Aft-mast Staysail only rig with no hull modifications
Posted: Sun Aug 25, 2013 4:41 pm
Many of us desire a simpler sailing rig for our Macs, and are wiling to give up some sailing efficiency in order to achieve the following goals:
1) Cockpit not intruded by mast when the mast is down. Boat can go from trailer to power use without any rigging effort at all.
2) Dramatically simpler mast raising and lowering, achieving a true 15 minute launch and load for most users, not just the young, athletic, or sloppy.
3) Far more convenient sail handling, especially while rigging/unrigging.
4) Similar performance as the stock rig.
5) Inexpensive to build and does not require modifying the hull.
You are not going to get a better sailing rig (in terms of efficiency) for the M or X than the stock Bermuda rig, other than by adding a second staysail aka cutter rig. No other rig has been shown to have better performance than a Bermuda rig, especially when pointing.
That said, the majority of other rigs are no less than 20% less efficient than a Bermuda rig: Gaff rigs, cat rigs, aft-mast rigs, and their brethren only loose about a knot of performance in a ten knot wind over a Bermuda rig, and generally only that when pointing. If you’re willing to give up that knot on a point of sail that Macs don’t do well anyway (and that most of us are used to compensating for), a lot of options open up. So we're definitely talking about reduced performance. As long as that's okay, a lot of options become possible.
An aft-mast staysail only rig
=====================
I propose a two-sail alternative to the Bermuda rig that uses staysails on the shrouds rather than a mainsail to reduce the rigging complexity of the Mac.
With this rig, the mast has no boom and no mainsail (technically). Its only purpose is to hold up the stays in tension.
Because there's no mainsail, there's no need for a slot so we can just use a 3" aluminum tube (0.110" sidewall thickness). This aluminum tube will cost <$100 and is available locally anywhere. It need not rotate nor be aerodynamically shaped, because it is not a component of the mainsheet foil (so yes, it’s just necessary drag).
We use a 3' tabernacle of rectangular aluminum tube, 3"x6", bolted permanently to the mast foot using the current boltholes for the mast foot and the mast raising system. This tabernacle has baby-stays at its 3' pinnacle going back to the lower-shroud chain plates to keep it in position with the aft-raked mast atop it. It is drilled and sized to accept the current mast foot. It has a mast roller at the aft top, abaft the mast foot.
The 20' mast is stepped in the current location, but angled back 10% (2 feet over 20 feet) so that the shrouds go straight down from the top to the current chain plates. The foot of the tube is cut at a 10% angle so that the current mast foot can be used.
As per current, the forestay does the work of keeping the rig under tension, and pins to the same bow chainplate location. The backswept mast will keep the forestay under a bit more tension, so we may need to go to the next size up of shroud wire, but that's fine many people do this anyway. Tension down from the side-stays is critical and will have to be kept at optimal, which is a tension that will put a 1" to 2" upward bow in the mast. There are upper shrouds only, no lowers, and no spreaders.
Spreaders and lower shrouds are not necessary because mast bend is not critical as there is no mainsheet.
The forestaysail is then a 170% drifter, flying 250 sq. ft. of sail when fully unfurled. It uses a luff pad to point a bit better. It also has two sets of jibsheets, one set rigged to the gunnel jib tracks and the other set rigged to the cabintop tracks. There’s nothing special going on rigging wise, just two sets of sheets and you keep the set not in use loose. This rigging allows you to furl the forestaysail in below 100% and immediately switch to cabintop tracks for better control, which is critical. It does mean you’ve got more sheets around, so I recommend tossing sheet ends into the cabin to keep them at hand but out of the way.
Here's where it gets different: We have roller-furling staysails on both the port and starboard spreaders in addition to the foresail. These staysails fly 100 sq. ft. of sail each, with their sheets going to the gunnel tracks just ahead of the blocks for the foresail.
The purpose of the mid staysails is to provide the ability to balance CE wherever you want it to be on any point of sail. Before tacking, you furl the leeward sail, then tack the foresail, and then unfurl the opposite sail which is the newly leeward sail. You use roller furling of the mid staysails and the forestaysail to balance the CE (easy to feel as a balanced helm). The mid staysails also replace the sq. ft. of the mainsail, and they provide positive helm control while pointing with a heavily reefed foresail.
Here's how the boat sails on all points:
1) Pointing: Headsail is reefed to a 70% jib, using the cabin-top tracks.
Side staysail is deployed 100%. This provides the extra sail to make up for the reefed headsail and provides the CE balance necessary for good pointing.
Not expected to be as good a pointer as a conventionally rigged Mac with a hank-on jib, but should be equivalent to a Genoa rigged Mac.
2) Beam reach: forestaysail is fully deployed; side staysail is deployed 50% for balance. The drifter should beat a conventionally rigged Mac on this point of sail.
3) Broad reach: forestaysail is fully deployed and the side staysail is fully reefed. The drifter will definitely beat a conventionally rigged mac on this point of sail.
4) Running: Both side staysails are deployed with whisker poles. The two balanced sails should beat a conventionally rigged mac on this point of sail, and the perfect balance should make it easier to get onto and stay on a plane when running. Whisker poles mount easily on the tabernacle.
How the rig trailers and stows:
Unpin the forestay as per usual. Shorter gin-pole but bolted at the top of the tabernacle and with a longer fixed line, is used to raise and lower the mast above the tabernacle. The mast comes to rest on two rollers: The aft mast crutch and the tabernacle roller which is bolted just aft of the top of the tabernacle.
Mast is unpinned at the tabernacle, and rolled back. There is a point where the mast rolls off the aft-crutch and is now supported only on the tabernacle crutch, and this occurs when the mast is still balanced behind the tabernacle. For this reason, you need to walk the mast forward from the cockpit (as we do now because of the spreaders).
Simplicity of the mast with no fittings, spreaders, or hardware below the forestay bail makes walking the mast forward much simpler.
Mast foot pins to the pulpit as current. Mast now protrudes back just two feet over the cockpit and is held 5' above the cockpit by the tabernacle, out of everyone's way. The mast’s balance fulcrum is at the tabernacle. The two side-stays roller furling sails will bend back into a U as they walk back with the mast. They can be unpinned at the chainplate and pinned to a bail at the foot of the mast if desired.
Summary of advantages:
1) All sails furl simply and inexpensively.
2) No boom means safer boat and less rigging complexity.
3) No spreaders or halyard dramatically simplifies mast lowering, raising, and moving.
3) Lowered mast does not interfere with cockpit use. Boat can be used normally with the mast down and pinned.
4) Mast is cheap, simple, and commercially available everywhere.
5) Boat sails differently on different points of sail, but overall as efficiently as the stock rig.
6) No modification necessary to the hull at all, and you can return to the stock rig at any time.
7) Full enclosures are dramatically simplified, as there is no boom or traveller to worry about. All sheet handling is outboard of the boat for a cleaner cockpit.
Alternative Mast Setup:
This is the same rig, but it uses a folding tabernacle that is 10' long. The tabernacle folds forward all the way to the bow pulpit. The mast atop it folds aft 14 feet from the pulpit, and rests on a carrier pole connected to the tabernacle base.
The rig is tensioned exactly the same way, except that the lower shroud chainplates are used to keep the tabernacle under aft-tension so that it does not fold back. It's the lowers that prevent the tabernacle from folding forward, and then the mast sits atop it. So these lower shrouds are under significant tension in opposition to the upper shrouds, which are pulling the head of the mast downward and the forestay which is pulling it down and fore ward.
This configuration has the major benefit of a mast that folds down into position automatically without any rolling or moving. To rig it, you unpin the tabernacle from the pulpit and lift it to vertical by hand, securing the "lower shrouds" which hold it in place once it's vertical. You then lift the upper mast into position and pin the forestay, putting the entire system under tension.
I have not figured out how raising the upper portion of the mast would work. I think it would take a fixed line from a mid-mast bail to a gin pole at the foot of the mast, and then a winch to pull down on the gin-pole, which would raise the entire assembly. Once the forestay is pinned, the gin-pole could fold up alongside the mast out of the way. In any case, it's complicated.
Another possibility would be to pin the forestay first, and then pull the tabernacle back from some location in the cockpit, which would cause the entire assembly to unfold and tension as all at the same time. You would then fix the lower shroud/tabernacle stays last.
Matt
Criticism?
1) Cockpit not intruded by mast when the mast is down. Boat can go from trailer to power use without any rigging effort at all.
2) Dramatically simpler mast raising and lowering, achieving a true 15 minute launch and load for most users, not just the young, athletic, or sloppy.
3) Far more convenient sail handling, especially while rigging/unrigging.
4) Similar performance as the stock rig.
5) Inexpensive to build and does not require modifying the hull.
You are not going to get a better sailing rig (in terms of efficiency) for the M or X than the stock Bermuda rig, other than by adding a second staysail aka cutter rig. No other rig has been shown to have better performance than a Bermuda rig, especially when pointing.
That said, the majority of other rigs are no less than 20% less efficient than a Bermuda rig: Gaff rigs, cat rigs, aft-mast rigs, and their brethren only loose about a knot of performance in a ten knot wind over a Bermuda rig, and generally only that when pointing. If you’re willing to give up that knot on a point of sail that Macs don’t do well anyway (and that most of us are used to compensating for), a lot of options open up. So we're definitely talking about reduced performance. As long as that's okay, a lot of options become possible.
An aft-mast staysail only rig
=====================
I propose a two-sail alternative to the Bermuda rig that uses staysails on the shrouds rather than a mainsail to reduce the rigging complexity of the Mac.
With this rig, the mast has no boom and no mainsail (technically). Its only purpose is to hold up the stays in tension.
Because there's no mainsail, there's no need for a slot so we can just use a 3" aluminum tube (0.110" sidewall thickness). This aluminum tube will cost <$100 and is available locally anywhere. It need not rotate nor be aerodynamically shaped, because it is not a component of the mainsheet foil (so yes, it’s just necessary drag).
We use a 3' tabernacle of rectangular aluminum tube, 3"x6", bolted permanently to the mast foot using the current boltholes for the mast foot and the mast raising system. This tabernacle has baby-stays at its 3' pinnacle going back to the lower-shroud chain plates to keep it in position with the aft-raked mast atop it. It is drilled and sized to accept the current mast foot. It has a mast roller at the aft top, abaft the mast foot.
The 20' mast is stepped in the current location, but angled back 10% (2 feet over 20 feet) so that the shrouds go straight down from the top to the current chain plates. The foot of the tube is cut at a 10% angle so that the current mast foot can be used.
As per current, the forestay does the work of keeping the rig under tension, and pins to the same bow chainplate location. The backswept mast will keep the forestay under a bit more tension, so we may need to go to the next size up of shroud wire, but that's fine many people do this anyway. Tension down from the side-stays is critical and will have to be kept at optimal, which is a tension that will put a 1" to 2" upward bow in the mast. There are upper shrouds only, no lowers, and no spreaders.
Spreaders and lower shrouds are not necessary because mast bend is not critical as there is no mainsheet.
The forestaysail is then a 170% drifter, flying 250 sq. ft. of sail when fully unfurled. It uses a luff pad to point a bit better. It also has two sets of jibsheets, one set rigged to the gunnel jib tracks and the other set rigged to the cabintop tracks. There’s nothing special going on rigging wise, just two sets of sheets and you keep the set not in use loose. This rigging allows you to furl the forestaysail in below 100% and immediately switch to cabintop tracks for better control, which is critical. It does mean you’ve got more sheets around, so I recommend tossing sheet ends into the cabin to keep them at hand but out of the way.
Here's where it gets different: We have roller-furling staysails on both the port and starboard spreaders in addition to the foresail. These staysails fly 100 sq. ft. of sail each, with their sheets going to the gunnel tracks just ahead of the blocks for the foresail.
The purpose of the mid staysails is to provide the ability to balance CE wherever you want it to be on any point of sail. Before tacking, you furl the leeward sail, then tack the foresail, and then unfurl the opposite sail which is the newly leeward sail. You use roller furling of the mid staysails and the forestaysail to balance the CE (easy to feel as a balanced helm). The mid staysails also replace the sq. ft. of the mainsail, and they provide positive helm control while pointing with a heavily reefed foresail.
Here's how the boat sails on all points:
1) Pointing: Headsail is reefed to a 70% jib, using the cabin-top tracks.
Side staysail is deployed 100%. This provides the extra sail to make up for the reefed headsail and provides the CE balance necessary for good pointing.
Not expected to be as good a pointer as a conventionally rigged Mac with a hank-on jib, but should be equivalent to a Genoa rigged Mac.
2) Beam reach: forestaysail is fully deployed; side staysail is deployed 50% for balance. The drifter should beat a conventionally rigged Mac on this point of sail.
3) Broad reach: forestaysail is fully deployed and the side staysail is fully reefed. The drifter will definitely beat a conventionally rigged mac on this point of sail.
4) Running: Both side staysails are deployed with whisker poles. The two balanced sails should beat a conventionally rigged mac on this point of sail, and the perfect balance should make it easier to get onto and stay on a plane when running. Whisker poles mount easily on the tabernacle.
How the rig trailers and stows:
Unpin the forestay as per usual. Shorter gin-pole but bolted at the top of the tabernacle and with a longer fixed line, is used to raise and lower the mast above the tabernacle. The mast comes to rest on two rollers: The aft mast crutch and the tabernacle roller which is bolted just aft of the top of the tabernacle.
Mast is unpinned at the tabernacle, and rolled back. There is a point where the mast rolls off the aft-crutch and is now supported only on the tabernacle crutch, and this occurs when the mast is still balanced behind the tabernacle. For this reason, you need to walk the mast forward from the cockpit (as we do now because of the spreaders).
Simplicity of the mast with no fittings, spreaders, or hardware below the forestay bail makes walking the mast forward much simpler.
Mast foot pins to the pulpit as current. Mast now protrudes back just two feet over the cockpit and is held 5' above the cockpit by the tabernacle, out of everyone's way. The mast’s balance fulcrum is at the tabernacle. The two side-stays roller furling sails will bend back into a U as they walk back with the mast. They can be unpinned at the chainplate and pinned to a bail at the foot of the mast if desired.
Summary of advantages:
1) All sails furl simply and inexpensively.
2) No boom means safer boat and less rigging complexity.
3) No spreaders or halyard dramatically simplifies mast lowering, raising, and moving.
3) Lowered mast does not interfere with cockpit use. Boat can be used normally with the mast down and pinned.
4) Mast is cheap, simple, and commercially available everywhere.
5) Boat sails differently on different points of sail, but overall as efficiently as the stock rig.
6) No modification necessary to the hull at all, and you can return to the stock rig at any time.
7) Full enclosures are dramatically simplified, as there is no boom or traveller to worry about. All sheet handling is outboard of the boat for a cleaner cockpit.
Alternative Mast Setup:
This is the same rig, but it uses a folding tabernacle that is 10' long. The tabernacle folds forward all the way to the bow pulpit. The mast atop it folds aft 14 feet from the pulpit, and rests on a carrier pole connected to the tabernacle base.
The rig is tensioned exactly the same way, except that the lower shroud chainplates are used to keep the tabernacle under aft-tension so that it does not fold back. It's the lowers that prevent the tabernacle from folding forward, and then the mast sits atop it. So these lower shrouds are under significant tension in opposition to the upper shrouds, which are pulling the head of the mast downward and the forestay which is pulling it down and fore ward.
This configuration has the major benefit of a mast that folds down into position automatically without any rolling or moving. To rig it, you unpin the tabernacle from the pulpit and lift it to vertical by hand, securing the "lower shrouds" which hold it in place once it's vertical. You then lift the upper mast into position and pin the forestay, putting the entire system under tension.
I have not figured out how raising the upper portion of the mast would work. I think it would take a fixed line from a mid-mast bail to a gin pole at the foot of the mast, and then a winch to pull down on the gin-pole, which would raise the entire assembly. Once the forestay is pinned, the gin-pole could fold up alongside the mast out of the way. In any case, it's complicated.
Another possibility would be to pin the forestay first, and then pull the tabernacle back from some location in the cockpit, which would cause the entire assembly to unfold and tension as all at the same time. You would then fix the lower shroud/tabernacle stays last.
Matt
Criticism?
