Most Economical Speed

[elad9000]

Has anyone tested their 28TE for the most economical speed (RPM) taking into account both fuel consumption and distance traveled? Maybe someone with a Floscan has run some tests. I usually run with two people, half tank of fuel and full water tank.

[craw_daddy]

I saw this in the general forum...

If the actual LWL of a 28 is 24 feet then any engine and prop combo that will drive it faster than 6.56 knots will cause it to plane. I would imagine a Cummins having more than 200 bhp would do that. My Yanmar 6LP has 315 bhp and it drives the boat about 15.7 knots at the "most efficient" engine speed of 3,200 rpm.

--Dave

[Mariner]

Generally speaking, you will find that the most economical speed is also the slowest. Unfortunately, this is not practical for most people, so they instead settle for a practical compromise, and cruise at a speed just below where the fuel efficiency drops off drastically.

[Dave39]

My Yanmar dealer said the 3200 rpm I "cruise" at would be the most efficient under normal conditions. No one should run a diesel at low rpm's for any length of time as you risk harming various engine elements.

[elad9000]

I hear 3200 rpm a lot a the "best" cruise speed but, that is about 85% of WOT at roughly 3800 rpm. Seems a high percentage. Also, I notice my gas engine car running at 3000 rpm at 70 mph. Don't diesels run at lower RPM than gas motors?

After having some problems with valve noises (had new seals installed) and experiencing a rocker arm failure I have run mostly at 3000 rpm. Used to run at 2800 but noticed large incremental speed at 3000 rpm. I do not see so much better speed at 3200 rpm.

Seems to me the "best" speed is 3000 - 3200 rpm. Just wondering if anyone has Floscan data to put a metric on the issue.

[Mariner]

I hear 3200 rpm a lot a the "best" cruise speed but, that is about 85% of WOT at roughly 3800 rpm. Seems a high percentage. Also, I notice my gas engine car running at 3000 rpm at 70 mph. Don't diesels run at lower RPM than gas motors?

After having some problems with valve noises (had new seals installed) and experiencing a rocker arm failure I have run mostly at 3000 rpm. Used to run at 2800 but noticed large incremental speed at 3000 rpm. I do not see so much better speed at 3200 rpm.

Seems to me the "best" speed is 3000 - 3200 rpm. Just wondering if anyone has Floscan data to put a metric on the issue.

Gas engines have higher redlines. In cars, since they have geared transmissions, they generally spend more of their lives at lower rpm's than a marine engine. But, to put things in perspective, most GM gas V blocks red-line at 5,500rpm. In a boat, it would not be unusual to cruise at 4,000 to 4,500rpm. So, comparatively speaking, you are running your diesel lower than you would a gas engine.

I feel like people have posted fuel curves here in the past, but a search didn't come up with anything, so maybe someone remembers where it's at. I know I've posted several for our boat, but that's a different hull and engine, so it wouldn't be of much use to you. The data is readily available, but of course, it will be unique for each boat, due to propeller selection, weight loading, and, of course, different engine models.

[mhanna]

To sum it up the fast you go the more efficiency you loose.
Here is the link to the past conversations of fuel usage. Both Maye Marie and myself posted some data showing usage and we seem to be real close.

http://albinowners.net/aog/viewtopic.ph ... sc&start=0


Matt

[RobS]

Matt, thanks for including that link, I read that last fall but forgot just how much data was there. Question: Has your engine been photo-tached? I did mine at time of survey last year and again last week to confirm. Dash tach reads 150rpm higher that actual. From what I have read on boatdiesel.com this is the norm for Yanmar.

[Donya]

According to our Flow scan unit that I installed in February of this year and after 62 hours of running it looks like BEP is 3050 RPM, 15.5 kns. 2.02 kmpg.

3250 RPM, 18+kns, 1.89 kmpg.

I think that it is still reading a little on the heavy side yet, it takes a 100 or more hours to get the calibration dialed in.

If your are not in a hurry, 1550 RPM , 6.8kns, 4.5 kmpg

315 Yanmar, motor box, tanks full, full gear onboard.

[mhanna]

Rob, I think what you mean is did I get the dash tach gauge checked to a external device ? No I have not, but I think as part of my engine work it will be checked.

I have a handhead for the car one but cant find sparkplug # 1 ....ideas ?




Matt

[RobS]

Rob, I think what you mean is did I get the dash tach gauge checked to a external device ? No I have not, but I think as part of my engine work it will be checked.

I have a handhead for the car one but cant find sparkplug # 1 ....ideas ?




Matt

A photo tach shoots a laser beam at a reflective mark on the harmonic balancer. Due to the reverse tranny the balancer is at the stern end of engine (nearest the bulkhead for the fuel tank)