Moving Lower stay chain plates inboard - Shrouds remain outboard

[alaskanviking]

How difficult is it to move my fwd/aft lower stay chain plates inboard. Searching around it seems I can bolt the plates to the side of the cabin maybe. Trying to figure out if this is something I can do without a nautical engineer, and simply bolt new chain plates to the cabin sides. To make it clear I do not want to move the shrouds, I will leave them outboard. Just the lower stays.

It’s a cutter rig so the purpose is to run a larger genoa staysail and point a little better by running front sails in between inboard lowers and outer shrouds. Large genoas, code zero’s ect will still have to go around the outside of the shrouds.


thank you

V/R

Robert

[JoetheCobbler]

It will alter the loading on the spar as well as the standing rigging.
The book Rigger's apprentice, by BrianToss has a few chapters on this topic, along with the formulas to calculate the loading.

[Cheechako]

Most cabins aren't really the strength you need. Taking them to a bulkhead and through deck is a possibility. But a lot of work. I've been through this a bit, not sure it's worth the amending.
You can adjust where the genoa sheets to a bit by amending the height of the clew on the sail, sail mods may be better to do than boat mods.
or
On two cruising boats I had my foresails built with room for ~ 2 ft+ pendant on the tack. (I also like to keep the sail off the deck offshore) That way I could figure out the best location vertically for the sail to reside on the headstay which gave the best sheeting point to the fairlead block. (see pendant in my avatar)

But be careful spending a bunch of time, $, and mods etc to improve for a large headsail. I find these cruising boats, well loaded, do not move that well to windward no matter the sheeting angle. They need some power and too tight to weather will not do it! It will if it's blowing hard, but you don't need the big headsail when it is blowing hard!

[psk125]

Besides the problems Cheech mentioned, attaching shrouds to the cabin trunk might pull the cabin off the deck. Probably not what you want to do. If you are moving the lower shrouds in order to point higher, stop perhaps a minute to think. The Genoa you have was built with an angle of attack set for going outside of the shrouds. Trimming it in at a tighter angle will probably stall it out. To make the tighter angle work you would need new sails, set to work at the tighter angle. Even with new sails, the tighter angle might not be faster. It will narrow the slot between the main and jib, making the main backwind more. Imagine trimming the jib in at such a tight angle that it ran right next to the mast. Your sail might be full, but it would not be pulling you forward much with no slot. If you want to improve upwind performance, a sailmaker might suggest getting rid of the inner forestay and getting a Solent-style 90 to 100% jib for the outer forestay. It might be cheaper than having the mast buckle from having the shrouds moved.

[tkeithlu]

Cheechaco and psk125 have got it. The shrouds/bulkheads are a structural unit. If you've got to mess with something, make it the sail and the sheet blocks. You can replace/return them. Move your shouds to the cabin top and demasting in a blow is your next learning experience.

[Rucksta]

Try a barber hauler tg adjust sheeting angle.
Low cost non invasive way to test for any effective performance gain

[alaskanviking]

Originally Posted by psk125

Besides the problems Cheech mentioned, attaching shrouds to the cabin trunk might pull the cabin off the deck. Probably not what you want to do. If you are moving the lower shrouds in order to point higher, stop perhaps a minute to think. The Genoa you have was built with an angle of attack set for going outside of the shrouds. Trimming it in at a tighter angle will probably stall it out. To make the tighter angle work you would need new sails, set to work at the tighter angle. Even with new sails, the tighter angle might not be faster. It will narrow the slot between the main and jib, making the main backwind more. Imagine trimming the jib in at such a tight angle that it ran right next to the mast. Your sail might be full, but it would not be pulling you forward much with no slot. If you want to improve upwind performance, a sailmaker might suggest getting rid of the inner forestay and getting a Solent-style 90 to 100% jib for the outer forestay. It might be cheaper than having the mast buckle from having the shrouds moved.

Not the shrouds. the shrouds would stay outboard as designed, the Genoa would still sheet around the outside of the shrouds, no change.

I'm talking about moving only the forward and aft lower stays inboard. This is to allow a larger overlapping staysail, sheeted in between the shrouds and lower stays. Such a staysail and sheeting arrangement would be able to point better in theory, but would add to the sail area and give a boost to the main from slot effect.

[PippaB]

I’m not overly pedantic about nautical terms, but in this case it helps everyone to be on the same page. Simplified, if they go to the side of the boat they’re shrouds, in this case your lower shrouds. If they go to the bow stern (or generally fore-aft on/near the centerline) they’re stays.

Many boats are built with their lower shrouds connected to the cabin/coach roof sides. Whether or not your vessel has the structure for that? I’d guess not, because why design/build that strength if you don’t use it, but only a thorough investigation of the structure would tell you.

W

[PerfectPirate]

Originally Posted by alaskanviking

Not the shrouds. the shrouds would stay outboard as designed, the Genoa would still sheet around the outside of the shrouds, no change.

I'm talking about moving only the forward and aft lower stays inboard.

First off, the term 'shrouds' covers both the upper and lower stays. However, the uppers are often referred to as the cap shrouds because in traditional rigs they used to run to a circular band just below the 'cap' on the top of the mast. So much for nitpicking terminology.


The lower stays take the bulk of the load placed on the mast by the mainsail. Think about it for a minute, where is the largest portion of the mainsail area? Between the boom and the spreaders. The area above the spreaders is usually about 1/3 of the area below the spreaders. Secondly, the lower spreaders brace the mast against 'pumping', where the wind and wave action induces the centre of the mast to move back and forth or from side to side. When the foresail and forestay are heavily loaded, they want to bend the top of the mast away from the wind. To do this, the centre of the mast has to flex into the wind, and it is only braced against this by the lower shrouds. So the stresses on lower stays can be severe and moving them further inboard changes the angle of the rigging loads, thereby reducing their effectiveness and increasing the required levels of tension. There is a reason why purpose-designed cruising boats usually have larger mainsails and staggered fore-and-aft lower stays, instead of single lower stays which are inline with the cap shrouds, as is common on racing boats. Really robust cruising designs tend to put their shrouds as close to the gunwale as possible, often going to external chainplates like on your Passport 42.


A fellow club member once decided to re-rig the lower stays on his C&C 39, moving them forward to the same robust chainplates which anchored his cap shrouds. He did this so that he could swing his boom out further while racing downwind, for whatever marginal performance increase that would give him. Because he had spent decades working in the boating business, he believed that his own knowledge and experience were sufficient to deal with the engineering issues. It all worked beautifully, for the first three weeks. Then he was hit by a gust of wind while racing. The windward chainplate pulled right through the deck, bringing a goodly section of main bulkhead with it. The mast folded up and had to be cut free, sinking to the bottom of the lake. It was only by a considerable stroke of luck that no crew members were injured. Since he had not had the rigging changes reviewed and approved by a proper marine engineer / designer, the insurance company denied his claim. It became a very expensive mess to sort out and cost him a year's sailing.


So, I'm with the guys who recommend talking to your sailmaker about a better way to work around your current standing rigging. If you do decide to make a change to the stays, make sure that the whole thing is reviewed and spec'ed out by a proper marine design engineer, and discuss it all with your insurance company first. For many of our good old boats, the replacement cost of a mast is sufficient to cause the insurance company to write off the boat. Last year, an owner in our harbour had his mast bent by an excavator, as the mast sat on top of his stored 1970's boat. Despite the fact that the boat had just been professionally refitted and renovated in the previous year, his insurance company said that they would write the boat off rather than replace the mast. Fortunately, the replacement cost had to be covered by the company which owned and operated the excavator, and they were obligated to make things right, so he did get a new mast out of the deal. But he still lost half a season of sailing.

[Patrigo]

I reckon if your knowledge is shrouded as it is, and stays that way, you should buy a fizz boat!

[guyrj33]

instead of moving the lower shrouds, move the clew of the staysail higher which will allow you to sheet further inboard.