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