General Performance Problems

[Slapshot]

I bought a new Tracker Targa 175 with a 115hp Mercury Optimax installed by Tracker as a package. I feel that it is not performing up to what it is capable and need some advice and or suggestions.

Performance specs:
WOT rpm - 5000 (Merc reccomends 5000 to 5750)
Prop pitch - 19 (diameter unknown)
GPS measured speed - 38-39 mph
Poor hole shot, I mean really bad
Cavitation plate on the leg about about even with the bottom of boat when trimmed all the way down, hard to measure.

When trimmed up just shy of cavitation, the boat handles very loose and you must maintain a firm hand on the wheel or it would spin all the way to lock to the left, very dangerous at full speed. If you trim it in just a little, you loose 2 mph, some rpm (cant remember exactly how much) and it handles very well.

When trimmed up just shy of cavitation, the prop will spin out on almost any degree of turn and once it has spun out, you have to bring the throttle almost all the way back to idle to get it to hook up again.

I have been through the prop calculator on the Merc website and it made three recommendations: a 3 blade aluminum 13.25"x17P, a 4 blade SS 13.75"x17P and a 3 blade SS 13"x18P.

Should trying another prop be the first step? Is there anything else that should be tried first?

Thanks
Stumped in Saskatchewan

 

[QC]

Re: General Performance Problems

Well first you need to know that what you are experiencing is ventilation, not cavitation, but that doesn't change anything.

Second, yes, even the Merc thing is saying you need to go down in pitch. That would get you better hole shot and higher in the Operating range.

Third, you need to read your Mercury manual and learn how to adjust the little vertical trim tab below the Anti-Ventilation plate . . . That will help with the steering issue.

Fourth, we love that loose feeling

Fifth, trim in for turning, trim out for going. That'll solve that problem.

Sixth, you might be able to set that motor up a little higher as she does sound slow. How many people? How much stuff? How much beer? Full live wells? Concrete anchors? Typical load? Don't buy any props until we nail a couple of things down, but she does seem over propped now.

Seventh, have you talked to the dealer?

 

[Slapshot]

Re: General Performance Problems

Thanks for the clarification, ventilation it is

My dad had it out last fall and was playing with the tab, must have it out of wack, i will take a wrench with me next time I go out. What confuses me is the difference with the last bit of trim. It goes from steady and neutral to real loose an pulling hard left.

Those numbers were with two guys set up for a day of tournament fishing, no beer, empty wells, lunches and gear, full fuel tank.

Dealer sucks, if I pay for a prop up front, he will order it for me. No returns. Thats why I want to nail down exactly what I need before committing.

 

[walleyehed]

Re: General Performance Problems

I've messed with alot of Trackers and the biggest problem I see with most is the boats are powered with 60-70% of max rated power and 9 out of 10 dealers don't have enough experience to know what prop should be on these under-powered rigs to make them work at all.
The dealer should have his rear kicked for not knowing your RPM with a normal load would be 700RPM off.
A 17P on your rig will be about the most pitch you will be able to use and some engine height changes-mounting bolts-needs to be changed to really make it efficient.
The Merc prop selector is backwards in the recommendation on 3-bld props.....If it recommends a 17P in aluminum, it should show a 16 in SS.
An 18P in SS will be about the same as a 19P in aluminum.
I would pass on any 4-blds...with the HP you have, you'll end-up loosing too much on top-end.

 

[rndn]

Re: General Performance Problems

My brothers 17.5 foot starcraft was getting some similar performance issues and was a real dog out of the hole. He dropped pitch 4 inches to get the motor rpm's up and went with an SS 4 blade prop to help it out of the hole. The 4 blade made a huge difference for holeshot so he could remove the hydrfoil, top end stayed the same, and he could plane at a much lower speed.

 

[walleyehed]

Re: General Performance Problems

It would be a shot in the dark to stab at a 4-bld...I've tested this.
The problem is "most" 4-blds are stern-lifters by the nature of design...they tend to want to "climb" up. It's takes a fairly high-tech design to get both good hole-shot and the needed over-all to bow-lift required out of a 4-bld. We fight this on many specialized application attempts, and if the customer is not willing to lift the engines mounting position to utilize the technology of the 4-bld, they end-up just as you said...dropping a tremendous amount of pitch to get the RPM right but the speed is never there.
This is the reason both Dhadley and myself try to optimize a set-up to the max before EVER dropping pitch...we're giving in to lower efficiency by doing this and it's a band-aid fix at best.
The 4-bld, in this case, would be a band-aid fix as well....a quality 3-bld at the right mounting height will give the best over-all performance.

 

[Slapshot]

Re: General Performance Problems

I found an independent boat performance shop that has a wall full of loaner props that is going to help me out. Also, I tried lowering the engine on the weekend and it appears the anti ventilation plate on the leg is below the hull, hard to tell as the skeg hit the floor before it was all the way down. It is supposed to be even or slightly above right? I will try backing it into a ditch and get it all the way down to see.

 

[QC]

Re: General Performance Problems

Just lower the tongue of your trailer to the ground . . .

 

[Slapshot]

Re: General Performance Problems - TEST DAY

Re: General Performance Problems - TEST DAY

OK - made it out on the water yesterday, here are the results of my testing
Top speeds were determined from a two way run, with and against the wind. It was windy.

1. Stock Aluminum 19P
Top speed with wind - 40.3 at 5200 rpm
Top speed against wind - 38.2 at 5000 rpm
Hole shop still crappy
Chine walks like crazy when trimmed up
Spins out on any turn when trimmed right up
At speed, the anti-vent plate was well down in the water
Trolling speed 3.2 MPH at 600rpm

2. 16P three blade quick silver Stainless
Top speed with the wind - 39.8 at 5950 - over speed alarm was beeping at me
Top speed against wind - 38 at 5800 rpm - still beeping
The anti-vent plate was well down in the water
Hole shot pretty decent, not what I expected though

3. 17P four blade Stainless unknown brand - honestly not a mark or number on it
Top speed with wind - 39.8 at 5500 rpm
Top speed against wind - 38.2 at 5400 rpm
Hole shop was weird, for about a second the engine kind of lugged as the bow came up, then it jumped and took off real well
No chine walk
When trimmed up, I was able to take any corner and not spin out, it actually powered out first
I was able to trim this prop up quite a bit more than the other two
At speed, the anti-vent plate was just visible at the rear edge, the front was still under the water.
Trolling speed 2.3 MPH at 600rpm

Conclusion:
I want to raise the engine at least one, maybe two holes and try the stock prop again. The two loaner props have to go back before I will get a chance to try them at the raised height. I have a feeling that she will run much better raised up.

How many RPM's should I gain by raising the engine per hole?

 

[walleyehed]

Re: General Performance Problems

In general, I've found it to be around 75rpm per hole..I "have" seen situations where 2 holes up gained about 250, it depends where you are in the power-band and what props you're using, but I would say you will see anywhere from 50-125rpm per hole, but count on 50-75.