Depth and Speed failed

[winsbury]

So after 9 months of refurbishment works, plumbing, wiring, welding, carpentry, glassing, rerigging, coppercoating etc etc we launched this weekend at last - hurrah !!! Many thanks to all those that have responded to my various questions over the months.

No leaks so I had an ear to ear grin however it soon became apparent that the nasa depth reading was bouncing all over the place and unusable, and the speed/distance system, a vintage 80's VDO Sumlog, seems to have given up the ghost too. Both were tested before launch and seemed okay so am a bit niffed to say the least.

The Nasa manual points to possible electrical interference although none of the other electronics are showing any signs of interference but unplugging the solar panel reduces the random readouts on the depth finder as does disconnecting the charging system from the wind generator but neither completely eliminates the spurious readings. As for the Sumlog I suspect the paddle wheel might have some excess grease from when I changed its O-rings but cant be sure without removing it from the hull fitting.

This leads to several dilemmas:

• Do I have to lift her out again to check/change the paddle wheel - there is access from inside but I have no idea if the top of the mounting tube is below the waterline so worried if I undo it she'll quickly flood. Also how to determine if its the paddle wheel or the display that has the problem, ideally with everything in situ
• Is there any special form of decoupling/screening/suppression required on the Nasa depth system known to work
• Will a new combined Nasa speed/distance system suffer the same interference issue ( assuming that's what it is and not a 'proper' fault.)
• Should I just bin the ancient gear and invest in a new n2k depth/speed/temp sensor and if so what one will interface with the Lowrance HDS 5M gen 2 that I have.

 

[Houleaux]

The top of the paddle wheel tube will almost certainly be below water level. Usually you unscrew the fitting, withdraw the wheel and then screw on a replacement cap to stem the flow while inspecting the transducer. Expect to get a little wet in the process! I get a water jet about a foot high, but take on very little water as it doesn't take me long to screw on the replacement cap.

 

[winsbury]

The top of the paddle wheel tube will almost certainly be below water level. Usually you unscrew the fitting, withdraw the wheel and then screw on a replacement cap to stem the flow while inspecting the transducer. Expect to get a little wet in the process! I get a water jet about a foot high, but take on very little water as it doesn't take me long to screw on the replacement cap.

Thanks, nice to know thats normal, I would have has a heart attack if that had happened unexpectedly. . I have the blocking cap so will have to pick a brave moment and hope to hell I don't drop it !

 

[AntarcticPilot]

Thanks, nice to know thats normal, I would have has a heart attack if that had happened unexpectedly. . I have the blocking cap so will have to pick a brave moment and hope to hell I don't drop it !

Don't worry - it's a bit scary the first time, but it really isn't a problem. The water doesn't come in withthat much force, so you can easily (if a bit damply!) can put the blanking cap on. I do it from time to time to ensure the impeller isn't growing weed.

 

[prv]

Don't worry - it's a bit scary the first time, but it really isn't a problem.

+1

I tried to do it as rarely as possible in KS, but only because it was mounted in a locker full of spare parts etc which I would have to empty first and then dry and repack afterwards. Only ever a couple of sponge-squeezes of water to get rid of though. If the transducer is in the bilge where it should be then no worries at all.

The one on Ariam is also mounted in a locker, but in this case there's room for me to glass in a length of drain pipe or similar around it, keeping the rest of the locker dry. A job I will get round to one day

Pete

 

[maby]

Thanks, nice to know thats normal, I would have has a heart attack if that had happened unexpectedly. . I have the blocking cap so will have to pick a brave moment and hope to hell I don't drop it !

Do make sure you have a companion nearby! Also a softwood plug...

Dunno about that particular model of paddlewheel, but most modern units include a flap valve in the tube which reduces the inflow of water quite a lot. Not something to do on your own - the first time at least. Have a bucket, old cup and sponge available to bail out and dry the bilge.

You need to learn how to do it - even if its working now, the wheel will almost certainly need cleaning before you next lift her for maintenance. Round the Medway we seem to need to clean it every two or three months.

 

[maby]

+1....

The one on Ariam is also mounted in a locker, but in this case there's room for me to glass in a length of drain pipe or similar around it, keeping the rest of the locker dry. A job I will get round to one day

Pete

I've heard of people cutting a suitable size hole in the bottom of a large yoghurt pot and Sikaflexing that to the hull round the transducer tube - it will catch most of the water and let you sponge it out. Unfortunately, you do have to do it the man's way the first time since you cannot fit the yoghurt pot with the sensor wire in place...

 

[Norman_E]

My old VDO log had no flap valve, but the diameter was fairly small so not much water came in between pulling it out and pushing the plug in. Wiring is often the cause of failure with these units especially as VDO used plain copper wire rather than tinned. If it spins freely when you pull it out but it still does not register, check the wiring. If it all looks OK there is one trick to try. On mine the log would often fail to register after a day or so with no movement. To get it going the method was to motor at about 5 knots or so, and send someone below to slacken the nut, and twist the log unit back and forth a few times as sharply as possible before returning it to the straight ahead position. That bit of a shake usually freed it and got it going.

 

[winsbury]

The Speedlog SL definitely doesn't have a flap - I peered out of it in wonder that such a big hole (probably about 25-30mm) should legitimately be in the bottom of the boat when we first got it. There was a good current in the harbour yesterday and the gps was showing 5.5kts sog very gently motoring downstream to the buoy so reckon there was at least 3-4 kts over the paddle wheel once we moored which should have moved any minor obstructions/grease.

I'm wondering if I stupidly put it in back to front after I changed the o-rings; its not keyed so can be adjusted to any angle, so perhaps the paddle is rotating in reverse although I would have expected it to still pulse and show a speed albeit inaccurately if that's the case. I also forgot to remove the wheel while we drove it down to the coast on the trailer although I cant imagine how that could damage the manual does say to remove it during transport and put the blank cap on instead. Certainly the straps on the hoist were no where near it so it wont have been that causing the problem.

 

[maby]

Don't beat yourself up over it - they are not the most reliable things in the world! Depending on your home waters, you may need to clean it every few weeks over the summer season, so you may as well learn to pull it now! It's not rocket science, but do have a friend on hand in case something goes wrong - it's difficult dialing the phone for help while you have one hand jammed over the tube to stay afloat! This applies particularly the first time you do it and in particular if you have never fitted the plug before - you don't want to be alone when you discover that the thread is stripped or someone has left the wrong size plug there!

 

[winsbury]

Don't beat yourself up over it - they are not the most reliable things in the world!

So I have discovered!

I have read that Airmar is/might be producing a combined depth / doppler speed sensor with n2k connection - for me this would be ideal as a replacement system for the Nasa depth and the VDO sumlog if I cant get them going again. Such a system would have the benefit of no moving parts to foul up and could be displayed on the plotter and a repeater but not sure if this is just a rumour to gauge potential demand.

 

[WestWittering]

I cleaned my wheel this weekend. Although I have a 'system' in place for a dry removal, I couldn't be bothered so I just removed it and pushed a soft wood plug in. Yes, the first gush of water is quite giddying, but took a couple of minutes to clean up. I am just posting to say there is a small direction arrow on the log, so check that yours is pointing the correct way. Mine was - it was just the boat was back to front . It didnt take long to get a mate to hold the log steady while I turned the boat around.

Di

(the last sentence was a joke, I have been sniffing the cork this afternoon... I just turned the log round)

 

[winsbury]

the first gush of water is quite giddying,

It usually takes something stronger for me

there is a small direction arrow on the log, so check that yours is pointing the correct way. Mine was - it was just the boat was back to front . It didnt take long to get a mate to hold the log steady while I turned the boat around.

Nice one - so just out of curiosity, did yours show zero speed when it was reversed or did it show a speed that was clearly inaccurate ?

 

[Bosun Higgs]

dont bother about the paddle wheel. These days I only put mine in for racing - rest of the time its GPS speed. More useful anyway since what you really want is your speed alomng ther course you have set, not through the water. The depth sounder clearly is an internal wiring issue

 

[maby]

So I have discovered!

I have read that Airmar is/might be producing a combined depth / doppler speed sensor with n2k connection - for me this would be ideal as a replacement system for the Nasa depth and the VDO sumlog if I cant get them going again. Such a system would have the benefit of no moving parts to foul up and could be displayed on the plotter and a repeater but not sure if this is just a rumour to gauge potential demand.

They certainly do exist, but have you seen the price? Cheaper to get the boat lifted every month to clean the wheel!

 

[WestWittering]

I confess that I am usually tied up snugly to a pontoon when I attempt any kind of maintenance - especially if it involves letting in water. The log was reading okay, but I thought I would give it a clean as I was fiddling about with some wiring down there anyway. It was after I interfered with it I remembered about the arrow & yes, I had replaced it back to front.

FWIW, I think it would just read zero if it was reversed - but sideways would be a different ball-game.....

Di

PS my log is clearly inaccurate as the log will show 5 knots and I am sure I am going much faster

 

[winsbury]

They certainly do exist, but have you seen the price? Cheaper to get the boat lifted every month to clean the wheel!

Actually no , Ive been looking for them but cant find the doppler one, all the ones Ive seen still seem to use paddle wheels - have you got a link to a retailer ?

dont bother about the paddle wheel. These days I only put mine in for racing - rest of the time its GPS speed. More useful anyway since what you really want is your speed alomng ther course you have set, not through the water. The depth sounder clearly is an internal wiring issue

Ah but
a) I'm a gadget maniac and its driving me mad that I have a speedo with no readout
and
b) I want a backup should the GPS fail for some reason ( US military manoeuvers for example. )

As for the wiring, there's a coax cable that's hardwired into the depth transducer and plugs into the back of the NASA display so not much chance of getting that wrong. I guess its possible the cable is damaged internally but that would necessitate changing the transducer which is permanently fixed to the hull or the NASA display is so poorly made ( he says somewhat expecting the usual wave of criticism of the brand ) that the slightest noise on the power supply makes it unusable. Every other instrument, including a NASA Navtex is working perfectly so why should this one be so badly affected ?

 

[prv]

A thought on the depth sounder - it's not a problem coupling the transducer to the water, is it? I mean like an oil-bath mounting where the oil has escaped, or trying to fire through a cored hull, or glued down with mastic but there's an air bubble and it's never worked properly?

How is the depth transducer mounted?

Pete

 

[maby]

Is the depth transducer through-hull, or is it glued internally? Our first boat had a NAASA transducer epoxied onto the inside of the hull and the performance is very dependent on having the right medium between the transducer and the hull - any bubbles in it will cause havoc!

OOPS - beat me to it!

 

[Fantasie 19]

Mate of mine did a little YouTube clip on it... about a minute in will give you an idea what to expect...