View Full Version : Speedometers different speeds

06-14-2008, 08:30 PM
The left speedo is off 2MPH from the right speedo, Any reason for this.?

My 15hr oil change went smooth, exept for a little rain.. Stormy weather today, tomorrow 85 and sunny. Kids went tubing today, skiing and boarding tomorrow.


james yarosz
06-14-2008, 10:11 PM
The small knobs below the speedos are there to adjust them.I set mine with a GPS.

06-15-2008, 07:04 AM
Thanks, I will give it a try.

06-15-2008, 11:01 AM
Unless you have Perfect pass. Then you have one speedo that adjusts with the knob and then the PP which requires your to use the menu to change the speed.

06-15-2008, 05:34 PM
I am a little surprise you are concerned about 2mph different in a system that probably has at least a 15% margin of error! I would be concerned if they were off by more than 7mph! The best bet is to set them with a GPS!

06-15-2008, 10:15 PM
Hey Z quit following me around. Especially after that Ms. Sled comment.

06-15-2008, 10:21 PM
Sorry Sled, notice when we have our boat I am not on the boards much as I am spending too much time on the water having fun. Well with no boat now I went to the boards and noticed you are over a hundred post ahead of me now!!!! I have to catch up sometime!!!

06-15-2008, 10:23 PM
Yeah I saw your # jump up a bit lately. I just moved my boat to my storage area for a couple of weeks until the lakes come back down. Maybe we can make a run for Ed's title?

06-15-2008, 11:28 PM
I set my speedos with GPS at WOT, then noticed at lower speeds I was off by 4 or 5 mph. So then I set #1 at WOT and #2 at 20mph using GPS
#1 is fine at 38+mph according to GPS
#2 is right all the time according to GPS

so I went back and set #1 at 20mph.

I know they are not perfect but that surprised me a little to have that much variance.

06-15-2008, 11:31 PM
Bamma, I know what your saying it can be very frusturating. You get them perfectly synched, and then at differnet speeds they react differently. Go figure!

06-15-2008, 11:37 PM
With a stock prop - a typical SKI boat is 3000 RPM = 30 MPH with two typical adults in the boat. I have verified this with handheld GPS.

And yes they go weird from time-to-time. I had a ski run where no matter how fast we were going, neither speedo read over 26. So My driver was pulling meat on a slalom ski at about 40 MPH before I let go. Things returned to normal immediately after....

06-15-2008, 11:42 PM
Well that used to be the case when everyone ran a 13 x 13 prop. Now the RPM's are higher than the speedos! We have a 11.5 x 13 on the LS and I noticed the difference from our old MasterCraft with the 13 x 13 which was like you stated. I am thinking of putting a 13 x 13 on it or trying a 12.5 x 13, which is what the local inboard dealer said he would let me try. This also explains the 42mph top end of a lot of these new boats. With the extra weight of the bigger boats and all the ballast that everyone uses plus the fact that wakeboard speeds are lower than slalom speeds the props are changing to a lower number of inches per revolution in order to get the optimum engine torque at the wakeboard speed.

06-16-2008, 09:53 AM
My right speedo was right on with my garmin gps. Then I notice I had two speedos(suprise suprise) Takes up useable real estate. Then i notices ist was slower than the other one and just posed the question for which one I use. (Equivalent to carrying two putters in the bag) Why???? LOL

Thanks I will get them in synch.

06-16-2008, 12:21 PM
The reason for two, I think, goes back to the early slalom boats. Year ago I was in a an old Nautique/MC? and they had one speedo on the dash and one on the engine cowling. for the spotter to watch. I am pretty sure the intent there was to help in judging speed through the slalom course. Kind of a 'keep the driver honest' sort of thing.. Apparently as they developed better timing methods through the course the need for that kind of oversight disappeared.

However, I still find it useful. My '99 Mobius still has pitot tubes for speed pickup (no paddle wheel nor PP nor GPS) and I find the dual speedos very useful for slalom. From time to time the speedos will pick up a weed or something and will quit. Most of the time it will clear itself eventually, but the second speedo becomes critical then.

06-16-2008, 03:10 PM
Unless you have Perfect pass. Then you have one speedo that adjusts with the knob and then the PP which requires your to use the menu to change the speed.


Are you saying that on PP equipped boats, one speedo is adjusted with the knob/dial under the dash, and the other speedo is adjusted using the PP?



06-16-2008, 07:43 PM
Cab, in boatw with PP the second Speedo is replaced with the PP. The dial is still under tha dash but it isn't connected to anything.

ANd yes the dual speedos is an old redundancy thing. Every tourney boat Iv'e been in for the past 20 some odd years has them. And yes it had to do with running the course and having consistent repeatable speeds. Theat is why PP was invented, then the magnets, and now the star gazer, it's all about consistent repeatable passes so that all competitors got the same pull. Also very important for any records that get broken.

06-20-2008, 11:50 PM

Maybe you shouldn't consider an LS!!! She only has 1 speedo!!!! Well that was the last time I saw her! Gosh when was that????? Please baby (Moomba LS of course) come on home we miss you!!!

06-21-2008, 04:42 AM
Just stick yer toe in the water......

06-21-2008, 01:16 PM
Yeah the pool looks really great and I will probably play with the big boat today. Haven't taken it out yet because of all of the wind and now thunderstorms we having down here. I guess I could put it in the lake and pull them behind it on the kneeboards. If I do I will get pictures! 25footer with twin outboards pulling skiers on the lake!!!! WAIT!!! How much will that cost me with the price of gas now a days?????

06-21-2008, 08:34 PM
Z, better do it or the kids will revolt!

06-22-2008, 01:07 PM
I thought the correct calibration was 3100 rpm equals 30 MPH.
( '99 Outback LS )

As far as two speedos goes, you also have a tach for a third backup. 36 mph tugging me around the lake is 3900 rpm. (Calibrated with speedos being set at 3100rpm=30 mph.

06-24-2008, 10:31 PM
Can anyone verify that the calibration is supposed to be 3100 rpm equals 30 MPH?


06-24-2008, 11:32 PM
That does not necessarly apply to new ski boats especially V drives. I know it is not quite the case with my Outback which is a AWSA approved ski boat.

06-25-2008, 12:40 PM
Mine is a '99 Outback LS AWSA approved.
I'll do some more research and post if I find out anything new.