jibjab

sheave box for 5mm spectra

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One of the little wheel doobers in the flanged double sheave box inside my mast base/step has disintegrated. At least, I think that's what it's called - it looks like that when you do a google image search.

It's for the jib and the main halyard - it's the main one that is broken. As it's a double one, I'll have to replace the whole lot. I wondered why it was so difficult hoisting the mainsail - now I know why :( We broke the jib halyard in the last race - when I was running the new spectra 5mm through the mast I noticed it.

My question I'm hoping someone might be able to help me with is - what can I replace it with? Do I need to drill out the rivets, and take the old one into a local chandlery and hope they have one that's similar? There seems to be a bewildering array of options and I honestly have no idea where to start. Your collective wisdoms would be greatly appreciated. I've taken a picture.. hopefully it has attached...

Screen_Shot_2020-03-05_at_13_25_59.thumb.png.dccd8f5709347daac0f05263427120b9.png

Cheers

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When you remove the broken part you will see a trademark on the side plates. Probably Harken or Schaefer. Drill to rivet heads off, be careful not to enlarge the holes in the mast wall.

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Hard to be sure from the photo, but it looks like when bent to fit it pinched the sheaves.

That is probably why the main halyard sheave looks so horrible, it couldn't turn and the spectra wore flats in the diameter.

Bend carefully and check for smooth operation when you do the replacement.

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14 hours ago, longy said:

When you remove the broken part you will see a trademark on the side plates. Probably Harken or Schaefer. Drill to rivet heads off, be careful not to enlarge the holes in the mast wall.

Thanks longy - I was reluctant to pull it out, for unknown reasons. I've now pulled it out, and it has Ronstan RF1008 stamped on the side. I can't find it anywhere on the Ronstan site, so I've contacted them to confirm my worst fears (they don't make them any more). It looks very similar to https://www.theboatwarehouse.com.au/sailboat-fittings-hardware/blocks-upright/riley-double-upright-block-29mm/ but without all the measurements it's hard to tell.

 

3 hours ago, ropetrick said:

Hard to be sure from the photo, but it looks like when bent to fit it pinched the sheaves.

That is probably why the main halyard sheave looks so horrible, it couldn't turn and the spectra wore flats in the diameter.

Bend carefully and check for smooth operation when you do the replacement.

That's a really good point ropetrick - I think you're spot-on there.

 

Thanks all for your help/suggestions - I'm hoping to be able to find one with three holes, and then bend the flanges to fit, miraculously fitting through the same holes...

sheave-box.png

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How about drilling out the riveted shaft, put two new sheaves in, probably less than $10, put a bolt through with a long neck, cut thread short, nylock nut.

Looks like the old one did the job for years not even turning, no need for perfection here.

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1 minute ago, BOI Guy said:

How about drilling out the riveted shaft, put two new sheaves in, probably less than $10, put a bolt through with a long neck, cut thread short, nylock nut.

Looks like the old one did the job for years not even turning, no need for perfection here.

That's not a bad idea - the old one did the job for 20 years as you say...

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1 hour ago, jibjab said:

That's not a bad idea - the old one did the job for 20 years as you say...

Thi lets you re-use the existing holes in the mast, much better than drilling new holes all in the same small area. Sheaves MUST ride on smooth shank of bolt - this may be the hardest part of the job.

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Hard to tell what angle the rope is turning.. from horizontal to vertical into the mast ?

Can you use a couple of floating blocks on saddles instead ?

If its not hard to access for maintenance, you could use something soft for attachment rather than a saddle.

 

How thick is that wall, given its the step, not the mast ?

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7 minutes ago, duncan (the other one) said:

Hard to tell what angle the rope is turning.. from horizontal to vertical into the mast ?

Yep, exactly - it's for the jib & mainsail halyards - you pull them horizontally to hoist the sails.

8 minutes ago, duncan (the other one) said:

Can you use a couple of floating blocks on saddles instead ?

I don't think so - it's fairly difficult to get my banana fingers down there, so putting a saddle in will be near impossible.

10 minutes ago, duncan (the other one) said:

If its not hard to access for maintenance, you could use something soft for attachment rather than a saddle.

I think it's hard to access, but I see where you're going with that - I'll have a look for something I can put.. what.. some dynex through lower down, and have a floating block on the inside, with the dynex exactly the right length to have the floating block in the right spot... interesting... hmmm...

13 minutes ago, duncan (the other one) said:

How thick is that wall, given its the step, not the mast ? 

It'd be a couple of mm thick I'd say... what are you thinking here?

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50 minutes ago, longy said:

Thi lets you re-use the existing holes in the mast, much better than drilling new holes all in the same small area. Sheaves MUST ride on smooth shank of bolt - this may be the hardest part of the job.

Not if you've got access to a lathe.

I've made new sheaves & axles (centre pins) for sheave boxes like this before for people. It's not really difficult or super high precision work.

Biggest hassle is usually extracting the thing. That job I try not to touch - I like things delivered to my shop clean & ready to work on.

FKT

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4 hours ago, jibjab said:

It'd be a couple of mm thick I'd say... what are you thinking here?

Just if the post is overbuilt compared with the mast, then it won't matter much if you need to drill new holes in it.

 

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5 hours ago, longy said:

Thi lets you re-use the existing holes in the mast, much better than drilling new holes all in the same small area. Sheaves MUST ride on smooth shank of bolt - this may be the hardest part of the job.

I''d use a Clevis pin

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I went down to the nearest reasonably stocked chandlery to see if they had a new sheave the same side. Sadly, they didn't. I ended up buying a whole new double-block that was fairly close size-wise to the existing holes in the flanges, and got a couple of bolts with lock nuts to fix it to the flanges. Here's the newly installed setup - sheaves run nice and smooth now. Hopefully that'll last another 20 years (like the first one).

2 hours ago, daffy said:

I''d use a Clevis pin

I looked for clevis pins the right size, but sadly, no one had what I needed. I'll stick my beak down there every time we put the mast up (before every race) just to make sure the nuts aren't coming off... she'll be right.. I hope.

Thanks everyone for your help and suggestions - I'm happy with the end result, and it's all thanks to you lot.

newexitblock.thumb.png.2f1c732fecac5ccbd96617b2650c82d0.png

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