411 fuel con. and extra tanks
I was wondering if anyone has fuel consumption and speed to rpm data on the 47 HP 4 Cylinder Perkins 4.108 Marine Diesel Engine on a an S&S Swan 411. My own ocean experience is 2,5 l/h at 1600 rpm for charging and about 3 l/h at 2000 rpm = 5,5 kts on a very calm sea.

Concerning the fuel tank discussion, on my last crossing, I added 10 x 20 liter jerry cans tied in the fore and aft cabins with a couple of cans on the windward deck. We crossed Trinidad to the Azores in 18,5 days, we consummed 70 liters of fuel for 27 hours of charging (about 2.6 liters/hour) - which means we didn't touch the jerry cans. Between the Azores and Malaga we motored for abput a day, but from Malaga to Perpignan we motored about half way. For my next crossing I will carry less and generate electricity with a Duogen. I prefer to concentrate my time and energy on finding the optimal weather route, play off the squals and use the motor as less as possible. I get more out of finding the fastest vmg and twixing the sails for the extra 0,25 knot. I have made numerous polar charts and determined the consumption of my engines but in the end there have always been too many variables in real sea conditions to achieve any degree of exactitude. I am totally against adding any additional permenant tanks. Though it takes some dextarity to haul up a 20 kg can and pour it into the fuel intake on deck in rough seas with out any sea water getting in and no fuel spills on deck, I would rather save the little "free" space below deck for multiple functions than fill it with a tank I may rarely ever use. And I guess I more concerned with trying to get stuff off the boat. Pippo 411/22

Pippo, I am currently exploring this. Have you considered fitting a water maker and using the third water tank to hold fuel.

I replaced my 4108 with the Perkins M65 and we get approx 7knts at 1900 revs giving 5lts per hour.

If you have any polars I would be very interested in a copy.

John, what i meant to say was that I'm happy with the tanks as they are, and when I need more capacity I just add jerry cans as needed. Concerning the polar, I don't have accurate instruments or a pc connection on board the 411. I've made a test polar (Excel file) that I can send you if you send me an email. Do you have a 411? If so let me know how this polar seems to you. On other boats I've made polars for different sea conditions for racing but this necessitates recording lots of data on a pc while sailing. Hope to hear from you soon, Pippo

Pippo.

Yes I own "Avista" a 411 no 10.

I also plan to use gerry cans in the short term, but this is not a long term solution for me. I am in contact with S&S in the USA and have asked them if they have polars, but no response so far.

If you have any polar measurements, I would be grateful for a copy. I am trying to set up my Seapro charting software for optimum routing.  

I conducted some sea trials last week on speed against / revs. 

Fuel consumption figures against revs are given in the manufactures engine specifications.  So I now have a complete tabulation for Perkins MD65.

My e-mail is;  j-g-bailey@btconnect.com

Pippo/John

Having just bought 411/025, Sophie B, are these polars available or updated? Would be most grateful for a copy, and if I can add to the data in anyway in the next few months (though we're going into winter) would be happy to exchange.


Thanks in advance

Tom[at]moultrie[hyphen]online[dot]com

Tom, I have the polar I was working on a few years ago. I'm not sure how accurate it is and would be very interested in your feedback. If you send me an, email address I'll send it to you. a presto Pippo

Thanks, Pippo

Tom@moultrie-online.com


Will add as and when I can

Tom

Pipo, this thread started some time back, but an update on my experiences. I chose to fit a water maker and this works well for me. Trying to increase the fuel capacity by utilizing one of the water tanks turned into an engineering nightmare so I did not proceed with this. My Perkins MD65 is performing very well and can charge the battery bank and run the water maker without any stress. I find I am getting 2.5 to 3 litres per hour at cruising revs of 1800 which gives me approximately 6 knots in most conditions. I decided to carry spare fuel in jerry cans like you.

John B
411 010

I had that engine in my Swan 41. Burned about a gallon per hour at 1800 rpm, cruising at around 6 knots in calm conditions. After 37 years of service converted this winter to a Yanmar 54 hp. We'll see how that turns out.

Just some comments on the two previous posts hoping that our mentor Lars Strom enters the discussion. Isn`t 1800 RPM a bit too low for cruising? I usually cruise at 2100 RPM and, I understand, it is considered pretty low as well. Moreover I was told that the expected fuel consumption for an engine like the Perkins 4.108 at cruising speed and smooth condition should be lower than 2 l/h.
I know that this a repetitive subject but I wonder what I/we should do to improve the performance of our engines: lower the pitch of the propeller and not be afraid to cruise at higher RPM?
Daniel, 411/004

Daniel, max torque on the Perkins MD65 is at 2300 revs. The most I can get is about 2200 out of the engine. The stern is then deep under water and consumption up to approx 5 liters. Pushing too much water.
I have configured my power train for max distance not max speed. I would have liked to have fitted a Bruntons Auto prop but the cost is high and I would then also need a prop brake as the gearbox is hydraulic.

Our hull shape is also not particularly good in terms of being driven / pushed by engines.

Dear All
Many things about propellers were presented in the thread dated 08 May 2010, suggest you take a look there. Here some comments to your posts now:

Pippo, the rpm, speed, and consumption is not dependent on the engine only, also the propeller is a very important link, and if not identical on two boats this can affect the performance. Swan 41 and 411 can be expected to consume about 2.5 to 3 litres/hour at 6 knots with efficient propellers, the rpms vary depending on engine, reduction ratio and propeller size.

CBinRI reports one gallon consumption at 6 knots, assume this is US gallons, 3.8 litres, Which type propeller did you have?

Daniel, John's engine is a M65 with a slightly lower max rpm than the 4.108.

John, you inform that the maximum achieved rpm is 2200. The nominal maximum is 2600 rpm for this engine, and this means that the propeller curve and fuel consumption given by Perkins do not apply. I have plotted the new propeller curve corresponding to 2200 rpm max in red on the appended diagram, the consumption is then 1.79 times higher at the same rpms. I would suggest that 6 knots is reached at 1600 rpm.

Generally it can be said that the lower the engine rpms the less fuel is consumed per mile, but idling should not be used, the consumption just to keep the engine running becomes dominant. Also, Perkins recommends that at least 25% of the full power needs to be used in order to prevent the engine from collecting soot, for John this conveniently is 1600 rpm.
Pls feel free to ask questions.
Kind regards
Lars
PS Unable to add diagram, generates error message

File size is 44 kb, but refused to upload

On second thought, I misspoke about my RPMs.  Last year I rarely ventured above 1800 RPMs as my engine was on its last legs and I rarely motored, other than on and off the mooring.  To get to 6 knots (or thereabouts) I would probably be more about 2200.  But I believe that about a gallon per hour was more or less right.

Dear Daniel
You would like to know what the optimum propeller pitch setting and rpm are for cruising specifically for your yacht.
For finding out this I did some serious number crunching assuming 15 hp propeller power at 6 knots with Perkins 4.108, reduction 2.91:1, and 21" 3-blade Max-Prop.
Your Max-Prop pitch is adjusted in two degree steps.
Here the results:
Pitch setting 18 degrees, 2367 rpm, thrust 2192 N
Setting 20 degrees, 2204 rpm, thrust 2201 N
Setting 22 degrees, 2061 rpm, thrust 2192 N
The 20 degrees setting produces the best results, although the differences are surprisingly small, about 0.4% measured in thrust. You may remember that 20 degrees was also recommended for achieving 3000 rpm at full throttle, although you probably never will attempt this.
Would appreciate feedback on the rpm actually required for 6 knots.
For determining the fuel consumption precisely an electronic gauge with sensors on the feed and return lines is required, or alternatively a calibrated day tank.

Kind regards
Lars

Dear Lars,
thank you, your reply could not be more clear and exhaustive. I think my propeller is already set at 20° but I will check.
I browsed again the thread you mentioned and indeed everything was already very well explained there - this is why I think my prop is already set well; unfortunately I tend to forget!
The important and very useful topics like this which are often spread over several threads and posts should be grouped in one document easily reachable... Lars & Matteo????
Regarding the fuel consumption, exact measurements in optimal conditions are probably not necessary: averages over normal cruise conditions are much more useful and we can easily compute them with the log book we all keep.
Thank you again for your patience, Lars!
Daniel, 411/004

Dear Daniel,

I would be glad to add a document on the "Manuals" section of Classicswan, do you think this could help?

In positive case if you could send me the text in word I will prepare a pdf doc and will upload it

Thank, and fair winds!

matteo (38/067 Only You)

Dear Lars. FYI on my Perkins MD65. I went for the first run out this session with the engine and in flat water. At 1600 revs 6.0/6.2knts. 1800 revs 6.5/6.8knts the stern is just touching the water. I then opened up the throttle to max possible 2400 revs 8.1/8.3knts. At this point the stern was under water to the extent that the exhaust discharge was going under water at times. (I have a non return flap fitted)
My normal cruising revs are 1800 which returns approximately 2.5 litres per hour. As stated before, anything above these revs gives little extra speed at a large increase in fuel consumption.

Dear John
Thank you for the information
You are right that the fuel consumption rises very steeply at higher rpms, with very little increase in speed.
It can be estimated that the engine output at 1600 rpm is about 17 hp, and at 1800 rpm 24 hp.
Wishing you pleasant sailing
Kind regards
Lars