Headstay sag

[Alan]

On the other forums I constantly run into the misconception that the headstay sag should be adjusted at the turnbuckle at the bottom of the headstay. This may seem to be the intuitive answer but it is by no means correct.That turnbuckle at the bottom of the headstay is for adjusting mast rake and absolutely nothing else. The tension in the headstay is accomplished by shroud tension in swept spreaders and/or backstay tension. For those boats like the newer Hunters with no backstay, the headstay tension is directly controlled by the cap shrouds. For this reason cap shroud tension needs to be a higher percent of breaking strength than for those that have a backstay.Headstay sag is a major factor in upwind performance as well as weather helm and degree of heel. Depowering the headsail and moving the CE forward as the wind builds helps to control both of these. A tight headstay that minimizes sag in these conditions produces the best performance and control.

 

[ThomasPrice]

Formula to adjust??

Great write up on an important subject that is so often overlooked by cruisers (not the long haul ones). Having raced on a Nelson Marek 39 and then a J90, both with running backstays, and the J105's and B38s5's with adjustable backstays, you are absolutely right about the affect headstay sag can have on performance. So, the question is, when you do not have running or adjustable backstays, what is the formula for tuning??? My Beneteau 473 has awful headstay sag and I've been told by my racing buddies to ignore it. Can't though!!

 

[John Nantz]

Ignore Headstay Sag???

Thomas - Your racing buddies said to ignore your headstay sag? I think this falls under the heading of "With friends like that who needs enemies?!"

 

[Benny]

Alan, your statement is correct but not entirely

correct. We have seen a few boats whith excesive headstay sag that was caused by replacement headstay wires that were cut to long. After tuning the rig to specs, in some the sag was corrected by a few turns of the turnbuckle, in others the wire had to be re-cut. When stating facts be aware there are very few absolute things in this world. It is very correct to say that the headstay turnbuckle should not be used as a tuning device to correct headstay sag but to state that it should never be used is incorrect. I would hate to see a sailor incorrectly tune and overtighten his riggin to correct a sag when the problem laid somewhere else.

 

[Alan]

Benny

When replacing any wire stay, the replacement is always made slightly shorter than the original. After installation and loading a wire stay will go through an 'initial' loading that will stretch the wire which increases its rest length. Riggers are aware of this and build replacement stays with this in mind. If a stay is made with equal length to the original, it will increase in length after its initial installation thereby being too long.None the less, as I stated originally, the headstay length is used to set mast rake which is the first order of business when tuning. If proper rake cannot be achieved then the stay is incorrect. Adjusting the headstay length IS only done for mast rake.

 

[MKing]

The Voice Of Reason

Thanks Alan! I mentioned in a post last week that Selden recommends shroud tension approaching 20% of breaking strength on their late model B&R rigs (no backstay) and got the impression that some thought I was off my medication. Why many will agonize over which type of oil is the best for their diesel and ignore their rig thinking close is good enough is beyond me. After all, it IS a sailboat! Have a great day!

 

[Alan]

Actually Mking

...if you look at the Selden rig tuning instructions they suggest that a backstay-less B&R rig use 25% not 20. The reason being that those cap shrouds are all that the headstay has to control headstay sag on these rigs.

 

[MKing]

Method?

Alan, do you use a Loos gauge or the folding rule method to measure tension? I've wondered which is more reliable.

 

[Alan]

Yes

I use a Loos gauge. I find it very convenient and easy to use. The accuracy of reading the actual number on the gauge is not as important as repeating the exact same on the opposite side.Also don't forget that the intermediate shroud works opposite the cap shroud. Tensioning the cap shroud bends the mast while tensioning the intermediate straightens the mast(on swept spreader rigs), but both apply tension to the headstay though not equally.

 

[MKing]

Let's See If I've Got This Right

Alan, check me on this. I tension the reverse diagonals to induce prebend, then use a steel tape run up the mast and pulled down to the chain plates to get in column. Set the head-stay for the correct mast rake using a plumb-bob run up the mast. Tighten my cap shrouds for head-stay tension which increases prebend then tension my lowers which usually brings prebend back to about right.

 

[Alan]

Pretty much

You can put the mast in column first as long as you don't tension the cap shrouds before you set the mast rake. Selden suggests the prebend be set by the luff curve of your sail. Generally that would be 1% but in most cases the B&R rig uses 2%.

 

[ThomasPrice]

Cruising boat bias!

Yes, that is because my racing buddy's see no purpose in trying to make a cruising boat go fast; it's futile in their mind. Instead, I should focus my attention on cupholders and working the anchor. I get the last laugh though, as I race on their boats, so when stuff breaks I chuckle and think about how to design a cup holder capable of holding a stemmed wine glass!!We'll see how what they think when we're blasting south in the Baja Ha Ha. I have cupholders, comfort and speed

 

[ThomasPrice]

Baby Stay Consideration?

Alan - my 473 is the first boat I've owned, raced or cruised on with a baby headstay. Is there any consideration for this when tightening the backstay and setting mast rake?

 

[Alan]

A baby stay

..is used to support the lower part of the mast. It is used in conjunction with the lower aft shrouds to maintain lower mast support at the lower spreaders. I would adjust the baby stay at about 3/4 of the lower shroud tension.