Speed Log Woes

[Dockhead]

I can't seem to catch a break with speed logs.


When I renewed my electronics in 2013, I installed an Airmar CS4500 ultrasonic log which was pretty good. It gave a pulse output which required an Actisense box to turn that into 0183 sentences but it all worked fine until the transducer died a few years ago. It was not all that accurate but pretty consistent and the data was kind of useful, although not accurate enough for decent true wind calculations.



I replaced it with an Airmar UST850 which is the NMEA2000 version of the 4500. It has been much, much worse, erratic reading and inaccurate.


I replaced that with the new DX900+, but that one was dead on arrival, so I never got a chance to see if it worked properly. I'm sending that in for repair.


But maybe this is a fool's errand? Maybe I just need to bite the bullet and use a Signet Blue Top like racers use? I have a B&G H5000 system which works well with this device.


I always thought the ultrasonic/electrostatic ones must be far better since they measure the water stream outside of the disturbed boundary layer, but unfortunately none of them seem to work that well.


Any tips? Are racers still using the Blue Tops?


I would dearly love to finally have decent true wind calculations so that I can finally do decent performance calculations against my polars.

[Dockhead]

No one?


I have possibly discovered the reason why my old CS4500 ultrasonic log worked so much better than the new UST850 -- it's NMEA2000, which introduces a lot of latency into the datastream. Someone did logs and demonstrated this.


So for wind and speed you do NOT want NMEA2000 instruments -- you want pulse or 0183. This could be a reason why my CV7 wind instrument works so much better than the WSO100 which I had before.


I was not aware that NKE make speed logs -- and they both ultrasonic and electromagnetic ones. Anyone have any experience? Maybe they'll be better than the Airmar ones.

[Franziska]

Just fitted a Nasa Marine Electromagnetic log.
Actually mounted the transducer while afloat which was a challenge (drill a hole into the hull while afloat!) but was in the end super easy.



NMEA 0183 compatable right of the box. Works with and without display. We connected it via multiplexeur to our Nav PC and did not bother installing the dedicated display as the data is on our WiFi stream from OpenCPN.



Big plus, no paddlewheel and much cheaper than Airmar or Raymarine, and, Nasa Marine has a very good and very responsive online support.



Btw. We got lucky and got ours brand new and second hand for 90€...

[Dockhead]

Originally Posted by Franziska

Just fitted a Nasa Marine Electromagnetic log.

NMEA 0183 compatable right of the box. Works with and without display. We connected it via multiplexeur to our Nav PC and did not bother installing the dedicated display as the data is on our WiFi stream from OpenCPN.

Big plus, no paddlewheel and much cheaper than Airmar or Raymarine, and, Nasa Marine has a very good and very responsive online support.

Btw. We got lucky and got ours brand new and second hand for 90€...

Congrats! Let us know how well it works.

[hjohnson]

Originally Posted by Dockhead

So for wind and speed you do NOT want NMEA2000 instruments -- you want pulse or 0183. This could be a reason why my CV7 wind instrument works so much better than the WSO100 which I had before.

That’s odd. One of the whole points of CANBus is that it’s deterministic and reasonably low latency. It’s what’s used to interlink, say, the transmission and engine computers in modern cars.

On my own boat, all of my instruments and sensors are individual N2K devices, and I have no issues getting reliable true wind calculations.

The instrument pack itself is a Garmin setup, which is an evolution of the Silva Nexus instruments. The relevant point here, though, is that the speed log (traditional paddle wheel type), the wind sensor, and the display heads are all separate N2K devices. They just interconnect through a standard N2K tee. Except when the paddle wheel fouls, it’s extremely consistent.

That bus is shared with my AIS (vesper XB8000), VHF (icom m506), autopilot (SIMRAD TP32), and my entire electrical system (Victron Cerbo GX, REC Active BMS and Wakespeed WS500). I doubt your issue comes from N2K.

[Dockhead]

Originally Posted by hjohnson

That’s odd. One of the whole points of CANBus is that it’s deterministic and reasonably low latency. It’s what’s used to interlink, say, the transmission and engine computers in modern cars.

On my own boat, all of my instruments and sensors are individual N2K devices, and I have no issues getting reliable true wind calculations.

The instrument pack itself is a Garmin setup, which is an evolution of the Silva Nexus instruments. The relevant point here, though, is that the speed log (traditional paddle wheel type), the wind sensor, and the display heads are all separate N2K devices. They just interconnect through a standard N2K tee. Except when the paddle wheel fouls, it’s extremely consistent.

That bus is shared with my AIS (vesper XB8000), VHF (icom m506), autopilot (SIMRAD TP32), and my entire electrical system (Victron Cerbo GX, REC Active BMS and Wakespeed WS500). I doubt your issue comes from N2K.

The guy I learned this from, graphed the data from N2K vs pulse transducers, so it's been demonstrated empirically, at least with regard to Airmar transducers.

The issue, he says, is that normal instruments used to compute true wind (your plotter or autopilot computer) don't have enough computing power, and therefore N2K transducers introduce damping at the transducer level.

That's why, he says, racers use pulse or at least 0183 instruments connected directly to their sailing computers.

I can confirm from my own experience that the newer N2K version of the Airmar ultrasonic speed log, the UST850, is much worse than the old pulse version, the CS4500.

I have an H5000 and so I will be doing it this way. I'm going to give a try with the NKE ultrasonic speed transducer; it gives a choice of pulse or 0183. The pulse leaves all the computation to the H5000, to which I will feed wind data from my CV7 as 0183 (at 4 hz).

Hoping this will give decent results. We'll see about the speed transducer. If that doesn't work, then I'll try a Signet Blue Top, but that will be a faff because it requires a different housing, so boat out of the water.

When we did the electronics on my friend's Discovery 67, I specified a tall B&G 7 series wind instrument connected to an H5000. Unfortunately the N2K speed log was unsatisfactory so we still don't have really good true wind, but the apparent wind is the best I've ever experienced on any boat.

What concerns wind instruments -- I am very pleased with the CV7. It's not quite as good as the 7 series B&G but other than that head and shoulders better than anything else I've used. I've got it about 1.2m above the masthead on a carbon pole, and I think it could be a bit higher. I have the racing version which gives data at 4hz (rather than 2), but there is a new racing version which gives 60hz, which I think could be beneficial. The 7-series gives 10hz via 0183.

[Franziska]

Originally Posted by Dockhead

The guy I learned this from, graphed the data from N2K vs pulse transducers, so it's been demonstrated empirically, at least with regard to Airmar transducers.

The issue, he says, is that normal instruments used to compute true wind (your plotter or autopilot computer) don't have enough computing power, and therefore N2K transducers introduce damping at the transducer level.

That's why, he says, racers use pulse or at least 0183 instruments connected directly to their sailing computers.

I can confirm from my own experience that the newer N2K version of the Airmar ultrasonic speed log, the UST850, is much worse than the old pulse version, the CS4500.

I have an H5000 and so I will be doing it this way. I'm going to give a try with the NKE ultrasonic speed transducer; it gives a choice of pulse or 0183. The pulse leaves all the computation to the H5000, to which I will feed wind data from my CV7 as 0183 (at 4 hz).

Hoping this will give decent results. We'll see about the speed transducer. If that doesn't work, then I'll try a Signet Blue Top, but that will be a faff because it requires a different housing, so boat out of the water.

When we did the electronics on my friend's Discovery 67, I specified a tall B&G 7 series wind instrument connected to an H5000. Unfortunately the N2K speed log was unsatisfactory so we still don't have really good true wind, but the apparent wind is the best I've ever experienced on any boat.

What concerns wind instruments -- I am very pleased with the CV7. It's not quite as good as the 7 series B&G but other than that head and shoulders better than anything else I've used. I've got it about 1.2m above the masthead on a carbon pole, and I think it could be a bit higher. I have the racing version which gives data at 4hz (rather than 2), but there is a new racing version which gives 60hz, which I think could be beneficial. The 7-series gives 10hz via 0183.

Regarding boat out of the water to mount a different transducer.


Even though it sounds intimidating it can be done fairly safely and with not more than a shot glass full of water coming in.

Keep calm and work carefully.

Possibly rig a portable pump for safety before proceeding as follows.

The installation area should be fairly flat at the transducer mounting location.



Here are the steps we used (of course anyone attempting this does so entirely at their own risk, we can not take any responsibility for failed attempts and/or results.):


1)

Get a sturdy transparent plastic cup with larger diameter than the transducer housing you need to install.



Get a flat thin (about 5mm) flexible soft closed cell piece of foam a bit larger than the cup opening.



2)
Place foam on table and cup opening onto the foam. Go around the perimeter with super glue. Wiggle the cup slightly then press it down until cured.



3)
Push blanking plug into the transducer housing from its outside (!). You might need to bevel the exterior inner rim slightly to do so, so that the O-ring can slide in.

Push it in as far as possible. This will leave a volume of about a shot glass full at the inner end.

Attach a piece of string long enough to reach from the blanking plug to deck level to the blanking plug.



4)
Prepare the inner hull mounting area with the backing plate.



5)
Apply your preferred sealing compound (we used Sika) in copious amounts around the flange of the future transducer housing.



6)
Diver goes into water with the "sealed" cup & a toilet plunger. The transducer housing floats alongside on its string, so that the diver can grab it once needed.



7)
Inside person drills a tiny hole at the mounting location.



8)
Diver goes to the position where drill sticks out. Puts toilet plunger about 30cm from it onto the hull. This only serves as handhold to keep diver stationary.



9)
Diver puts cup centric over the drill sticking out, piercing the foam gasket while doing so. Person inside retreats the drill. The water pressure will now start holding the cup in place diver only holds it for safety too.



10)
Person starts drilling transducer hole with holesaw from inside. Make sure your holesaw has exactly the right diameter required and is deep enough.



11)
Diver should see guiding tip of holesaw at exactly the same spot where the pilot was.

Eventually the complete holesaw will appear behind the foam gasket. Do not press to hard with the holesaw during breakthrough.



12)
Remove holesaw and plug on the inside.



13)
Person inside presses piece of soft close cell foam against hole from inside and then knocks so that diver is aware that they are ready.



14)

Diver grabs transducer housing with the blanking plug inside and sealing compound on the outside.

Then removes cup and pushes transducer housing gently into the hole.

Person on inside removes foam when they feel the housing touching it.

Diver pushes housing all the way in and inside person screws gasket and retaining nut on.

Diver wipes away excess sealing compound outside.



15)
Person inside pushes blanking plug out from the inside by inserting the transducer.



Job done, all happy.

Good luck!!

[Dockhead]

Originally Posted by Franziska

Regarding boat out of the water to mount a different transducer.

Even though it sounds intimidating it can be done fairly safely and with not more than a shot glass full of water coming in.

Keep calm and work carefully.

Possibly rig a portable pump for safety before proceeding as follows.

The installation area should be fairly flat at the transducer mounting location.

Here are the steps we used (of course anyone attempting this does so entirely at their own risk, we can not take any responsibility for failed attempts and/or results.):

1)

Get a sturdy transparent plastic cup with larger diameter than the transducer housing you need to install.

Get a flat thin (about 5mm) flexible soft closed cell piece of foam a bit larger than the cup opening.
2)
Place foam on table and cup opening onto the foam. Go around the perimeter with super glue. Wiggle the cup slightly then press it down until cured.

3)
Push blanking plug into the transducer housing from its outside (!). You might need to bevel the exterior inner rim slightly to do so, so that the O-ring can slide in.

Push it in as far as possible. This will leave a volume of about a shot glass full at the inner end.

Attach a piece of string long enough to reach from the blanking plug to deck level to the blanking plug.

4)
Prepare the inner hull mounting area with the backing plate.

5)
Apply your preferred sealing compound (we used Sika) in copious amounts around the flange of the future transducer housing.

6)
Diver goes into water with the "sealed" cup & a toilet plunger. The transducer housing floats alongside on its string, so that the diver can grab it once needed.

7)
Inside person drills a tiny hole at the mounting location.

8)
Diver goes to the position where drill sticks out. Puts toilet plunger about 30cm from it onto the hull. This only serves as handhold to keep diver stationary.

9)
Diver puts cup centric over the drill sticking out, piercing the foam gasket while doing so. Person inside retreats the drill. The water pressure will now start holding the cup in place diver only holds it for safety too.

10)
Person starts drilling transducer hole with holesaw from inside. Make sure your holesaw has exactly the right diameter required and is deep enough.

11)
Diver should see guiding tip of holesaw at exactly the same spot where the pilot was.

Eventually the complete holesaw will appear behind the foam gasket. Do not press to hard with the holesaw during breakthrough.

12)
Remove holesaw and plug on the inside.

13)
Person inside presses piece of soft close cell foam against hole from inside and then knocks so that diver is aware that they are ready.

14)

Diver grabs transducer housing with the blanking plug inside and sealing compound on the outside.

Then removes cup and pushes transducer housing gently into the hole.

Person on inside removes foam when they feel the housing touching it.

Diver pushes housing all the way in and inside person screws gasket and retaining nut on.

Diver wipes away excess sealing compound outside.

15)
Person inside pushes blanking plug out from the inside by inserting the transducer.

Job done, all happy.

Good luck!!

I'll leave that method to far braver people than I! Yikes! I find it psychologically hard enough just changing the inserts with the boat in the water. Cutting a hole with the boat in the water? Nein danke!

[Franziska]

Originally Posted by Dockhead

I'll leave that method to far braver people than I! Yikes! I find it psychologically hard enough just changing the inserts with the boat in the water. Cutting a hole with the boat in the water? Nein danke!

🤣 All good just wanted to give you the option. Bitteschön!