How to protect a deck-stepped mast from freeze damage

[tessellate]

I know of two boats that had to replace their masts after the deck-stepped mast base froze in the winter. Both of them happened to be Jeanneaus in the Pacific Northwest (Vancouver to Seattle area). Boats in this area typically don't haul and unstep for the winter. We have a year-round sailing season, but on occasion there can be snow and temperatures below 32 F (even down to 10F in a few recent winters). 

Any tips on foolproof ways to prevent mast freezing (other than taking it down)? This is such a serious problem (very expensive to replace a mast, especially if you have to do it every winter!) that it seems worth taking every precaution to address. 

In the two masts that cracked I'm guessing they had limber holes / drain holes at the bottom that got plugged up by debris and weren't checked / cleared. Is it necessary to drill additional drain holes? 

Even drain holes may be no guarantee because I'm imagining ice could build up from freeze/thaw cycles and block the hole. Would it be worth directing a heater from inside the cabin towards the base of the mast? 

[zaphod]

I can't say I have ever heard of that happening. What model boat were they? What make of mast?

[Charlie-Bravo]

Not heard of this issue either, and would have thought that as long as the mast can not collect a sizeable height of water in the mast, it isn’t a likely occurrence. 
Suggest attempting to fill your mast a bit with a hose, and engineer a way of seeing how much collects at the mast base …. endoscope perhaps.

CB

[tessellate]

The one I know it happened to was a 2001 Jeanneau SO 43. It was Kaiquest, Sarah + Will's former boat (Hydrovane couple). They wrote about it here: svkaiquest.com/2017/08/08/just-a-last-minute-mast/

The other boat I recently heard of it happening to I can't remember the model / particulars. 

But I think the way it would happen is a lot of water does go down masts - from halyard sheaves, etc - and typically we might have rain at mid-day when it's warmest but freezing temps overnight. So if an ice plug accumulates then water can freeze on top of that, creating a bigger plug. Keel stepped masts don't have this issue to worry about. 

[mikebz]

If the bottom part of the mast is completely watertight then tip some (aluminium friendly) antifreeze down it?  A bit of a pain if you to climb up to a sheave to do it. 

[MartyB]

Have not read the link. With that said.....

I have to wonder IF the real issue was water getting into the wood spacer many of the older boats have below the mast step. Water gets in their via the wire thru hulls, screws holding the plate in one place. Rot occurs. On some of the colder winters we've had, the water in the wood spacer freezes, cracks the cabin top.....
This is not just a Jeanneau issue, many brands have this issue. I believe there are at least two write ups on the main page hints and tips area. I should write up the work I did to my 85 Arcadia. 3 of the 4 Arcadia's in the Salish sea have had to replace this wood spacer. One was dismasted doing a Swiftsure race.
I knew of the issue before hand. Realized I had a sinking mast step, pulled mast, replaced wires, mast step, old vhf wire to newer version, etc.

My 02 on the why this has occured.

Marty