6 Apr 2007

Hook Corrosion Rates in Salt Water


I was asked one day “what about all those fish that get away and end up swimming around with a hook in their mouths ?”

Well, undesirable as it is, it does happen and aboard our Gamefishing vessels, we always use hooks made from Duratin when using real baits, bait / lure combinations or in a lot of our wahoo and large marlin lures. Duratin, I explained, in contrast to Stainless Steel, corrodes rapidly in seawater so the hook quickly deteriorates and falls out or is ejected by the fish.

It then occurred to me that I had never actually seen a study of just how long it takes to corrode a hook to the point where it is likely to drop out or be expelled by a fish so I conducted an amateur bench test:

I selected a range of hooks we most commonly use aboard our game boats. I included only one Stainless Steel light gauge (Maruto SS1920) as a comparison to the Duratin hooks.


The following hooks were tested:

HOOK

SIZE

USE

1. Mustad 7766D (Duratin) –

8/0

rigged baits and skirted lures for wahoo

2. Gamakatsu SL12S Saltwater fly big game hooks

10/0

Light tackle rigged baits for sailfish

3. Mustad 39960D (Duratin) Tuna Circle hooks

13/0

rigged baits for marlin & sailfish

4. Maruto SS1920-2X Stainless Steel

6/0

Small to medium skirted lures

5. Gamakatsu Live Bait hooks, High Carbon Steel

6/0

Deepwater jigging / Bottom fishing

6. Mustad 7794BD Treble

1

Small Bibbed Minnows

Each hook was crimped to 100lb monofilament line using a 1.6mm Brass double sleeve and suspended in a container of seawater. Containers were made from cutting the top off plastic drinks bottles, screwing them down to a bench and using the tops to hold the bottoms. The seawater was refreshed daily and the hooks inspected at the same time each day. To test, each hook was removed, held with the shank horizontal, point down and a weight of five pounds was suspended from the bend of the hook near the barb to see if it had weakened sufficiently to bend or break. In the case of the treble, the weight was suspended from only one of the hook bends.


RESULTS

Gamakatsu SL12S – Corrosion started within 1 day

Mustad 7766D – Corrosion started after 2 days

Mustad 7794BD Trebble – Corrosion started after 2 days

Mustad 39960D – Corrosion started after 3 days

Gamakatsu Live Bait – Corrosion started after 4 days


Thereafter up to day 10, apart from some continuing mild surface rust and furring on the Duratin hooks, everything seemed to stabilise and nothing much happened.

On day 10, the Maruto SS1920 Stainless Steel hook finally showed some discolouration and then on day 12, some minor rust spots on the eye and shank.

On day 14, all the hooks were tested with the 5lb weight and all passed with flying colours. There did not appear to be any deterioration in strength in any of the hooks.

After 21 days the hooks were removed, lightly wiped with a cloth, photographed and strength tested.

All hooks showed widespread corrosion except the Gamakatsu Live Bait and the Maruto Stainless Steel hooks which only showed slight corrosion on the hook barb and bend. The Duratin light gage SL12S was the most heavily corroded. A second SL12S that was dipped in salt water each day but suspended in air corroded far more heavily than the one suspended in salt water – presumably because of the increased levels of oxygen in air verses a still container of seawater.

Dispelling My Duratin Myth

The results were a bit of a surprise. The Stainless Steel hooks performed as expected however the Duratin hooks lasted significantly longer that I thought they would. In fact, after 21 days suspended in salt water, despite some surface rust, they were as strong as ever. Even the barbs were still intact.


CONCLUSION

In reality, a hook in a fish’s mouth would have constant movement of seawater over its surface which would accelerate corrosion however the only way for us to test this would be to suspend the hooks in a live well.

I didn’t want all that rust in my live well !

I had observed that a Duratin hook, used at sea and put away without a wash in fresh water is basically useless within days. This led me to believe that, if left in a fish, the hook would deteriorate rapidly and fall out within days.

I was quite wrong. Duratin hooks survive much longer than you think. We will continue to favour Duratin hooks because they do rust out much faster than Stainless Steel hooks however I stand corrected on their rates of corrosion if lost fish. Its not a matter of days, it’s a matter of weeks.

2 comments:

John said...

"Its not a matter of days, it’s a matter of weeks."

or months? or years? who knows? it wasnt tested. noble effort though. i appreciate this work.

john

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