Solent Stay Question

[bobsadler]

i realise that the solent stay should attach to the mast as close to the forestay attachment point as possible but is there some rule of thumb or calculation to determine what would be the maximum allowable distance (say as a % of mast height above deck or similar) between the solent stay and the headstay attachment points before running back-stays would be required?

[Steve Pope]

With a solent stay you are relying on the existing backstay/s to take the load. generally the solent stay uses the same attachment point as the forestay. That being said I imagine that you could drop down 300mm or so if you had another attachment point there or were prepared to constuct a new one.

[GordMay]

I'd agree /w Steve, that connecting the Solen-Staysail 200-300mm (8-12") down (from backstay attachment) shouldn't over-stress the mast extrusion; but this is really a question for a Structural Engineer.
(Ian?)

[Pblais]

what would be the maximum allowable distance (say as a % of mast height above deck or similar) between the solent stay and the headstay attachment points before running back-stays would be required?

It's not a rule of thumb. It's going to depend on the mast and the other rigging. We have no running backstays on this boat. We do have a 4th set of shrouds. The design would allow the removal of the spreaders but they put them in so it wouldn't look odd. This boat was a cutter from the drawing board on. Converting a sloop may or may not yield the results you think.

It's about mast deflection so includes more in the computation than just the distance to the masthead. Our last boat had running backstays but the mast was so overkill it didn't need them given the small size of the head sail.

I would look at sail area then back into if you need running back stays. Our headsail is about 2.3 times the area. It works well going from one wind condition to the next. We can reef each a little to expand the range without giving up all the sail shape. I would expect you already have a head sail much larger than we do. The ability to use it is going to depend on the size and what you expect to use it for. Once you figure that part out you can determine the size of the slot between them (6ft is a good minimum). At the end you can compute the deflection on the mast. It would not be a rule of thumb.

[bobsadler]

I was planning on using the solent stay only for a hanked-on storm jib or a hanked-on, working "emergency" jib if the furler on the forestay developed problems.

The reason I was asking about the separation was that it looked like I would end up with about 3ft (1m) separation at the mast to keep the inner stay parallel with the outer (though i have to admit that was more for aesthetic considerations than anything else). Other than that they could be about 1ft (0.3m) apart.

Currently have forestay dimensions I = 16.62m (55ft), J = 4.37m (14ft)

[Steve Pope]

Apart from aesthetics there is no reason to have the stays parallel, In the few Solent stays I have seen they are not. The only possible down side is that if you have an overlapping fore sail it will be easier to tack it with a few turns on the drum to allow it to pass between the 2 stays easier. This also goes for a conventional inner forestay.
Depending on how you rig a conventional staysail setup you may not need to use the running backstays often except in heavy weather and using highfield levers makes it pretty easy anyway.

[bobsadler]

i found the following recommendation in the selden mast on-line catalogue (page 31): "(if) the cutter stay is located 3 - 6% of the height of the foretriangle below the existing forestay ... (then) ... running back-stays are not required"

Seldén Mast AB

since selden do not reference this to a particular spar section or rig design i guess it's as close as we'll get to a "rule of thumb" (given it comes from a manufacturer's documentation i suspect it is conservative)

the spar on "karen m" is from selden

[jjt]

If you draw a line between the upper back stay attachment and the lower solent stay attachment, the point in the fore face of the mast where the line crosses through is the lowest safe point of the forastay upper attachment

[Pblais]

since selden do not reference this to a particular spar section or rig design i guess it's as close as we'll get to a "rule of thumb"

I really don't think there is a decent rule of thumb expecially given this isn't going to be something you are adding to your standard configuration. Given you are not really going to use it most of the time but only in emergencies. I would say just install it all the way up perhaps as noted by jjt and as far forward as practical to get a good point on the deck for a backing plate. The bottom attachment has to be some place structural to carry the load of the sail. That would assume you had a forestay but just not a working furler. If you lost the forestay totally the odds will be great that you will have bigger problems at hand.

[bobsadler]

jjt: i was interested in your advice so i laid the rig out on CAD (i'm in central asia and the boats in the u.s. but i have pretty good dimensional data).

projecting the solent stay thru to the back-stay attachment on the headbox results in the solent stay meeting the forward face of the mast at about 7 1/2 - 8% of foretriangle height below the forestay attachment

[jjt]

Bobsadler:

In fact any position on top of this point is safe (tensioning the solent stay you only get compresion on the mast and tension on the back stay)

Any position bellow that point will also generate a flexing force on the mast.

How far bellow the point can you go? Depends on the section of the aluminum mast. The lower you go, the bigger flexion you get. At some point, you will need to add running back stays to control flexion (we will not be talking about solent stay any more).

There are other very important considerations about solent stays:

The reason for the solent stay is to hoist a small headsail without unrolling and changing a big genoa while the weather is building up. So you need to to define the position of the top, clue and tack corners of the sail.

First, find a strong place to fix the tack corner (as recommended by Pblais), you may need to add a strong chainplate fixed to a structural
bulkhead in the front or the back of your chain locker (special care must be taken if your deck is a sandwich structure). Check that the Highfield Lever you are going to use (to fix/remove the stay) fits the chainplate.

Knowing the position of this point you can apply the procedure described in my previous post to determine the top attachment of the solent stay (remember that the foresail halyard exits the mast quite bellow the forestay top attachment to avoid jamming the halyard while rollerfurling)

Finally (and very important) if the tack corner is not very close forward to the forestay you will need also to position 2 strong fix points (or two little rails) to hold the sheets blocks of the solent sail. I guess that the position of this points should be 12/15 degrees from the centerline starting at the tack corner. (this angle is a first guess from my part: you should check the this angle measuring the one you already have in the foresail of your boat).
If the tack corner is close to the forestay, you can use the current genoa rail for the sheets (with the car in the forward position). Otherwise the angle will be too big to sail close hauled with the solent sail.

I'll like to make clear that I'm neither a proffesional rigger nor a naval architect, I am just walking your same steps and this recomendations are what I already found out on the subject.

Hope you understand my english (it's not my mother language), and this thoughts helps you in your project.

Juan José

[bobsadler]

jjt: that's a great answer. i'm a mech engineer but my structural stuff is a bit rusty (like 30+ years!!) but, yes, the compression situation i agree with.

the nauticat 42 has a re-inforced deck pad-eye about 12inches aft of the forestay deck attachment point; that's what i plan on using

that's pretty good english!

many thanks

bob

[Pblais]

the nauticat 42 has a re-inforced deck pad-eye about 12inches aft of the forestay deck attachment point; that's what i plan on using

You want more than just a backing plate on this. This really has to be directly tied to something structural like a bulkhead. A backing plate is fine for a jack line but not this.

[jjt]

Pblais:

I agree with you.

A 95% G3 or even a storm sail will pull considerably.
In my case, I'm glassing a permanent bulkhead against the back of my anchor locker just to strongly fix the chainplate.

Juan José

[bobsadler]

yes, i'd meant to say it was going to be tie-rod reinforced