Sometimes you have to be cruel to be kind. When, back in 2014, I saw the mainsail on Peter Kewish’s Jeanneau Sun Way 21, I found it hard to be polite about it. In fact, as Peter reminded me, I recommended it be recycled as a dust sheet.

In the end it did rather better than that, finding a home with someone who wanted a nautically-themed shower curtain complete with sail numbers. So everyone was happy and the modest sum Peter made from the deal went towards the one thing without which his boat would never sail properly: a new mainsail.

During our outing three years ago we discussed many ways in which the boat’s balance and performance could be improved. In the space of a couple of hours in Poole Harbour before the rain and wind swept in, we had limited opportunity to improve matters but covered enough ground to satisfy ourselves that Jenn-Oh could be encouraged to sail a great deal better than she had been.

A problem of pointing

As with many boats, Jenn-Oh’s problem was making upwind. She would fly along downwind at an impressive lick, but pace and pointing on the wind were where she let herself down.

This had been evident in the Round the Island Race in 2013: boats she passed around the back of the island left her languishing in their wakes on the long beat to the finish. She pointed lower and struggled for speed, carrying substantial weather helm at the same time.

The old mainsail had stretched to such a degree it was almost useless upwind with the deepest point of the sail now well aft.

Peter had been conscious that the lack of a mainsheet traveller wasn’t helping. He was also concerned about the way the headsail was sheeted. Our assessment in 2014 confirmed that both these factors presented problems.

We found other issues too – principally that the rigging was too slack and that the mainsail, even though we managed to improve its shape by some judicious tweaking, was ready for retirement.

I left Peter with a number of ideas to consider. Most of them did, unfortunately, involve spending money, a new mainsail being at the top of the list.

A permanent solution was also needed for the headsail’s sheeting arrangement to replace our temporary fix – either that or a new headsail of a different design sheeted in a different way, which would cost rather more.

Another area we addressed was how to sheet the mainsail. Given that traveller systems can be expensive and, on a family boat, in the way as well, I rigged up a temporary bridle to demonstrate a low-cost alternative.

And then there was the rigging. I rarely find rigging that’s as tight as it should be and on our first outing I had to set to with the rigging tools before we could assess the effects of any other tweaks. It’s impossible to carry out a thorough rig assessment when you’re under way and up against the clock, so we did what we could in the time, left the rake as it was and accepted that more work would be needed.

Time for an update

After our sail I spoke to some sailmakers to see what ideas they had about the rig in general and the headsail in particular. The mainsail simply needed replacing, whereas the headsail’s configuration and sheeting arrangement called for rather more thought.

We left it that Peter would let me know what he decided to do, on the understanding that he wasn’t keen to spend more than necessary. It would be easy to invest more than the value of the boat in making improvements.

Some owners might have done nothing further, but Peter covers a fair few miles in his little boat and was eager to get her going better, so he didn’t just leave it at that. And that’s why Peter, Jenn-Oh and I met again on the same stretch of water three years later.

We had more sun and no immediate threat of wind and rain this time, but still had to watch the time so Peter could get back up the river and on to his mooring before water gave way to mud.

The headsail

This had presented a problem on our last outing, partly because the sail was getting old and stretched and also because it appeared to have appreciably more overlap than shown on Jeanneau’s original drawings.

That might be why it didn’t match the deck hardware.

A barber-hauler of sorts helped reduce the previously wide sheeting angle

Since Peter decided to keep it going for the time being, he adopted a modified version of the temporary sheeting arrangement we had fixed up last time with blocks and line.

While having the standing rigging replaced, he took the opportunity to have the forestay shortened to reduce the rake. At the same time, he raised the furling drum by 4in (10cm), helping the headsail’s leech to clear the spreaders and the foot of the sail to flop over the pulpit.

As a bonus, the higher clew created a better sheeting angle (in the vertical plane) with the new barber-hauler arrangement.

The new mainsail

With a mainsail like she had, it was little wonder Jenn-Oh had been struggling upwind: it was more hand-brake than driving force.

As a Dacron sail stretches with use, not only does it become baggier but the deepest point (the draft) also moves aft.

A new sail will be cut with its draft about a third of the way aft from the luff towards the leech. Once the draft moves beyond the half-way point as the cloth stretches – a problem principally with woven fabrics rather than with laminates – the sail generates more heel and weather helm than forward motion.

As the draft in Jenn-Oh’s sail was about two-thirds of the way aft, she had no chance. The lightweight sail didn’t even have a bolt-rope to allow the luff to be tensioned properly.

On our first outing we pulled what strings we could to improve matters, but there was only so much we could do.

The new mainsail offers a much better flying shape

Budget sails: problems ahead

The mainsail that was on Jenn-Oh when we sailed the first time was an example of how low-quality sails can prematurely spoil a boat’s performance. It was quite old, and it was certainly cheaply made. Not fitting a bolt-rope is inexcusable.

This sort of thing is a common problem, especially on production boats towards the lower end of the price range. Builders often supply budget sails on the basis that buyers won’t know any better and wouldn’t be prepared to pay more for the boat if it came with a decent suit.

Some builders in particular have a reputation for skimping on the sails, and it does them no favours. If, as is often the case, the boats are on the tender side to start with, they will struggle upwind once the sails start to stretch.

Excessive heel and leeway and a heavy helm are classic symptoms in conditions when the boat should not be over-powered or need reefing. Peter’s sailing experience always allowed him to get home, if not as fast as he would have liked, but anyone less competent could find themselves struggling.

If this sounds familiar, have a good look at your rig and sails. If the sails can’t be pulled into a decent shape by someone with experience of what to look for, think seriously about replacements.

Also bear in mind that older second-hand boats run on a budget often have cast-off sails from another type of boat. There are all sorts of reasons why they might not do the job as well as they should – even if they do appear to fit the rig. Headsail sheeting angles are one of the most common problems, as is the type and positioning of deck hardware.

What’s the difference?

While beating down the harbour to meet me for our second sail, Peter found himself out-pointing a slightly larger and much newer trailable cruiser.

‘All the things we discussed last time seem to be making a big difference’, he told me. ‘The new main certainly is. There’s so much more power from it and I’m not getting the weather helm I used to. It’s still there, but much reduced.’

Something else he has noticed is the ability to make upwind under mainsail only. It was impossible with the old main.

I saw Jenn-Oh again in last year’s Round the Island Race, when she performed appreciably better than she had in 2013.

Much remains that could still be done to get the best from her. I was wondering whether Peter might have adopted my idea of a mainsheet bridle, but he couldn’t find a way to make it work and not get in the way with several people aboard.

The standing rigging needs regular checks to make sure it’s up to tension, otherwise the sag in the forestay will hamper upwind performance.

And then there’s the headsail. Although a good deal more efficient with the new sheeting arrangement, it’s still past its prime and, more than likely, not the right sail anyway.

What matters is that the boat performs so much better than she did. A new mainsail and new standing rigging have been good investments and the other mods have been done for the cost of a few second-hand blocks and some line.