The Offshore Voyaging Reference Site

Going Up The Mast at Sea

This article should not be acted on without reading the entire series.

So far in this series we have covered a huge amount that, together with a careful read of the excellent comments thereto, will enable each of us to come up with a mast-climbing system that meets our needs and tolerance for risk—there is no such thing as risk free.

But what happens if we need to go up at sea? Let’s take a look.

First off, we need to clearly understand that going up the mast at sea is one of the most challenging and dangerous tasks a sailor will ever be called upon to do.

I can’t overemphasize this. We can go up the mast hundreds of times when the boat is at rest in smooth water with a system that works perfectly for our needs, and still be totally unprepared for going up at sea when the mast will be swung through a huge arc by swell, even on the calmest days.

The Reality of Mast Climbing at Sea

Just imagine for a moment that the boat is rolling 10 degrees (not much at all) either way and the masthead is 60 feet above the water.

That means that the mast will be swinging through a distance of nearly 21 feet (6.5 meters) on each swell.

Wait, it gets worse. Say the wave period is 5 seconds, which is quite typical offshore in light to moderate weather. Then we will swing through that full arc—assuming no damping, more on that in a minute—at an average speed of 4.2 feet/second.

I know, that does not sound too bad, after all it’s only 2.8 miles per hour, but wait, it gets worse again…much worse. Every 5 seconds we will be decelerated to zero and then accelerated back again to the same speed in the other direction.

And it’s that acceleration and deceleration that can, if we lose our grip and swing clear, smash us into the mast that is likely coming the other way at us with crippling force. How much force? Sorry, way past my math abilities. Let’s just say this is really going to sting.

But wait, it gets worse for a third time. The movement of a boat offshore is not in just two directions, as I have portrayed above. It’s multi-dimensional, with pitch and roll mixed together in unpredictable and ever-changing ways.

And then we need to remember that wave height and period are not constant at sea. So every so often a wave will come along that’s at least twice as high as the others and can catch the boat wrong-footed, perhaps rolling her to 20 degrees either way. It only takes one of those to perhaps pry our terror-fuelled grip loose and set us off on a wild free swing, ending with being smashed into the rig.

OK, now imagine it’s blowing 25 knots and the significant wave height is 15 feet…wait, let’s not, too terrifying…anyway, I’m sure we all get the picture.


All of the above applies to monohulls, but what about multihulls? One could be forgiven for assuming that their huge form stability solves the problem, or at least makes mast climbing easier.

And that’s true in small waves where the width of the hull spans the entire wave length, but as soon as the wave length exceeds the beam of the multihull (or length if bow-to the waves), which happens at quite low wind speeds at sea, everything changes.

And when the distance between crest and trough (half a wave length) equals or exceeds the multihull’s beam, the cat or tri will immediately roll to conform to the angle of the front and back face of each wave, without the damping of the monohull’s keel and ballast, resulting in a more violent motion, albeit at lower amplitude.

This is not intended as a criticism of multihulls. In fact, I’m a big fan, to the point that a trimaran was on our recent boat-purchase shortlist. My intent is only to point out that multihull owners need to read on, too…so don’t go all clannish on me, OK?

Do We Need To Do This?

Given how dangerous mast climbing at sea is, before we get into the how, we need to think about whether we are even going to go up in a given situation…i.e. the if. So let’s look at that: