This isn't about MacGregors... but you're my friends,

[arknoah]

Judy,

Looks great!

[Johnacuda]

congras, that looks like she will be a really fun sail. I can't wait to hear if the design, fitting, or usage is the most fun.

[Newell]

Judy,

Haven't flown my new Main yet, will see you at Havasu and have a question about reefing.

Why do the Uppers and Lowers cross before reaching the chainplates on your rigging? Is there some advantage?

[Judy B]

Judy,

Haven't flown my new Main yet, will see you at Havasu and have a question about reefing.

Why do the Uppers and Lowers cross before reaching the chainplates on your rigging? Is there some advantage?

They don't actually cross, it only looks that way in the side view. The spreaders are swept 22* aft and the uppers attach at the outboard ends of the spreaders. the lower shrouds attached at the base of the spreaders. The lower shroud chainplate is further aft than the uppers.

Take another look at both the side view and the stern view

Call me with your question about reefing, please

[seahouse]

Judy -

Along those lines (sorry, bad pun ) have you made a choice of shroud and forestay diameter yet?

- Brian.

[Judy B]

Judy -

Along those lines (sorry, bad pun ) have you made a choice of shroud and forestay diameter yet?

- Brian.

Calculations indicate that the forestay and side shrouds should be 4 mm (5/32") and the back stay should be 3 mm (1/8")

The calculations are based on the righting moment of the boat (5.5 kN-M @ 30 degrees, at max designed displacement of 2800 pounds) and the geometry of the rig, which is shown below.

[Newell]

Why do the Uppers and Lowers cross before reaching the chainplates on your rigging? Is there some advantage?[/quote]

They don't actually cross, it only looks that way in the side view. The spreaders are swept 22* aft and the uppers attach at the outboard ends of the spreaders. the lower shrouds attached at the base of the spreaders. The lower shroud chainplate is further aft than the uppers.

Take another look at both the side view and the stern view

Call me with your question about reefing, please

[/quote]

I can see a strength advantage for the hull in having the shrouds attach to separate and spaced chainplates but I don't understand the advantage of having the uppers attach forward of the lowers? It would seem that the uppers need more purchase (increased angle to the mast at base plane) than the lowers, like the backstay. Is the plan to fly the jib between the shrouds for better pointing?

The roach of the main looks to contact the backstay, so are you contemplating an ajustable backstay or will the bending of the sail as it flies eliminate the overlap?

[Judy B]

I can see a strength advantage for the hull in having the shrouds attach to separate and spaced chainplates but I don't understand the advantage of having the uppers attach forward of the lowers? It would seem that the uppers need more purchase (increased angle to the mast at base plane) than the lowers, like the backstay. Is the plan to fly the jib between the shrouds for better pointing?

The roach of the main looks to contact the backstay, so are you contemplating an ajustable backstay or will the bending of the sail as it flies eliminate the overlap? [/quote]

In the side view, the mast will have a small amount of prebend tuned into it. The tension on the cap shrouds pushes the spreaders forward, bending the mast a little.

The lower shrouds act as check stays, they prevent the mast from bending too far forward in the middle. They stabilize the mast in the fore and aft plane. So if you want the lower to act as a check stay against bending the middle of the mast too far forward, you have to anchor it at least 12 or more degree aft of the attachment point on the mast.

The wider the angle, the greater the vector component working in the direction you want. With an angle that's too narrow, at the tension in the wire contributes too much downward compression on the mast, and doesn't provide enough stabilization against buckling of the mast column.

Nope, the mainsail will not overlap the backstay. I'm a cruiser, and I definitely do NOT want to have to deal with a roach getting caught on the backstay.
International Marine is going to put the boat into production, and if a racer wants me to build a sail that overlaps the backstay, I'll do it.

Btw, this started as a project to update my old boat by spending a few grand on a new keel and new mast. When the factory saw it, they offered to give me a new boat and trailer at a greatly reduced cost if I would give them the rights. After I got agreement from the architect, we made a deal. I get a new boat and International gets the rights to the design plans.

The engineering plans are by Jim Antrim. I will provide the layout for all the sail handling hardware and a design drawing for a set of cruising sails by me. With the engineering output from Jim, I can do a proper specification of the deck hardware to handle all the loads safely.

[finding41]

Judy that's a sweet deal!
I have to talk to Roger!

[Judy B]

Judy that's a sweet deal!
I have to talk to Roger!

You are joking, right?

Roger does his own a naval architecture and engineering.
He doesn't need to trade you a boat at his cost to pay you for architectural and engineering services.

Let us know how your talk with Roger goes

All the development costs are being paid by me, not the builder.
This boat is being engineered by a big name architect, not by Redneck Engineering
The engineering is being done properly, and it's expensive. Big $$$$.

I'm paying the fee$ for the naval architectural design and engineering.
I'm paying the fee$ for the rig design and engineering,
I'm "paying" the fee$ for the sailplan design and deck design - with my own time.

The only thing "Free" to me here is my time, and that's not free.
it's a good deal for me, but It's still costing me big bucks out of pocket.

Is a really sweet deal for the builder.
It's not costing HIM a penny.
He gets to develop a new boat with $0 at risk.

[Catigale]

It looks great except for that green hull....even slower than blue....

[THE CUSCUS]

Judy that's a sweet deal!
I have to talk to Roger!

He probably wasn't kidding

Nice concept & design Judy. I bet it will be a fine sailing boat, and quick at that! Nothing like taking a production design and improving it with both design and materials. If it were a car, we would call it a hot rod. Is there such terminology for boats & boaters?

[Dimitri-2000X-Tampa]

Calculations indicate that the forestay and side shrouds should be 4 mm (5/32") and the back stay should be 3 mm (1/8")

The calculations are based on the righting moment of the boat (5.5 kN-M @ 30 degrees, at max designed displacement of 2800 pounds) and the geometry of the rig, which is shown below.

Hi Judy, congrats on your new project!

Your standing rigging calculations do make me think about MacGregors, primarily the fact that the forestay on the 26X is thinner (1/8) than the side shrouds at (5/32). Now I don't know anyone who has had a failure (without a valid reason) and I know some people have beefed up the forestay just out of caution but my question has to do with putting heavier sails on the 26x than what it was originally designed for. As we know, the stock sails are very light (4oz I think) so if you put heavier sails on (ie 6+ oz), by definition, the weight aloft increases. So does that change the geometry of the rig, the righting moment and the safety factor of the original standing rigging?

Dimitri

[Judy B]

Hi Judy, congrats on your new project!

Your standing rigging calculations do make me think about MacGregors, primarily the fact that the forestay on the 26X is thinner (1/8) than the side shrouds at (5/32). Now I don't know anyone who has had a failure (without a valid reason) and I know some people have beefed up the forestay just out of caution but my question has to do with putting heavier sails on the 26x than what it was originally designed for. As we know, the stock sails are very light (4oz I think) so if you put heavier sails on (ie 6+ oz), by definition, the weight aloft increases. So does that change the geometry of the rig, the righting moment and the safety factor of the original standing rigging?

Dimitri

No,
No, and
No.

Let me explain using real numbers, numbers from my own project. You'll have to ask Roger if you want the numbers for a 26X

1.No. The geometry of the rig doesn't change when you add weight aloft. The weight aloft changes.

2. No, adding weight aloft does not increase the loads on the rig. It reduces stability and makes the boat more tender
Adding weight aloft "neutralizes" ballast.
The boat gets more "tender" and heels further for a given wind speed or sail area. You have to reef sooner.
The boat will capsize more easily.
But the forces on the rig remain the same.

3. No, Going from 4 oz to 6 oz adds only about 1.75 pounds of weight aloft. The maximum righting moment is 4060 ft-pounds. (and that occurs at about 40 degrees of heel. That extra weight aloft "uses up" a little of the righting moment only in the sense that the boat will be more tender by less than (by way less than 1%). It doesn't change the maximum righting moment, which is the sole determinant of how much of a load the wind can place on the sails before the boat tips over.because of #1 and #2

QED

That's overly simplified, but for practical purposes its accurate.

However, if you add gear and people to the boat that generally DOES increase the righting moment.... so if you add a couple of six packs of beer as ballast to the boat, that will increase the righting moment. If you add so much beer that you exceed the designed capacity of the boat one the following things will happen: you'll lose the rig or you'll fall overboard or you'll get arrested for DUI and get taken to jail -- thereby getting the weight of the boat back within the designed capacity so all is right within MacGregor-Land again .

None of that would have anything with physics, but I'm sure somebody will blame the boat's engineering

Seriously, boats are engineered to handle the forces at maximum allowed capacity. Then a safety factor is thrown in on top of that to allow for less than perfect maintenance. MacGregors don't lose masts because the wires are too small. The wires on the Macs are fine!!!! Macs lose masts due to metal fatigue and corrosion. The wire strengths are more than adequate . There may or may not be other problems but wire size ain't one of 'em!

For decades I have been trying to convince people that bigger forestays or shrouds are rarely needed on a properly engineered boat. Wires fail due to bad installation practices or lack of maintenance or physical depreciation. In fact there are numerous drawbacks to increasing the wire diameters having to do with the elasitic modulus of the steel and the force.

Fair winds,
Judy

[DaveB]

Dimitri,
I went with a 5/32 headstay. Reason is there is a lot of movement from the Head Sail and I wanted backup if a strand or two broke without me knowing it. Also noticed a slightly less bend in the stay beating to windward,even with toggles both ends.
Side stays don't have Sails attached that put stress on fittings like a headstay would.
Judy made me a new 7 oz main sail that is great for beating to windward and motersailing, it is hard to flake bringing it down. I would go with a 6 oz.
I can say the new main with two top full battens has a much greater reach to windward without backing off main. I use a 105 jib only.
Dave