Back stay tensioner, why, mast head rig

[nukey99]

We have a 1983 E35-3, which has a fully operational hydraulic backstay tensioner. Given the boat is a keel stepped mast head rigged sloop, what is the function/value of the adjustable backstay? I don't think I can bend the mast enough to impact mainsail shape. I could adjust headstay tension, but we have a furling system, so I see little value in that.

What am I missing?

 

[ConchyDug]

Depends if you just wanna cruise and not fiddle with another control then yeah it's probably not worth it to you. If you want to point higher and go faster then a backstay would add value. It controls headstay tension which is super important on all sailboats and on an inline spreader masthead it bends the mast as well to some degree(varies between mast designs). So yes you have a furling headsail but even furled it'll be bagged out in higher winds which is drag and lower pointing ability, so that may or may not be acceptable to you. Kinda depends on your sailing style. From what I've seen on my 38 you get pretty significant bend(3-6")in the top 1/3 of the mast around 2200psi. I'm not familiar with the 35's mast but if you crank the adjuster on to max tension at the dock and sight the mast/feel the headstay tension you can determine what it does.

 

[Slick470]

We had a hydraulic backstay adjuster on an C&C 35mkIII that I used to race on. As mentioned by ConchyDug, it primarily was used to control headstay tension even with a furler. The main on that boat was pretty flat, but in conjunction with the babystay we could get some mast bend and board out the main. Another thing was downwind, we were able to quickly loosen the backstay to allow the mast tip to rotate forward which helped with flying the spinnaker.

It's just another tool for sail trim. When my friend was done racing that boat, he put on a manual adjuster and I'm not sure he's touched it since finding a "good enough" setting. On our Ericson/Olson 911SE I use the hydraulic adjuster often even on simple day sails and it makes a noticeable difference in how the boat handles.

 

[nukey99]

Thanks for the input, it is much appreciated. I'll play around with it a bit and see the impact on sail shape etc. I know it is functional, as I released the pressure, the ram went up about 2 inches. I pumped it back down to the original setting. Our previous sailboat, a Catalina 320 had an adjustable backstay, but it was a split stay with a Pully system to tension it. Given the relative power of hydraulics, I'm going to be cautious on how far I tension it.

We just moved our boat from Bellingham marina to Blaine Marina, around 30 NM trip. Unfortunately, light wind and right on our nose, so we ran the diesel all the way up. It was nice that the little tractor engine, pushed us along at 5.9 KTS though the water at 1900 RPM. The fuel gauge didn't move!

 

[Prairie Schooner]

Hi Jim,
We're adding an adjuster to our rig this year. We had all new rigging in 2022, but the adjuster wasn't in the budget then. I'm looking forward to using it to flatten the main in higher wind and generally have one more thing to mess around with. As we're mostly cruisers, it's probably overkill. But we all have different ways of enjoying sailing. Mucking about with sail trim is one of mine.
Cheers, Jeff

 

[Pete the Cat]

I am an old 505 dinghy sailor and back in the day, working with the noodle we used for a mast was a key tool for shaping everything--amazing speed differences in highly variable sailing conditions up and down wind with fractional lightly built rigs. I rebuilt and owned a racing Folkboat here on SF Bay for a few years and used a pulley backstay system there that was helpful in changing the shape of the fractional rig to allow maximum droop in the headstay downwind and move it all back to go upwind--this was more than headstay tension it was tightening the whole rig to take the pounding going to weather. I am no rigger nor rockstar boat driver, but I am really skeptical of hydraulic backstay adjusters production boats with masthead rigs. Seems to me they have much less movement options and may have some danger. While it is true you can get the top of both of my masts (A Tartan 37 and an Ericson 32-200) to move a few inches, I keep thinking that adjusting the jib halyard tension probably gets you as much or more shape forming control than adjusting the backstay on either of these boats. I keep wondering if folks are keeping their mast head jib halyard tension constant and bending the rig back a few inches and wondering if they are doing permanent stretch damage to the luff of their sail--the movement is 1:1 stretch. In a fractional rig, a backstay adjuster makes more sense to me. But I am one of those guys who releases his roller furling jib tension when I leave the boat to avoid permanently stretching the luff--I imagine I want to retain the fullness of the sail downwind. I have also seen boats in the yards where there are cracks in the stem and keel fittings from folks overdoing the adjustment or leaving it in--they make me nervous when I see them on production mast head boats. So maybe I am nuts. Just an alternate view of backstay adjusters.

 

[Slick470]

Think of changing the backstay tension as changing forestay sag. As the wind increases, the load on the headsail puts pressure on the forestay and it will sag to leeward in the middle. This sag deepens the luff curve and puts more power into the sail. It also tries to pull the masthead forward. On a masthead rig, applying backstay pressure at a minimum counteracts the force at the mast head, but increasing the pressure also allows you to take some of the sag out of the forestay which in turn flattens the sail and brings the center of effort for the sail forward. For a lot of the boats I've raced on a rule of thumb was to try to keep that sag to 12" in the middle by having someone sight up forestay from the pulpit. This gives you more driving force and less heel. On a masthead rig with inline spreaders this added tension will often cause the middle of the mast to bend forward which flattens the luff curve of the mainsail.

On a fractional rig, especially with inline spreaders, backstay tension mostly bends the top of the mast aft, sends the middle of the mast foreword, and primarily affects the main. This can actually reduce the pressure on the forestay. On this type of fractional rig to counteract the mast bend and reduce headstay sag you really need runners.