Knots or Speedometer gauge...

[WillandShay]

Hey Everyone!

I am an automobile guy, so I am trying to figure out how the gauge reads speed.

There is a hollow tube that leads from the gauge to the back of the boat, it is just hanging slightly under the boat. How does this determine the speed of the boat.

Pictures are awesome and would help me to understand how to fix/repair this item if this is not normal.

Thanks!

Will

 

[jigngrub]

Re: Knots or Speedometer gauge...

Boat speedo's aren't that accurate, for an accurate reading you'll need a GPS. Just a small inexpensive hand held unit will work.

 

[QC]

Re: Knots or Speedometer gauge...

That type of speedo is actually an air pressure gauge. The thing hanging down is a pitot and allows water to enter the line, as speed increases the water compresses the air in the line and the needle should move. They usually don't work below 10 MPH or more, but some are actually accurate. However, they should not be relied upon for anything serious without verifying with a GPS. Remember they show water speed, so if you are in a current of say 3 MPH you will read 3 MPH fast downriver and 3 MPH slow upriver relative to a GPS.

First thing to do to troubleshoot is to blow air into it and see if you can get the needle to move. You can try at the head or the tube or the pitot and narrow down a possible clog in the line.

 

[WillandShay]

Re: Knots or Speedometer gauge...

That type of speedo is actually an air pressure gauge. The thing hanging down is a pitot and allows water to enter the line, as speed increases the water compresses the air in the line and the needle should move. They usually don't work below 10 MPH or more, but some are actually accurate. However, they should not be relied upon for anything serious without verifying with a GPS. Remember they show water speed, so if you are in a current of say 3 MPH you will read 3 MPH fast downriver and 3 MPH slow upriver relative to a GPS.

First thing to do to troubleshoot is to blow air into it and see if you can get the needle to move. You can try at the head or the tube or the pitot and narrow down a possible clog in the line.

Is it required to work? If not, then we will probably but this on the back burner. As the more important gauges will be for the engine readings.

Will

 

[jigngrub]

Re: Knots or Speedometer gauge...

Is it required to work? If not, then we will probably but this on the back burner. As the more important gauges will be for the engine readings.

Will

I'm pretty sure it isn't, tiller type boats aren't equipped with speedos.

 

[NavyChief]

Re: Knots or Speedometer gauge...

They've never been too accurate for me. Usually 5-8 mph difference from the GPS. If it's lose the pitot will flip up and not give u an accurate reading. Or like it could be clogged. You can get a cheap automobile gps - $55-$75 for speed and also use for coordinates and location. They ARE more trouble than they are worth. I use a smart phone with a gps app that gives me speed in mph, knots, distance travelded, avg speed, max speed, heading and also creates a track (I have iPhone).

 

[WillandShay]

Re: Knots or Speedometer gauge...

They've never been too accurate for me. Usually 5-8 mph difference from the GPS. If it's lose the pitot will flip up and not give u an accurate reading. Or like it could be clogged. You can get a cheap automobile gps - $55-$75 for speed and also use for coordinates and location. They ARE more trouble than they are worth. I use a smart phone with a gps app that gives me speed in mph, knots, distance travelded, avg speed, max speed, heading and also creates a track (I have iPhone).

OK. Sounds like we should just use a GPS if speed is a factor. But, we are going to be in small lakes and whatnot so speed will be minimal unless skiing, but of course everyone is speeding to get the skis up and going.

Thanks!

Will

 

[superbenk]

Re: Knots or Speedometer gauge...

You could get one of these

http://www.teleflexmarine.com/products/instrumentation/instrumentation/gps-speedometers/

Hrm, I might have to consider this myself (didn't realize they existed before this thread & a quick Google search)... Only $81 from here:

http://www.keenzo.com/showproduct.asp?z=1&id=4425347

 

[zopperman]

Re: Knots or Speedometer gauge...

NavyChief, what iPhone app is that!?!?

 

[superbenk]

Re: Knots or Speedometer gauge...

NavyChief, what iPhone app is that!?!?

AgileSpeed is a decent free one.

http://www.agilespeed.com/

 

[metriccrescentwrench]

Re: Knots or Speedometer gauge...

You could get one of these

http://www.teleflexmarine.com/products/instrumentation/instrumentation/gps-speedometers/

Hrm, I might have to consider this myself (didn't realize they existed before this thread & a quick Google search)... Only $81 from here:

http://www.keenzo.com/showproduct.asp?z=1&id=4425347

That's only the indicator head. You still need to purchase a gps receiver (in the literature Teleflex calls it an "antenna"). If you've got an unused hiking gps laying around it should work as long as it has a NMEA 0183 output.

 

[superbenk]

Re: Knots or Speedometer gauge...

Ah, bummer. Didn't read that far. Oh well, my boat isn't worth something that fancy anyhow.

 

[WillandShay]

Re: Knots or Speedometer gauge...

I think my phone has the VZ Navigator. It tells all the items needed like a GPS as well. But I think that unless you do not buy the unlimited package then it is 9.99 a month.

Will

 

[H20Rat]

Re: Knots or Speedometer gauge...

You could get one of these

http://www.teleflexmarine.com/products/instrumentation/instrumentation/gps-speedometers/

Hrm, I might have to consider this myself (didn't realize they existed before this thread & a quick Google search)... Only $81 from here:

I knew those were out, didn't realize they were under $100 though.. Hmmm, think it might be time for an upgrade! It would be nice to get rid of the speedo pitot and tubing entirely, one less thing hanging off the transom. I've got a relatively cheap depthfinder (cuda 350) that has NMEA output on it.

To the OP... Yeah you won't be needing a speedo much if at all. Depending on the level of skier and how often you pull them, its nice to have some indication of what speed they want to be at. Saves some faster/slower hand signals if you can go right to the correct speed. (of course, if you have skiers at that level, look at getting a perfectpass GPS installed)