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-   -   Jack Lines (https://www.sailnet.com/forums/general-discussion-sailing-related/329536-jack-lines.html)

colemj 05-07-2019 09:47 PM

Re: Jack Lines
 
Sheesh, I've got Chef2Sail telling me I don't represent SN boaters in general, and you telling me I don't represent multihull cruisers. Some of us have multihulls for the comfort and space and livability, and not to buzz around at maximum speed in the bay on an nice day. 8-10kts is fast enough on a 6-day passage with 2 aboard. Slower and safer in crappy weather. We will never stuff a bow at 15kts cruising, and I bet you wouldn't either. That was just puffery.

Our cruising boats are reefed from the cockpit. Definitely no big deal, and much safer and easier. Why bring up the off-watch person from a valuable short sleep on a long passage to do something so fundamental and easy?

We don't have jacklines on our hardtop, and see no reason for that. Do monohulls have jacklines on their bimini's? Cabin top has nothing to access - the mast is accessed from the deck, and there is nothing on the boom necessary to access that isn't within inches of the gooseneck. Besides, sitting on the cabin top on a catamaran is relatively safe, and it would take tremendous force to move one there. The boat doesn't heel, doesn't generate high and long force vectors in any direction (lots of high, short vectors), and the cabin top is pretty much the center of rotation and pitch on a catamaran.

Why would I tie a 12' tether to a tree when I only use a 6' one on the boat? Why don't you actually do the math you claim for the conditions you claim? Anyone who has been on a boat will understand that a free drop fall on a 6' tether is not the same as a stumble or slide on a 6' tether - there is friction and counter rotation/inertia/momentum involved in those. You claim physics otherwise, so show your work.

Mark

pdqaltair 05-07-2019 11:21 PM

Re: Jack Lines
 
Quote:

Originally Posted by colemj (Post 2051600614)
Sheesh, I've got Chef2Sail telling me I don't represent SN boaters in general, and you telling me I don't represent multihull cruisers. Some of us have multihulls for the comfort and space and livability, and not to buzz around at maximum speed in the bay on an nice day. 8-10kts is fast enough on a 6-day passage with 2 aboard. Slower and safer in crappy weather. We will never stuff a bow at 15kts cruising, and I bet you wouldn't either. That was just puffery.

No it was not. I didn't claim I was typical either.

Our cruising boats are reefed from the cockpit. Definitely no big deal, and much safer and easier. Why bring up the off-watch person from a valuable short sleep on a long passage to do something so fundamental and easy?

Didn't say I brought some one up. I also see no reason to limit a thread to a single style of sailing. Sometimes I sail slow and easy. Sometimes I do not.

The other obvious corollary to this line of reasoning is that jacklines are not needed at all, since everythin can be managed from the cockpit. There is some logic to that. Or PFDs. And most often, I don't use either.


We don't have jacklines on our hardtop, and see no reason for that. Do monohulls have jacklines on their bimini's? Cabin top has nothing to access - the mast is accessed from the deck, and there is nothing on the boom necessary to access that isn't within inches of the gooseneck. Besides, sitting on the cabin top on a catamaran is relatively safe, and it would take tremendous force to move one there. The boat doesn't heel, doesn't generate high and long force vectors in any direction (lots of high, short vectors), and the cabin top is pretty much the center of rotation and pitch on a catamaran.

Why would I tie a 12' tether to a tree when I only use a 6' one on the boat?

I didn't say a 12' tether. I said 12 feet of slack (your tether is on the center line; go 6' to windward and then stumble 6' past it = 12 feet. This is the worst case. But if you can do this with 6' of slack without bruises I'd be surprised, since I cannot.

Why don't you actually do the math you claim for the conditions you claim? Anyone who has been on a boat will understand that a free drop fall on a 6' tether is not the same as a stumble or slide on a 6' tether - there is friction and counter rotation/inertia/momentum involved in those. You claim physics otherwise, so show your work.

A 3' fall over the rail = 3x170#=610 ft-pounds.
A 3' fall takes about 0.4 seconds and reaches a final speed of about 8 knots.
I'm betting a fall across the deck, including a downhill stumble, can easily reach 8 knots. Most joggers average about 7 knots.

Adjust the assumptions as you see fit. The conclusion is only that they are comparable and that there is nothing magic about a vertical drop.


Mark

I'm not being critical. I'm not sayin' this is going to happen on your boat. I'm sayin' these are the forces that the World Sailing and ISO standards are based upon; catching a 6' drop of a grown man in wet gear. It is described in the ISO standard.

dadio917 05-08-2019 12:45 AM

Re: Jack Lines
 
We use webbing secured to a pad eye maybe (guessing) 6 ft. aft from the tip of our 2' sprit and pad eyes on each side just at the front of the cockpit. Can easily enter and exit the cockpit tied in. Cockpit has two pad eyes. Doesn't take long to put out and take in so we only have them out on passages. Always rinse them wit fresh water and dry when done. The webing does get slippery if stepped on.

SanderO 05-08-2019 10:20 AM

Re: Jack Lines
 
How does one secure 1" dacron webbing to a pad eye?

Opinions please:

Use one length of dacron webbing secured to aft pad eye at the starboard outside forward end of cockpit coaming.... run to the starboard bow cleat, thru and around and then across for deck to the port bow cleat, run thru and around and then back the an aft pad eye at the port outside forward end of cockpit coaming. Obviously a failure would render both lines useless as jack lines at least temporarily.

Minnewaska 05-08-2019 10:32 AM

Re: Jack Lines
 
truckers hitch so tension could be applied?

Jeff_H 05-08-2019 10:36 AM

Re: Jack Lines
 
Quote:

Originally Posted by SanderO (Post 2051600704)
How does one secure 1" dacron webbing to a pad eye?

Opinions please:

I would assume that you add an eye to the 1" webbing by having the eye professionally sown by a company who is certified to do that kind of structural sewing. Then you shackle the eye to a hardpoint. But that is part of why I like the dyneema line inside of a piece of webbing. The dyneema can be spliced with an eye that achieves most of its original strength. The webbing provided UV protection, and slip risk reduction. The webbing would need to stitched over the dyneema at the splices but that is okay in my mind since the webbing is not structural.

Jeff

SanderO 05-08-2019 11:17 AM

Re: Jack Lines
 
I am wondering if I can't use 2 D rings which tighten when the webbing is tension... I have something like this to tension my dodger bows. Getting rings sewn professionally is a bit of a pain but doable.

pdqaltair 05-08-2019 03:38 PM

Re: Jack Lines
 
Quote:

Originally Posted by SanderO (Post 2051600724)
I am wondering if I can't use 2 D rings which tighten when the webbing is tension... I have something like this to tension my dodger bows. Getting rings sewn professionally is a bit of a pain but doable.

You would have to be sure the buckle system would hold 5000 pounds. Although this can be done with buckles, I belive rings slip at MUCH lower values. it would require testing.

Both Practical Sailor and Sailrite have published sewing test results for DIY. The methods are specific but doable.

pdqaltair 05-08-2019 03:42 PM

Re: Jack Lines
 
Quote:

Originally Posted by SanderO (Post 2051600704)
How does one secure 1" dacron webbing to a pad eye?

Opinions please:

Use one length of dacron webbing secured to aft pad eye at the starboard outside forward end of cockpit coaming.... run to the starboard bow cleat, thru and around and then across for deck to the port bow cleat, run thru and around and then back the an aft pad eye at the port outside forward end of cockpit coaming. Obviously a failure would render both lines useless as jack lines at least temporarily.

One problem with a single length of webbing is that you double the stretch. Polyester is already arguably too stretchy (it's right on the edge for larger boats).

Additionally:
* If you have to cut one loose, now you have none.
* If you damage one (chafe?) both must be replaced.

pdqaltair 05-08-2019 03:48 PM

Re: Jack Lines
 
Quote:

Originally Posted by Jeff_H (Post 2051600716)
I would assume that you add an eye to the 1" webbing by having the eye professionally sown by a company who is certified to do that kind of structural sewing....
Jeff

Does this exist? In a practical sense, not really.

In a former life I manufactured climbing gear, and generally, we are talking self-certifications though ISO (6 sigma break testing program). That's it and many are not. Realistically, a sailmaker will do it. You will also need to source the correct webbing, which is a problem.

You are right that the Dyneema approach is probably best for DIYs. Fewer question marks and a solid finished product.


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