safety issue, added/adding a mast raising system

[centerline]

i have owned two sailboats and added a mast raising system to both of them.
the system is very similar in operation to the macgregor mast raising system....

on my current boat, i have raised and lowered the mast many, many times, and even bounced the mast as it hung from the system when testing it after I built and installed it....

then... after is has been working flawlessly for the past year, i went to raise the mast on friday, and just as i was beginning to take the load on the rigging to lift the mast out of the crutch, the tabernacle suddnely pulled loose from the cabintop:cry:....

it did not pull completely out because i was just beginning to take the strain, but it peeled up a couple of inches and tore the fiberglass. but if i would have had the mast in the air 6ft and it gave way, it would have been a disaster.....

unlike hand raising, the raising system creates a lot of forward pull on the mast/tabernacle until it becomes more erect, and it was this initial pull that caused the tabernacle to peel forward.

upon inspection and closer study, I realized there was only one 1/4"bolt holding the rear of the tabernacle to the cabintop, but two at the front.
it NEEDS to have the two bolts to the rear to support the stress created as the mast starts up....
but in addition to only having one bolt at the rear, none of the bolts had any washers or other backing hardware under the nuts..... so the little 1/4" nut was free to pull thru as it pleased....

i feel fortunate to have found this out without a catastrophic event to my rigging, but it would have been better to have done a thorough inspection and rebedding of the tabernacle myself and prevented this from happening.

the tabernacle on your boat may be fine for hand raising/stepping the mast, but when using a raising system, there is more stress added that should be addressed before the problems arise

the event set me back about 40 minutes, but didnt ruin my weekend, as i carry a couple spare backing plates for when I need to add a piece of hardware, or something like this arises.
i removed the old bolt and used a longer one and pulled it all back into place and clamped it down with a backing plate like it should have been to begin with.
but i will have to do a more extensive repair to the glass when i get the boat home to insure a good watertight seal.....

 

[MrUnix]

Glad you caught it before more extensive damage occurred!! Does your raising system use a gin pole or were you pulling directly from the top of the mast?

Cheers,
Brad

 

[centerline]

i use a gin pole and the rigging connects to a bail on the mast at 6ft from the tabernacle... I dont use the halyard for normal raising or lowering, but will snug it up when i lower the mast to cross under a bridge in choppy water. it gives additional support, but using the halyard alone wont secure my mast from swinging side to side...

 

[tkanzler]

i use a gin pole and the rigging connects to a bail on the mast at 6ft from the tabernacle...

And that's where most of the uplift at the tabernacle comes from. Using a live gin pole and a halyard or other line to beyond the CG of the mast would result in primarily shear load at the tabernacle fasteners, and potentially some uplift from the height of the hinge above the tabernacle. Putting the butt end of the gin pole on the bottom of the mast would negate the uplift, too.

Not that there's anything wrong with uplift at the tabernacle, as long as the fasteners and deck can handle the load.

 

[centerline]

And that's where most of the uplift at the tabernacle comes from. Using a live gin pole and a halyard or other line to beyond the CG of the mast would result in primarily shear load at the tabernacle fasteners, and potentially some uplift from the height of the hinge above the tabernacle. Putting the butt end of the gin pole on the bottom of the mast would negate the uplift, too.

Not that there's anything wrong with uplift at the tabernacle, as long as the fasteners and deck can handle the load.

I agree... it does offset the ratio of shear vs uplift on the tabernacle quite a bit with it rigged as I have it.
but even lifting from the halyard, with the mast attached on a pivot bolt about 3" above the "shear" level there will still be a lot of lifting force on the rear tabernacle bolts as the force is trying to pull the mast forward, even though the front bolts will be under shear stress alone.... and when it cant move forward because it has a solid foundation, the mast will begin to find its easiest route of travel is upwards....
but when there is not enough bolts/backing plate to hold the foundation secure (at the rear of the tabernacle), it can peel out with the tabernacle trying to roll forward as mine did....

 

[tkanzler]

Yeah, I forgot about the substantial height of the hinge from the deck. The Mac X and M boats have a hinge plate, with the fulcrum barely off the deck, so uplift is minimal. Glad no real damage was done on yours. I ripped the tabernacle out of another boat once when the mast went over sideways as I was putting it up, learning things the hard way.

 

[Catketch]

Holy crap, the exact same thing happened to me on Tuesday! The winch seemed to be harder to turn than usual, so I left things hanging about a foot off the mast roller and re-checked my rigging to make sure that nothing was stuck. I then gave the handle another crank to see if it turned easier and POP!!!, the back bolt pulled right through the deck.

The bolt did have a washer but it was no bigger than the nut and, as such, was absolutely useless. I spent yesterday fiberglassing over the damaged spot and it rained all day today, so I haven't had a chance to try raising the mast again. When I do, I'll be a heck of a lot less inclined to ignore a tight winch.

Luckily, I was just raising the mast in the back yard to check out the rigging...it would have been a major PITA if it happened at the launch ramp after trailering the boat a couple hundred miles for a cruise.

I would urge all you Mac guys with a mast raising system to check your aft step bolt and back it up with a good sized backing plate (or at least a really big washer).

Dan

 

[Benny17441]

Been there done that. Once dropping a mast and a 2nd time was dismasted underway. On both occasions just epoxied the bolts back in the holes. I believe that if we had added a backing plate the first time that when the boat got dismasted the 2nd time that it would have torn a chunk out of the cabin top making the repair much more complex and costly. It is this part of the cabin top that holds the mast. Like you indicated it worked flawlessly many times but the strain and frequency undoubtedly took its toll. I would consider adding more bolts and frequently inspecting it for any looseness before adding backing plates or too large washers.

 

[Catketch]

Your point is well taken, Benny, but it depends on the step. Mine has a slot long enough to allow the mast to fall over with damage only to the thin metal of the step. I don't know if that is the specific design principle for the slot, but it seems like it would serve that purpose nicely. On the down side, if you let the mast sit high on the track when raising, you greatly increase the pulling force on the forward bolt (which is what I believe happened in my case). A step with a short slot would almost certainly cause severe damage to the cabin top during a dismasting.

 

[anchorclanker]

I guess all the better reason to boost it up by hand from the cockpit, and then up on the deck. Mine has a plate under the mast step, plus a mast support, so I dont think it would do that, but no sense testing it.

 

[tkanzler]

Just for reference, and anyone not familiar with the Mac boats, this is the mast step (kinda short to be called a tabernacle, I think) used on the 26X and M boats. The mast has a matching piece pinned to it, and hinges at the end with the loop and pin. The gin pole pins to the other end.

Since the hinge pin is so close to the deck, and the base is so long, there's negligible, or even negative, uplift on the step and hardware when using a gin pole, though of course the bolts wouldn't go into compression.

 

[caguy]

It's important to raise the mast as high as possible before cranking the winch. The first foot or two are the most stressful. I watched a guy do the same thing a couple of years ago in the parking lot at MDR, ruined his whole day. That is one rationale for using a gin pole that seats on the bottom of the mast itself and attached to the forestay on the other end. The mechannical advantage of having a 10'+ pole vs a 7' pole is significant.
As suggested by tkanzier this may be a good time for an upgrade. Check out Dwyer's hinging base plate. They run about $40 they also make a deck organizer plate to go with it.