Alignment of mast pivot with shroud (chain) plates

[Dingo]

the existing holes for the mast plate SEEM to put the hole for the mast pivot forward of a line joining the chain plates across the boat.  By about 1.5 inches.

Before I screw the new mast plate  to the deck, can someone re-assure me please that this measurement is wrong, and the mast pivot point and shroud plates should be in a straight line ?

TIA -


Pic is of the new mast step made by a local shop in 3mm (1/8th stainless), with some extra holes for "Something Useful Later On".  Ironically, it would have been cheaper and quicker to order from Hutchins in the USA, who have been extremely helpful with emails. 

[marc]

On my 19, the holes in the mast tabernacle and the shroud plates are not in line. I know that the shroud plates are aft of the pivot point and 1.5 inches seems about right, but I'm not at my boat to measure.  If I get to my boat tomorrow, I'll measure for you. As far as the plate you have, it looks like it is built heavier than the stock tabernacle I have on my boat. Those extra holes will come in handy too.
Marc

the existing holes for the mast plate SEEM to put the hole for the mast pivot forward of a line joining the chain plates across the boat.  By about 1.5 inches.

Before I screw the new mast plate  to the deck, can someone re-assure me please that this measurement is wrong, and the mast pivot point and shroud plates should be in a straight line ?

TIA -


Pic is of the new mast step made by a local shop in 3mm (1/8th stainless), with some extra holes for "Something Useful Later On".  Ironically, it would have been cheaper and quicker to order from Hutchins in the USA, who have been extremely helpful with emails. 

[skip1930]

" the existing holes for the mast plate SEEM to put the hole for the mast pivot forward of a line joining the chain plates across the boat. "



On all Com-Pac 19's the tabernacle and the vertical slot for the bolt and butterfly nut going through the tabernacle, mast, and through the far side of the tabernacle is always ahead of the chainplates.

On my rig I place one flat washer, each side, between the mast and the inside of the tabernacle to take up a little space and additionally the same size washers are under the head of the bolt and butterfly nut to assist in carrying the load. Makes a nice 'pinch'.

The tabernacle never really carries much load. Not sideways, not forward, and not backward. It's not structural.

If you ever play with the compression post ... it [the tabernacle] just basically places the mast atop the compression post. [Bare in mind that the compression post never sits on the boat's bottom but rather is always bolted with two lag screws through the plywood bulkhead with space underneath the post. Just slap the compression post up under the cabin roof, screw the lags in and be done with it. That's what the factory does.

As per centering ... Think about it. What keeps the mast from falling forward when you push the mast up to vertical with a loose back stay?

The mast goes up with the back stay very loose so the pin [or furler pin] can be inserted through the tang in the bow or bow sprit [if your boat is so fitted].

The ONE thing that prevents the mast from continuing forward are the port and starboard stays [shrouds]. So the tabernacle must be slightly forward of the shrouds.
When sailing the sails and mast 'pull' the boat, that effort is carried to the hull by these stays.

As to the chainplates, each handle one stay. The angle for the stays at the spreaders is different than the stays going to the top-0-mast. So use a separate pin for each chainplate and stay combination. Don't put both stays on one pin through two chainplates.    

Right, left, forward, and back stays center-up the mast. You want the mast straight up and down. Not raked in any direction.
Check this by crawling into the vee birth and sight up the mast to verify the straightness of the mast. Look~see through the open hatch.  
You'll be amazed how little tweaks on the turnbuckles can move, bend, and pull a kink into the mast tube.
And make your spreaders horizontal. Pull them down or push them up with your boat hook before messing with the stays.

"Be mindful that overly tight stays tend to push the mast through the bottom of the boat." Don't do that.

When sailing, the stays on the lee side will be slack while the stays on the windward side will be tight.

What was wrong with the old tabernacle? Why make a new one? Hummm, 1/8 inch is 'way strong'. The ultimate working strength of steel is 10,000 lb times the thickness in decimal divided by 4... so about three hundred and twelve pounds. Makes no difference if its s.s. or black iron.

Bang her back into shape and screw the tabernacle back down to the cabin top.
If the hardpoint [wood] is rotted 'tween the fiberglass just dry it best you can and dump in some epoxy and when cured, screw the tabernacle back down.
If you through bolt the tabernacle down to the cabin top and the mast falls down, that will probably tear up the cabin fiberglass and make a bigger hole. No through bolts. Let her pop free by pulling the screws out of the wood.

Well that might answer your question.

In the last five or six years I have not disconnected any side stays. The mast lays off center on 2 x 4's U-bolted on the bow pulpit and stern pulpit. Off center to get in and out of the companionway easier.

skip.

[MacGyver]

I was reading this and thought, well 1.5 inches isn't bad.... but then I started calculating in my mind how this would affect the rig, and really I think it would be a detriment overall.
Having it forward would help however to cause the side stays to act as a slight back stay. not significant though.

I like this tabernacle you had built, If installed right, it should really be nice when raising and lowering as it would certainly be more sturdy than that of the original.

I just put my boat into storage....... Otherwise I would measure for you.

Mac

[marc]

Hello Dingo,
Took a measurement today. The center of the mast pivot hole is 3 1/8" forward of the center line of the hole through the chain plates. My boat is a 1999. Hope this helps.
Marc

[skip1930]

3 1/8" is very close to my centerline to centerline.

I tied a tight string through the port and starboard chain plate holes in front of the turnbuckle thickness.
From across the cabin top the string to the tabernacle's mast hole was three inches.

Three inches ... That's not all that important, as long as the side stays are behind the mast and the mast is straight up and down.
Turn buckles make up for factory variances. Yes side stays 'pull' the boat along.

Truth be told, I'll bet the combination of the head stay, back stay, and the four side stays could support any CP-19 if lifted by the masthead using a crane and not pull the tabernacle out of the cabin if all 6 stays were adjusted 'a little too tight.  I would not recommend it ... just talking.

Let's see, two thousand ponds divided by 6 is only 333 lb on each stay ... hummm, plausible.

My dolphin stay under the bow sprit parted when I was sailing hard, I wonder how many pounds that took? It's the same diameter and strand count as as all the other stays.

skip.  

[Dingo]

thanks everyone for the friendly and technical advice.

Guess I'll align the shroud plates across the boat, then place and screw the tabernacle some 3 and a smidgen inches ahead of the line.


Making progress but it's slow and with no sister boat within a thousand miles to go and look at, I've got to check each stage.

thanks again