Please identify this sensor? Attached to my transom

[Mattyp11]

Hey all,
this came on my old bass boat. Fairly new to boating world. It's attached next to the transducer for the fish finder.
Please help identify so u can use it\ensure function.

Thanks!

 

[Bondo]

Ayuh,..... Welcome Aboard,..... That's a pitot tube for a speedometer that reads air pressure,.....

 

[Mattyp11]

Awesome, thanks!

 

[QBhoy]

Reads water pressure usually.

 

[Bondo]

Reads water pressure usually.

Ayuh,...... With air pressure,......

The water rarely gets more than a foot or so up the tube, unless ya unhook the other end,......
'n then it'll pee on yer legs,.....

 

[QBhoy]

Ayuh,...... With air pressure,......

The water rarely gets more than a foot or so up the tube, unless ya unhook the other end,......
'n then it'll pee on yer legs,.....

Ah. Honestly never even thought of it that way. Every day a school day on here. Fair play Bondo.

 

[Alumarine]

Ayuh,...... With air pressure,......

The water rarely gets more than a foot or so up the tube, unless ya unhook the other end,......
'n then it'll pee on yer legs,.....

Or if you notice the carpet is soggy and your feet are wet your first thought will be you've got water up to the deck!

 

[robert graham]

Lots of folks these days use a GPS device to measure speed....and I'd expect it's more accurate anyway....

 

[JimS123]

A GPS measures speed over land. In other words, if you are going against a 10 mph current and the boat is doing 10 mph, your GPS will read zero.

A quality pitot tube / pressure gauge when new will provide water speed data to within 1 mph. The problem is that the hole in the tube eventually gets plugged, and the hose gets cracked from age, and thus the actual boat speed data deteriorates with age. Its all about maintenance.

When my GPS average data upstream vs. downstream doesn't equal my dashboard pitot data I know that I need to do some cleaning.

 

[Old Ironmaker]

A GPS measures speed over land. In other words, if you are going against a 10 mph current and the boat is doing 10 mph, your GPS will read zero

That is something I have never experienced and there are some serious currents here on the Great Lakes. Why would the satellite tell you aren't moving if the GPS co ordinates are changing?

Some boats will have a wheel on the old transducer to give you speed as well. Amazing how accurate pitot tubes and wheels can be. Our modern aircraft still use pitot tubes for air speed. More than a few airliners have crashed due to a plugged pitot tube. One came down because someone forgot to remove the masking tape over them after painting it, many lives lost for a few pieces of painters tape and someone not doing a 2 second task.

 

[JimS123]

That is something I have never experienced and there are some serious currents here on the Great Lakes. Why would the satellite tell you aren't moving if the GPS co ordinates are changing?

OK, lets think about the Niagara River for example. The current is linear and predictable. Let's assume the speed is 10 mph under the Peace Bridge. So you set your boat throttle so the boat is actually moving 10 mph. Now head upstream.

Your pitot tube and paddle wheel both show 10 mph. But look at the shore - you are actually standing still.

In this case the GPS coordinates are NOT changing, and thats why the GPS says zero.

GPS shows speed over earth. Pitot shows speed over water.

 

[Scott Danforth]

and after 7-10 years when the GPS speedo is going belly up.... my 32 year old pitot tube speedo still reads accurate enough

 

[SDSeville]

OK, lets think about the Niagara River for example. The current is linear and predictable. Let's assume the speed is 10 mph under the Peace Bridge. So you set your boat throttle so the boat is actually moving 10 mph. Now head upstream.

Your pitot tube and paddle wheel both show 10 mph. But look at the shore - you are actually standing still.

In this case the GPS coordinates are NOT changing, and thats why the GPS says zero.

GPS shows speed over earth. Pitot shows speed over water.

This may be an ignorant question, but if you are really standing still, why would you want to think you are moving at 10 mph? I would think you want to know haw fast you are actually getting from point A to point B.

 

[JimS123]

This may be an ignorant question, but if you are really standing still, why would you want to think you are moving at 10 mph? I would think you want to know haw fast you are actually getting from point A to point B.

A person can think whatever they want to think. I realize this can be a hard concept for some people to get a grasp on. I once had the same discussion with an old guy across the street. His logic was that his boat performed better when he went downstream....LOL.

My analogy was merely to illustrate why GPS and pitot readings sometimes are different. If you want to go from land point a to land point b, use the GPS. If you want to set the boat speed in the water to troll for fish, use the pitot.

Obviously my river example was mathematically sound - but not a real life boating scenario because it would take a long time to get to Capistrano...

 

[garbageguy]

JimS has explained it, and done the math very well.

Regarding pitot tubes, they use change in pressure, typically of a gas such as air, to estimate various characteristics of the flow of a fluid. Fluids can be liquids or gasses. the gas we refer to as air is pretty readily compressible, while the liquid we refer to as water is difficult to compress. This presents an ideal situation to use a pitot tube to estimate speed relative to the water a boat is in - without getting things wet (when all is working according to design).

 

[Old Ironmaker]

I am a slow learner Jim but once I learn it I can teach it. Many times running The Ottawa River rapids in a tinny I had that little 9.9 WOT and I was going backwards or the shore was moving forwards. But I get it JimS123, sort of. By the way I have fished under the Peace Bridge many times. I didn't have a GPS on board because GPS hadn't been invented yet. Our sonar was a flasher and it was hi tech for it's time. The cool thing was launching on the NY side of the river and tying off in Ft. Erie to get a coffee at Horton's.

 

[QBhoy]

A GPS measures speed over land. In other words, if you are going against a 10 mph current and the boat is doing 10 mph, your GPS will read zero.

A quality pitot tube / pressure gauge when new will provide water speed data to within 1 mph. The problem is that the hole in the tube eventually gets plugged, and the hose gets cracked from age, and thus the actual boat speed data deteriorates with age. Its all about maintenance.

When my GPS average data upstream vs. downstream doesn't equal my dashboard pitot data I know that I need to do some cleaning.

Most of my pilot tube speedos have been fairly accurate at certain speeds, but not so much at fast speeds. Usually a little optimistic. The campion I have will go off the clock at over 70 mph near top speed, but at top speed will show slower, despite the gps speed increasing. Presumably due the the trim angle of the drive.
My other boat has a paddle wheel. This seems more accurate more of the time...but unusually, it shows a speed a mph or two below gps speed. Go figure !

 

[Silvertip]

Another way to look at this upstream/downstream/speed over land/over water is to anchor your boat in a river that has a known (roughly) current. Let's assume that current is 10 MPH. With a pitot driven speedometer, the speedometer would show 10 MPH because that's the speed water is passing the pitot. You are anchored so the boat is not moving and a GPS unit would show zero MPH because your are -- well -- going zero MPH. OK -- now lets reverse things and let the boat FLOAT downstream. Now the speedometer would show zero MPH because the boat and the current are going the same speed and water is not passing the pitot but rather going "with it". Even though the speedometer shows zero, the boat is actually going 10 MPH. On the otherhand, a GPS unit would now show 10 MPH because the boat is indeed moving across the land (water in this case) so boat position is actually changing.

 

[JimS123]

Another way to look at this upstream/downstream/speed over land/over water is to anchor your boat in a river that has a known (roughly) current. Let's assume that current is 10 MPH. With a pitot driven speedometer, the speedometer would show 10 MPH because that's the speed water is passing the pitot. You are anchored so the boat is not moving and a GPS unit would show zero MPH because your are -- well -- going zero MPH. OK -- now lets reverse things and let the boat FLOAT downstream. Now the speedometer would show zero MPH because the boat and the current are going the same speed and water is not passing the pitot but rather going "with it". Even though the speedometer shows zero, the boat is actually going 10 MPH. On the otherhand, a GPS unit would now show 10 MPH because the boat is indeed moving across the land (water in this case) so boat position is actually changing.

OMG, finally someone can actually figure it out.

On another note, we had my old woodie out this afternoon. Leaks a little bit, but then again so do I.

She's 67 years old now and is equipped with an old state-of-the art speed-o-meter. Yes, a 67 year old original equipment pitot tube.

Just for laughs I took my hand held GPS along and compared the 2 readings at WOT. Now, of course the old pitot doesn't read below 10 mph, but at a rapid 24 mph it was spot on.

When I said "original" I lied. I DID replace the full length of tubing from the head to the pitot.

So, what's up with that?

 

[tpenfield]

Often when I find myself at point A, I wonder how fast I can get to point B. Then I realize that if I am not moving, my GPS coordinates are not changing.