Mast corrosion

When we purchased Shamrock, we noted salt crystals and what appeared to be some minor corrosion at the base of the mast and mast step. When we replaced all the mast lights and repaired the wiring last year, I began to clean and scrape most of the loose flaking paint, salt crystals and corrosion from the base of the mast, bottom 2".

We had the boat surveyed last week, only item of note was the mast base and step, noted as minor corrosion, nothing serious.

As Paul Harvey says, “now for the rest of the story.” As noted earlier, near the base of the mast on the port side was the DataMarine knot log, no plug to install while cleaning, this must have been intersting trying to service this with water gushing in? We replace the knot log with the new knot log sender as well as the depth sounder, still new in the box, they tried to adapt the Data Marine depth sender to the new West Marine Multi-data display, naturally it didn’t work properly. There is also a Dyna Plate for SSB, to which the mast, chain plates, stem and boomkin fittings are bonded.

I got into the cleaning mode today while the Svendsens guys were applying the last coat of barrier coat and bottom paint. I scraped and wire brushed the mast step and base of the mast, the hardest area to reach required laying on the port seatte and working on the area of the mast where the bonding wire was attached to the mast step. Suprise, suprise, surprise, as Gomer Pyle would say, I found a 1" diameter corrosion depression in the mast near the base ajacent to the bonding wire, 2/3 the depth or the mast thickness.

We are planning on pulling the mast next week after we launch, we are planning on cutting the last few inches off the mast and adding a shim under the mast. While the mast is out, we are planning on touching up the paint and get ready to sail.

I talked to the guys in the yard, they tend to believe the bonding of the mast is often found to cause a corrosion issue in this area. I tend to agree in part as the corrosion spot is directly above where the bonding wire is attached to the mast step, however the depression is not at the very bottom of the mast in contact with the step? I tend to believe allowing saltwater to pool around the mast after cleaning the knot log sender, possible drainage from the chain locker and lack of a proper drain in the mast for rainwater was probably more of a contributing factor to corrosion.

I’m going to Svendsen’s in about 2 weeks to pull my mast for new wiring and to replace standing rigging.

Adventure also has corrosion around the base of the mast at the step and the mast is not bonded. It looks as if the step and mast might not separate very easily so instead of trying to lift the mast off the step, I plan to remove the step lag bolts from the keel and raise both mast and step about table height. I can then use a woooden block and hammer or heat or whatever it will take to remove the step without undue strain.

Marty, how are you planning on shimming the mast after cutting off the corroded part?

John Purins

Svendsens Marine has a check list of things you as an owner should and can do prior to having you mast unstepped (removed). Please follow the check list as it will save you considerable time and money.

The list is basically:

  1. Remove your sails.
  2. Remove your Boom.
  3. Wrap tape around the threaded portion of your turnbuckles to show where the turnbuckles were before the rig was loostened.
  4. Remove the cotter pins inside the turn buckles.
  5. Straighten the cotter pins at the chain plates to make them easy to remove, do not remove them.
  6. Remove the turnbuckle cotter pins in the dolphin striker turn buckles and slacken tension of the dolphin striker to relieve downward tension of the bowsprit.
  7. Secure all lines to respective components, roller reefing lines to the drum, halyards to the mast.
  8. If you have the conventional dinnet table, remove it. Remove the interior mast collar-teak trim. Loosten the mast boot, make sure it comes free.
  9. If you have anything attached to the mast on the interior of the boat remove this as well, ours had a 1/4-20 drain bolt, even this will catch when clearing the cabin top.
  10. Disconnect all wires at the base of the mast, good time to check wiring for corrosion in connections. If you have an older mast examine and plan on replacing wiring and light fixtures as necessary. If you have any easy pilflerable item like a quick disconnect masthead tricolor remove and store it.
  11. With a hand bilge pump and small suction tube, pump any remaining water out of the the mast through the wiring hole at the base of the mast. Replace the water with penetrating oil of your chosing. Have 1/2" thick oil asorbent pads ready to catch the oil as the mast step comes free.
  12. Remove the hatches around the mast.

We have a Forespar aluminum mast and step with 4 bolts securing it to the hull. The typical proceedure is to unscrew the bolts and lift the mast, with a sledge hammer and a block of wood against the mast step they drive the step from the mast. If you did not remove the dinner table, it is now in the way and probably getting banged up! This is a tough job and the yard guys need fighting room, so remove the table.

Best wishes,

When cutting a small piece off the base of the mast, the yard cuts penolic spacers to place under the mast and longer bolts. Standing rigging remains the same length.

In cases where more extensive damage is present, the yard will have to find a section of mast extrusion to match your mast, butt joint and sleeve the section on to obtain the original length. In extreme cases the mast will have to be replaced.

We are planning on pumping out the remaining water in the base of the mast and pumping in penetrating oil, lots of it. I suspect as usual, we will wind up using a block of wood and a sledge hammer to drive the mast step from the mast, probably break it in the process. If necessary, the yard will build a new mast step and use phenolic shims to get the heigth back after cutting off the corroded section. At present, we are only talking about cutting off a few inches, will know more next week as the mast comes out.

If you have the conventional dinning table as we do, attached to the forward bulkhead and a aft post and socket arrangement as we do. I recommend removing the set screws in the aft post at the top of the post (underside), then remove the bolts in the forward bulkhead, the table then lifts off. Don’t force the yard to work around the table, to easy to bugger up. I also removed the teak trim around the mast inside.