Adding a Backstay Adjuster


Tag: upgrades rigging

Submitted by Jon Vez

 

Following is the procedure I used to install a backstay adjuster on my 1999 320. This method requires no drilling and will work fine if you use a bimini.

The 320 has a substantial masthead type mast with no real ability to bend, so the purpose of the adjuster is not to induce mast bend, but to tighten the forestay when sailing upwind. Tightening the forestay allows you to point higher, reduce heel, and lessens the tendency to round up in strong breezes.

This configuration also allows you to back off the tension on your backstay for improved sail trim when off the wind. Many sailors see a backstay adjuster as an upgrade just for racers, but I believe that this upgrade is equally compelling for cruisers as well. Having a well trimmed boat with less healing and better upwind performance simply adds to the pleasure of sailing!

To create the attachment points for the adjuster, you will simply replace the clevis pins at each backstay tang with a D shackle. The pin that comes with the D shackle replaces the original clevis and the ‘D’ portion becomes your attachment points for the adjuster’s blocks and tackle.

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I chose to create an adjustment on each side of the backstay. I originally took this approach to increase purchase, but there is the added benefit of creating less clutter in the cockpit. The starboard side is my ‘course’ adjustment and the leeward the ‘fine’ adjustment.

The actual installation time was about 3 hours for two people including tuning the rig.

Here is the parts list:

2 - D Shackles with 3/8” Clevis Pins (Photo #1)

1 - Harken Triple Bullet Block (part #086)

1 - Harken Triple Bullet with Cam & Becket (part #095)

3 - Harken 308 2.0 Single wire blocks

1 - 6mm, 2mm ID Stainless Ring (Part #94-21)

1 - Single ratchet block w/cam (if you choose to use a single adjustment setup, you do not need this block)

20 - Feet of low stretch line (I used T900) with splice to part #086

30 - Feet of 5/16” Sta-Set spliced to part #095

The steps involved:

  1. Ease the backstay tension by loosening the toggles as much as possible. Create a bridle by running a line attached to each stern cleat (you will use this to attach the main halyard to in order to support the mast while you are changing out the clevis pins, so make sure the line is strong enough for this job!)
  2. Attach your main halyard to the bridle and winch the halyard tight. You will need enough tension to create enough slack to completely back off each backstay toggle.
  3. Assemble the 3 wire sheaves around the Stainless O-Ring to create the adjuster and run each back stay leg through the appropriate sheave (photo #3).
  4. Remove the old clevis pin and replace with the 3/8 pin & D-shackle and reattach the backstay shrouds. You can now back off and remove the bridle set up.
  5. Attach the ratchet/cam blocks to each ‘D’ shackle and rig the tensioning lines. (*Note: If you only want to use one side to adjust your backstay, simply terminate one side to the D shackle and attach a ratchet/cam block to the other.)
  6. Run the 20 feet of line from through the lower wire block and run the bitter end through the starboard side ratchet block. This is your ‘course’ adjuster. The spliced end will be on the port side spliced to the triple bullet block (photo #4)
  7. Rig the 30 feet of line through the triple bullet block and down to the bullet block with cam and becket (photo #2)
  8. Tune the rig. Using a Loos gauge, back off the backstay tension as much as possible. Take gauge readings while tensioning the backstay with the new adjuster to find the ‘neutral’ tension—the tension you had before the adjuster was installed. Mark this location on the coarse side with a permanent marker. Tension up your backstay as much as you can and mark the line here as well. In this position the forestay should be bar tight and will be the upwind position.
  9. Go sailing!!

 

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Photo 1: D Shackle with 3/8 clevis-replaces original clevis & Starboard side cam 

 

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Photo 2: Port side adjuster

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Photo 3: Turning blocks that make up the adjuster

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Photo 4: Triple Bullet block (Harken part #086)

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Sean Kaldor

Thursday, October 25 2012 @ 10:13 AM EDT
Very clean and effective. Thanks!

Chris Perez

Monday, May 20 2013 @ 12:53 PM EDT
Jon - How is the backstay adjuster working for you? What tips can you add since you started using it? Is upwind performance improved? How and under what conditions? Is downwind performance improved? How do you know when the rig is tensioned enough for going upwind? Have you marked both adjustment lines in order to repeat the trim? Can one over trim? Any dangers? Thank you. Chris Perez

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Land lubbers no more.

Jeffrey Hare

Tuesday, August 06 2013 @ 01:40 PM EDT
Just wanted to add a note to the posted procedure for adding a tensioner to the split backstay. There is no need to add a bridle to the mast to support it whilst the back stay is removed; the job can be done by just releasing one side of the split back stay. The sheaves that squeeze the stays together come apart and one can be installed on the stay still attached and then onto the unattached one. The sheaves can then be slid up to the end of the split with a boat hook and then the stay reattached. I did this by myself but would be very easy with two folks. John Morrison 1999#574

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Jeffrey Hare
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