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Old 16-02-2016, 18:17   #46
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Re: Change to Deck Stepped Mast

the problem you describe does not warrant deck stepping the mast for all the reasons given so far.If you could find a same section piece you could "sleeve" whatever length you feel is compromised. /that means cutting off the offending part, adding a piece of the same material inside the original mast and the new piece and riveting the pieces so there is no movement. By cutting off just enough to get the sleeve inside you get a good tight repair. But shimming the step a few inches sounds like the way to go.
I did install a deck stepped mast on my boat but for reasons different than the ones you cite. My boat came with a replacement mast that designed to be deck stepped with spreader fittings at heights that would only work if it were deck stepped. It was a lot of work to design and build the compression post and its step, add chainplates because the mast was a double spreader whereas the original (gone when I bought the boat) was single spreader. Good luck with your repair.
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Old 17-02-2016, 06:13   #47
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Re: Change to Deck Stepped Mast

This is the sort of discussion that worries me about this forum.
Most of what has been said demonstrates a lack of basic engineering knowledge.
If a keel stepped mast is correctly chocked at deck level, then whatever lateral load is taken as shear in the mast is transmittted into the deck. At a first pass estimate this will be similar to the lateral load transmitted from a deck stepped mast into the deck.
If a keel stepped mast is not correctly chocked then the unsupported length may be longer than a deck stepped mast and a stronger section may be required.
A judgement gets even harder if you take into account the lateral stiffness of the deck, or any give in the chocking. There may then be a situation where the keel stepped mast is not adequately support at a point where it was designed to be supported.

As for a repair it has been correctly pointed out that a mast step of any height will create a support for the mast that doesn't provide lateral support and hence defeat the purpose of keel stepped.

A sleeve would be easier to design and install, but be wary of rivets.
The compression load in the mast doesn't decrease below the deck (although the bending moment does)
To get an estimate of the load in a mast, add up the strength of all the stays, factor by their angle and take say 25%, then the strength of the halyards, again adjust for angle and factor by 10%. The sum will give you an idea of the load that will need to be taken by your rivet group. Now design your rivet group.
For a welded repair, try and design it so the weld is in compression not shear, then it's strength is irrelevant, if it yields it won't go anywhere, and will probably work harden. If the repair is a sleeve and hence the weld is in shear, then design your welded edge as a exaggerated saw tooth and get 2 or even 3 times the weld length.

My final two peneth, is that keel stepped masts are most likely used because they are cheaper and easier than deck step masts. That extra six feet of extrusion is cheap.
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Old 17-02-2016, 07:06   #48
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Re: Change to Deck Stepped Mast

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Originally Posted by Bluebeard View Post
This is the sort of discussion that worries me about this forum. Most of what has been said demonstrates a lack of basic engineering knowledge.

To get an estimate of the load in a mast, add up the strength of all the stays, factor by their angle and take say 25%, then the strength of the halyards, again adjust for angle and factor by 10%. The sum will give you an idea of the load that will need to be taken by your rivet group. Now design your rivet group..
Uhm.... OK...
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Old 17-02-2016, 08:58   #49
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Re: Change to Deck Stepped Mast

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Uhm.... OK...
+1

Glad to have company on the naughty step, innit?
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Old 17-02-2016, 10:09   #50
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Re: Change to Deck Stepped Mast

To the OP, there is so much information in this thread which is just Flat Out WRONG, that it would take me 2-3hrs to point them all out.
I hate to sound like I'm on a high horse here, but such is simply fact. And there is Zero point in giving new members, or those who don't know rigs & rigging, wrong & or misinformation.

OP, do yourself a favor, & have a couple of riggers take a look at things, & give you estimates. After, at a minimum, reading Brion Toss's book, The Rigger's Apprentice.
Then, between the 3+ sources of info, you'll know what to ask, & what the best course of action to take is.

To most of the other posters in this thread, I'd Highly recommend reading this book as well, & or waiting for the new edition in April.
Via reading all of 2 chapters of it, it'll dispell most of the fallacies in this thread. In addition to adding a lot of knowledge, & "tools" to your skill set.

PS: You can also find Skene's Elements of Yacht Design online, as well as downloadable in PDF, online, for free. And it's far from the only relavent tome.
Ditto on looking up references for Mast Scantlings, etc. http://www.bing.com/search?q=formula...B7877809B3D2FF
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Old 17-02-2016, 10:20   #51
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Re: Change to Deck Stepped Mast

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Originally Posted by UNCIVILIZED View Post
...there is so much information in this thread which is just Flat Out WRONG, that it would take me 2-3hrs to point them all out...
Instead of 2-3 hours, how about 1 short paragraph simply listing a few specifics?
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Old 17-02-2016, 10:57   #52
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Re: Change to Deck Stepped Mast

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Originally Posted by Don C L View Post
I can't think of a boat over 32', besides the Pearson Vanguard that has a deck stepped mast...

Our Luders 36 has two deck stepped masts 😀

Many new production boats up to and over 40 feet have decked stepped mast.

All of which is beside the point, changing to deck stepped is a bad idea for all reasons noted above. And to the OP, it would be far more expensive than repairing or replacing the existing mast.


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Old 17-02-2016, 11:14   #53
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Re: Change to Deck Stepped Mast

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Instead of 2-3 hours, how about 1 short paragraph simply listing a few specifics?
I'd certainly be more inclined to accept that uncivilised's comments were well-meaning - rather than being motivated by something less worthy of our appreciation - if he were to specify which posts are WRONG and why.

My suspicion is that self-aggrandisement and self-promotion may prompt some of the unpleasantly dismissive posts by some industry professionals here.

I'll happily apologise if I'm mistaken.
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Old 17-02-2016, 11:17   #54
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Re: Change to Deck Stepped Mast

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Originally Posted by unclemack View Post
I'd certainly be more inclined to accept that uncivilised's comments were well-meaning - rather than being motivated by something less worthy of our appreciation - if he were to specify which posts are WRONG and why.

My suspicion is that self-aggrandisement and self-promotion may prompt some of the unpleasantly dismissive posts by some industry professionals here.

I'll happily apologise if I'm mistaken.
I would appreciate it if you would go stalk someone else.
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Old 17-02-2016, 11:36   #55
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Re: Change to Deck Stepped Mast

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I would appreciate it if you would go stalk someone else.
My post, although quoting yours, was addressed clearly to uncivilised's previous comments.

Somewhat surprised by your groundless accusation and would appreciate an explanation.
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Old 17-02-2016, 11:52   #56
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Re: Change to Deck Stepped Mast

fourwinds-
"frankly I didn't realize G10 was in the "plastics" family. Instead thinking it was more kin to fiberglass," Which is why what us Colonials call "fiberglass" is more commonly known as "FRP", short for "finer reinforced plastic" since the fibers aren't always glass, and the resin is always "plastic". Ultra-high density polythene and similar materials are also used, they have sufficient compressive strength and are easier to obtain and work with. Looks like a block of white "cutting board" plastic under the mast, that any cad/cam machine can cut to shape.


Adamaris-
As others have said, you're looking at a world of pain and expense for no good reason. It is normal and common to just slice off a couple of inches at the base of the mast (VERY carefully and neatly) and then just have a new taller mast step installed under it. A steel or aluminum weldment, or a plastic one, depending on loads and what is accessible.
Look on the web for Wally Bryant's web site about his C&C 38 "Stella Blue". This is one of the many projects he did in order to bring his boat back up to new condition, and when you read about how meticulously his projects were done, you'll see this IS the right way to go. Fastest, simplest, cheapest, strongest....unquestionably the way to go.
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Old 17-02-2016, 13:48   #57
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Re: Change to Deck Stepped Mast

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fourwinds-
"frankly I didn't realize G10 was in the "plastics" family. Instead thinking it was more kin to fiberglass," Which is why what us Colonials call "fiberglass" is more commonly known as "FRP", short for "finer reinforced plastic" since the fibers aren't always glass, and the resin is always "plastic". Ultra-high density polythene and similar materials are also used, they have sufficient compressive strength and are easier to obtain and work with. Looks like a block of white "cutting board" plastic under the mast, that any cad/cam machine can cut to shape.


Adamaris-
As others have said, you're looking at a world of pain and expense for no good reason. It is normal and common to just slice off a couple of inches at the base of the mast (VERY carefully and neatly) and then just have a new taller mast step installed under it. A steel or aluminum weldment, or a plastic one, depending on loads and what is accessible.
Look on the web for Wally Bryant's web site about his C&C 38 "Stella Blue". This is one of the many projects he did in order to bring his boat back up to new condition, and when you read about how meticulously his projects were done, you'll see this IS the right way to go. Fastest, simplest, cheapest, strongest....unquestionably the way to go.
This would appear the way to go. Although the OP has stated the keel step has already been raised to I believe what he said was the floor-boards, there would be no reason why the step could not be raised a few more inches. I would be looking to adding some gussets if possible below the floor board to increase lateral support. Good luck.
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Old 17-02-2016, 14:22   #58
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Re: Change to Deck Stepped Mast

Well, look at it this way. If he goes to a deck-stepped mast, that's going to need a compression post or frame under the mast, going down to the keel anyway.


There's NO way that will be less of an engineering project than a taller "step" or "sleeve" under the existing mast.


And some of the current offshore racing rules are talking about physically pinning the mast into the mast shoe, so that it cannot be lost if the boat rolls. A deck-stepped mast has generally been called "inshore use only" because it can be lost so much more easily in a rollover. All those designers who specify expensive keel-stepped masts, may not be totally mad. May not.(G)
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Old 17-02-2016, 14:27   #59
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Re: Change to Deck Stepped Mast

Quote:
Originally Posted by UNCIVILIZED View Post
To the OP, there is so much information in this thread which is just Flat Out WRONG, that it would take me 2-3hrs to point them all out.
I hate to sound like I'm on a high horse here, but such is simply fact. And there is Zero point in giving new members, or those who don't know rigs & rigging, wrong & or misinformation.

OP, do yourself a favor, & have a couple of riggers take a look at things, & give you estimates. After, at a minimum, reading Brion Toss's book, The Rigger's Apprentice.
Then, between the 3+ sources of info, you'll know what to ask, & what the best course of action to take is.

To most of the other posters in this thread, I'd Highly recommend reading this book as well, & or waiting for the new edition in April.
Via reading all of 2 chapters of it, it'll dispell most of the fallacies in this thread. In addition to adding a lot of knowledge, & "tools" to your skill set.

PS: You can also find Skene's Elements of Yacht Design online, as well as downloadable in PDF, online, for free. And it's far from the only relavent tome.
Ditto on looking up references for Mast Scantlings, etc. http://www.bing.com/search?q=formula...B7877809B3D2FF

Why not a objective statement. What you said totally undermines this forum, are we to believe no one but you?


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Old 17-02-2016, 15:25   #60
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Re: Change to Deck Stepped Mast

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Originally Posted by hellosailor View Post
And some of the current offshore racing rules are talking about physically pinning the mast into the mast shoe, so that it cannot be lost if the boat rolls. A deck-stepped mast has generally been called "inshore use only" because it can be lost so much more easily in a rollover. All those designers who specify expensive keel-stepped masts, may not be totally mad. May not.(G)
I find that to be a very interesting comment about a "deck stepped" spar only good for inshore use" ... How many ocean crossings and circumnavigations have been done in small boats with deck stepped masts?
A positive answer to that question of course, doesn't necessarily make it a safe thing to do, but the fact remains a properly rigged, deck-stepped spar, can survive a rollover, particularly if it is securely attached to the coach house roof in a Tabernacle that is securely bolted down.
I would love to post a picture of my spar and tabernacle, but I have yet to succeed in learning how to post pics on this website.
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