Better Boat Speedometer

I'm getting tired of the my pick-up tube style speedometer. I've been looking into paddle wheel type speed logs. Hows the reliability and accuracy?
My boat is a 19' Tahoe Q5 IO(runabout). It stays in the lake for 6 months out of the year. I'm worried about a paddle wheel getting gunked up.

They have gps based speedos now as well with increments to the 1/2 mph, suposed to be extremely accurate[& pricy].No personal experience.Anyone use these?

Buy a little handheld GPS unit and mount it on your dash. They are extremely accurate! Plus you can take it out when you aren't using the boat and use it other places!

Switching to a paddle wheel type speedo can get $$$ because you have to install a computer box to control it and you other gauges as well.

Install Perfect Pass and solve two problems at once.

Once you have an accurate speedo, you'll notice how much your speed drifts.

just my $.03

I have found a company called Navman. They have a unit with a transom mount paddle wheel transducer p/n s2100. several sites have this for under $100. They also offer thru-hull mount transducer - around $110. I think it can be removed for cleaning and the hole plugged. I have also considered a fish finder 4150 from Navman - It gives speed, water temp, distance, & depth (my depth finder is also crappin out). Fish finder is a little overkill but the price is right - $160 for complete kit, no computer needed, transom mount transducer with sensors for speed, temp, & depth all in one

About GPS speed:

As long as "Selective Availability" is turned off AND you happen to get a favorable orientation of satelites, AND the unit has been on long enough or recent enough to capture and update its knowledge of the currently available satelites, GPS can give you a great indication of your absolute speed, relative to a fixed point on land.

Unfortunately, that may have any relation to what you want to know.

If you are running on a lake that has little or no current, it is probably close enough. If there is a current, then it is all wrong. The wakeboard rider won't give a damn how fast the river is flowing, he wants the speed relative to the water he is riding on.

Imagin you are on a river flowing 5 MPH. If your engine is off and you are just floating along with the river, what speed would you think you are going? The GPS will tell you 5 MPH. If you start up and idle up river, the GPS may say you are going 0 MPH, but the wake behind you will tell you otherwise.

Selective Availability is another issue. I believe it is off now, and has been for 5 years or so. Prior to that, it was turned on, and the military can choose to turn it back on at any time. With Selective Availabilty on, you can get a reading of several MPH while tied to the dock!

As for the paddle wheel speedometers, except for Perfect Pass I wouldn't recommend any for pulling wakeboarders. The ones available on fishfinders/depth sounders generally update the display so slowly that it would be hard to hold an accurate speed. There are some great units intended for sailboats, but they are intended for operation around 8 MPH and may not even work at 20 MPH, plus they are very expensive.

The paddle wheel sensors that I have had were all thru hull and were capable of being removed with the boat still in the water, which would allow you to clean it out if necessary plus you could install a "dummy" in its place and not keep the paddle wheel in the water all the time. I have a big cruiser with one of these and have only had to pull it twice in 8 years to clean it out.

I have had tournament ski boats for over 20 years, and the standard proceedure has always been TWO speedometers. It used to be two complete units, but now it is one display with two pickups, and the display unit chooses which pickup it uses (or you can manually select it). With two units you have a much better chance of one of them working.

The new "combo - pitot/digital" are both good and bad. The good part is that you still have the needle display like you are used to seeing, instant response, and you can run wires from the dash to the transom instead of a tube. The bad part is that when the pitot tube acts up the display can go nuts.

Now with my wakeboard boat I have both: Perfect Pass and the pitot speedometers. This is sort of like the old joke: A man with one watch knows what time it is, a man with two is never really sure. The two speedometer systems do not agree on what the speed is, but they are both repeatable and that is what counts. If you ride behind your boat at 22-1/2 MPH you may need to adjust a little when you go to someone elses boat. That's just the way it is.

My boat has twin speeds that never agree, but I bought a eTrac Mariner (or something like that) off eBay for $80 and I have it mounted to my dash. It has become all we use now, plus it has some really cool other things for navigating.

Hey Monster, is that eTrac a GPS unit? How often does the speed update? Maybe you could throw one in with the tower I ordered ;-) (#4247268)<-Where is that tower?

For accuracy you may get of gps but will not reister a drop in speed on a hard cut quick enough with a boarder on. paddle wheel system is by far the best, no blockages ect.

Ricky,
I would guess it updates every 2-3 seconds, not that sure but it done a much better job than the two speedo's that are now just a reference. I'm trying to get hooked up with a Perfect Pass and when that happens the GPS is yours :-) If your tower did'nt ship Friday then it will go out Monday, the season slowed down a little later than we planned for. Give us a call on Monday if you dont have the tracking number yet.

Bill

My 2002 Supreme V Pro Sky came with a Mercury Marine "Smartcraft 5000" system installed. It has a digital LCD panel between the tach and speedo (I never look at either)on the dash. It has the ability to display all engine information including balast tank volumes and can be set to switch from paddlewheel to GPS speed at a specific speed. I find that I use the display with RPM and MPH in bold 1 inch display when I am towing someone. The display also includes a small digital depth reading which is real handy as well. A combination of RPM, speed and a view of the wake in the mirror allows me to adjust things to get the perfect wake. I do notice that GPS is only updated every few second so while accelerating it gives some big jumps in speed but until the wake is 'set' I rely more on RPM than speed to get the rider up in comfort without overcooking the speed.

While the Smartcraft 5000 is a real neat system I have no idea what it would cost on the open market or whether it would be an effective aftermarket add on. I have never seen a price advertised and there is no pricing information in the Mercury Marine home page. Does anyone know what this system sells for?

Rod "selective availability turned off"??
"President Turns Off GPS Selective Availability' 05/02/00 http://geography.about.com/library/weekly/aa050400a.htm
seems its been off for a while now, mine updates very fast garmin gpsmap76 but i do agree it is not for any moving body of water as this will render the reading inaccurate. Use it to calibrate your PP or speedo by making runs in both directions -down river and up river

Bob:

Yep, that's right, it has been turned off for the last three years or so. Prior to that it was mostly on. The first time some terrorist or enemy uses GPS to their advantage you can bet it will be turned back on.

As a calibration tool, it would work great. Pick a time when it tells you that you are going 0.0 when you know you are standing still, and then for the lenght of your run it should be fairly accurate.

As someone else pointed out, the slow update that is typical of a handheld GPS unit would make it difficult to hold a constant speed, especially if the boat was not stable at the speed you wanted to go.