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Author Topic: Attaching Cheek Block to Boom  (Read 5458 times)

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kurt

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Attaching Cheek Block to Boom
« on: March 16, 2010, 01:30:29 PM »

Hello everyone,

Replaced my MKI w a MKII boom sourced from Catalina.  Would like to attach a cheek block permanently for Reef #2 a al MKI style reefing to the boom.  (Using the internal single line setup for Reef #1.)  Don't want to install a track like the MKI's.

I am not sure yet if I can reach into the boom and hold the nuts for screws to attach the cheek block to the boom.   If I can will use screws.  If not, considering aluminum pop rivets.   Had good success pop riveting my new steaming light in last weekend and think this may be a good solution here as well.  Am I missing anything here?  Seems like the rivets should more than handle the sheer loads generated?  

Thanks,

Kurt
« Last Edit: March 16, 2010, 01:42:58 PM by kurt »
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Rick Allen

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Re: Attaching Cheek Block to Boom
« Reply #1 on: March 16, 2010, 02:23:51 PM »

Have you considered tapping it?  Is the alum to thin on the boom?  I just tapped a cam cleat to the mast and it works very well.

Just a thought...
« Last Edit: March 16, 2010, 02:24:34 PM by Rick Allen »
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Rick Allen, C34 IA Commodore
Former owner of "PainKiller", 1988 C34 MKI, Sail#746, std. rig, wing keel.

pablosgirl

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Re: Attaching Cheek Block to Boom
« Reply #2 on: March 16, 2010, 04:25:39 PM »

Hi Kurt,

You do not want to use Aluminum pop rivets!  Just when you need that reef the most in a 35K wind, they will sheer off!  The cheek block for the reef will be carrying the whole load of the foot of the mainsail since the reef does not have the benefit of the groove in the boom to help spread the load across the length of the foot of the main sail.  The tack of the mainsail in the full hoist position is held in place by both the out-haul and the bolt rope in the foot of the mainsail that slides in the top groove of the boom.

The problem with pop rivets is that the rivet is composed of a soft aluminum shell designed to deform (flare out) as you draw the center aluminum post through it.  The post then breaks under a predetermined tension force to sheer off the center post below the rivet head.  Please note the words "soft", "deform", and "sheer" in this description.  Not what you want in a high load application.  Pop rivets are fine for the steaming light and even attaching the small cheek blocks for your lazy jack lines to the mast, but these are not high, continuous loads as a first reef point is.

If you cannot back the bolts with nuts, I would tap the boom and use SS bolts as Rick Allen recommended.  The sheer strength of a SS bolt is way greater that that of a Aluminum pop rivet.  Be sure to use a bedding compound between the SS cheek block and fasteners and the boom that is suitable for dissimilar metal contact.  This will prevent corrosion of the aluminum boom (the more reactive metal) and the unsightly bubbling of the finish of the boom.

I have raced dingy's for 20+ years and have seen 3/16" pop rivets fail at the most inopportune times because of high load and corrosion.  To quote a famous C34 Forum contributor.... Just a thought.
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Paul & Cyndi Shields
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John Langford

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Re: Attaching Cheek Block to Boom
« Reply #3 on: March 16, 2010, 06:19:45 PM »

Isn't there a spare sheave at the end of the MkII boom and internal fittings designed to accommodate a second reef? I took my second reef line off some time ago but the boom on my MKII definitely has all the hardware in it for a second reef.
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Cheers
John
"Calypso"
MkII, #1431

kurt

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Re: Attaching Cheek Block to Boom
« Reply #4 on: March 16, 2010, 09:35:58 PM »

Thanks everyone.

Now starting to wonder now if the Schaefer Marine Cheek Block 2" Sheeve with 1750 lbs breaking strenght is strong enough.

Yes, I could go with internal reefing for the second reef but this would force me to add a block at the mast, change to a 3 or double deck organizer, add another clutch, modify the dodger to allow room for 3 lines...   For a reef (second) I use once or twice a year thought the MkI approach would be simpler and get the job done as it did for both reefs previously.

Thanks again,

Kurt
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waterdog

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Re: Attaching Cheek Block to Boom
« Reply #5 on: March 17, 2010, 12:18:29 AM »


The problem with pop rivets is that the rivet is composed of a soft aluminum shell designed to deform (flare out) as you draw the center aluminum post through it... 

I replaced every rivet and fastener in my mast and boom.   Any rivet that attaches anything is stainless steel (with nylon washers).   As my rigger said, "use aluminum rivets for filling holes for cosmetics, anything else should be stainless steel."    A large stainless rivet has some holding power - I attached my radar with rivets.

Save aluminum rivets for sealing up the foil pouch of mahi mahi before you throw it on the barbeque... 

You are quite right, a cheek block needs a threaded fastener (with lanacote on the screw and a plastic barrier between the block and boom.) 
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Steve Dolling
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cmainprize

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Re: Attaching Cheek Block to Boom
« Reply #6 on: March 17, 2010, 07:17:53 AM »

Hi Kurt
If you disassemble the end of the boom you can reach a long way in.  But I don't think you can make to far enough for a second reef cheek block.  I have a MK11 boat with the single line reefing.  I just added cheek blocks to the front of the boom for both reef 1 and 2 and a double cheek block to the rear of the boom to lead the lines aft.  I drilled and taped the boom.  I found the single line reefing difficult at best.  The boat is fairly new to us, but it only took one reefing exercise to realize single line reefing does not work for me.

Cory
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Cory Mainnprize
Mystic
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Roc

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Re: Attaching Cheek Block to Boom
« Reply #7 on: March 31, 2010, 05:39:25 AM »

Cory,
Do you have a picture of how you modified your single line to a double line.  I'm interested in doing the same.

Thanks!
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Roc - "Sea Life" 2000 MKII #1477.  Rock Hall, MD

pablosgirl

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Re: Attaching Cheek Block to Boom
« Reply #8 on: March 31, 2010, 06:16:42 AM »

Hi Kurt,

At 1750 lbs. the check block should be strong enough.  I just remembered an old rigger's trick.  If your arm cannot reach the holes from the end of the boom, take a wooden (or fiberglass) batten and tape or wire tie a box/combination wrench to one end of it with the box end extending just beyond the end of the batton.  Using masking tape, tape the nut into the box end of wrench, but only tape the side of the nut that will not make contact with the boom.  Also, cut a slits in the tape over the whole in the nut in an x pattern to allow the bolt to go through the tape without lifting the wrench off the nut.  You can use some Permetex #2 to stick the washer to the nut before inserting the assembly into the boom.  Work on the farthest away bolts first to avoid interference from a nut already placed.

Paul
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Paul & Cyndi Shields
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cmainprize

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Re: Attaching Cheek Block to Boom
« Reply #9 on: April 06, 2010, 04:06:02 AM »

Roc
I will take a pic this week when I get back to the boat.  The setup is very simple.  I found the single line reefing was a nightmare at best.  I went back to separate tack and clew lines for both reefs and lead the four lines to cockpit via the port coach roof.  We also use a stack pack mainsail cover so all the extra line drops into the bag when the sail is stowed.  Keeps everything nice and neat.

We only had room for five rope clutches on the port coach roof so we had to decide what lines we wanted to have run to the cockpit.  The reefing lines take up four clutches on the port side.  The spinnaker halyard and spare Genoa halyard are now at the mast.  We raise or spinnaker from a sock at the mast anyway so this works better for us.

Cory
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Cory Mainnprize
Mystic
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Roc

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Re: Attaching Cheek Block to Boom
« Reply #10 on: April 06, 2010, 04:37:32 AM »

Cory,
Pictures of your rope clutches would help too.  I'm thinking I can do a double line reef by ending the mainsheet line at the block on the port side (I see no reason for a double ended mainsheet).  That will give me a spare turning block below the traveler to run a second reef line.  I really would appreciate seeing your set up becaues this is something I do need to modify.
Thanks!
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Roc - "Sea Life" 2000 MKII #1477.  Rock Hall, MD
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