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Anke and I are building our next boat, and writing about it at ABargeInTheMaking.blogspot.com. Access to the net comes and goes, so I'll be writing in fits and spurts.

Please feel free to browse the archives, leave comments where you will and write, and I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Saturday, March 19, 2016

Cargo Booms for Cruisers

http://www.tug44.org/tugboats.trawlers/ceres-sail-freighter/images/ceresfreighter-1.jpg
CERES unloading, using her sprit as a Cargo Boom.
Note the 'universal joint' is a simple snotter.

Boom boom boom boom
A-haw haw haw haw
Hmmm hmmm hmmm hmmm...

-- From Boom Boom by Johnny Lee Hooker


Cargo Booms for Cruisers

A Cargo Boom is a durn handy thing.

Boarding or off-loading cargo (including groceries, luggage, tools, flotsam, what-have-you), a dinghy, an MOB, a pet. Raising a mast, a large hatch, an anchor. Heeling the hull to lift clear of that rock ledge you clipped...

A Cargo Boom is a durn handy thing!

The jargon of cargo handling is extensive and not always perfectly standardized. Here, I'm going to use terms as I've heard them used in my area. For those who care, there are many fine hairs to split.


A fully rigged Cargo Boom

Boom Derrick

The derrick (referring to the whole setup) pictured above is very common, though on small boats, seldom so thoroughly rigged. Essentially, it has a universal joint more or less fixing its derrick/boom heel to a mast, a topping lift to control lift aka hoist (vertical lift/lower) and guys to control swing (horizontal rotation).

A sailboat already has a mast, halyard (generally with multiple purchase) and likely a boom (and/or spinnaker pole). Thoughtfully rigged, the halyard can be transferred to the lift point of the boom (if not already so rigged) and guys added, and shazzam... you've got your cargo boom! Best yet, this kind needs no additional stowage when not in use.

Once set up, the boom can be more or less short and horizontal (preferred for amateurs) or more or less long and vertical (preferred by professionals). In both cases, the topping lift should be at near right angles to the boom.

In the short, horizontal case, the topping lift should be at an acute (sharp) angle to the mast (which then supports the load mostly in compression. The boom is only holding the load away from the mast, in this case, and is under much less stress than if it were near vertical.

Consider a halyard attachment which is easy to shift, with enough extra length to drop the boom end to deck level. Consider a universal joint that can handle the full range of potential boom movement. Consider bungee lines to gather rigging (such as lazy jacks) that go slack during boom operations. Consider supplemental backstays to support the masthead (low stretch line or wire in all stays... nylon is stretchy and can be dangerous!).

Stowing a dedicated cargo boom can be inconvenient. Rigs with spars set on one side of the mast have a section along the mast side opposite the spars that will never be swept, called the chimney. A boom may be stored vertically in this location. Consider using the boom as a side rail (like a lifeline) when not in use.


The pole isn't labelled... it's lower center and angled... the load is hanging from it.


Gin Pole

A gin pole is simply a near vertical boom with no mast.

Essentially, the heel is securely fixed to the deck, and the head inclined over some useful hoist point.

It can be rigged to hoist and swing around that point, but operation is complicated. More commonly, it is guyed (stayed) in one position, and lifting tackle used to hoist the load.

This type is less useful for cargo, and is generally improvised for raising a mast.



A-Frame

An A-frame derrick is a spread pair of poles lashed at the apex, and working in compression. Tackle hoists from the apex, and the fore and rear (aft) guy swing a load up and along a line perpendicular to that of the legs.

On board, this can be set up on the sheer, and cargo hoisted, then swung inboard.

Be aware that the guys can develop immense tension loads if their lead becomes too acute, and the threshold is reached and surpassed in surprisingly short order. If overloaded, something is likely to give - a guy or your sheer structures, most likely - and the A-frame can whop flat like a mouse-trap. Ya feel me, Mouse?

Be sure to limit the swing to short hops, keeping the A-frame near vertical at all times. Consider raising the guy anchors to improve their lead to the apex (closer to right angles).

Downside of A-frames is that they're a lot to stow. On the other hand, they work well at barge ends. Many rigs can be improved by A-frame masts, so it can pay its way between jobs.

I sometimes dream of an aft A-frame, flying a double stays'l rig on roller furlers. Whatta toy!


Cautions

Keep in mind that, even with relatively light loads, some wicked forces can develop.

As cruisers, our setup is likely to be DIY and... well... funky. Do familiarize yourself with forces involved and safety procedures, and follow them scrupulously! Do not pass under a load or allow anyone else to do so. Move slowly, with good communication among all present. Keep lift/lower and swing in/out operations separate.

Consider familiarizing yourself with vector diagrams to help assess loading. Consider which forces are acting in compression, and which in tension. Consider keeping your boom either short and close in (when used horizontally), or long and close in (when used vertically). Consider hoisting only modest loads.

Cultivate a state of healthy paranoia!












16 comments:

  1. I was thinking that a spare yard would be quite stout, compared to a lighter batten. If stored in your chimney, held up by a spare halyard, it would be good as a backup and quick and easy to deploy when needed. It would also double as a mast raising ginpole

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    Replies
    1. Good thought. Spare yard implies a primary yard. Where and what is the primary? Otherwise, if you meant spare mast, then I understand.

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    2. A yard on a Junk rig is the topmost batten that the halyard attaches to, usually more robust than the rest of the battens

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    3. Hi Dennis,

      I agree. Other 'hats' for a spare yard include boomkin, dinghy mast, spinnaker pole (or boom).

      All in all, the increased diameter increases the range of possible uses.

      Dave Z

      BTW, RE 'Yard' vs 'Lug'... the so called junk rig is sometimes accurately classed as a fully battened, standing LUG rig. Hence, the topmost spar is technically a 'lug', and my personal preference.

      The term 'yard' seems to have bled from square sails (and lateens?) to lugs, and on to JR. Gaff sails depend from gaffs, however, and not yards, despite being as 'square' as any lugsail.

      Common practice seems to call it a yard in JR, at least in the British sphere of influence. I'm reluctantly switching over for improved communications. 8)

      Delete
    4. Hi Dave, looking through Van Loan's Design and build your own junk rig, he has a diagram where he names all the parts. It's from this diagram that I learned to call it a "Yard"

      Delete
  2. Nice and highly anticipated post, Dave. Thanks!

    Some thoughts:

    1) I wondered if we're really talking about cranes, hoists, or derricks? Or maybe all? Did some searching. The terms are sometimes differentiated, but often used interchangeably. "Crane" seems to be the umbrella term for all of the stork-leg-like mechanisms, and "hoist" seems to only be the lifting gear (rope and pulleys). The U.S. Army Field Manual on Rigging (FM 5-125) is quite useful in differentiating and demonstrating use:

    http://www.globalsecurity.org/military/library/policy/army/fm/5-125/fm5-125.pdf


    2) Where exactly is the "chimney" on a junk rig, and how would it be used? Is the crane boom (hinged at bottom) inside the sail parrels with the mast, and kept lashed to the mast and so stationary while the sail is up? If so, then is the sail completely lowered in order to unlash and use (lower/raise) the crane?


    3) A-Frame Derricks:

    ** How would an A-frame derrick handle lateral movement of a load?

    ** Does proper derrick use ever involve swinging said load through the legs of the derrick to increase its horizontal range? Maybe this is the aforementioned and prohibitive "mouse" dilemma.

    ** Does such a derrick type have any inherent benefits over other crane types?

    ** How would such a derrick mast on a studly sailing triloboat improve sailing ("Many rigs can be improved by A-frame masts")?


    4) Which of all types of crane-y things would be easiest to operate single-handed?

    Yoda


    ReplyDelete
    Replies
    1. Hi Yoda,

      Sorry; seem to have missed this...

      RE Crane vs hoist vs derrick: I imagine (as your sources do) that there are authoritative distinctions. In practice, however, even among professionals, there seems to be considerable overlap. Like so many things nautical, the lines aren't clearly drawn.

      In AK, a 'hoist' is tackle that handles a vertical lift. 'Derrick' is rarely used. 'Cranes' are a motley lot. Maritime and timber riggers often use a different set of terms.

      So, if there's a critical difference, I iron it out and we get on with the job.


      RE the 'chimney': On a lug rig (including JR), this runs the length of the mast on the side opposite the boom when sheeted in.

      As the boom (and sail entire) is set to port, say, then let out to 90 degrees (perpendicular to the vessel's centerline), on one tack, it's fwd of the mast and on the other, aft. That's three sides of the mast (aft, port, fwd) swept by thee boom. The sbrd side never is. That's the chimney.


      RE A-Frame Derricks:

      To handle lateral cargo movement, the legs must straddle the line of travel. Depending on length of hoist, one can often pull the load somewhat off line.

      If you reposition the legs, you can 'walk' the load along in short hops in any direction (each hop in a single direction, cumulative like walking around a bend).

      Yes, the load can swing between the legs. AND the A can lean toward the pickup point, travel up and toward the set-down point 'hopping' the load along (riverboats called the process of moving the whole boat over sandbanks 'grasshoppering' using a similar approach).

      This is where good prevention is crucial... when leaning the A one way or the other, past a narrow, near vertical position, it begins to develop very high apex loads which can break a preventer. The cargo load then 'snaps' the frame flat, like a mousetrap.

      The benefits of A-frames, relative to others are a) the legs, working in compression, can support enormous loads, compared to topping lifts and guys working in tension (picture two 4x4s vs a half-inch line); and b) they lift the load as the apex travels along an arc whose radius is the distance from the apex to the midpoint of the straddled legs... this is often a uniquely useful property, especially with very heavy loads.

      In general A-Frame masts are used to eliminate mast induced turbulence along the luff of the sail. I likely wrote too enthusiastically, though, as their windage may well represent a net loss to efficiency.

      I've thought about an A-frame mast, set aft, flying a double stays'l rig. Replacing ketch rig, this would have little extra windage. The stay set sails would angle aft, producing lift at the bow... good for most hulls and maybe especially barges?

      My choice for single handing would be a shortish, near horizontal boom mounted on mast or tabernacle and topped by the halyard.

      Clear as mud? 8)

      Dave Z

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    2. "Clear as mud?"

      Mississippi Delta; blue water up ahead. Thanks for all of that.

      I think I found the perfect simplistic setup:

      http://www.dir.ca.gov/Images/t8img/4885-26.gif

      =================

      Conversely, in a simple boom set-up on a mast, where pulling the hoist line to one side to move the load left or right won't be enough lateral cargo movement, it seems to me that one of the following two things must become true:

      A. The mast itself rotates to allow lateral movement.
      or
      B. The boom rotates around a stationary mast.

      Option "A" has complications that I don't even want to think about. Option "B" seems easier. However, after looking at a gazillion crane / derrick drawings and photos, I haven't yet found one that clearly shows what type of mast collar mechanism would allow that easy rotation.

      The closest I've come is the middle drawing (really gotta zoom in on it) of the Atkins Giant:

      http://www.atkinboatplans.com/Misc/Giant.html

      If anyone has any ideas about that collar doohickey, please let me know.




      (Simplistic set-up: 4/1 - sorry, couldn't resist ;-). Can you believe that anyone is really ballsy enough to erect that thing and use it?!? The power of financial motivation is truly astonishing.)

      Delete
    3. Hi Yoda,

      A universal joint allows vertical and lateral motion, and sometimes twist.

      Working from low tech up, possibilities include:

      Snotter (as CERES in the initial photo)
      Lashing (my fave)
      Linked rings (or shackles, carabiners, etc)
      Jaws (gaff-like variations)
      Goosenecks (as seen in Atkins' GIANT)

      All these can be combined in part for minor variations on the theme.

      Gate hardware can sometimes be pressed into service.

      Dave Z

      Delete
    4. Dave,

      Good sensible list of possibilities. I'd been searching for goosenecks (once I stumbled onto the word), but still not finding good examples. However, the more I look at that end of the solution spectrum, and its associated complexity level, the more I like the idea of lashings, too. The only obvious downside is time and effort. The lashing would have to be tied and untied between each use.

      Main question about lashings: After all lashed up and ready to go, once the boom is under load, what keeps the lashing (and boom) from sliding down the mast like a kid with outsized hand-me-down pants?

      Don't think the tightness of the lashing can be relied on to do the job. In real life, stuff slides. Also, the lashing can't be too tight or it will not provide the range of mobility needed in other axes.

      Yoda

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    5. A grommet can permanently roven and siezed between mast and thimble (forming a figure-8) can be left permanently in place with thumb or prison cleats (similar to a fairlead) to prevent slippage but allow rotation. The heel of the boom can clip to this via a siezed carabiner or gated hook.

      Some lashings are designed to hold well on a spar. Variations on constrictor knots and rolling hitches can be made pretty reliable. Thumb cleats hedge your bet (this could be a short, angled peg set into the mast... but can let water into its set hole, so glue and/or bed well).

      BTW, rotation isn't likely necessary... a loose joint will likely cover all the range you need.

      Try searching images for "spinnaker pole fittings" and "gooseneck sailboat boom traditional" and "gooseneck herreschoff boom" for a range of hardware approaches.

      One I'd add to my list is trailer hitch ball and socket.

      In general, we live in a time where specialized rigging is very expensive, but there is an abundance of inexpensive hardware that can be adapted. The job is to construct an inexpensive, robust and handy universal joint. Lots of possibilities, especially if you live near a junk yard!

      Dave Z

      Delete
    6. Reeve (v.) (reeved, roven). My "Word of the Day" :-)

      1. to pass (a rope or the like) through a hole, ring, or the like.
      2. to fasten by placing through or around something.
      3. to pass a rope through (the swallow of a block).

      ---

      A funny, alternate meaning:

      http://www.etymonline.com/index.php?term=hog-reeve&allowed_in_frame=0

      Delete
    7. RE the alternative meaning, the REEVE'S TALE was always my favorite of THE CANTERBURY TALES.

      8)

      Dave Z

      Delete
  3. Dave,

    Reminder: Please take a look at the questions above when you have time. Not rushing you. Just want to leave that reminder in here as a placeholder and the following note before I forget what I'm thinking about. No rush ... I know you're getting ready to get back to work on Wayward.

    And while I'm at it ;-), it would also be really nice if you could expand on your previous comments about A-frame masts. For example:

    "I sometimes dream of an aft A-frame, flying a double stays'l rig on roller furlers. Whatta toy!"

    What a tease! What would such an animal look like, especially the sails and their attachment positions? Would those be really big twin staysails that replace the customary aft sail on your ketch?

    Location of the A-frame: Maybe mounted near the stern. Or better yet, as I'm actively trying to envision it, mounted at the midpoint longitudinally (one foot of the A on each side of the boat straddling the superstructure; first 8 feet of both A legs would be vertical, then angled to a peak afterwards). The A-frame mast/derrick combo would be leaned aft 30-45 degrees and secured in a leaned position for sailing and more so for cargo. Would require backing the boat up to cargo for loading/unloading.

    I should mention that the boat layout in my current draft is the reverse of normal T32x8. The cockpit would be interior, combined with the living quarters, and forward near the bow for easy forward visibility. The enclosed cargo hold/flex space would be behind that, aft near the stern, with no appreciable gap between the two interior sections. Together the two sections would be about 20' (8' cargo/12' living). Plus, approximately 6' fore deck and 6' aft deck. Total of +/- 32'.

    I'd attach a drawing, but it seems that in Blogger the comments do not allow graphics.

    Instead, I tried to time-warp us back to the days of Pong and did an "x" drawing, all with letters, but comments removes all the spaces -- crap. It was so cool. You'll have to use your imagination. :)

    Yoda

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    Replies
    1. Hi Yoda,

      Yes, the Stays'l rig would be twin heads'l (replacing the main). They often have a smaller driver (yawly/ketchy mizzen)hung from the apex and setting aft.

      While a single mast works for these, an A-frame would have lateral stability and be useful as a heavy lifter to bring stuff over the transom.

      Of course, to work, this takes a lot of over-clever and irritating hardware and procedures to transform between cargo and sailing use.

      It's a tease for me, too... have never felt the energy to pursue it!

      RE your layout to rig: In choosing mast placement, my priority has always been to keep it out of the bunk and gangways. If you can line up with superstructural bulkheads, you pick up a lot of support for free.

      Sounds good; good luck!

      Dave Z

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  4. Sometimes, when it comes to the developing world, we're just babes in the wood ...

    World-class DIY multi-function cargo/work boat wannabe porn:

    http://www.youtube.com/watch?v=7odAbL3Ygts

    ReplyDelete