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Old 16-02-2016, 05:37   #16
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Re: Change to Deck Stepped Mast

I'd want to examine the condition of the mast thoroughly before deciding anything or even unstepping it.
That includes removing paint, pitting, any filler & measuring the depth & extent of pitting & any other faults. Pitting could be serious but may not be.

If mast height & section agrees with the original designs and condition is acceptable why replace it with a different used one?

Before unstepping it I'd take all possible measurements from a fixed permanent mark on the mast.

I'd mark, measure and photograph the positions of the step, partners/chocks, rigging screw settings & anything else that could be forgotten if the mast were to be off the boat for longer than expected.

Masts can be and often are sleeved/spliced by the way, never done it myself though.
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Old 16-02-2016, 06:01   #17
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Re: Change to Deck Stepped Mast

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Originally Posted by ausnp84 View Post
I'd hate for someone to take away from this thread that a keel stepped mast can't be cut down and used as deck stepped. As Uncivilized said, best to talk to a rigger.

n
Why not? It's true, unless the mast was over designed with extra safety factor, which will then be reduced by going to deck stepped.

The pinning effect of having support at the keel and at the deck limits buckling. As a result the stiffness requirement of a keel stepped mast is lower than that of a deck stepped mast, even if they reach the same height over the deck.

Yes, talk to a rigger. But even if the mast section is strong enough to function as deck stepped, they will tell you to fix your current configuration. In the absence of some other compelling reasons, redesigning to a deck stepped rig would be nuts.
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Old 16-02-2016, 06:17   #18
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Re: Change to Deck Stepped Mast

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Originally Posted by chris95040 View Post
Yes, talk to a rigger. But even if the mast section is strong enough to function as deck stepped, they will tell you to fix your current configuration. In the absence of some other compelling reasons, redesigning to a deck stepped rig would be nuts.
Hang on, that's not what I'm saying. I agree with you that if a boat has a keel stepped mast, there would have to be a really, really good reason to change that configuration to deck stepped. The work alone would far outweigh any benefits.

What I was saying is that I'd hate for someone to read this thread and take away that keel stepped masts can't be cut down and used as deck stepped (presumably on a different vessel). Sure, every mast profile and brand is different but riggers have a good understanding of this and will be able to advise.

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Old 16-02-2016, 06:18   #19
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Re: Change to Deck Stepped Mast

Adamaris...

Welcome to CF!

Without further adoooooooo... On to the subject...

Quote:
Originally Posted by Ann T. Cate View Post
It will benefit you to talk to someone to engineers masts, but I'll give it a little go. The deal is that the mast sections (its thickness) are predicated on having both the support of the mast step and from the deck penetration. You would be better off to cut off the corroded part , and shorten the rig, keeping it essentially the same. the cheapest alternative.

In essence, you risk dismasting.

Ann
Deck stepped masts are far stiffer than keel stepped masts for the above reason given by Ann... You really should get the book:
http://www.amazon.com/The-Complete-R.../dp/0070648409

It is a wealth of information...

Going to a bigger or thicker tube needed for deck stepping will TOTALLY mess up your stability figures, and also possibly create a dangerous situation going that route...

Quote:
Originally Posted by UNCIVILIZED View Post

Ann's correct, in that you can't just take a keel stepped mast & use if for a deck stepped mast on the same boat. Or at best, you might sneak by, if someone does all of the math on mast design for you, & gives it the nod.
IE; If for some odd reason you're serious about such, talk to a rigger first.

Though even then, you're looking at $5-figures to do such a conversion, or close to it, easily. So you're better off to fix what's there.

The reason why you can't do such a direct swap, is that you can use a much less stiff, & lighter weight tube, if a mast is keel stepped, than if it's deck stepped. And in general, keel stepped masts are more robust.
Just more confirmation of a simple switch being a bad idea... from Uncivilized... a VERY knowledgeable and practical poster/member/dude/cool-smart-guy...

Quote:
Originally Posted by ausnp84 View Post
I'd hate for someone to take away from this thread that a keel stepped mast can't be cut down and used as deck stepped. As Uncivilized said, best to talk to a rigger.
It CAN be done... just not safely without modifications... If you were to simply cut your stick and plop it on the deck... you would need a TON of modification... coachroof structural work and additional staying and chain plates...

Quote:
Originally Posted by Adamaris View Post
Hello and thanks for the replies...

One of the reasons I was considering changing to deck stepped is that it is highly likely that the mast has been shortened before. The mast step is almost up to the cabin floor level, the inside of the mast has quite severe pitting over the first foot and although I havent removed the external paint I suspect filler has been used to hide he effects of corrosion. There is some minor bubbling of the coating which I dont really want to scrape until the mast is off the boat.

The boat is from the mid 70's and I even wonder if the mast is original to the boat, many boats of this era had wooden masts. Ive also seen several models of this boat with deck stepped masts, which made me consider this as an alternative...

If I cant resolve this issue I may have to consider a used mast as a replacement.

Thanks again
I'm still betting that a "custom" mast step is your best solution... Even if you had a significantly tall step... if it were anchored well, it would simulate the mast extending to the original step...

Used masts are cheap... around $1k is normal... of course swapping it out will add a lot of rigging expenses...

Start with some pics of what's going on... If deemed that the best option is swapping something out... You FOR SURE will need to do a bunch of legwork and get all of the data on your current (or proper) stick... primarily stiffness Ixx, Iyy, AND weight/ft...

We'll try and help as much as we can!
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Old 16-02-2016, 06:25   #20
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Re: Change to Deck Stepped Mast

Quote:
Originally Posted by unclemack View Post
I'd want to examine the condition of the mast thoroughly before deciding anything or even unstepping it.
That includes removing paint, pitting, any filler & measuring the depth & extent of pitting & any other faults. Pitting could be serious but may not be.

If mast height & section agrees with the original designs and condition is acceptable why replace it with a different used one?

Before unstepping it I'd take all possible measurements from a fixed permanent mark on the mast.

I'd mark, measure and photograph the positions of the step, partners/chocks, rigging screw settings & anything else that could be forgotten if the mast were to be off the boat for longer than expected.

Masts can be and often are sleeved/spliced by the way, never done it myself though.
For sure find out what's going on before pulling the rig !

Quote:
Originally Posted by chris95040 View Post
Why not? It's true, unless the mast was over designed with extra safety factor, which will then be reduced by going to deck stepped.

The pinning effect of having support at the keel and at the deck limits buckling. As a result the stiffness requirement of a keel stepped mast is lower than that of a deck stepped mast, even if they reach the same height over the deck.

Yes, talk to a rigger. But even if the mast section is strong enough to function as deck stepped, they will tell you to fix your current configuration. In the absence of some other compelling reasons, redesigning to a deck stepped rig would be nuts.
I think so too....

Quote:
Originally Posted by ausnp84 View Post
Hang on, that's not what I'm saying. I agree with you that if a boat has a keel stepped mast, there would have to be a really, really good reason to change that configuration to deck stepped. The work alone would far outweigh any benefits.

What I was saying is that I'd hate for someone to read this thread and take away that keel stepped masts can't be cut down and used as deck stepped (presumably on a different vessel). Sure, every mast profile and brand is different but riggers have a good understanding of this and will be able to advise.

n
That makes more sense...
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Old 16-02-2016, 06:57   #21
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Re: Change to Deck Stepped Mast

Adamaris, so you are saying you have a very tall mast step already. ("The mast step is almost to the floor level") I'm sure you realize that is unusual and not ideal. Probably not the kind of support a keel stepped mast needs.

Could be a case for a mast repair like would be done for a broken mast if you could find a donor section from another mast. Or maybe a used mast fit for purpose that has the speaders located where needed, to minimize refit.

At any rate, I'd stick to keel stepped. And since your issues are beyond my pay grade I'll wish you luck on go on about my rat killin'.

Beat of luck with repair, hope you are sailing again soon.
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Old 16-02-2016, 08:46   #22
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Re: Change to Deck Stepped Mast

If very much of the mast needs to be removed, a raised mast step is not the answer, as it can create a "hinge". Proper repair would include sleeving a new section onto the good portion of the old mast.
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Old 16-02-2016, 09:40   #23
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Re: Change to Deck Stepped Mast

I could be wrong here, but first thing that came to my mind would be to have a collar welded on the bottom of the mast and get it the height you need it, or fabricating a base to make up for what you have to cut off.

It just seems to me an easier job than glassing in and finding that perfect block of wood to now support the mast anyway to the coach roof or the glass and bulkhead work that would be required to deck step it, since you have to pull the mast regardless of what you choose to do.

The only reason I can ever think to want to change from keel to deck is when a tabernacle is required, otherwise it would have never crossed my mind as an option.

What am I missing?
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Old 16-02-2016, 09:41   #24
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Re: Change to Deck Stepped Mast

This some kind of joke? Your coach roof is not designed for the compression loads nor the lateral forces. You will rip off the roof, if not crush it. Your stays are probably designed with the reduced lateral forces from keel stepped mast.
What you need to do is get a naval engineering analysis done to see what kind of deck reinforcements are needed along with any alterations of rigging that may be needed. Your going to spend way more on coach roof reinforcements than simply getting another mast, or welding a shoe on the old one.
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Old 16-02-2016, 10:20   #25
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Re: Change to Deck Stepped Mast

As the owner of a boat with a deck-stepped mast, I say stick with the keel step! If I could switch to keel step, I would. Mine would require major remodeling to make the switch. And your boat especially has potentially tremendous loads on the mast, roughly equal to the displacement.
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Old 16-02-2016, 10:28   #26
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Re: Change to Deck Stepped Mast

I would call Bob Perry; he is ( I think ) the designer of the Tayana 37. Not sure what he charges now but in the past his consulting rates were very reasonable. Unless his views have changed he will confirm for you that a mast section that is stiff enough for a keel stepped mast is substantially undersized for a deck stepped mast on the same vessel.
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Old 16-02-2016, 10:44   #27
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Re: Change to Deck Stepped Mast

While a properly done deck stepped would probably be ok, It's not hard to make a higher support, or extend your extrusion and cut a few inches off your mast. The added extrusion doesn't necessarily have to completely match your mast shape... it's in compression.
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Old 16-02-2016, 11:21   #28
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Re: Change to Deck Stepped Mast

Might be nice to check if mast butt was trimmed previously as a quick, jack it up in place fix....check overall length add once...


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Old 16-02-2016, 11:32   #29
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Re: Change to Deck Stepped Mast

You absolutely cannot do this without some serious input from a marine engineer. It may be that the mast would be fine, all depends on the section but the rigging calc's for deck stepped are significantly different to keel stepped. Spreaders would be in a different place and you risk throwing the who thing out of balance - ie overboard! At least get aread of the 'Riggers Handbook' before doing anything.
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Old 16-02-2016, 11:36   #30
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Re: Change to Deck Stepped Mast

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You absolutely cannot do this without some serious input from a marine engineer. It may be that the mast would be fine, all depends on the section but the rigging calc's for deck stepped are significantly different to keel stepped. Spreaders would be in a different place and you risk throwing the who thing out of balance - ie overboard! At least get aread of the 'Riggers Handbook' before doing anything.
You definetely need input from a NA. the loads on the deck change dramatically as the mast step at the deck needs a lot of lateral support. The bit above about the spreaders being in different spots and the loads being different is just incorrect!! the length of mast being supported doesn't change at all and the loads that the mast puts on the rig don't change. The big change is that the deck needs to be a lot stronger laterally to support the sideways loads of the mast pushing port and starboard, with the step at deck level being a sort of hing point.
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