Turbulence over sensors

[Graham_Wright]

I am fitting a fishfinder (for wreck finding;- pretend diver although probably past it by the time it works). On a Raymarine E80 system, the fishfinder with a DSM300 will give a picture of the bottom and a depth readout for other instruments BUT only if the plotter is switched on.

Desiring to know depth even when the plotter is off, needs an echo-sounder and a separate transducer.

Add to that a log and I've ended up with three in-line holes in the hull.

Appreciating that, for best performance, the water flow over the transducers needs to be non turbulent, I have attempted to fair in the hull shape sympathetically to the transducer performance.

(Be patient, I'm getting there!)

Sailing boats do not have nice flat horizontal bottoms so that the beam is vertical in both directions.

Thus, the fairing is quite complex with a need to tend for the requirements of not only each transducer but also those downstream.

Does anybody (told you I'd get there) have any suggestions to test how streamlined the fairing is whilst the boat is on the hard? I wondered if something similar to a smoke stream as used in wind tunnels would be possible.

 

[nimbusgb]

1 - turn on system and test against a known wreck/feature at various speeds!

2 - Failing that an underwater video camera and some harmless food dye?

> whilst on the hard ? You could try just using a laminar stream of water from a hose, wouldn't need to be faster than a few knots so not tremendous.

 

[nimbusgb]

You will have to turn off the normal depth sounder when the dsm is on and visa versa since they will interfere with each other.

 

[tobble]

not sure you can achive anything meaningful on the hard, as you will be 'experimenting' with a very different fluid than the in use ne, i.e. air instead of water. Also I'm not sure how you could interpret the results even if you were sucsessful in the experiment. I think you'd be just as well doing it by eye, making all curves and transitions as smooth as poss.

I'm guessing you don't fancy filling one or two of the holes and moving the transducers futher apart or sideways? if you are happy messing around with glass and epoxy it's very straight forward.

 

[Graham_Wright]

[ QUOTE ]
I'm guessing you don't fancy filling one or two of the holes and moving the transducers further apart or sideways? if you are happy messing around with glass and epoxy it's very straight forward.

[/ QUOTE ]

The constraints were bilge keels so can't mount between because of reflections, the hull has a pronounced upwards sweep towards the bow and it also has quite a "V" shape.

Moving athwartships would require a lop sided fairing which would probably be more difficult.

However, they would not then interfere with each other laminar flow wise I guess.

Time will tell!

 

[Shanty]

You may be too far down the road for this, but have you considred NMEA2000?

If you can find a suitable NMEA2000 transducer, you could connect both your E80, and a suitable display to the transducer via NMEA2000, and operate with either or both displays switched on.

You would then only need one transducer in the water.

 

[Graham_Wright]

I am committed to what I have but the fishfinder transducer is higher power than the depth sounder and feeds directly to the Raymarine DSM300 (which I'm still saving up for!).
I don't know what protocol the DSM300 will output.

 

[ChrisE]

Not sure what your problem is.

I have a Raymarine fishfinder DSM300 feeding a 70 series plotter on the yacht with a protruding sensor (looks a bit like the head off a putter) immediately in front of the keel and it picks up wrecks, rocks and the bottom with no problems.

 

[Graham_Wright]

I don't know if I have a problem! I was asking for suggestions to establish if I do or not before launching.

If you read the subsequent post, you will see I have bilge keels and each protrusion needs to leave clear water for the following one.

As I also said;- "time will tell".

 

[ChrisE]

Hmm, didn't appreciate two keels.

Still I don't see the prob if mounted in front between keels, afterall these things work on cathedral hulls of fishing boats and the geometry of those would give a fair amount of turbulence. Still you'll find out once in the water.