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Old 09-06-2017, 11:02   #1
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Keel stepped mast turning blocks design

I've been researching how to properly mount mast turning blocks for a keel stepped mast. '

Backstory: I've rebuilt my whole deck and I had to put several layers of glass around the mast as this area had sagged. It was solid, it's not sagging when I step on it, and now it should be very solid with the new glass/epoxy but something has deformed the deck at some point in the past. There was a heavy layer of filler underneath the old teak to make it level so these damages are pre teak refit 20 years ago. I suspect that the rod that holds down the deck to counter the turning blocks and shroud load might have been too tight when shrouds have been released and subsequently the deck flexed.

I will now put in three turning blocks on either side of the mast. Having put time and effort into restoring the original shape I don't want to accidentally increase headroom underneath. I don't wanna blow wads of cash on a Selden mast ring so I'm trying to come up with a solid solution that transfer turning block loads to the mast.

What do you people think about using eye bolts and an eye nut on the middle one on each side of the mast that connects to a pad eye riveted to the mast via a turnbuckle? Has anyone seen similar solutions?

Some might say that the rod should suffice, but I don't feel to comfortable adding 4 more blocks by the mast without addressing this. I don't want to put the blocks on the mast above deck as the lines would run too high.
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Old 09-06-2017, 12:04   #2
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Re: Keel stepped mast turning blocks design

Thru deck bolts may introduce leaks. Mind this well when building. You can skip the buckle/rod part and use spectra rope. And the eye you want to add on the mast may block the mast next time you want to pull the stick out.

There are flush mast fittings that you can slide an eye fitting in. Look up Selden catalogue.

You can skip the on-mast fitting if you tie the blocks to the base of the mast.

Cheers,
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Old 09-06-2017, 12:06   #3
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Re: Keel stepped mast turning blocks design

I have a 35'er, the turning blocks are tapped into an aluminum backing plate inside the coachroof in a thicker section at mast partners. It has a single 1/4" down rod to the mast step, with a pad eye on deck.
Never a problem...I were a design engineer...not necessarily a blessing for your deck strength as it may vary from mine.

Pad eye riveted on mast below decks looks like an oops for pulling stick?

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Old 09-06-2017, 13:46   #4
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Re: Keel stepped mast turning blocks design

Valid points! I'd have to check, but I think I have about an inch clearance between mast and hole.
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Old 09-06-2017, 21:02   #5
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Re: Keel stepped mast turning blocks design

Just DIY a plate that surrounds the mast at deck level, & connect it to the tierods. You needn't even unstep the mast to install one. Build it out of 2 layers of 6mm aluminum, with an oval cutout for the mast in each sheet. Then bandsaw both sheets in half, cutting them in half via slices at 90 deg to each other. And use machine screws to hold the layers together once they're in place around the spar's base. Adding attachment points for the blocks & tierods as required. KISS

One other option is to mount your mast base blocks to a stout slab of aluminum, & connect this to a piece of strong angle aluminum belowdecks. To which you attach the tie rod to the center of itís vertical web.

Or you could even use a seperate piece of angle aluminum as the belowdeck's backer for each block. Drill a hole through it's vertical web. Ease the edges of the hole, & lead Spectra lashings from each to the upper end fitting of a tierod or Spectra tierod.

The number of solutions is only limited by your creativity.

IMO, a trick one would be to remove the teak for perimeter size X around the mast's base. And replace it with DIY FRP plate which has it's top couple of layers made of clear coated woven carbon fiber.
Then just add a couple of coats of UV stabilized varnish over the carbon every year. Though be sure to postcure the resin/plate, as black surfaces get hot enough to rise above the Tg of a lot of resins. So check the one of whatever you choose to use.

PS: You may have damp or rotten deck core in that whole area, & much of that near to it. Caused by prior holes for mast base blocks. Which would explain the deck compression there. And you need to ascertain if this is the case prior to building high load structures atop or underneath of it.

I say this as it's common to have decks constructed in a sandwich consisting of ply/core/teak. And when the core gets wet, things go to s**t. Up to & including dampening/rotting the ply, or at least infesting it with wood eating bacteria.
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Old 10-06-2017, 06:07   #6
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Re: Keel stepped mast turning blocks design

My perimeter x = beam /length

Around the mast balsa rot wan't the issue, but I had stress fractures around the hole that were propagating, these were ground back, filled and glassed over. Along with the existing roof reinforcements the layers of glass I've put down should make it really solid now.

I just need to transfer the loads to keel/mast. It will also have to look decent inside the cabin. I was thinking a stainless eye nut wouldn't be too invasive, but angle bars would.
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Old 10-06-2017, 18:23   #7
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Re: Keel stepped mast turning blocks design

I would use tangs, attached to the mast with ss screws, instead of the pad eye below deck, so you could easily remove them when its time to pull the rig. Great idea otherwise.
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Old 11-06-2017, 04:58   #8
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Re: Keel stepped mast turning blocks design

So then you want tie rods that don't look like tie rods? You can use some line jacket (cover) to braid a Turk's Head onto the mast tube, overtop of a bit of friction tape, to use as an anchor for some "soft padeyes". It'll more than hold any kind of vertical load that you want to put on it, all while looking pretty, & being low profile.

Same principle as a Prusik Knot, Rolling Hitch, or Icicile Hitch. And you can use a flavor (color, & braid pattern) of (cordage) cover which matches you interior decorum.
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