Ideal Cruising RPM's

Paul_S · 01 August 2016, 07:23

I know it's a case of how long is a piece of string....but that said, what rpms do you guys normally cruise at.

My outboard is a 2012 150 Yamaha Fourstroke.

I cruise at 4,000 rpms, but would truthfully prefer to be at around 4,500, but it sounds like I am thrashing it and I don't want to tear it up. It does sound much sweeter at 4k, but hauls ass better at 4.5.

Thoughts?

matata · 01 August 2016, 08:22

A short storey long!! We decided passengers don't chat and stop enjoying the cruising experience above 25knots, between wind, waves thumping etc. 20knots is a little slow, so for us its 23/23 knts at 4250 (depending on prop) Also when you say best cruising speed do you mean best for range? I would have thought 4250 is probably best range revs also (approx).nik

Pikey Dave · 01 August 2016, 09:05

The first thing you need to determine is whether you are correctly propped. Can you reach your WOT range with your normal load? If so, it's a case of what's comfortable/economical for your rig. I have a Suzuki DF140a lean burn. The most economical rev range is around 4500 which just happens to be around 25kn. I am propped spot on at 6000rpm WOT. If you are correctly propped you won't be stressing your engine at 4500, assuming your engine's WOT is around the 5500-6000 mark

Lions led by donkeys

jonp · 01 August 2016, 09:15

My yam 4 stroke has a max rpm of 6300, I have no problems running at 4700 for long periods to get offshore. An average day on the water is normally over 100km.

According to Yamaha Au these engines are designed to run at even higher rpm for long periods at a time without causing any problems. Why not ask a reputable Yamaha dealer or Yamaha UK.

Jon

Paul_S · 01 August 2016, 10:15

Quote:

Originally Posted by jonp

Why not ask a reputable Yamaha dealer or Yamaha UK.

When there's such a plethora of informed members on here

Xk59D · 01 August 2016, 10:33

Your sig says it is a merc 150?

If it is a yam then Davie if the one to ask on here for an informed answer.

HUMBER P4VWL · 01 August 2016, 10:52

It also depends on your boat as to what power is needed to keep you on the plane at that "relaxed sweet spot". As you say yourself, you'll "feel" when it's right or stressed.

The same 150hp engine will vary in terms of the sweet spot from boat to boat I'd imagine.

We cruise at 3800-4200 with a 2 stroke 175 optimax on a 6.3 rib, depending on load. My mate has the same engine on a bayliner type cuddy 6.5m and needs to sit at about 4600-4800 to "feel" relaxed, as there's much more weight.

And all that varies on the prop you have on, as others have said.

Paul_S · 01 August 2016, 11:19

Quote:

Originally Posted by Xk59D

Your sig says it is a merc 150?

If it is a yam then Davie if the one to ask on here for an informed answer.

Haha, it is a merc. I don't know why I said Yamaha, perhaps it's a subliminal desire to own a yammie

or a sign that early morning posting needs to be better monitored.

paintman · 01 August 2016, 11:35

Quote:

Originally Posted by Pikey Dave

The first thing you need to determine is whether you are correctly propped. Can you reach your WOT range with your normal load?

^^^This.

Paul_S · 01 August 2016, 14:53

I will get out on the boat next week and see what wot is, then repost.

Pikey Dave · 01 August 2016, 14:58

Quote:

Originally Posted by Paul_S

I will get out on the boat next week and see what wot is, then repost.

👍 need to get the fundamentals right before you start tweaking😄

Lions led by donkeys

Maximus · 01 August 2016, 19:03

Ideal revs all depends on Sea Conditons in my experience

It's often much better to up the revs..(and speed) to get on top of the waves for comfort of crew.. and stability..things like loading.. Wave direction and trim will make a big difference too.
If you have a fuel flow meter (in calmish conditions) it's sometimes interesting to see the fuel figures and revs changing in relation to changing Trim..(Hull angle of attack) where even small changes impact...That will soon indicate to you the most efficient low Drag combination and Cruising speed (revs) for your own Boat,Hull,and set up..although it will alter with loading ect as said
Ultimately you soon get to know your Boat,and it becomes a matter of "feel"

Pikey Dave · 01 August 2016, 21:46

Quote:

Originally Posted by Maximus

Ideal revs all depends on Sea Conditons in my experience

It's often much better to up the revs..(and speed) to get on top of the waves for comfort of crew.. and stability..things like loading.. Wave direction and trim will make a big difference too.
If you have a fuel flow meter (in calmish conditions) it's sometimes interesting to see the fuel figures and revs changing in relation to changing Trim..(Hull angle of attack) where even small changes impact...That will soon indicate to you the most efficient low Drag combination and Cruising speed (revs) for your own Boat,Hull,and set up..although it will alter with loading ect as said
Ultimately you soon get to know your Boat,and it becomes a matter of "feel"

Adding to what Maxi says, surprisingly with the modern DFI engines, faster actually gives improved economy within limits. I get better economy at 4500 rpm than at 4000 rpm due to the lean burn feature. My Etecs were more efficient at 4700 than at 4200. You need accurate mpg data to find the optimum combination of rpm & trim.

Lions led by donkeys

Paul_S · 02 August 2016, 14:38

Does anyone have a good way to get mpg's. Like I said I have a 2012 Mercury 150 fourstroke. I have just a few gauges....speed, rpms tilt and fuel (nothing even for oil pressure or temp).

I do have a Lowrance HDS7 which has a page for engine information, but I don't have it connected to the outboard.

What's the best was to do this. Standalone fuel flow, or Lowrance.

Pikey Dave · 02 August 2016, 17:25

The best way is to create a nmea2000 network & link the engine to your HDS, this will give you all the info you need. I don't know what you already have, so can't advise on how easy/expensive this would be.

Lions led by donkeys

Xk59D · 02 August 2016, 17:32

Engine data on the plotter is the way to go for me, not a separate flow gauge.

If you have nmea currently on the boat that is half the battle?

It will pay for itself over time in fuel saved if you monitor it. It is surprising what a couple of clicks of trim does to the lph usage.

Paul_S · 02 August 2016, 18:15

I'm at the boat next week, so i'll have a look and update the thread.

Jeff · 03 August 2016, 09:01

Do you have the smartcraft speed and tach gauges Paul ? They should be able to show fuel flow (ltr/mile) fuel used, oil pressure etc in the lower LCD screens

Paul_S · 03 August 2016, 11:13

Hi Jeff, pictured below is my helm. My gauges are like me...the non smart version. There is a screen on the chartplotter to show engine data, but non of it registers, it doesn't appear to be connected to the outboard.

I may be wrong and it just needs to be configured correctly, but my guess is I don't have the NMEA 2000 network connected between the plotter and the outboard.

If that proves to be the case (and I'm sure it is) I am assuming to connect the 2, I would need a NMEA 2000 wiring and t's (a starter kit?), plus an interface of some kind to connect the merc fourstroke to the wiring.

Any thoughts.

Xk59D · 03 August 2016, 12:20

in order to tell if you have nmea then take the plotter out and see if anything is plugged into it is probably the simple way to do it.

similarly you could check the engine interface and see if a cable is in there too.

given the plotter doesn't show anything and you have non smart gauges i assume you don't have any NMEA on there so you are bang on in you will need a starter kit and the engine loom potentially.

Literally a few clicks of trim is the difference of 2-3 litres per hour on my rib so depending on your usage it could pay off quickly. i have probably done maybe 800 miles in last year so mines has paid for itself for sure.

cheers