Mast Step Repair

[SeanR]

Dave,

I am in the process of re-coring the coach top (with balsa). The affected area is from the keel hoist to the front of the coach roof. Appears most came in around the downhaul block mounted on the coach roof. I am not sure if the mast step is wet, but given the degree of rot and water I am willing to bet it is. Spider cracking is visible in the gel coat around the mast step. Not alot but some. I have removed the step plate and poked around in the bolt holes but nothing is soft or wet.

I am doing the coach top from below and realize the mast step must be done from above. Have you completed your repair? What are your recommendations for build up (glass, plywood, etc.) for the area under the step? From below, there appears to be a white or light grey material above the metal plate. Any idea what this is and does it have to be removed? Thanks.

SeanR

[dave]

The Coosa board still sounds like the best bet to built thickness AND have something that's waterproof. I'm going to stay away from an aluminum plate inserted in the mix and use mutliple layers of heavy carbon cloth instead, combined with 1708 Knytex fabrice for the majority of the rest. I use that fabric in 95% of my repair work, great stuff. I will also be buying some carbon tubing to use as compression struts for the machine screws that bolt the step on. I don't want to use SS because of the bonding problem to the rest of the repair. Of course the whole plan is to keep the water out, but that's tough to do sometimes no matter how hard you try and no matter what one uses. I do think that this method will do the trick though because with everything combined and rebuilt properly, there should be no compression and/or movement of any part of the job which is what leads to the caulking seal breaking in the first place. As I have already stated so many times before, even if water ever does get in if there's nothing to absorb it and rot or corrode, there's not a problem. The original aluminum plate that the SS machine screws tap into just acts like a battery once wet. As the corrosion process advances the aluminum oxide actually expands the dimensions of the plate and tends to push everything apart, making matters worse. The same thing brings down mountains as water freezes in minute cracks in the rock, over eons. Aluminum corrosion works MUCH faster!!!!

[SeanR]

I take it you are talking about removing the aluminum base plate? Is it attached to the keel trunk or does it just set on top? I feel like I should be able to see it from underneath, but cannot. Also I notice the underside of the cabin top is not tabbed to the keel trunk. Should the repair include installing tabs or let it ride separately?

SeanR

[dave]

It's in there. You will surely find it when you cut all the junk out. The plate was glassed in when the deck was laid up and then whole arrangement just sits on top of the board trunk to take the compression load. You probably wouldn't be getting the cracks around the step if there wasn't an issue, and moisture is the issue. Tabbing in won't make the mast step area any stronger. The trunk has to be glassed/bonded to the deck somehow or you couldn't sail the boat with the board partially raised without risk of tearing the trunk out. I would bet that the top of the trunk was covered with the same goop that was used in the mast step to bond it to the deck upon installation.

Dave

[Marionete]

the tapered / curved area surrounding my mast step began to fracture as well, so I replaced the core under the step plate only. You can cut through the gelcoat and cloth layers using a grinding wheel or a small (4 1/2 inch) circular saw. Just use the bolt holes as a guide and saw out the area inside the "dots". The mast step is thicker forward than aft. Once you peel away the 3/8 of glass, you'll find plywood - and probably wet as well. You can cut this away or use a chisel, but you'll get to the plate under that layer. You might give the opened up step a few weeks to dry out before enclosing it again.

The rest is just a rebuild. I used coosa bluewater 126 and tapered the aft end. I also stair-stepped the layers of glass to distribute the load and tab the new cloth into existing. It's a good idea to insert some dummy bolts into the screw holes while glassing back together - othewise you'll need to drill and tap the holes to accept the bolts again.

Make sure to flatten any dimples in the stainless plate before re-fastening. Caulk the entire perimeter edge of the plate before re-attaching, caulk the deck bolts as well. I have yet to "field test" the repair. but you can't tell that the mast step was repaired if you do it this way. Otherwise, there's always the cosmetic issues to deal with.

[SeanR]

Ok, I'm with you so far. Can you explain the carbon tubing compression struts for holding the SS machine screws that hold the mast step in place? I'm a little lost there.

SeanR

[dave]

They may or may not be necessary on this job with these materials but it's such a large project that for what little extra is involved, I'm going for it. After remembering what the mast base looks like I've changed my mind about the type and placement of the compression tubes. Because the mast base is rounded it REALLY point loads the SS plate and the deck directly underneath. That's where two small diameter carbon compression tubes would help absorb and distribute some of the load between whatever type of plate that you use and the top [outer most] skin of your repair. This is actually easier than it may sound. Once you have your area ready for the Coosa Board to go back in, cut that to fit and bond the sections [if it takes more than one thickness] together, but not to the deck yet. Then [after it's cured of course] set your bonded Cossa Board section back in place and do some careful measuring and figure out where dead center of the mast butt will sit. Using this as your center, and with a piece of wood for a backstop, drill a couple of plugs out of the Coosa Board with 1" hole saw, side by side. The kerf that is made by the hole saw will allow one to wrap the plugs with carbon fiber plenty thick enough to take the compression, but when added to what's already being done the darn thing should be compression proof. It's relatively easy to figure out how much carbon cloth you will need to fill the kerf, just wrap it dry and see how many times around you will need to go to fill the void. I would then lay these up and let them cure, sand to fit the holes and then bond them into the holes. You could use SS tubing too but it gets right back to the bonding issue, plus when you need to mill the top or bottom of the Coosa Board section to make it smooth, the tubes will grind/sand down with it instead of heating up like metal and melting the Coosa Board.

I am going to use Vinyl Ester resin for my repair because it's easy to work with and cures like polyester and becomes sandable/toolable quicker than epoxy and it's stiffer than epoxy, and it's cheaper. Epoxy is stronger but this is all compression anyway and the bond strength is way high.

Like Marionete says, make sure your SS mast plate is flat and true. Mine looks like it was run over by a truck, that's how bad the deck was caved in. Hey, we still kicked everyones butt for both series and the overall that season. Just imagine what the boat will be like when everything is in the right spot and aint saggin'!

Dave

[Mookie]

'Bump'
Hello everyone, I know the mast step repair has been well covered, but one question: would solid fiberglass or fiberglass board be a better build up material than coosa board? It might weigh a little more, but in that small area it wouldn't be significant. Opinions? Experience?

[AJ Oliver]

Hey Mookster -

Short answer is yes, in fact we used solid glass with chopped strand, sort of like "mini re-bar."
The repair is not difficult - easier than doling the deck area under the cockpit winches or stanchions.
There is a trick to deal with the point loading on the base plate.
And another trick to put a permanent end to water intrusion down through the base plate.

If you give me your email I'll send you photos.

Disclaimer - All these ideas were from my brilliant machinist crew guy.
I was just smart enough to do what he told me.

[Mookie]

Thanks AJ,

I cut out the entire mess down to the trunk, removing the very corroded aluminum plate along the way. Ground a flat spot and bedded a replacement stainless steel plate with West System epoxy and 404. Then rebuilt the step with a solid stack of 1/2" G10 epoxy plates. To spread the final load and eliminate point loading, I greased the mast step plate and bolted it onto the final layers of wet cloth and epoxy for a conformal fit. That's the briefest of descriptions with the details left out. So far so good.

Bill

[Mookie]

AJ,

Had I seen your generous offer of photos before wading into the repair myself, I would have gladly taken you up on it! This is what I came up with on my own, in blissful ignorance.

Thank you,

Bill

[Ed]

Still unclear if the repair is done from the inside to remove plywood and then a new 4.5 inch plug placed into the mast step area?

If so, how big an area to peel the carpet to be comfortable??. I saw 13 in across and 16 in long . Another section on each side of the trunk about 5 inches as well. IS THIS WITHIN THE 13 INCHES ACROSS AND 5 INCHES AFT?

Is the 4.5 inch plug alone enough or not to keep sailing? Do I lay up fiberglass. coosa board, or bond in g10 or fiberglass to replace wet wood from under, and then do the plug from the top? Is high density west 404 and epoxy enough for the plug - as I don't compete in class the weight is not an issue for me.
Just being reluctant to start - I supposed none of this corrects the spider cracking on the deck but keeps it from getting worse.

[AJ Oliver]

Several of you mentioned concern over point loading on the base plate.

My genius mech crew also noticed a depression on the plate where the mast base rests.

So he welded an extra piece of stainless to the plate, about 1/8th I think

Problem solved