Chotu's Advanced Running Rigging Thread (lots of pics)

[Lee Jerry]

Originally Posted by Chotu

so here are the results for the actual mainsheet load:

Foot of sail: 20ft
Luff of sail: 55ft
Assuming attachment point at 20ft at end of boom.

Load @ 15 knots: 1055 lbs
Load @ 20 knots: 1876 lbs

I think there should have been a reef in before I hit 20 knots, but to assume worst case scenario, i put it in anyway.


1876lbs is 850kg. a FAR cry from 7000kg (which is more than my boat weighs)

glad we went through the exercise because this explains why it works on all the boats that have it and why it works on that very skimpy metal in the pic jedi put up. The sky is not falling.

Did the on-line calculator you used say anything like "for typical cruising monohull?" I bet it did.

Remember in your standing rigging thread (and about a thousand others) where it's talked about cats having higher shroud / stay loads because they don't heel? That applies to main sheet loads as well. So, your cat will have higher load than the calculator shows.

Does you cat have a square-top or high roach main? If so, your cat will have higher load than the calculator shows.

Are your sails made of high-tech material (carbon, etc.) and not dacron? If so, your cat will have higher load than the calculator shows. High-tech control lines, too? Higher loads.

Thus, if you re-read what catsketcher wrote, he's probably more "right" than you'd like. He said something like 'half the weight of the boat or more' and threw out the 7000kg number. Maybe he didn't realize the actual weight of the boat, or maybe he meant lb instead of kg. Regardless, I expect that a reasonable design main sheet load for your boat is closer to "half the weight of the boat" than it is to 1876 lb.



As for the other boats that have the main sheet / traveller on the cockpit roof, do you know how they did that? The short answer is "they planned for it."

I don't recall, but did you give any structural details of your cockpit roof? It's an add on, right, not part of (nor built with) the house roof? How strong is it? Can you walk on your roof? Is it connected to the cabin (roof) on the forward end?

[catsketcher]

Last go of this before I ban myself from the thread.

There is a huge difference between crosscut dacron monohull sheet loading and square top laminate cat mainsail loading. The Harken calculator is for the former.

A Gunboat 48 weighs 10 000kg in loaded trim - Hence the large figure of 7000kg. Incorrect on my part, half the displacement would be 50 000N of load.

I have sailed fast large cats and the mainsheet loads are immense and in reality really scary. You wind on the large winch, fed through a multi part tackle and keep on more and more to reduce twist - you wind on stress into the sheet until the breaking of a block would kill someone if they are in a "dangerous quadrant". These things really do play on your mind as the 12mm sheets start twanging like guitar strings.

So you need to design for peak potential load - then you have to factor in that the mainsheet system has to work at well below its rated load so it does not suffer from fatigue failure - so you add a fudge factor. Also, if it has any composite then you also have to add some more fudge factor becausre of off axis loading, same for point concentrations and for shock loadings.

You never want certain parts of the boat to fail - the parts you can't fix in one minute with spares in your tool box. So the attachment points, the basics and the blocks themselves all need to be specced well above the load you will get when fully loaded and caught with full sail up as you lift a hull. This is the MINIMUM load you should cater for. Then add fudge factors and this goes up. You should never factor in the need for sail reduction with chainplates, keel bolts, winch attachments or sail control systems.

I have said I think this is a bad way of designing a critical piece of a catamaran's structure. Following good plans is essential for those parts that are structurally vital.

[Chotu]

Originally Posted by Lee Jerry

Did the on-line calculator you used say anything like "for typical cruising monohull?" I bet it did.

Remember in your standing rigging thread (and about a thousand others) where it's talked about cats having higher shroud / stay loads because they don't heel? That applies to main sheet loads as well. So, your cat will have higher load than the calculator shows.

Does you cat have a square-top or high roach main? If so, your cat will have higher load than the calculator shows.

Are your sails made of high-tech material (carbon, etc.) and not dacron? If so, your cat will have higher load than the calculator shows. High-tech control lines, too? Higher loads.

Thus, if you re-read what catsketcher wrote, he's probably more "right" than you'd like. He said something like 'half the weight of the boat or more' and threw out the 7000kg number. Maybe he didn't realize the actual weight of the boat, or maybe he meant lb instead of kg. Regardless, I expect that a reasonable design main sheet load for your boat is closer to "half the weight of the boat" than it is to 1876 lb.



As for the other boats that have the main sheet / traveller on the cockpit roof, do you know how they did that? The short answer is "they planned for it."

I don't recall, but did you give any structural details of your cockpit roof? It's an add on, right, not part of (nor built with) the house roof? How strong is it? Can you walk on your roof? Is it connected to the cabin (roof) on the forward end?

I did it at harken.com.

do you really think an online calculator takes into account heeling to lower the force on the mainsheet? Do you think it is that advanced?

if it does, exactly what angle of heel is it using? Because it certainly didn’t give me a range from 0 to 10° or 0 to 30° or anything. what angle of heel is it using to make its calculation for wind spilling off the sail?

do I have to do this from first principles? Using the area of the sail and showing my work? You don’t think I can rely on the online calculator?

Square top? unfortunately no. maybe next set of sails
Carbon sails? i wish. unfortunately no. dacron

7000kg is close? no. not by a long shot. my entire boat doesn’t even weigh 7000kg. if this ridiculously wrong number was close to true, you think my rudders would resist this force? no! the boat would spin around in a circle with the main up. or… with this silly number, if the force were vertical, the boat would lift free of the water in 20 knots of wind and fly through the sky.

My cockpit roof IS the house roof.
Not part of the house roof? it IS the house roof
can’t walk on the roof? huh? what kind of POS do you think i built?
connected? again it IS the house roof.

nothing is right in your post

[Chotu]

F=PA(C)

C= drag coefficient (1.0)
P= pressure = 1/2 d x v^2
v= velocity of wind = 20mph in this calculation
d= density of air = .075 lbs/cuft
A= surface area = a triangle = (1/2)*55x20

F = PA(C):

P = 1/2 dv^2 = 1/2 x .075 x 20^2 = 15
A = 1/2 x 55 x 20 = 550
C = 1

F = PAC = 8250 lbs TOTAL FORCE on the entire area of the sail @ 20mph

8250 lbs force on the ENTIRE sail with no heeling not even CLOSE to the 15,423lbs (7000kg) specified

NOTE: this force is divided up between the mast base, the shrouds and the mainsheet!

At first glance, looking at 1876 lbs at the tip of the triangle when the whole luff/ is fixed to the mast sure doesn’t seem too far off to me.

It’s 3am. i have to leave in 3 hours. i’m not doing the moment arm stuff right now, but the 8000 lbs is distributed across the whole sail horizontally and vertically. there is no vertical movement unless i’ve lost the rig.

therefore, it’s the same math as the force to open a door. it’s the force you’d apply to the door knob. that’s the mainsheet load.

i’ll leave it to the reader to go through that exercise. i’m going back to sleep

[Chotu]

here is how the 8000 lbs is distributed across the sail and to the mainsheet.

qualitatively, looking at the diagram, since i’m not staying up all night proving people wrong (which i can do later if it’s really necessary), you can CLEARLY see the summation of the 8000 lbs total force over the length of the boom. Distance matters.




I can prove all of these wild numbers and theories wrong when it’s not 3am. in a few days, when i have time to waste doing this . i’ll have to do the integration to to convert the. uniform distributed load to a point load for a cantilever. but… i’m sure you’ll see harken isn’t wrong. you can make all kinds of arguments to try to pretend the online calculator is inaccurate but you’re wrong. Feelings and fear aren’t more important or more accurate than math.

[Chotu]

or using the rigging doctor’s math, which is the same as mine, then super simplified for the sheet load explicitly:

https://www.riggingdoctor.com/life-a...culating-loads


550 sqft x 20mph^2 x .00431 = 948 lbs load on the mainsheet.

Double it for the ultimate safety margin and NO WAY…. It’s the 1800 lbs (816 kg) i came up with at harken.

quite a coincidence, isn’t it???

if anyone has a problem with this, take it up with the rigging doctor if you think he is wrong. (he’s not - you are)

Now let’s stop derailing this thread with fear and nonsense and get back to the point. The point is the arrangement of the main sheet. How to place the sheet such that it’s most simple to use, given the constraints of the arrangement of the deckhouse roof

[MicHughV]

I was watching some Youtube video of the AC75's doing their thing, and it seemed that regardless of the wind direction, these boats always seem to be hard on the wind, due to the apparent wind effect. ie, you never see the main nor the small jib cracked off much beyond the centerline of the boat. Even when jibing those boats, the main only flops over a small amount.

With this thought in mind, I wonder how much of this would apply to you, as you also have a fast steed. Maybe not in the same realm of an AC75, but certainly fast.

Ice sailboats also sail with main sail sheeted in hard due to their speed.

This brings up the question of your optimum mainsheet control attachment points.

Though I've sailed on some cats and tri's, I'm no expert in this field, but it seems that some thought needs to be thrown at this, given that you have a faster than average boat.

The mainsheet not only controls the placement of the main boom relevant to the wind direction, or apparent wind condition as the case may be, but also provides leech tension, especially so, when the mainsheet is attached near the arse end of the boom.

Like others on this thread, besides being a lifelong sailor, I am also a State registered structural marine engineer (retired now), and this issue is tugging on my brain cells as to how best to approach this to come up with the ideal solution for your particular boat and circumstances.

That's all one thing, but the other thing is to also have the mainsheet tailing end located in a position favorable to the helmsman or relatively close by for a crew/skipper to be able to make adjustments as needed.

This would also apply to reefing lines, halyards and so on, not mention the jib sheet winch locations, furling lines and so on.

On my Beneteau all these lines are led back to the cockpit, some come in on the port side and others on the starboard side. It's quite a jumble of lines, blocks, pulleys and winches, etc, but being a mono, most everything can be reached by the helmsman, but your boat, being a cat has a lot more real estate and some kind of centralized command center would make most sense to me.

If you have the opportunity to look at how other cats and tri's do this, it may provide a starting point on how to accomplish yours.

Any Gunboats in your neck of the woods would provide and excellent source, or maybe you can peruse the Youtube video's of Gunboats in action to gleen some insight on how things are accomplished on those boats.

It's difficult for me...and others on this thread to provide suggestions, as we are not on the boat, so we can't see with our own eyes the lay of the land so to speak.

Just my 2c for the evening as this thread is now approaching 12 pages of discussion.

[Lee Jerry]

Originally Posted by Chotu

I did it at harken.com.

do you really think an online calculator takes into account heeling to lower the force on the mainsheet? Do you think it is that advanced?

if it does, exactly what angle of heel is it using? Because it certainly didn’t give me a range from 0 to 10° or 0 to 30° or anything. what angle of heel is it using to make its calculation for wind spilling off the sail?

do I have to do this from first principles? Using the area of the sail and showing my work? You don’t think I can rely on the online calculator?

Square top? unfortunately no. maybe next set of sails
Carbon sails? i wish. unfortunately no. dacron

7000kg is close? no. not by a long shot. my entire boat doesn’t even weigh 7000kg. if this ridiculously wrong number was close to true, you think my rudders would resist this force? no! the boat would spin around in a circle with the main up. or… with this silly number, if the force were vertical, the boat would lift free of the water in 20 knots of wind and fly through the sky.

My cockpit roof IS the house roof.
Not part of the house roof? it IS the house roof
can’t walk on the roof? huh? what kind of POS do you think i built?
connected? again it IS the house roof.

nothing is right in your post

According to the Harken site, on the bottom of the calculator page:

So that doesn't appear to be wrong. Why do you think they may say that? Why don't you contact them about the load estimate for your boat?
(Edit - the picture is small, but I don't have enough interest to fix it.)

I never said the 7000kg number was right. Maybe re-read what I wrote. (And your "examples" are non-sensical.)

The rest of my post was questions seeking clarification about your boat. I don't see how they could be "wrong."


I am, however, coming up with a hypothesis as to why this thread may have less participation than the standing rigging thread.

[Lee Jerry]

Originally Posted by Chotu

F=PA(C)

C= drag coefficient (1.0)
P= pressure = 1/2 d x v^2
v= velocity of wind = 20mph in this calculation
d= density of air = .075 lbs/cuft
A= surface area = a triangle = (1/2)*55x20

F = PA(C):

P = 1/2 dv^2 = 1/2 x .075 x 20^2 = 15
A = 1/2 x 55 x 20 = 550
C = 1

F = PAC = 8250 lbs TOTAL FORCE on the entire area of the sail @ 20mph

8250 lbs force on the ENTIRE sail with no heeling not even CLOSE to the 15,423lbs (7000kg) specified

NOTE: this force is divided up between the mast base, the shrouds and the mainsheet!

At first glance, looking at 1876 lbs at the tip of the triangle when the whole luff/ is fixed to the mast sure doesn’t seem too far off to me.

It’s 3am. i have to leave in 3 hours. i’m not doing the moment arm stuff right now, but the 8000 lbs is distributed across the whole sail horizontally and vertically. there is no vertical movement unless i’ve lost the rig.

therefore, it’s the same math as the force to open a door. it’s the force you’d apply to the door knob. that’s the mainsheet load.

i’ll leave it to the reader to go through that exercise. i’m going back to sleep

Originally Posted by Chotu

here is how the 8000 lbs is distributed across the sail and to the mainsheet.

qualitatively, looking at the diagram, since i’m not staying up all night proving people wrong (which i can do later if it’s really necessary), you can CLEARLY see the summation of the 8000 lbs total force over the length of the boom. Distance matters.




I can prove all of these wild numbers and theories wrong when it’s not 3am. in a few days, when i have time to waste doing this . i’ll have to do the integration to to convert the. uniform distributed load to a point load for a cantilever. but… i’m sure you’ll see harken isn’t wrong. you can make all kinds of arguments to try to pretend the online calculator is inaccurate but you’re wrong. Feelings and fear aren’t more important or more accurate than math.

Originally Posted by Chotu

or using the rigging doctor’s math, which is the same as mine, then super simplified for the sheet load explicitly:

https://www.riggingdoctor.com/life-a...culating-loads


550 sqft x 20mph^2 x .00431 = 948 lbs load on the mainsheet.

Double it for the ultimate safety margin and NO WAY…. It’s the 1800 lbs (816 kg) i came up with at harken.

quite a coincidence, isn’t it???

if anyone has a problem with this, take it up with the rigging doctor if you think he is wrong. (he’s not - you are)

Now let’s stop derailing this thread with fear and nonsense and get back to the point. The point is the arrangement of the main sheet. How to place the sheet such that it’s most simple to use, given the constraints of the arrangement of the deckhouse roof

Your grasp of the loads and the load path is...well, underwhelming.

FWIW, the rigging doctor used the exact same monohull equations as Harken, so no, not a coincidence.


The reason the Lagoons et al can carry the main sheet on the "roof" with "just" a couple stanchions is not that hard to understand. The roof is acting as a beam with the strong section (direction) oriented horizontally. It is a strong, stiff bean in this direction. Thus, when the sheet pulls sideways on the end of the roof, the load (i.e. the racking) is transferred down the beam and is reacted by the entire house. The vertical component of the main sheet acts on the weak axis of the roof, and therefore the stanchions are added to react that force.

Here's a little experiment you can do to help you visualize it. Take a credit card and pinch (hold it on) one end with it parallel to the ground. Say this is the right end. First, at the left end push horizontally (parallel to the ground) sideways. Next, push down vertically on the left end. See the difference?

Note that I am in no way saying your boat is capable of the same. I don't know anything about its structure or what kind of POS you built.

[Chotu]

agreed about the shock loading. The regular load is just a place to start. To show the load isn’t more than the weight of my entire boat.

I must say I’ve never had an accidental gybe in my life because I don’t sail a boat like that, putting it in danger, but, I have to account for that anyway.

[Chotu]

Originally Posted by MicHughV

I was watching some Youtube video of the AC75's doing their thing, and it seemed that regardless of the wind direction, these boats always seem to be hard on the wind, due to the apparent wind effect. ie, you never see the main nor the small jib cracked off much beyond the centerline of the boat. Even when jibing those boats, the main only flops over a small amount.

With this thought in mind, I wonder how much of this would apply to you, as you also have a fast steed. Maybe not in the same realm of an AC75, but certainly fast.

Ice sailboats also sail with main sail sheeted in hard due to their speed.

This brings up the question of your optimum mainsheet control attachment points.

Though I've sailed on some cats and tri's, I'm no expert in this field, but it seems that some thought needs to be thrown at this, given that you have a faster than average boat.

The mainsheet not only controls the placement of the main boom relevant to the wind direction, or apparent wind condition as the case may be, but also provides leech tension, especially so, when the mainsheet is attached near the arse end of the boom.

Like others on this thread, besides being a lifelong sailor, I am also a State registered structural marine engineer (retired now), and this issue is tugging on my brain cells as to how best to approach this to come up with the ideal solution for your particular boat and circumstances.

That's all one thing, but the other thing is to also have the mainsheet tailing end located in a position favorable to the helmsman or relatively close by for a crew/skipper to be able to make adjustments as needed.

This would also apply to reefing lines, halyards and so on, not mention the jib sheet winch locations, furling lines and so on.

On my Beneteau all these lines are led back to the cockpit, some come in on the port side and others on the starboard side. It's quite a jumble of lines, blocks, pulleys and winches, etc, but being a mono, most everything can be reached by the helmsman, but your boat, being a cat has a lot more real estate and some kind of centralized command center would make most sense to me.

If you have the opportunity to look at how other cats and tri's do this, it may provide a starting point on how to accomplish yours.

Any Gunboats in your neck of the woods would provide and excellent source, or maybe you can peruse the Youtube video's of Gunboats in action to gleen some insight on how things are accomplished on those boats.

It's difficult for me...and others on this thread to provide suggestions, as we are not on the boat, so we can't see with our own eyes the lay of the land so to speak.

Just my 2c for the evening as this thread is now approaching 12 pages of discussion.

that’s very observant of you especially coming from monohulls. you are correct that sheeting is almost never way out there like that on these boats.

usually much tighter thanks to the apparent wind

my most recent thinking (after a day away snowboarding) is to just put a couple of blocks pretty close or on the attachment point of the upright columns.

if you look at the pictures of all of the other Catamarans that sheet from the roof, many of them have that set up. So that would be good for me. Especially at first.

if I have to go really deep downwind i’ll just use the spinnaker or the jib if it’s too windy, including furled a bit in very strong conditions.

from there, I can add functionality for easing the boom way out if I want to, but you’re completely right about these boats. they don’t need the main sheeted way out often at all.

I think you are forgetting what I am doing for the sail control table (also called a plinth by millionaires). i’m attaching a picture to remind you.

as for looking at other boats, I know it is already 12 pages but if you scroll back a bit, we have about half a dozen boats in this thread with pictures that sheet exactly the way I’m looking to do it. just like all of those other boats do. my specific most similar gunboat sheets down at the bottom of the main beam. they only made 6 of those boats. but that system does not work with my davits so it won’t be happening. I’ll be sheeting from the roof.

it seems as though the thread did actually have a productive outcome, despite nearly going off the rails because here we are. There is a plan.

1) guy wires outboard of the columns to take racking forces away from the roof

2) columns and davits stay as is - columns could practically do the job on their own already like they do on all the boats in the pics in this thread

3) a block at the attachment point of each column at the roof level- even better if i can find a way to get those blocks more outboard at roof level

4) usage: close hauled to reaching - use mainsail as described above. deep runs: use spinnaker or jib or even mainsail with bad trim

5) future: later i have to add a sprit and additional furler to house another sail. the quiver is not quite complete. at this time i can revisit the sheeting to see if i need more control such as a downhaul outboard to get better sail shape when on deep runs using the main

That’s a solid plan.

Now i can start designing the running rigging layout and submit the plan here in this thread and continue this thread properly for the running rigging in general, which was the point of it

[s/v Jedi]

Hey Chotu do not forget, you need a fuse in the sheet of course, otherwise she flips

[Chotu]

Originally Posted by s/v Jedi

Hey Chotu do not forget, you need a fuse in the sheet of course, otherwise she flips

Now THAT is some real rigging talk. I would like to explore this for sure.

there is no doubt my boat can flip just as easily as all of the upside down gunboats LOL.

my sister ship is single-handed a lot of times and goes up and down from north atlantic to caribbean all the time. none of these problems happen to him. But, I would like something in place potentially to help release the sheet quickly.

honestly, rather than a fuse I feel like I would prefer a slip mechanism. almost like a pin that pulls out in case of emergency.

do you know how in workplaces they have big red stop switches? do you know how on a city bus when you want to get off at a stop you pull on a string and it notifies the driver? do you know how some trains or small rides or automated monorails have that same type of string as a bus but it applies the brakes and stops the train?

I think that kind of system would be cool. An emergency stop wire that runs around that anyone can pull from just about any part of the boat.

I know that introduces some human error, but I really don’t like the idea of a fuse that can blow out earlier than expected. It did not work well on the rudders. The whole idea of a fuse is not too appealing to me. but I have no idea how this works with line stoppers. I don’t think it would.

certainly some kind of provision should be made for this. Because certainly my boat can get into trouble over canvased.

[malbert73]

Originally Posted by Chotu

or using the rigging doctor’s math, which is the same as mine, then super simplified for the sheet load explicitly:

https://www.riggingdoctor.com/life-a...culating-loads


550 sqft x 20mph^2 x .00431 = 948 lbs load on the mainsheet.

Double it for the ultimate safety margin and NO WAY…. It’s the 1800 lbs (816 kg) i came up with at harken.

quite a coincidence, isn’t it???

if anyone has a problem with this, take it up with the rigging doctor if you think he is wrong. (he’s not - you are)

Now let’s stop derailing this thread with fear and nonsense and get back to the point. The point is the arrangement of the main sheet. How to place the sheet such that it’s most simple to use, given the constraints of the arrangement of the deckhouse roof

Hi Chotu- such a cool boat and can't wait to see it continue being fit out.
Small friendly suggestion- I'd have more patience for what you see as "dissenting opinions." Your defensive and borderline aggressive responses to some posts will shut these folks (and others) down just when you want opinions to help guide you, not a bunch of "yes people" just agreeing with you.
A simple "duly noted, and I still think my design can meet all possible loads" goes a long way to promoting open conversation

[MicHughV]

Yes, now you are applying some logical thinking.

The location of the posts, while presenting a logical "structural" point of connecting the mainsheet, may not be the " optimum" location as they are too outboard from the centerline of the boat.

Here's the thing. You've gone to great lengths to build this fast steed, but without the correct sail setup, you are depriving yourself of the correct motive power to move it to it's best capabilities.

The logical thing to do....imo...is to install a "track" to span between the two posts. The mainsheet will then just go up and down from the end of the boom to the car on the track. Sidewise movement of the " car" is accomplished by small block and tackle setups on each end of the tracks, a pretty standard setup.
This will allow you to set the main " exactly" where it needs to be.

Both the mainsheet and track car control lines can can be led forward to a location most appropriate for your helm location.

Again, using my Beneteau as an example, all these lines come thru' the lower portion of the dodger, to a winch immediately behind the dodger.
Each control line has it's own cam cleat, so the line can be locked down, and the line released from the winch to allow another line to to wrap around the winch.

Again, just floating some ideas for your consideration.