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Old 20-08-2017, 12:07   #1
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Block on top of 380 mainsail or not.

My 2 year old 380 came with a block on top of the main to make it easier to raise. This is regular sail, not square top.

2 weeks ago friend who had my boat called to say that the main halyard let go. A trip up to the top showed nothing up there to hold it up. They put a shackle up there, re attached the main. When I got back to the boat, I saw that the block was damaged. See pic. My assumption is that they over hoisted the main, broke whatever the fitting holding the halyard to the mast is (not sure it is a shackle or not as I didn't see how it was fastened originally) and the block on the head of the sail.

I am not sure I like having a block on the main. The block I have does not swivel, so it is in a wierd orientation, perpendicular to fwd/aft position. However, I know those who have swivel blocks have problems with twisting. So either way there is an issue.

I have an electric winch to raise the main. Right now I usually hoist it by hand to about 2/3 height anyway.

Is the 2:1 advantage really worth it on the 380? I am really thinking of just attaching the top of the halyard to the top of the main, and saving another 45' of line that I wind up coiling.
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Old 20-08-2017, 21:42   #2
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Re: Block on top of 380 mainsail or not.

With 1:1 halyard you will have another advantage - the ability to replace halyard without a trip to masthead.
If you stay with 1:2 arrangement - there is no shackle at mast head. The halyard is attached to a pin that sits at the aft end of the madt head, either with an eye splice at the end of the halyard or a knot around the pin.
The block MUST be parallel to the sail and without swivel. Just find a block that has the adequate connector e.g. with a swivel that can be locked in the position you need.
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Old 21-08-2017, 06:45   #3
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Re: Block on top of 380 mainsail or not.

Mark, Thanks. Guy who fixed it just put a shackle up there. The eyesplice looks good. Assuming now that by bringing up the main too high he must have damaged the pin and it failed, fell, etc.

Assuming you have this on the 400? I am not sure I really need this 2:1 purchase just to raise the main...Also, any idea who makes a block for this load with a lockable swivel? Appreciate the help.
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Old 21-08-2017, 06:59   #4
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Re: Block on top of 380 mainsail or not.

$0.02 worth of advice here, and worth every penny:

You can hoist that main with a 1:1 purchase on a calm day in the bay. On that black night when you are trying to sweat the last 12" of hoist in after putting in the second reef, you might wish you had the extra power.

Lagoon has built more than a few 380's and have refined the design pretty well.
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Old 21-08-2017, 07:30   #5
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Re: Block on top of 380 mainsail or not.

A winch provides way more power than the sail would ever need to be raised. Sheeting in a genoa in 25kts of wind needs way more power than raising a sail. Making it 2x easier on the winch, the winch doesn't care. A 2:1 block means 2x less power, but for 2x the time (you need to move 2x the length of line).
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Old 21-08-2017, 08:58   #6
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Re: Block on top of 380 mainsail or not.

Quote:
Originally Posted by jbinbi View Post
Mark, Thanks. Guy who fixed it just put a shackle up there. The eyesplice looks good. Assuming now that by bringing up the main too high he must have damaged the pin and it failed, fell, etc.

Assuming you have this on the 400? I am not sure I really need this 2:1 purchase just to raise the main...Also, any idea who makes a block for this load with a lockable swivel? Appreciate the help.
Mainsail head block - Rutgerson. I am sure there are other similar by Harken and more. Not rare but costly...
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Old 21-08-2017, 09:06   #7
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Re: Block on top of 380 mainsail or not.

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Originally Posted by jbinbi View Post
A winch provides way more power than the sail would ever need to be raised.
OK, if you say so...

I live aboard and cruise the Caribbean on an FP Lavezzi 40; a slightly lighter boat, with a slightly larger main than a L380. I can tell you that on my boat, achieving proper halyard tension on a loaded main takes all the power I am happy to apply on an 11mm halyard with 2:1 purchase. If you want to go 1:1, I'd think hard about upgrading to dynema or the like.

Then again, it's all about how you use your boat.
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Old 21-08-2017, 16:16   #8
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Re: Block on top of 380 mainsail or not.

Grateful made a good comment. I suggest you use Dyneema or similar low stretch halyard line for a single halyard. If it is exposed to the elements, an external halyard, it should have an overall jacket such as Sampson Warpspeed. 10 mm / 3/8 in. Warpspeed at 9800 lbs breaking should be sufficient. One issue is that most line stoppers may slip when the mainsail is under load with a 1:1 purchase when it may have have been ok with 2:1. The simple solution is to leave the line on the winch otherwise it may be best to use 2 stoppers in series.
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Old 23-08-2017, 12:08   #9
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Re: Block on top of 380 mainsail or not.

I think using a 2:1 halyard lessens the compression load on the mast compared to a 1:1. So less wear and tear on the mast from compression loading I guess.
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Old 23-08-2017, 12:11   #10
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Re: Block on top of 380 mainsail or not.

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I think using a 2:1 halyard lessens the compression load on the mast compared to a 1:1. So less wear and tear on the mast from compression loading I guess.
Not exactly...
Half load x 2 lines.
Load is equal.
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Old 23-08-2017, 12:16   #11
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Re: Block on top of 380 mainsail or not.

Another issue which may have caused this damage to the block is due to twist in the line. When you wrap the line around a winch, that twisting gets transferred to the line which works its way up to the block. If the line is twisted and the block is forcibly raised against the twist, I would expect to see the kind of damage to the side of the block as shown in your photo.
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Old 23-08-2017, 12:57   #12
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Re: Block on top of 380 mainsail or not.

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Originally Posted by Privilege View Post
Another issue which may have caused this damage to the block is due to twist in the line. When you wrap the line around a winch, that twisting gets transferred to the line which works its way up to the block. If the line is twisted and the block is forcibly raised against the twist, I would expect to see the kind of damage to the side of the block as shown in your photo.
Good point. Another reason for 1:1, not 2:1. I think I will try the no block solution for a bit. Won't cut the line just yet in case it is not as good.
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Old 23-08-2017, 13:02   #13
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Re: Block on top of 380 mainsail or not.

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Originally Posted by meirriba View Post
Not exactly...
Half load x 2 lines.
Load is equal.
Try googling 2:1 halyard v mast compression - consensus seems to be 2:1 reduces compression by 25%. This is reason a lot of high performance dinghy's go for 2:1 or even a halyard lock (which reduces compression load to 50%).

It seems the compression load on the mast is the sum of force applied down the luff and the force down the halyard.

Also think about load on the sheave and bolt. If there is 100kg load on a single halyard to pull the sail tight, then the load on the sheave itself with 2:1 will be half , i.e. 50Kg, the other 50% is held by the mast head where halyard is tied off.

I would suggest that you do not use the same halyard line used on the 2:1 for your 1:1, some one posted that dyneema (if not already used would be good) if dyneema is already in use you may need to increase the diameter of the halyard to stay within designed specs and then you need to think about twice the load on the winch and jammers and any other load bearing elements in the halyard system.

I appreciate this is a Lagoon not a Volvo race boat, but I don't know what latitude the mast designers put in for their considerations for halyard specs.
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Old 24-08-2017, 01:12   #14
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Re: Block on top of 380 mainsail or not.

Quote:
Originally Posted by Bean Counter View Post
Try googling 2:1 halyard v mast compression - consensus seems to be 2:1 reduces compression by 25%. This is reason a lot of high performance dinghy's go for 2:1 or even a halyard lock (which reduces compression load to 50%).
It seems the compression load on the mast is the sum of force applied down the luff and the force down the halyard
.
As I understand it, the total force required to keep the sail aloft is identical, as you hint by last sentence above. So it does not matter how it id divided among the lines.


Also think about load on the sheave and bolt. If there is 100kg load on a single halyard to pull the sail tight, then the load on the sheave itself with 2:1 will be half , i.e. 50Kg, the other 50% is held by the mast head where halyard is tied off.....
This I agree to wholeheartedly
I have high regard to Google, but physics comes first.
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Old 24-08-2017, 06:35   #15
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Re: Block on top of 380 mainsail or not.

This topic was covered in 42' Leopard - Do I Really Need a Double Halyard ?

Also to test the physical theory I got a boat hook and placed vertically it on a set of bathroom scales. I hung a bucket of water weighing 20 pounds on boat hook =20 lbs. This equals the halyard lock scenario.

I then hoisted the bucket with a 1:1 pull over the top of the boat hook - reading on the scales 40 lbs.

Hoisted the bucket with a 2:1 and reading was close enough to 30 lbs so a 10 lb reduction in load on the scales = 25% reduction on compression from single line pull causing a 40 lb load.

So we are talking about the load on the mast not the boat. Anyway I am now satisfied that 2:1 decreases compression load on the mast itself.
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