Yesterday as I was reassembling my Nacra 5.2 mast and it occurred to me that an area of important discussion that I had not seen in the forums, or the technical photo albums was on sealing masts up. We often hear about boats going turtle and the problems that causes, but I at least have not seen anyone discuss how to go about sealing a mast up or that rivets are essentially little holes that can let copious amounts of water in, or slowly let moist air in. Not to mention that it is really impossible to hermetically seal a mast up, so how to you deal with getting moisture out of a mast once it is in?
My rebuild has given me a great big hole to deal with and I have decided to use that as the way to occasionally air the mast out and drain water out of it (from condensed moisture). But I would be curious to know how other boaters deal with this problem, or do they even know about it? I have to believe boaters in humid areas have multiple ways of dealing with this problem.
I did some video of how I sealed the mast head up, along with the mast hound and the rivets. I am totally good with any and all comments about how I did this. If I need to do something different, now would be a very good time to know about it. I also suspect that these steps are not carefully done by our boat manufacturers so we all should take time to inspect these areas and to beef up the defense against water infiltration.
https://www.youtube.com/watch?v=dMqKhR1qNyY
dg
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dg
NACRA 5.2 #400
This End Up
Original owner since 1975
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Sealing a Mast Head and Rivets
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Posted: Aug 15, 2016 - 10:50 PM
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Posted: Aug 16, 2016 - 07:56 AM
I was just about to take my mast head off the other day and re-seal it. Got new rivets and everything. Then I realized that there are rivet CASINGS that should probably be used which I didn't have. The rivet goes inside the casing thus eliminating the hole. Murrays has them.
Edited by tnell on Aug 16, 2016 - 08:01 AM.
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Tim
Collierville (Memphis), TN
Supercat 15--sold :(
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Posted: Aug 16, 2016 - 10:31 AM
I doubt those are necessary for a mast head casting. They are going to be very hard to pull with a standard riveter and require a steel mandrel rivet that is going to rust and stain. I think they may be more appropriate somewhere where the part is getting worked around very hard, like a Hobie frame member, rudders or something like that. They would also not help where the rivet hole is not completely round. Here is the link and info on these:
http://www.murrays.com/19-5020.html
I think in the case of the mast head that taking care with some silicone application would be better. If you use these you need to coat the jacket with something to isolate the stainless from the aluminum mast.
dg
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dg
NACRA 5.2 #400
This End Up
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Posted: Aug 16, 2016 - 12:16 PM
Based on something written by Matt Miller regarding adding closed foam when installing comp tips I am planning on adding some to fix a leak. Apparently comp tips were leaking at the joints.
http://www.hobiecat.com/forums/viewtopic.php?f=14&t=9644
I haven't figured out how I am going limit the foam to the top few inches of the mast yet. This is the same foam that is used in boats for flotation. It is 2 lbs per cubic foot and I do not think I would use more than a 1/4 cubic foot to seal the mast. It is not supposed to absorb water. -
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Posted: Aug 16, 2016 - 02:11 PM
I have had some recent experience with this. The mast on my SC15 leaked at the head and hound. This resulted in going turtle after a capsize and a difficult righting. I removed the mast hound, cleaned it all up, bedded it with 3M 5200, and refastened it with machine screws into tapped holes. The screws are the manufacturers recommended method. I also needed to install an Aussie hook at the masthead. This required removing the cap in order to through bolt the hook. The cap was originally riveted. This item, too, I bedded with 5200 and machine screwed into place.
I did the same with the base. While I had the base off i tilted the mast head down and filled it with water. No water leaked out at the head or hound. I reattached the base in the same manner. On a later occasion I removed one of the screws from the base. As I loosened the screw air came out of the hole. I had positive pressure in the mast due to it heating in the sun. I found it possible to seal a mast airtight.
I believe sealed head stainless steel rivets are available. A dab of 5200 in the hole prior to setting the rivet and a dab in the hole in the rivet will seal it up nicely. All SS rivets are a bitch. Get the best rivet gun you can.
I had a situation on my H14 with a leaking masthead on a non-com tip. It had a stock Hobie foam block with an aluminum plate just below the mast head shiv block. I siliconed the foam in and sealed down the plate with 5200. This leaves only a small area below the shiv.
DG the mast in that video is pristine! Is that a refinish?
http://www.hansonrivet.co…sed-end-blind-rivets.htm
Edited by gahamby on Aug 16, 2016 - 03:13 PM.
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'82 Super Cat 15
Hull #315
Virginia
Previously owned: '70 H14, '79 H16, '68 Sailmaster 26, '85 H14T
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Posted: Aug 16, 2016 - 02:52 PM
If a 40 year old mast can be pristine, then maybe. This is all part of the This End Up rebuild. The mast was sanded, coated with an Awlgrip Wash Coat, then 3 coats of Awlgrip 545 (most of which gets sanded off), then 3+ coats of Awlgrip 2000 Jet Gray (that was a bit...h).
For pulling anything but aluminum rivets you need one of these type tools, or maybe a pneumatic tool:
Interestingly enough this thing was no more expensive than a good standard riveter on ebay.
Even if you used a solid rivet I suspect that some number of times the the rivet would not seal the hole. The bulge created by the mandrel does not always create a perfectly symmetrical bulge before it breaks off. Some other step like you are taking is required in my opinion to seal any kind of rivet. I think threaded screws would be better, but again something is then needed to keep the stainless screw from galvanically corroding the aluminum.
We also need an engineer to step up and tell us the math on how much more righting weight is required for every once put into the end of a mast, for a given mast length and for say an ounce of water or material.
You can see more of the images on my 5.2 project in the Technical Albums on the Rebuild of This End Up.
dg
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dg
NACRA 5.2 #400
This End Up
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Posted: Aug 16, 2016 - 03:09 PM
Yep, that's a good riveter. Aquarius Sail, who makes the SuperCat and Arc catamarans recommend tapped in machine screws for all their fasteners. I find with a good bedding compound corrosion is minimal. I swear by 3M 5200. I'm sure there are other opinions. I paint the inside of all my castings with zinc chromate primer green. I haven't noticed any condensation in my mast. Perhaps a couple of packs of silica stuck to the inside of the mast base would answer the condensation problem. I hope to sail tomorrow so I'm not pulling anything apart. I will advise the next time I have the base off.
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'82 Super Cat 15
Hull #315
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Posted: Aug 16, 2016 - 04:07 PM
Very simple, it's a teeter-totter problem. Unfortunately,our Americam friends still hold onto that archaic British system of measurement.
Think of a simple balance beam weigh scale. Next, we need to understand grade 10 physics, & units of measurement.
One cc(cubic centimetre) of water weighs 1 gram, therefore 1000 cc is 1 litre, & weighs 1kg,(kilogram-2.2lb).
My nacre 5.7 has a 30' mast. So, 1/2 litre(500 cc) of water in the end weighs 500 grams, (appx 1.1lb). 1.1lb x 30'=33 lb holding the mast down. To get it back up, you need 33ft lb more on your righting line. You can accomplish that by having 33 lb at a distance of 1' from the pivot point, 16.5 at 2', or 11lb at 3'.
You see, very simple.
I have ignored a small bit of physics,(statics & mechanics), in that when on its side, the mast is below horizontal, therefore requiring slightly less than the examples. As the mast comes out of the water, to horizontal, that is when the greatest righting force is required, hence the propensity to get it about 3' off the water, then no more. Once the mast moves above horizontal, the required force decreases. You know this, the further your mast comes up, the less the force required.
The example is static conditions, no wind. If you have the mast into the wind, you benefit. Wind pushes on the tramp, but the boat is dragged in the water,creating what we call a "couple" (arm x force), helping to right you. This righting moment pivots around the dragging hull. Obviously, the stronger the wind, the greater the couple assisting you, & the less mass you require to hike out.
I can solo right my 5.7 in a 20mph wind,less than that I need to use the righting bag. In dead calm,I need the Colorado Big Bag full.
Going back to your post, & using those horrible British units of measurement, for every ounce in the mast head, you need to balance it by your righting moment. An ounce at 30' requires a 2 ounce at 15', or 10 ounce at 3'.
Do your kids & grandkids a huge favour, petition your Gov't to join the 21 Century & adopt the Worldwide system of measurement, no one else uses that anymore, & it greatly complicated teaching & retention of physics.
Ie, I "weigh" appx 85kg, do you know how many "stone" you weigh?
No, lbs is not a value of mass, it equates to force, & these mis representations of units are the basis for much misunderstanding of fairly smile problems.
Ok, that's the end of my rant.
Edited by Edchris177 on Aug 16, 2016 - 04:24 PM.
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Posted: Aug 16, 2016 - 04:41 PM
You repeatedly said "grams" and "weighs", but a gram is not a unit of weight, it is a unit of mass. So perhaps there is some confusion even among the modern world!
Edited by tnell on Aug 16, 2016 - 05:01 PM.
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Tim
Collierville (Memphis), TN
Supercat 15--sold :(
Hobie monocat--given
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Posted: Aug 16, 2016 - 04:43 PM
You repeatedly said "grams" and "weighs", but a gram is not a unit of weight, it is a unit of mass. So perhaps there is some confusion even among the modern world!
apparently I'm confused too because i can't figure out 1. how not to double post, or 2. how to delete one when i do
Edited by tnell on Aug 16, 2016 - 05:03 PM.
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Tim
Collierville (Memphis), TN
Supercat 15--sold :(
Hobie monocat--given
Vanguard 15--traded for...
Nacra 4.5--sold
Nacra 5.7
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Posted: Aug 16, 2016 - 04:50 PM
Sailors, always give a little thought to the loads involved when deciding how to attach/secure an item.
If we are talking a mast head plug, ie Hobie, Nacra etc, from legacy boats, or a mast base, realize there are essentially no dynamic lads on the part. The rivets only serve to hold the part in place, same goes for the end cap of a H18 boom.
Don't get wound up about Monel, or SS rivets, & exotic sealers. Coat things with marine silicone, & pull regular AL rivets. The forces hold the part together, the rivets just keep it there when the mast is down, silicone will seal it just fine. I have just coated the rivets on several Nacra masts, along with the joints at head, & base, with marine silicon. The masts float, & because there is no air exchange, there is no condensation. Using this simple, & cheap method, I experience a "whoosh" when drilling out a rivet on warm day.
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Posted: Aug 16, 2016 - 04:58 PM
Ed, that makes good sense. The only real loads would be on the stuff attached in the middle. Shrouds, traps, halyard hook, etc. I will probably revisit the topic of sealing up my masthead because I have no idea how long it's been. For the hounds I'm just go over it with good sealer.
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Tim
Collierville (Memphis), TN
Supercat 15--sold :(
Hobie monocat--given
Vanguard 15--traded for...
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Posted: Aug 16, 2016 - 05:18 PM
So much for the math. If you don't have a way to get that additional weight hiked out you are still screwed.
I would also reiterate the point that it is not adequate to seal just the rivet with silicone. The rest of the perimeter of the part as in the case of a halyard hook or a mast hound must be sealed. It is bad assumption that the mating surfaces of the part and the rivet fully seal the hole. It may not be a large leak, but it is a leak.
dg
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dg
NACRA 5.2 #400
This End Up
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Posted: Aug 17, 2016 - 12:08 AM
You are quite correct, my apologies. It is always a difficult choice when you don't have any idea of the background of your readers. Do you stick with completely correct terminology, & perhaps the message gets lost, or do you interject laymans terms, knowing they are not technically correct, but will get the message to all readers.
In this case I meant to enclose "weigh" in quotations to indicate the ambiguity. I'm sitting in Beijing, been up all night, & yes, I should have worded some of that differently.
I don't think you can delete a post. To prevent "doubles", only click SUBMIT once. It looks like nothing happened, but if you then click on the HOME button, you will see your reply posted. It seems to grind away for longer than it used to, leading one to think it didn't post.
If you really want a project, you could pull the masthead & base, but I would save that for winter, if at all. Just wipe the perimeter with acetone, then apply a thin smear of marine silicone. It won't leak. The 5.7 mast will go under to about the hound, unless you turtle. As bear noted above, that may not seal something like the hound. Hopefully, when it was installed they put a dab of tape, or sealant on the underside. I couldn't be bothered drilling out Monel rivets to see. I just added a thin bead of silicone around the edge of the hound & the diamond tangs, it's still there 5 years later.
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Posted: Aug 17, 2016 - 09:23 PM
Ed I'm going to have to disagree with you there on the mast head. At least on a Super Cat. The main halyard shiv hangs over the back of the mast. When hoisting the main there is quite a bit of load. Once you drop the ring into the hook there is quite a bit of load there. One of our sailors on the Lower Potomac just had the rivets tear out of his original Aussie hook while under sail. He'll be thru bolting his new hook. Me personally, I like my stuff "screwed and glued".
Silicone is ok for a sealer, not so much an an adhesive. But hey, to each his own
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Posted: Aug 17, 2016 - 10:02 PM
Ed, I was just kidding you about the mixed units. Thanks very much for you advice on the 5.7.
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Collierville (Memphis), TN
Supercat 15--sold :(
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Posted: Aug 18, 2016 - 12:59 AM
Fair enough, I would not recommend silicone as an adhesive.
I'm interpreting you post to read the hook pulled out?
I agree, that part won't survive with AL rivets, same for the mast hound. Both are made from SS because they are stressed. For the hounds, & hook on the H18, I would use factory spec rivets, with a sealing tape underneath to create a barrier between AL & SS.
On the older Nacra, (TNELL boat), which uses a small slug on the halyard, the plug is mostly under compression, rivets just hold it in place. I would not bother pulling SS rivets there. In those cases you are only looking to seal the joint.
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Posted: Aug 18, 2016 - 01:18 AM
Ed, yeah I got ya. On OUR boats there's no real load on the masthead (or base).
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Tim
Collierville (Memphis), TN
Supercat 15--sold :(
Hobie monocat--given
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Posted: Aug 18, 2016 - 11:46 AM
I gotta add, the stress on the mast base when stepping is going to be severe. I've seen an H16 base tear off during stepping. Corrosion and age played a part.
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Posted: Aug 18, 2016 - 11:55 AM
The rivets pulled out of their mounting holes at the masthead.
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'82 Super Cat 15
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Virginia
Previously owned: '70 H14, '79 H16, '68 Sailmaster 26, '85 H14T
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