Topic: DIY tow fish and archéology, a prehistoric dugout

[abraquelebout]

ther's a few week, one of my friend call me to goes on a river whith towed fish

and whe find this : a prehistoric dugout a dive on it confirm this thing !!!!
i join picture,  800 khz at 3 meter under grund
yes , huminbird is very performant

[Jolly Roger]

Cool!

Do you know what did they dig out there?


Regards / Harry

[Rickard]

Well done!

I think dugout is a logboat. Is that what you mean Abra?

Rickard

[abraquelebout]

yes, a logboat 
i find 2 others on a side scan view in 200 m of river in same portion
one is sure because one of my friends dive on it
and there's another wreek but i don't know what is it
i think a gabare 15 m x 5 m probably recent (1800 - 1900)

[Jolly Roger]

Now I understand Abra,
and that makes it even better! Congratulations!

The second target is also interesting indeed. Let us know what you find out after the dive.

I found something similar with my fish, but only after I reviewed some recordings with Hummviewer:





I'm not sure what it is, because I wasn't diving there. The target is in 42 meters and not far away from another interesting contact. I might be wrong, but the dots and lines look to me like the ribs and planks of a silted in wreck.

I'll try to get the guys from the water police with their brandnew ROV there and let them take a look at it....

Best regards and wishes from Germany

Harry

[abraquelebout]

good picture,
it may be a sunken wood boat
after the finding, the archéologist of the SRA (régional service of archéology ) paid me DR DEPHT !!!
good idea
the same day, 2 picture
a small recent boat (4,5 m) and a nother logboat

[Jolly Roger]

Wow Abra,
That's amazing!! What type of ground do you have there? Sandy or muddy? Can you give us more details about the boats? Length, estimated age etc. would be interesting.

And what a nice move of your archaeologists to sponsor you Dr. Depth. That's what I would call a "win win situation"  .

Best wishes / Harry

[abraquelebout]

in this part of river there is sand and mund
the logboat are so ancient than when whe tuch it,it grave in dust
one of my friend find a galo-roman wreek, may be 200 after jc
and on another part of this river whe find vicking jewelry  and arms
i dive on my hobbies with scientist and archeologist it's interresting.
the wreek on my picture are small, 4,50 m x 1,40 for recent, may be 15mx5 m for gabarre
4 at 5 m x 0,8 or 0,9 m for the logboat
whe find much dishes, pottery,earthenware
the romans are present in past on this part of river (near Saintes in french and rochefort)
there's a large part of history near home, Richelieu, La rochelle, colbert etc for recent people
more recent wreek in sea, cargos, war ship, submarine, planes...
deeply the beautifull day.

[Kimi]

Jeah .. to have the transducer in in the boat, and not in a towfish, can be good sometimes. Especially when looking for something in shallow waters.

They have been looking here in Finland for a Dutsch ship called De Catrine, also called the silverbrigg. Late 10 years even the navy, and some pro wreckhunters have search for it, in hope to find the silver that should be founded in the wreck.

I had some good ideas about where the bottom of the wreck could be found, so I dived and scanned the seabottom around a rocky and nasty reef. When I was looking for a good place to anchor the boat, I suddenly saw something on the screen! Holly moses.. there was a wreck up on the reef in very shallow water, (10ft) . The only way to find the wreck was to navigate over the reef. I suppose no other wreckhunters had ewer tough the the wreck could still be up on the reef, after 220 years. Usually no wreck would lay on a rock or reef over the first winter. The ice would sooner or later break them in pieces, and push them down in deeper water.    Good for me! 

The waves on the reef is the reason to the poor quality of the screenshot.

No.. I haven found any silver.. yet!

[sonar2000]

Good pictures, Kimi... You are right in that a tow fish is not as good as the mounted transducer in the shallower water.  I see that the transducer was bouncing a bit so must have had some waves on the reef.  Keep us up todate on findings and great work..  Chuck

[abraquelebout]

yes
if there's no depht, the hull mounting is good, but whith a towfish you can reduce noise and movment of waves.
on the river for my picture there's 8 or 10 m
a towfish permit past the transducer at 3 meter than ground and more details can be find.
if the tranducer was hull mouted, i'm sure than i can't find the logboat,
there's 2 years whe find a wreek in 3 meter depht.
the wreek jup the reef and sunk in large hole, nobody think that: a 40 m wreek in 3 meter depht at 300 meter than beach !!
whe find the bell last year
i work whith 60 m cable, and it' true 50 m on small boat take more places but a small movment of boat may be compensate
for a good picture i think there's 3 important parameter
a constant speed (2knt may be good), no movment on boat or towfish, and the position of target / tranducer

[Jolly Roger]

Good job Kimi, congratulations!!

Maybe I should take a look at my target first before I call someone else, hehe....

I agree with abra on the fish: Less noise, less movement and closer to the ground makes a good chance to see what others have missed. In shallow water (up to 5 meters) it's a different story. The transom mounted transducer makes it easier to navigate and handle the boat. Dragging the fish behind might end in tears if the fish gets caught and ripped away.

Keep us posted Kimi. I guess most of us would show up for a victory party  .


Best wishes and good luck!

Harry

[Kimi]

yes
if there's no depht, the hull mounting is good, but with a towfish you can reduce noise and movement of waves.

Agree whit that! I plan to build my own towfish for next summer. Just have see what you guys are doing first! 

Keep us posted Kimi. I guess most of us would show up for a victory party

Well.. if I hit something "big" you can come and visit me in prison. According to federal laws in Finland, all wrecks older than 100 years, belongs to the marine museum. = state!

But as we use to say "the kingdom is wide, an the emperor is far away". Or "hit, dig and keep you mouth shut! 

Kimi..

[Kimi]

One question to you guys that are "playing"  whit a towfish.

Can you operate the boat and towfish all alone, or do you need a second person to handle the cable?? 

[abraquelebout]

hi  kimi
it's depend, if im alone i make a passage at 1 or 3 m depht at 455 khz to see if there's no trees or thinks to crash the tow fish, i take  an image of the chosen area, and after i make few passage at 3 meter than ground at 800 khz to see details
if there' an obstacle i chose dehpt to avoid it.
when whe are two or three reliable people, one make direction, one scaning,and the other the navigation (gps to computer mapping)
but you can work alone
good luck with the autority
in france whe must declare all thing whe find in sea to the governement
i work with the agrément of "direction recherche archeologie sous marines"
whe put point in area and they give search autorisation
it make lot of papers but if the coast guard came all thing is ok but whe don't have right to  take of any thing

[Jolly Roger]

You've propably read my post about my fish Kimi.

I'm always alone when I'm out scanning. No problem when I'm out without the fish, but when I have the fish deployed, I sometimes wished I would have a copilot to take care of it. Most of the time it's no big deal to drag the fish, but if the water depth is changing a second man on board would be a great help.
Luckily the bottom of the lower part of Lake Constance is very challenging, because their are no reefs or sharp drop offs.

If you want to build a fish Kimi, don't make it too heavy. My fish weighs around 25 kg and that's way to heavy to be handled without a winch. I'll make a lighter one from PVC tubes and will also build a depressor wing to get the fish on depth in winter.

The weight is not only a handling issue. Safety is also concerned and this advice came from Rickard. Getting caught by the cable and pulled over board isn't a party foul if you have to keep afloat with 25 kg extra weight.

Plastikboot from Munich uses a downrigger to keep his fish on the desired depth. I haven't looked into this idea closely, but I think it's quite good, especially if you're alone on the boat.

Keep us posted

Harry

[Kimi]

n france whe must declare all thing whe find in sea to the governement
i work with the agrément of "direction recherche archeologie sous marines"
whe put point in area and they give search autorisation
it make lot of papers but if the coast guard came all thing is ok but whe don't have right to  take of any thing

Quite the same here! However, the maritime museum makes a good job, and there are lots of nice people working there, but also a few xxxholes. That's the reason why most of the "older" wreckdivers prefer to make their own investigations. The bad thing is that a lot of valuable information stays inside some very small groups. But someday i think we can work together again.

You've propably read my post about my fish Kimi.
Yeps.. looks like a "heavyduty" militarydesign 

If you want to build a fish Kimi, don't make it too heavy. My fish weighs around 25 kg and that's way to heavy to be handled without a winch. I'll make a lighter one from PVC tubes and will also build a depressor wing to get the fish on depth in winter.

Something like that was what I also had in mind.
Have seen some pictures of some lightweight constructions whit very thin towingcable. And that's something I would like to start with (lowcost).  I cant see any other problems whit a lightweight construction that it can be hard to get it down to a deep of 20-30 meters?? The other problem there might be is that the towfish starts to behave like a swimming fish? Hope that it can be avoided whit a long thin tail whit large fins?

Kimi..

[Jolly Roger]

Your concerns about the behaviour of a light fish was on my mind when I built mine. Therefore I thought the fish has to be heavy.
During the construction I had my first doubts about the handling abilities and they proved to be right. The fish works fine, but the handling is the real problem.
A winch would help a lot what the weight concerns, but then I will have a problem with my cable setup. The transducer cable isn't designed to withstand the rough handling for long. If it gets squeezed between the tow cable and the winch head, I think i will have a breakage within the transducer cable. I would have to have a second man on board to operate the winch AND reel in the transducer cable separately at the same time.

There are heavy duty cables on the market, but these cost way too much for a low budget fish.

So I think the solution is a light weight fish with a depressor wing.

For the stability in the water I think the longer the fish the more stability is has and wont "run away" to the sides. The hook up point of the fish is also critical. I guess the further forward the better. The trick is propably to find the right compromise between axial stability and position of the fish in the water while dragging.

Another thing: I hope Humminbird will listen to our pleads and comes out with a tow fish transducer.......

Let's keep our fingers crossed!

Harry

[Humminbird_Greg]

“I hope Humminbird will listen to our pleads and comes out with a tow fish transducer”
No word on that but than I haven’t given up yet!

On the stability of the towfish: if you used a PVC pipe and did not enclose the nose of it wouldn’t that work like a tail fin as the PVC pipe is straight?