cmedsailor
Well-Known Member
I made a couple of tests and have found out that my 2-blade fixed propeller must be the “ideal” size (“ideal” is subjective of course because there are people who prefer a slightly oversized propeller to give more speed at lower rpm; I wouldn’t mind that either if I had to choose a propeller!!). Anyway in my case “ideal” means that I can increase rpm up to maximum of 3500 rpm and speed keep increases all the way up to maximum. Thus there is always reserved power in case is needed.
What surprises me though is the fact that at various rpm up to 2500 speed increases slowly (or better say linearly) but at 2600 there is extra “push” of 0,5+ knots simply by increasing rpm by 100. For example motoring against 18 apparent wind, 2500 rpm will give around 5,3 knots whereas 2600 around 6. In no other rpm is the increase so sharp.
Could this be where the maximum torque of the engine is? Or could this be the best rpm to use as cruising speed?
The engine is a Volvo Penta MD2030D and “torque curve” given by Volvo shows that the maximum torque of 63NM is at 2400 rpm.
What surprises me though is the fact that at various rpm up to 2500 speed increases slowly (or better say linearly) but at 2600 there is extra “push” of 0,5+ knots simply by increasing rpm by 100. For example motoring against 18 apparent wind, 2500 rpm will give around 5,3 knots whereas 2600 around 6. In no other rpm is the increase so sharp.
Could this be where the maximum torque of the engine is? Or could this be the best rpm to use as cruising speed?
The engine is a Volvo Penta MD2030D and “torque curve” given by Volvo shows that the maximum torque of 63NM is at 2400 rpm.
