Converting a mast to a tabernacle?

[Cap'n Creosote]

What are the forumites thoughts, pro's and con's of stepping a mast in tabernacle?

I have a 28ft Atlanta/Macwester with an aluminium mast approximately 32ft high and approximately 5½" x 4" section.


I will probably need to lower the mast for maintenance and replacing the rigging this winter.
Although it is deck stepped, it stands in a collar about 3 inches deep. So I will have to get the boatyard to lift it and lower it for me.

My last boat had a 24ft wooden mast in a tabernacle. I could raise and lower that one single handed.

I am wondering if it would be worthwhile to convert this one to a tabernacle mounting while it's down, so that future repairs and maintenance would be a bit easier. (Assuming the use of an A frame of course)

but what sort of problems might I encounter?

1. Stainless steel fabrication? (sounds costly?)
2. Or galvanised steel (cheaper but would there be a problem with electrolytic corrosion?)
3. Could a pivot hole just be drilled through the mast or would it need internal reinforcement?
4. any other problems I haven't thought of yet?

Is it just too large and too heavy and I should just forget the whole idea?

 

[DownWest]

Done this recently for a friend with wooden mast. The hole in the mast is for pivot only, the rigging load will be taken by the foot in the bottom of the tabernacle. Used galvanised steel, but it was for a wooden mast. Stainless and ally are not too friendly either, need isolating paste. Look at the galvanic tables (can't find mine right now) a galv/steel one might be OK.
A

Slight prob with galv shops, they usually have a minimum charge. 40euro here.

 

[Lakesailor]

This page may be of interest. It refers to a 17ft trailer-sailer but has some important features.

 

[DownWest]

Interesting Lakey,
But I can't see why one should weld a tube in to the mast to take the pivot tube, if the only load is swinging it down. The hounds are usually just a bolt through, with all the rigging loads..? Perhaps a loose tube to stop the bolt crushing the mast section, but again, only usefull up the mast. This needs a 'stress analysist' or better an ENGINEER.
A

With apologies..

 

[VicS]

1. Stainless steel fabrication? (sounds costly?)
2. Or galvanised steel (cheaper but would there be a problem with electrolytic corrosion?)

Other way round as far as corrosion goes. Stainless would be likely to cause corrosion of the aluminium ... galvanising should be fine.

 

[fergie_mac66]

http://www.catamaransite.com/mast_lowering.htm

many of the The 9m and 8 m catalacs have (32 Feet approx)mast in galvanised tabernacles the masts are alloy the shrouds are shortened and are fitted to stainless stands That replaced the chain plates see sketch
Its fairly quick to do and I havent heard of any mast problems over the last 2/30 years.There a tube through the mast for the pivot bolt and a wedge arrangement at the bottom of the tab' to take mast loads

Ps Galvanised tab' is definitely way to go

 

[Cap'n Creosote]

Thanks for the comments so far. Interesting link to seahawk page.

I'd been thinking about a tube through the mast too. But as I can't take the mast to the welder, I would have to pay for the welder to come to the mast!
The whole point of being able to lower the mast myself, is to save money. Aren't I a cheapskate.!
I expected the costs of keeping a boat to be higher than originally estimated. But I'm going to have to be very careful with my grand plans. I could end up with my modifications costing more than I paid for the boat.

Thanks VicS, correcting my incorrect assumptions about corrosion. I could fabricate and weld mild steel myself. And then get it galvanised.

 

[fergie_mac66]

The tube through the mast on the catalac is alloy and is not welded its sort of pressed/peind over

You could do it with 2 tubes inside each other one slid inside the mast to the drilled holes the other threaded throug from the outside then peined over to keep in place

 

[oldsaltoz]

problems you might encounter.

1. Stainless steel fabrication? (sounds costly?)
Not a good idea then. But have you considered Aluminium, our old 28 footer had an alloy tabernacle, just thick plate welded on 3 sides, after 30 odd years the shackles through the side plates were a bit worn but still plenty of life left in them.

2. Or galvanised steel (cheaper but would there be a problem with electrolytic corrosion?) There will be some corrosion, particularly if you have shackles and pulleys attached to the cheek plates on each side, they will make short work of removing the coating.

3. Could a pivot hole just be drilled through the mast or would it need internal reinforcement.
Ours had a tube inside as a pacer (not welded) and external spacers on the outside between mast and thick allot plates with a small gusset each side of the hole/s.

Note: You can get your original name back, just send Dan (admin) an e-mail with details.

Avagoodweekend......

 

[William_H]

Mast tabernacle

Yes you definitely should do it. Almost all boats around here have mast lowering arrangements to clear bridges. Many are much bigger than yours.

You don't say what the material is used for the existing collar. If it is Al or SS you should use the same material to attach side plates upward to take the pivot bolt. You will have to cut away the front of collar to allow the base to slide forward as the mast comes back. You will have to remove the collar to get the welding done.
I would suggest that a large diameter bolt (12mm) will have adequate bearing area on the mast wall which will only take weight as the mast goes down. You will have to arrange enough free play in the hole so that mast weight when up is on the base not on the bolt.

As a matter of interest the base on my much smaller mast consists of a flat SS plate with a spine fore and aft up the middle. The aft end (further aft than the where the mast sits) of the spine goes up another 15mm to take a hole for the pivot bolt. The mast itself has a cover plate over the bottom of the mast with a slot up the middle(for the spine) The mast has 2 lugs welded on to the back at the bottom. These lugs are just far enough apart for the spine to go between. A bolt only about 30mm long does the job.

The advantages of this arrangement is that when the mast is going down any swing of the mast left or right results in just a small movement in the close spaced lugs. The base does not attempt to keep the mast straight left to right in going down so if it does swing no damage is done. he lugs just get spread a bit. Other systems with wide (10cm) spacing get the lugs snapped off with any swing. Which of course should be controlled.

My mast Al sits on Stainless plate with no corrosion problems. It comes down several times per season. The mast bottom is painted but that doesn't last long under the pressure.

Good luck I think you will be pleased you have made the mod. olewill

 

[TamarMike]

I think Macwesters had galvanised tabernacles so should be no problem there (n.b as Atlantas were sold in various stages of completion the mast foot arrangement varied, yours sounds a bit like mine though many had tabernacles)

 

[jon711]

Lowering mast

Having converted a mast, to a lowering tabernacle system, I just thought that, I may be able to give an input.

We had a customer come to the yard, asking to convert his deck stepped mast to a tabernacle. We purchased parts off Pegasus Yachts (They had the necessary bits, designed and in stock) to make an A frame.

Not too sure who made the tabernacle (It was 20 years ago!!)

It was an easy job to convert the mast to the tabernacle system..

Do you always sail on salt water? We did not even consider galvanic corrosion on this job, and even if you sailed on salt, it would be irrelevent, IMHO....

 

[CAPTAIN FANTASTIC]

How offten will you need to drop your mast down? perhaps once every five years?. To lower and raise back the mast, the cost is normally about £60; The cost to make an "A" frame and the tublenuckle plus other staff will be significally more. Too much hassle for the benefits. Also, the Macwester masts were heavy sections (mine is), I would not like to drop my mast to often.

 

[DownWest]

Cost: As the OP is able to weld it himself, very little. It took me about 2 hrs to make the one above. Galve is about 2 euro a kilo of iron work, notwithstanding the 40 euro min. I acid washed the steel and the galve people said if you wait, it will be done in an hour. As for the A frame, wood is fine. Or perhaps just the spinny pole on the centre line?
A

 

[Lakesailor]

Interesting Lakey,
But I can't see why one should weld a tube in to the mast to take the pivot tube, if the only load is swinging it down. Perhaps a loose tube to stop the bolt crushing the mast section,

I was considering this conversion and was wondering about the welding. There are no crushing loads as the author mentions using a domed nut to limit the compression of the side plates.
I wonder if it was in case the relatively large hole weaked the mast section and would be a failure site. The Seahawk mast is a small section lightweight affair. Perhaps welding the tube in place would restore integrity.

 

[DownWest]

If drilling an 8mm, or 10mm hole so close to the bottom of the mast compromised it's integrity, I would worry a lot more about the rest of the rig. There should be no compression from the bolt, other than to stop it rattling. The tabernacle should be a snug fit to the mast, but not tight. A side note, my little gaffer has the tabernacle tall enough to mount the goose neck, making it much easier to drop with the sails attached.
Also saw a (Vivier) boat with no pivot bolt. The top of the tabernacle was rolled back at the rear and the mast had sort of wide hook. Drop mast between side plates, slide forward until hook engages with rolled top and pull on hoisting tackle. Prob not suitable for an oval ally section, but interesting never the less.
Andrew

 

[Lakesailor]

On the boat I am thinking about the mast is more of a dinghy section and is very light as well as being 35 years old. I am less than keen to cut holes in it. The hounds do have what appear to be tubed fixings through the mast with peened over ends. Perhaps I am over-cautious.
That last point is along the lines of my thinking. With side plates, rivetted to the mast, (or even a clamp around the mast made from alloy sheet) extending aft and having a pivot bar across them you could engage the bar in cups (notches) on the top of a lightweight tabernacle. Once raised, of course, the mast sits on the tabernacle base, perhaps with a slightly raised plug to engage in and locate the mast foot. The geometry could allow for the pivot bar to have lifted from the cups as the mast came to the vertical. The shrounds would pull the mast firmly down on the base.

 

[jswindel]

Just had a look at the Seahawk tabernacle and I noticed that it is firmly bolted through the cabin roof. Is this a good idea? The tabernacles on my last two boats were fairly lightly screwed to the cabin top. The idea was that should the worst happen and the mast get blown sideways whilst being raised or lowered, the tabernacle screws would rip out of the roof rather than rip the top of the cabin off. Both of these boats had light, hand raised masts which you hung onto as you pushed them up, so they didn't use an A frame or bridle for stability. That might not be feasible on your boat.

 

[Lakesailor]

It seems that there is a plank of wood glassed into the coachroof along the centre-line of the boat. The bolts would go through that. As you say, it's a lightweight mast and the combination of a sturdy coachroof, the tabernacle and the person holding the mast it should be OK. If the mast fell it would damage itself terminally anyway, so persuading it to stay upright is better. Can't see the coachroof being damaged.

 

[Cap'n Creosote]

Making the tabernacle fixings as a weak point has it's merits but the forces trying to push it forward as you start to raise the mast must be considerable. I don't like the idea of starting to raise the mast only to see the Tab' tipping gently forwards.

I think I'd prefer to bolt it down firmly and just take care when raising.

This is also the only time when there would be any significant pressure on the pivot bolt hole. If the mast wall looks too thin, I suppose I could pop rivet ali' plates either side of the mast to increase the bearing area.

Thanks to all.
John

Time to get the drawing board out, I think.