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Old 12-09-2011, 10:33   #1
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Reef Line Tension

I am sizing hardware (turning blocks and clutch) for my reef lines and outhaul that will be run to the cockpit on a 36ft sloop using 3/8" line.

The mainsail size is approximately 250sq/ft (41ft luff and 11ft foot). Using the following mainsheet load calculator (Mainsheet Load Calculator) says a 25-30kt wind is between 2151lb to 3098lb but I expect the loads on the outhaul and reef lines to be significantly less. Obviously, the higher the wind, the less sail will be used so that also will reduce the load.

Does anyone know this value?

I originally estimated about 1100LBs (500KG) max so I was looking at the SpinLock XTS clutch which is capable 2200LB(1000KG) but it does not fit well. The XAS apparently is slightly shorter and will be easier to position but only has a SWL of 990LB(450KG).

Thanks for any help you can provide.
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Old 12-09-2011, 10:42   #2
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Re: Reef Line Tension

Thinking out loud here: wouldn't you get the outhaul number on the load calculator you're using by using 0 (zero/zed) for the "D" factor in the equation?
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Old 12-09-2011, 10:51   #3
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Re: Reef Line Tension

Quote:
Originally Posted by ADMPRTR View Post
I am sizing hardware (turning blocks and clutch) for my reef lines and outhaul that will be run to the cockpit on a 36ft sloop using 3/8" line.

The mainsail size is approximately 250sq/ft (41ft luff and 11ft foot). Using the following mainsheet load calculator (Mainsheet Load Calculator) says a 25-30kt wind is between 2151lb to 3098lb but I expect the loads on the outhaul and reef lines to be significantly less. Obviously, the higher the wind, the less sail will be used so that also will reduce the load.

Does anyone know this value?

I originally estimated about 1100LBs (500KG) max so I was looking at the SpinLock XTS clutch which is capable 2200LB(1000KG) but it does not fit well. The XAS apparently is slightly shorter and will be easier to position but only has a SWL of 990LB(450KG).

Thanks for any help you can provide.
How deep will your reef be? Further, you can use the formula Clew load = SA x V^2 / 100 on the reduced sail area (when reefed) to determine the loading on the reef point and go from there.

FWIW...
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Old 12-09-2011, 10:59   #4
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Re: Reef Line Tension

Yes, I thought of that. which is 1173LB(25kt) to 1690LB (30Kt) but I wasn't sure if that is accurate as the loads on the mainsheet and outhaul/reef lines are similar but different.
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Old 12-09-2011, 11:09   #5
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Re: Reef Line Tension

Personally, using that calculator I would set the luff and foot lengths equal to the reefed sail size, and the mainsheet distance to zero, since you are looking at the load on the reefing line, which is the new clew of the sail. If I use 10,35,30, and 0 I get a load of 1300 lbs.

And I would expect the load to be greater than the calculator estimates. Remember, once you reef you have a loose-footed main. All the forces that are transmitted to the mainsheet come to the boom through the reefing line. There is no other load path (with a full main, unless it is loose-footed, the bolt rope in the track transfers a fair amount of that load). In addition, the reefing line also becomes the outhaul, so there is that load on the line as well. I don't have any numbers, but my experience is that reefing lines are pretty highly loaded.

Hope that helps, since I don't have numbers to give.
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Old 12-09-2011, 11:17   #6
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Re: Reef Line Tension

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Originally Posted by ADMPRTR View Post
Yes, I thought of that. which is 1173LB(25kt) to 1690LB (30Kt) but I wasn't sure if that is accurate as the loads on the mainsheet and outhaul/reef lines are similar but different.
Under normal circumstances, one end of one's reefing line passes through the reef cringle, down and around the boom and is tied to itself on one side of the sail, and down and too the boom-end turning block on the other side. When taken in, the sail is hauled down to the boom and out toward the boom end. The resultant of the vectors of the tension in the line on either side of the cringle is what resists "clew load" at the reef cringle (the new "clew"). Accordingly, the loading in the reefing line due to tension is less than the indicated "Clew Load" although one would have to have the specific geometry of the sail, boom arrangement to make such a calculation. (Note too the the formula given above is only a conservative approximation of the actual loads as mains are rarely loaded normal to the plane of sail.) Accordingly, using the indicated "clew load" would seem to be safely conservative.

FWIW...
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Old 12-09-2011, 11:20   #7
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Re: Reef Line Tension

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Originally Posted by svHyLyte View Post
How deep will your reef be? Further, you can use the formula Clew load = SA x V^2 / 100 on the reduced sail area (when reefed) to determine the loading on the reef point and go from there.

FWIW...
Thanks. That helps a lot. Using the outhaul as example (which would be a full 250sq fit of sail) that would be 1563lb for 25kts although my boat has a block and tackle on the outhaul which reduces it to less than 782lbs (assuming at least a 2:1 ratio).

Estimating reefs:
Reef#1 at 38' luff and 9' foot is approximately 167sqft with a load of 1069lb.
Reef#2 at 35' luff and 7' foot is approximately 123sqft with a load of 765lb
Reef#3 at 32' luff and 5' foot is approximately 80sqft with a load of 500lb.

Assuming these values are correct, with Reef #1 I would be exceeding the SWL of the clutch by 100lbs or more in a 25kt blow and 550lb in a 30kt blow.

I guess the question to answer is what is the margin of safaty with that SpinLock XAS clutch?
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Old 12-09-2011, 11:25   #8
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Re: Reef Line Tension

Typically it is assumed that the reef clew loads (on the sail) are equal to the mainsheet loads. Basically, the max loading is driven by the boat's righting moment at 30 degrees of heel - no matter if the sail is full or reefed you have the same righting moment at the same heel angle. However, on most reef line set-ups, the reef clew line has a 2:1 purchase on the reef clew grommet (one end on the reef line is tied to the boom, which gives a 2:1 purchase). So, excluding friction, the loading on the line is roughly 1/2 the loading on the sail reef grommet.

Net net, you would be conservative if you took the reef line loads = to the mainsheet loads, you would be aggressive/optimistic if you took the reef line loads = 1/2 the mainsheet loads (because you are ignoring friction and loading angles), and middle of the road if you used 75% of the sheet loads.

Given the varous calculations, the XAS looks somewhat marginal.
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Old 12-09-2011, 11:37   #9
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Re: Reef Line Tension

Only the load on my outhaul is reduced so the single reeflines I will use the conservative calculation where reef line load = main sheet load. Using the calculator instead of the equation results in lower numbers which are all in the SWL except for #1 in a 30kt wind (In which I would probably be either reduce further or better yet hide is some well sheltered anchorage ):
25kt
#1 = 896
#2 = 647
#3 = 439

30kt
#1 = 1291
#2 = 932
#3 = 613

Thank you all for your help, proving once again what a great place the CF is!
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Old 12-09-2011, 11:40   #10
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Re: Reef Line Tension

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Originally Posted by estarzinger View Post
Given the varous calculations, the XAS looks somewhat marginal.
If this was your boat, would you find a way to get the XTS to work?
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Old 12-09-2011, 11:57   #11
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Re: Reef Line Tension

Wouldn't the load on the reef line be 1/2 the clew load, as it's acting as two lines?
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Old 12-09-2011, 12:01   #12
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Re: Reef Line Tension

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Originally Posted by ADMPRTR View Post
If this was your boat, would you find a way to get the XTS to work?
I certainly try to avoid using hardware that's borderline as there are always unexpected shock loads.

What's the specific difficulty using/fitting the XTS?
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Old 12-09-2011, 12:15   #13
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Re: Reef Line Tension

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Originally Posted by estarzinger View Post
I certainly try to avoid using hardware that's borderline as there are always unexpected shock loads.

What's the specific difficulty using/fitting the XTS?
In order to place the clutch in the fully opened position (to release the line), the handle has to be extended forward of the housing. The space I have so so tight that the handle is blocked by the forward edge of the dodger and would be resting against the dodger with some pressure when in the open position.

It may be workable but is not very convenient and I am concerned that the handle could be broken. When mocking it up, I actually had to unzip the dodger window pane to get it fully open.

Apparently the XAS is 1.5" shorter when fully open so that will give me more space to manipulate it.

With a clutch like this, what happens if the SWL is exceeded. Does it blow up or just release the line? If it only releases the line (without damaging the clutch) then on those few occasions when I am in 25+kt winds I can use a spare cleat to help relieve the pressure (which sort of defeats the purpose of having a clutch but it may be a suitable work around).
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Old 12-09-2011, 12:28   #14
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Re: Reef Line Tension

Quote:
Originally Posted by ADMPRTR View Post
Only the load on my outhaul is reduced so the single reeflines I will use the conservative calculation where reef line load = main sheet load. Using the calculator instead of the equation results in lower numbers which are all in the SWL except for #1 in a 30kt wind (In which I would probably be either reduce further or better yet hide is some well sheltered anchorage ):
25kt
#1 = 896
#2 = 647
#3 = 439

30kt
#1 = 1291
#2 = 932
#3 = 613

Thank you all for your help, proving once again what a great place the CF is!
I would want my #3 reef to stand up to the loads a 40 knot wind would provide. Having a reef blow out during a gale is a great way to begin a Charlie Foxtrot.
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Old 12-09-2011, 12:36   #15
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Re: Reef Line Tension

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I would want my #3 reef to stand up to the loads a 40 knot wind would provide. Having a reef blow out during a gale is a great way to begin a Charlie Foxtrot.
So that would target a load of 1090 to 1280 (depending on which calculation). The upper value exceeds the XAS SWL by 30%. Is is reasonable to expect in that situation to use a spare cleat to help relieve the tension?

BTW, what do you mean by "great way to begin a Charlie Foxtrot", please?
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