George Dewey

Installing attachment point on masthead crane

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My boat currently has a 2:1 main halyard, with the end attached at the masthead. To make this happen, the PO removed one of the aft sheaves and connected the end of the halyard to the axle pin with a D shackle. Now, I want to put the sheave back but keep the 2:1, so I need to figure out how to attach the end to the crane. I could just drill a new hole in the side plate (of the crane) for the shackle but I'm concerned it might wear the hole. I could drill through a side plate and the middle one and install a new clevis pin, but it will be very hard to drill it square so both holes line up. Maybe install a padeye on the side of the crane?

Any thoughts? Thanks...

IMG_2414.JPGIMG_2411.JPG

 

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Are you going to run a halyard over that 2nd sheave??

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20 minutes ago, longy said:

Are you going to run a halyard over that 2nd sheave??

Yes, so both sheaves will have a halyard. But the second halyard won't be 2:1.

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Drill a hole in the center web thru one of the large lightening holes as far outboard as you can to clear the lines on the sheave . Install shackle or long shackle straddling the web and dead end the 1:2 to it.

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Might be an idea to check with the rig builder or rigger before doing that. That’s everything hanging on the crane by the look of the pictures. 

What boat, and what sail plan and rigging setup?

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23 minutes ago, Feisty! said:

Drill a hole in the center web thru one of the large lightening holes as far outboard as you can to clear the lines on the sheave . Install shackle or long shackle straddling the web and dead end the 1:2 to it.

  Try to have your hole as high into the center rib as a long shackle allows. Keep distance aft of first part of halyard short, too much spacing can restrict the headboard from rotating as the sail is let out.

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5 hours ago, mad said:

Might be an idea to check with the rig builder or rigger before doing that. That’s everything hanging on the crane by the look of the pictures. 

What boat, and what sail plan and rigging setup?

It's a 2004 Beneteau First 36.7.

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6 hours ago, Feisty! said:

Drill a hole in the center web thru one of the large lightening holes as far outboard as you can to clear the lines on the sheave . Install shackle or long shackle straddling the web and dead end the 1:2 to it.

 

5 hours ago, longy said:

  Try to have your hole as high into the center rib as a long shackle allows. Keep distance aft of first part of halyard short, too much spacing can restrict the headboard from rotating as the sail is let out.

Thanks everyone...

Great point about the headboard. 

What load should the shackle need to support? Would this one do:

http://www.apsltd.com/forged-long-shackle-6mm-pin.html

 

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Rather than using a shackle to attach the end part of the 2:1 a common solution on multis is to drill a hole through the top plate of the crane in the appropriate spot, poke the halyard up through it and tie a stopper knot. Make sure you de-burr the hole well.  In your case it will be a tad off centre but if you put a chafe jacket over the first few inches where it touches the centre web all will be good and you've done it without adding any extra weight at the top.!

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excuse the really rough sketch up but this...with a big stopper knot at the top.

Screen Shot 2018-05-02 at 5.27.33 PM.png

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14 minutes ago, Mitre cut said:

Rather than using a shackle to attach the end part of the 2:1 a common solution on multis is to drill a hole through the top plate of the crane in the appropriate spot, poke the halyard up through it and tie a stopper knot. Make sure you de-burr the hole well.  In your case it will be a tad off centre but if you put a chafe jacket over the first few inches where it touches the centre web all will be good and you've done it without adding any extra weight at the top.!

That's a cool idea! Or maybe I could use a dog bone? 

I would need a bigger hole than with a shackle, probably 1/2 inch. Won't that weaken the crane?

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I dont think it will weaken the crane enough for you to worry about it, there is plenty of other metal there doing the job . A dog bone would be a nice clean solution. The hole only needs to be big enough to get the halyard through.

I used this set up with a 10mm halyard on a 49sqm square top mainsail for 5 years and it took that long for it to fail. The break was not at the figure 8 knot but about 1/2" below below the top plate of the crane. If you did an 8 knot and moved it 2" down the halyard every season trimming the excess tail off as you went it should give you reasonable reliability.

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8 hours ago, jarcher said:

That's a cool idea! Or maybe I could use a dog bone? 

I would need a bigger hole than with a shackle, probably 1/2 inch. Won't that weaken the crane?

The top plate of a masthead assembly is there to keep the vertical plates aligned & prevent them from twisting/bending off sideways.  They don't support much load. A single 1/2" hole would be OK (really smooth the edge of the hole, & use chafe sleeving)

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1 hour ago, longy said:

The top plate of a masthead assembly is there to keep the vertical plates aligned & prevent them from twisting/bending off sideways.  They don't support much load. A single 1/2" hole would be OK (really smooth the edge of the hole, & use chafe sleeving)

Would a 3/16th inch or 1/4 inch hole in the center vertical plate weaken the structure? 

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