Mast Base Block Strength

[Warren Kaplan]

I'll be running some lines aft to the cockpit next year on Sine Qua Non (CD27). I'll be installing a "halyard organizing plate" from Dwyer Aluminum Mast below the mast step. This plate has 14 holes onto which I'll attach swivel blocks to lead the lines aft. I called Harken and they suggested their 57mm Air Blocks (not Carbo Air Blocks). The sheaves are the right size for the 3/8 line I'll be using. I'll be running at least the main halyard and probably a set of reefing lines and a cunningham line back (thru deck organizer, rope clutches and I'll have a winch). I may bring more back if I like it. But here's the question...how strong should these blocks be on a CD27. The 57mm airblock (Harken #1950) has a safe working load of 1655 pounds and a breaking strength of 3310 pounds. A less high tech harken block (#1540) has a safe working load of 1800 pounds and a breaking strength of 5000 pounds and is less expensive than the airblock ($65 vs $85 at Wests). Now if I were only buying one block, it wouldn't be a big deal. But I may have half a dozen blocks shackled on before I'm done and that starts to add up. I want a well constructed block that won't fail or have to be replaced every 2 years. I'll want one with some reserve strength in case I have to haul on those lines with the sails under load. But do I need blocks that have 1655 or 1800 pound working loads or can I get away with blocks SAFELY with lower load capacity, and therefore with a lower price, on a CD27? I'm open to suggestions for any "quality" blocks that can do the job.
Thanks,
Warren Kaplan
Sine Qua Non
CD27 #166 (1980)



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[Larry DeMers]

Warren,

Those blocks are nice quality, but way overkill in breaking strength I think. For your halyard, I doubt that you will have to apply more than 50 lbs of downward pull on the halyard at worst, but to be safe, double that to 100 lbs. You might end up with 150 lbs. then at the bitter end of the halyard that the winch will have to provide traction for. The total working load would then be 150 lbs. Reefing lines are a similar number, although I can see a case where the final loading on the block could be high due to the resisances in the system getting large when the reefing line is tightened to almost the very tight point. THe loading then is hte highest of all, but again, I cannot imagine it would be more than say 100 lbs. For safety, double that too.
So both examples would be fine with a 1000 lb breaking strength block rather than 3x that. It would still be more than you need, but that's ok to this extent. It would be convenient if you sized these turning blocks to serve in an emergency capacity, should another block fail while you are out and about. With these turning blocks pressed into service as an emergency block to be used on the main boom for instance, replacing a boom mounted block..it'll get you home anyway, even if it needs jury rigging.

I wonder if West Marine's 'Advisor' articles talk about what breaking strength various sizes of boat should have? Or Nigel Calder?

Cheers,

Larry DeMers
s/v DeLaMer
Cape Dory 30

I'll be running some lines aft to the cockpit next year on Sine Qua Non (CD27). I'll be installing a "halyard organizing plate" from Dwyer Aluminum Mast below the mast step. This plate has 14 holes onto which I'll attach swivel blocks to lead the lines aft. I called Harken and they suggested their 57mm Air Blocks (not Carbo Air Blocks). The sheaves are the right size for the 3/8 line I'll be using. I'll be running at least the main halyard and probably a set of reefing lines and a cunningham line back (thru deck organizer, rope clutches and I'll have a winch). I may bring more back if I like it. But here's the question...how strong should these blocks be on a CD27. The 57mm airblock (Harken #1950) has a safe working load of 1655 pounds and a breaking strength of 3310 pounds. A less high tech harken block (#1540) has a safe working load of 1800 pounds and a breaking strength of 5000 pounds and is less expensive than the airblock ($65 vs $85 at Wests). Now if I were only buying one block, it wouldn't be a big deal. But I may have half a dozen blocks shackled on before I'm done and that starts to add up. I want a well constructed block that won't fail or have to be replaced every 2 years. I'll want one with some reserve strength in case I have to haul on those lines with the sails under load. But do I need blocks that have 1655 or 1800 pound working loads or can I get away with blocks SAFELY with lower load capacity, and therefore with a lower price, on a CD27? I'm open to suggestions for any "quality" blocks that can do the job.
Thanks,
Warren Kaplan
Sine Qua Non
CD27 #166 (1980)

demers@sgi.com

[Warren Kaplan]

Larry,
Thanks for the input. I didn't think I needed all that "strength" in those blocks since heretofore I've been raising the main, reefing the main, and hauling on the cunningham using the "armstrong" system. Not even a winch. I know I sure didn't generate anywhere near 1800 pounds working load with that technique! If I had to generate that much pull I'd have to be the "incredible hulk" roaming the foredeck. Alas, some people do refer to me as the incredible hulk, especially when Sine Qua Non takes a starboard list when I'm walking up the starboard side of the deck. Too bad hulk doesn't necessarily equal strength!

Warren



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[Ed Haley]

The turning block itself can double the applied force depending on the angle the exit line makes with the device. At the bottom of the mast, the force on the turning block sheeve will by itself almost be double your effort force. But, as Larry says, 1000 lbs breaking force is sufficient for halyards even when winching aboard a CD27.



eghaley@twcny.rr.com

[Andy Denmark]

Hi Warren,

We have typically used Schaefer Size 5 blocks for these applications and never had a failure. I suggest you get the ones with the aluminum or stainless sheaves as the plastic sheaves seem to deteriorate from sunlight over time. Sheave breakage seems to be the primary failure mode for these blocks. I had Schaefer put a metal sheave in a block some years ago as such a thing wasn't in the catalog. When I told them what I wanted it showed up by UPS the next week.

Consider upgrading to 5/16" Sta-Set X halyards when you replace your halyards. This is nearly as strong as wire and with virtually no stretch. Use knots, not splices, at the halyard shackles. Knots keep you from sucking the halyard into the sheave box. I use a simple overhand knot and sew the tail down. Has worked without fail for years.

Hope this helps.

Andy Denmark
CD-27 #270 "Rhiannon"
Oriental, NC (where there are more sailboats than people!)





trekker@coastalnet.com

[Jerry J Commisso]

Hi Warren,
Check out Garhauermarine.com. I replaced all the blocks on my CD30 with Garhauer. And on a Cutter that adds up to a lot of blocks. They are very high quality and also very inexpensive, compared to any of the other manufacturers. They have two styles to choose from, with bearings and without. You can only buy from them directly either by mailorder or at shows. I would recommend these blocks to anybody who wants to add on or upgrade. Good luck.

Jerry J Commisso
CD30c CHELSEA ROSE

I'll be running some lines aft to the cockpit next year on Sine Qua Non (CD27). I'll be installing a "halyard organizing plate" from Dwyer Aluminum Mast below the mast step. This plate has 14 holes onto which I'll attach swivel blocks to lead the lines aft. I called Harken and they suggested their 57mm Air Blocks (not Carbo Air Blocks). The sheaves are the right size for the 3/8 line I'll be using. I'll be running at least the main halyard and probably a set of reefing lines and a cunningham line back (thru deck organizer, rope clutches and I'll have a winch). I may bring more back if I like it. But here's the question...how strong should these blocks be on a CD27. The 57mm airblock (Harken #1950) has a safe working load of 1655 pounds and a breaking strength of 3310 pounds. A less high tech harken block (#1540) has a safe working load of 1800 pounds and a breaking strength of 5000 pounds and is less expensive than the airblock ($65 vs $85 at Wests). Now if I were only buying one block, it wouldn't be a big deal. But I may have half a dozen blocks shackled on before I'm done and that starts to add up. I want a well constructed block that won't fail or have to be replaced every 2 years. I'll want one with some reserve strength in case I have to haul on those lines with the sails under load. But do I need blocks that have 1655 or 1800 pound working loads or can I get away with blocks SAFELY with lower load capacity, and therefore with a lower price, on a CD27? I'm open to suggestions for any "quality" blocks that can do the job.
Thanks,
Warren Kaplan
Sine Qua Non
CD27 #166 (1980)

liasboat@aol.com

[Warren Kaplan]

Larry, Ed, Andy, Jerry,

Thank you all for the advice. I know can set up a plan on how I want to do this. Man, I just get an education every time I sign on to this board! Thanks again!

Warren



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