Where is the speedometer sensor/pitot on my Starcraft?

[Eastern Yooper]

Have an '03 Fishmaster with a factory installed speedometer. Well, the speedo quit working this morning.

I assume there's a clogged pitot or sensor of some sort on the hull... but damned if I was able to find it.

Anybody know where its located?

[MSUICEMAN]

are there little roller things at the transom of the boat near the bottom? most non-gps speedos do it by little paddle wheels installed at the bottom of the transom.

steve

[Jason Adam]

I think if you do not have an exteranlly mounted pitot, your speedo pickup hole will be in the lower unit assembly. I'd check your manual for your your outdrive or OB.

[TimT]

ditto on what Jason said. I'd bet you have an alpha one drive, and you'll notice a little hose near the bottom of the outdrive. It's possible that the hose just came off, but it's highly likely that it's just plain bad. Mine went bad within the first month of ownership and fixed under warranty. Just take a look down there, you'll see the thin hose I'm talking about.

[MSUICEMAN]

well i just learned something... surprises me that they use pitot tubes... as well, they measure static pressure which you can find speed, but they are kinda touchy, and well, the fluid flow under your boat isn't exactly ideal to get numbers from. I've worked with pitot tubes quite a bit in college for class and research, and they are quite interesting.

steve

[TimT]

I should've said near the bottom of the outdrive where it comes through the transom. The pickup hole for the water is just a little hole near the bottom of the outdrive. I suppose it's possible that it's plugged. The first thing i'd check is to see if the hose is off, though.

[FishTales]

You didn't say if it was an outboard or i/o, I will assume being a Fishmaster it is and outboard, click on the link and check out the Teleflex Setup. Is there a chance your pickup got knocked off ?

Speedometer Pickup (http://www.tflx.com/pdf/marspd~1.pdf)

[Eastern Yooper]

Yep, she's an outboard. 100 hp 4-stroke Yami.

There is a air-tube that runs from the speedo to the rear of the boat, where it connects to a tube on the outboard. That tube runs internally down to just above the lower unit where I spy a small hole that I gather to be a built-in pitot pickup for the speedo connection.

Does that sound right?!?

[MSUICEMAN]

other than a mechanical problem, could be a transducer problem. pitot tubes measure static pressure, which through bernoulli's theorem can be correlated into a speed. the thing is what happens is this goes through a transducer and turns it into an electrical signal (usually mV). then this has to be converted using either a map or an equation into speed. If this transducer gets messed up, you will either get whacky or stupid results.

Honestly-don't know where the ducer is or how it is packaged in boats, this is strictly knowledge from the lab.

steve

[Eastern Yooper]

I clepped-out from having to take any college mathematics... and besides, we C-J guys have an especially difficult time comprehending/understanding anything remotely having to do with math in general, let-alone complex pythagorium theories, amps, ohms, E=Mc2, or the like. In fact, it wasn't until my sixth year at Lake that I finally figured-out that a case of beer contained 24 cans. :)

Anyways..... I've got a speedo on my fishfinder that works fine. I've got a speedo on my GPS that works fine.

I'm talking about the factory-installed, built-in speedo thats on the left side of my dash:

http://photos.imageevent.com/yooper/yooperfirstalbum/websize/99999999999999snapshot.jpg

Here's the airhose tubing that goes from the speedo to where it connects to the main motor harness:

http://photos.imageevent.com/yooper/yooperfirstalbum/websize/9993_snapshot.jpg

The air tubing runs internally to this opening just above the lower unit. Am I correct in assuming this is the sensor/pitot (?) for my speedo:

http://photos.imageevent.com/yooper/yooperfirstalbum/websize/4_snapshot.jpg

[RJF]

My four stroke Mercury, built by Yamaha has the hole in the lower unit. Yup, I'm sure you have found it. Round hole on the front of the lower unit. Gotta be in front, on the leading edge.

[RJF]

And, BTW, this is the only boat speedometer that I have ever seen that matches the GPS speed. Most all I have seen are always off by quite a bit.

[FishTales]

I have a 75 hp 4 stroke Merc, just took a good look at it and the pickup line goes in the top with all the wiring and cables, then it goes down the center of the pivot tube, it comes out just above the lower unit and connects to a fitting that goes into the lower unit.
I have no hole on the leading edge, but I think it gets the water pressure from water pump intake area.
The line of holes that goes right through the lower unit where you would put on the muffs.
That's the only place that I can see where it would get it from.

[Eastern Yooper]

Thanks for the info guys; I learned something new from all this.

Now to figure-out whats wrong with it......