Need some help researching fuel consumption

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
N

nmcafee

Member
Joined
Sep 1, 2020
Messages
15
Location
United States
Wife and I are putting together a 3 year plan that will have us puttering around the Gulf and Bahamas in a ~55 foot cruiser. Am trying to consider fuel consumption as part of our criteria to narrow down potential boats. One that keeps hits a lot of the things on my list is a Sea Ray 550 Sedan bridge.

Is there a good way to research fuel consumption? Most of our cruising will be in the 10-12 knot range.

Most that I see in our price range (150-200K all in) have dual 705 hp detroit diesels.

Any advice on how to research fuel burn?

Thanks in advance, have just joined the site and trying to soak up as much info as possible.
 
As a newbie, I just called up the selling broker and asked for inventory lists(for tankage volumes) and range/consumption figures. Obviously, take any seller supplied figures with scepticism but you should notice a pattern of typical figures appear.

Note that this can vary wildly based on cruising speed. I also corrected to a given speed (back to 6 knots full displacement for me) using an online calculator. Again this is indicative only but allows for an approximate apples to apples comparison between different vessels.

I'm not sure what numbers you are expecting but big 2 stroke detroits are HUGELY thirsty at speed.

This is the calculator that I used:

https://www.vicprop.com/calculator.htm

Good luck
 
20-years ago, I spent about 5 years as a full time delivery captain along the pacific coast. Dearth of fuel stops and long runs means fuel range was a normal question. Owners were rarely even close to accurate - if I'd listened to them, I'd still be bobbing somewhere off Cape San Martin.

For a boat your size, I typically started with 1 gpm at around 9 kts and adjusted based on gut feel. I'd actually guess that's around what the searay you mention would do. Further, my hunch is that at 12 kts, fuel efficiency would decrease by at least 30% and throw a pretty big wake. My understanding is diesel in the Bahamas starts at $5/gal and goes up pretty quickly from there. Running at 25 kts can easily burn 50-60 gph which means you'll spend a lot of time thinking about fuel and replenishing your credit card.

As an aside, if fuel costs will keep you at slow bells, you might want to consider a boat with bigger rudders that is designed for semi displacement speeds. Your A/P will thank you for it.

Good luck!

Peter
 
Last edited:
Greetings,
Welcome aboard. If you're simply "puttering around" and not doing any LONG cruises at higher speeds, fuel costs will be way, way down the list of concerns.
Get the boat you like and enjoy it.
 
nmcafee said:
Wife and I are putting together a 3 year plan that will have us puttering around the Gulf and Bahamas in a ~55 foot cruiser. Am trying to consider fuel consumption as part of our criteria to narrow down potential boats. One that keeps hits a lot of the things on my list is a Sea Ray 550 Sedan bridge.

Is there a good way to research fuel consumption? Most of our cruising will be in the 10-12 knot range.
Click to expand...


I dunno those engines, but...

If you run that boat somewhere between 7.5-10 kts you'll probably be getting best possible.

When we ran our 450s at anywhere under 1200 RPMs, we got between 1.5-2.0 NMPG... according to the Cummins fuel consumption curves and our typical speeds at that rate.

FWIW, fuel was never our largest expense.

-Chris
 
Thanks for replies

I appreciate the guidance and opinions. My wife immediately jumped to the largest boat we could find in our price range. I keep saying we don't need a 4 cabin floating apartment. Down deep I dont really care if we have unused space, however, I see us cruising between Florida and Bahamas in the non-storm season and up the east coast spring/summer. The difference between most 52 footers (my target range) and low 60 footers (hers) seems to be monumental in gas cost.

I have 15K budgeted for fuel for 1st year of living. Would love for that to get us 5000 miles instead of 2500.
 
10-12kts and you will burn a lot of fuel on a SR 550 with 892. Basically plowing a hole in the water. Probably 15-20gph total

8-9kts way better on fuel. Probably 10gph total.

If you don't really need a boat that big, get something smaller.
 
nmcafee said:
I appreciate the guidance and opinions. My wife immediately jumped to the largest boat we could find in our price range. I keep saying we don't need a 4 cabin floating apartment. Down deep I dont really care if we have unused space, however, I see us cruising between Florida and Bahamas in the non-storm season and up the east coast spring/summer. The difference between most 52 footers (my target range) and low 60 footers (hers) seems to be monumental in gas cost.

I have 15K budgeted for fuel for 1st year of living. Would love for that to get us 5000 miles instead of 2500.
Click to expand...

"I have 15K budgeted for fuel for 1st year of living. Would love for that to get us 5000 miles instead of 2500"

The 550 Sedan Bridge should get you better than 5000 miles at 7 knots and less than 2500 miles at 20 knots.
Your largest variable will be the speed at which you choose to travel.
 
Here's how I would suggest going about this. Fuel consumption is significantly dominated by the boat's speed. Other factors are displacement and water line length, but they pale in comparison to speed .


For any given boat, the weight and length are fixed, so the only thing you can control is your speed. The more speed, the more HP required from the engines, and the more fuel they will burn to create that HP. Ignore the number and size of the engines, that's almost immaterial, and completely immaterial compared to speed.


Boatdiesel.com has a calculator to compute the HP required to move a boat at a certain speed. https://boatdiesel.com/Members/Calculators/PowerRequired.cfm?TZ=-4&SC=1440.900 You enter in the type of hull, weight (displacement) and length, and the speed you want to move. It will then tell you how many HP are required to do that. To be conservative, assume a diesel can product 16hp per gallon per hour. So if the calculator tells you you need 64hp, you will burn 4 gph. You can then some math to computer nautical miles per gallon (NMPG), range, etc.


I think what you will find, considering boats all of about the same length and displacement, is that fuel consumption will be pretty much the same, provided you run them at the same speed.
 
I was astounded to find I burned ~20 GPH on a 2003 33' SeaRay Sundancer once. 20kts. Twin 425 Mercruiser (gas). I would imagine a 55' would be a lot more...
 
Perhaps, since this is a new venture for you, you & your wife should carefully consider, how you want to cruise I.e. how far each day cause that will significantly affect your choice.
10-12 knots sounds good but doesn’t work - as Ski said you will be just plowing a big hole in the ocean and burning fuel for no gain. Now you are back to 7-9 knots burning 5-6 gph, or 16 knots burning 3 times that. At 8 knots average, a good day on the water only gets you 60-75NM. Does that fit with your expectations/lifestyle?
We are used to 7 knots, but know a lot of good folks who go crazy at that speed. Others cruise at 7-8 knots but relish being able to plane to get somewhere quickly for lifestyle Considerations or (perceived) safety. For most of us, fuel is a pretty small part of the Total cost of boat ownership, not unimportant but probably doesn’t drive the purchase algorithm as much as many assume.
 
Speed Kills ,,,,, your budget.

On a cruise there is hardly reason for speed , just plan on 60-70 miles a day its easy inland as the miles are shorter.

Most IO boats about 25 ft will do 20-25 statute MPH at 10-12 MPG.

IF speed is a Requirement , space is all you give up.

If speed is a Desirement , bring a thick billfold.
 
Last edited:
FF said:
Speed Kills ,,,,, your budget.

On a cruise there is hardly reason for speed , just plan on 60-70 miles a day its easy inland as the miles are shorter.

Most IO boats about 25 ft will do 20-25 statute MPH at 10-12 MPG.

IF speed is a Requirement , space is all you give up.

If speed is a Desirement , bring a thick billfold.
Click to expand...

Assume you meant GPH, not MPG above....
 
boathealer said:
Not disagreeing with you, but do you have any data pointing to that? Everything I can find shows "typical" being 2-4 mpg. One example:

https://www.activefisherman.com/boat-specs/boat-fuel-economy

6-10mpg, seems to be the exception, not the other way around.
Click to expand...

First wass our 22' Bayliner with a single IO - about 6 nmpg (heavier and older).

Then various boats with outboards including a 19' , 22', 24' and a few shorter ones.
The outboards varied by type (2 vs 4 stroke) and size but were mostly 4 strokes.
Depended mostly on the weight of the boat and how fast you wanted to go..
 
Instead of counting staterooms, look at the lay out. A bigger owner's stateroom, a larger 2nd stateroom or split the space between the 2 remaining staterooms.
On a boat that size, 2 dry heads with 2 decent showers.
Now, everyone is worried about the main engine going belly up so either a 'get home' engine or a 2nd engine.
On a middle 50 or 60 ft boat, you should have more than enough closet space.
Maybe you wife is going to move friends onboard forever?
Personally, I think a mid-50ft is large enough for 4 people.
Cost of fuel? If you are burning too much, slow down. There is nothing wrong with traveling at hull speed especially when you know you have lots of reserve speed to beat the tide or get the best slip, etc.
Remember, you asked us to 'spend your money'. LOL
Now if you want to remain within budget..... be reasonable. 2 staterooms, one dry head, one main engine, a nice generator, A/C and a galley in which YOU will enjoy cooking. SMILE
 
Last edited:
You must log in or register to reply here.

Similar threads

R
Thrusters Not needed??
2 3
Replies
67
Views
5K
Hippocampus
H
Roger Long
Rolling, rolling.
Replies
12
Views
2K
Kit_L
Kit_L
RickyD
How many things can go wrong in one day???
Replies
15
Views
3K
sealandsky
sealandsky
O
Hello All, Looking for Research Help
Replies
8
Views
1K
orange150
O
G
Power ratings and a new engine decision: Need some help
Replies
26
Views
3K
OldDan1943
OldDan1943

Latest posts

Back
Top Bottom