Tabernacles - Mast Hinge

[hectoretc]

Greetings all,
I purchased and installed a D&R tabernacle this summer following the instructions provided "and then" read some postings in the DSII dedicated forum that made wish a hadn't (followed the instructions).
I cut the mast at the designated spots and reassembled, end result being the tabernacle is a few inches above the cuddy top.
I have since read in several postings that others have installed the tabernacle higher so that the boom can be left attached when the mast is lowered. This seems like an excellent idea for at least three reasons.
1- (obvious one) The boom stays on which saves the need to detach and store it. Also easing the disassembly challange of lowering the mast for low bridges etc.
2- The mainsail could be left attached to the mast and stored on the boom making sail prep and storage faster.
3- A shorter upper mast section when it is taken down (is it still called de-stepping when a tabernacle is in use?).

I assume there is a specific reason the installation instructions give precise measurements where to cut, but I don't know what those reasons would be.

So now having done what I did and hindsight being 20/20, I guess my options are one of three.
A- Leave it alone and deal with it.
B- Acquire a new (longer) lower section of mast to raise the tabernacle, and further cut town the upper mast to maintain the correct length.
C- Install a 2nd tabernacle higher up, giving two options for mast removal.

Questions for the audience...
For option B, is there a source for 4-5 feet of mast base out there in the retail market or do I need to find someone with a previously bent/broken mast on craigs list.
For option C, is that a really stupid idea? Part of another discussion brought out some comments that many people don't even insert the front pin on their tabernacles because it is a vertical weight/stress point, and the stays manage the lateral stress so it's really not needed. Would that logic provide that a 2nd tabernacle (definitely pin the lower one) would also not seriously compromise the strength of the mast?

I'd be interested in hearing your thoughts.
Thanks,

[Alan]

I'll leave the question of what to do to the experts, but if you have a Dwyer mast, you can buy just the mast extrusion by the foot from www.dwyermast.com.

[hectoretc]

Thanks for the link Alan, definitely the way to go.

Thanks again!

[jdoorly]

Before you do anything else, (with the hinge at the deck) try leaving the boom and mainsail on the mast and lowering the mast with a gin pole or a-frame- I think it should work just the way you want!
But, if you want a hinge up higher I would not use the Dwyer type of 'tabernacle', it cannot take the extra and potential forces at work when it is located higher than deck level. However, my mast hinge works great and it was easy to make. I have even dropped the mast several times, due to senior moments, and it sustained no damage.

[hectoretc]

Thanks jdoorly,
I'll have to look again, but I didn't think the boom gooseneck would be able to flex the full 90 degrees needed to leave it attached while lowering the mast. Maybe I'm wrong, but I"m visualzing it and I just don't remember a hardware joint that would allow that much vertical flex.

Do you have any drawings, descriptions or a couple really close up shots of your mast hinge (even one directly of the hinge section from the cockpit?) If not, I can probably extrapolate how it works. At the minimum, can you tell me how far up from the sole is your cut? Aluminum or Stainless?
I should warn you that every time you answer me It'll probably result in more questions and work on your part.
When I get interested in something, I have a tendancy to milk everything I can from anyone who knows anything, so I excuse you in advance and will not be offended if you don't have the time or inclination to keep going down this path.

Looking at the photo, I see the pin and key at the top of the lower section which would suggest that the pivot point is the lower bolt, but I would expect that would cause the mast to hit the boom when lowered, unless the boom drops prior to the mast coming down, but there is no sail attached, so... can't see what would be holding it up now?

Thanks again!

[jdoorly]

I think your right about the gooseneck inhibiting the boom from getting parallel to the mast. Sorry, I didn't go that way and apparently didn't think that through. You are also correct in your description of the tabarnackle.



The top two stainless 1/2-13 x 3 1/2" bolts go through a fender washer, the 3/8" x 2" x 12" aluminum side plate, another fender washer, then through the upper mast then a third washer, through the other side plate, another washer, and a nylon insert lock nut.

The third bolt down is the safety lock. It goes through the side plate, the lower mast (stub), and the other side plate. I modified the bolt by drilling a hole through the threaded end and installing (by hand) one of those wiggly cotter pins. When installed the mast will stand without stays, though I wouldn't go sailing that way. I have sailed twice without it!

The fourth bolt down is the mast pivot (hinge). It is similar in assembly to the top bolts but goes through the lower mast.

In the picture in the earlier post the boom is being held above its normal position (to give better headroom while working around the cockpit and better clearance for the hatch to open). When the main is set the boom is probably 4 inches lower, and when the mast is down it is usually another 4 inches below that. There is clearance for the boom and mainsail. I use slides on the mainsail and leave the sail attached to the upper mast. I also formed a piece of sheet metal into a gate for the bolt rope feed. I think there are 3 slides below the feed, some in the feed, and the rest are above the feed.

I cut the mast 26" above the deck, and the the upper mast and lower mast have 1/4" clearance between them with the mast up.

At the top of the tabernacle, in front of the two side plates, is a 1/4" x 3" x 5" aluminum support plate with three #8 machine screws on each side going through the support plate into tapped holes in the side plates.

Lastly, since the side plates are not as wide as the mast section is long, I added two 3/32" thick by 2" by about 6" long aluminum sheets to make a strap which is through bolted to the side plates. This adds strength by completing a 'box' section, and also acts as a stop to keep the upper mast from going too far forward when being raised. Of course you could make the side plate a bit wider (or shim them) and do a 2" tall plate here similar to the front support plate. I may do that in the future.



My boom rests on a boom gallows and the mast is lowered onto a 2 foot tall extention on that boom gallows. For me this keeps the mast about 7 feet off the pavement. I keep an orange flag on the mast head when trailering. To unfasten the pivot bolt and move the mast forward and re-secure it, for trailering, was a pain I decided not to endure.

[hectoretc]

Wow... awesome and thanks so much for the detailed description. This is really great!

As fore-warned, I have a couple follow-up questions please...

When the mast is upright you commented there's a 1/4" gap between sections, so obviously the weight and pressure of the assembly (mast, sails, standing rigging, downhauls etc.) is on the four bolts through the aluminum mast. The upper bolts likely are cranked pretty tightly, but the bottom bolts have to be loose(r) to allow the pivot etc. Do you have concerns or experienced any "ovaling" of the bottom holes? Does the aluminum seem strong enough to support that load? Obviously its doing the job and looking at your photos there doesn't seem to be any evidence of it, just curious if that's given you any thoughts in hindsight? Would there be any benefit for an additional (maybe inside the mast) supporting brace with yet a 3rd bolt down the lower mast to provide some additional vertical support for the pivot bolt? I have no idea if it could even be done... just rambling here.

You essentially made a locking pin out of a bolt by drilling the hole in the removable bolt. Is that because you couldn't find a 1/2 inch clevis pin or other hardware to fit that hole, or is there something else in play at that point where you wanted a real bolt in there?

Thanks also for the comment on the gate over the feed slot. I've been staring at my mast ever since I first raised my slug mounted mainsail thinking it need something like that wondering what it would look like. Is your gate it rigged on a slide, or do you just put up the sail, screw on the plate and keep a screwdriver on the boat in case you ever need to remove the sail?

I was going to ask about the boom... but I guess it's obvious now, I assume you slid it into place before the tabernacle went on, and then obviously it stays on the mast (the point of this whole exercise). If you ever need to remove it for whatever reason, you take out the bottom bolt, remove the tabernacle and then pull the boom up and out.

On that note, is this still called a tabernacle or shall we call it the "jdoorly masthinge"* (*patent applied for)

Finally, my boat came without sails, and so I purchased an inexpensive used set (budgets budgets) which turned out to be a loose footed mainsail, I don't recall if you've stated one way or the other what you have for your setup, would you envision that would make any difference for this design?

Again.. thanks so much for the info. I can't wait to fabricate away... (my wife would call me a dork at this point...)

[jdoorly]

When the mast is upright you commented there's a 1/4" gap between sections, so obviously the weight and pressure of the assembly (mast, sails, standing rigging, downhauls etc.) is on the four bolts through the aluminum mast. The upper bolts likely are cranked pretty tightly, but the bottom bolts have to be loose(r) to allow the pivot etc. Do you have concerns or experienced any "ovaling" of the bottom holes? Does the aluminum seem strong enough to support that load? Obviously its doing the job and looking at your photos there doesn't seem to be any evidence of it, just curious if that's given you any thoughts in hindsight?
Yeh, I did think about the stresses in the tabarnackle. I originally designed a bronze shoulder bushing at the pivot but I could not find any. I finally spread the stress a bit by increasing the bolt size from 1/4" to 1/2". I haven't yet seen any wear in the aluminum but I expect to someday, then I'll seach again for bronze bushings. The top bolts are firm, certainly no play. The pivot bolt which also has fender washers is pretty tight as well, but not stressing the mast.


Would there be any benefit for an additional (maybe inside the mast) supporting brace with yet a 3rd bolt down the lower mast to provide some additional vertical support for the pivot bolt?
If your not comfortable with the strength issue you should beef up the design until your happy with it. I would think the easiest way to make it stronger would be to increase the length of the side plate to 18" and spread the bolts out more. however, adding another bolt to the lower mast would mean another bolt to remove when changing the up/down attitude of the mast. Perhaps 5/8" or 3/4" bolts would spread the stress more and keep an FEA analysis in earth tones, but a bronze bushing would be easier on the aluminum than stainless, but the stainless is closer to aluminum galvanically. Trade-offs, trade-offs, trade-offs!



You essentially made a locking pin out of a bolt by drilling the hole in the removable bolt. Is that because you couldn't find a 1/2 inch clevis pin or other hardware to fit that hole, or is there something else in play at that point where you wanted a real bolt in there?
A clevis would work fine, but I wanted to minimize play. Also True Value is 5 minutes away but only has a zinc clevis, and West Marine is 60 minutes away and has a stainless clevis.


Thanks also for the comment on the gate over the feed slot. I've been staring at my mast ever since I first raised my slug mounted mainsail thinking it need something like that wondering what it would look like. Is your gate it rigged on a slide, or do you just put up the sail, screw on the plate and keep a screwdriver on the boat in case you ever need to remove the sail?
My gate is a simple affair; 1/16" aluminum a couple inches longer than the feed, a #8 screw above and below to hold it in place and the left side (toward sail slides) is doubled over for a smooth edge. However, I saw a generic feed gate that uses a spring to allow slide ingress/egress (so no screwing needed) for about $20 in Small Craft Advisor within the last few months. I will probably buy or make one of those. I keep a lot more than a screwdriver onboard!



I was going to ask about the boom... but I guess it's obvious now, I assume you slid it into place before the tabernacle went on, and then obviously it stays on the mast (the point of this whole exercise). If you ever need to remove it for whatever reason, you take out the bottom bolt, remove the tabernacle and then pull the boom up and out.
Yup!



On that note, is this still called a tabernacle or shall we call it the "jdoorly masthinge"* (*patent applied for)
I don't know that anybody else has done a hinge a couple feet above the deck, so there should probably be some descriptive adjective, but a tabarnackle 'houses' and pivots a mast base, is usually at deck level, but the pivot is usually below the goosneck. So maybe call it a gooseneck hinge. By the way, some would say this tabarnackle is inherently dangerous. I disagree, using a Dwyer hinge above the deck is inherently dangerous because it can allow the upper/lower masts to go 'out of column'. However, it should be understood that it is important to secure the lower mast (stub) base to the floor and adequately at the partners (deck). If it falls on somebody's head I'll tell 'em I got it from you!


Finally, my boat came without sails, and so I purchased an inexpensive used set (budgets budgets) which turned out to be a loose footed mainsail, I don't recall if you've stated one way or the other what you have for your setup, would you envision that would make any difference for this design?
It shouldn't make any difference, but I envy you; your in a good position to have a furling main!

I got the aluminum bar at http://www.metalbytheinch.com

[hectoretc]

It shouldn't make any difference, but I envy you; your in a good position to have a furling main!

I got the aluminum bar at http://www.metalbytheinch.com

Oh Man... don't get me started on a furling main... the last thing I need right now is another good idea! (maybe next winter)

And thanks huge for the referral to Metal by the Inch! What a great website. It makes my project list seem a lot more manageable right now!

Seriously... Thanks again for the inspiration and information. Greatly appreicated. I'll post some pictures when/if I get this done.

[hectoretc]

Speakling of Metal by the inch...

So I'm ready to order the materials to build a copycat of jdoorly's mast hinge, and as mentioned elsewhere, unfortunately I have installed a D&R tabernacle about two months ago right where the instructions stated, just above the cuddy top, now obviously wishing I hadn't...

For the mast hinge setup, I know I will need my lower mast piece to be about two feet longer than it is now (after cutting it for the tabernacle) so I'm planning on buying a new section of mast, and I know I'm going to cut my upper mast piece about 2 feet up from where the tabernacle is now, leaving me a 2 ft. section of free mast...

So how stupid of an idea is it to take that 2 feet, and put it at the bottom of the stack between the step and the bottom of the existing mast base, and then either use the tabernackle as a joiner (basically permanently bolted together) or else a full wrap of 4-6" wide aluminum around the seam to reinforce it... no question at that point in the mast it's gotta be 90-95% vertical stress on the joint, probably some minor flex pressure while raising/lowering the mast but again that could be managed by a good solid joint.

I sort of started with that question at the beginning of this post, asking about having two tabernacles installed at different heights. I can appreciat that putting another joint above the existing tabernacle would create a weak stresspoint like trying to stand a chain on it's end, but if I move that stresspoint down inside the cuddy where it can be reinforced as much as needed... shouldn't that be OK?

Is this a really bad idea, rather than buying 5 ft of mast stock and replacing the lower piece entirely?

Thanks for your thoughts.

[GreenLake]

Some people would say that cutting a mast to add any form of hinge is a bad idea. And to them it is, because the way they sail the boat, they can tell the difference.

Where the mast hinge (tabernacle) is at deck level, there's nothing magical about the construction of the part below the hinge. It simply acts as a compression post, and does not require being made from profiled aluminum. Any setup that can take the compression load would be fine.

In your case, you are interested in having the sail slot below your jdoorly special™. That's one difference. The other difference is that the boom pushes at the top of your lower section, trying to bend it with the mast partners (cuddy opening) as a fulcrum.

This bending moment is the reason that simply leaving your extra mast hinge in place is a bit complicated.

However, your idea of turning around the lower section and then reinforcing the joint should work. If I had to do it, I might use some hardwood, like an oversized dowel, gluing it into the mast section after removing the hinge. (Making sure to epoxy that in place and covering the wood with epoxy on all sides).

A metal sleeve might work as well, whether riveted or glued in place. If the sleeve has about the same thickness as the wall section of your mast profile that would probably be sufficient in strength.

Finally, you could simply use a few layers of laminate. Four or five layers of suitable glass tape, spiral wound should be plenty strong for the purpose.

My rough guess is that if the reinforcement holds your weight, applied sideways, then you shouldn't have any problems. It's just a guess, but I would definitely make that test.

[jdoorly]

I would be comfortable with any of the suggestions by Greenlake. But there is a standard method for lengthening a mast section. Mast makers, like Dwyer, can only get mast sections up to 25(?) ft long and must therefore scarf sections together to make long masts. What they do is take an extra section of the same mast profile about 10% of the total length of the mast, and cut away the slot area (after 20% of mast). The scarph section can now be folded in a little, but it's enough to slide half into one mast section and then the other half into the second mast section. Then put in a lot of equally spaced pop rivets in to hold it together and spread the load.

I would not feel comfortable re-using the Dwyer tabarnackle as it fails when side force is introduced. The gooseneck hinge does not fail due to side force and can hold the mast up without stays. The attachment of the lower mast base to the floor and keelson should be sturdier than for the standard one piece mast base, especially in the for'n'aft direction. OOOPs, I meant athwartships!

[hectoretc]

As described in too much detail above, I'm working to trade my tabernacle in for a higher cut "jdoorly mast-hinge*" (*patent probably not yet applied for but should be) and as part of that exercise I cut off about 24 inches of mast between the existing tabernacle & where the new hinge is going to be and flipped the lower portion of the mast so the tabernacle is now inside the cuddy. There have been a couple posts above this one about how to better seam the joint in the cuddy because the tabernacle may have too much flex, and so I took off the tabernacle today to play with some ideas, and realized it is made of two mast steps (castings screwed to the cuddy floor) and two stainless hinge pieces.

I disassembled the tabernacle and then bolted the two step pieces together using the existing holes and screws and bang... I have a joiner for the mast sections that is strong, very firm and rigid.


(screws not tight... gotta take it apart again)

Looking at D&R's website, I see the step castings cost about $16 each and the tabernacle goes for $85 so I'm money ahead to buy two new steps to rebuild and sell the tabernacle. (watch for a good deal coming your way).

Anyway, anyone looking for a somewhat straightforward way to seam a mast, this might work for you too, but it does add 1/2" to the mast length that needs to be accounted for somewhere.

[hectoretc]

I would be comfortable with any of the suggestions by Greenlake. But there is a standard method for lengthening a mast section. Mast makers, like Dwyer, can only get mast sections up to 25(?) ft long and must therefore scarf sections together to make long masts. What they do is take an extra section of the same mast profile about 10% of the total length of the mast, and cut away the slot area (after 20% of mast). The scarph section can now be folded in a little, but it's enough to slide half into one mast section and then the other half into the second mast section. Then put in a lot of equally spaced pop rivets in to hold it together and spread the load.

I would not feel comfortable re-using the Dwyer tabarnackle as it fails when side force is introduced. The gooseneck hinge does not fail due to side force and can hold the mast up without stays. The attachment of the lower mast base to the floor and keelson should be sturdier than for the standard one piece mast base, especially in the for'n'aft direction. OOOPs, I meant athwartships!

Hi jdoorly,

Just want to be sure I understand your message. In your last paragraph above, you comment the lower section of mast should be sturdier than the original. Does that mean you did something to beef up your mast base and/or step mounting? Maybe do the insert you suggested for the full length of the lower section to create a pseudo-double thick mast section? And as far as reinforcing the step, would you suggest adding a plate under the step that distributes the weight and directional pressures over a wider area of cuddy floor?
I just want to be sure I understand and get it right.
Thanks, Scott

[jdoorly]

Scott, the problem is just as you say, new pressures and vectors not seen by one-piece masts will occur at the lower mast base and at the partners (deck). They will, imho, also 'work' your clever connection of your 2 lower mast sections until the 1/4-20 bolts get wobbly and fail, sorry, it really is creative though.

In the newest pic in your 'cracked' thread it looks like you have a mast base casting screwed to the floor and you place the bottom of the mast onto that casting to deploy the mast. This means you probably have one or two 1/4" screws holding the mast end in place. I assume you have a standard reenforced, but beat-up, hole in the deck that you guide the mast into but it has lots of play all around.

It is one thing for the floor and its underpinings to support the weight of the rig and downward pressure from stays. It's quite different types of force when you pull a horizontal mast forward using a gin pole or a-frame rig raising/lowering the mast.

My mast base is a stainless "U" channel 6"x2 1/2" with five #10x4" ss screws holding it to the mast step (under the floor). It has 7 sets of holes in the sides which are used to set mast rake by putting a 1/4" pin through an appropriate hole, then though the mast base casting (the mast), which needed a hole to be drilled in it, then through the opposing hole and cotter pinned. That came with my boat. But I modified it and it's still in prototype and I'm still working out the bugs. This was originally an attempt to raise the mast so I could rake it more to gain weatherhelm. I kept adding 3/4" blocks plus a wedge block so the end of the boom wouldn't hit my head! Now it is approching instability in athwartships direction- it needs to be wider, but maybe i'll spring for a 4' section of DM2 or make a 'big' sailboat type tabarnackle. Don't know yet.

My partners is a big "U" bolt I put through a block of wood and bolted to the deck. This is also still in prototype and has problems as well. It only tightens to the front of the hole (reducing rake) and to keep the lower mast from bouncing around it needs to be tighter than I thought, so now the wood is cracking at the deck thru-bolt holes. I'm thinking about how to mount screw hole bosses to threaded rods to gain for'n'aft motion...