Block/ deck organizers vs load?

[andreas.mehlin]

So, 500 sq ft mainsail. 25 kts of wind. Load on halyard about 2000lbs.
With a deck organizer and line coming in at 45 degree angle, gives 73% of 2000lbs = 1460lbs. Correct?

Genoa halyard ...lets say the same numbers as the mainsail.

So, a deck organizer with 4 sheave (main halyard, Genoa halyard, spinn halyard, centerboard lift) with safe working load at 1600lbs (brl at 4000 lb), would not be very suitable?

[Benz]

It depends on whether the attachment points of the organizer (I'm guessing it's two fasteners) are rated to 4000# BL, or whether each individual sheave pin is.
Also, will you be flying the genoa and spinnaker at the same time? And lastly, how heavy is the centerboard?
If you're flying 500 SF of mainsail in 25 kts, it's probably time to reef.

[andreas.mehlin]

Originally Posted by Benz

It depends on whether the attachment points of the organizer (I'm guessing it's two fasteners) are rated to 4000# BL, or whether each individual sheave pin is.
Also, will you be flying the genoa and spinnaker at the same time? And lastly, how heavy is the centerboard?
If you're flying 500 SF of mainsail in 25 kts, it's probably time to reef.

Haha, yeah it would be time to reef. But u know...sometimes wind can pick up fast, and before it has been reefed - I still have to fight those 25kt

No I won't fly the spinnaker at the same time as the genoa....

Number of fasteners in a 4 sheave is 4.

...but yeah, the question is if the load rating is per sheave and not the total?

[Matt Johnson]

Most brands seem to have the same SWL of their 2,3 or 4 sheave organizers. It makes sense this is not a cumulative, but each "blocks" SWL, since most are through bolted through each sheave. The only time I've seen a reduction of SWL is when stacking.

Matt

[GordMay]

Originally Posted by andreas.mehlin

So, 500 sq ft mainsail. 25 kts of wind. Load on halyard about 2000lbs.
With a deck organizer and line coming in at 45 degree angle, gives 73% of 2000lbs = 1460lbs. Correct? ...

A 2,000Lb Load at 45 Deg has a Tension Factor of 1.414, hence the block will see an effective load of 2,828 Lbs.
A 2,000 rated block, used at 45 Deg, has a Reduction Factor of 0.707, hence an effective rating of 1,414 Lbs.

Tension Factor = Inverse of (Sling Angle) Reduction Factor

[GordMay]

... Tension Factor = Inverse of (Sling Angle) Reduction Factor

Sling tension is the weight of the load divided by the number of sling legs, times the sine of the angle (the sine of 90° = 1, & sine of 45º = 0.7071).

[Matt Johnson]

Here is Harken's info which shows the organizer would have 76% of the load at 45 degrees:

https://www.harken.com/article.aspx?id=12857

Matt

[Captain Bucknut]

Now I’m no master rigger, but I do know enough about physics to be dangerous. Using round numbers, you assume your 2,000 lbs of force on the halyard at the head. At a 1:1 ratio that force is being applied on the halyard at the mast block. Said halyard travels down the mast to another block which reduces the force on the halyard to a 2:1 ratio. At the organizer you would have a total of a 3:1 ratio and with a wrap around the winch you are at 4:1. So your force at the organizer would be reduced to 1/3rd of the overall force or +/- 700 lbs. I would think that if you had a 4 sheave organizer with 4 bolts rated at 4,000 lbs would be plenty of strength. I would think that you would want to worry more about reinforcing the cabin top with a plate as that would be your weak point in the equation.

[thunderhoof]

Note what funjohnson said above re stacking. If the sheaves are stacked say two to an axle, the sheave furthest from the deck has typically 1/2 the load bearing capacity of the lower one. I believe both Harken and Lewmar have this information in their literature.
Also, the organizer body should bisect the angle the lines are turning so that the load is in line with the row of mounting points.
A good practice is to position the organizer and orient the lines so the most highly loaded lines lead straight through the sheet stoppers directly to the surface of the winch drum. This reduces side loading (friction) in the stoppers.