Outboard size for smaller inflatable, speed?

[MarkSF]

I have an Achilles LS4, which is 8ft6. I weight 280 lbs. I'm wondering about what size outboard to get for it. The manual says 6hp is the maximum.

I'm thinking of either going for the maximum, and hoping it will plane, or for a 2.5 or so and forget about planing. There's a 2.5 Suzuki that catches my eye.

So will a 6hp make it plane? If not I might as well just go for the small light o/b. I've heard stories of this size dinghy still not planing with 5 or 6 hp.

Could some people tell me what speed they get with what size engine?

TIA

[dabnis]

I had a raft about the same size as yours with a soft floor and a 2HP
Honda outboard. With 2 of us it wouldn't plane but was more than
adequate going against the wind and chop. Nice thing is that the motor
is light to carry and easy to mount, about 27 lbs. With your weight and another person on board I think a 6HP motor might not get it to plane unless
you have a rigid bottom boat?

Dabnis

[MarkSF]

Originally Posted by dabnis

I had a raft about the same size as yours with a soft floor and a 2HP
Honda outboard. With 2 of us it wouldn't plane but was more than
adequate going against the wind and chop. Nice thing is that the motor
is light to carry and easy to mount, about 27 lbs. With your weight and another person on board I think a 6HP motor might not get it to plane unless
you have a rigid bottom boat?

Dabnis

So do you know what speed you got? I would like 10 knots. I want to use the boat to explore some of the south bay creeks and the extra speed would be useful.

[sailortjk1]

Could some people tell me what speed they get with what size engine?

10'6" Zodiac Air Floor
15HP 2-Stroke Mercury
20Knots with me and one dog by the hand held GPS

[Mark1948]

I have a similar Achilles with a 5hp. I have not had the pleasure of it plaining. I suspect the dynamics of the craft are not conducive to plaining plus you will generally be in a mooring area and should be under controlled speed. I find the 5 perfectly workable not excessively heavy then I am not hauling and storing it on board, another consideration.

[MarkSF]

Originally Posted by Mark1948

I have a similar Achilles with a 5hp. I have not had the pleasure of it plaining. I suspect the dynamics of the craft are not conducive to plaining plus you will generally be in a mooring area and should be under controlled speed. I find the 5 perfectly workable not excessively heavy then I am not hauling and storing it on board, another consideration.

Thanks - so any idea of your top speed?

[pdqaltair]

9-foot inflatable sportboat with 3.5hp and 170-pound crew will just plane at about 12-14 knots. Add ANY wieght, and we just throtle down and go slow.

I'm afraid 2.5 with 280 pounds might be a bit light in some wind conditions. I'd figure either 3.5 for going slow, or 10 to plane.

[Faster]

It's quite unlikely you'll plane with 6 HP - esp with any other extra gear or people. I wonder how much more speed 5 or 6 HP will really give you over a 2.5 given you're not going to plane anyway.

But I'd go for the 3.5 just to get the neutral gear... nice light weight still for handling up onto the mothership, and our Nissan 3.5 has proven extremely reliable on our 8 footer.

[JimsCAL]

I agree that a 9.9 would be needed to get up on a plane reliably with any load. A 2.5 or 3.5 would be adequate to push the boat at non-planing speeds - say 4-5 knots. I would go with the smaller engine. I have a smaller hard floor Achilles with a Yamaha 2HP 2-stroke. Engine is only 22 lbs and makes hauling it in and out of the inflatable a snap. I never tow the inflatable with the motor attached.

[dabnis]

Originally Posted by MarkSF

So do you know what speed you got? I would like 10 knots. I want to use the boat to explore some of the south bay creeks and the extra speed would be useful.

I would guess about 5 knots on a calm flat water day with 2 people and gear in the boat. Not sure what your carrying or mounting situation is but for a little guy like me the light weight is really appreciated. I have a whole lot of full throttle hours on the 2HP Honda over a lot of years and it still runs perfectly.

Dabnis