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Commercial Fisheries News
Volume 34 Number 5
January 2007
Cutting loose: Knife grip, shape matters
In the November issue, we discussed the events leading up to and resulting in the drowning from entanglement in trap rope of James Tippett aboard the Virginia Ann. This time, we’ll address the importance of having knives readily available to cut free from an entanglement.
Through our study team’s discussions with lobstermen during the survey of entanglement risks in 1999 and 2000, we collected many suggestions about ways to recover from entanglement in trap rope.
These ideas included taping a sharp knife upside down on oilskins or suspenders, placing a knife inside the boot or alongside the calf, and mounting knives under the rail and on the transom.
Eric deDoes, president of Plante’s Lobster Escape Vents Inc. in Somerville, ME, called CFN after seeing the November article to say he has developed and produced a plastic sheath for the typical red-handled knife used by fishermen.
This sheath is designed to hold the knife tightly so that it can be mounted upside down on oilskin straps or suspenders. This upside-down position is recommended because it allows a fisherman who is caught in rope to pull the knife down out of the sheath safely and not up near the face.
The hand motion that removes the knife from the sheath in a downward stroke also starts the knife moving in the direction toward the rope. The upside-down knife can be removed easily by either right or left hand.
Fishermen can place the readily available red-handled knife or one of similar size in the molded plastic Plante sheath.
Larger grip
Plante’s also offers a knife with a larger handle. The company takes the red-handled knife and over-molds it with orange thermal plastic rubber, helping to ensure better gripping in forceful and/or emergency situations.
The modified grip has a flange on the end that prevents the hand from slipping off the handle while removing the knife from the sheath and while cutting the rope.
I asked Jack Dennerlein, associate professor of ergonomics and safety at the Harvard School of Public Health, to comment on how to choose a handle that might be used in a forceful gripping situation. He offered this reply.
“When thinking about a handle size to optimize grip strength, we need to think about Goldilocks – small is too weak and big is too weak, but the middle (size) is just right,” he said.
Professor Dennerlein explained that the fingers and thumb work together best when the fingers can oppose the thumb or the base of the palm. As a result, the optimal size of a handle depends on two things: the geometry of the tool and the size of the hand.
For linear grips, where two levers are squeezed together such as in a pair of pliers or a staple gun, the optimal size on average is 2-3/4" For round grips such as screwdrivers, most power tools, and knife handles, the optimal diameter is on average 1-5/8".
Tennis anyone?
If you ever bought a tennis racket, you probably tried out various grip sizes. Racket salespersons often use the “rule of thumb” that says, when holding a racket, the thumb should overlap the middle finger to the first knuckle.
When considered in light of Jack Dennerlein’s comments, this racket grip rule seems to satisfy the biomechanics of thumb opposing fingers and nicely approximates the suggested screwdriver handle diameter of 1-5/8".
The take-home lesson is that a too-small or too-large knife handle will not result in optimal grip strength.
Knife placement
Fishermen have varying preferences for knife placement. Some choose inside a boot, but this can be a problem if the trap rope is wrapped around the boot, if the free hand cannot reach the knife, or if the boot falls or is kicked off during the entanglement incident.
Others prefer to put their knife on their belt. This placement can work but only as long as either hand can reach the knife and clothing does not render the knife inaccessible.
The preferred location from a safety standpoint is high on the chest, taped to the suspenders or oilskin/overall straps. A jacket or slicker could reduce the accessibility of the knife but it would probably be easily reachable by either hand.
Lobstermen who have survived an entanglement and others also place knives under the wash rail and in several places inside on the transom. A knife could also be placed on the hauling side of the stern hull. I have seen leather and metal straps as knife holders.
For all knives, whether mounted on person or boat, it’s important to replace them periodically to ensure that a sharp knife is ready when needed.
FISH SAFE:
• For emergency use, choose a knife with a handle that optimizes your grip strength.
• Tape a sheathed knife upside-down on suspenders or oilskin straps.
• Attach knives in multiple places under the wash rail and on the transom.
• Replace all knives periodically to ensure sharpness.
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