has it started suddenly or gradually?

Has it been over heated?

How much oil are we talking?

If it isnt going out the exhaust or leaking somewhere then it must be burning it.
Generally 1000hrs shouldnt be worn out, thats equivalent to about 100,000km

 But it has never had a drama. Mind you mine only has about 110 hours on it.

by the sounds of things you need to go back to the oil consumption basics. 

Do do a compression test with all plugs out.

if the compression seems down a bit (particularly on 1 cylinder) squirt a couple of small pumps of oil in the cylinder and test again. If the compression proves to be far better you have piston ring dramas / excessive cylinder wear. 

If the compression reads much the same after adding a squirt of oil in the cyl then it's most likely a bent or buggered valve. 

Failing all that, give the oil a good flush out by first draining, then fill with cheap throw away oil, run for 5 mins at low rpm then drain again. Make sure all is drained well and also change oil filter at the same time. Refill with a 15/40 oil and check the level of oil consumption and also crankcase blow by afterwards(there should be a crankcase breather hose that runs back into the air box which you can monitor how much it is breathing)

hope this helps

scano 

 Thanks guys I appreciate the responses

I have only recently purchased the boat and have probably done 30 hrs run time most of the time sitting on approx 4500 rpm 

and have prob used about two litres of oil in that time 

Apart from the using oil it seams to run perfect 

I'm really not good with motors and no bigger all about them but I'm guessing that I'm in for bad news

 I'll just have to see what they say when I get the service done

In your guys opinion If I keep the oil topped up will I damage it further if I keep using it

thanks

 It's like me saying to my dr I got high blood pressure but can I keep on living the way I am full time?

i would be changing the oil to start with and making sure you got it filled to the exact correct level first. Engines filled with too much oil can burn oil over time as well.

u located in the metro area? I am happy enough to have a look at it with you if ya need a little extra guidance? I have serviced my own Honda 4 stroke for several years now and never had an issue. 

 Hi Scano 

I apreciate the advice and your offer are but I'm not mechanically minded at all so I'll save up and pay the experts to have a look 

thanks again