How to get MOB back into an X????

[Frank C]

Moe,
I absolutely agree that the length of the vang tackle is a problem, and I knew as I wrote it that my "collapse span" was a fallacy ... just figured it was already complicated enough to visualize the lifting potential. One easy solution is to reduce purchase ... but if we agree on the potential, then it's valuable or important enough to work on solving those problems. Later for that. (Realistically, part of this answer is that the lift probably needs be only 30 inches to get MOB's "cheeks" over the transom).

Regarding backstay sag, it's essentially nil. The MOB will pull the backstay taut as he's scraped across the transom (only half comical). There's surely no appreciable bend in the mast.

Regarding the calculation of compound purchase ... this stuff always confuses me, and I think I must change my earlier 12:1 estimate. Let's make some assumptions, just for grins.

Assume the triangle is an equilateral six feet .... I think that's close to accurate. Also assume that the backstay tabs are 3 feet above water line, so we've placed the top-center block at ~8 feet, which is plenty of height.

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IIRC, height of 'this' triangle is the sq.root of 
(6 squared) minus (3 squared)   =  about 5 feet.

Now, just to make the math easy, assume my vang tackle spans 6' at the starboard, plus three other legs of that same length - 24' total (was this clear in earlier description?). That is, a 6' line dead-ended at starboard quarter, up to the center-block, and two more lines of same length from center block to port quarter .... plus the 6' vang down to starboard. Assume that I could completely collapse the vang a perfect 6' (for easy math). That means I've shortened the starboard side by 3 feet and the portside by 3 feet, but the lift is only 1.5 feet.

My tackle was six feet long, and included 4 strings. So by collapsing it I've pulled 24 feet through the tackle in order to erase six feet from the stb side. Those six feet (erased) are now allocated over four reaches to aft quarters ... meaning each of the four lines are now shorter by 1.5 feet. (Take 4 lines of six feet, eliminate one and reallocate, now there are 4 lines totaling 18 feet, or 4.5' in each line).

The total pull of 24 tackle-feet thru the vang actually delivered only 1.5 feet of lift - I think that it's actually 16:1.
Maybe? ... maybe not? I think maybe yes.

[Moe]

Nope... 8:1. The 6' taken up by the 4:1 vang will be seen as a 3' shortening (lift) on the port side where it's 2:1. The distance between the double block and the starboard tang isn't changing (if you assume the double block doesn't sag) and doesn't contribute to purchase.

[Frank C]

Moe,
No, no, no. Another take ... easier approach (EXAMPLE TWO).

If my backstay tackle is pulling on BOTH lines - across the double block at the top of the triangle - pulling on both of them simultaneously -

in that case, collapsing the tackle by 5 feet (quite realistic) delivers a lift of 2.5 feet across the port transom with purchase of 8:1. The tackle is 4:1 and the bottom-to-top blocks deliver 2:1.

On EDIT: (simplifying the cascade example) a 4:1 tackle pulling a single line thru a top-centered single block delivers 8:1 purchase. A five-foot tackle will lift MOB 30 inches. A seven-foot tackle can lift a MOB 42 inches. For either lift ....

... a 200-pound MOB would require 25 lbs. of pulling (maybe 30# allowing for friction, etc,). If the Mate cannot apply 30 pounds to the tackle tail, she can always lead it to the starboard winch. That's less than ideal, but better than freezing, or becoming shark lunch!

On EDIT: Since there's no necessity for the port side to be twin lines, a single six-foot line, just exits a single block at top-center and attaches to the top shackle of a six-foot vang-tackle. Collapsing this tackle by ~ 5 feet delivers a 30-inch lift at 8:1 purchase. This tackle might easily be expanded to 6:1, so a diminutive mate could easily lift a 200-pound MOB with 12:1. (200 divided by 12 ~ 18 pulling pounds). Except that I've already invested in the double blocks, I'd now use triples for a cascaded 12:1. Lift is still determined by length of the starboard leg of the triangle.

Problem: the six-foot lifting line does not reach the water, and the tackle can't squeeze thru the top-center block. Solve this with a 3-foot pendant to the MOB's chest harness.

[Moe]

Okay... I think you're beginning to get it... it isn't 12:1 or 16:1 as you originally though. As I said, it's 8:1 and you're right... a 25 lb pull should lift a 200 lb man. But the 4' lift that was feasible is now down from 4' to 3' to 2.5'.

[Frank C]

Let's make sure I have this right...

The shackle of the double block is attached to the backstay that runs to the top of the mast. - YES

There's a line that runs from the starboard tang up and over one sheave of the double block - TRUE

down around the sheave of a block who's shackle is nornally attached to the port side tang - TRUE
(but now with a new carabiner btw block & tang)

back up and over the other sheave of the double block - TRUE

down to the shackle of the upper fiddle block of the 4:1 vang - TRUE
(of course it's only 3 inches btw top of vang & center-upper block, a surmountable problem)

the shackle of the lower fiddle block of the 4:1 vang is attached to the tang on the starboard side. - YES

to use this setup to lift a COB, you want to disconnect the block normally attached to the port tang and attach it to the COB -
YES for the original example.

I contend that this is a 16:1 system. Not only is a 16:1 system too much for my backstay (my current configuration), it's too much for a practical MOB lift. While nice to have that amount of purchase, it cannot deliver a 30 inch lift unless the apex is moved too high to reach (for tackle maintenance). My second example, now edited just above, is much better.

[Moe]

I agree it's 16:1 for bending the mast, but only half that for lifting a COB.. and I think we both agree on that.

[richandlori]

Math...smath...so what you are telling me is that if you have an unresponsive MOB on a Mac you should jsut keep sailing off because you can't get them back on the boat over the port or starboard side? Don't buy it.

The next time I am at the boat with the admiral, we will be doing some test with me in the water and her on the boat. Theory is theory, but this is important enough to give it some pratice.

Rich

[Frank C]

... Don't buy it.
The next time I am at the boat with the admiral, we will be doing some test with me in the water and her on the boat. Theory is theory, but this is important enough to give it some pratice. Rich

I scrounged around and found some pix of my backstay, looking to be closer to 7+ feet tall (following post). I can rig this adjustable backstay (& hoist) using cascade of either 8:1 or 16:1, but they are two different rigs. If I'm wrong I'll admit it, but I'm still unconvinced, so that might be for a different thread. Meanwhile, Moe & I can agree to disagree on cascading purchase.

More importantly Rich, I agree with you that this topic IS VERY important, so I stood at the mirror and did some measuring. Take issue with my assumptions if you will ... but here they are:

• My MOB Assumptions
  - MOB has a harness "D" ring at breastbone, which is at water surface
  - MOB must be lifted so butt-cheeks are "at or above" transom or gunnel
  - MOB measures 30" from crotch to breastbone
  - Transom is 8" above waterline, requiring 38" of dead lift across the transom
  - Gunnel is ~42" above waterline, less 6" of heel, requiring 66" of dead lift to clear gunnel
  (add 12" more to clear the cabintop - are all lifelines down?!)

Some more observations too, many of them already cited in the early thread. You or I could do all this; in fact, you or I might manage to hook under her armpits and brute lift an Admiral up to the gunnel, but I'd bet that few Admirals could even rig this list?

• * Rig at boom's end a 6-foot lifting tackle at 8:1 (plus tail) .... about the length of the Genny sheet ... but of course, you want this tackle already rove & hanging at-the-ready.
  
  * Better yet, rig a 4:1 tackle to use hand-over-hand, or tail to the sheet winch if necessary. And exactly how should it tail to the sheet winch? ... a lot of rigging.
  
  * Now use jib halyard to end-position and suport the boom at 6' over water.
  
  * If you were sailing, she de-rigged the sail and then re-rigged for this lifting.
  
  * Or, one might just rig the jib halyard thru boom-end and down for the lift, routing it to a sheet winch (is length adequate?). If the lifting line goes upmast, downmast, then crosses the deck to a winch, you need amply strong blocks at top and at base of mast.
  
  * If the boom rises during the lift, it means she must lift that much more so you'll clear the cabintop instead of cockpit gunnel. We hope the lifelines are dropped both places ...
  
  * Need a method to cleat-off the halyard and then swing boom & MOB toward the gunnel ... unless the pitching hull swings him - OUCH!

Would anyone have the time, awareness or patience to do half of that!? Seems unlikely. I suppose the 26M transom is too narrow ??? So, I don't have an idea of what to suggest. But for my 26X, as follows next ...

[Frank C]

MOB Hoist & Recovery over 26X Transom

For a 26X, the backstay hoist suddenly makes so much sense, even though my available transom clearance (width) is limited:

• * Granting that it requires some forethought when designing the adjustable backstay ...
  * Requires only about a 3-foot hoist (explained in preceding post).
  * Hoist is a permanent fixture in the rigging, always rigged, always ready.
  * Can help an able-MOB who is weak, clip-on to "assist" up the ladder.
  * Brief EMERGENCY Instructions: "Unclip port tang, Clip to harness, PULL starboard tail!"
  

Docked at Ayala Cove, Angel Island, backdrop of Tiburon Peninsula; also showing
halyard turning block, custom deck organizer, Garhauer RV and adjustable backstay (at-the-ready).

Backstay tackle is a single line rove into three ~7-foot legs,
stb up, down to port & back up, plus a 7-foot vang tackle, down to stb.

Lazy Bay Sunday, wind @ 10 knots, backdrop SW tip of Angel Island with distant Berkeley Circle;
MOB recovery hoist clearly rigged and ready, operates from port or Stb, also from motor deck,
potentially even when hove-to.

While I always believed the transom is the best 26X recovery method, I'm now even more convinced. The adjustable backstay, with some minor added mods, possibly makes feasible the recovery of an immobile or semi-conscious MOB. I doubt it's feasible in any other manner.

However ....COUNTERPOINT:
I readily admit that the transom recovery has a major disadvantage .... that one must approach MOB under power, THEN KILL THE MOTOR, and secure MOB with boathook or similar, or risk injuring the MOB. Motor-ON recovery might be possible with a crew of three (2 aboard), but it's absolutely impractical and unsafe with crew of two (one aboard).

But then ... one crew recovering a MOB will be difficult in any case, and recovery over the cockpit gunnel is certainly no easier.
Three CRITICALLY important recovery rules for one-on-one recovery:
1) DON'T prop-chop the MOB
2) DON'T FALL IN trying to recover the MOB!
3) (Probably should tether oneself to both aft cleats for the duration)
Doesn't change my mind, the backstay hoist at transom is the quickest, surest way to recover a disabled MOB (probably any MOB) to a 26X.

[Frank C]

I agree it's 16:1 for bending the mast, but only half that for lifting a COB.. and I think we both agree on that.

Oops - sorry Moe, I missed this point. You are correct & I was wrong.

It is 16:1 when pulling aft on the mast because all four lines are moving. Putting that another way, the double block is moving (single block stationary). When lifting at the transom, it's only a single block that is moving to lift the MOB, (double block stationary) halving the purchase to 8:1. (Lifting on this rig of the single block is no different than lifting with a hook on single line).

Fortunately this is an example where less is better. With six-foot legs on the triangle, at 16:1 purchase, mast-aft potential is way more than needed. Two nice things about the long purchase ... it requires less muscle to pull, AND it's adjustment potential is twice as fine. It's nice that it demands lots of rope thru the tackle (16") to move the mast by one inch, since we should limit mast movement to (?) only 5 or 6 inches.

But the disadvantage at 16:1 is it only offers 18 inches of lift in a six-foot tackle. Yet, by using the single block to lift the MOB, the tackle is "automatically converted" to half-strength, or MOB recovery mode - and the lifting range doubles - three feet from a six-foot tackle. This requires absolutely no thinking, rigging or manipulation - just clip the portside single block to a pendant on the MOB's harness and voila. Could not be more perfect for an emergency scenario.

This auto-conversion feature can also be used to "auto-reposition" the lifting tackle from center-hull to a better spot, between the motor and port rudder, but I'll need to do some scribbling to plot that.

[Tony D-26X_SusieQ]

No wonder our Admirals like these boats so much. If we are unfortunate enough to go overboard there isn't much for them to do besides call the insurance man and pick up the check.

[Moe]

If we are unfortunate enough to go overboard there isn't much for them to do...

That's especially true

if we aren't wearing a PFD... we'll sink pretty quickly if unconscious or had the wind knocked out of us

if we're in cooler water and aren't wearing an immersion suit... we'll rapidly be unable to contribute to our own resuce

if we've been drinking... we may make our own rescue more difficult

if we haven't taught them how to get the boat back to us and stopped, especially with sails up... we may not be able to swim to it

if we haven't taught them how to use the MOB button on the GPS, read our Lat/Long off it, and how to make a distress call on the VHF... a rescue boat or other boaters may be able to get to us a lot quicker than the spouse could get us back on board

if we haven't practiced COB drills... it's one thing to have talked about it, another to have gone through the motions