Buying second hand sails pro's and cons= value for money

I would definitely invest in decent sails - particularly a replacement mainsail, by the sound of things. As a SAILING BOAT, the SAILS should be top of the list of investment priorities - just below safety stuff (which includes primary safety, such as keeping hull seaworthy and watertight).

I am constantly amazed by people who seem happy to spend large sums of money on other stuff - engines, electronics, heating, TV & sound systems. But persevere with ancient sails on a sailing boat.
Any old rags will blow any old tub downwind at moderate speed. But going upwind a decent set of sails set properly will be massively more efficient, pointing higher, going faster and heeling less. Baggy sails cause both excess heeling and drag - meaning crew get cold wet and seasick (refer to start solo sailing threads) making slow progress, whereas boat with good sails is going flatter and faster, overtaking other boats around which is great for crew morale as they get into shelter, and perhaps the warm pub, sooner.

It was very noticeable in the Baltic that many of the locals sailed older boats with expensive / high tech sails, for enjoyable sailing in light winds. By contrast many/most British folks had big / expensive boats with cheap / inefficient sails.
One classic case, we left harbour and like all the Swedish, Danish, German and French boats hoisted sail and had an enjoyable mini “regatta” sailing at our best in the gentle breeze. The entire rest of the British flagged boats left later and motored with sail covers still on, making no attempt to sail. Each to their own, but effectively “motor boats with masts”.
 
I would definitely invest in decent sails - particularly a replacement mainsail, by the sound of things. As a SAILING BOAT, the SAILS should be top of the list of investment priorities - just below safety stuff (which includes primary safety, such as keeping hull seaworthy and watertight).

I am constantly amazed by people who seem happy to spend large sums of money on other stuff - engines, electronics, heating, TV & sound systems. But persevere with ancient sails on a sailing boat.
Any old rags will blow any old tub downwind at moderate speed. But going upwind a decent set of sails set properly will be massively more efficient, pointing higher, going faster and heeling less. Baggy sails cause both excess heeling and drag - meaning crew get cold wet and seasick (refer to start solo sailing threads) making slow progress, whereas boat with good sails is going flatter and faster, overtaking other boats around which is great for crew morale as they get into shelter, and perhaps the warm pub, sooner.

It was very noticeable in the Baltic that many of the locals sailed older boats with expensive / high tech sails, for enjoyable sailing in light winds. By contrast many/most British folks had big / expensive boats with cheap / inefficient sails.
One classic case, we left harbour and like all the Swedish, Danish, German and French boats hoisted sail and had an enjoyable mini “regatta” sailing at our best in the gentle breeze. The entire rest of the British flagged boats left later and motored with sail covers still on, making no attempt to sail. Each to their own, but effectively “motor boats with masts”.
I've raced dinghies a fair bit, some with brand new sails, some with pretty old sails.
You often find that sails can look pretty terrible, but if they are set on the rig to the best of their potential, the difference between old and new is not so great.
A 2% speed deficit would be enough to send a racer into complete depression, but might make little real difference to a cruising sailor.

Many of the rubbish looking sails you see on yachts could simply do with some adjustment? Move the jib cars, adjust halyard tension, outhaul etc Free off the leachline after the wind has dropped etc.

So if the OP' s main is horribly baggy, first thing I'd suggest is getting a good sailor to take a look at the way it's set.
There may be something which can improve it significantly for little cash or even none!

The main on my new to me boat is not brilliant, but it drives the boat OK and isn't going to fall apart soon.
I'm considering fitting a cunningham. The outhaul will be re-hashed with some decent blocks. Likewise the kicker.
I will be making sure the reefing system works properly.

But if I want to race, I do it in another boat.
 
Get a good main. It will transform your appreciation and enjoyment of the boat. You’ll have more fun, more smiles and you will get value from day one. Well worth it.
 
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