Rebuilding my mast step

[Wind River]

My 1982 Hudson Force 50 main mast step is in need of repair. At some point in it's life it got water at the step and the plywood underneath began to deteriorate and compress.

It is a wood mast that was stepped directly onto the parquet wood floor with 5/8 plywood under the parquet. Below that there is 4 layers of 3/4" plywood before it comes in contact with a large fiber glassed block that continues to the keel. Just aft of the mast there is a rod that goes from the deck down through all the layers of plywood. From my research, this is to keep the deck from buckling up from the pull of the shrouds on the hull.

This plywood arrangement seem to have worked for 30+ years but I am always looking to better an original design if warranted. I have remove a large area of the parquet and the first and second layers of damaged plywood. It is likely I will remove one more layer just under the area of the mast of about a 12" x 12" square as there still seem to be a slight sag there.

I would like to build this back up using something that is not compressible and can't rot. I am considering using G10 Garolite for this. It is quite expensive for the quantity and thickness I will need, but if it is worth it I will use it. Only the area directly under the mast would need the G10 and the rest of the plywood would be laminated back in place and the parquet restored. The mast would sit directly on the G10. Since there will still be two layers of plywood below the G10 I could bridge this by drilling several large holes through the plywood to the solid step and insert G10 solid rod to bridge this to the solid step

Is this overkill? Is there a reason the wood mast should sit on a wood step?

[UNCIVILIZED]

Since I’m not there to fully inspect things live, my answer below is skewed towards goofing towards the overkill end of the spectrum. So take it with a grain of salt. And I’m thinking that you’re savvy enough to modify my comments to best adapt my plan to best suit the boat, & how she’s put together. Also, some of the below is written for some of the less experienced tool guys here on CF.

So. Based on the configuration of the damage to your current step, specifically the cracks in the plywood seen in the 2nd pic down on the LHS, were it me, I’d use a ¾”+ thick piece of G-10 for the top & bottom plates of the step. And in between them I’d use multiple layers of thin (3mm) plywood bonded together with epoxy. With the G-10 & plywood being bolted & bonded together (again, with epoxy). So that you wind up with a giant structural sandwich comprised of G-10, & (rot-proof) plywood, similar in construction to a cored composite. And I’d anchor the tie rod, & any other high load components to the G-10.

A bit part of the reason for the G-10 being located directly underneath of the heel of the mast is that it’s likely that compressive loads are what cracked the current plywood pieces almost completely through as seen in the above mentioned image. And also that these loads compressing the wood are what aided in it’s early demise via causing the layers of the plywood to come adrift like playing cards from a deck. Thus losing structural integrity.
Which, G-10 won’t compress in this manner, & should also prove better in resisting such cracking.

The reason for the overkill being that on some boats the mast step can see loads in excess of twice the displacement of the vessel. So a stiff, strong base for the mast step is definitely called for. Though it needs to be built with an eye towards properly distributing the loads into the rest of the boat. So without being there live, I can’t say with 100% certainty how best to do this. Though tying in the suggested step base above likely wouldn’t be too difficult. Just don’t terminate any stiff, strong, load bearing structures too abruptly. Nor have them putting all of the load on just a small section of the boat’s keel (interior structural framing).

Another material that is commonly used to construct mast steps is aluminum. As it’s light, strong, inexpensive, fairly easy to bond to, & machines well with woodworking tools. And it could be substituted everywhere above where G-10 is mentioned. However there are plenty of other viable materials that could be used for this. The properties of which can be found at Online Materials Information Resource - MatWeb And there are links to suppliers of any material you can dream up to be found on said website.
The key material properties to look up are With the important one's being; tensile strength, compressive strength, yield strength, & izod notch impact test/resistance. And there's a good thread on sources for G-10 here Good G10 source found - Fix It Anarchy - Sailing Anarchy Forums

[Wind River]

Thank you for your response.
The only thing that might resemble the plywood cracking all the way through are the black marker lines I drew on the plywood so I can duplicate the exact location of the "key hole" the mast locates in should I remove the next layer of plywood. If there is something else I am missing please point it out to me as I don't see it.

In the attached picture the red lines are where the edges of the 4 layers of plywood end that make up the step. The other layer of ply is the floor and what the parquet is attached to. I was hoping I would not have to remove all of the step as part of it goes under a wall.

The other picture is what I had in mind and the would keep the bottom two original layers of the plywood step and replace only the area under the mast of the third layer (3rd up from the bottom) that seems to still be in mostly good condition.

Thoughts?

[Suijin]

Originally Posted by Wind River

My 1982 Hudson Force 50 main mast step is in need of repair. At some point in it's life it got water at the step and the plywood underneath began to deteriorate and compress.

If it's not going to get wet again, then there is really no specific reason to go with the G10; you can build a platform with ply and epoxy that will be structurally adequate and if well sealed, should give you long life. Obviously, the more of it you build out of G10 the longer it's going to last, but that is very likely overkill if you don't have water coming down the mast and your don't have water hitting it from the bilge. It's always tempting to make something better than new, but if it's the difference between it lasting 50 years and 100 years the cost benefit is not with you. "Perfection is the enemy of good enough".

All that said, the actual pocket for the mast does not strike me as deep/secure enough, but it has performed well up to this point so I suppose it's all good. That would probably be the greatest benefit of using G10 for the top, for me; more lateral/shearing strength than wood, if properly bonded and secured to the entire assembly.

Whatever you build, do make sure you design in some drain channels, if only to protect the bottom of the mast.

BTW, the post you mentioned, from your description, is a "panting rod". It's purpose is to stabilize the coach roof, and, as a result, the hull sides. It keeps the whole hull from "breathing" in a seaway during cycling stress from the shrouds.

[Wind River]

Originally Posted by Suijin

If it's not going to get wet again, then there is really no specific reason to go with the G10; you can build a platform with ply and epoxy that will be structurally adequate and if well sealed, should give you long life. Obviously, the more of it you build out of G10 the longer it's going to last, but that is very likely overkill if you don't have water coming down the mast and your don't have water hitting it from the bilge. It's always tempting to make something better than new, but if it's the difference between it lasting 50 years and 100 years the cost benefit is not with you. "Perfection is the enemy of good enough".

All that said, the actual pocket for the mast does not strike me as deep/secure enough, but it has performed well up to this point so I suppose it's all good. That would probably be the greatest benefit of using G10 for the top, for me; more lateral/shearing strength than wood, if properly bonded and secured to the entire assembly.

Whatever you build, do make sure you design in some drain channels, if only to protect the bottom of the mast.

BTW, the post you mentioned, from your description, is a "panting rod". It's purpose is to stabilize the coach roof, and, as a result, the hull sides. It keeps the whole hull from "breathing" in a seaway during cycling stress from the shrouds.

Thanks for your input and especially this:
"It's always tempting to make something better than new, but if it's the difference between it lasting 50 years and 100 years the cost benefit is not with you. "Perfection is the enemy of good enough"."

I tend to think that there is always a "better way" and that way is worthwhile. Not always true....... the worthwhile part of it anyway.

The pocket for the mast is 1-1/2" deep. Drain holes were on my list of "better way - improvements". I think if they were originally there I would not be doing this repair today.

Thanks for the proper term of the panting rod. I knew what it's purpose was but could not remember what it was called.

It would seem a combination of sealed plywood and a some G10 is going to be a good solution.

Thanks again, all input is welcome.