Vulcan or M2: the anchor question I can't close yet

Anchor choice is the gear question I keep reopening and keep failing to close. Rocna Vulcan or Mantus M2 for the 50-foot cat we're researching, and I can't name a clear winner yet.

Here's the part I can actually calculate. Say we anchor in 10 metres of water with about 2 metres from the waterline to the bow roller. That's 12 metres of vertical distance. At 5:1 scope, the standard I'd use in settled weather, that's 60 metres of rode out. Getting ready for a blow, I'd go 7:1, which is 84 metres. The 10 mm chain I'd want weighs roughly 2.2 kilograms per metre, so 84 metres is about 185 kg of chain, hanging over the bows of a boat whose whole premise is that it's light. The anchor itself is almost a rounding error next to that. The chain decides where the weight goes, and on a catamaran with four kids' worth of gear stacked in the hulls, I care a lot about that.

That pulls me toward the smaller anchor and shorter chain than the old monohull instinct says, and it's the first place my own reasoning makes me nervous. Cats are windage machines. A 50-footer with a bridgedeck and a hardtop swings and snubs hard, and a bridle takes most of that load if it's set up properly. But the anchor still has to reset in a wind shift at 3 a.m. without waking a four-year-old and a one-year-old. I'd rather carry the extra weight than negotiate that.

On the two candidates, what I can say from reading owner reports, and not from my own tests, is this. The Vulcan has a reputation for setting fast and for fitting a wide range of bow rollers because it has no roll bar. The M2 gets praised for resetting and for its bolt-together shank, which matters if you've ever tried to stow a one-piece 25 kg anchor in a locker. The fix that really matters in both cases is the same: oversize, hot-dip galvanized, and a bridle that keeps the load off the windlass.

What I haven't resolved is whether to go one size above the maker's chart for our displacement. My instinct says yes, because the chart assumes a boat that isn't loaded for five years of living aboard, and the price difference is a few hundred dollars against a boat that costs several hundred thousand. But that extra size lands on the bow, and I've already written that our gear list is heavier than the brochure payload. Every kilogram I add forward is a kilogram I'm taking from somewhere else.

So here's where I am. I'd probably buy the Vulcan for the roller fit, one size up, and spend the money I save on shortening the chain run with a deep-water rode backup stored amidships. But I'd want to see both anchors set in grass, sand, and soft mud on a cat of our size before I'd stake a night's sleep on either one. If any of you have anchored a 45 to 50 foot cat on one of these for a season, I'd like to hear what dragged and what didn't.

The weight budget behind this question lives in the boat worksheet, if you want to see how the numbers stack up.