nasa speed and distance log

[chrissy]

I have been down to boat today what a corker of a day !

My problem is with my nasa speed distance instrument it powers up ok but does not register any speed when underway.

I have removed the paddle wheel and it is not covered with weed etc. Have tried spinning the paddle wheel but still does not register. Does it just need calibrating or is it U/S and can you by new paddle wheels.

 

[theoldsalt]

Usually the paddle contains a magnet that induces voltage pulses in the coiled wire of the transducer body. The instrument counts the pulses and provides a readout converted to speed.

So 3 things can go wrong.

1. Loss of magnet

2. Open circuit in the coil or cable going from the instrument to the transducer.

3. The instrument is no longer converting the pulses to a speed so is faulty.

I suggest check cable/coil continuity first.

 

[Appledore]

Available on eBay:

http://www.ebay.co.uk/itm/NASA-Mari...ecialistRadioEquipment_SM&hash=item519d740c3c


I had to replace mine last year as it disintegrated!

 

[VicMallows]

Have you checked the awful 'belling-lee' TV style connector? Quickly making and breaking a shorting connection on the instrument socket should give you some sort of speed indication. Slowly turning the paddle wheel with an ohmmeter connected to the transducer you should see the read-switch opening and closing.

Vic

 

[Seajet]

Chrissy,

when I had a boat with a paddlewhweel impellor, it was forever going u/s requiring withdrawal, hopefully with a steady nerve - or even better, a trusty crew - to put the cap on, while hoping it didn't get cross-threaded which might lead to an awkward moment.

Check for wee beasties, not just weed; they take up residence in an surprisingly short time,I'm talking of days not weeks, that's on the South UK coast.

Also one has to keep an eye out for weed on the surface and do one's best to go around it.

Though I have to say I'd never rely on such an in-hull log for accuracy, hence the recent thread about trail logs, or if not wishing to appear old fashioned I suppose gps with a bit of nav' knowledge in the back of the mind is the answer.

 

[VicMallows]

I had to replace mine last year as it disintegrated!

I hope it was just the transducer! ... remember the skin fitting failures a few years back

'OldSalt' ... I am fairly sure that the Nasa transducer uses a simple reedswitch, rather than an inductive pickup.......but I stand to be corrected.

Vic

 

[chrissy]

Yes had to put one hand on skin fitting while looking at paddle wheel and then pump out about 2 gallons of water out of bilges!! I couldent find the cap will have to use a wooden bung.
I am not really worried about the accuracy of the instument for navigation purposes its just that i am selling boat and want to get everything working properly to maximise price.

Thanks all.

 

[VicMallows]

Though I have to say I'd never rely on such an in-hull log for accuracy, hence the recent thread about trail logs, or if not wishing to appear old fashioned I suppose gps with a bit of nav' knowledge in the back of the mind is the answer.

It rather amuses me. Before we had DECCA or GPS all we could do was hope our Log reading was reasonably accurate, and then make our best guess at the tidal stream in order to work out our SOG / distance travelled /position.

Now that we know SOG/VMG and position to extreme accuracy we seem obsessed with wanting to know what our speed-through-the-water is....but want the old unreliable instrument to tell us.

Vic

 

[theoldsalt]

Vic,

Quote : I am fairly sure that the Nasa transducer uses a simple reedswitch, rather than an inductive pickup.......but I stand to be corrected

You may very well be right - It just goes to show how out of touch I can be with new technology.

 

[blackbeard]

As already mentioned all these devices (not just NASA ones) are a magnet for all types of fouling, weed barnacles etc but also, apparently, shrimps like to live in them.
There's another type of fouling which it took me some time to realise.
If you take out the paddlewheel (splosh!) you can gently push out the little brass spindle on which the paddlewheel revolves, which not only allows a really good clean up of the whole assembly but also you can gently clean up the spindle itself. It seems to acquire, after a while, accretions which form a rough surface on which the paddlewheel fails to revolve. Put wheel and spindle back, replace unit in housing (splosh!) and (assuming problem lies in non-rotation of paddle wheel) all should be well - for a while.

I'll agree that all such devices are not as essential as they used to be.

good luck with finding that sealing cap (or NASA could probably find you a spare)