I'm not a real genius when it comes to physics. If I'm using a 2000lb Warn winch and doubling the pulling power using a snatchblock ( double line pull), do I need one with more than 4000lb. strength? The reason I ask is because I found a good deal on a scissor type block at a local mountain climbing outlet but it's only rated at 3850lbs. I thought my Warn block had a 4000lb. rating when in fact it has a 7000lb. rating. Isn't this overkill for a 2000lb. winch?

Can someone maybe explain how force is exerted while using a double line pull? Does the force on the pulley block increase? Or because of the mechanical advantage it offers the winch, would the actual force on the block decrease? Thanks for any info.

 

Good question, Foreman 4X4. You highlight an important safety consideration; a ****** block's capacity must exceed that of its associated winch.

A ****** block must handle TWICE the line tension applied.

For example, you're stuck. You anchor your ****** block to a strudy oak tree (using a nylon strap as a tree protector), having threaded your winch cable through the ****** block pulley, then back to your quad's bumper.

You activate your winch to its maximum line pull, say 2000 pounds at the reel wrap you're operating with.

The ****** block "sees:" 2000 pounds of pull from the pulley to the winch (there's 2000 pounds of tension in your cable, right?), plus an additional 2000 pounds of pull from the pulley to the front bumper. Lessee, 2000 plus 2000 equals: 4000 pounds total.

Because of "equal and opposite" considerations, your quad "sees:" 2000 pounds extraction force in the line connecting the winch with the ****** block, plus 2000 pounds extraction force in the line segment between the ****** block pullley and the front bumper, or: 4000 pounds total extraction force.

(I won't go into the "Levi Jeans Paradox," where two teams of horses try to separate a pair of Levi's, at this time!)

The ****** block pulley shaft, sheave, bearings, side plates, hook (if you have one; a scissors-type typically does not), all load-bearing components must handle twice the line tension, in this case, a total of 4000 pounds.

Now, is the mountaineering winch block you found adequate for your Warn 2000 application? A qualified answer is necessary.

Some marginal risk is involved in MY answer; you must make your own. I think the mountaineering winch block will work because of the very conservative ratings placed on "man-rated" devices. A large safety margin is built into equipment certified to lift human beings; or, for that matter, for overhead lifting (I think a safety factor of 5 is required for this designation; notice, ATV winches bear notification, "Not For Overhead Lifting").

Also, seldom will you operate your winch at maximum line pull; ESPECIALLY if you use a ****** block--your line pull cannot exceed half the extraction force you require.

If I liked the mountaineering winch block and its price, I might go for it, IF THE PULLEY IS OF SUFFICIENT DIAMETER (you don't want to crimp your wire rope by using too small a pulley); however, given prices I've seen for mountain-climbing equipment, I'd be surprised if it costs less than the AW Direct or ATV Parts Warehouse options provided you in a previous topic.

Anyhow, a ****** block must handle the total stress of twice the line tension. Class dismissed; this will be on your quiz! (Hey, if anyone doesn't realize it, I'm joking with that last remark! Foreman4X4, you asked a perfectly good question and I've tried to answer it as well as I can.)

BTW, some good winching tips and techniques can be found at www.superwinch.com

Tree Farmer

 

Here also are some good deals on ****** blocks that are way over a needed ratting.

 

Treefarmer, thanks for the information. Your post makes " Snatchblock Physics " understandable. I was actually kind of suprised at the prices the mountaineering store offered. The block I was looking at was $24.00 and rated at 17 kilonewtons. I think it would serve the purpose but I'm going to get another Warn block from ATVPARTS. They have them on sale for $37.00 which is the cheapest I've seen for the Warn 7000lb. snatchblock. Thanks to all who responded to my questions, your information has been great.

 

Glad you found the information useful, Foreman4X4! Your choice of the Warn block appears a good one; I don't think you can go wrong there. When its moment comes, that Warn block can be a lifesaver for your father-in-law; you selected a thoughtful gift.

trx430ex, you provide some interesting alternative choices; one of the smaller blocks from that source might be useful for rigging angle pulls.

Good wenching, er, winching, all!

Tree Farmer

 

Spent the weekend riding up at the property, and much of that time winching out 2wd machines with my 'Cat and ****** block. All I can say is, Damn, I'm glad I went with a 4x4 and a winch-I love my 'Cat. Anyway, to get to the point about ****** blocks, the one thing I found from most of the mountaineering suppliers was that they did have good ****** blocks, but as Tree Farmer stated-for man use. Most of those designated for "man use" meant "nylon or cotton rope only", or "not intended for wire rope".

I found many of them that did have suitable weight ratings for decent prices, but after a closer look, determined pulley size to be too small, or not capable of handling wire rope. Most of the winches come with a 3/16" wire rope if I remember correctly. I found the Superwinch ****** block to be a great piece of equipment, for around $30. Again, I'd like to thank Tree Farmer for suggesting it. It is the hook type, with hitch pins, which somebody mentioned in previous posts on another topic to be a hassle, or trouble in the mud and snow. That may be true, but one option here is to just hook it up and leave it there. I was taking it on and off for a while, then ended up just leaving it on the front of the 'Cat full time. It's always there when I need it, and makes those "light" duty pulls even easier for both the 'Cat and the winch. I do carry an extra 100' of matching 3/16" aircraft cable in the box up front for the longer or more difficult pulls as well.

Anyhow, just a thought. Happy winching!

Mike

OH, anybody have any nifty ideas about making a "dead man"? I somehow managed to bury the 'Cat in a huge mudhole with no trees or rocks in sight. Made it impossible to winch out unless I had a anchor of some kind, possibly a 2" square tube with point on one end, and hook on the other? Any ideas? Thanks!