Kite Knifes: Force required to cut line.

Nak · Since 19 May 2005 4280 Posts Camas Site Lackey **CGKA Member**

I hurt my back yesterday, so I'm off the water for a few days. Got bored, so I ran some tests with my force gauge. Pretty damn eye opening. I used two knifes: a standard single bladed hook knife that comes with most harnesses, and a "Captain Hook" double bladed hook knife. Tests were done with a force gauge on a test bed. Q-line and 800 pound spectra were cut.

Here's the results:
SINGLE BLADE HOOK KNIFE
Q-LINE FORCE REQUIRED - 58 POUNDS
800 POUND SPECTRA FORCE REQUIRED - 184 POUNDS!!!!! : Shocked

DOUBLE BLADE HOOK KNIFE
Q-LINE FORCE REQUIRED - 2 POUNDS
800 POUND SPECTRA FORCE REQUIRED - 2.5 POUNDS

Needless to say, I'm ordering a couple of more Captain Hook knifes, and immediately throwing out all of my single blade hook knifes! I don't want to get into a brand thing here, and there are other dual blade hook knifes. But, there ain't no damn way you're going to cut 800 pound lines, in the water, in an emergency, with a single blade hook knife! I thought this was pretty important to pass on right away.

Mark · Tue Jul 22, 08 5:43 pm

Sorry to hear about your back.
Can u post some pics of the two knives used?

Great info Mike!

pdxmonkeyboy · Tue Jul 22, 08 5:44 pm

dude, post some links. I want some of that capt. hook action.

kyle.vh · Since 11 Jul 2007 713 Posts city of angels Addicted

wow, you're so productive when you're board. nice work.
yeah post pics or links to the models.

wylieflyote · Tue Jul 22, 08 5:58 pm

Not pimping... just the first link google came with:
http://www.kitesurfari.com/store/capthook.html

I have one of these, but I'm noticing some corrosion right at the business end after 1 year of mainly salt water fun. I guess it's just one more thing to rinse off at days end.

Nak · Tue Jul 22, 08 6:14 pm

Thanks for the thought on the back Mark. Very Happy

I think I'll be fine in a day or two...

Here's the pics. The Captain Hook knife is available locally at a couple of different shops. I'd pick one up there. Also, NSI sells them. I tested a third knife, also a double blade hook knife. This one comes standard with a certain brand of harness... Anyway, 7 pounds to cut Q-line and 11.5 pounds to cut 800 pound spectra. Very acceptable.

Of the three knives, only the Captain Hook had been in the water. It's seen a few sessions of salt water, and a lot of fresh water. The other two knifes were brand new. The single bladed hook knife showed significant damage to the blade after cutting the spectra. I think the next cut would take a lot more force...

Diggy · Since 25 Nov 2006 342 Posts Gorge to Coast Obsessed

Great information! Thanks.

Yardsale · Since 29 Mar 2005 387 Posts Portlanastan Obsessed

This one works way faster......... Shocked

Kataku2k3 · Since 14 Aug 2005 3753 Posts Los Angeles, CA Videographer

Cool info, Mike! Now we need to see what it takes to cut the nylon fishing net rope... When I lost my kite the other week at Stevenson, my bar caught around one of the buoys downwind. Made my kite do a few huge power loops, but after a couple tows by Ken, I got it untangled. At the time, I was wondering how bad it'd be to cut the rope (though I'd probably never actually do it). Laughing

jsj · Since 11 Sep 2006 83 Posts Hood River

interesting test; did you have any tension on the lines when you did the tests or were they just looped over the knife?

State of stress in the fibers might have an effect - I know when I'm cutting kite line if I don't have a hot razor I'll put the line in tension to make it easier.

$0.02

jsj

EdG · Since 19 Dec 2005 425 Posts Just a Kook that's Obsessed

Nak · Tue Jul 22, 08 8:57 pm

The only tension on the lines was that applied by the knife. In the case of the single bladed knife, that was a LOT of tension! Very Happy

I wanted to test worst case scenario, and the lines you have to cut may not have tension on them.

I just tried rigging the lines under tension, but due to the geometry of my test bench I was unable to actually measure the results. (I could set it up so, but it would be more work than I really want to do. Very Happy

) Results seemed to be similar. Getting the Captain Hook knife anywhere near, like within 6 inches, a kite line under tension resulted in a cut line. Wink

Seriously, it went through the line like it wasn't there. I was unable to cut the 800 pound spectra with the single bladed knife with this setup. The blade was damaged by the previous cut, but that is real world too, I think. If you have to cut one line, you'll probably have to cut more. Also, I was holding the knife instead of having it rigged to a test bench. It's damn hard to apply that much force with the little handle...

The negative to the double bladed hook knifes is that the size of what you can cut is limited. Mark has the right idea carrying a diving knife as well. Thumb's Up

kitezilla · Since 22 Jun 2006 453 Posts gorge Obsessed

Here is a link to a detailed discussion of almost all aspects of kite hook-knives, for those who want more details:

http://www.kiteforum.com/viewtopic.php?f=1&t=2343820&start=0&st=0&sk=t&sd=a&hilit=kite+knife

For those who want the short version...just follow Nak's advice, and get a double bladed hook knife.

Here is a picture of the line cutting test device that I have been using to test and monitor the cutting ability of my own hook-knife, along with 5 other types of hook knives. My test results have been in harmony with that of Nak.

trevorsmith · Since 25 Apr 2005 501 Posts PDX Addicted

Nak · Wed Jul 23, 08 7:28 am

Nak · Wed Jul 23, 08 7:35 am

Kitezilla, very interesting rig you have set up! The orange knife in the picture, which knife is that? The large throat on the hook should allow it to cut pretty large line...

Mark · Wed Jul 23, 08 9:16 am **dive knife**

Here is a pic of the dive knife I use. It has a line cutter "hook" as well as a serrated section. It clips into the sheath and can be removed by pressing both "blue" sides of handle at once.

clips to my harness. Decided to carry it when the fishermen strung a net out from Stevenson....