Under Mast Step Shimming Material?

[delmarrey]

Originally Posted by zeehag

if aluminum corrodes so fast, then why is your mast made of aluminum?? it should last a a few years for ye.

The problem being is that mast bases usually sit in a pool of water, normally on the inside where one can not see, even deck stepped. If there are drain holes, they get plugged with dirt in a short time and hold the moisture just the same.

If you take two pieces of flat aluminum and screw them together face-to-face and spray them with salt water and keep them in a humid environment, they will swell up so bad between them they will look like old battery terminals.

One solid piece is fine but when you mate two pieces together................

I'll take some pictures later today.

[Cheechako]

starboard would be great.

[tropicalescape]

Originally Posted by zeehag

if aluminum corrodes so fast, then why is your mast made of aluminum?? it should last a a few years for ye.

Aluminum oxidises and if you wipe the powdered white oxi. off it makes things worse.leave the powdered oxidation on the surface and it will provide a thin wall of protection,wipe it off and it will accelerate the process...you already knew that ,didnt you?...DVC

[skipmac]

Originally Posted by zeehag

if aluminum corrodes so fast, then why is your mast made of aluminum?? it should last a a few years for ye.

In my case it was an aluminum mast sitting in a steel mast step in a wet bilge. Caused a galvanic reaction and the base of the mast inside the step became the sacrificial anode. The only corroded part was the section in contact with the steel. Common Pearson problem. When I hauled there were three other Pearsons in the yard, two of them had the mast out for the same reason, the third had already done theirs a couple of years before.

[Cheechako]

aluminum out in the air with occassional alst water dousing doesnt corrode that fast, but in a damp bilge, close to other metals and things... makes a nice pile of powder!

[skipmac]

Here's the bottom of the mast I had to cut off. You can clearly see where the Al was sitting in the steel step.

[delmarrey]

Originally Posted by Cheechako

aluminum out in the air with occassional alst water dousing doesnt corrode that fast, but in a damp bilge, close to other metals and things... makes a nice pile of powder!

Here is an example.
This my mast which hasn't change much in the past 10 years b/c I keep after it. I haven't touched it all winter so it's due for some clean up and spray lube/preservative.
I do plan to take it down and cut off a couple inches and shim it back up before heading out next summer. But it's not critical for just bobbing around here in the Sound.

As you can see, aluminum on aluminum, on a plastic shim, on more aluminum. The dark stuff is water coming out, with all the rain today. Up about an inch from the base close the the wires is a pitted spot. When I bought the boat the flooring was right up against that spot. Didn't know that wood could cause erosion, huh! I cut it away and no more progress in that spot.

I need to buy a new mast base casting as this one has about had it. But I am going to set it up on a G10 shim about 18" square, tapered up to the mast base casting. I don't care what it costs!

Anyway, one can see what happens to aluminum pieces mated together w/o insulation.



.

[skipmac]

And the new step. The bottom is 3" to make up for the piece cut off the mast. You can see the Al plate sandwiched between. There are also drain holes in the step and matching notches in the base of the mast.

The base is mounted with silicon bronze lag screws that fit the same holes used by the original step. The two sections are screwed together with silicon bronze screws. Where the screws pass through the Al plate a large hole was drilled in the Al so the bronze screws do not touch the Al plate and the space in the hole filled with butyl rubber.

[neilpride]

Rain water trough the mast draining at the base? We solve this isue this time with a nice idea, we fabricate a plastic template around of the interior mast section with 2 round pieces of pvc hig enough to keep the rain water in this kind of plastic collar, electrical wires pass trough this 2 round pipes trough the end of the mast at the mast step, now before to step the mast, we slide this collar with a kind of flexibe epoxy around to about 4or 5 inches at the deck level, because we install a track in front of the mast for spinaker stuff etc. there is a opening in the bottom with a sheave for lines control and the rain water drain just there.

I tested the other day when is raining cats and dogs , not a drop in the mast step area, dry , mean a dry bilge to . Fantastic.....

[delmarrey]

I might add; I had to clean out about a 1/4" of mud and other debris that had collected inside the base (6 internal halyards), and so bad that the water was actually running out the wire holes (P & S).

neilpride, do you have any way of cleaning out your dam?

[youmeandthed]

don't forget to put a coin under the mast.

[delmarrey]

Originally Posted by youmeandthed

don't forget to put a coin under the mast.

Wouldn't that cause electrolysis from dissimilar metals?

[neilpride]

Originally Posted by delmarrey

I might add; I had to clean out about a 1/4" of mud and other debris that had collected inside the base (6 internal halyards), and so bad that the water was actually running out the wire holes (P & S).

neilpride, do you have any way of cleaning out your dam?

If we unscrew the 4 screws holding the block seave to the mast we get a nice window to vacum all the **** there, we do previously because all the aluminium bits , broken rivets, and other stuff fall here when we put the mast up .

[silverp40]

We had the same problem as other Pearson owners with their masts: dissimilar metals in the bilge plus internal halyards that drain all the water in there.

This solution worked very well for the last 5 years. Underneath the alum step, there is a 2" epoxy and matt/wr step that does not interact with the metals. No corrosion at all yet, mast or step.