boat speedo help

[hollygolly]

Hi there.
I have been cleaning out the deck of my boat, and on removal of the deck board i found a plastic plug similar to a drain pipe. On removal i found a sensor about 4 inches long with a small impeller at the base, which i assume to be something to measure the speed of the boat in the water. What puzzles me is that the cable coming off it is coaxial cable? Can anyone explain what type of sensor this is and what type of gauge i would need to get this working?
Thanks

 

[PETER]

wat kind of boat engine is it inboard or outboard

 

[hollygolly]

it is outboard.

 

[PETER]

any chance of a picture mate

 

[hollygolly]

hi. Will have to be the weekend. Trying to explain is difficult, but it has a white plastic pipe about 5 inches long going through the hull and then the 4 inch section with the impeller on goes into the tube and screws on a bit like the connector of a sink "U" bend. It has an arrow on when screwed down indicating the front has to be pointing toward the front of the boat. The cable is about 3 or 4 mm dia black with the inner being the same as coaxial core.. ?

 

[KeithB]

Sounds like a sounder transducer with a speed wheel.

 

[hollygolly]

Hi Kieth
It does not look like the picture you posted? If it is what you say how is it rigged to work? I take it the coaxial cable would be for the sounder, but how will the speedo work?

 

[KeithB]

The sounder normally displays your speed.

 

[mark]

it will need a dedicated instrument if its a paddle wheel. coax is standard on paddle wheels. it will show your speed through water not speed over ground which makes it useful for measure currents/tide flow. went through the corran narrows a few years ago on boat with one. the log (instrument attached to the paddle wheel) said we were doing 14knots. the gps said we were doing 3 to 4!

 

[hollygolly]

Hi Mark.
Any idea if it needs to be a dedicated unit or will any unit do? And what sort of dial/unit am i looking for?
Thanks

 

[mark]

it depends to a point on what paddle wheel you've got. The head unit needs to count the pulse from the paddle wheel to display the speed. Navman digital ones are probably the cheapest, but chances are you'd buy one and it would come with its own wheel. I've got an old Brooks and Gatehouse analogue one in the shed. The Rolls royce of yottie instruments in their day!

2 dials, one speed one distance, so it works out miles through water as well as speed through water. Might work. your welcome to it if its any good

 

[hollygolly]

Thats very kind of you Mark. I will take a picture of the wheel and set up and you may be able to tell me if it will work. Watch this space as they say.

 

[mark]

but sure how much help it might be like!

 

[hollygolly]

here are some images of speedo paddle wheel if anyone can help.

 

[mark]

looks almost certainly like a paddle wheel from a NASA digital log. either a clipper or a target 2. they both use the same paddle so either instrument would work

keep an eye on ebay, you might find a second hand unit relatively cheap

 

[hollygolly]

hi yes just looked on ebay it is identical to the clipper one, but £100 inc delivery is abit steep! stick with my fish finder/plotter i think.
Thanks anyway, if the one you have in the garage will still work i will be happy to take it off your hands mind.

 

[mark]

if you want it you can have it. can't see any reason why it couldn't be made to work. they all basically just count pulses from the paddle wheel. so it may work but you might need to make a new dial for the gauge or do the metal maths to work out speed depending if it is counting too many or too few pulses