Making a mast tabernacle - Help needed please.

C

carl170

Well-Known Member
Joined
13 Nov 2003
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235
halcyon23.blogspot.co.uk
Hi everyone. Once again I need your assistance.

I recently put a post up here as I was looking to find a mast foot for my ancient Sparlight mast, which has no foot, so I cannot lower the mast. Sadly, I was unable to find one from the sources suggested by other PBO forumites.

So, I have decided that the next best thing will be to have a tabernacle constructed out of steel or stainless steel (not sure which).

I need to supply the measurements to a fabricator, who will weld one together for me.

It will be a simple affair, which will be a base plate with 2 sides and a back welded on.

However, supplying the measurements for this is proving to be trickier than first thought. It appears that when actually looking at how the mast step is mounted, I noticed that the metal horseshoe shape (that the mast is fitted into) has a small baseplate and is actually bolted into 3 larger wooden pads used as risers. In turn these are bolted together by 4 large corner bolts which go right through the boat.







Again, I cannot seem to autoload the images!

I need to take this all into account when supplying the measurements. I measured the plate thickness from a tabernacle used on a larger westerly and it seems to be about 5mm thick, so I will ask for 5 or 6 mm thickness too.

Will I be best off having a base plate that is the same size as the wooden pads, or just have i.e. a bit smaller like the current mast step and the screw this down into the wooden pads? As long as the mast placement is correct, I am assuming this will be ok (please correct me if I am wrong).

The next issue is something I have no clue about. Where exactly do I mount the hole that the mast will pivot on, and how do I drill it? A drill press will be essential, which is about as much as I know.

Also, I am thinking I need a little play when the mast foot connects with the baseplate, as all the pressure needs to be on the mast plate, not the bolt! I read on a wooden boat forum that a leather pad can be used to compress this a bit?

Lastly, What size bolt and do I use washers to separate the mast from the tabernacle etc? How do you stop the mast sides from being squeezed inwards? Does the mast need to be reinforced etc?

Sorry for all the questions, but it seems to have so many variables. I may be over complicating things, but I like to be sure!

I would love to hear from anyone who has tackled this. I will not be the first, nor the last!
Thanks in advance for any help anyone can offer.
Regards

Carl
 
ProDave,

I had thought of trying to get someone to cast this, but I have heard from current Halcyon owners that it is still very tricky to raise as the load is so high on that point. The mast is 27 feet long and the foot breaks very easily if any sideways pressure is put on them.

This leads to the question, who can cast something like that?

Cheers

Carl
 
carl170 said:
Hi everyone. Once again I need your assistance.

I recently put a post up here as I was looking to find a mast foot for my ancient Sparlight mast, which has no foot, so I cannot lower the mast. Sadly, I was unable to find one from the sources suggested by other PBO forumites.

So, I have decided that the next best thing will be to have a tabernacle constructed out of steel or stainless steel (not sure which).

I need to supply the measurements to a fabricator, who will weld one together for me.

I would love to hear from anyone who has tackled this. I will not be the first, nor the last!
Thanks in advance for any help anyone can offer.
Regards

Carl
Click to expand...


Hi Carl

No sure if this is the sort of thing you are thinking about.

On this mast/tabernackle the mast will pivot by removing the bottom 'through bolt', however the bolts do not just go through the mast walls but through a welded in tube which passes 'through the mast' this gives the mast strength and also prevents it being squashed when you tighten the bolts.

My mast is also 'oval' and I have about 6mm clearance either side between the mast and the tabernackle sides.

The whole tabernackle is mounted with 4off 12mm dia ss bolts which pass through the tabernackle and wood base right through the coachroof and through a 20mm thick backing plate inside with 25mm dia washers under the nuts.

The tabernackle is mild steel but galvanised after manufacture and after 20 years there is no signs of any rust, the 12mm dia bolts passing through the tabernackle and mast are stainless steel.

My mast by the way is 30' high and the base of the mast does not sit on top of the base plate of the tabernackle (about 20mm clear), this is so it will turn easily when pivoting

Hope this might help

Mike


View attachment 45790
 
Last edited:
Mike,

Thansk for your input. That looks brilliant - just the sort of idea I had in mind.

The only tricky thing would be the welding of the tube. I don't know anyone who can weld ali though.

Is it the tube that supports the mast then? I thought the whole idea was that the weight was taken by the foot of the mast. My mast has some sort of concrete or epoxy plug fitted (presumably to make sure there is strength there).

Food for thought though.

Regards

carl
 
mastbase.jpg

I would disagree with the need for a traditional high sided tabernacle as seen in the pictures. From OP photos it looks like there might be some free space around the mast ali within the cast ali box. If so then a SS collar 2mm thick around the base of the mast like 25mm high. The collar is in the form of a clamp with lugs that bend backwards away from the mast that will enable the existing bolt to pass through the lugs. Now unfortunately this bolt is up higher than is desirable. This height means that as the mast pivots back the front bottom of the mast may foul the front of the cast ali box. If you have room at the front for this small movement forward then all well and good if not you may need to mount a pivot bolt lower than the existing bolt. (or cut away some
If you do not have room around the sides of ali box for a collar then you may have to make a bigger SS box or get lugs welded on the the back bottom of the mast.
Another option might be to fashion a box out of angle ali or SS spaced to fit the sides of the mast plus collar.
If these collar lugs are wide spaced ie 50+mm apart then if the mast swings sideways in transit down there is a great tendency to snap off the lugs. If they are really close together ie a "wheelbase" of less than 25mm then with slop in the bolt it can accommodate more swing sideways without damage. Swing should be controlled in transit down but accidents do happen.
Just a few more points. The pivot bolt need not be very big. I use a 6mm 1/4 inch bolt for my 27ft (light) mast. It works in a much larger hole so there is lots of slop. This gives more play for the mast to swing sideways on the way down and of course once the mast is up there is no load on the bolt. I can easily remove it. This bot and the box the mast sits in are there to hold the base of mast in location both fore and aft and sideways.

In the photo of my mast the base sits astride a plate with a spine down the middle which has a raised area of the spine at the back which takes the pivot bolt. So mast pivots on one piece of 3mm SS on edge on the deck to 2 lugs with a gap between them of about 6mm. As you can see form the photo the mast has lugs welded on and a bottom plate also welded on. I think however that the collar type clamp forming 2 lugs will work well. The loads when the mast is in transit are mostly tryiong to force the mast base forward and are greatest with the mast near horizontal. This load can be minimised by having a crutch at the transom to catch the mast which is as high as possible. PM me if you have any further questions.
A completely different option might be to leave the base as is and make up Lakesailor's A frame gantry to lift the mast from above centre point out of your SS box swing the mast to horiziontal and lower to the deck. Perhaps not the best for lowering for bridges but possibly OK for maintenance. good luck olewill
 
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Olewill,

That is a very clever solution! I need to give this some serious thought. The hardest part about the tabernacle will be finding someone to weld alloy. Everyone I know only welds steel!

The idea about making a collar may be workable. As previously mentione there is a plug of concrete in the bottom to hold the shape, so a collar fitted around may just have enough room. I need to find some card about 2mm thick and see how much wiggle room I have.

I had thought this would be a fairly common modification on any yacht that is sailed on a river!

Maybe not!

Regards

Carl
 
carl170 said:
Mike,

Thansk for your input. That looks brilliant - just the sort of idea I had in mind.

The only tricky thing would be the welding of the tube. I don't know anyone who can weld ali though.

Is it the tube that supports the mast then? I thought the whole idea was that the weight was taken by the foot of the mast. My mast has some sort of concrete or epoxy plug fitted (presumably to make sure there is strength there).

Food for thought though.

Regards

carl
Click to expand...

Hi Carl

Yes the mast is secured by the two SS bolts passing through the tubes and as said the mast does NOT sit on the base, if the mast sat on the base you will not be able to swing it in the tabernackle.

Don't forget the aluminium mast is not that heavy (I can certainly pick mine up) and you will find a local fabricator will be able to weld aluminium no problem, I would buy the tubes and drill the mast all ready for the welder to just weld , this will save cost and time.

Mike
 
Caer Urfa said:
Hi Carl

Yes the mast is secured by the two SS bolts passing through the tubes and as said the mast does NOT sit on the base, if the mast sat on the base you will not be able to swing it in the tabernackle.
Click to expand...

I saw one on a wooden boat forum. There was a leather pad a mm or two thick which took up a bit of compression. I am gessing this may be why the bolt is slightly smaller than the holes in the tabernacle plate, to allow that last bit of movement?

The westerley in the club has no pad or shim and I notice that the mast points back slightly. As you say, you cannot swing it square into the tabernacle.

I have also seen another system where the mast foot and the mast base have slight angled bases and then lock together like two triangles coming together to make a rectangle (hope this makes sense!).

What to do eh?

Regards

Carl
 
Hi Carl,

that mast you saw may well be raked deliberately for sail balance and handling properties on that particular boat, presumably for possibly an attempt at pointing to windward or to increase weather helm; though it seems a tad unlikely on the boat in question, but there's no accounting for some people as we've just found when moving house !

As mentioned, welding alloy is no great rare science, has google not helped find anyone local ?

Also re mast foot - hopefully a pivoted job - have you tried Sailspar ? They're a very helpful lot.

A tabernacle is jolly useful, but it takes careful thought & design first re loading and wear on the holes in the mast and how to protect it from wear - and not least against galvanic disimimar metal corrosion - and one has to be sure of the fore and aft mast situation re sail balance & handling, as generally once the mast is in a fitted tabenacle you're stuck with it !
 
On My last boat a Hunter27 in the bottom of the tabernacle there was a was a piece of hard wood that the mast sat on when fully raised. This was fixed and not a removable wedge. With the shrouds compressing the mast I would not like all that weight to be on one bolt especially if it was not sleeved, I imagine the hole would soon elongate and the shrouds go slack.
 
pete said:
On My last boat a Hunter27 in the bottom of the tabernacle there was a was a piece of hard wood that the mast sat on when fully raised. This was fixed and not a removable wedge. With the shrouds compressing the mast I would not like all that weight to be on one bolt especially if it was not sleeved, I imagine the hole would soon elongate and the shrouds go slack.
Click to expand...

As long as the mast can't move and the shroud wires are normal, I don't see a problem; ' T Ball ' fittings seem to work OK, though I don't happen to have them on my mast.

Being experienced with alloy via aircraft I might fit some sort of anti-chafe/ wear under the apertures for T-Ball bits but otherwise shrouds on alloy masts seem to do fine, as long as there's an internal anti-compression tube.
 
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