Hi
I am currently re-powering my 2000 Bav 34 from a MD2020/S120 (20HP)to a D1-30/S130 (30HP) . My current prop is a LH fixed 2 blade 14x11. Have been recommended by Clipper marine that the original boats fitted with the 30HP MD2030 would have had a LH 15x11 but a local marine engineering has recommended a 16x11.
Can anybody confirm the original MD2030 had the 15x11?
Any issues if i go for the 16x11 as I clearly want to have more power hence engine change?
Cheers
Richard
Keep in mind that the 16x11 prop will require more power for it to turn at the same rpm as your 15x11 prop. That might mean that the engine cannot achieve the required rpm where it would normally achieve maximum power output.
On my previous boat, a Leisure 27, this was retrofitted with a Beta 20hp engine which replaced the original 13hp Volvo. However, this was done by the previous owner and the original propeller used with the Volvo engine was retained. Unfortunately although the Beta engine had a higher horsepower output, the original prop which suited the slower revving Volvo engine, was too big for the more powerful Beta. As a result the Beta was not able to achieve maximum power output where the higher rpm needed to turn the prop could not be achieved. With nothing to lose, I removed half an inch of blade length from each propeller tip, and this enabled the engine speed to increase by about 300rpm, and pushed the boat speed up from six knots to a comfortable seven. Well actually it wasn't that comfortable because while the speed was easily there, the boat's steering became very twitchy such that maintaining the higher speed became a chore rather than pleasant. My point is that the propeller size, the engine power and rpm, and the speed achieved all have to be very carefully considered in order to get the best solution. With your 34 ft boat the economic speed is very approximately equal to the square root of the waterline length. So if you have a waterline length say of 32 ft, then your boat will be driven economically at around 5.6 to 5.7 knots. To achieve a higher speed you need a lot more power with consequent higher fuel consumption. Your new engine is 50% more powerful, so you should get an increase in speed, but whether your engine can cope with a sixteen inch blade is something that you may find becomes an expensive exercise.
