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Backstay tension adjuster

The standard backstay tension adjuster was nearly impossible to handle by hand with it's 1:16 exchange ratio. We wanted something that was lighter in weight and easier to handle so we asked Harken in Sweden to come up with something for us. The result was a 1:48 ratio exchange adjuster with Dyneema lines. The backstay in it self is still the original one in steel wire. All fitting was done by us so we have to say that this was quite easy to do without any professional assistance.

Update 2020-10-23:
The backstay was changed few years ago to Dyneema. I also like to add acomment here regarding the "red rope". Dont buy it before you have fixed everything else. Depending on how your final settings will be, length of the ropes used between the blocks, the lenght of the "red rope" can bee too much or too little. I dont know how to calculate the need of the "red rope" in advance but i know for fact that if you change something in the backstay or the lines between the blocks, it affects the "red rope" a lot. Use some old rope untill you are done with everything, it will save you money and a hassle of having alot of rope at the steering wheel area.


1. This is how the end result looks like. We did all the fittings and Dyneema splicing by our selves which saved us a quite nice amount of money and we learned a lot about splicing.


2. Detail of the new Harken T2 Carbo block. Beautiful block indeed! Not to mention the splicing... 


3. The deckfitting. We used a toggle to witch we attached the Dyneema's with a nice spliced eye.


4. The upper tripple block.


5. The lower triple block with becket and cam. To put the rope in place in the triple blocks was probably the most difficultiest of all the jobs. We ended up in the Harkens office so they could do it correctly.

Material we used:    
(All pictures with courtesy of Harken www.harken.com)

57 mm Carbo T2 Single Block (Soft-Attach Block)
Brand Harken
Product no 2152
Sheave dia. (in) 2,1/4 (57 mm)
Length (in) 3,1/16 (79 mm)
Weight (oz) 2 (57 g)
Max. line dia. (in) 7/16 (11 mm)
Max. working load (lb) 792 (359 kg)
Breaking load (lb) 2380 (1080 kg)

40 mm Triple Carbo AirBlock (Triple Block - Swivel)
Brand Harken
Product no 2640
Sheave dia. (in) 1,9/16 (40 mm)
Length (in) 3,11/16 (94 mm)
Weight w/shackle (oz) 4,6 (118 g)
Shackle pin dia. (in) 3/16 (5 mm)
Max. line dia. (in) 3/8 (10mm)
Max. working load (lb) 1455 (660kg)
Breaking load (lb) 3050 (1383kg)

40 mm Triple Carbo Block w/Cam - becket, Swivel



Product no


Sheave dia. (in)

1,9/16 (40 mm)

Length (in)

4,5/16 (110 mm)

Weight w/shackle (oz)

8,3 (235 g)

Shackle pin dia. (in)

5/16 (5 mm)

Max. line dia. (in)

1/4 (6 mm)

Max. working load (lb)

900 (408 kg)

Breaking load (lb)

1800 (816 kg)




75 mm Aluminium Mastcollar ESP Block
Brand Harken
Product no 6056
Sheave dia. (in) 3 (75 mm)
Length (in) 4,5/8 (117 mm)
Weight (oz) 7,8 (221 g)
Clevis pin dia. (in) 5/16 (8 mm)
Max. line dia. (in) 3/4 (19 mm)
Max. working load (lb) 3000 (1361 kg
Breaking load (lb) 4721 (6000 kg)
57 mm Aluminium Padeye ESP Block
Brand Harken
Product no 6065
Sheave dia. (in) 2,1/4 (57 mm)
Length (in) 3,11/16 (93,5 mm)
Weight (oz) 4,5 (128 g)
Clevis pin dia. (in) 5/16 (8 mm)
Max. line dia. (in) 5/8 (16 mm)
Max. working load (lb) 2100 (850kg)
Breaking load (lb) 4190 (1900kg)


Following products were used:
Red rope: Armare Dynecruise 6mm, 12 meters
Grey rope: Dyneema, Gottifredi Maffioli DSK75 Ultra, 6mm, 16 meters (please read update comment from 2020-10-23 on the top of the page)

Delivered by Harken store in Stockholm (click to go to website)



Thanks to its single braid construction and to the exclusive HTR treatment, which emphasises the excellent mechanical properties of the Dyneema SK 75 ultra high molecular weight polyethylene fibre, this top performance rope offers the best combination of lightness, resistance and durability. Its tremendous strength, its extremely low stretch and improved creep stability make this lightweight and waterproof rope the perfect solution in nearly all racing applications, whose performance will last long. The special coloured coating provides better abrasion resistance and easier handling of the rope, especially during splicing, and it would make sleeving simpler, in case it was necessary.


  Technical Characteristics
        Manufacturer   Gottifredi Maffioli S.p.A.
  Country   Italy
  Homepage   www.gottifredimaffioli.com
  Construction   Single braid
  Core   Dyneema DSK75 ULTRA with HTR treatment and polyurethane coating
  Diameters   2 - 20 mm
(larger diameters on demand

Extremely high strength, very low stretch and minimum creep

  Suggested usage   Strops, lashings and purchase systems  subject to high static loads, halyards on hydraulic ram, aft rigging
    Silver     White     Black
  Brochure   Click here
  Mechanical and physical properties
  Diameter Breakig Strength* Linear Weight
  mm [kgf [g/m]
  2 450 2,35
  3 900 4,70
  3,5 1350 7,05
  4 1825 9,35
  5 2750 13,9
  6 3850 18,4
  7 5950 27,4
  8 6950 31,9
  9 8475 41,5
  10 11000 50,8
  12 14100 73,8
  14 17150 87,7
  16 21750 120


* spliced strength