"The time has come," the walrus said, "to speak of many things . . ."

[Red_Dog]

In this case, it's boom vangs, main sheets and travelers.
Ok, I think I've got an understanding those controls
- boom vang, down wind, controls horizontal angle of the boom.
- sheet controls twist of the main sail
- traveler controls the angle of attach for the main sail
- topping lift, not useful really

I also have a on-the-fly adjustable back stay. My boat is a Hunter 28.5 with the B&R mast head rig, inducing a 4" to 6" aft rake in the upper third of the mast.
So, how do I best utilize my adjustable back stay?
My assumption is that easing the back stay would stretch the leech. Conversely, tightening the back stay would relax the leech.
But, how do I know what to do when, under what conditions?
Thanks,
Alec
- adjustable back stay, an upwind control that when tensioned slackens the main sail leech, de-powering it while adding tension to the fore stay shifting power to the jib.
(edited as feed back helps to refine my basic understanding.)

 

[SG]

The boom vang simply "increases" the vertical angle of the boom by pulling the end down. On angles which are sufficiently close to the wind, this can be accomplished by the main sheet if the traveller is set properly. As the mainsail moves out, and horizontal angle of the boom moves out beyond where the traveler can pull the boom directly down, the vang is really necessary to achieve the flattening of the sail.

The top vs. the bottom portiongs of the sail really is less of an issue with just the vang. You have the outhaul (which pulls the clew back) and halyard tension. With some sails, you also have a leach "line" which you can use to control fluttering of the trailing edge of the sail.

Tensioning the back stay (if you can and your rig will allow for it) allows you to affect the flatness of both the main and fore sail.

The topping lift really is generally used just to keep the boom end from crashing down when the sail loses pressure as a result of the track, gibe, or dropping the main by releasing the halyard. I don't think it's too useful to controlling sail shape EXCEPT in very light winds with a relatively heavy boom and sail.

A good number of these controls are interactive and in some cases you can us a combination or one-for-other(s) -- maybe not perfectly, but...

That's one of joys and challenges of trimming sails. :^)))

 

[rgranger]

@Red_Dog my sail trim knowledge is only empirical and I don't pretend to have a complete understanding but here is how I go about adjusting my sails.... Anytime the wind is behind the mast, I let out both my traveler and my mainsheet to leeward and I tighten the vang. I then play with the relative traveler and sheet positions until the tell tales fly right. I tighten the vang to keep my boom from riding up and gives my sail a better shape. I have mid-boom sheeting so anytime the wind is in front of my mast, the main sheet serves to keep my boom from riding up so I usually loosen the vang. It does not make perfect sense to me but I do notice the sail shape is better if the vang is loose when pointing.

When the wind is in front of the mast, I bring my traveler to windward and then let out the sheet until my tell tales are correct. My H26 is relatively new to me and it does not have a formal traveler (something I'd like to correct) so I take a line to my sheet and pull it to windward using the windward winch. It is not ideal but I can feel the boat speed up and heel less when I do this. The pic below is my jerry rigged "traveler" system. You can also see my vang is loose in this picture.

 

[Red_Dog]

The boom vang simply "increases" the vertical angle of the boom by pulling the end down. On angles which are sufficiently close to the wind, this can be accomplished by the main sheet if the traveller is set properly. As the mainsail moves out, and horizontal angle of the boom moves out beyond where the traveler can pull the boom directly down, the vang is really necessary to achieve the flattening of the sail.

The top vs. the bottom portiongs of the sail really is less of an issue with just the vang. You have the outhaul (which pulls the clew back) and halyard tension. With some sails, you also have a leach "line" which you can use to control fluttering of the trailing edge of the sail.

Tensioning the back stay (if you can and your rig will allow for it) allows you to affect the flatness of both the main and fore sail.

The topping lift really is generally used just to keep the boom end from crashing down when the sail loses pressure as a result of the track, gibe, or dropping the main by releasing the halyard. I don't think it's too useful to controlling sail shape EXCEPT in very light winds with a relatively heavy boom and sail.

A good number of these controls are interactive and in some cases you can us a combination or one-for-other(s) -- maybe not perfectly, but...

That's one of joys and challenges of trimming sails. :^)))

I'm a little off on my understanding of the vang. You cleared that up for me.
It's the adjustable back stay that I'm really lacking understanding of. I can, at any time, ease or tension the back stay. I know there's reason for this. However, I have of who, what, where, and when.
I should note my boat was at one time setup for racing. I would think this is when the adjustable back stay was set up.

 

[dlochner]

I'm a little off on my understanding of the vang. You cleared that up for me.
It's the adjustable back stay that I'm really lacking understanding of. I can, at any time, ease or tension the back stay. I know there's reason for this. However, I have of who, what, where, and when.
I should note my boat was at one time setup for racing. I would think this is when the adjustable back stay was set up.

The backstay does a couple of things.

When tension is added the belly of the mainsail moves forward and on a masthead rig the forestay tightens which reduces forestay sag. This allows you to point higher.

 

[Davidasailor26]

On your fractional rig the backstay is going to add mast bend. Primarily that will pull the midsection of the main forward, flattening the sail. You want that when the wind is getting up to the range where you don't need more power. It will also straighten the headstay a bit, improving pointing as dlochner says.

SG is right about the topping lift - really only use it to add twist when the wind is too light to hold the boom up. But usually when the wind is that light you don't want much twist anyway, so I'd just leave it off.

I think of the Vang and sheet both as twist controls. The sheet is the primary twist control while the boom is over the Traveller (up wind and close reaching). Aft of that the Vang holds the boom down or lets it ride up for twist. Traveller is angle of attack, and outhaul is draft.

 

[jeepbluetj]

What they said...

Sheet, vang, traveler all can adjust twist in the main. It's point of sail dependent. And all the controls affect each other.

Oversimplified: the vang is a down-wind control. Upwind, where you've not needed to ease the mainsheet past where you can use the traveler as the angle-of-attack control, the vang is not needed. (this is boat dependent, and there are other factors you may wish to put vang on for - like too weak main tackle to flatten the sail, etc... )

When the traveler is your main angle-of-attack control - the sheet controls twist. Heading down, when you hit the bottom of the traveler and you start to ease the mainsheet - now the vang is needed to control twist (keep the boom down) and the sheet is AOA control.

 

[Red_Dog]

I've done some poking around about this as well. What I found:

- back stay adjustment is an upwind control, in wind speeds over 10-12 knts.
- It is used to de-power the mainsail, spilling the wind (this may also be part of what dlochner mentioned about moving the belly to the fore of the sail).
- while de-powering the main sail, by tensioning the fore stay, power is maintained in the jib (genoa).
Subject again to a more refined understanding.

I apologize for using bullet points. At this stage of trimming sail knowledge reducing to bullet points makes it easier to understand. As knowledge increases, hopefully, I won't need them. I edited my original post to better reflect what I've learned for you all.

 

[rgranger]

Thanks @Red_Dog

I did not really understand what tensioning the back stay did.

BTW: Big fan of bullet points....

 

[rgranger]

So for someone like me who has swept back spreaders instead of a back stay.... is that what "running" back stays are for?

 

[victorhoisington]

To add to the discussion and just my basic understanding of each of the controls:

- mainsheet and vang can be used to control twist in the main. Tighten the vang when running down wind and the main flattens, loosen the vang and you can induce twist in the upper part of the main to spill some wind and keep from being overpowered.
- Backstay - tight when going upwind to tighten the jib and noted point higher, loosen when running to induce a bit of fullness in the jib for better downwind performance.

I'm sure if Jackdaw is around he will have more to say on this topic.

great discussion

 

[Cowpokee]

So for someone like me who has swept back spreaders instead of a back stay.... is that what "running" back stays are for?

My understanding is that running backstays are typically used on fractionally rigged or cutter rigged boats to counter the mast distortion where the upper foresail is attached to the mast.

 

[dlochner]

So for someone like me who has swept back spreaders instead of a back stay.... is that what "running" back stays are for?

My understanding is that running backstays are typically used on fractionally rigged or cutter rigged boats to counter the mast distortion where the upper foresail is attached to the mast.

Yes. On boats with bendy masts the runners keep the mast from being too bendy and counter act the lateral forces from the jib. On masthead boats the help to keep the mast from pumping fore and aft and possibly inverting. The runners are only tensioned on the windward side, the leeward runners are left slack.

Swept back spreaders, if swept back enough, eliminate the need for a backstay.

 

[dlochner]

I apologize for using bullet points. At this stage of trimming sail knowledge reducing to bullet points makes it easier to understand. As knowledge increases, hopefully, I won't need them. I edited my original post to better reflect what I've learned for you all.

Once you have learned the very basics of what each control does, go sailing! The real learning will come when you apply the bullet points and look at the tell tales to see what it does to the sail shape and efficiency.

If you don't have tell tales on the main, install them at the end of each batten pocket. The goal is to get all the tell tales streaming aft, except the top tell tale, that can flick forward once in a while. When a main sail tell tale is flipping forward the sail is stalling and losing power. Sail trim is as much an art as it is a science or bullet points.

 

[john6206]

On my first boat I developed a really nice scar on the cockpit sole where the boom would come crashing down every time I lowered the main. Yes, I knew what the topping lift was for, I just forgot to reattach it. . . . Every time!

I think after awhile I just started sailing with the topping lift attached. I think it probably slowed me down 0 knots. My plan was to install a boom-kicker and ditch the lift, instead I sold the boat.

 

[Red_Dog]

So for someone like me who has swept back spreaders instead of a back stay.... is that what "running" back stays are for?

Any boat can have swept spreaders, that in and of itself doesn't mean much. "Running" back stays, you're on your own, haven't a clue.
Now, if you are Hunter owner of a post '96 boat: Hunter, moving away from racer/cruiser designs to cruisers, moved the chain plates to the gunnels and eliminated the back stay (The chain plate location had something to do with PHRA rules). That setup is a 2nd generation B&R rig. At this time I also believe they started using a fractional rig instead of a mast head.
If you're not the proud owner of a post '96 Hunter, sorry buddy, once again, you're on your own.
DL, that's why I ask questions. I am sailing and learning. What's the only way to learn to sail - go sailing! Muck it all up, learn more, go sailing, repeat.

 

[rgranger]

@Red_Dog I have a Z-spar fractional rig from 1995. I do not have a back stay.

I did a bit of snooping and it seems that running back stays are a big deal on mast head sloops as a way to support the middle of the mast and keep it bending to far to leeward when the genoa is full. Anyway, that is my best understanding of it after watching this video.

 

[Red_Dog]

@Red_Dog I have a Z-spar fractional rig from 1995. I do not have a back stay.

As to your rig, I am a bit mystified. I looked up your boat on SailboatData.com. Sure enough, I was looking at a fractional rig of the traditional type sans back stay. How Hunter pulled off this magic is beyond me.

The video did explain use of running back stay well. (I would like to point out though; if you look over his shoulder when he's in the cockpit, his boat has what appears to be an hydraulic adjustable back stay.) His explanation of column stability makes sense. Your mast is a column. What you see as mid-section "pump" is very similar to a standing wave, e.g., the vibrations of a car's antenna as you drive.

The smaller sections created by stay or bracing divides the longer column into several small columns combining to make the whole. The smaller columns are less prone to deflection making the whole column more stable. I have a fork brace on my motorcycle for the same reason.

Yes, running back stays on your boat would add greater stability to the whole. The added benefit is less wasted energy through column deflection, a stronger overall column, being able to increase the power your head sails. Larger genoas would definitely benefit from they're use.

Don't know if this is enlightening or confusing. I do hope enlightening.
Alec

 

[rgranger]

@Red_Dog Yes all good. Thnx

I don't think I need a running back stay. I have upper and lower shrouds that come to a set of chainplates that are aft of the mast so the mast cannot tip forward. The lower shrouds function to some extent as a running back stay and stabilize the mid-section of the mast.

 

[jssailem]

@rgranger you are likely correct. The running back stays serve to maintain the mast in column. If you tried to add a fore sail that would put stress on the middle of your mast it would be a way of supporting the mast from being to stressed in the area of attachment. Some folk add a big head sail to the mast by putting a block at the top. It can cause the mast to be stressed at the top where it is not supported. Adding a running back stay to counter this stress is an option.