On Jun 5, 8:17*pm, Oscar wrote:
On 6/5/2012 6:26 PM, Tim wrote:









On Jun 5, 5:10 pm, *wrote:
On 6/5/2012 4:38 PM, Wayne.B wrote:

On Tue, 05 Jun 2012 10:28:52 -0400, * *wrote:

The facts:
9'X5' inflatable with inflatable keel and hard floor.
5hp 4 stroke engine.
7 1/2 X 7 3 blade prop.

Here's what's happening:
Engine runs smooth as silk.
At about 1/2 throttle GPS measures 4 1/2 MPH
At full throttle GPS measures a little over 5MPH
There is no noticeable change in pitch or DB between 1/2 and full throttle.
Engine doesn't seem to be bogging down.
Speed increase between 1/2 and full throttle is gradual even though
throttle is advanced quickly.
Boat bottom is clean.
Prop is in excellent shape.

Questions:
Is this normal?
Should I try a lower pitched prop?
Do I need more Horsepower?
What do you think?

===

As others have mentioned, you are running up against the hull speed of
the dinghy and don't have enough power to get on plane. * My
experience with inflatables is that you need at least 8 or 9 hp to get
on plane with 2 adults, and 15 hp is even better. *A Doel-Fin on the
outboard is also a big help.

I assume you have a rigid transom? *If so it should have a
manufacturers plate somewhere which states your max horsepower rating..
That's usually about the right number for everyday use.

http://www.basspro.com/Doel-fin-Hydrofoil-Stabilizer/product/27337/88...

I doubt they make doel fins small enough.
I suspected HP was the problem and you guys confirmed it.
I suppose the best thing to do is use just enough throttle to drive it
to hull speed and be satisfied.
thanks for your input.

But i you could get at least a 10-12 and put on it, I'd say you'd
bemore pleased with it's obvious performance, but also better fuel
economy per a set distance.

Reality is Tim, that the boat is performing within its design parameters
and I'm good with that.

Ok. I was thinking you were wanting more performance out of it-
something to push the hull out of the water.