Beneteau 361 - what speed to expect?

[Philip_Oceanis 361]

Beneteau 361 - what speed to expect (motoring)?

I am just checking something on my engine and would like some help please.
I own a Beneteau Oceanis 361. What speed over water (not SOG), more or less, to expect when running the engine at 2500rpm on flat water, no wind (or very little anyway) with a clean hull and a clean 2-blade fixed propeller?

My engine is a Volvo Penta MD2030D, but any similar 30hp engine could give me some ideas of what to expect.

Thanks

 

[DougM]

A wild guess:
Not much more than 5 knots. More throttle isn't going to give much more speed. Its kind of a law of diminishing returns. That maximum speed is determined by the water line length of the boat. I would estimate that your maximum hull speed is probably not much more that 7 knots under any condition.

Maybe someone here can drag out their old fluid dynamics book and find the exact formula. I wrote a paper on this once, but I suspect the brain cells in use then have long since checked out.

 

[agaliha]

Real world answer

My Beneteau 361 with Maxprop and Yanmar 3GM does 6 knots (with a clean bottom in flat water) at 2500 rpms. Knotmeter is confirmed by GPS chartplotter. I can squeeze out a little more by going to 2800 rpms, but the most efficient seems to be about 2000 rpm at 5 knots.
Burns about 1/2 gallon per hour at 2500 rpm, I think. Anyone confirm?
Agaliha

 

[Philip_Oceanis 361]

Thanks a lot agaliha.
I seem to get exactly the same speed like you. Around 6 knots on 2500 rpm. I changed anti-fouling as well as made some repairs to the reverse gear so I was not sure about the "performance" under motoring. But it seems that it's normal. And yes i also get 5 knots at 2000 rpm.
Out of curiosity how does the maxprop performs against waves? This is where I have a biiiiig disadvantage with my 2-blade propeller. I see speed dropping to even 3-3.5 knots (unless I am sailing of course which gives a completely different feeling and performance to this lovely boat).

PS: Hopefully I will order soon that Campbell Sailer I have in mind....

 

[agaliha]

afirmed

Philip,
I love my maxprop. I can't tell the difference between it and a fixed prop under power. Reverse is great. Sailing when folded is great, too. Best of both worlds. Do you have any data on fuel consumption?
Agaliha

 

[Philip_Oceanis 361]

Philip,
Do you have any data on fuel consumption?
Agaliha

I have calculated consumption at 2500rpm to be around 2.5-3lt/hr (well it's a rough guess and it's probably more 2.5lt than 3lt). Looking at the internet to find a conversion rate - I am not familiar with gallons - this must be around 0.70-0.75 gallons per hour.