Perfect Pass random issue

[Waternut]

So our club boat is a 2000 ski nautique and we have the older Perfect Pass running in rpm mode. It's not the GPS version but we are using the multi line display.

 

Anyway, on to the problem. We've been running the same setup and configuration for 4-5 years but yesterday the boat was running fast. We ended up just doing a quick adjustment and taking 65 rpms off the speed (aka -65rpms). First thing I checked was crew weight but that was accurate. Skier weight was accurate. Tried turning the cruise and engine off/on a few times. We skied the rest of the day with the -65 rpms and everything was fine so it's not like it was a fluke timing error but very curious how it just seemed to mess up all of a sudden. This adjustment was based on course times and not speedometer readout.

 

My only other thoughts are prop related but typically you only ever lose speed with the prop if a blade hits something or you get weeds on the prop/rudder. Before we go and re-baseline the cruise, anyone have an idea of how the cruise got off in the first place?

[keithh2oskier]

Bimini down when it was calibrated with it up?

 

Maybe you didn't eat your Wheaties and weren't pulling hard.

[Waternut]

Bimini was up both times. It was two of us skiing with the same result.

[Deanoski]

Wind weight all kinds of different factors with pp Classic It just set RPM not speed

[Zman]

@Waternut. How far off were your fast course times? What were the times? Same for both directions?

[JayG80]

Someone in the club read the thread on Premium fuel ;-)

[BraceMaker]

What I would suspect first is that you have an engine malignment that has finally worn the strut bearings enough to not be adding friction which acts like a couple of extra ponies.

 

Or perhaps you got different fuel than normal either maybe you typically run premium and the boat doesnt need the octane or you typically run regular and it got a wiff of high test?

 

Potentially poor continuity on the tach wire may be giving a bad signal and engine may be running higher rpm than it thinks.

[Waternut]

Haha on the premium fuel comment. I don't know what the owner puts in honestly but he's the only one who buys gas for the boat.

 

As for times when I was driving, I got +0.02-0.04 sec slow with a gentle headwind at -65 rpms on 32mph and 34mph. On the tailwind I went to -70 rpms and was getting +/- 0.01 sec pretty consistently. I ignore any pass where the skier doesn't make all 6 turns because that always ends up running a hair fast.

[UWSkier]

Anything else acting up? Are you sure the PP has good clean power and ground connections? Or, any chance a meddling kid got into the boat and started farting around with it while the adults weren't paying attention (something I'd have done as a kid) and screwed up baselines?

[BraceMaker]

@Waternut I mean the @AdamCord post brings it up - but its a 2 way street.

 

If you put 93 octane in a lower compression boat that doesn't need it you do lose power, if you want to run it and take advantage you can take your older boat, install a hot coil, gap the plugs wider, run the boat with more advance and get the power out of that 93 octane. But in this scenario it will be more powerful running 87 if you are running a factory style ignition system because it runs "safe" (rich, low gap spark with a retarded timing adjustment)

 

What people miss is that octane is really a stability index. If you've ever lit a match to diesel versus gasoline you know the difference 93 vs 87 is not on the same magnitude but it is very much factor.

 

You take a TBI boat that was designed to run properly on pump regular gas (non-ethanol preferable) and you toss 93 in it and it cannot get hotter spark or more advanced to fire that fuel off. It doesn't mechanically have that ability in the system.

 

New boats are the opposite if they are designed to be able to fire 93 off to good effect the computer sees one instance of preignition and shuts it down till there are no instances of preignition.

[Waternut]

I'll ask the owner if he changed fuels. I know the 2000 SN is supposed to run on 89 octane but I don't know if he runs that or not... At the same time, someone at the gas station could've put the wrong fuel in the wrong tank as well so we'll have to see if things change next week.

 

I've built my fair share of performance engines and I agree that high compression engines do benefit from higher octanes assuming they need it to prevent knocking. I don't know that I've ever seen a reduction in power by having too much octane though. I've always considered that more rumor than fact.

 

That said, I was super skeptical of a big enough change to notice but after a little math, I'm beginning to question myself. In a car, on the street, I stand behind my original notion that you won't notice a 2-3% power difference that you'd get by maximizing the octane rating to prevent knock. However, in a ski boat with a specific time, a 2-3% increase/reduction in power and A LOT of drag that boats have, 2-3% might actually be the 1/2 - 3/4 of a second or so that we're seeing.

[BraceMaker]

@Waternut ya remember the symptom you are troubleshootong was a slightly hot time when an older calibration was working fine.

so all that has happened is that your engine is reacting faster to PP down the lake, more pep in its step than it had.

[DW]

Throttle return spring condition? Not pulling throttle back like previous. Any work done on boat before the run?

[Zman]

Along the lines of what @DW suggested, check all your connections where the main throttle cable and the PP cable come together on the throttle plate. Be sure this is adjusted per the PP installation manual. Check mounting for the servo as well.

No one removed something heavy from the boat?

Might want to complete a new calibration at the various speeds you use, and see how well it holds up.

[Waternut]

Well I went back to the course today and asked a few questions and confirmed our previous results. The boat still has solid times at -65rpms on 28-32mph. I think 34mph would've been a bit better at -55rpms but could just be the skier bullying the boat.

 

The owner said he's been running 87 octane for many years. Said he tried 89 and 93 early on and never noticed any difference in boat characteristics or times and has run the cheap 87 ever since. Keep in mind this is a guy who will often ask about times if the boat is +/- 0.25 seconds.

 

I won't be able to ski again at that lake for another 2 weeks but I think if it's still off at that point, I'll probably just manually reprogram all the speeds if someone else doesn't do it first.

[Doug]

How were the people skiing yesterday? We have had in the pass lakes that have had a algae bloom that plays havoc with PP boats its like oil on the surface . We have had to take as much as 100 + rpm out of the baselines but your skiers would fill it. Its like ice skating

[Waternut]

Interesting point @Doug. We don't really have algae so much but coontail is our big problem and it will bog the boat down heavily if it gets on the prop or rudder. I'd say if anything we've been skiing better the last two weeks but I'm not sure it's water related as much as we're finally getting back into the swing of it after slowly progressing through the summer.