You could try sitting one of those owl bird repellers on your boom. I've seen them used a lot on beach house balconies, but don't know how well they work.

Fred Bevis looked into this and reported thus in Sydney Amateur's journal:
LETTER TO THE EDITOR February 2012
Dear Sir,
I have been pursuing a detailed analysis and specific testing of methods and objects suitable to deter seagulls from perching on Warana and thereby disrupt their long-range objective of creating another Nauru. The methods explored to this point have been strings with CDs (Beethoven to Beatles tested) strung on a string above the boom, an owl imperiously looking back along the boom, a specifically-designed hawk suspended above the boom which moves in the breeze and the most recent testing of two coiled red-bellied snakes placed on the stern. I am saddened to report none of these tests has met with significant success. The latest snake approach looks very intimidating to humans at first glance and so it is with seagulls as the photo attests.
I am forwarding a copy of this photo to the purveyors of this “bird- scaring” device with a request that they consult the warranty terms as the product is self-evidently “not fit for purpose”.
I have now turned my mind to first principles and have come to the conclusion that what hitherto had not been a problem has been brought about by more seagulls being attracted to the increasing schools of small fish being attacked, from below, by larger fish and the seagulls feeding on the collateral damage from the attacks. The first principles' conclusion is therefore the reintroduction of high concentrations of tin, lead, zinc and copper to antifouling paints to diminish the attractiveness of the harbour to the small fish, their predators and as a consequence diminish the food supply for seagulls.
You know it makes sense.
Fred Bevis

The swallows and seagulls will always win I use lots of sea water to soften it and scrub with boat cleaner.

Thanks for everyone's advise. And Cisco, I know the joy of white cockatoos. Grew up on a farm. I remember many times having to take the shotgun off dad whilst reminding him that they are a protected species. He really wanted to get a couple of shots off to find out just HOW protected they were.....

I've tried everything, the best is the snake, or plastic bags to creat noise.

The worst was the net, because it's a pain to use each time you sail, followed by the owl. The seagulls saw it as threat, so continued to attack it, poopoping all over the place on the process.

Tie the snake to the foredeck, one is usually enough.

Michael.

We also have a seagull problem down here in Tassie.
Our old timber boat comes out of the water each year and a few years ago we painted the cabin so left the netting off when she went back in the water as we didn't want to walk all over the soft paint, and guess what....the seagulls didn't go near her for two weeks!!
After some head sratching we realised that the boat has to 'smell right' for them to sit on it. If you clean the boat regulary you get alot less crap, the build up is expenetional.
So apart from fresh paint what else do they not like the smell of? Well after some experimentation it happens to be vicks vapour rub!!!
We made some little holders (one jar lid on top of another, bigger on top and help apart by a spacer) and it kept the birds away!
Unfortunately with a 38 x 14ft boat there was always a spot where the smell would not be and you had to put up with the smell yourself!!

So in conclusion, we use netting with a homemade rotator on the radar dome and it works very well. With practice I can take the netting off/on in about 5min but am looking at putting a small spinnaker bag at the base of the light pole to bunch the net into when using the boat to save time.

Is there any ultra sonic type devices that can be used to scare them off?

Ive tried plastic bags,cd's owls,netting,flags etc All with varying degrees of success and inconvenience. I'm thinking of tieing tree branches to the mast cause Ive never seen a seagull sitting in a tree

The most success I ever had was just a simple string along the boom. Friends have crazy spinning devices set up too. It helps if all boats around you have something setup so birds don't hang out in the area.

I have also had the instance where a Possum has been found on an Etchell that was on a mooring. We found it whilst hosing out the boat. The Possum was not very happy with us.

two inch wide caution tape

cisco said...

animusmh12 said...
I have also had the instance where a Possum has been found on an Etchell that was on a mooring. We found it whilst hosing out the boat. The Possum was not very happy with us.

What!! Was he eating the seagulls that dared to venture on his domain??

It was weird however we were pretty close in to the beach where there were a lot of trees...