Possibly none! It might be possible to have a better guess if you knew the RPM the engine was doing, the size of prop and how much of the throttle range seems to just make more noise and not go any faster.Hi folks.
I can achieve 9.25 km per hour with a 2 HP on my 2.5 meter inflatable sib. , flat bottom air floor. Any idea what kind of increase in speed I'd get with a 3.3-3.5 HP. On same sib. ?
Yes. Does "air floor" = high pressure drop stitch (with a proper valve) or like a cheap airbed/lilo? The latter will be harder to plane. Either will be very sensitive to trim/loading and engine position. Its sort of fun to plane a tiny sib - but many areas you want to use such a boat are not suitable for planing and on anything but flat water it soon becomes exhausting. You might manage to plane with 3.5HP if you get everything else right - but 5HP is more likely.Is it possible to plane on a flat bottom sib.
It has a high pressure drop stitch floor, only my self on board 80 percent time.Possibly none! It might be possible to have a better guess if you knew the RPM the engine was doing, the size of prop and how much of the throttle range seems to just make more noise and not go any faster.
Yes. Does "air floor" = high pressure drop stitch (with a proper valve) or like a cheap airbed/lilo? The latter will be harder to plane. Either will be very sensitive to trim/loading and engine position. Its sort of fun to plane a tiny sib - but many areas you want to use such a boat are not suitable for planing and on anything but flat water it soon becomes exhausting. You might manage to plane with 3.5HP if you get everything else right - but 5HP is more likely.
Yes 9.5 kmph isnt bad . I'm looking to achieve 12-13 kph alone and also to hold the 9.5 kph with a passenger on board.9.5kph is already over hull speed but not planing. You may go a bit faster with a 3.5 if you get the trim right and you are light, however you may find it difficult to stay on the plane in any sort of waves or wind. Flat bottom even with air floor are not designed to plane and are limited to 5hp but the hp is there to move weight when used for their normal role as load carrier.
Ok. This is also important , currently I loose a lot of speed with a passenger on board with the 2 HP.You will be able to plane/surf a bit easier down waves.
You will go slightly faster at the expense of getting much wetter, going into waves, chop or strong winds.
The bigger motor should be less affected by extra passenger weight.
All dependent on the prop, if the 2HP is making peak power revs, but the 3.3 is bogged down by too big a prop,
Personally, I wouldn't pay extra for a 3.3 unless I regularly carried lots of weight in fairly exposed waters with a longish trip.
No you won't achieve either of those reliably without going to 5hp.Yes 9.5 kmph isnt bad . I'm looking to achieve 12-13 kph alone and also to hold the 9.5 kph with a passenger on board.
My Yama 2HP struggles to rev on a highly loaded boat, so it probably only works at 1HP.Ok. This is also important , currently I loose a lot of speed with a passenger on board with the 2 HP.
Thank you for your reply.No you won't achieve either of those reliably without going to 5hp.