MD 2030 Engine optimum RPM?

[nightowle]

I have a Bav 35E with the MD 2030 motor and often cruise at 2900 RPM.  This can produce close to or at 7knots with a slack tide.  I'm not sure how much extra fuel I'm burning at this engine speed.  I have a twin blade fixed prop (probably standard issue from new.)

Out of curiosity, what RPM are you usually cruising at (assuming you've got a similar engine)?

[Salty]

Hi nightowle,

If you select the “Home” page, then go to “Search” and type in “Fuel consumption” the system will look out all of the occasions within your search parameter and present you with each occasion when that subject was discussed. There’s a lot of them as you can see from the photos below, though whether there is one for your specific boat and engine, is something else. Please also keep in mind that boat speed and fuel consumption can vary considerably depending on a range of circumstances and despite considering identical boats and identical engines and engine rpm as you will see from one of my postings on that very subject.
Happy hunting !

[Symphony]

2900 is far too high for continuous use, although the engine will not suffer. The general rule is that cruising should be at between 65-70% maximum power which is also in the most efficient  specific fuel consumption range. For a 2030 2400rpm is the usual cruising speed. As the graphs show fuel consumption rises rapidly once you go above this, not only because the engine is producing more power but also because the speed increases at a slower rate. So the small increase in speed is relatively very expensive in terms of fuel consumed and reduction in cruising range under power.

I had a 2030 in a 37 used primarily for chartering in the Med which did over 3000 hours in 7 seasons, mostly cruising at 2400rpm and using well under 2l an hour.

[Escapade]

Hi, Nightowle
I have a B35E like yours with MD2030 engine and a 3 blades feathering Kiwi prop.
In a sea/wind conditions like you indicate I am getting approx. 7 kn at 2600 rpm.
Incidentally you are right about your 2 fixed blades prop, it is the standard supply (I still keep it as spare)
Cheers.

[Symphony]

Hi, Nightowle
I have a B35E like yours with MD2030 engine and a 3 blades feathering Kiwi prop.
In a sea/wind conditions like you indicate I am getting approx. 7 kn at 2600 rpm.
Incidentally you are right about your 2 fixed blades prop, it is the standard supply (I still keep it as spare)
Cheers.

That is not necessarily good. The engine is designed to run to 3600 and should be fitted with a prop that enables it to run at minimum 3300. The speed you are getting suggests that your prop is too "big" - that is the pitch is too high and is overloading the engine. While in the short term this may not seem do do any harm, long term it can shorten the life of the engine. When a new engine is commissioned it has to be shown that it is capable of achieving the required revs otherwise the warranty is void. Appreciate yours is now an old engine, but the principles stay the same. restricting rpm by over propping also means you are unable to access the  full power the engine is capable of producing.

[nightowle]

Thanks guys,

and Symphony.....I assume you're talking about Escapade's engine that might be over taxed, correct?

[Symphony]

Yes, that is why I quoted his post in my reply.

[Ricd]

Agree with Synphony..we commissioned a new D1-30 and VP fixed 2 blade last season and for warranty needed to run through the full rev range up to 3200 to demonstrate we achieved hull speed c.7 kn for our B34 at roughly max revs. We typically cruise at around 6kn which we achieve at 2200rpm

[Escapade]

Hi, Nightowle
I have a B35E like yours with MD2030 engine and a 3 blades feathering Kiwi prop.
In a sea/wind conditions like you indicate I am getting approx. 7 kn at 2600 rpm.
Incidentally you are right about your 2 fixed blades prop, it is the standard supply (I still keep it as spare)
Cheers.

That is not necessarily good. The engine is designed to run to 3600 and should be fitted with a prop that enables it to run at minimum 3300. The speed you are getting suggests that your prop is too "big" - that is the pitch is too high and is overloading the engine. While in the short term this may not seem do do any harm, long term it can shorten the life of the engine. When a new engine is commissioned it has to be shown that it is capable of achieving the required revs otherwise the warranty is void. Appreciate yours is now an old engine, but the principles stay the same. restricting rpm by over propping also means you are unable to access the  full power the engine is capable of producing.

Hi, Simphony
I understand what you say, but if I would be over propped I should be unable to get high rpm. On the contrary I can achieve 3200 rpm easily (I have never tried to push further as my user manual indicates max rpm 3200-3600) but with very limited increase in speed as the stern is ploughing down.
As I shall lift out in January for maintenance, would you suggest I should reconsider the prop pitch? So that I get say 7kn at 3000 rpm rather than at 2600-2700 as it is now?
Cheers