Planing

[billnpat]

Can anyone tell me if gas is saved by running at "cocktail" RPM or by planing?

I've spoken to 2 different experienced captains and gotten opposite opinions!!

Also, what is considered "cocktail RPM on a 310 SeaRay....

Thanks!:smt001

Also would wear and tear on the engines etc, be more prevelant going at slower speeds"""""

 

[SCORPIO]

No question, cruising at 6 knots will use less fuel than planing speeds. On my 300, 6 kts. is a fast idle that burns like 5 gph per engine. At 24kts planing, I'm burning like 14gph/engine.

 

[Bel_Mar_Pointe]

Can anyone tell me if gas is saved by running at "cocktail" speed, or by planing?

I've spoken to 2 different experienced captains and gotten opposite opinions!!

Also, what is considered "cocktail speed?" on a 310 SeaRay....

Thanks!:smt001

Cocktail speed eh? The absolute best nm/gl results for my boat are at around 1000rpm, which is damn slow, maybe cocktail speed. The next most efficient range is between 3200-3800rpm and on plane. Plowing water at around 1500-2000rpm I am sucking more than twice the fuel than while on plane. There are charts that show this data, I just recall the source. I'll take a look-see.

 

[Jimmy Buoy]

If you have 50 miles to go, it might be somewhat cheaper to go "cocktail" speed, but it would take 5-7hrs to arrive vs 1.5-2hrs at planing speeds. Also, if you are in any kind of a chop, you'll also be more likely to spill those cocktails :smt009 while rolling in the waves off plane.

If you have 3hrs to kill, sure cocktailing would burn much less fuel than 3hrs on plane.:thumbsup:

Bottom line is that it depends on what your objective is - get to a destination within a certain time frame or just spend some time out on the boat.

I like cocktailing myself! :grin: (going slow too)

 

[mwph]

Stricktly from a math standpoint...

6 knots @ 10gph for 6 hours = 60 gallons for a 36 knot trip.
24 knots @ 28gph for 1.5 hours = 42 gallons for the same trip.

Scorpio - Does this sound right?

 

[Sundancer]

If you look at the curves, the most miles per gallon is at idle. No throttle at all! Of course, who wants to take THAT long to get anywhere?? The other problem with idling is that you won't make much headway against a current or wind.

 

[SCORPIO]

Depends on what your intended desitnation is. If you are on a 36kt trip, it wouldn't make sense to idle there. On a strictly gph basis, slower is better. On a miles per gallon basis, planing would be better. If I were to run 36kt at idle, I'd probably do it on one engine at 5gph and burn 30gal. but thats just hypothetical.

Like George Carlin used to say, "theres no two ways about it, therer are two sides to every coin".

 

[billnpat]

:thumbsup:Thanks for the replys..

We were just thinking of cruising around not going anywhere in particular since we're new boaters to a new area, we just want to explore nice n easy.....and enjoy the water...

1000 rpm is our ideal for cock tailing.........:smt001

 

[tobnpr]

:
1000 rpm is our ideal for cock tailing.........:smt001

Ummmm...
Sexual preferences notwithstanding...I prefer cocktails, myself...

But, whatever floats your boat...

Sorry, I couldn't resist...

 

[Four Suns]

This is like the argument about how electric cars get better gas milage... since they use no gas, it's true!

I'm not convinced that running a boat designed for planing at displacement speeds saves any money. If you consider the substantial increase in hours as well as the maintenance due to not running an engine properly and the effect on the boat's value, I'm guessing running a boat within the design envelope is better.

Boats that are designed to run at displacement speed (less than 10 knots) have small engines put in them so they are running at the engine manufacturers recommendation for continuous RPMs. My QSM-11's are not designed to run at 650 RPM's for hours on end and if I do, they are going to get crapped up from the engine not running hot enough to not enough fuel and lubrication running through the internals.

So.. if I'm running 1/3 the speed, I am going to have 3 times as many oil changes for a given distance I need to travel... along with all the other issues from idling an engine all day long. Not worth it IMO.

Also, your hull form and running gear (i.e. rudders) are designed for a certain amount of water flowing over them to work properly. If you've ever been caught in a squall/storm/heavy seas, you found out that your rudders don't provide too much directional control with the idle speed prop wash. My boat can not point into a 60mph wind at idle... the wind controls the boat. A Nordhaven has a rudder the size of a door. A Sea Ray has rudders the size of note pad.

So... you may save 30% on fuel but you'll up all your other costs and increase your depreciation.

My 2 cents.

 

[320Bob]

Bill,
I think part of the problem is I think your boat predates the SmartCraft system that I and many others have on their newer Sea Rays. This system gives you a number of operating parameters that would answer the question you are asking. As others have pointed out, running at planing speed indeed reduces your mpg but increases your gph (gallons per hour). If you want to use the least amount of fuel for a given distance then run on plane. If your are more interested in getting more hours out of a tank(s) full, then run at cocktail speed.

I've found that around 1,500 rpm to be a good cocktail speed using 5.5 gph. If I go up to 2,000 rpm my gph go up to around 11 and my speed is only 2 knots higher so not much bang for the buck. Another issue that no one has mentioned about cruising at lower rpms is battery charging. When I first got the boat my port batteries were depleted and the CO alarm was going off until we throttled up to 2,000 rpm. Since I have a generator, I can run below this level and still be able to charge the batteries running at lower rpm. To have enough water running past the rudders to effectively use the steering wheel, I have found that I need to be at around 1,000 rpm.

Gary's point about more frequent oil changes would apply if you plan to run your boat more than 100 hours per year. In my first month of ownership I have put 7 hours on the boat which would be around 50 for a whole season which I think is fairly typical usage. The manual says change the oil every 6 months (a season up north) or every 100 hours. Since I would have to change the oil at the end of the season anyhow, it's not an issue for me.

What I plan to do is spend most of the boating hours at 1,500 rpm cocktail speed but an equivalent number of boating miles at planing speed since I like to cruise fast also.

 

[Gofirstclass]

I have a FloScan fuel monitoring system on my boat and when I installed it I did tests at every 200 rpm's from idle to 4400 rpm's.

I was somewhat surprised to find that at idle and up to about 1200 I got right at 1 mpg. Above those displacement cruising speeds and up to about 3000 rpm's the fuel economy dropped dramatically because I was plowing through the water.

Once I reached 3200 and the boat came fully up on plane and the economy went back up to 1mpg. It stayed there until about 4000 rpm's. At that point the secondaries start to open and the economy again drops off.

IMHO if you're cruising to a destination the advantage of operating at planing speeds vs displacement speeds is that you are putting about 1/3 the number of hours on the engines. That lower number calculates into less frequent oil changes, tune ups, etc.

Running on plane also helps reduce carbon build up in the engine and they seem to run better when they've been run on plane for any distance.

 

[magster65]

I'm just using the smartcraft numbers but it seems my last few DA's (on my 4th) see the best mpg at under 1100 rpm or over 3600 with a 'bad' range from 1200 to 3000 or so(ish) rpm where planing isn't 'right'. My 290 seems to like 4000 rpm (high 30's mph).
Anyone experienced anything much different?

 

[billnpat]

This is like the argument about how electric cars get better gas milage... since they use no gas, it's true!

I'm not convinced that running a boat designed for planing at displacement speeds saves any money. If you consider the substantial increase in hours as well as the maintenance due to not running an engine properly and the effect on the boat's value, I'm guessing running a boat within the design envelope is better.

Boats that are designed to run at displacement speed (less than 10 knots) have small engines put in them so they are running at the engine manufacturers recommendation for continuous RPMs. My QSM-11's are not designed to run at 650 RPM's for hours on end and if I do, they are going to get crapped up from the engine not running hot enough to not enough fuel and lubrication running through the internals.

So.. if I'm running 1/3 the speed, I am going to have 3 times as many oil changes for a given distance I need to travel... along with all the other issues from idling an engine all day long. Not worth it IMO.

Also, your hull form and running gear (i.e. rudders) are designed for a certain amount of water flowing over them to work properly. If you've ever been caught in a squall/storm/heavy seas, you found out that your rudders don't provide too much directional control with the idle speed prop wash. My boat can not point into a 60mph wind at idle... the wind controls the boat. A Nordhaven has a rudder the size of a door. A Sea Ray has rudders the size of note pad.

So... you may save 30% on fuel but you'll up all your other costs and increase your depreciation.

My 2 cents.

Thank you....well taken :thumbsup: