Mast and boom: Matching set for emergency dismasting

Discussion in 'Sailboats' started by JosephT, Oct 23, 2018.

  1. JosephT
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    JosephT Senior Member

    As a sailor I have always wondered if any sailboat/yacht manufacturers designed a matching mast with the inner diameter of mast just above the deck is slightly larger than the outer diameter of boom. Such a design would allow one to cut the mast down (e.g. with a hacksaw), cut away the extra mast rigging and insert the boom into the mast foot.

    Unfortunately, over the years we have seen some seen some poor examples of makeshift masts (out of a boom, wooden poles, etc.). The very recent example below from the Golden Globe race by Gregor McGuckin deserves serious praise. He was sailing a Biscay 36 Masthead ketch. Both he and a nearby competitor were dismasted and he managed to rig his mainmast boom (or perhaps his aftmast) and a couple of storm jibs. Off he went to rescue his competitor! The two are now sipping beers in Perth, Australia.

    [​IMG]

    The lessons learned during this race have been a valuable learning lesson to be sure. Going forward, I would say any boom that doesn't fit nicely inside its mast foot (e.g. one that is cut near flush with the deck) is potentially useless in a real emergency.
     
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  2. JamesG123
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    JamesG123 Senior Member

    There really only needs to be a socket of some sort in the roof foot or where it passes thru the roof (partners?) to hold the base of the "mast" in place laterally. The standing rigging is what holds it down and in place. So as long as the gooseneck fitting or the traveller end of the boom will fit within that, it should work fine. You really don't want to give up any of your mast, er.... boom length by sticking it down into the deck.

    I would think a more important consideration is making sure that your boom has the fittings and hardware to quickly attach emergency standing rigging, be they foreshortened stays or halyards, without having to engineer and improvise something. I don't think boat or mast mfgs. provide that at present time?
     
  3. JosephT
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    JosephT Senior Member

    Hi James, totally agree on the need to insert the boom into a shallow footing to preserve what little length you have. As for deck rigging, I've seen people use spare halyards for emergency rigging, but if I were serious I would opt for a pre-measured & cut backup rigging cable I could use to attach to the top of the boom-mast, which could them be routed to the forestay & backstay turnbuckles.

    Really proud of Gregor's effort to get his boat under way. It serves as a good benchmark for others.
     
  4. sharpii2
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    sharpii2 Senior Member

    Such a system is likely to fail under compression loads. The boom portion will simply be driven further into the mast stub portion.

    The first sailboat I ever owned was dismasted. The cheap hardware store fitting to one of the four stays parted. The mast was down so quickly I didn't see it fall. It was suddenly missing. Well, actually it wasn't. It was down on the deck. The butt of the mast scooted out of the mortice mast step, so the mast ended up laying neatly across the deck.

    There may be a lesson here. Maybe masts should be deck stepped instead of through deck stepped, so the step will fail shortly after some vital shroud does.
    This will make the mast more likely salvagable, as much of it will still be on the deck, instead of in the water, where it must be jettisoned to keep it from impaling the hull.

    My understanding of dismastings is that they happen when the boat is rolled over by a wave. The mast strikes the water and this load over stresses the support system. Then the mast fails from bending loads some distance up from the partners. This is why the butt of the surviving part ends up in the water.
    If it ended up on the deck instead, the poor sailor may be able to fight the rest of it back on board then secure it to the deck until the worst of the storm passes.

    Just a thought.
     
  5. JosephT
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    JosephT Senior Member

    Very good points Sharpii. The temporary mast should be rigged and only sufficient cloth raised within the delicate sailing conditions that would be allowed (e.g. fair winds vs gale conditions). You definitely don't want to overload it.

    As for your thoughts on a deck stepped mast that's an interesting approach. One would be hard pressed to raise larger masts again without a crane on shore. They're just too big & heavy. What if:

    1. The deck step mast was mounted on a lateral pivot.
    2. The turnbuckles for the standing rigging contained shear pins.

    I tell you what is also interesting are these telescopic mast patents. What if you had one of these (or perhaps a backup) while sailing in the Southern Ocean. Conceivably you could lower the mast before a gale hit. In my opinion, the rigging would need to be adjusted on a cranking system below deck (would make life easier). e.g. Big gale is coming:

    -Drop sails
    -Lower mast and wind extra rigging to proper tension (aftstay, backstay, port & starboard shrouds)
    -Raise storm sails

    When fair weather returns use reverse process.

    US8826840B1 - Collapsible mast and rigging for a sailboat - Google Patents https://patents.google.com/patent/US8826840B1/en

    A couple of other notable patents that are similar might work too.

    US6000354A - J.P.V.'s telescoping mast - Google Patents https://patents.google.com/patent/US6000354A/en

    US4016823A - Retractable sailboat mast - Google Patents https://patents.google.com/patent/US4016823A/en
     
    Last edited: Oct 24, 2018
  6. JamesG123
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    JamesG123 Senior Member

    The occurrence of demasting isn't high enough to justify the cost, weight, and complexity which is why those patents are not in common use. Not when you can just run a lanten or junk rig.
     
  7. JosephT
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    JosephT Senior Member

    No question it would add weight and cost. At a minimum a lateral pivot on a deck stepped mast (e.g. using a heavy duty hub & axle attachment) would be a good consideration. Most dismastings occur when the boat is hit from port/starboard. Thus, inserting some shear pins in the mast hub axle and the port/starboard turnbuckles would be a good idea. They could be calculated to give way, for example, at 7.5 tons of force, where the max shear load of the mast is 8 tons. Same with the shroud turnbuckles. That way, if you lose the mast you could theoretically:

    -Stabilize the mast to prevent damage & lower sails.
    -Remove old shear pins in mast foot and port/starboard shroud turnbuckles.
    -In calmer seas run a line up the mast about 15ft or so.
    -Ease the port/starboard shroud tension.
    -Hoist up the mast on a winch and insert a new shear pins into mast foot and port/starboard shroud.
    -Re-apply proper tension to port/starboard shrouds.

    I'm really quite surprised shear pins for standing rigging have not been a serious consideration. They are used on heavier structures. If designed properly they could alleviate the need to cut everything apart, request a mayday evacuation, etc. Ideally, a mast shear test should be done prior to completion of the boat design & test process. Looking further there appears to be some controversy in how to compute rigging & shroud tension. Regardless of that, shear pins are worth exploring. Provided the math is done right and it is backed by an empirical test (mast shear test) this approach could alleviate masts lost at sea and the additional damage they cause.

    Rigging Loads https://www.classicmarine.co.uk/articles/guide-for-gaffers/40-mast-theory/157-rigging-loads
     
  8. JosephT
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    JosephT Senior Member

    On further investigation shear pins (and electronic load cells) have been used on the standing rigging of racing yachts. The load cells are nice as you can monitor the stresses while under way and take action in advance to avert a catastrophe. For the GGR race, that might mean diverting to port to replace an overloaded shroud cable. The same approach could be done for a mast attached with a good hub & axle. I would probably go for a static load test vs trying to overload the mast on a sea trial. Nevertheless, practicing a mast failure recovery using the approach above would be a fun exercise. With the right test plan I think it can be done.
     
  9. JamesG123
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    JamesG123 Senior Member

    Evaluating stay line pins is already tricky enough as it is when they made as durable and as strong as can be. It would be pretty much impossible for a rigging inspector to be able to tell how much "life" a sheer pin has left in it, and none is going to bet his shingle on it. It will be "when in doubt, change 'em out", probably on a rediculuously, but-coveringly, short interval. Which again, will ramp up costs (in pins and sending people up the mast). This is okay for "racin'" but not very practical in a cruiser.
     
    Last edited: Oct 24, 2018
  10. JosephT
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    JosephT Senior Member

    Most definitely you would want to change them out before any respectable offshore trip. The digital load cells (shear pins linked to digital stress gages) are a smart investment in my opinion. You can monitor the loads on the pins and take preemptive action to replace them and adjust your rigging too.

    One thing is for sure: There is always room for improvement! Losing this many masts in one race: unacceptable!
     
  11. sharpii2
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    sharpii2 Senior Member

    There have been a number of cruising sailboats built over the years with deck stepped masts and mast raising gear. These are usually not intended to cope with dismastings, but to allow lowering the mast so the boat can get under low canal bridges. Such mast raising gear is not light and can be a constant nuisance on deck. It is generally an "A" frame which has the exact pivot axis as the mast. To raise the mast, the "A" frame is first erected with a line, usually a halyard, attached to the apex of the "A" frame and some point above the Center of Gravity of the mast. Another line runs from the apex to a turning block on the bow. A third line, possibly an extension of the forestay, attaches to the top of the mast.

    The apex of the"A" frame is then hauled forward until it is near deck level then the forestay extension is attached to something sturdy on the fore deck. Then the forestay is reattached, and the job is done.

    I certainly would never recommend doing this on a rough sea and a constantly gyrating and pitching deck. But during the first calm after the storm, this could be a real possibility.

    A boat I designed while in school had 7 x 49 wire rope instead of the more typical lower stretch 1 x 19 type specified for its standard rigging. This was to enable repairs at sea. This type of wire rope certainly stretches more but it is more resilient, which is what I was after. This boat also had a deck-stepped mast, a short, solid mast, a relatively long boom, and a gaff.

    A crude version of this system could be improvised at sea. Executing this task could take days or weeks to accomplish with much of this time spent waiting for suitable weather.
     
  12. JosephT
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    JosephT Senior Member

    Hi Sharpii, yes most adjustable mast concepts I have seen show an A frame concept, and these include many other types of vertical masts (e.g. utility pole, cargo boat mast, etc.). The wire rope you mention would be a good band-aid in place of standard rigging cables. Wire reinforcements would make it stronger than regular halyard lines, for example. It just blows my mind that manufacturers haven't come up with a suitable emergency rigging system. The ingenuity of the skipper is all anyone can count on. This year along we've seen sailboats dismasted and rescues performed...when the hull and deck are in perfectly good shape! Thus, there is a need for a replacement mast. Every offshore boat should have one in my opinion.
     
  13. nota
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    nota Junior Member

    I wonder if the old boys had the right idea with top masts that near all ocean sailing boats used
    and often lost without putting the boat in peril

    and with modern stuff like CF maybe a good idea again

    keep your al mast but cut it way down to a double reef sail size if ocean crossing
    and have thick wire and deck gear
    and use a set of light air sails to a top mast light built of CF for little wind times
    neat if the top bit collapse or comes down some how
    but needs not be heavy or super strong
     
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  14. JosephT
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    JosephT Senior Member

    Very good points nota. I've read stories about sailors who bring spare lumber on board that can be used to fabricate an emergency mast, boom, tiller, etc. If there space to accommodate it and you're not sure if the boat will survive a storm...that is a very good idea. Wooden ships of days gone by always had spare lumber on board. Today...everyone seems to rely on satellite phones, EPIRB, etc. A smaller version of the approach below would do!

    Arghhhh!!!!

    "When masts were lost, additional pieces of wood - spars, smaller masts - might be hastily tied to the stump. This is one reason why a sailing ship traditionally carried at least one replacement for every mast or spar. A huge main-mast could not be replaced in the heat of battle, but given the slightest opportunity, some sort of jury-rig could be set up, and some sort of canvas could be hung from it to supply power."

    [​IMG]
    The Pirate Empire: Repairs at Sea http://thepirateempire.blogspot.com/2015/10/repairs-at-sea.html
     

  15. JamesG123
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    JamesG123 Senior Member

    Not to mention a ready supply of replacements was available along any suitably forested coast.
     
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