I Found a Rig

[Chotu]

Here are some pics.

Anyone see anything I should be cautious about?
All lines are to be led to and controlled from a spot about 3ft from the base of the mast. Lots of turning blocks and rope clutches to be used to control everything in my design.

Also, I see all those sheaves on the boom. Are those there to do a triple reef on the main?

Does this look appropriate for my boat just by sight alone? Anyone see a reason not to get it from the pics?

[Chotu]

Originally Posted by fourlyons

Yes, if this mast came off a boat of the same size (length and width), weight, and sail area, basically the same righting moment, it should work fine. If the other boat was heavier or had more sail area it would still work, it would just be heavier than you need.
Further having a different beam doesn't mean the spreader angle is wrong. Spreaders are used to ensure the proper (minimum) angle at the top of the mast, and of course to support the spar to keep it in column under load. But if the spar section were stiff enough and the beam wide enough, you could dispense with the spreaders all together, as some boats do.
If you measure the fore and aft and side to side dimensions, wall thickness, and taper and contact a spar manufacturer, they should be able to give you the numbers you need.

Right. Good point about the spreaders. It’s a double diamond rig so the spreaders are just for that. I was picturing monohull stuff.

[Fore and Aft]

Chotu I am impressed, a bit of perseverance and a rig has turned up. My main question is why are they selling it? Besides that it looks fairly good in the pictures with a nice self tailing winch. A lot of the masts I see being recycled have wire winches.
As for the 5 foot difference have you done the calculations on how much sail area you are losing? Maybe a longer foot on the Genoa or slightly bigger MPS might make up the difference.
Cheers and good of you to let us know what's happening.

[Chotu]

Originally Posted by Fore and Aft

Chotu I am impressed, a bit of perseverance and a rig has turned up. My main question is why are they selling it? Besides that it looks fairly good in the pictures with a nice self tailing winch. A lot of the masts I see being recycled have wire winches.
As for the 5 foot difference have you done the calculations on how much sail area you are losing? Maybe a longer foot on the Genoa or slightly bigger MPS might make up the difference.
Cheers and good of you to let us know what's happening.

Thank you!

They are selling it to convert the boat to a displacement power cat live aboard. No more sailing.

One of the forum members deserves all the credit actually for noticing this for sale and alerting me. While I’d like to take credit and think it was due to my perseverance, i can’t. Ha ha.

I was thinking the same.

Bigger roach on the main, wider sail area lower to give the same sail area at the end.

However, I don’t know the implications of this approach. I just plain don’t know rigs. I am more of a user of rigs and less of a designer.

It has some old sails to get by with for now and later I could get some new ones made up.

Kind of excited here but VERY nervous because I don’t know what I’m doing. I really need a lot of help and input on this part.

The penalties for mistakes here are enormous. Almost as bad as when I was infusing my first hull.

[Chotu]

Should I extend this mast at the base? Should I try to compensate with different sail cuts so there is more roach?

It’s all very confusing to me.

[Dockhead]

Originally Posted by Chotu

. . . Bigger roach on the main, wider sail area lower to give the same sail area at the end.

However, I don’t know the implications of this approach.. .

You don't really want to reduce the aspect ratio of the mainsail by lengthening the boom. Lift is more a function of leech length than sail area. Increasing sail area without increasing leech length will add drag disproportionately and hurt your upwind performance.


There are upsides to less sail area as well as the downside of less power in light conditions. With less sail area you can carry more sail in stronger wind without reefing, which is good for performance in those conditions. Shorter rig has less drag altogether. Shorter rig with lower CE will be less capsize risk.



This rig might be good as it is. You might make up for the sail area in light conditions with Code 0 and/or assy chute, which are good to have in any case.



You should really consult a designer and get him to crunch some numbers for you.

[Chotu]

Good points!

I had forgotten about aspect ratio being one of the most important factors.

I’d definitely have to extend this thing.

I’m most concerned with light air performance. That’s what the boat was built for. I’m trying to end up with a boat that needs early reefing and does well in calmer conditions, so I don’t need to motor often.

Originally Posted by Dockhead

You don't really want to reduce the aspect ratio of the mainsail by lengthening the boom. Lift is more a function of leech length than sail area. Increasing sail area without increasing leech length will add drag disproportionately and hurt your upwind performance.


There are upsides to less sail area as well as the downside of less power in light conditions. With less sail area you can carry more sail in stronger wind without reefing, which is good for performance in those conditions. Shorter rig has less drag altogether. Shorter rig with lower CE will be less capsize risk.



This rig might be good as it is. You might make up for the sail area in light conditions with Code 0 and/or assy chute, which are good to have in any case.



You should really consult a designer and get him to crunch some numbers for you.

[chris95040]

Originally Posted by smj

So if he took the used mast and rigging, used the original sails that came with it and kept the same basic geometry for the shrouds and stays and their attachment points then he would basically be replicating the rig as it was on the original cat, so no problems.

Replicating a rig from one boat onto another is only correct if the boats themselves had similar righting moments.

A popular and dangerously incorrect assumption is that you can copy and paste a rig from one boat to another. You seem to think it’s just a function of sail geometry. It is not. All else being equal, if one boat has a higher righting moment, it needs a beefier rig (stiffer mast, or more spreaders, etc).

[Benz]

I would not modify--that's a can of worms what with getting the mast track to line up, moving the gooseneck, all that jazz. The pics show a strongly-built stick with welded parts, and one that's been proved already. Altering that can't make it better or stronger, but it will be expensive. Improve your light air performance with a screecher--put it out forrard on a bowsprit ("Longeron" in multihull speak) if you need more area.

[smj]

Originally Posted by chris95040

Replicating a rig from one boat onto another is only correct if the boats themselves had similar righting moments.

A popular and dangerously incorrect assumption is that you can copy and paste a rig from one boat to another. You seem to think it’s just a function of sail geometry. It is not. All else being equal, if one boat has a higher righting moment, it needs a beefier rig (stiffer mast, or more spreaders, etc).

I could understand this train of thought if the boat was a monohull, but would this also be applicable for a catamaran?

[Chotu]

Originally Posted by chris95040

Replicating a rig from one boat onto another is only correct if the boats themselves had similar righting moments.

A popular and dangerously incorrect assumption is that you can copy and paste a rig from one boat to another. You seem to think it’s just a function of sail geometry. It is not. All else being equal, if one boat has a higher righting moment, it needs a beefier rig (stiffer mast, or more spreaders, etc).

I’m not understanding this.

The boat doesn’t heel (more than a few degrees).

Why does any of this matter if the rig is about the same size and from a similar size boat?

The righting moment of my busy comes from the beam and to a lesser extent, the beam of each hull.

My boat doesn’t roll over in a gust an neither does the catamaran this rig came off of.

How does anything you’re saying apply when a boat doesn’t heel?

[chris95040]

Originally Posted by Chotu

I was looking forward to some posts like this.

Can you tell me how to buy a used mast then?

No one knows the ixx, iyy or weight of a used mast. Yet all the time people are buying them, selling them, putting them on and off different boats.

So how’s it done?

If you can’t trust a mast of a nearly identical size cat, how do you go about finding a used mast?

I’ve been struggling with this a long time.

And for a long time folks have been telling you: A naval architect or nerdy rigger can take a cross section geometry and tell you Ixx Iyy *in minutes*.

‘No one knows ixx iyy or weight of a used mast’ is convenient fiction. It is false, I can personally attest to it.

You are in that ‘get it done and don’t over complicate things’ mindset necessary to get out from under that project but attempting to fit a custom rig to a performance cat without doing (or hiring out) any math is a decision you will surely regret when the smoke clears. Call a naval architect. They bill by the hour. You’ll learn something.

Originally Posted by Chotu

I don’t see how if it’s stiffer, there can be a problem. I also don’t see how if it’s less stiff there can be a problem when it’s already circumnavigated on the same size catamaran.

If it’s stiffer, it’s likely heavier. Since it’s really, really long, that can be a problem. Or not!

If it’s less stiff than your designed rig but it came from the ‘Same size catamaran’, this might imply similar righting moments between the two boats. In this case your assessment that the less stiff rig is Ok might be correct, and your yacht’s designer got it wrong. Feeling lucky? [emoji849]


Long story short,

1. Get the ixx iyy of your designed rig

2. Get a used mast of similar ixx iyy

3. Use your designed sail plan and standing rig arrangement.

[Chotu]

Originally Posted by Benz

I would not modify--that's a can of worms what with getting the mast track to line up, moving the gooseneck, all that jazz. The pics show a strongly-built stick with welded parts, and one that's been proved already. Altering that can't make it better or stronger, but it will be expensive. Improve your light air performance with a screecher--put it out forrard on a bowsprit ("Longeron" in multihull speak) if you need more area.

Ok. Point taken. But if a new one is $60,000 to $70,000 and this one, including everything you see here, traveler, chain plates, furler, shrouds/stays and some old sails is $10,000... wouldn’t it make a little sense to take on the mods?

Interesting about the longeron. I was considering doing that instead of a bow beam earlier but people on boat design dot net trashed the idea of having one.

[Chotu]

Ok. Thank you for this direct post. I’ll get the geometry and calculate ixx and iyy.

I’ll also see if it is listed anywhere on my plans. Certainly it can be calculated from my plans.

Originally Posted by chris95040

And for a long time folks have been telling you: A naval architect or nerdy rigger can take a cross section geometry and tell you Ixx Iyy *in minutes*.

‘No one knows ixx iyy or weight of a used mast’ is convenient fiction. It is false, I can personally attest to it.

You are in that ‘get it done and don’t over complicate things’ mindset necessary to get out from under that project but attempting to fit a custom rig to a performance cat without doing (or hiring out) any math is a decision you will surely regret when the smoke clears. Call a naval architect. They bill by the hour. You’ll learn something.




If it’s stiffer, it’s likely heavier. Since it’s really, really long, that can be a problem. Or not!

If it’s less stiff than your designed rig but it came from the ‘Same size catamaran’, this might imply similar righting moments between the two boats. In this case your assessment that the less stiff rig is Ok might be correct, and your yacht’s designer got it wrong. Feeling lucky? [emoji849]


Long story short,

1. Get the ixx iyy of your designed rig

2. Get a used mast of similar ixx iyy

3. Use your designed sail plan and standing rig arrangement.

[chris95040]

Originally Posted by Chotu

I’m not understanding this.

The boat doesn’t heel (more than a few degrees).

Why does any of this matter if the rig is about the same size and from a similar size boat?

The righting moment of my busy comes from the beam and to a lesser extent, the beam of each hull.

My boat doesn’t roll over in a gust an neither does the catamaran this rig came off of.

How does anything you’re saying apply when a boat doesn’t heel?

Lol. If you crack a book on rig design righting moment will appear on page 1.

The ‘righting moment’ is what the mast is pushing against. Imagine a mast on a canoe. It would not have to be very stiff because the canoe will fall over before the rig breaks.

Your stiffer boat will need a stiffer mast.

You are right that a mast from a similar cat is possibly up to the task. Hire someone who has made it past the first page of a rigging textbook to help you evaluate that. [emoji3]