Yes, you can by different pitch blades, but more information is needed before suggesting whether it is worth doing it. I assume you have a 30hp engine and if it is a Volvo then a 16*11 is a common size for that size boat. If you post details on the actual boat and engine/gearbox and what you want to achieve or fell what is currently inadequate you might get better advice.
Thanks will check them out.
No you won't get that without severely overpropping. The engine is rated to 3600rpm with cruising revs +/- 2400 to give you around 5.5 knots. 16*11 is the correct size and you should be able to achieve 7.5 knots at between 3400-3600. You could increase the pitch by 1" which will bring the revs down by approx 250 for any given speed but you need 15hp to get 6 knots and at 2000rpm the engine is only capable of producing 12hp. So a 16*12 would likely give you your 6 knots at 2400, rather than 5.5knots with the current propeller.
Happy to accept your estimates, to be honest I havent revved over 2k very often. Will try and get some 12 blades priced up and will be giving her a bit more welly this season. Thanks.
My engine instructions, same engine, say that the ideal running speed is the max revs minus 400 rpm, ie around 3000. I think that most of us will find this much too high and I think that Tranona's 2400 is nearer the mark. In my slightly lighter boat of 5.4t that was my most usual speed for passage-making and gives me around 6.4kn. With a clean bottom in still water more than 5m deep I get around 6kn plus 0.1kn for every 100 rpm over 2000. I have only occasionally run at 3000, such as when being told to hurry by Dover harbour, but have often run at 2700 when I need to push against wind and sea. On one occasion I ran at 2700 for 24 hours when returning from Ireland with only short breaks to check oil and water filter. This is likely to be better for the engine than running it too slowly, so I am told.
Running at low revs like that leads to coking up the exhaust elbow prematurely. These little engines like running hard and 2400 is the "ideal" as it is peak torque and lowest specific fuel consumption. Periodically run it hard - 3000 plus for 20 minutes to help burn off deposits .
Thanks what prop are you running?
Volvo 2 blade folding, as I said earlier
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I bough just that from Darglow a couple of years ago. A great product from a terrific company.
While I agree - I also have a Featherstream - it is not necessarily appropriate for the OPs boat which is an IOR style cruiser racer with a 30hp Volvo saildrive - more than enough power. He already has the correct prop, but his aim is to reduce cruising revs which can only be achieved by over propping. Another 1" pitch on the prop will drop revs by around 250 but his target of 6 knots at 2000rpm is unachievable.
oops, sorry about that and thank you for your postsVolvo 2 blade folding, as I said earlier
Thanks , I will re calibrate my expectations.
I think perhaps you could get used to running at slightly higher revs. To a motorist this slightly goes against the grain but mid 2000s is quite normal for this engine. My 2030 is only starting to run sweetly at 2000 rpm and I only use lower revs reluctantly such as in confined waters. My impression is that my prop is much more efficient at higher revs and although there is clearly a limit my fuel consumption per mile is actually fairly flat over this range. In my imagination I suppose that at lower speeds there is quite a lot of 'slippage' making the prop less effective, and this is certainly true when bashing into a head sea.
