Prop question - weak top end and slow hole shot

[HybridMX6]

I've had this motor for about 5-6 years now, it's a 2001 Johnson 55hp 2cyl commercial outboard, with an odd 23" shaft. Outboard is/was manual everything. I've since converted it to power everything, including a CMC PT130, and when that was mounted I used it to raise the outboard the 3" I needed, since my transom is a 20" transom. I've had a stainless prop on it since I got it. It's made my Michigan Wheel, Rapture model, and is 13 1/4x17p. I have no guages to go with this outboard,so I can't give my top RPM since I don't know. The boat is a 16' Tracker Grizzly aluminum boat, so not much weight to it really. Top speed as recorded by GPS with a normal load (which is 6g of fuel, myself, and my gear), is 33mph. It seems to take forever to get up on plane if I have just 2 people in the boat, so an additional 130lbs (it was woman). Before I purchased this outboard, I had a 1978 35hp Johnson on it with one of their factory SS props and it would do right at 30mph, so would think a 55hp newer style would gain more than 3mph, and the hole shot is worse.
Any help would be appreciated, including if you want any more info,I will see what I can do.
Thanks You

 

[steelespike]

Re: Prop question - weak top end and slow hole shot

Without your rpm its nearly impossible to tell much.
Using the calculator backwards 33 mph with a 2.42 gear ratio (a guess)
10% slip(guess) 17" prop indicates 5512 rpm.
Is the motor able to tuck in good with down trim?
Does the boat respond to up trim?
An induction tach is about $50 and will work on any motor.
is the bottom clean and smooth?
No dents near the transom or elsewhere?
Is the motor in excellent tune?

 

[HybridMX6]

Re: Prop question - weak top end and slow hole shot

Yeah, I may have to buy a tach. But I'll answer what I can.
Yeah, I can trim it all the way down and take off, when I'm by myself, it's ok at best, with more weight in it, it's gets slow.
If I trim the motor up while moving, the boat starts to porpoise if I'm WOT. If I back off a tad, it goes away. Don't know if that helps or not.
Bottom is as it was new. Not exactly fiberglass smooth, since it's all welded you can see a few slight variations around the welded areas, but no dents or anything.
Engine is in good tune. I cleaned carbs, changed plugs, etc. almost a year ago, and use it pretty frequently. At that time, it was missing on 1 cylinder when idling. Tune up fixed that.

 

[jestor68]

Re: Prop question - weak top end and slow hole shot

A weak hole shot and top end indicates the need to drop pitch to the next lower size; in this case a 15" pitch.

For the best bang for the buck, I recommend Solas. The aluminum Solas props have proven to outperform some stainless props. The Solas Rubex would be the best price, as it includes all the hardware needed for installation.

 

[steelespike]

Re: Prop question - weak top end and slow hole shot

The only thing we know for sure is the speed and prop size.
very likely a 15 will improve hole shot and rpm But you really need the tach to determine what your actual rpm is.
It appears you may all ready be at max rpm.You also need a tach to confirm the new prop results.

 

[jestor68]

Re: Prop question - weak top end and slow hole shot

The only thing we know for sure is the speed and prop size.
very likely a 15 will improve hole shot and rpm But you really need the tach to determine what your actual rpm is.
It appears you may all ready be at max rpm.You also need a tach to confirm the new prop results.

So it's just a question of which does he buy first; the prop or the tachometer.

 

[HybridMX6]

Re: Prop question - weak top end and slow hole shot

Well, easiest thing to try is to swap props. I forgot I had a spare one they gave me when I bought it, it looks like a refurb'ed Michigan Wheel aluminum prop. After a bit of staring trying to read the #'s under the paint, and some wire brushing to reveal them, it's a 13.5"x15p, so I put it on the boat and will give it a shot as soon as I can. I may buy a tach anyways though, so is there a specific brand that people say is better, or just whatever I can find?

 

[steelespike]

Re: Prop question - weak top end and slow hole shot

As far as the induction type the Tinytach is the most common and seems to work well when carefully applied.
There are others that we haven't heard anything bad to this point.
The tach is the key to best performance and the health of your motor.