This morning it feels as if we are the only boat on the lake. The barely risen sun is pale, displaying the sharp cold day but too weak to challenge it. As we leave Le Bouveret harbour behind and head west towards Geneva, the Alps are a brooding presence on our left, still mostly in shadow except at their snowy peaks, which deflect the sun like raised blades-

The further we travel, the wider the lake looks and the smaller the fibreglass hull pushing us through the water seems. If I were here alone, I might be overwhelmed by how little of this world I displace as I move through it. Alone, it is easy for me to let go, to slip beneath the surface of the day and surrender my heat to the pull of the cold indifference of the universe. Basic physics perhaps, heat going to cold. The inevitable triumph of entropy. Yet saying such things aloud draws unwelcome attention at my age, so my thoughts stay silent and solitary.

I am not alone, of course. This is not my boat. I am Stefan’s guest. He stands at the wheel, straight and strong, wearing shorts despite the cold and looking determinedly ahead as if his steady gaze is what moves us forward. He is the force behind our almost-dawn patrol. This boat is his realm. I am… cargo, brought along because his wife, my daughter, Sarah, wants me onboard.

Sarah has stationed herself a little behind Stefan, her arm resting on his shoulder, sharing his view of where we are going and how we will get there. She touches him often. It does not seem to be a sexual display or even a territorial one but rather the satisfaction and comfort of connection. Fifteen years of marriage seems to have worn a Stefan-shaped groove in my daughter so that his absence makes her feel incomplete.

I don’t understand Stefan’s appeal. He is all steel and sharp edges, a chisel carving grooves but remaining unchanged. Yet Sarah, my bright, energetic, insatiably curious daughter, clearly loves this man. Perhaps it is Stefan’s purposeful focus that calls to her. His relentless hunger for the world to be the way he thinks it should. What must it be like to be the person at the centre of Stefan’s focus? To be the woman that he is passionate to shape and to own? My imagination fails me.

Stefan’s appeal is not something Sarah and I talk about. He is one of our shared silences, like me divorcing her mother, like her leaving England (and me) to make her home here in Switzerland, like the words we both know I am starting to lose.

Sarah’s head turns towards me, as if she has felt my gaze, and she gives me a smile that is part love and part concern before turning back to Stefan and the view of his chosen horizon.

I turn my back on them to see where we’ve been rather than where are going. Marcus, twelve-years-old, with his father’s build but his mother’s softer, fuller face, is standing at the stern, leaning out over the water with complete confidence that makes me ache to pull him back and make him safe but also makes me quietly hopeful.

“Look, Grandad,” he cries, in the perfect English of the bi-lingual from birth, “Look at the wake we’re making”.

I stand beside him. I’d like to put my arms around him but he is already too old for that. The lake is calm today and our wake ripples out behind us in a wide V that ridges the surface of the water without breaking through it.

“The lake is so calm today that we’re making a perfect Kelvin wave pattern.”

I set aside my professional personae as an engineer, don the physics-free mantle of grandfather and ask: “What is a Kelvin wave pattern?”

“It’s the pattern we’re making in the water now. You see the way the water feathers out into V-shaped ridges behind us? I’m studying it at school. Do you know what the cool part is?”

He doesn’t wait for my response but rushes onwards, powered by enthusiasm and pride.

“The waves are at an angle of 19.5 degrees. Exactly.”

“And why is that cool?”

Marcus gives me a glance that shows a little disappointment at my failure to keep up.

“Because it’s not just our wake. It’s EVERY wake. It doesn’t matter how big the boat or how fast it’s travelling, on calm water the wake is ALWAYS 19.5 degrees.”

His certainty in this knowledge is as complete as his pleasure in the structure that it reveals the world to have.

“I see,” I say, “That is cool. How do you know it’s true?”

As soon as I say it, I regret inserting the possibility of doubt into the glittering fence of knowledge that Marcus has constructed but his reply shows him to be untroubled.

“Lord Kelvin proved it. With parametric equations. Look, I’ll show you.”

While I’m still absorbing the idea that my twelve-year-old grandson knows what a parametric equation is, pushes his phone at me, showing a Wikipedia page with the familiar equations on them. I’m more impressed by the fact that the Swiss mobile phone network reaches us in the middle of the lake than I am by the equations.

“I’m surprised that you already understand the use of parametric equations for solving boundary value problems, Marcus.”

“Oh, I don’t,” he replies with a smile. “Not yet anyway, but that doesn’t make the wake any less cool.”

I am a little stunned by the pragmatism of this. I think of all the time and effort I’ve wasted in my professional life because I’ve never been able to be that pragmatic.

I feel a hand on my elbow. Sarah is there, a beaker of coffee in her hand.

“Drink this, dad. The day is colder than it looks and we’re still a while from Ouchy yet.”

I take the beaker from her and sip the hot liquid. Stefan roasts his own coffee and the little boat is equipped with a coffeemaker as complex and expansive as the radar, The coffee is strong but fragrant. Just the smell of it lifts my spirits.

“What have you two been up to?” Sarah asks, placing her hand on my shoulder and looking down at Marcus.

I sip my coffee to hide my pleasure at the connection Sarah’s touch signals.

“I was watching our wake and I found out that grandad didn’t know what a Kelvin wave pattern was, so I explained it to him. He thinks it’s cool.”

“Really?” Sarah says.

Marcus’ prideful but benign outburst has made her smile but behind the smile is the shadow of anxiety. What would it mean if I’m really starting to forget basic physics?

“Yes,” I say, “I really think it’s cool. 19.5-degree waves. Every time. Very cool.”

Watching the anxiety fade from Sarah’s face is like watching a cloud move to reveal the sun. I let myself bask in her brightness for a moment.

“Marcus, your father wants you to check the course to Ouchy. Go help him.”,

Marcus is in motion before Sarah can finish saying “En y va“.

Sarah and I stand side by side, looking back towards the now distant Le Bouveret harbour.

“I remember you teaching me about the Kelvin Wave Pattern when I was twelve or so,” Sarah says.

“What a strange thing to remember”, I say.

“Well, it made my physics teacher think I was a genius when he started playing with ripple tanks and it made everyone else think I was weird but the real reason I remember it was because of what you told me it meant.”

I say nothing and try to look wise.

Sarah pushes her elbow against mine and says, “You’ve forgotten, haven’t you?”

“Well, it was a long time ago. It doesn’t mean that..”

We both know what it doesn’t mean and how soon that may no longer be true.

“What you told me,” Sarah says, refusing to acknowledge even the ghostly presence of my incipient dementia, “was that it meant that we all leave the same shaped wake behind us,whatever our size or speed and that it’s where we’re going that matters. I liked that.”

“That was said by a younger and much more optimistic man,” I say.

“Well, I liked him. I still do.”

There is a pause where I know I should say something. I want to say something. I just don’t know what the something is.

“Anyway,” Sarah says, half turning towards her husband and son, “today, my men and I are headed to Ouchy where we’ll have filets de perche at the Hotel Du Port. That seems a fine destination to me.”

Sarah closes her hand around the one I’m holding my coffee in and looks up into my face.

“Let me add some brandy to that for you, dad. You’re on holiday after all.”

I’m not really on holiday. We both know that. I’m here on a kind of trial. Sarah wants me to move to Switzerland, “so we can be together as a family.” What she means is so that she can manage my decline. That’s not going to happen. I haven’t found the words yet but I’m here to say goodbye. I will manage my own decline, pre-emptively and finally. In the meantime, I’ll spend what time I can with her and Marcus.

Sarah heads off to add alcohol to my caffeine and I turn back to watch the wake, which still feathers out behind us on the calm surface of the lake.

When I told Sarah about Kelvin’s Wake Pattern all those years ago, I believed it to be true. Everybody did. It was a pleasing sign of order in the physical world. Now fluid dynamics are better understood and we know that Kelvin wasn’t completely right. In a finite depth, we don’t all leave the same shaped wake. The more weight we carry, the narrower our wake becomes.

My wake has been narrower than Sarah’s for a while now. Soon there will be no wake at all.

“Here you go, dad”, Sarah says, handing me the brandy-laden coffee.

There is another pause. This time I don’t wait for words. I put my arms around her and hold her for a moment. She’s a little stiff at first. I’ve never been a person who hugs. Then she hugs me back and we stay like that for two or three seconds that seem both too long and too short.

I let her go. That’s part of why I’m here after all.

“So,” I say, sipping the coffee, “What exactly are filets de perche?”

Sarah raises an eyebrow, the way her mother used to, stays silent for a beat and then says: “Something I hope you’ll like. Little fish from the lake, cooked in butter and served with frittes. You’ll eat it a lot when you’re here.”

“So you’re luring me to Switzerland with exotic dishes like fish and chips?” I say.

“I’m not luring you, dad. I’m bringing you home, to your family.”

“That’s a very loving thing to do,” I say.

There’s another pause in which we both listen to what hasn’t been said.

I raise my beaker and proclaim, “To fish, chips and homecomings”.

Sarah smiles, shakes her head and moves back to her husband and her son.

I sit in the stern, watching them, letting the brandy do its work and ignoring the wake behind me.