Mast foot/tabernacle construction advice

[jpeach]

Hi Folks,

I'm contemplating doing a mast replacement on my 28ft ketch. It's a custom built boat from the 80s, so this would be just another modification!

Currently it has a main mast of about 9m from Proctor, which has seen better days - lots of surface corrosion and holes from old fittings. I've come in to posession of a nearly new Zspars mast at the yard I'm in from someone converting a motorsailor to a motor boat. In most ways it could be adapted to fit the size and geometry of the existing mast + spreaders + standing rigging. Its about 1ft too long currently so i've got some scope to cut it down

I'm contemplating the mast foot arrangement though. And with the change giving myself the possibility of raising and lowering the mast myself.

The current mast is deck stepped, and the new one would be too, and there's two options

1 - get and fit a new mast foot from z spars

2- build a more robust tabernacle with a pivot point maybe 1ft from the coachroof/mast base

In an ideal world i'd be keen to go for the latter, but struggling to understand

1) how the mast base would make contact with the base of the tabernacle/coachroof when raised to transfer compression loads and still be able to pivot - would an angle need to be built into the tabernacle/cut into the heel of the mast? or some sort of wedge?

2) how to approach getting the tabernacle tight enough to the mast sides to prevent lateral movement when the mast is raised but still free to swing.

Any input or advice on the above would be greatly appreciated!

Alternatively, do folk have any experience of self-raising a mast of this side with a more conventional foot - by using a gin pole or a frame? Most things online seem to apply to smaller spars

For reference this is a smaller version of the type of zspars mast foot i'm talking about https://forums.sailboatowners.com/attachments/1718493888313-gif.225442/ (can't find a photo of the right one easily)

 

[Boathook]

My boat has a tabernacle and the shrouds fixing point is raised up to keep tension whilst the mast is lowered to stop it swinging side to side. I will try to get some pictures and post here in the next few days.

Had the same set up on a previous boat and lowered the mast once with help from 4 friends. Mast went back up with the yard crane as so much easier !

 

[William_H]

I would not seek to get a tabernacle as in parallel posts either side of mast tight enough to avert swing sideways when mast is in transit. (ie 45 degrees) Just too much leverage you need to be able to stabilise the sideways movement with stays. If stays are inline (abeam) the mast then use chain plate extenders to get pivot in line with mast pivot.
Now you need to decide what cabin top etc will be in the way of mast when it is down in support crutch. This assuming you will pivot the mast backwards. Pivot forwards might be an option given it is a ketch which may have mizzen mast up. This may be strong enough to user as a gin pole.
You could use parallel posts to get pivot point up high off deck. (ie 1ft as you mention). Or you could just build up a grp or wood base to get a pivot a few inches above deck. All depends on what height you need.
Yes the bottom of the mast needs to take the huge compression forces downward when sailing on to the deck and then the support post under neath. You need to havee lots of free play in the pivot so no load on the pivot axle when sailing.
Deck mounted bases have the pivot at the back of the bast so base of mast initially lifts up off the base.
My mast a lot lighter than yours has lugs welded to the back of the mast bottom and a plate welded across the mast bottom. Also seen is a casting with lugs that the mast sits on. There is a spine 2cms high on the base which helps locate the mast and stop twisting forces. In my case base is on a GRP plinth about 2cms high but shaped to get mast base level on a sloping cabin top.
Around here many boats (hundreds) are homed in Swan River. Masts must be lowered to traverse under bridges. Your size is typical of so many boats but many much larger which lower their masts for bridges while under way. Horrible procedure but you get used to doing it. Support of mast sideways is essential.
As I write this my river club have an event to Rottnest Island such that maybe 12 of my friends will be lowering their mast to traverse the bridges this morning and doing the same thing tomorrow on return home. About half those boats are bigger than yours. ol'will

 

[LittleSister]

Yes the bottom of the mast needs to take the huge compression forces downward when sailing on to the deck and then the support post under neath.

Don't forget, in designing your tabernacle, that the mast foot is one of the main components (along with the mast stays chainplates and mainsheet) dragging the boat forward and sideways through the water under sail. You need something - a socket for the mast foot, bolt or whatever - to prevent the mast moving forward or sideways under loading from the sail, and to transfer those substantial loads to the deck and any beam under the deck.

I would imagine that the pivot bolt a foot above the deck alone might not be good for that, or would at least require significant bracing, especially laterally, to successfully do that.

 

[syvictoria]

Not sure where you're located, but mast lowering with a tabernacle and a pole (often utilising a spinnaker pole) or A-frame (better, as it vastly reduces potential sidewards movement) is a common setup on the Norfolk Broads, so you could look there for inspiration. Yours is perhaps larger than many alloy masted yachts there, but there are a number of 28+ footers with this setup, many having their origins in the hire fleet where things need to work reliably and easily. I've seen a couple of DIY setups where the pulpit has been made to double up as an A-frame. It's a clever arrangement, although perhaps not always the most graceful looking design. Here's an example:
1965 Norwegian Troll 32 Motorsailer

 

[Fantasie 19]

I have a boat with a tabernacle and it makes dropping a raising the mast considerably easier, but you still need to guard against the mast swinging side to side when raising lowering... if you want to go the tabernacle route, you also need to make sure that the mast is internally braced between the holes used for the hinge/screw.. mine has a tube inside the mast that the screw then goes through - I'm assuming because you're supporting the weight of the mast on just two holes in the side of it otherwise, but it will also protect again crushing the mast by overtightening...

 

[Refueler]

I have had 2 boats of my own with the tabernacle .. and I LOVE THEM .... I wish my present 25ft'r had it ... but she has the slot and blade arrangement ...

OK ... to assist the mast with vertical compression ... a wood or hard rubber wedge shape in the base of the tabernacle - so the mast pivots in and heel sits on the wedge. But not taking all weight - it should share with the bolt. Its a good idea to have a through tube and plates either side to avoid mast alloy being worn and elongated.
To help prevent sideways movement of the mast on the pivot bolt ... you could put a rubber or wood disc either side ... but TBH - none of mine had such and there was a small gap between mount sides and mast ... never had mast move ..

Raising and lowering .... I advise against a single gin pole ... too easy for mast to fall off to side ... better to have a light A frame ...

William H talks about extending cap shroud chainplates to be level with mast pivot bolt ... this is a good idea if you want to raise / lower mast often ... but if you only want to raise / lower rarely - basically to service mast - then its not really needed - if you use an A frame and careful.

 

[LittleSister]

Re-reading the thread and picking up on your second question, I agree with William H that you can't rely on the tabernacle to stop the mast swinging from one side or another. You would risk damaging the mast and/or tabernacle, or tearing the tabernacle out of the deck, if the mast swung to one side.

Chainplate extenders
Instead you need to support the mast laterally much higher up its length. One way to do this is with an A frame, another (more common?) way to do this is to use the cap shrouds or a temporary pair of not-too stretchy lines taken from the mast head or other point high up the mast, and secure the other end to chain plate extenders to (usually) temporarily (could possibly be permanent) raise the point at which the shrouds are anchored to the boat to points in line with both the height and forward/aft position of the pivot bolt you are swinging the mast on as you raise/lower it. (It does not matter if the temporary point of attachment of the shrouds/lines are slightly inboard or outboard of the normal position. These shrouds or other lines are not put under tension while raising or lowering, but must have no slack.

Typical shroud extenders I have seen are two stainless bars of a measured length each side, to lift the pivot point and hold it securely in the forward and aft directions. The lower end of one would be fixed to an appropriate deck fitting (e.g. lower shroud chainplate, guardwire stanchion base) forward of the mast pivot point, and the other to a similar aft of it. (It does not matter if these fittings are a little inboard or outboard of the cap shrouds' normal position.) The other end of the two bars are raised and fixed together (exactly in line with the mast pivoting point.

If you are using existing shrouds for the job, you need to cut them to insert complementary fittings (e.g. fork and eye, or (smaller boats only?) a pair of interlocked hard eyes) at the raised attachment point, with the short lower section top end fitting interlinked with, or reconnectable with, the lower end fitting of the main upper section, so that the shrouds can be removed from the shroud extenders and refitted to the normal chainplate fitting once the mast is raised and supported in place by the fore and aft lowers or whatever. (The lower section of the shroud is redundant while lowering and raising.

The new shroud anchor point created by the chainplate extenders could also potentially be used for lines to hold a gin pole in position centrally (might need lateral support?).

I am amazed that I cannot find a picture online of either the type of chainplate extenders I am trying to describe, nor a shroud with a 'junction' to use them. Perhaps someone has such picture or could draw a diagram?

A Different Method (Little Sister patented!)
I have also raised a mast on a 22 footer without chainplate extenders or A-frame, using a slightly complicated system of lines of my own devising. The mast foot had a pivot bolt at the back of the mast. The pivot point was on the cabin roof, so typically significantly above the level of the chainplates. While the mast was down I connected the backstay, aft lowers and cap shrouds in place (adjusted very slightly longer/looser than normal), and left the forward lowers, cap shrouds forestay unconnected. (Pay attention that all the stays are run correctly and not tangled around one another or the mast, spreaders, etc!) In theory the cap shrouds could connected at this point, but I needed to attach something else through the cap shroud chainplates, as explained below.

I used a spinnaker pole as a gin pole, fixed to the spinnaker pole eye fitting on the front of the mast. I tied lines from the forward/top end of this gin pole to the forward lower chainplates to hold it central. I knew these lines would loosen as the mast was raised, but the gin pole would only be able, I reckoned, to fall a little to one side or the other of the centre line, and would be held in that position on whichever side as the mast came up, and so it proved. From the forward/top end of the gin pole I tied my the end of my mainsheet block and tackle normally attached to the boom, and the other (mainsheet car) end to the bow fitting where the forestay would normally terminate (the mainsheet block there had a cam cleat which was extremely helpful, but I had to adjust the angle it made to the block for this job). Also attached to the front/top end of the gin pole was a strong 'lifting' line taken over the spinnaker halyard block.

And now the cunning bit (if I do say so myself!), the other end of the lifting line was not fixed to the mast, but tied in front of it (securely!) to two lateral lines, each taken to the cap shroud chainplates on either side of the boat, and making an angle of IIRC about 45 degrees to the mast. As the mast is raised the distance between the cap shroud chainplates and the mast reduces, (which is why you can't simply use the cap shrouds to hold the mast centrally as the mast is raised/lowered) but the tension on the mainsheet tackle/lifting line pulls the lateral lines taught. If the mast falls a little to one side for the other, all the tension from the comes on the opposite lateral line pulling (in practice holding) the mast centrally again.

Once the mast is upright it is held quite securely by the lifting line/mainsheet tackle forward, the backstay and aft lowers aft, and the aft lowers and lateral lines, er, laterally. You can now connect the forestay and forward lowers at your leisure. With the four lowers then holding the mast laterally, you can now disconnect the lifting line and lateral lines, fit the cap shrouds, and then tension the rig.

My system worked OK (with just myself and my not particular tall, strong or mechanically minded girlfriend of the time), but an A-frame would have been much less stressful. I was very aware that had any one of a number of lines, fittings or knots failed, a very expensive disaster was likely. A mast is very easy to control by someone standing on the boat when it is near horizontal, and also when it is very nearly vertical, but it's the crucial bit when it's halfway up that it becomes unwieldy and where the danger lies, especially if the boat is afloat and could roll, or if it's windy. (Might be less of an issue if you have a crew of several tall, strong people.)

 

[William_H]

One important point to make is that an A frame (I use 2 spinnaker poles) will not stop the mast swing from side to side as it goes up/down. If the boat is on the water the mast swing sideways, heels the boat over to make gravity increase the swing and things go bad very quickly. On a small boat people movement on on deck can precipate the swing. Not quite such a risk if on the hard.
The A frame can be substituted with a single guyed pole but 2 poles seems easier.
Shroud extenders are the best choice for a mast head rig with in line shrouds. For a fractional rig, chain plates aft of abeam the mast of course no good.
One fiddly method and not so positive is to attach a bulldog clamp to the stays around level with the mast pivot. A tackle on each side runs from this clamp down to a point on the gunwhale a similar distance forward which is adjusted or continually adjusted to keep shroud tight through the traverse.
I have seen a trailer sailer 26ft fractional rig with permanent intermediate shrouds down to chain plates on cabin top outer edge which does hold mast central in traverse but does not aid mast support when sailing.
On my little boat with usually enough crew I rely on a man on cabin top holding mast central. But last raising did have a calamity after 45 years of raising lowering evry winter I got careless. I keep promising to add dyneema additional stays which can be unclipped and tied back to mast. (next winter) i am just reluctant to fit more chain plates to cabin top.
Fred drift. I mentioned friends from club in an event requiring mast deop for bridges yesterday. I have done this event many times but just too old now. I am so glad I was not there. The weather was horrible. 1000 am start and no wind for a few hours and 40 degrees temperature. ol'will

 

[Refueler]

OK .. on reading various I think some explanation / detail is needed :

I've had various forms of mast foot / step .... ones that mast slots over ... ones with mast slot that sits over a blade .... ones with tabernacle high and low versions ... tabernacles with single and dual pin .... (keel stepped as well - but not relevant here).

Misconception by some : A frames do not stop sideways movement of mast during raising / lowering. But the advantage of A frame is that it does not need side guys to prevent the frame falling to side as a Gin Pole does. I know Gin poles do - it happened to me and luckily mast survived the fall.
The mast is more easily controlled by one man as long as boat stays steady ... any helper remembers to to NOT move about - just guide the mast up / down.

Notice that even furling gear can stay as is ... the curve it makes is not a problem and can easily be gathered up to stow.... I did later change to having furling gear and forestay 'loose' and only use the halyards to A frame.

OK ... Extended chainplates .. excellent idea - but the question becomes either permanent - needing new cap shrouds or cut old. If temporary - then how to connect to mast ? If you clamp the exosting cap shrouds - you introduce a sharp bend in the wire .... not a good idea - so it means having two lines hoisted up to create the necessary side control guy lines.

Tabernacle and its mount to deck ... if the Taberbacle is believed to be capable of 'ripping' out of decxk - then either you have a bad mounting or an unusually strong mast ! I have seen in yards BENT masts where its fallen to one side and mast itself has bent just above the tabernacle. I have been lowering my Tabernacle mast on a boat I had some years ago - Sanpdragon 23 ... my 9yr old son and I ... no frame or poles ... we did it for lift out / lift in .. servicing mast etc ... but one time in Langstone Hbr .. a bunch of Jet Skis decided to carve up the mooring area while mast was going down .... luckily we managed to stop it twisting / going too far sideways .... to this day - I believe that because the tabernacle had a small gap from side plates to mast - that allowed the mast to move enough ... saving it.

Of course now that I have the truck with HIAB ... mast work for me at home is a doddle .... but I still have the A frame ready to do its job.

 

[Boathook]

My boat has a tabernacle and the shrouds fixing point is raised up to keep tension whilst the mast is lowered to stop it swinging side to side. I will try to get some pictures and post here in the next few days.

Had the same set up on a previous boat and lowered the mast once with help from 4 friends. Mast went back up with the yard crane as so much easier !

I got to the boat but didn't take pictures as I didn't refit the tabernacle. I've got extended cap shroud fittings so the stays pivot just below the mast pivot point so stopping / reducing the mast swinging side to side.

I still prefer a crane as the mast is heavy and around 35 feet long. Add on all the extra bits such as headsail furling, radar, etc it is a lot of weight.

 

[William_H]

I got to the boat but didn't take pictures as I didn't refit the tabernacle. I've got extended cap shroud fittings so the stays pivot just below the mast pivot point so stopping / reducing the mast swinging side to side.

I still prefer a crane as the mast is heavy and around 35 feet long. Add on all the extra bits such as headsail furling, radar, etc it is a lot of weight.

It is one thing to be able to lower mast down in to a crutch at the stern (for traversing under bridges) but if you want to remove mast or work on it you have physically lift it off the boat or at least slide it forward until you can reach mast top. All difficult with heavy/long mast. Note when mast is down in stern crutch it is usually quite over balanced with an up load on the base or tabernacle.
I helped a friend l;ower mast on water under way on a 20fter .only to find base was screwed to deck with very corroded bras screws. The base lifted off the deck and only physical push down stopped mast top ending up in water. ol'will.

 

[Refueler]

It is one thing to be able to lower mast down in to a crutch at the stern (for traversing under bridges) but if you want to remove mast or work on it you have physically lift it off the boat or at least slide it forward until you can reach mast top. All difficult with heavy/long mast. Note when mast is down in stern crutch it is usually quite over balanced with an up load on the base or tabernacle.
I helped a friend l;ower mast on water under way on a 20fter .only to find base was screwed to deck with very corroded bras screws. The base lifted off the deck and only physical push down stopped mast top ending up in water. ol'will.

Of course its often case that mast gives a rearward bias in weight ... and as per my 25ft'r ... it takes 2 good people to lift mast and slide it fwd to even up ... but I can say that my mast and most would not have enough aft of crutch ... it would need over 50% of mast to overbalance. If that was not true - taking the pin out of the mast base would have mast pivot into the water ... none of any boats I have did this .. I took pin out and mast stayed as is.
I appreciate that some boats have longer masts and it is possible.

If your pal's mast base lifted out - then maybe its good that happened .. 'brass screws' ??? My 19ftr .. my 23ftr and my present 25ftr all have substantial bolts on doubled deck plate etc. Reckon you could lift the boat by it !! And did he have his crutch s far aft as possible right at transom ??

I am lucky of course that I have own HIAB and home mooring channel ... so lifting mast on / off boat - moving along boat is a simple job ... In fact I now use the HIAB with its winch to raise ... lower mast ... ( boat nose into bank ... midship lines out to each side to hold her 90 deg ... HIAB then attached ... mast up / down as needed. Boat then turned to be alongside ... HIAB then lifts mast off boat etc.). Joys of own facilities !!