Transducer Location / P319 installation

[PNG Divers]

I am currently in the process of designing a sidescan unit for personal use & not wanting to re-invent the wheel was thinking along the following lines.

Transducers - As the centre distances seem to have been optimised by John Bauchat I was planning to use 6off Airmax P319.
How Should these be mounted in the fish ie can it be internally to reduce the possiblity of water ingress or do they need to be through the side wall of the fish ?

If through fit has any body any experience of sealing the transducers & will they be OK at say 30m-4b.

Many thanks

Andy

[Rickard]

Hello Andy!

A year ago I was in the same stage of plans for a transducer array as you are now. Since then I have finnished the project and learnt a lot on the possibilities and shortcomings of this type of construction. (see my tread) I can't recall having seen any material from John Bauchat but I can guarantee there is no way to overcome the fundamental drawbacks with this type of system. There is an optimal solution but this solution is still hopelessly inferior to a "professional" array. The reason for this has to do with the distances between the piezos inside the transducers. The housings of the transducers are much thicker than the maximum allowed interpiezo distance. This distance should not exceed half a wavelength, about 2 to 5 mm depending on the frequency. If you grind away the flanges on the P319 the interpiezo distance will still be at least 20 mm. If you are worried about the water resistance of the P319 you can select some of the many other transducers that are better designed to withstand water. All conventional fishfinder transducers have that capability. But, this is a much smaller problem compared to the issue of interpiezo distances.

Regards,
Rickard

[PNG Divers]

Richard

Thanks for the info. I'll have a more detailed review of your thread later but looks very helpfull.

The P319 array spacing details can be found at http://www.beugungsbild.de/
Regarding the concerns raised with the fundimentals of the array I was thinking along the following lines:
Build the fish to accomodate a 6off P319 array & if didnt give me the required results rebuild with a airmar 41-515-1-01 sidescan array -
Beam angle -3bd, 50deg athward, 0.5deg alongtrack, impedance 60ohms, OK upto 1350W @ 2% duty cycle. (US$1666).
Drawing attached.

Im still concerned over water ingress into to fish if the transducers have to be mounted through the side wall. Partucularly if using the 41-515-1-01 array as it appears to designed to be surface immersed.

The sales details associated with P319 appear to detail that it is feasible to mount internal to the hull but Im unsure of the effect to the side scan application ?

Andy

[Rickard]

Hello again Andy,

I hate to say that the simulations at http://www.beugungsbild.de/ are not correct. They show the beam patterns at a very particular moment in time during a wave cycle. If the beam patterns are integrated over time they show much less supression of sidelobes. Simulations of equally spaced arrays don't need to consider this but when the spacings are uneven this is critical. I made René Pascal aware of this many months ago but there is still no comment at his site. My results have been confirmed by professionals in Norway (http://heim.ifi.uio.no/~ultrasim/geometry.shtml). But it was René's simulations that inspired me making my own array with all the fun and new experiances so I don't blame him for anything.

Rickard

[PNG Divers]

Rickard - See your point.

If you had got £300 to spend on transducers what would you get ? & on what spacing.

Any more than £300 (assuming its any good) & you may as well save up for airmar bespoke sidscan array.

Have you got any more details on your cork trials ?

Thanks for the interest

Andy

[Rickard]

Andy,

I would shose the Airmar sidescan, or why not one of Burton's arrays. I guess there is enough work left to give the feeling of having made one's own sidescan even if you buy a ready-made sidescan transducer.

As there is very little to gain from having more than three (3) transducers in a fishfinder array the cost for such a poor-mans-sidescan doesn't need to be larger than that. Unfortunately, there is no simple rule for the proportions between interpiezo spacings. Optimal spacings depend on the shortest possible interpiezo distance so one has to know the exact dimensions of the particular transducer and then try out the spacings in a simulation. In case the spacings turn out to be very small the main lobe will be wide. A fourth transducer can then be helpful.

The cork experiment was successful. The vertical beam width became much larger. There were no traces of interference from the cork. However, since energy was more dispersed and to some extent absorbed in the cork I had to increase effect and sensitivity a lot to get good sonograms.

Regards
Rickard

[Glennk]

Rickard - See your point.

If you had got £300 to spend on transducers what would you get ? & on what spacing.

Any more than £300 (assuming its any good) & you may as well save up for airmar bespoke sidscan array.

Have you got any more details on your cork trials ?

Thanks for the interest

Andy

For that money you could get a real nice transducer array from G. Burton ( www.burtonelectronics.com) that would give you a much better image than any home-made transducer will.

Look at some of the pictures we have posted here in this forum, just search for burton, and you'll find plenty of pics.

Glenn

[PNG Divers]

Taking all your points on board.

Currently thinking along the lines of - until tomorrow when it will probably change again !

Make fish to accomodate 3off (possibly 4) airmar P79 E60 each + delivery.
This should (I think):
1/ allow easier adjustment of angle.
2/ deduce water ingress concerns as they are design for in-hull fitment.

If the result dont live up to much replace them with a Burton transducer.

What is the best material to manufacture the window in the fish that the transducer fires through ?

Thanks

Andy

[Rickard]

Ok,

But I would use the simplest and cheapest Airmar, the dual frequency P74 puck transducer for trolling motor mount. I don't think you have to worry about ingress of water in the P74 so there is no need for a waterproof fish. But be sure to buy transducers from the same batch as Airmar uses several different piezos in their transducers.

In-hull transducers are designed to send sound through polystyrene.

Rickard

[PNG Divers]

I contacted Airmar Eurpoe but they detailed that they didnt carry the P74 as a stock item but could get them on 3 month delivery. I will ask again for a price.

Airmar confirmed that the P79 (600W) can transmit through 1/2-5/8 inch (12-16mm) of fiberglass.
So fiberglass looks like the way forward for the window area.

The P74 units are only designed to be water proof at surface immersion so i'm still planning on waterproofing the fish but may well use the P74s if there is a big enough price against the 79s.

Thanks for the info

Andy