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Discussion Starter · #1 ·
Probably hard to imagine without pics but I noticed the starboard spreader/lower shroud tang on the mast had pulled away at the top due to two rivets having popped. A large bolt in the center of the tang as well as two lower rivets still appears solid but the top of the tang has pulled away from the mast about 1/8".

How critical is this and would you continue to sail the boat until it gets fixed? I do plan to get the repair done ASAP but might take a couple weeks to get done.

I have no experience with marine rivets. Are there special rivets for alum mast and/or any other secrets I need to know to do the repair? It looks like a pretty straight forward fix - drill out old rivet heads, clamp tang to mast and rivet. If I have to, upper shroud could be loosened to let spreader to flex for proper tang fit to mast. Does this sound about right?

Thanks...
 

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If the remaining 2 rivets in that tang give out on a windy day you might lose your rig. How critical is that? Keel stepped mast I believe, or maybe not.
Addressing it ASAP seems the right priority.
You might replace all the rivets and even the tang itself if it is at all bent or stressed. For that matter you could inspect and update all your tangs as they are probably as old as the ones that failed.
 

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Take a look at McMaster Carr's high strength stainless rivets. You can use Lanocote to prevent corrosion. The real question is how did the old ones rip out. Are the holes in the mast distorted?
 

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Yes, fix it before it gets worse or someone gets hurt. It doesn't sound like it should be a very difficult or time consuming repair. Two weeks?
 

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I would think you need a hydraulic riveter to drive those rivets so this is not a DIY job. The holes on the mast need to be inspected and the tang evaluated to do it right. This is a job for an experienced rigger.

Do you know how this happened? When?

Tod
 

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I would think you need a hydraulic riveter to drive those rivets so this is not a DIY job. The holes on the mast need to be inspected and the tang evaluated to do it right. This is a job for an experienced rigger.

Do you know how this happened? When?

Tod
+1 I agree. Do not sail the boat, and get this fixed right, asap. You lose a spreader, you lose the rig.

Also, let me take a second to debunk any theory that there's any difference between a deck stepped mast or a keel stepped mast when it comes to support. A keel stepped rig is no stronger. The rig doesn't get support from going through the deck (at least not substantial enough support to make any difference during a shroud failure). If a shroud or D1 V1 lets go on the weather side, the stick breaks. Period. I've seen it happen, aluminum masts are not very strong, if the shrouds and spreaders don't support it, the stick folds over pretty darn easy in my experience.
 

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keel stepped is just easier when replacing rig items individually...usually there is enough support to keep the mast up with only a backstay and forestay...

I did so recently

how the mast loads are spread on or off the keel and onto the deck is another subject all together

peace
 

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This is a small boat right? I'd drop the mast (especially if it has a tabernacle) and use the time while it is down to inspect everything closely and fix it. It isn't just age of the rivets that made them go, something else must be going on in the neighborhood of the tang.

You don't need a hydraulic riveter to drive small (3/16" or 1/4") stainless rivets. You do need a mechanical one with a lot of leverage (a small hand one won't work). I use this low cost one:
Amazon.com: Astro Pneumatic 1426 1/4-Inch Heavy-Duty Hand Riveter: Home [email protected]@[email protected]@http://ecx.images-amazon.com/images/I/[email protected]@[email protected]@3137XUWS76L

It is pretty low quality and probably wouldn't last long under regular use, but is good for the limited use that an average boat owner will have. It has no problem handling 1/4" stainless rivets.
 

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+1 I agree. Do not sail the boat, and get this fixed right, asap. You lose a spreader, you lose the rig.

Also, let me take a second to debunk any theory that there's any difference between a deck stepped mast or a keel stepped mast when it comes to support. A keel stepped rig is no stronger. The rig doesn't get support from going through the deck (at least not substantial enough support to make any difference during a shroud failure). If a shroud or D1 V1 lets go on the weather side, the stick breaks. Period. I've seen it happen, aluminum masts are not very strong, if the shrouds and spreaders don't support it, the stick folds over pretty darn easy in my experience.
Good advice since sailing with a broken shroud is an emergency only option. This mast needs to come out and be fixed. And by a professional rigger.

However, a keel stepped mast is substantially stronger. On the order of 50% stronger. However often this strength advantage is then bled away by the designer since it allows a smaller profile, smaller rigging, saving a lot of weight up the rig.
 

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Please provide some data to back up that statement.
Without going into the engineering this is a quote from Eric Sponberg who is one of the premier composite mast engineers in the world, a forensic mast expert and a pretty well known NA otherwise.

...whether a mast is stepped on deck or on the keel is immaterial to the material used to build it. A keel-stepped mast is always stronger than a deck-stepped mast, on the order of +50%, because of the fixity provided by the deck partners. Therefore, if it is inherently stronger, it may also be a slightly smaller cross-section, and therefore lighter, than a deck-stepped mast. Although, a true detailed comparison may need to be made because the keel-stepped mast is longer.


Eric
 

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I think 50 is quite a stretch

the point about failure is the same however...if all lowers are snapped then the mast will buckle no matter if its keel stepped or deck stepped

I do prefer keel stepped though...
 

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ps composite as in carbon fiber?
 

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Carbon fiber, aluminum and fiberglass. I don't want to get into someone else's vc, but he has done a lot of pretty well known boats and is the go to guy for free standing/unstayed masts. The Freedom and Nunsuch lines are his (I believe). He is a pretty well regarded NA who specializes in mast designs.

Is his 50% number exact? No probably not it was a response to the relative strength of deck vs keel stepped, not intended to be an exact number. Wether it is 47% stronger, or 52% stronger, doesn't matter much for general purposes, but if one of the premier mast designers in the world says it's roughly 50% stronger, absent strong evidence to the contrary that's the number I am going with.
 

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gotcha unstayed is a whole nother shebang...you are absolutely right there and quite a different subject than standard rig talk

but for a simple keel stepped versus deckstepped on a stayed mast and boat id say there is very little difference in stregth in complete working rig...

like mentioned before stronger or not a keel stepped mast will buckle just as easily if unsupported when losing lower or intermediates on a double spreader rig as on a deck stepped mast

totally different animales here

not to mention nonsuch and unstayed rigs use round an tapered masts like windsurf masts
 

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Christian,

Assuming everything else is the same, a keel steep gains the lateral support of the partners, switching the entire design from a cantilever to a stayed beam. Deck stepped masts are much much weaker. Of course a mast only need to be strong enough, which is why in practice both work fine, and have different trade offs.

But if you keep the same extrusion, and the same rigging, a deck step will be substantially weaker than keel step.
 

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stumble while I agree on some points with you it means little when you have a failure that will make you lose tension on one side hence buckling the mast

the mast will go down if this happens keel stepped or not

where it fails changes

and I also dont beleive that deck stepped masts(the mast itself) is much much weaker

that is a false statement

the partners like you say add stiffness and keel stepped masts act much more in unison with the whole boat if you will especially if tangs are used at the deck entrance to andf from the mast to other points of the hull

I guess we see things a bit differently

again I prefer keel stepped....I also think keel stepped masts suffer less from oil canning hulls versus deck stepped

especially if the support beam on said boats has failed or sagged or detached from the underside of the deck mast step which is common on many old boats

anywhoo

cheers

oh and just to play devils advocate deck step masts do have their pros...tabernacling them is one and also in the off chance you lose both lowers and uppers on side by mistake, failure, etc it is possible that the mast simply lean over into the water and have much less damage

when a keel step mast fails damage usually is catastrophic.

ever see a hobie mast fail?

it just plops over to the side and bam into the water tie it up again and your good to go....

wish it were that easy on bigger boats
 

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How much additional support do you think the partners add? Lets say there's 7' below decks, you're really only getting 7' above decks. I don't consider that 50% more. Also the support would be less the longer the stick is.

Consider the source, was that article you quoted defending the use of unstayed/freestanding rig design? Or was it a direct comparison between stayed deck stepped and keel stepped rigs?

I don't know for sure, but I'm having a real hard time wrapping my brain around how the partners of a modern rig adds 50% to the strength of a stayed mast. Sorry, one selected quote isn't going to sell me on that idea.
 

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Discussion Starter · #19 ·
Thanks for the input on the repair. I am working on it and not sailing in meantime :-(

The mast is deck stepped and too long to come down in the slip. So my plan at this point is c-clamp the tang back into position and replace all 5 rivets on topside of tang (above spreader). Only two of the five appear broken but all will be drilled and replaced. I will then have rigging checked before sailing again.
 
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