Major Mast Step Repair - Please Advise

[James S]

Originally Posted by gixerjen

Hmm, thinking about it, I would be reluctant to use ally. Unless I could hundred percent remove all condensation between the 2 skins, ally would corrode.... Anyone used nylon? Wouldn't compress, wouldn't corrode, really easy to machine / drill etc??

Yep...wouldn't even have to be as fancy/expensive as nylon...any junk mass plastic may be OK...ABS maybe.

[Target9000]

Originally Posted by gixerjen

Also, the first sketch is one off the internet that should represent pretty much what my pencil sketch does..... his surveyor signed his work off??

On the first drawing you posted, it showed the bulkhead as being able to line up directly under the mast. Your pencil drawing shows this is not the case and therefor a truss is called for. I was confused until your most recent photo and explanation.

I second what the other say about it. Extend it vertically as much as you can to distribute the load. I'd use a big backing plate too.

[gixerjen]

Originally Posted by Target9000

On the first drawing you posted, it showed the bulkhead as being able to line up directly under the mast. Your pencil drawing shows this is not the case and therefor a truss is called for. I was confused until your most recent photo and explanation.

I know, sorry, it was a fairly rubbish representation to anybody who hasn't seen the boat.......


Any tips for glassing the repair up?

[James S]

Your "bracket" may actually end up being a 2x4 or 2x6 lag bolted from the bulk head side...if it extends down to the sole it may look cleaner...although the sole will not carry any of the load....the lags do.

[gixerjen]

Originally Posted by James S

Your "bracket" may actually end up being a 2x4 or 2x6 lag bolted from the bulk head side...if it extends down to the sole it may look cleaner...although the sole will not carry any of the load....the lags do.

Sole and lag?? What do these terms mean please?

I was going to make it at least 6" square in the horizontal, and 8 x 6 in the vertical, where it bolts to the bulkhead. Out of 10mm thick stainless plate.

[Cheechako]

Why not just fill the whole cavity with fiberglass and resin?

[Target9000]

Originally Posted by gixerjen

Sole and lag?? What do these terms mean please?

I was going to make it at least 6" square in the horizontal, and 8 x 6 in the vertical, where it bolts to the bulkhead. Out of 10mm thick stainless plate.

Sole = floor
Lag = the type of bolt you would use to join the "bracket" to the bulkhead.

[Bash]

I'm thinking that a stainless compression post is the way to go. In my boat, the bottom plate for the compression post lies directly on the keel. That seems to be the strategy that will give you the most solid structure.

[gixerjen]

Originally Posted by Cheechako

Why not just fill the whole cavity with fiberglass and resin?

Ermmm, cos it's kinda big and deep?! I think I've really got to fabricate the glass panel off the boat, to encapsulate the ply / ally / nylon pad, then refit it back in the existing space. I was hoping to repair / reuse the part I cut out as I will never be able to replicate radii (radiuses?) like that....

Originally Posted by Target9000

Sole = floor
Lag = the type of bolt you would use to join the "bracket" to the bulkhead.

Ta! Will reread your post.....

Originally Posted by Bash

I'm thinking that a stainless compression post is the way to go. In my boat, the bottom plate for the compression post lies directly on the keel. That seems to be the strategy that will give you the most solid structure.

She's a bilge keeler, not sure I can brace to the bottom of the boat like that in this case?

[Charlie]

Sorry been away for awhile. I'm not sure but I think the idea of the truss has been dismissed. What I saw used was a truss formed like an arched bridge with a webbing inside. The arch and the webbing were made of aluminum square tube and then had a plate which could be bolted to the bulkheads. Not being an engineer but following the load paths I could see where there might be an unusual stress on the plate you are proposing. For instance when on port tack the pressure of the rig would be pushing against the 1 3/8" timber. Assuming there is a bulkhead there to offer sheer support it should be fine but there is the possibility of the mast acting like a gigantic lever. If an arch was used the load would be spread over two bulkheads. I am not familiar with the type or size of boat so the pressures may be too small to worry about deforming the timber.

I think I have a plate if you want me to draw a picture ?

[boatman61]

I used 2 section of scaffold poles and collar... threaded on one end and a plate welded to the other...
Screw the collar right down on the lower(Keel) piece then attatch the other and adjust till happy.. need to measure up right..
Did it on a Hurley... worked a treat..
Mind... I had cut out the non crucial bulkhead...

[Cheechako]

[QUOTE=gixerjen;815962]Ermmm, cos it's kinda big and deep?! I think I've really got to fabricate the glass panel off the boat, to encapsulate the ply / ally / nylon pad, then refit it back in the existing space. I was hoping to repair / reuse the part I cut out as I will never be able to replicate radii (radiuses?) like that....



Ya, just thinking.... you're probably not going to buy one square foot of fiberglass.... most likely in a wide width. Depth is what.... 5/8" plus the reused top piece? So several layers of glass with resin, mush the top piece back on and hold in place. One homgenious repair!

I see nothing wrong with the bracket, most the load is down.... unless the rig's awfully loose! I'm sure it lasted for years with no support. A nice bracket under there should be good to go for a lifetime.

[osirissail]

Just about everything has been covered - except - the bottom of the bulkhead underneath the mast. Normally there are floor (sole) boards and beams underneath that support the floor and bulkheads.

- - What is the condition below the bulkhead down to the keel? Normally a compression post is a stainless steel tube/pipe that is anchored to the keel and runs vertically up to underneath the mast step. This completes the connection between the downward thrust of the mast and the bottom of the boat (keel).

- - If the bottom of the bulkhead being used as a compression post has driven or warped the floor boards (sole) downward and whatever is underneath then you have not fixed anything. Start from the keel and work upwards to the mast step and be sure that there is solid support and no buckling or bending anywhere in between.

- - You might consider permanently fixing the problem by installing a stainless steel tube/pipe between the keel and mast step. This is what you will see on larger boats with deck-stepped masts.

[tropicalescape]

Originally Posted by osirissail

Just about everything has been covered - except - the bottom of the bulkhead underneath the mast. Normally there are floor (sole) boards and beams underneath that support the floor and bulkheads.

- - What is the condition below the bulkhead down to the keel? Normally a compression post is a stainless steel tube/pipe that is anchored to the keel and runs vertically up to underneath the mast step. This completes the connection between the downward thrust of the mast and the bottom of the boat (keel).

- - If the bottom of the bulkhead being used as a compression post has driven or warped the floor boards (sole) downward and whatever is underneath then you have not fixed anything. Start from the keel and work upwards to the mast step and be sure that there is solid support and no buckling or bending anywhere in between.

- - You might consider permanently fixing the problem by installing a stainless steel tube/pipe between the keel and mast step. This is what you will see on larger boats with deck-stepped masts.

this is the way my boat was made but the compresson tube seems to be plan old steel..might change it to stainless..good luck ..DVC

[osirissail]

The dynamics of hull and mast works by the hull/bilge of the boat exerting an upward resistance to the mast which is being pulled downwards by the shrouds/stays which are also attached to the hull.

- - That is the shrouds and stays pull down on the mast while pulling up on the sides of the hull.

- - That mast pushes down on the bottom of the hull in the middle of the boat. Transverse bulkheads (perpendicular to the long axis of the boat). The transverse bulkheads keep the sides of the hull from being bent inwards which is sometimes referred to as "canoeing."

- - In a deck stepped mast boat the downward loads have to be transferred from the cabin top to the bottom of the boat which is normally done by a compression post (pipe/pole). This completes the "diamond" shaped force diagram and the system works. The actual "keel" is not part of this force diagram, only the hull and the mast and stays/shrouds.

- - It appears that your boat has a longitudinal bulkhead that is being used as a compression post/support. I am assuming that your problem as described is the cabin top "sinking" under the downward loads of the mast/rigging.

- - An off center bulkhead as you described will do either one of two things or maybe both. First it has to be connected/supported by the hull at the bottom to complete the force diagram. If it is not, then most likely the cabin floor (sole) has buckled downward which is not an uncommon problem. Secondly, the bulkhead itself could have developed a "bow" or bend allowing the mast step to displace downward.

- - In any case, you need to correct the problem of the "connecting segment" between the bottom of the mast and the bottom of the hull. It makes no difference what kind of keel you have.
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