On 6/5/2012 11:13 PM, Tim wrote:
On Jun 5, 8:17 pm, 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.

Yes and no. I would like it to go faster but I'm not willing to throw
more horses(and weight) at the problem. This thing gets packed away
after almost each use so it needs to be relatively easy for me to set up
nearly singlehanded. I'm not the musclebound hulk I used to be ;-)