How can I reduce getting catapulted?

I know it is inevitable,but I seem to have a bit of a problem.
I am a returning windsurfer of little experience,but am keen to get back into it.
Currently I have a Bic Techno 150l and a Bic Lambada longboard,along with a 6.2 and 7.0 sails.
I am using the harness And just getting into the straps.The problem is,I cannot seem to depower easily when I get a gust,and I end up flying like Biggles.I am starting to worry about smashing up my sail and board,plus myself,and finding it very annoying.
Today was probably the strongest I have been out in,maybe 20/25 knots and the problem was magnified.Maybe it was too windy for me,but I wonder if my setup needs tweaking.
I read somewhere that the boom should be at chin height and the harness lines should be about 28 inches?
When I set up like this it feels too close to the sail with little "give" or flexibility,is this correct?
Any tips on harness line length and position gratefully received.
Maybe I should just go out in lighter winds to begin,but I would like to nip any bad habits in the bud,plus I do not think my sail and board can handle too many more crashes like I had today.
Cheers,
Bleary.

Thanks Hardie,I will try that next time I think.I don't mind falling off,but being flung into the mast and sail will end in tears I think.

If you're quick enough you can pull on the front hand and push with the back hand at the same time to depower the sail. Second, if it's strong get in both straps as quickly as possible, once you are in the straps you can controll a lot of wind just by hanging low. Another cause of catapult is moving the mast over the eye of the wind, you cannot go over the handlebars if you keep the mast racked back.
And the harness lines look short when you are not planing, if it's strong you should hook in just between entering the first and second strap...

Thanks for the advice guys,they make a lot of sense.Sounds like I need to get back quicker,rather than mucking around and getting caught out with the rig too vertical.
what distance from the mast should I have my lines setup?currently I have them @ 40 cm back along the boom.
So lots of down haul flattens the sail also,I was putting a fair bit on,but was worried about breaking something,lots of out haul when windy also?
Cheers for the help.

Thanks Windxstasy,very good tips.
My sails are a 7m North Tonic and a 6.2 Neil Pryde Diablo,they are in okay condition so far,trying not to spear through them!
I do also have a smaller board,it is a 106lt AHD Inspiro,but I think that is a step too far at the moment.I will try to balance the sail/harness lines as you say,something felt "out" today,so maybe that was it.
15/20 knots would be perfect,but I need to deal with what I have I guess.
Ta for the advice,will try tomorrow!

Get down low to the water and hang your weight off the boom with long harness lines..that will stop you from being pulled over so easily.Push out with your seat away from the lines pull. If the lines are long enough you shouldn't pull the rig over the top of you too much.
Keep an eye upwind for gusts so you aren't caught off guard.Then you can be ready to pull in with the front hand and depower the sail a bit for the strong stuff and back to normal after its gone ( if it's very gusty). If its gusty and youre not in the straps all the time you can see a gust coming and put the rear foot in the strap ( just keep your weight on the front one until it hits for board trim). As a lightweight I do that a lot to avoid the risk of catapults as I'm then anchored for when it hits.

Agree with Windxtasy's advice on board volume. I've had a few nasty catapults when sailing a bigger board in stronger winds. One catapult was captured on my GoPro. After this crash I sailed the rest of the day on a board 30 litres smaller and had no problems.

5.5 severne gator will rig on a 430

Hi Bleary. If you can find a local sailor your height and weight, he/she would be a good person to speak to. Just a few points from when I was an intermediate (which may/may not work for you):

When over powered (or as default when an intermediate sailor), I use the front hand under hand grip. This grip (it feels weird to start with) depowers the sail by putting your weight through that arm which you naturely do when out of control. As you become more efficient sailor and use smaller gear, the normal front grip method might be better (ie: on small wave gear when under powered, I use normal grip). Have a play.

Regarding boom height, chin height is about where I have it on average, but don't settle with this advice. Have a play to see what is most comfortable. During a session, I normally change my boom height and outhaul a few times. Some sailors have a set position and don't touch it. Some guys have it real low, others real high. It depends on what works for you. This is a dicussion in itself.

Since you are starting out, you're very inefficient sailor, so you'll be on bigger gear to plane around with the advanced guys your weight/height, but as the years go by, you'll be able to do more with less.

Windxtasy: I disagree about your harness line position tip. Bigger sails (ie: 6m) use apparent wind. If a sail used purely real wind, then what you suggested would make sense.

Best thing to prevent catapult is getting in both straps, especially the back one, so if your not always in them yet, push yourself to learn that now. On the bic they're pretty far outboard I think so it can be a bit tricky in the beginning, but once you're in catapults will be almost none-existent, at least that's how it was for me

P.S. If you don't want to break your sail always hold on to the boom, if you don't want to break the technos sensitive nose when u still have the tendency to catapult a lot get a jezz knob.

Thanks for all of the great feedback guys,I very much appreciate it.
I will try again tomorrow with the great tips I have read here.
Thanks again,
Bleary.