GPS speedo and accurate tach?

[VMaxhp]

I've got a 2000 Crownie 225 BR. The tach is showing intermittent problems (recently since upper gear change). When the problem does come up, its always significantly over reporting the engine RPM. Today, I put a dwell/tech on the engine and a spark plug wire and at idle, the dwell/tach was showing 600 while the panel gauge was showing 1700-2000. Also, the speedo doesn't even kick in until I'm up to about 18mph or so.

Has anyone installed a GPS based speedo (or at least an accurate speedo) and any comments on the tach?

Thanks!

 

[JoLin]

Re: GPS speedo and accurate tach?

Take the tach out of the dash and look at the back. See that little screw that turns to point at one of several numbers? Note the number it's pointing to now, then turn it back and forth a few times, ending at the same number. I and a few other people have solved that problem this way. Corrosion can build up at the screw and cause false readings. Anyway, it's a simple thing to try and eliminate as the problem.

Any gps or gps-based speedo will give an accurate over-the-ground speed reading. Don't know what a gps speedo costs, but I'd rather put the money toward a real marine gps. If all you want is a speed reading, you can use the portable gps from your car for that.

 

[Philster]

Re: GPS speedo and accurate tach?

What is the speedo's setup? Interfaced with your GPS unit or is it a stand-alone unit w/ its own antennae? Some units are slow to react based on how they are interfaced with your GPS unit and how it outputs the signal to the GPS speedo.

GPS speed shows your actual progress across the planet. For navigation, it leaves a standard marine speedo in the dust when it comes to understanding progress, fuel economy, actual progress to waypoints, etc.

For understanding a boat's performance (engine, prop, etc), a marine speedo which reflects speed over water is best.

 

[Silvertip]

Re: GPS speedo and accurate tach?

What is the speedo's setup? Interfaced with your GPS unit or is it a stand-alone unit w/ its own antennae? Some units are slow to react based on how they are interfaced with your GPS unit and how it outputs the signal to the GPS speedo.

GPS speed shows your actual progress across the planet. For navigation, it leaves a standard marine speedo in the dust when it comes to understanding progress, fuel economy, actual progress to waypoints, etc.

For understanding a boat's performance (engine, prop, etc), a marine speedo which reflects speed over water is best.

Here we go again:

1) anchor your boat in a 5 MPH current. It will measure 5 MPH (if it is sensitive enough). Is that speed over water? Is it speed over ground? Is it speed over the planet? It is definitely not speed over water. It is none of those. You are not moving for heavens sake. therefore your speed is zero. The only benefit a marine (pitot) speedometer shows you in this example is that the river current is 5 mph.

2) Using a GPS speedo, do the same test. It will show zero also which is indeed your true speed over the planet, over the water, and over the ground. (In case I lost you -- that speed is zero)

3) Now travel upstream with a standard pitot marine speedo. If the speedo shows 35 mph you are actually doing only 30 mph against a 5 mph current. Going downstream if your speedo shows 30 mph you are actually going 35 mph with the 5 mph current.

4) Repeat that test with a gps and you will find current doesn't matter -- the gps shows your true speed over the ground and the planet and current is of no consequence. Upstream it will register 30 mph and downstream 35. Upstream you are working against the current so boat speed is slower than it would be going downstream since the current is carrying you. In either case, the GPS is a far more accurate measure of speed and distance since it works off a stationary reference point (satellites) rather than moving water.

 

[H20Rat]

Re: GPS speedo and accurate tach?

Here we go again:

1) anchor your boat in a 5 MPH current. It will measure 5 MPH (if it is sensitive enough). Is that speed over water? Is it speed over ground? Is it speed over the planet? It is definitely not speed over water. It is none of those.

In either case, the GPS is a far more accurate measure of speed and distance since it works off a stationary reference point (satellites) rather than moving water.

So for your first part, there is no question. It is your speed over water. Not sure why that is even a question! Lets say you hop out of your boat at this point. The speedo is telling you how fast you need to doggy paddle to get back to your now anchored boat!

A GPS isn't always better either. It depends entirely on your use case. Lets say I'm wakeboarding in that same river with a 5 mph current, and using a GPS based perfectpass. (In case anyone doesn't know, its cruise control for a boat to maintain a specific speed) I usually wakeboard at 20mph, so going downstream, i'm going to be going 15 mph, and when I turn around I'll be skipping across the water at 25 mph. A pitot or paddlewheel doesn't care about current and will maintain the same speed no matter what. (perfect pass and its clones are available in both GPS versions for lakes, and paddlewheel versions which work on either at expense of a little accuracy.)

 

[hungupthespikes]

Re: GPS speedo and accurate tach?

Sorry Silvertip I'll go with Philster for the boat's performance is better off with the speedometer.

If your trolling and the action of the surface bait is set up for 7 mph,. The bait action will be 2mph up stream on the GPS and 7mph on the dream-meter. Down stream the action will be at 12mph GPS and 7MPH on the dream-meter. The bait action is the constant, 7MPH, the boat is moving at 7mph over the surface of the water. So the accurate measure of speed is the pitot and the bait action is proof.
The GPS fails big time.

huts

 

[JimS123]

Re: GPS speedo and accurate tach?

If you care about performance or trolling, a marine spedo is necessary. If you just want to see red digitals a GPS is neat. The real answer for us Boatmen is to have both.

To answer the original question (re. an accurate speedo), yes I've installed several and they were spot on. Airguide and Teleflex make good pitot units. Install per directions and seal the hose and they'll work for years. Optionally, any of the paddle wheel sensors work well too, but they usually lack the accuracy at the higher speeds.

No wind, no current - GPS right on, pitot +- 1 mph, paddle +- 3 mph. The advantage of a paddle is that it will display the low range (0 up), while a pitot starts at about 7 mph.

 

[Philster]

Re: GPS speedo and accurate tach?

I will stand by my position regarding speedos.

Go 10 MPH (speed over water) against a 10 MPH current and you will see your GPS speed as zero. Unless your marina, home or fuel dock are floating, un-tethered to earth, you are getting no closer to your destination. So, GPS for the win because it is giving you your honest progress when it comes to navigating the planet, even if you have just 10 miles to go.

Boats navigate. Captains, even of little boats, need to know progress across the planet because their destinations are not floating with the current.

To set a boat up, the pitot-tube speedos and similar speed-over-water readouts are best; they are pretty accurate, too. These speedos are about measuring your propulsion setup, which propels you - ta da -- across water.

That's it. If you navigate, you want a GPS speedo. If you set a boat up or want to know how she is running, your easiest way to determine that is a non-GPS device measuring speed over water.

 

[NYBo]

Re: GPS speedo and accurate tach?

If you care about performance or trolling, a marine spedo is necessary. If you just want to see red digitals a GPS is neat. The real answer for us Boatmen is to have both.

Being someone who likes as much info as possible (within limits :redface, I agree completely. Especially if boating where the current changes speed and direction, like a tidal estuary.

 

[Silvertip]

Re: GPS speedo and accurate tach?

Sorry Silvertip I'll go with Philster for the boat's performance is better off with the speedometer.

If your trolling and the action of the surface bait is set up for 7 mph,. The bait action will be 2mph up stream on the GPS and 7mph on the dream-meter. Down stream the action will be at 12mph GPS and 7MPH on the dream-meter. The bait action is the constant, 7MPH, the boat is moving at 7mph over the surface of the water. So the accurate measure of speed is the pitot and the bait action is proof.
The GPS fails big time.

huts

Be careful how you state your examples. If the lure requires 2 MPH "over the water" as you suggest, and if you indeed travel at 7 MPH on an upstream current of 5 MPH then your speed over the earth would be 2 MPH as you stated. So where is accuracy difference? If you are going downstream and want the same lure speed so you adusted your boat speed to compensate for the current. Wouldn't I do the same thing on GPS. We know the current is 5 MPH, you want a lure speed of 2 MPH, so I go 7 MPH on GPS -- not 12 mph as you suggest). How can this be? The current is carrying the lure at 5 MPH correct? So if boat speed is 7 MPH the lure is moving downstream at your required 2 MPH. You see -- everyone ignores the fact that the water also is passing over the face of the earth. If it wasn't the oceans would dry up.

 

[VMaxhp]

Re: GPS speedo and accurate tach?

Thanks for all the input! I did get a chance to test the boat yesterday with an inductive (clamp on plug wire) digital dwell/tach and the Feria (sp) Tach is intermittently reading way high. As to the speedo, we're pretty much only lakes here so not much current. My current speedo only starts reading at about 18 mph or so. Sounds like time to change the pitot tube and line. I'll probably also bring an older automobile GPS with me as skiers tend to like the range at the very low end of the current pitot/speedo setup.