Finding a lost propeller with Echo sounder ?

C-NUMB · 24 July 2012, 04:52

A friend of mine lost a relatively expensive SS propeller (roundabout 1200 euros), from a outboard. Its a small prop about 15 inch diam. The search area is relatively narrow(within 200 x 200 meters), depth is less than 20 m. The water is not clear so having a diver searching it
without accurate position would be a huge job.

But, how about using a echo sounder to locate it first? What type of kit(leisure level...) would be needed to find such a small piece, or is it a totally mad idea?

I think the sea bed is solid rock with a unknown layer (guess pretty thick) of sediment on top

captnjack · 24 July 2012, 05:23

You won't see it with any normal depth sounder. You need a magentometer (which will vastly exceed the value of the prop unfortunately)

I had friends who found a hydroplane prop which came off when the shaft broke at 150mph. They don't go far, you need a precise location when it fell off though.

ncp · 24 July 2012, 06:21

Captjack, what about downscan or sidescan from Hummingbird/Lowrance/Simrad?

Pikey Dave · 24 July 2012, 08:08

I have Raymarine HD Sonar on BP & can easily see lobster pots, small rocks & wreck debris. It depends greatly on the nature of the bottom. If it's firm sand or flat rock you would pick it up with a high end setup, if it's soft mud or weed, forget it. Even if you do see a "lump" you won't be able to differentiate between metal & a rock or any other crap down there, it might mean a lot of "bounces" for the diver. If it was my prop & I had the time & inclination, I'd be diving & doing circular rope searches. Find a diver with a rebreather, at 20m he should be good for 3 hours

Dhf · 24 July 2012, 10:04

Without Navy equipment it's a bit like this......

The Velvelettes - Needle In A Haystack - YouTube

I take it insurance is out the question?

Mollers · 24 July 2012, 10:12

Had a mildly comical search mission yesterday trying to find a mooring stone that hadn't been used for 10yrs. A pal was paddling the 2.3 with one oar, I was hanging over the transom with my face in the oggin directing him through a snorkel. The viz in the river wasn't good. After many passes over where we knew the stone to be, Lee heard a splash, looked around and I'd gone. A few secs later I emerged, chest deep standing on the thing.

jyasaki · 24 July 2012, 15:10

Drop a weighted down line in the center or the area, and have the diver use a reel to spiral out from there. Doubt you'll find it with any kind of consumer electronics commonly on boats.

jky

captnjack · 24 July 2012, 15:47

Quote:

Originally Posted by ncp

Captjack, what about downscan or sidescan from Hummingbird/Lowrance/Simrad?

In mud, no way. Even the 800 hz HDS system doesn't have enough resolution. If the bottom were hard packed sand, maybe there'd be enough of a signal to see it. Assuming it wasn't lumpy with rocks around it. The object needs to be big enough that the wavelength of the transducer signal has not spread out (as it spreads from the cone of projection) to be longer than the size of the object.

With sidescan you are looking for "shadows" and a prop on the bottom is horrible at casting a clear shadow. A shoebox would be easier to see since its got a hard edge. The prop doesn't have a hard straight edge to cast a good shadow.

Channel Ribs · 24 July 2012, 16:02

It is possible, been there and got the t shirt.

You need to be a very experienced sonar operator and you need a good resolution, but other than that you just need patience.

captnjack · 24 July 2012, 16:14

Quote:

Originally Posted by Channel Ribs

It is possible, been there and got the t shirt.

You need to be a very experienced sonar operator and you need a good resolution, but other than that you just need patience.

Very flat water is also required

As a diver I could search the 200m x 200m area with line faster than I could find it any other way.

wellhouse · 24 July 2012, 16:17

Quote:

Originally Posted by C-NUMB

A friend of mine lost a relatively expensive SS propeller (roundabout 1200 euros), from a outboard. Its a small prop about 15 inch diam. The search area is relatively narrow(within 200 x 200 meters), depth is less than 20 m. The water is not clear so having a diver searching it
without accurate position would be a huge job.

But, how about using a echo sounder to locate it first? What type of kit(leisure level...) would be needed to find such a small piece, or is it a totally mad idea?

I think the sea bed is solid rock with a unknown layer (guess pretty thick) of sediment on top

have you tried contacting your local dive club, most are obliging and it will give them something to do for a couple of hours? Be prepared for the bar bill!

C-NUMB · 24 July 2012, 18:40

Good comments, seams to be fifty fifty..... In the past my first ever outboard (johnson 2hp) dropped from the transom during towage. That one we tried to dive but in vain, difficult circumstances regarding visibility and sea bed.

Sounds like diving is more effective than sonar, was just thinking how these new downscan fish finders would be up to such task and to make a preliminary positioning before diving.

On leisure boats haven't used much sonar, previous one was a Shakespeare with the flashing led...

, but will install something on the SR this summer.

Diving club sound like a good idea unless we can borrow a boat with top notch sonar.

Maximus · 24 July 2012, 19:22

Quote:

Originally Posted by wellhouse

have you tried contacting your local dive club, most are obliging and it will give them something to do for a couple of hours? Be prepared for the bar bill!

I agree its the way to go, and your best bet, they'll see it as a good training exercise,and you could save a nice few Euro's...provideing ofcourse they're not all Rampant Alkies

As for spotting it on Sonar ect, unless it fell off thr QE2! forget it.

Boatnomad · 24 July 2012, 21:52

This "might" be a help?

Nauticalia Trade Sales : Sea Searcher Recovery Magnet

A1an · 24 July 2012, 21:59

Quote:

Originally Posted by Boatnomad

This "might" be a help?

Nauticalia Trade Sales : Sea Searcher Recovery Magnet

On stainless?

SPR · 24 July 2012, 22:06

works in cheap s/s lol

s.

Pikey Dave · 25 July 2012, 06:32

Quote:

Originally Posted by SPR

works in cheap s/s lol

s.

Some very expensive stainless is magnetic

think expensive kitchen knives on magnetic racks. It's something to do with the crystaline stucture of the steel, I think, probably wrong

wellhouse · 25 July 2012, 07:49

Quote:

Originally Posted by A1an

On stainless?

Stainless steels are a very broad group of metals. The name was adopted as a generic term for steel alloys with a minimum of 10.5% chromium. The chromium gives the steel its 'stainless' properties - essentially corrosion resistance. On the surface of the metal, a very thin chromium-rich oxide layer is formed which is inert - i.e. it prevents the steel from rusting. The advantage of stainless steels over plated steels is that, if scratched or damaged, the steel will 'self-repair' as a new oxide layer is formed. In plated steels, scratches in the plate will often lead to corrosion of the steel underneath.

In general, the higher the proportion of chromium, the stronger the corrosion resistance of the steel. In addition to chromium, other metals are added to give the steel particular properties such as strength and malleability. Specifically nickel is used to strengthen the oxide layer.

As for whether they are magnetic, the answer is that it depends. There are several families of stainless steels with different physical properties. A basic stainless steel has a 'ferritic' structure and is magnetic. These are formed from the addition of chromium and can be hardened through the addition of carbon (making them 'martensitic') and are often used in cutlery. However, the most common stainless steels are 'austenitic' - these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the steel and makes it non-magnetic.

So the answer is yes/maybe, the magnetic properties of stainless steel are very dependent on the elements added into the alloy, and specifically the addition of nickel can change the structure from magnetic to non-magnetic.

The following company website has a useful high-level definition of the broad stainless steel categories. parkrow.org

THE ANSWER IS MAYBE !!!?

tonto · 25 July 2012, 07:59

Quote:

Originally Posted by wellhouse

Stainless steels are a very broad group of metals. The name was adopted as a generic term for steel alloys with a minimum of 10.5% chromium. The chromium gives the steel its 'stainless' properties - essentially corrosion resistance. On the surface of the metal, a very thin chromium-rich oxide layer is formed which is inert - i.e. it prevents the steel from rusting. The advantage of stainless steels over plated steels is that, if scratched or damaged, the steel will 'self-repair' as a new oxide layer is formed. In plated steels, scratches in the plate will often lead to corrosion of the steel underneath.

In general, the higher the proportion of chromium, the stronger the corrosion resistance of the steel. In addition to chromium, other metals are added to give the steel particular properties such as strength and malleability. Specifically nickel is used to strengthen the oxide layer.

As for whether they are magnetic, the answer is that it depends. There are several families of stainless steels with different physical properties. A basic stainless steel has a 'ferritic' structure and is magnetic. These are formed from the addition of chromium and can be hardened through the addition of carbon (making them 'martensitic') and are often used in cutlery. However, the most common stainless steels are 'austenitic' - these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the steel and makes it non-magnetic.

So the answer is yes/maybe, the magnetic properties of stainless steel are very dependent on the elements added into the alloy, and specifically the addition of nickel can change the structure from magnetic to non-magnetic.

The following company website has a useful high-level definition of the broad stainless steel categories. parkrow.org

THE ANSWER IS MAYBE !!!?

Good! Now i know!

m chappelow · 25 July 2012, 22:44

Downside with the sea searcher magnet is that its just about one directional and it won't draw itself to a nearby object unless it's just about dropped onto it , I used to keep one on the fishing boat if I needed to pick up the mooring chain ,
having said that if it gets a good flat surface to stick to it takes some getting off unless you start doing a load of twisting .
Only last week we were messing about with one and it supported my mates weight 14 stone from a steel beam .
Just tryed mine out using various stainless oddments from the dogs bowl right through to 30 mm bar and it wouldent stick to any of it .

funny thing is in the advert for it when they first came out it says ( recover lost outboard engines ) well to say most outboards legs are Aluminium and the only steel part would be the flywheel encased with a plastic cowl , that is unless it's an old Seagull and even then it would be the flywheel that it could stick to as everything else is stainless, Aluminium or Brass .
Oh and keep it away from computer monitors as I have just sucked all the display to one corner of the screen with it .