How to stop the cabin top lifting?

[Rikds]

I am going to bring my main halyard and reefing lines back to the cockpit. The boat is a 1969 S&S 34 whose cabin roof is a bit flexible. Most systems seem to install tie rods from the mast ring to the mast below deck. What is wrong with the system in the drawing attached?
Stainless steel angle riveted or bolted to the mast above and in contact with the mast ring. They will be covered by the mast boot and allow space for a SS fabricated angle which will take all the pullies (reefing lines, kicker, halyard, topping lift etc.) I might put an HDPE shim between the angle and the mast ring.
The deck cannot move, the mast can be removed without removing them, mast wedges still fit...... what can be wrong? What have I missed?

Ihave attached a drawing (I think, I'm new to this site!)

 

[tviveen]

Hi Rikds,

With the approach you are suggesting you will put all the strain on the bolts or screws you are using to secure the “pulley plate ”. They might break out of the deck under high loads after a wile. The second thing you need to consider is that you will need some strong angle plates to bolt to the mast. A bending moment will occur right in the corner of the angle plates, “ Moment [N/m] = Force [N] * distance [m] The resistance to bending of a profile depends on the type of material used and the moment of inertia, “ Moment of inertia [mm^4] = 1/12 * Breath [mm] * Height [mm]^3 ’’ In laymen’s terms, you need something like box profile, or a beefy L plate if you want to go with this approach.
The third thing you want to consider is the compression in the mast, by effectively attaching the pulleys to the mast, opposed to the keel plate by a rod or dynema line is increased. I would strongly recommend constructing a padeye on the deck, and attaching a dynema line from the keel plate to the bottom side of the padeye.

Cheers!
Tim, Naval architect.

 

[Rikds]

Hi Tim, many thanks for your input, just what I was hoping for! I completely understand your points.
I have attached modified drawings with reinforced angle brackets and a backing plate (which I would have installed anyway) for perusal. I don't think the upwards loads are so great as to pull it through the deck and I intend adding significant epoxy and biax reinforcement between the backing plate and the deck underside, tapered as approved.
However I will look at getting some eye nuts and adding them to the bolts which locate the mast step and adding others to the bolts through the pulley ring and its backing plate. That way the angle brackets will not be needed.
I note that Selden tie the deck to the mast just below the deck which obviously puts the load into the mast, not the mast base.
http://www.seldenmast.com/files/excerpts/595-808-E-68-71.pdf

My problem is trying to do all this without too much disassembling of the interior!

Any further feedback much appreciated.

 

[tviveen]

Hi Rikds,

The changes to the desing seem sufficient! The selden solution is also a good one. I realised that the compression loads on the mast will probably be much lower than on a racing yacht, and that the mast is probably overdimensioned. Therfore i think the load wont cause any problems!

Cheers and succes to you!

Tim

 

[Rikds]

Thanks Tim, now I have to decide down which route to go!!
I appreciate your input.