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Old 17-02-2016, 17:07   #61
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Re: Change to Deck Stepped Mast

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Originally Posted by Sailorbob8599 View Post
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.

Volvo 65s have deck stepped masts, I think they be safely called offshore boats.


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Old 17-02-2016, 17:17   #62
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Re: Change to Deck Stepped Mast

Proper engineering can overcome almost any inherent design weakness. I don't say it is a "rule", just that the vast majority of boats--that have not been engineered at extreme cost for very specific purposes--don't do it that way, by choice.


And of course then you're trying to build a 27' boat, it becomes a much lesser engineering job to secure that size spare, than the tree trunk on a 45' boat. Of course if you don't roll the boat, there's not much to worry about. If you do roll the boat, pressure on the sails may snap anything anyhow. Personally...I prefer never to find out where that limit is.


A deck stepped mast has the great advantage of keeping your drier, one less big hole in the deck. That's a very good reason to consider using one.
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Old 17-02-2016, 17:31   #63
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Re: Change to Deck Stepped Mast

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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)
When the boat rolls, deck or keel stepped... it's likely coming up without a mast anyway!
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Old 17-02-2016, 19:35   #64
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Re: Change to Deck Stepped Mast

I think the racing rule was written anticipating that a "properly prepared" vessel will have the sails furled or stowed and be running under bare poles before being rolled--in which case the pin holding in the mast might just save it. Not from everything or all the time, but usually when they propose something like that, it is after hearings have determined that masts already have been lost, intact, in just those circumstances.


Certainly simple enough to plan ahead and make sure there IS a retaining pin, in the odd event that does happen. Like the retaining pins we all have in our hatchboards, right?
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Old 17-02-2016, 19:48   #65
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Re: Change to Deck Stepped Mast

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Originally Posted by Sailorbob8599 View Post
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.
When you open a post, you will see a paperclip right above the box here. Click that and a box will open up that will have some "browse" buttons. click them and then look through your computer for the photos you want. It may be better to export them in a smaller form to your desktop first. Then hit the button "upload" and wait till they are ready. I'd like to see your shots because I am in the process of rebuilding my mast support!
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Old 17-02-2016, 19:51   #66
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Re: Change to Deck Stepped Mast

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When the boat rolls, deck or keel stepped... it's likely coming up without a mast anyway!
Yeah, I thought that was odd too!
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Old 17-02-2016, 19:55   #67
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Re: Change to Deck Stepped Mast

Guys, my apoligies for the way in which I worded things. I'd have been wiser to have just bowed out.
- So, yeah, with regards to manners & decorum, I "stepped on my meat with golf shoes".
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Old 17-02-2016, 22:26   #68
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Re: Change to Deck Stepped Mast

Some thoughts on mast & mast step fixes. And to the errata to which I (poorly) alluded earlier.

- Firstly, there IS a Lot of GOOD information in the thread.
The catch being, there’s also enough which isn’t accurate, that if you don’t know which is which, it makes it tough to know what the viable courses of action for a fix are. Or, to base some of one's personal "rigging knowledge toolbox'' upon.
So I’ll try my best, to hit the glaringly obvious incongruities.

And No, DON'T take my word for things. I highly encourage folks to get out there & study how boats & their systems are designed & put together. In additon to establishing working relationships & friendships with marine industry professionals. That, as well as learning the "why" behind how rigging (& other things) are done, on their own. Ditto on testing such stuff out.
The size & cost of my sailing reference library is rediculious. But to me, it's invaluable.

Okay, Basics: It is a flat out FACT, that a deck stepped mast on a boat Must be of a stronger tube section, than one which is keel stepped.
I only state this, as for some, this info bit, seems to still be unclear.

On Fixes:
If you’re going to crop a bit off of the foot of the mast tube, it needs to be trimmed so that the base is both 100% even, as well as perpendicular to, the mast tube. Which is far, far more difficult to do with the mast partially in the boat, jacked a short distance above the step.
Especially as it’s a lot tougher, if not impossible, to get in there to use the “normal” power tools, used to shorten masts.

The reasons for needing to make the cut square include the fact(s):
- The base of the mast can see vertical compression loads in excess of twice the weight of the boat (or more) at times. So, if the base of it doesn’t have full contact with the step, the bits which are in contact have to take up the extra load.Which I can’t imagine that the spar appreciates
- If it’s base isn’t cut square, the mast is going to want to lean towards the edge/section which is cut the shortest. Be that Port or Starboard, or Forward/Aft.
Which again, puts uneven stresses on the tube. And can also create problems when tuning the rig – as in the standing rigging.


It’s possible, & in some circumstances, common to add length to a mast, using a section of tube which matches the original extrusion. Although I’m only familiar with it being done in the above deck portions of a mast.But it may at times be done at the base? On that one, I’d defer to a rigger.

However, from a loading standpoint, logic would say that you want to add a piece to the tube, which is off the same size & section as the spar. Even/especially at it’s base. Or you could risk creating a stress riser where the mismatched portions meet.
As again, the base sees a lot of load. Much more so than most other portions of the spar. So you'd want to minimize discontinuous load pathways, that, or create a higher risk of failure.


When masts are sleeved internally, usually it's to join 2 long tube sections. As it’s difficult to transport mast which exceed a certain length.
When this is done, the internal joining sleeve is tapered at both ends. Both in shape & in thickness at the perimeter of it's edges. Also, the 2 mast tube pieces to be joined, are often cut in a pattern much resembiling a bevel, as opposed to just butt joining them.
Both of these practices are done for the same reasons which one bevels the scarfs when structurally joining 2 pieces of wood. - So as to prevent creating any hardspots at their juncture.

The one other time when masts are commonly sleeved internally, is in order to allow for the use of a tube section which is both lighter in weight/section, as well as lower windage, than a bigger tube would be. - So, mostly it’s a racing boat thing.

This kind of internal reinforcement sleeving, most often runs from the mast’s butt, up to about the 1st spreader, on a triple spreader rig (for example). As the lower section of a spar is the section of the mast which takes the most load on any boat. And on boats with spinnaker poles/pole tracks, the load down low imposed by said poles, adds even more pressure to the mast tube.

When masts are sleeved; be it to join 2 longer sections of a spar together, or to stiffen up the lower panel section of a spar. Sometimes the internal sleeve connecting them is plug welded in place, & sometimes it’s riveted/bolted AND glued there.
In my experience, usually on the lower sections of a spar, things are fastened together mechanically. And higher up, such as at the mid-point of a spar, where the 2 pieces are joined, either method is used. But most often, they're welded.
There being a number of reasons why one may be chosen over the other, especially in this (latter) application.


Regarding the welding of aluminum. Yes, with most alloys, it does significantly weaken things. In some instances this is critical, & others, not so much.
However, there's a "fix". It being, that in highly loaded areas on spars, doubler plates are commonly added in many areas where things are welded. Such as where tang bolts pass through the mast, where spreaders are mounted, or where vangs are attached, etc.
The; when, what size, what shape, thickness, & how, of them, is dictated by the alloys being used, as well as by the numbers which the NA/spar designer comes up with for the loads in those areas.

For example, if you look at the middle/rhs of the page here http://www.cal40.com/files/TEMP001.pdf you can see the “Doubler”, which both strengthens the mast tube, & also serves as the mounting point for both; the spreaders, & lower shroud tangs/tang bolt, on a Cal 40.

Note, that underneath of this doubler plate, there will be a compression tube inserted (& welded) transversely into the mast, for the tang bolt. It’s purpose being, to stabilize & strengthen the mast against the point loadings added by the; tang bolt, shrouds, & spreaders. And also to prevent the loads on the bolt, & to some degree by the spreaders, from dimpling/crushing the mast tube wall. Thus inducing a beer can failure.
So, then in some instances, such added tubes may also act as spreader bars.

In order to regain the strength lost to welding in aluminum, to my knowledge, there are 2 fixes:
~ Re-heat treat the part. Which on if you weld something onto a mast…
~ Time; as in, over the span of many years, the strength slowly returns to the metal on it’s own.



When it comes to Mast Steps for keel (or deck) stepped masts, there’s no one material or design which need be used.
- Some (most) steps hold the mast base in position by virtue of being a male/female type socket.
- Others pin it in place, in the fashion of a cross bolt.
- And yet others have the built in facility for adjusting the position of the mast butt in the fore & aft direction, for purposes of rig tuning. Be the tuning adjustment for 20 minutes, or years.



For the construction of Deck Chocks there are also a variety of design types, & of materials used for them: Wood, plastic, rubber, foam.And even adjustable setups.Which use either rigging screws (turnbuckles), block & tackle arrangements, or on big boats, hydraulic rams.

The purpose of adjustable Deck Chocks is, again, to allow for tuning of the mast, based on wind & wave conditions, sail combinations. Or even to tune the mast optimally for say, one specific mainsail.
That, or; an hour, one short race, a full day, or significantly longer.
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Old 17-02-2016, 22:52   #69
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Re: Change to Deck Stepped Mast

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Hello, new to the site but have bee a lurker for a while....

I have an old Tayana 37 in need of some serious work, the boat is out of the water and I'm going to start work on the deck in a few weeks. One of the projects I want to undertake is changing from a keel stepped mast to deck stepped. I have some corrosion at the base of the mast and don't want to go to the expense of a new mast...

Has anyone undertaken this project and what are the pro's and cons.

Thanks
Bad idea. Apart from the engineering issues you now have to address it will reduce the value.

Trim the corroded bit and raise the step. Effect a good spartite collar at the deck and do it right.

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Old 18-02-2016, 04:07   #70
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Re: Change to Deck Stepped Mast

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Originally Posted by unclemack View Post
+1

Glad to have company on the naughty step, innit?
I think we come by it naturally...

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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.
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Originally Posted by Terra Nova View Post
Instead of 2-3 hours, how about 1 short paragraph simply listing a few specifics?
Aww Come on now TN... Have you EVER seen a "short paragraph" from Uncivilized ???

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Originally Posted by Jman View Post
Volvo 65s have deck stepped masts, I think they be safely called offshore boats.
I think you may be right...

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Originally Posted by UNCIVILIZED View Post
Guys, my apoligies for the way in which I worded things. I'd have been wiser to have just bowed out.
- So, yeah, with regards to manners & decorum, I "stepped on my meat with golf shoes".

As long as we can rib ya and all have some fun... Well... It would be nice to also:

A. Make sure somebody doesn't do something dangerous
B. Help a fellow sailor with a problem
C. Learn and refine through collaborative thought...

Thanks for the efforts!
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Old 18-02-2016, 04:12   #71
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Re: Change to Deck Stepped Mast

All,

Thanks very much to all of you for your comments, I appreciate that everyone is giving their opinon for free and like many subjects there is no black and white answer. As I have seen several T37's with deck stepped masts I thought this would be the easiest/ cheapest way around my problem, I have no probem with the fibre glass work or making a compression post but didnt understand the issues with mast strength and lateral loading..

From the consensus it seems that repairing the base of my mast will be the best option. Ive made a few enquiries locally, to riggers and and a local fab shop which specialises in aluminum to see if the base of the mast can be replicated to form a sleeve style repair, all have reserved judgement until they see the mast off the boat. Once I have the profile measurements I'll get more idea of whats feasible.

Anyway thanks for your help again
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Old 18-02-2016, 06:15   #72
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Re: Change to Deck Stepped Mast

Great reply Uncivilized!😃😃😃 only tiny comment. Marine grade aluminum welds do not get stronger over time. The trick is not to weld in highly stressed areas. That does not mean you can't weld. For none experience person it is difficult to identify.


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Old 18-02-2016, 06:18   #73
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Re: Change to Deck Stepped Mast

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All,

Thanks very much to all of you for your comments, I appreciate that everyone is giving their opinon for free and like many subjects there is no black and white answer. As I have seen several T37's with deck stepped masts I thought this would be the easiest/ cheapest way around my problem, I have no probem with the fibre glass work or making a compression post but didnt understand the issues with mast strength and lateral loading..

From the consensus it seems that repairing the base of my mast will be the best option. Ive made a few enquiries locally, to riggers and and a local fab shop which specialises in aluminum to see if the base of the mast can be replicated to form a sleeve style repair, all have reserved judgement until they see the mast off the boat. Once I have the profile measurements I'll get more idea of whats feasible.

Anyway thanks for your help again

Talk to Bob Perry ( he posts alot on Facebook) He'll give you the correct info! there should be no problem converting, just its alot of work to fix your issue compared to cutting an inch or two off the bottom and adding the sam amount to the mast step!
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Old 18-02-2016, 12:46   #74
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Re: Change to Deck Stepped Mast

The Euler formula for buckling is Critical Buckling Load = C*Pi*Elasticity*Moment of Inertia/L squared. Where C is a factor based upon the end fixture, and L is the length of the column. All else being equal the L is the biggest factor since it is squared.


Provided that the compression post is reasonably substantial and the deck structure it is fixed to gives it a reasonable amount of lateral support, if the keel stepped mast is shortened to deck stepped it should then attain a considerably higher critical buckling resistance.


I suspect that the real reason that masts are keel stepped is that they are cheaper to install and overall can be lighter. However I have noticed that the boats requiring urgent rescue in the Southern Ocean after roll overs generally had keel stepped masts and that the reason they then started to take on water was the large hole ripped in the deck when the mast buckled?
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Old 18-02-2016, 13:18   #75
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Re: Change to Deck Stepped Mast

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The Euler formula for buckling is Critical Buckling Load = C*Pi*Elasticity*Moment of Inertia/L squared. Where C is a factor based upon the end fixture, and L is the length of the column. All else being equal the L is the biggest factor since it is squared.


Provided that the compression post is reasonably substantial and the deck structure it is fixed to gives it a reasonable amount of lateral support, if the keel stepped mast is shortened to deck stepped it should then attain a considerably higher critical buckling resistance.


I suspect that the real reason that masts are keel stepped is that they are cheaper to install and overall can be lighter. However I have noticed that the boats requiring urgent rescue in the Southern Ocean after roll overs generally had keel stepped masts and that the reason they then started to take on water was the large hole ripped in the deck when the mast buckled?
Yep, Euler's. and the "Slenderness Ratio." Which is why I had questions early on in this thread. The longer the column in compression the more at risk it is. If the stays hold the spar in perfect straight column, then it can withstand the compressive forces, but one bad bend at the wrong moment and... failure.
Ever notice your mast pumping while sailing? Ever look up to see the forward bend in the mast?
"Buckling is characterized by a sudden sideways failure of a structural member subjected to high compressivestress, where the compressive stress at the point of failure is less than the ultimate compressive stress that the material is capable of withstanding. "
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