Could use a little advice. Aluminum or Fiberglass for this?

[Jopinot]

In that situation I’d look for a heavy Aluminium Extrusion. (Not sure if the suppliers will cut to length for you). Maybe an aluminium trailer manufacturer might have offcuts. Look for a large C Section weld it back to back. Fold some playe if you can’t get the extrusion. I’m not a fan of bolted structural aluminium (holes and fasteners invariably give issues and good welding looks cleaner) if you can get flanges Waterjet cut from (grade 5083 or 6061) plate it will look as good as it’s ever gonna be.
Good luck!

[allene222]

I clearly don't have the expertise to design your mast extension but I will share the things I would worry about. As a designer, the goal is to worry about what might go wrong and design a structure that deals with those issues. First as I think others have said, you need a compression post to take the load from the bottom of your mast to the bottom of the boat. That needs to be a single piece and not multiple sections or else the design gets way too complicated. Next, you are going to have a huge side load at the top of that post. You will also have huge forward load. Your mast needs to be bent to have stability unless you have forward and aft lowers. Otherwise the mast is not stable fore and aft. All those side and forward loads on the top of your compression post means it isn't a compression post. I would consider adding shrouds at the top of your new post to take that load to the hulls. Those would be a huge pain as they would be in the way. On the other hand, you could add a mast extension out of a much smaller section than your existing mast and add another set of shrouds at the top of the new section and have something that is similar to what has been done for hundreds of years. That way you won't have to find out why people did it that way instead of the way you are considering.

[Chotu]

This is getting a little difficult. The posts are starting to put me into a design spiral or whatever here.

Now I’m getting very confused.

Then again, I’m not sure if the posts are even talking about my boat. They seem to be talking about other boats. Maybe that’s what’s getting confusing.

Talking about compression posts going all the way to the bottom of the boat? The bottom of the boat doesn’t exist at the mast step area. It’s just clear open air, then water underneath the mast step beam/bulkhead. Posts like that make my head hurt..

Allene: i’m trying to follow your logic. I sort of follow. But I have a traditional double diamond spreader rig like you find on most catamarans. A forestay and two swept back shrouds. That’s it. But with a double diamond spreader and a set of lowers.

Are you picturing just some random mast like a pole sticking up into the air? Doesn’t seem like you’re picturing my boat.

[JMaav]

Originally Posted by Chotu

…Instead, I’m just going to extend the boat.

Just one question?

W. H. Y. ????

Why would you mess with the engineered design of your boat? You are talking about affecting your center of gravity, your moments of inertia, your ability to maintain a true course, your ability to weather a storm, changes to all of your stays, changes to the transfer of weight into your hull from sail power…

Hate to say this, but I read your comment and all I can think of is “what an idiot”…

[Chotu]

My rig looks something like this. I think the lower shrouds are lower though. They’re not as high as this. And it has a portion that sticks up above this also.

[rslifkin]

Originally Posted by JMaav

Just one question?

W. H. Y. ????

Why would you mess with the engineered design of your boat? You are talking about affecting your center of gravity, your moments of inertia, your ability to maintain a true course, your ability to weather a storm, changes to all of your stays, changes to the transfer of weight into your hull from sail power…

Hate to say this, but I read your comment and all I can think of is “what an idiot”…

You clearly haven't read the thread. This isn't about changing the mast height from design or anything. It's about raising the mast step to get the designed height from a slightly too-short mast that Chotu was able to obtain (and raising the mast step also avoids needing to move the boom gooseneck higher on the mast).

[Chotu]

Originally Posted by JMaav

Just one question?

W. H. Y. ????

Why would you mess with the engineered design of your boat? You are talking about affecting your center of gravity, your moments of inertia, your ability to maintain a true course, your ability to weather a storm, changes to all of your stays, changes to the transfer of weight into your hull from sail power…

Hate to say this, but I read your comment and all I can think of is “what an idiot”…

Are you really too mentally deficient to read the thread before you make a post? Really? Then you also call somebody an idiot when you yourself don’t even know what you are talking about?

This post should be taken off by the moderators actually.

Just to educate your dumb ass, since you are too stupid to read the thread, everything you are talking about is wrong. Literally everything in your post is completely wrong.

I AM Putting up the mast in my design. How dense are you,???

[Chotu]

Originally Posted by rslifkin

You clearly haven't read the thread. This isn't about changing the mast height from design or anything. It's about raising the mast step to get the designed height from a slightly too-short mast that Chotu was able to obtain (and raising the mast step also avoids needing to move the boom gooseneck higher on the mast).

Thank you. Calmer heads prevail. I still don’t appreciate the guy calling me an idiot. That should be taken right out of here by the moderators. Hopefully they can also delete my post above where I am responding to him. I don’t mind that going also.

I sure hope you do get to come down this winter when we do the sailing. It might be a good excuse to warm up. I know it’s not too toasty in Rochester in say February or something.

[Renoirpierre]

Hi Chotu

I wish I could provide some detailed engineering guidance but I don’t have all the details and am more qualified than some but not qualified enough.

The bottom line for me (and I have read all the posts) is that in addition to the vertical compression loads there will be some significant lateral/shear loads that need to be managed.

You will need to understand (if you don’t already) the magnitude and direction of those loads and design a connection that effectively manages and transfers those loads to the boat.

If you don’t want to use standing rigging/guys (I wouldn’t) then you will need to design a moment connection to handle the loads. I would suspect that the loads and associated design will push you towards a certain material.

[allene222]

Originally Posted by Chotu

This is getting a little difficult. The posts are starting to put me into a design spiral or whatever here.

Now I’m getting very confused.

Then again, I’m not sure if the posts are even talking about my boat. They seem to be talking about other boats. Maybe that’s what’s getting confusing.

Talking about compression posts going all the way to the bottom of the boat? The bottom of the boat doesn’t exist at the mast step area. It’s just clear open air, then water underneath the mast step beam/bulkhead. Posts like that make my head hurt..

Allene: i’m trying to follow your logic. I sort of follow. But I have a traditional double diamond spreader rig like you find on most catamarans. A forestay and two swept back shrouds. That’s it. But with a double diamond spreader and a set of lowers.

Are you picturing just some random mast like a pole sticking up into the air? Doesn’t seem like you’re picturing my boat.

My thought is that whatever your mast sits on is designed to take the significant lateral loads to the hull. It is also designed to take the compression load and transfer that to your hulls. If you build a pyramid then the top of that pyramid needs to serve that function. A compression post is something that is used on monohulls that do not have keel stepped masts and I was just borrowing the terminology. But I think your bigger issue is going to be the lateral loads. If you run some stays from the top of your pyramid and engineer it correctly that might work. If you just depend on your structure then your mast step now has a huge twisting load it was not designed for which could very well break it.

My thought was to add kind of the equivalent of a top mast that old square riggers had. The point being that the loads are less on top so extending the top might be the way to go. You would need another set of standing rigging to support it if you did it this way. Perhaps a mast builder could extend it and modify one of their extrusions to mate up with your existing mast. If you mast is not tapered, that might not be that hard as you would have excess strength and material which could be tapered to the new section.

Maybe your platform idea is better. The main point I am making is you likely need to prevent it from exerting a torque on the mast step.

One final point. Your rigging is sized for the angles you have and if you decrease those angles by adding a riser at the bottom you might would be increasing forces in several places. I assume you have calculated that and I can't. I did get some exposure to these issues when my new mast was made after I was dismasted a few years ago.

[rslifkin]

Thinking about it, would it be possible to get someone to splice a non-matching extension onto the bottom of the mast? I'd think it should be possible to splice it to a different extrusion with a little creativity. And then the mast and extension would be 1 piece, keeping the lateral loads at the mast step on the crossbeam (so it might be easier structurally). Because the splice is below the boom, matching stiffness shouldn't matter much, as long as the piece being added is at least as strong.

[Chotu]

Originally Posted by allene222

My thought is that whatever your mast sits on is designed to take the significant lateral loads to the hull. It is also designed to take the compression load and transfer that to your hulls. If you build a pyramid then the top of that pyramid needs to serve that function. A compression post is something that is used on monohulls that do not have keel stepped masts and I was just borrowing the terminology. But I think your bigger issue is going to be the lateral loads. If you run some stays from the top of your pyramid and engineer it correctly that might work. If you just depend on your structure then your mast step now has a huge twisting load it was not designed for which could very well break it.

My thought was to add kind of the equivalent of a top mast that old square riggers had. The point being that the loads are less on top so extending the top might be the way to go. You would need another set of standing rigging to support it if you did it this way. Perhaps a mast builder could extend it and modify one of their extrusions to mate up with your existing mast. If you mast is not tapered, that might not be that hard as you would have excess strength and material which could be tapered to the new section.

Maybe your platform idea is better. The main point I am making is you likely need to prevent it from exerting a torque on the mast step.

One final point. Your rigging is sized for the angles you have and if you decrease those angles by adding a riser at the bottom you might would be increasing forces in several places. I assume you have calculated that and I can't. I did get some exposure to these issues when my new mast was made after I was dismasted a few years ago.

Yes. Definitely. This post makes a lot of sense. Thank you. I am following it all.

One thing I know is there is not a mask section available to extend this. I have to extend it using something or other to move the mast step point up. Like you are mentioning in the post.

The pyramid is designed as a pyramid so that I wouldn’t need to use stays. Nothing is going to turn the pyramid over. No amount of sideloading. Well, of course if all of the compression load came against it maybe it would. But it does not. It’s almost all in compression with hundreds of pounds in side loading.

But then I was looking at doing the compression post. Because it sounds quick and easy. As the side loading goes up, who knows if the gussets would be enough to hold the thing in place and not break? That is troubling me today. And really stressing me out actually.

The pyramid is the only stable structure. The other ones rely on cantilever for side loading. Which is very tricky stuff.

At least I have already calculated the angles of the shrouds and forestay. They are well within all parameters. Well within the limits known to rigging a boat. There is actually very little change to them. Just a few degrees. They are still within spec.

There are maximum and minimum angles to watch out for. I have done all that math last spring. Before ever looking at this idea.

The issue here is I really don’t know what the side loading is. That’s a big problem. I don’t know how much it’s going to be. That makes it difficult to do the compression post. Unless I put a set of wires down in all directions from it really. It needs them fore and aft and athwart ships.

That’s definitely a Knogo. Because it will ruin the deck. I won’t have a place to do anything. Or run my lines. That would be a mess.

So maybe it’s actually back to the pyramid. It’s the only structure that geometrically stable it will keep the mast step located in one position and not allow it to move at all.

[Chotu]

Originally Posted by rslifkin

Thinking about it, would it be possible to get someone to splice a non-matching extension onto the bottom of the mast? I'd think it should be possible to splice it to a different extrusion with a little creativity. And then the mast and extension would be 1 piece, keeping the lateral loads at the mast step on the crossbeam (so it might be easier structurally). Because the splice is below the boom, matching stiffness shouldn't matter much, as long as the piece being added is at least as strong.

I mean, yes. That could work. Only issue is I’m about six months out now and still don’t have a couple of brackets done for putting my crossbeam on. That’s how bad these people are.

I have gone through a dozen welders. Or a machinists or fabricators or whatever.

Just last week the one that seemed most promising and kept me waiting for six months, but at least they were working on it, decided to kick it to somebody else. And this other shop isn’t working on it at all.

But that was my original design.

An aluminum “x” of internal bulkheads viewed from the top. Then whatever Mast section surrounding it.

The place that just made me wait six months to not get my brackets done had a different idea. They were going to make 58” long strips of aluminum on a big brake. Four strips. And then bend those to match the curve of my mast. Then weld them together. But they couldn’t get the people with the brake to do the work.

I’m so stuck here. I’m basically lost at this point. I’m having one of my meltdowns here. Overly stressed and can’t figure it out. And I need to have it ready this week to start for whatever I’m doing.

I just want to get this thing rigged. And I’ve been waiting so so so long for the stupidest little things. I’m afraid to outsource anything. Because if it takes more than six months to make a couple of little brackets, how long would it take them to do this? And when I say them, I mean anybody.

It’s a good idea. I like it. I just don’t think I can get it done.

[Chotu]

Oh yeah. Also, I am working with those riggers that bought the rigging company on the forum here. But they don’t want to touch the mast extension. It’s not something they know how to do.

I just can’t seem to find anybody. That’s my main problem. I don’t have anybody to do any of this stuff. No matter how many people I try, nobody actually works or does the work. They just take the work and hold it.

[Chotu]

Originally Posted by rslifkin

Thinking about it, would it be possible to get someone to splice a non-matching extension onto the bottom of the mast? I'd think it should be possible to splice it to a different extrusion with a little creativity. And then the mast and extension would be 1 piece, keeping the lateral loads at the mast step on the crossbeam (so it might be easier structurally). Because the splice is below the boom, matching stiffness shouldn't matter much, as long as the piece being added is at least as strong.

Actually, thinking about this for a moment, isn’t this the same thing as doing the other methods? Although much faster if I could actually get it done?

As in, the stiffer section at the bottom you were talking about would not been the same as the top one and creating a stress spot where they join.

Then I will be back to worrying about the side loads again right?