Non-cooks are easily pleased when they eat out. All the food that lands on their plate is a bit of a mystery anyway, and not understanding the nuts and bolts of putting a meal together, or recognising the labour-saving bits and bobs available to the chef, they inhabit something of a fool's paradise. People who are charged with the daily task of feeding everyone else are tougher nuts to crack, since they have much more insight into the whole business of preparing food. Of course, regular cooks routinely yearn to eat out, if only for respite from the daily puzzle of what to make for tea. Those who eat their food don't feel the same need. Well, they already have the services of a (free) cook, don't they?

But regular cooks have to balance their eating-out urge with the strong probability they will end up with food that is no better, and possibly worse, than that which they could make at home. They have to train themselves not to complain churlishly when the bill comes, even though they know they could have produced something a million times better for a fraction of the cost. This was precisely how I felt after eating at Cruz, the newly refurbished boat that has just opened for business on the crowded Shore in Leith. Performing the gastronomic equivalent of a post-mortem examination on the cooking, the inescapable verdict was the food was a fairly crude, ham-fisted job.

I had set out with a spring in my step. It was Friday night and the whole day I had been looking forward to eating out, stopping myself from gravitating towards everything navy blue and stripy in my wardrobe, all the while humming the Captain Pugwash tune. Eating on a boat sounded like fun. The menu looked plausibly good on paper and offered the bonus of being reasonably priced, with most main courses coming in between £13 and £14.

Once aboard, we had to admit the interior was the opposite of nautical, more like a rather bland canteen in some corporate HQ.

Still, we were hopeful but, with each course, that hope faded. A slab of grey game terrine with an over-firm consistency had the deadly coldness of the mortician's slab. A perfectly competent red onion and redcurrant confit couldn't revive it. A "tarte Tatin" of red pepper, red onion and artichoke looked more like a sad little lopsided vol-au-vent than anything that might live up to the promise of the name. Had a class of second-year schoolkids concocted it, you might clap encouragingly. The salad dressing tasted like pure vinegar, yet the chef is French. Silly me, I had always thought the ability to make a decent vinaigrette was a core Gallic competency.

The fish in my bouillabaisse - red mullet, I think, silky white fish and one prawn - was fine, but I could produce a similar effect at home by reducing a jar of commercial soupe de poisson and poaching off the fish in it. The fish was overshadowed by the incongruous presence of turned, steamed potatoes that tasted as though they had been cooked much earlier.

The customary rouille (garlic mayonnaise) that should go with it was inappropriately sweet and resembled a Marie Rose cocktail sauce.

Rack of Orkney lamb proved to be a better proposition, nicely roasted, rosy, tender and with a fine flavour. It came, however, with a dispiritingly large pile of workaday mushrooms and was swamped by a sauce that tasted as though it had a dash of every condiment in the kitchen in it, so producing a sweet, vinegary mélange of too many shrill flavours.

Deconstructing my lime and mango cheesecake, it struck me as an elementary assembly job of cream cheese, insufficiently sweetened, mixed up with tasteless, turnipy mango and lime zest, on a simple biscuit base. I suspect the dry chocolate pudding was baked several minutes too long to be molten in the middle as intended. Its slapdash "red fruit coulis" tasted like little more than defrosted summer fruits.

In price terms, Cruz is mid-market: £60 to £70 for two with wine. But that's a significant sum to pay for someone else's lack of effort. It makes you more inclined to eat at home and put in some effort of your own.

Cruz, 14 The Shore, Leith 0131 553 6600 Lunch/dinner: £15-£25 Food rating: 4/10