View Full Version : Two Speedometers?
06-26-2006, 05:23 PM
This may seem like a stupid question and don't ask why I'm just now asking this since I've had my Mobius for 4 years now but...does anyone know why there are two speedometers on the dash? I'm thinking of pulling one out and putting in the Pefect Pass system in it's place. However, I don't want to screw anything up should they be linked together somehow. Thanks,
06-26-2006, 05:27 PM
It is a requirement for tournament ski boats.
I don't think they are linked in anyway and I highly recommend a perfect pass.
I don't know ANYONE how has PP that does not swear by it!
06-26-2006, 05:59 PM
Its always been two for tournament ski boats... perhaps there was a fear of one breaking... definately get PP and remove one of the Speedo's.. I got mine from skidim.com and he ordered me the white moomba logo display so it looks factory. The tuning knob on the speedo will have to be cut so you can screw your knob back on. This way you wont have a hole in your dash.
06-26-2006, 06:04 PM
Thanks for the info guys. Speaking of that tuning knob, I always seem to spin it around wiping the boat down, etc. hence messing up my speed setting. I can usually get it close by pulling someone that I know likes the same speed everytime and watching their reaction but it would be nice to be more accurate. Is there a device out there than can accurately tell you your current speed? GPS?
06-26-2006, 06:09 PM
I keep my handheld GPS in the glovebox so that I can calibrate it each time out. I usually set the left one to wakeboarding speeds and the right on to slalom speeds as they are not entirely accurate.
I will be adding Perfect Pass to replace the right one next year.
06-26-2006, 06:09 PM
i time my PP with magnets in the slalom course and from there calibrate the digital speed display on PP. I do believe GPS can tell you the speed, but I have never tried it... there are plenty of others on here that probably know how to do that.
06-26-2006, 06:35 PM
I use a GPS to callibrate my speedos. One thing that you may want to keep in mind... I use my boat on a river with a slow current. when I go against the current the speed is exact when I go with the current the speedo will read anywhere from 1.5 to 2mph off what the actual speed is. I believe it is because the speedos are callibrated by the RPM of the engine.
06-26-2006, 10:27 PM
I also take my GPS every time i go out just in case i bump the calibration knobs. I may be corrected, but I believe that one is a paddle wheel speedo and the other is a pitot tube speedo. I just had Perfect Pass installed and they removed the right one which i believe is the paddle wheel and replaced it with the digital speedo.
06-26-2006, 11:07 PM
I do not remember seeing any pitot tubes on the boat. I am pretty sure that both speedos run off of the paddle wheel and the dual speedos are for failure purposes. If one speedo fails, the other one is used instead. Perfect pass and the remaining speedo both run off of the paddle wheel.
06-26-2006, 11:22 PM
Your speed is off because of the water current and not because the speedo was calibrated to rpm. The GPS is measuring your land speed only while the speedo is measure in the speed at which the water passes under the hull of your boat. If you set your speedo by your GPS going upstream, the speedo will always read the same as the GPS in that direction. Once you head downstream though, the GPS will show you as moving faster at the same indicated speed on the speedo. To help keep relative speed across the moving surface of the water the same in both directions to help out boarders or skiers you need to know the water current speed. Make a run upstream at a set speed on your GPS and see what your speedo says. Make a downstream run at the same speed on the GPS and see what the speedo says. Take the difference in speedo readings and you'll have your water current speed. Add that number to your GPS speed running upstream and subtract it going downstream and you'll have you actual water speed. In your case though, it sounds like the currect speed is slow enough that you wouldn't really notice a difference.
I think the whole dual speedo is still kind of a carry over from tournament requirements when boats all use the pitot tube speed pickups. Each speedo had its own pickup so they could be used independently to verify each other. Since paddlewheels have been in use, both speedos are wired to the same paddlewheel so there isn't really a way to use one to verify the other. I think they keep them both in there now for a few different reasons. One reason is simply because it's always been sort of a trademark and something that is different about tournament boats. Secondly because there is still a chance that a speedo could fail during a tournament and you'd need the second one as backup. Lastly, because perfect pass is becoming almost standard they just put it there if you don't get perfect pass so they don't have to change the dash or the build process around it thus making everything easier and more uniform.
06-27-2006, 12:30 AM
Long, long, time ago, in a lake far, far away ....
If memory serves me correctly, the two speedo thing first(?) appeared with one on the Dash Board for the driver, and on on the motor clamshell for the spotter (who is also a judge). This would allow the spotter to help keep an eye on the speed as kind of a checks/and/balances system to prevent the driver from favoring a particular skier.
Our 99 Mobius uses dual pitot tubes (on opposite sides of prop) so the speedos are independent. This has come in handy, especially on lakes that are weedy when the pickp may become temporarily obstructed.
We use a GPS to verify (because we do not have a slalom course to time (and who knows how accurate most recreational courses are anyhow?).
Then there is the old standay that 30 MPH is 3000 RPM. I have found that to agree with the GPS with some accuracy. However, weight in the boat may effect that, as my a different propeller (not stock).
06-28-2006, 12:54 AM
The GPS is a great tool for setting speedos, but for those of us w/o them, higher horsey motors, and a plethra of prop. options, I use 3800 rpm = 36 mph. This will get you pretty darn close. Brian Raymond
06-28-2006, 05:49 AM
Brian - you're back! I thought maybe marketing had either stolen you, corrupted you, or shot you.
Ya gotta admit it is a little funny - ya build a boat with two speedometers – and the tech guy tells you to use the RPM dial.
06-28-2006, 02:59 PM
Just to add my $0.02, my 2001 Ouback has two paddlewheels driving the two speedos. And to my understanding, in order to be AWSA approved to pull in a tourney, the boat must have two speedos. Although with PP now being so prevalent, the requirements might have changed. If one was curious enough, they could dig around the AWSA's website (www.usawaterski.org) and find out the most recent requirements. I know that they have a list of boats that are approved to pull ski & wake tourney's. I am glad I have two b/c one of my paddlewheels is dragging some and the right speedo is not accurate and sometimes does not work at all. I guess I need to take apart the housing and clean it.
07-09-2006, 10:13 PM
Dual speedometers can be used for different events. You can set one speedo. to slalom course speed of 34 mph and the other for either wakeboarding or barefoot speed. I've found using the GPS that setting the speedos at one speed may be different at another event speed.
04-11-2008, 01:19 PM
one measures the speed by what the engine says its running at and the other says what the speed of the water or air is going past the boat at.i think.
04-11-2008, 02:16 PM
Heck just stick yer toe in the water....if it makes a wake, you're moving...if it doesn't, you're sitting still!
Just trying to help
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