a 15 hp. I think I've found a sweet spot with my 3.3M sib with an 8.0 to 10 hp-range 2 stroke, with a 9" diameter, 9" pitch prop. I've come to realize faster isn't always better with these sibs. For me sibs are about storage convenience. Access to remote lakes. Portability. Having a light weight engine is a huge part of the convenience. The light weight two-stroke In the 8-10 hp range suits me very well.
The proper inflation psi has a huge effect on the boat's handling at higher speed. The faster you go the trickier it can get. Payload weight distribution, outboard engine weight and HP rating offer more variable factors to the boat's stability at speed.
I'm fortunate to have multiple small outboards, props and a couple of boats to experiment with. I've gained a fair bit of experience quickly this spring. So far I've settled on my 1990 8.0 Merc 2-stroke a my top choice for my soft floor 3.3M SIB. Still more experimenting will be done. I was out last week with my 7.5 Merc 2 stroke. It performed pretty good also. It had a 7" pitch prop. I want to try it again soon with a 9" pitch prop.
It seems to me 15 hp and its relative top speed can't be fully utilized unless you are on smooth water conditions. On rough water these sibs bounce around a fair bit and beat you up. You likely can't rip a 7.5 hp outboard wide open in rough conditions, let alone a 15 hp. I think I've found a sweet spot with my 3.3M sib with an 8.0 to 10 hp-range 2 stroke, with a 9" diameter, 9" pitch prop. I've come to realize faster isn't always better with these sibs. For me sibs are about storage convenience. Access to remote lakes. Portability. Having a light weight engine is a huge part of the convenience. The light weight two-stroke In the 8-10 hp range suits me very well.
The proper inflation psi has a huge effect on the boat's handling at higher speed. The faster you go the trickier it can get. Payload weight distribution, outboard engine weight and HP rating offer more variable factors to the boat's stability at speed.
I'm fortunate to have multiple small outboards, props and a couple of boats to experiment with. I've gained a fair bit of experience quickly this spring. So far I've settled on my 1990 8.0 Merc 2-stroke a my top choice for my soft floor 3.3M SIB. Still more experimenting will be done. I was out last week with my 7.5 Merc 2 stroke. It performed pretty good also. It had a 7" pitch prop. I want to try it again soon with a 9" pitch prop.