Honda 15
Mike The usual rule-of-thumb for auxilliary power is 4 HP per ton of displacement, plus about 20-30% for transmission, shaft & prop losses. The C250 displaces 3600 lb (assuming the heavier model), so about 10 HP should be all you need to move the boat to hull speed. The extra HP may be handy if you're motoring into a stiff wind and/or current. But it comes at the price of additional fuel consumption. The 9.9 HP & 15 HP Hondas weigh about the same (roughly 100LB +), so there shouldn't be any great differences in the trim along the pitch axis. Given their weight similarities, I suspect that Honda might be using the same basic block & just "souping it up" (e.g., wider bore, longer stroke, carburation, etc.) to get the 15 HP rating. That said, the 9.9 HP model might be more reliable in the long-term. Fitting a larger outboard (10 - 15 HP) is probably do-able, given the motor mount on the transom is sufficient for the weight & size. Make sure you get the shaft length sized properly to be able to be immersed completely when going through swells/waves/wakes. Honda makes 15" to 25" shaft lengths for the 9.9 HP model, but I didn't see the 25" listed for the 15 HP. I've included the Defender Industries web link to their inflatables & outboard engines specs & pricing pages (click on "Boats and Motors"). I bought my Nissan 8 HP dinghy engine there & their prices/service was very good. --Ron
