Seeking advice for a project or do you want to share the outcome of one? Various technical tips and questions.
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Post by amusgrave » Sun Mar 23, 2008 11:37 pm

For long distance motoring, who many RPMs do you guys run your engines at. I usually keep the MD2020 on my D-34 to 3000 rpms, but see the range on the engine is 3200 to 3600.

Any thoughts???
Alan Musgrave
D34-P, Hull #106
Toronto, Canada

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Post by Lars » Mon Mar 24, 2008 9:49 am

Hello Alan
Diesel motor runs well at 75% of top RPM.
My VP2030 with VP 3-blade folding 17*12 has top RPM at 3600RPMs and I run the engine at 2700RPM and the D34 makes 6,8-7,1 /br Lars

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Post by Alyssa » Mon Mar 24, 2008 7:56 pm

We have a 385GL with an MD2040 and a standard fixed 2 blade prop.

We normally run somewhere between 2,000 and 2,500 rpm depending on wind, sea conditions and whether we are in a hurry or not! This would normally give us about 6.5 knots, with a typical fuel consumption of 2.3-2.6 litres/hour.

Normally, more than 2,500 doesn't produce much extra speed...and much greater fuel consumption!!

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Re: RPMs

Post by saralu » Fri Apr 04, 2008 11:36 am

Lars wrote:Hello Alan
Diesel motor runs well at 75% of top RPM.
Fair Winds

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Engine RPM

Post by barry_n_janet » Sun Apr 13, 2008 9:48 pm

We run at 2000 RPM when motoring and this give about 6 knots in waves below 1m. When in a hurry we raise this to 2500. We have never had a boat as quick as the D40P and we are still happy with cruising speeds.

When we came back from Madeira to Portugal we ran the engine at 1500 and we achieved 4.5 knots. We did this fearing we might need to motor all of the 500+ miles and we were not sure of our tanks/boats range. The wind appeared after 27 hours and allowed us to sail the remainder. Read about our 500 Miles to Windward on our web site.

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Post by Peter Richardson » Wed Sep 10, 2008 8:50 pm

I have a new D34 with a VP D120 engine and a 2 bladed folding prop. I tried to get the order changed to a D130 2 months after the initial order but Dufour said it was too late to change. The DI20/30 series are designed to give more torque at lower revs than the 2020/2030 series and have a lower maximum rev range of between 2800 and 3200. I believe this is to meet new emission regulations.

I get about 5.7 knots at 2000rpm and 6.1 knots at 2300rpm but max revs are only 2800 which gives about 6.7 knots. I queried the max revs with VP but they say it is better to have the engine working hard to reach 2800 than spinning easily up to 3200.

Just over 6 knots at 2300 rpm is a good cruising speed, and very economical, in flat water with moderate headwinds but it falls off in strong headwinds. I believe the DI30 engine is supplied with the same prop so it would give the same figures at lower revs but I assume it would be able to reach 3200rpm which would give a speed in the mid 7 knots.

I am slightly disappointed about only having the smaller engine but on the plus side access for maintenance is much better as is fuel consumption.

Does anyone have the DI30 in a D34 to compare performance?

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Post by emira » Sat Sep 26, 2009 3:03 am

I have a D34 with a volvo D1 30
on 2000rpm i get 6,7 knots thats a good crusing speed

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Post by Pauli » Sat Sep 26, 2009 9:16 am

emira wrote:I have a D34 with a volvo D1 30
on 2000rpm i get 6,7 knots thats a good crusing speed

I also get this speed with my D34 with a Volvo D1 30

However, it depends on the wind and sea conditions. I am satisfied with to get 6,0 knots in average speed, at 2000 rpm

At this rpm's, the fuel consume is moderated... from 2 to 2,2 litres/hour. In 24 hours (a whole day) the consume goes from 48 to 55 l/day... more or less, a little more than 1/2 fuel tank, which capacity is 90 litres


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Post by TimOnders » Fri Oct 02, 2009 5:02 pm

You can generally find the preferred cruising RPM from the manufacturer's data for the engine (the torque and power curves).

For a D1-20, the cruising speed is about 2400 RPM. For a MD2020 (older D34s) it would be about 2800 RPM.

The other thing you need to do is to match the prop to the engine. You want the engine to be able to reach its full-throttle speed (3200 for D1-20, 3600 for MD2020) at full throttle, not before. If it doesn't make it to the full-throttle speed, your prop is too big. If it makes it too easily, it's too small.

The rule of thumb is 1" of pitch = 200 RPM, although since the selection of blades for the Volvo folders is somewhat limited, you may need to guess a little bit more. On the plus side, blade sets aren't that expensive right now (~$250 USD).

We just replaced our MD2020 with a D1-20 but retained the original sail drive (long story - I'll post soon). Volvo had changed the gear ratio in the newer sail drives to match the slower D1-20 (the prop speed is identical), so we're going to a 16x11 prop (stock is 15x9) to compensate for the lower prop speed. It's not optimal, but it should work out ok.

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