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Old 18-12-2014, 14:14   #1
Eyr
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New Blocks for Mainsheet on 45 Footer

After complaints from the crew (and myself) when taking in on the mainsheet during the last season I have had a look at the blocks in the system. They are a sorry bunch.

The boat is a Beneteau First 45f5 with mid boom sheeting led forward to the mast and back into the cockpit through a Spinlock rope clutch and to a size 43 winch. The current setup is 3:1 and the main is about 48 square metres.

We do mostly cruising, and one big cruising regatta each year. I don't need fancy race stuff, but would like some advice as whether to increase the purchase or not and tips as to which blocks to get...

Thanks!
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Old 18-12-2014, 15:43   #2
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Re: New Blocks for Mainsheet on 45 Footer

Another possible source of extra friction is either too large line used for the size of the blocks or line that has become stiff with age (like me). Either one will increase the effort in sheeting in the main. Our mainsheet, on a similar size boat with similar setup, is 10 mm spectra core double braid. At around 10 years of age, it has become quite stiff and there is a lot more effort required... replacement on the to-do list!

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Old 18-12-2014, 15:47   #3
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Re: New Blocks for Mainsheet on 45 Footer

Quote:
Originally Posted by Eyr View Post
After complaints from the crew (and myself) when taking in on the mainsheet during the last season I have had a look at the blocks in the system. They are a sorry bunch.

The boat is a Beneteau First 45f5 with mid boom sheeting led forward to the mast and back into the cockpit through a Spinlock rope clutch and to a size 43 winch. The current setup is 3:1 and the main is about 48 square metres.

We do mostly cruising, and one big cruising regatta each year. I don't need fancy race stuff, but would like some advice as whether to increase the purchase or not and tips as to which blocks to get...

Thanks!
Garhauer makes good blocks at a reasonable price.
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Old 18-12-2014, 18:33   #4
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Re: New Blocks for Mainsheet on 45 Footer

I doubt it's the blocks. If I remember right the 43ST is just above 40:1 purchase, with the 3:1 blocks you are running 120:1 total purchase. Assuming an input power of 20lb, which is very minimal for a fit person (the normal assumption is 50lb) that gives you 2400lbs of load. Frankly at this point your deck gear should be starting to fail.

I think you either have a reacing problem, or a series of seized blocks.
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Old 18-12-2014, 19:43   #5
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Re: New Blocks for Mainsheet on 45 Footer

A picture might help, but Beneteau does not generally oversize their blocks or use too many that have ball-bearings. As Stumble suggests, you may have some that have seized or which don't spin freely. The setup you describe - a 3:1 mechanical advantage - is not a lot for a main as big as yours. We have 8:1 on our 36 m3 mainsail - but no winches. The size of your sheet winch makes up for that, but your setup, however, going from midboom forward (along/under the boom), then down (along the mast) and then aft to the cockpit (along the cabintop) adds a lot of friction in the turning blocks without adding any mechanical advantage. If any of these aren't running freely, trimming the main is going to be more work than it has to be.
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Old 18-12-2014, 21:05   #6
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Re: New Blocks for Mainsheet on 45 Footer

Talk to the folks at Harken, & or www.APSltd.com Harken makes, & has always made excellent blocks. Their Air/Big Boat blocks being my favorites on the planet.
Also, if you go to their website, they have diagrams of how to choose what kind of mainsheet (or other system) which you want, as well as what sized blocks are appropriate for your sized boat with such a system.


They also have the formulas listed for how to calculate sheet loads for various sails (although the one for mains is a bit screwy, as it comes up with far higher load number for mains than for jibs of the same size). But if you give them a call, they're more than happy to talk to you... including/especially the customer service department.


Plus, often enough, you can pick up older gen. Big Boat blocks used, like on Ebay, dirt cheap. Just make sure that they weren't used with wire, as it scores & scars the sheaves, which will cause rope sheets to wear out a lot faster.
And if you run across some which don't come with shackles, those are easy enough to find.
And there are, of course newer, & new Harken blocks around. On Ebay, as well as at lots of vendors at less than retail prices. You know, last year's model at good sized discounts.


I hear good to great things about Karvers, but don't have much experience with them. And would pass on most Lewmars. They tend to be rather fragile compared to their catalog, load ratings. Especially on mainsheets, where blocks regularly get slammed.


NOTE: Sometimes the blocks which you have just need a good servicing (deck/cheek blocks included). Disassembly of the block, & a good cleaning & polishing of all of the moving parts. A little bit of rust, salt & dirt, can really add up, to cause some older block designs to lose efficiency, or plain old freeze up. And it's a great season for doing such maint.
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Old 19-12-2014, 00:55   #7
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Re: New Blocks for Mainsheet on 45 Footer

Thanks for your input!

The blocks are not totally seized, but not far from it. The setup is actually 4:1, see photo.
The line is covered dyneema and 12 mm. I don't know how old it is, it was on the boat when I bought it last year. Might be worth it to give it a proper wash?

Had a try at different calculators to estimate the loads. The simplest suggest mainsheet load in kg is 25 x mainsail area in square metres and to add 50% because of mid-boom sheeting. That means 25x48 = 1200 kg + 600 totalling 1800 kg. That means that I would need blocks with a Mean Working Load (MWL) of 2000 kg, but because the angle of deflection is 180 degrees the load on the block is 200%. Resulting in a need for blocks with a MWL of 4000 kg (8800 lb).

Seems the advice given to search Ebay is a rather good one. Blocks this big are expensive. 😛
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Old 19-12-2014, 00:56   #8
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Re: New Blocks for Mainsheet on 45 Footer

Here's a photo of the setup.
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Old 19-12-2014, 18:07   #9
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Re: New Blocks for Mainsheet on 45 Footer

That's a pretty terrible set up. At a minimum the bottom should be a side by side block not two seperate ones. I would probably go to fiddle blocks with a becket to get a better lead.

Personally I really like harken, but I would absolutely think about Karvers.
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Old 21-12-2014, 14:04   #10
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Re: New Blocks for Mainsheet on 45 Footer

It's more than terrible, and that is why I want to change it. The question still stands though, how do I properly size the blocks?

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Old 22-12-2014, 17:35   #11
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Re: New Blocks for Mainsheet on 45 Footer

Can you find the part number and manufacturer of what you have? Generally it is easier to just replace size for size as opposed to figuring it out mathematically. Obviously what you have hasn't broken, just failed due to time. So whatever strength they are should be good enough.

The formula is below if you want to work it out that way. It will give you the total sheet load, which is divided by 3 for the blocks, but the fastening system (shackles) need to be able to carry the whole load. So unless you are getting really minimal I would just go with stuff rated to carry the whole load at the blocks.

Something like the Karver cascade below on the top and bottom, with the sheet eye spliced thru the hole in the top block acting as a becket.

Harken
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Old 25-12-2014, 02:31   #12
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Re: New Blocks for Mainsheet on 45 Footer

On sizing, & I'm using your formula & the numbers which you've provided, said information has you looking at/for blocks based on 34-35kts of wind. Probably not a likely number that you're main will see (at least without 2 reefs in it). For if it does, either your boat will heel, & spill the load, or you'll dump the traveler & sheet until you can get it reefed.

I don't know where you snagged the formula in question, however, it's likely that they print it thusly, both to cover their backsides, as well as to provide some safety factor in blocks to account for things like accidental jibes (which I'd imagine is when the majority of mainsheet systems lose blocks).
I also gather that, you've neither spoken with (or emailed) Harken, nor been to their website. Re; Getting help on choosing blocks.

That said:
- On their old school blocks, the 4" (or 4.5") Big Boat blocks should be fine (YMMV). Per sheave, the working load on them is 5,000lbs, with a 10,000lb rated breaking load. Keeping in mind too, though, that these aren't new blocks, so condition (speaks to severity of usage) is key.
- On their newer, Air Blocks, I'd figure that you'd be fine with their 75mm blocks. The non Low Load variants. Though you'd probably be fine with their 75mm Low Load & Runner blocks.
Albeit given the consequences if that's incorrect, well, let's just say it would be foolish (to put it mildly), not to speak with Harken first. Ditto on asking them about the other style of block mentioned earlier.

BTW: They've got some nice blocks on sale @ Harken at the moment, likely some other spots too. And if you speak with a retailer nicely, given that it's not exactly the sailing High Season in the N. Hemisphere, you might be able to work out a discount.
There were also some SMOKIN deals on blocks sized as above on Ebay, a week ago, moments after my 1st post here. Perhaps some of them are still around. I saw a couple of setups that would have worked for about $500 (not including shipping, plus some spectra lashings). Just boom & traveler blocks combined, not including ones to lead things to the deck, or cheek blocks.

Just when you're looking at blocks, do a reality/sanity check. Ask what wind strength, based on your main's size, will it take to reach the block in question's breaking point? Then add in a safety factor.
For me, using Harken's, on the main on my boats, I'd figure the load on the system @ 22kts (as by then on most any boat you'd have reefed, plus in non-metric units, at that wind speed, it works out to 2lb/sqft KISS). Then I multiply by 4-5 typically, & size things from there.

Though the "safety factor" thing, & how much to figure in part, is a bit of a trick question/judgment call. I say that as I've seen brands of blocks which I'm not a fan of, fly apart (non shock-loaded) at 20% of their rated working load. And others, not even flatten bearings when run on boats 2.5x their rated size/load.
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Old 25-12-2014, 03:22   #13
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Re: New Blocks for Mainsheet on 45 Footer

NOTE: Correction regarding Safety Factors above. When I was explaining my process for figuring block size, I said Breaking Load, where I meant Working Load. The same is also true on doing a reality check on other brands of blocks.
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Old 27-12-2014, 07:00   #14
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Re: New Blocks for Mainsheet on 45 Footer

Thanks a lot for your input.

The blocks in the system right now are one double with a sheave diameter of 100 mm (3.9") from Goiot. The others are without names and about 80 mm i diameter.
The load formula was found at an other forum. When I put my data into the Harken calculator, P=16.70 m (54.79') and E=5.70 m (18.70'), it gives a load of 1825 kg (about 4000 lbs) at 25 knots (12 m/s), which would be about time to put in the first reef.

You are quite right about it not being High Season Uncivilized, today is sunny, but with a temperature of -16 degrees Celcius (3 degrees Farenheit) there is not a lot of sailing going on here in Norway. I have tried contacting my local dealers, but Christmas puts everything on hold over here, so still awaiting a reply. I have been recommended Ronstan or Selden by my sailmaker, with Selden being easier on the wallet. They make a 100 mm plain bearing block with SWL of 4000 kg which should be plenty enough, still searching Ebay tough, the Karver's look nice.

Thanks again for your help, and Merry Christmas to you from the Land of Ice and Snow!
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Old 27-12-2014, 07:26   #15
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Re: New Blocks for Mainsheet on 45 Footer

Oh man...

That was hard work just lookin' at the setup let alone leanin' on the tail end...

I like cascades there too... plenty O room for it...
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