Author Topic: DIY Towfish (Lowbird type) Nose cone ?  (Read 902 times)

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Offline DiveExplorer

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DIY Towfish (Lowbird type) Nose cone ?
« on: January 03, 2018, 01:26:03 PM »
Hello sonar and towfish people.

I´m about to make my second side scan sonar towfish. The first one is 10 year´s old and I´m still using it and it totally works. It was made from PVC and plastic and the cable only 65 feet long with HB extensions.

But this one that I´m about to make will be made from aluminum pipe and AL fins. I will be using Lowrance (LSS-2) and HB transducers. I want to have the cable to be 100m (300 feet) of CAT6e or CAT7 cable.

But i´m running into little problem about nose cone or I need putting something on the front end of the pipe to close it. The cone I used on my first towfish was made from plastic bottle that I filled with glue. And yes it still works :)

Can some one give me advise what can I do about nose cone ?  I want it to look somewhat professional.

The pipe is 80 mm (3") in diameter, 2,5 mm (0,1 inches) thick and 1,20 m (47 inches) long.

THX

DiveExplorer





Offline Rickard

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Re: DIY Towfish (Lowbird type) Nose cone ?
« Reply #1 on: January 03, 2018, 02:36:02 PM »
Hi,

I use a 50 m cable and my towfish weights 13 kg (28 lb). To get the fish down to 30 m I must move very slowly, less than 1 knot. Therefore, I think you need a very heavy towfish to benefit from 100 m cable. My advice is; make the nose cone of lead.

Rickard

Offline Rüdiger

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Re: DIY Towfish (Lowbird type) Nose cone ?
« Reply #2 on: January 04, 2018, 03:50:48 AM »
Hi

Purely in terms of flow, the Towfish does not need a nose, the smooth, continuous tube can even have a stabilizing effect. But you will need a lot of ballast to be able to tow so deep.

mvh
Rüdiger
Sorry
English is not my first language !
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Offline FishinLite

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Re: DIY Towfish (Lowbird type) Nose cone ?
« Reply #3 on: January 04, 2018, 06:36:56 AM »
You might want to look at model rocket nose cones, like this one

https://www.rocketarium.com/Build/Nose-Cones/3?cPath=19_209&

Offline DiveExplorer

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Re: DIY Towfish (Lowbird type) Nose cone ?
« Reply #4 on: January 04, 2018, 11:07:56 AM »
Yes maybe I'm pushing it way to much to have the cable 100 meters long ( 300 feet ). The towfish would be heavy and making great strain on the line and cable.

Maybe It will be enough to have like 60 to 80 meters long cable (  200 to 260 feet ) , and make depressorwing ?
But I'm not sure if I can make one and I think its difficult make a good depressorwing ?

But there is a great knowledge here and good solid info.  :)

The model rocket nose cone is a clever idea  :D


Offline Rüdiger

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Re: DIY Towfish (Lowbird type) Nose cone ?
« Reply #5 on: January 05, 2018, 02:37:21 AM »
Hi

A towfish does not have to look like a rocket. This form comes from the fact that you had to accommodate the individual piezoelectric elements and oftentimes the electronics. However, since we use a ready-made transducer, a towfish can also look like a fighter jet, quasi a depressorwing only.
Note, however, that a depressorwing means additional strain on the tow cable.

mvh
Rüdiger
Sorry
English is not my first language !
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Offline abraquelebout

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Re: DIY Towfish (Lowbird type) Nose cone ?
« Reply #6 on: January 05, 2018, 09:43:59 AM »
hi and happy new year

for a use in 50 m depht i use this towfish, ila_rendered
wheigt 16 kg of lead,65 m cable.
fin's are surf fin's, strong pvc pipe, nose cone is made with cuted aluminium botle.
one sail boat rail with is chariot for balance point and it's ok.
One of my friend hit wreek in 30m depht last year and the LSS2 ducer is crashed,
now i have for project to re-use this towfish, change the cat 7a câble (he had 3 years) for 70 m cable, take out the HDSI/lls2 and put the méga ducer in place

i'm agrée with rüdiger, rocket is not essential issue, but verry stable towfish must be do

Offline Rüdiger

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Re: DIY Towfish (Lowbird type) Nose cone ?
« Reply #7 on: January 06, 2018, 03:15:47 AM »
Here are ready depressorewings:

https://zwingdownrigger.com/

mvh
Rüdiger
Sorry
English is not my first language !
http://de.groups.yahoo.com/group/SOB-International/

Offline DiveExplorer

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Re: DIY Towfish (Lowbird type) Nose cone ?
« Reply #8 on: January 06, 2018, 05:04:36 AM »
That's intresting, I like this idea.. :)

Yes trying to take the towfish to more depth to scan deeper waters is challenging. I have read from those that have been working in oceanographic and underwater surveys says as a rule of thump that the cable out length need to be three times the water depth. And yes boat speed is a big factor also. Challenging DIY projects like this is fun. All of you that have put so many workhours, thinking and money in to this and share it is remarkable and unselfish. Thumbs up.


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