Swept back spreaders

[Daydream believer]

A lot of those Hunters are roller reefing main, which implies an additional constraint of a straight mast.
Hence they end up with a lot of rigging.
Even so, it shows the consequences of not having a backstay are not trivial.

So if he cannot have a straight mast, what can the Op expect of his mast by moving the rig to 5 degrees- A pre bent mast? By how much & does this suit the cut of his sail? If there is no back stay does he lose the ability to provide greater bend prior to first reef for a short while to flatten the sail.
Has the OP considered a backstay flicker at the mast head. Very common on some French performance craft up to 30 ft. Some are quite exagerated in their length

 

[Laminar Flow]

To be clear, the angle of 5 degr is the angle of the shroud to the mast when viewed from the side, as per the diagram I posted. It basically indicates how far aft from the maststep the chainplate/spreader tip will be. This is quite evident from the side view diagrams shown in the hunter video.
When viewed from above (plan view), the spreader may well be angled back some 20 - 30 degr from 90, hence the 120 degr for the Bergstrom rig.

Re Hunters. I have had a look at quite a few of them and their Bergstrom rigged, backstayless masts are dead straight. It is also very common for them to have structural issues with the anchoring of their single, high-load chainplates.

Taking the shrouds to the deck edge has no effect on the fore & aft staying, but it does reduce the compressive load on the mast, which is a consideration in today's lighter built boats. Masthead rigs with their narrow shroud base and long forestays to allow large, overlapping head sails require very robust hulls to absorb the loads. The lighter loading of fractional rigs, more easily absorbed by lighter hulls, is one of the reasons for their current popularity.

 

[Wing Mark]

To be clear, the angle of 5 degr is the angle of the shroud to the mast when viewed from the side, as per the diagram I posted. It basically indicates how far aft from the maststep the chainplate/spreader tip will be. This is quite evident from the side view diagrams shown in the hunter video.
When viewed from above (plan view), the spreader may well be angled back some 20 - 30 degr from 90, hence the 120 degr for the Bergstrom rig.

Re Hunters. I have had a look at quite a few of them and their Bergstrom rigged, backstayless masts are dead straight. It is also very common for them to have structural issues with the anchoring of their single, high-load chainplates.

Taking the shrouds to the deck edge has no effect on the fore & aft staying, but it does reduce the compressive load on the mast, which is a consideration in today's lighter built boats. Masthead rigs with their narrow shroud base and long forestays to allow large, overlapping head sails require very robust hulls to absorb the loads. The lighter loading of fractional rigs, more easily absorbed by lighter hulls, is one of the reasons for their current popularity.

That's wrong.
The shrouds of the Hunter are deflected aft by the spreaders, the cap shroud viewed in profile meets the mast at an angle of nearer 10 degrees than 5, as best I can scale it off a photo.
There are also a few intermediate shrouds of course.
Not all Hunters seem to have straight masts and roller mains.
Some look to have a pretty big fore-aft section to the mast.

Rig design by internet forum isn't going to end well.

 

[Daydream believer]

To be clear, the angle of 5 degr is the angle of the shroud to the mast when viewed from the side, as per the diagram I posted. It basically indicates how far aft from the maststep the chainplate/spreader tip will be. This is quite evident from the side view diagrams shown in the hunter video.
When viewed from above (plan view), the spreader may well be angled back some 20 - 30 degr from 90, hence the 120 degr for the Bergstrom rig.

Re Hunters. I have had a look at quite a few of them and their Bergstrom rigged, backstayless masts are dead straight. It is also very common for them to have structural issues with the anchoring of their single, high-load chainplates.

Taking the shrouds to the deck edge has no effect on the fore & aft staying, but it does reduce the compressive load on the mast, which is a consideration in today's lighter built boats. Masthead rigs with their narrow shroud base and long forestays to allow large, overlapping head sails require very robust hulls to absorb the loads. The lighter loading of fractional rigs, more easily absorbed by lighter hulls, is one of the reasons for their current popularity.

So you are suggesting that the plan angle at deck level is in fact 120 degrees - Which is what the OP really wants to know & your reference to 5 degrees is a little missleading without the referencing to chainplate position. I think that the plan angle does not change significantly as one goes further up the rig & that it remains at 120 degrees on plan all the way. It would place undue strain of the lateral load of the spreader. Looking at it horizontally from the side is clearly incorrect as one cannot determine the exact angle from that. Only surmize.

 

[Wing Mark]

So if he cannot have a straight mast, what can the Op expect of his mast by moving the rig to 5 degrees- A pre bent mast? By how much & does this suit the cut of his sail? If there is no back stay does he lose the ability to provide greater bend prior to first reef for a short while to flatten the sail.
Has the OP considered a backstay flicker at the mast head. Very common on some French performance craft up to 30 ft. Some are quite exagerated in their length

What's going to pre-bend the mast? Lowers? Spreaders? Baby stay? Chocking at the deck on a keel-stepped mast?
Bend can also come from the kicker pushing the gooseneck forwards and main leach tension pulling the masthead back in a fractional rig.
Works well enough for dinghies not to need to reef.

Unless a great deal of thought is put into the design, I'd expect the 5 degrees to become 4 degrees as the shrouds stretch under load and the boat flexes a little, then the mast will go out of column and fall over the bow.

 

[Laminar Flow]

So you are suggesting that the plan angle at deck level is in fact 120 degrees - Which is what the OP really wants to know & your reference to 5 degrees is a little missleading without the referencing to chainplate position. I think that the plan angle does not change significantly as one goes further up the rig & that it remains at 120 degrees on plan all the way. It would place undue strain of the lateral load of the spreader. Looking at it horizontally from the side is clearly incorrect as one cannot determine the exact angle from that. Only surmize.

In a rig without backstays it is the fore and aft angle between shroud and mast that determines the load on the mast when sailing down wind, for example. Regardless of the swept back angle of the spreader, they can remain the same in a multiple spreader rig all the way up, it is the panel length and the length of the spreader that determines the fore and aft angle of the shroud to the mast.

It would appear that the OP has raked his masthead forward, thus moving the upper shroud attachment forward and, consequently, the spreader tips aft. He now wants to follow suit with his chain plates to reduce interference of the boom on broader courses. Ironically, any change in angle, mast to shroud, will be virtually undetectable and moving the chainplates further forward would not be advisable.

But hey, it's a free country and everyone is of course at liberty to do as they like.
If it's ok, I shall continue to consult my own sources, considering that they have served me well when I calculated, designed, built and modified a number of rigs, some for larger, ocean-going craft.
While I have lost, or nearly so, a couple of rigs at sea, none to date were of my own design and not for want of trying either.

 

[Daydream believer]

What's going to pre-bend the mast? Lowers? Spreaders? Baby stay? Chocking at the deck on a keel-stepped mast?
Bend can also come from the kicker pushing the gooseneck forwards and main leach tension pulling the masthead back in a fractional rig.
Works well enough for dinghies not to need to reef.

Unless a great deal of thought is put into the design, I'd expect the 5 degrees to become 4 degrees as the shrouds stretch under load and the boat flexes a little, then the mast will go out of column and fall over the bow.

We are not talking dinghies & the load required on a vang on a cruiser needed to give any sygnificant mast bend would be so high that it would not be possible to do it. On my boat I have 16:1 & sometimes give a couple of turns on the winch ( taking care not to damage the boom) , but because the mast is already stressed the vang has no effect on mast bend. If the the mast is forced to bend the plan angle at the spreader increases, not decreases.
To bend my mast I have reducing tension on the mids & lowers & apply backstay tension to bend the mast.
Up wind the mainsheet normally pulls the boom down ( depending on wind strength & amount of twist required) applying leech tension . Off wind the kicker will not be bending the mast due to boom angle.
On a dinghy one can give the tackle a quick heave & place relatively miles more bend on a flexible spar, so it is not at all relevant to cruisers . The Op is not sailing a laser off the leech of the sail. Quite the reverse in fact

 

[Wing Mark]

We are not talking dinghies & the load required on a vang on a cruiser needed to give any sygnificant mast bend would be so high that it would not be possible to do it. On my boat I have 16:1 & sometimes give a couple of turns on the winch ( taking care not to damage the boom) , but because the mast is already stressed the vang has no effect on mast bend.
To bend my mast I have reducing tension on the mids & lowers & apply backstay tension to bend the mast.
Up wind the mainsheet normally pulls the boom down ( depending on wind strength & amount of twist required) applying leech tension . Off wind the kicker will not be bending the mast due to boom angle.
On a dinghy one can give the tackle a quick heave & place relatively miles more bend so it is not at all relevant to cruisers . The Op is not sailing a laser off the leech of the sail. Quite the reverse in fact

I was just listing the potential controls which can bend a mast.
Bear in mind the OP says there is negligible rig tension, so there's much less holding it straight.

 

[blush2]

I've come across 22°.

When we got Blush she had straight spreaders, running backstays and checkstays. We wanted to simplify the rig for double handed sailing so got a designer to put a scheme together. She now has spreaders at 22 1/2 degrees and running backstays. The shrouds go to the outside of the hull, and we still have the tweaker backstay to allow us to twist off the top of the sail.

She already had three sets of Genoa tracks, we use the outers for a No1, sheets going outside the shrouds, and a spare sheet if we want to harden up to the inner track, which case we usually roll in a couple of turns.

 

[Ceirwan]

When we got Blush she had straight spreaders, running backstays and checkstays. We wanted to simplify the rig for double handed sailing so got a designer to put a scheme together. She now has spreaders at 22 1/2 degrees and running backstays. The shrouds go to the outside of the hull, and we still have the tweaker backstay to allow us to twist off the top of the sail.

She already had three sets of Genoa tracks, we use the outers for a No1, sheets going outside the shrouds, and a spare sheet if we want to harden up to the inner track, which case we usually roll in a couple of turns.

Two week too late, but when I had my rig professionally redrawn to move the shrouds outboard to the hull, an spreader angle of 22 degrees rake aft from the mast was specified by the designer.
The original was 10.5 degrees & achieving proper forestay tension was not really possible, and the mid section of the past was prone to panting.

Its now like a new boat.