Sail materials and weights.

I often think of having a different set up on my yacht.

The sails are 8oz Dacron - very heavy I believe.
I see boats over taking us in light winds of <10 knots and I know they have lighter sails that can fill easier in light winds.
Especially when wind is light and aft the beam, mine keep sagging and the boom starts clanging away as the swell hits. I set up a preventer to control the boom, but this alone doesn't help fill the sail. I've tried sailing just with the genoa, but not much improvement.
I'm thinking of a much lighter Gennaker or even another genoa on a furler in front of the existing headsail.

Currently my 14t yacht with heavy sails doesn't like light air!

I'm interested in your opinions.

Cheers!

it is my understanding that bigger heavier boats need more sail or more wind to "get going" a smaller lighter boat will reach hull speed earlier, although this hull speed will be less than a longer water line boat.

Lighter sails will definitely be more efficient at picking up light winds.

The slatting you experience is due to the wind force in the sails being less than the "rolling" force of the waves on the boat. This is especially annoying off the wind where the apparent wind drops off further.

Ways of counteracting this are using preventers as you state (which then block wind onto foresails) a spinnaker (light cloth), twin headsails or motoring under bare poles (yuk).

on my boat I use twin headsails (both on furlers) downwind - one poled out. Trade wind sailing is then a breeze and she will steer well with a wind vane. if the wind increases, just furl one or both sails. a spinnaker is the other option, but is a bit of work in varying conditions compared to the twins.

Same as yours Now and Zen !
I like to maintain 5 to 6 knots. Anything under 12 knots I start the Perkins anything over 25 I start the Perkins......my advise if you go lighter don't use your old man electric winches!
I would be keen to give you a race some day!

That's the frustrating thing about cruising in Queensland - a lot of the time you have a light breeze that ends up being close to dead downwind. If the main is slatting, there's probably not too much you can do about it - a headsail or spinnaker on its own would probably not have enough drive to give you a reasonable speed, either. Often this happens the day after a significant blow: the wind eases but the seas are still up, so that even if you've got maybe 9-12kt of breeze, you can't generate enough power to stabilise the main and/or make significant speed through the slop.

Your best chance is to head up enough to bring the apparent wind forward a bit, hopefully enough to get both the main and headsail or spinnaker setting. Watch your VMG toward destination, it can be surprising how much off track you can head yet still be better off due to the extra speed. If you anticipate wind changes through the day (eg, at the moment the SE trades usually are SSE in the morning and swing to E by afternoon), you can often minimise the cross-track error over the whole day.

We have an assymetric spinnaker in a sock, and find we use it a lot on light days. Typically if a trial with just the main gives us over 3 kt, it's worthwhile breaking out the assy as it will get us to 5 kt or more.

PS we're not far behind you, currently at Digby Island. But going no further north than the Whitsundays this year.