Slower and slower

Well, I haven't discounted fouling, but she was cleaned three months ago. Having said that, we didn't get anything like the gain I expected form being clean at the time, and now we've lost what little we gained.

The transom's not noticably more sooty, so I don't think the injectors are iffy (besides, if they are we must be the most unlucky boat in history as I've replaced 8 of the buggers already).

The primaries were a little but gunky, but not horribly so. I haven't changed the engine filters yet, and the air filters weren't bad. I also had the intercoolers apart earlier in the year and cleaned those out.
 
I recon, the best test is to run the boat at say3500 revs, or whatever you can remember the previous speed at. Lets say you used to get 22 at 3500 revs, but now only get 18. It has to be some outside source thats slowing you down, as the props are going round at the same speed as before.

I've never found weight to make much difference, filling my 45 gallon reserve tank dont make any difference, so a bit of junk wont.
 
If you were in the Med, I would definitely say that you've got fouled sterngear but since you're in the UK, it's unlikely that your sterngear is heavily fouled but it's probably worth a lift to check and eliminate that possibility. You could have unknowingly damaged a prop but, if you had and it was causing such a large reduction in rpm, you would probably feel a vibration
Have you checked the throttle cables for slippage? It would only take a small reduction in throttle movement to cause a significant rpm reduction and, if one engine isn't pulling max rpm, it's likely that it won't allow the other to either
 
I would guess fouled sterngear. I think we've had a lot more sunshine this year than last on the south coast and probably the water is a little bit warmer.

I'm sure I remember being told that the little critturs are fairly inactive until the water gets to about 19C and then they go wild.
 
I had my SC35 in the water in March/April all nice and clean on D4 260's at 38Knots. (I know the comics only make her good for 32 but I have this verified by GPS and mate on a rib), but I do know how to look after a ladys bottom.

Middle of May to middle of June she sat idle in Chi marina. I took her out and boat speed had dropped to 33 knots and up to 35 knots after a good thrashing. But I was still 10% down, so wet suit and googles on to see what was happeneing at East Head. Normal slime on the hull water line, but the dreaded worm was all over the stern gear, except for the props which were as clean as a wistle.

So this all happened from clean in 3 months.


I also noticed that the port was less infected than starboard, and I moor on a hammer head with starboard nearest all the other moored boats and slacker water.

Water temperature in the harbour has been hovering around 17 to 20 degrees for nealy a month now, and this could have a lot to do with it. Although today water temperature is 25 degrees.
 
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