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LShulan

Fuel economy 2003 Signature 320 with 350 Mag

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I’m looking at a 2003 320 with MerCruisers 350 MAG with bravo 3s.  Anyone have an idea of GPH @ cruising speed which I understand is around 3,000 rpms but not sure of typical speed.   Also, anything special to lookout for during survey or walk around?   

 

Thanks. 

 

Larry S

Bayville, NJ

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You will be consuming 10 to 12 GPH per motor at 3000 RPM cruise, if the boat is correctly propped to achieve full recommended WOT.

At WOT you will be gulping around 24 GPH per motor.

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  • It will NEVER come close to being like a car with the same sized engine & horse power.

Buying & enjoying a boat requires to have enough money for gas without worrying. If the amount of money is a concern?  Do not buy that boat.

Get caught 10 or 50 miles from home. In a HIGH wind trying to push you backwards ?  You better know where the PROTECTED gas docks are. And be able to dock. Or duck behind a SOLID pier with a huge ship to hide behind until it is safe enough to get to a gas dock.

I have had the engines WIDE OPEN to maintain the front of the boat into sudden wind & waves. The gas GOES VERY FAST in such a emergency. Ask how much gas is consumed at WOT

A boat is nothing like driving a car.

Disregard all the above about various gas consumptions.  Too unpleasant. 

With 2 engines the consumption doubles. Cruisers EAT  gas at any speed . In wind they can go backwards sometimes at WOT......Prop selection is SUPER SUPER important in a cruiser

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3 minutes ago, cyclops2 said:
  • In wind they can go backwards sometimes at WOT......

Where do you come up with this stuff??? 

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From being 81 years old on boats with lucky drivers.    Where do you get your facts from ?

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I can say I have never seen a cruiser being blown backwards under full throttle...  That's a fact. 

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12 minutes ago, Phillbo said:

I can say I have never seen a cruiser being blown backwards under full throttle...  That's a fact. 

Oh come on Phil. I’m sure with both engines off (throttles forward on the stops), a trolling motor pulling, hurricane Andrew blowing full tilt on the nose and a sail the size of the old Pontiac Silverdome and it’ll happen for sure.

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So I have seen a well hit golf ball go up, the wind caught it and blew it right back at my buddy in the middle of the fairway where it landed about 10 yards from where the ball was struck. The ball continued to roll backwards, right past my buddy and ended up 5 yards behind him. I was LMFAO :tofunny:

Here is how it happened ..... the green was a good 40 ft above where we were in the fairway, we were at the 150 yard marker and there was a sustained 30-40 MPH wind coming right at us..... gusts were higher! My buddy hits a loooonggg ball so he was hitting a 9 iron to the green :slap:..... and well I already told you how it ended up.

true story

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Brother in Law did a similar one at Saw Grass In Florida. Very windy at Christmas week. His son Tees off. Second later we hear a small caliber gun shot. WE lay down for a while. Get up & run for the golfcart. Jump in & see the bullet hole in the windshield from a golf ball. :clapsmiley:

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1 hour ago, cyclops2 said:

Brother in Law did a similar one at Saw Grass In Florida. Very windy at Christmas week. His son Tees off. Second later we hear a small caliber gun shot. WE lay down for a while. Get up & run for the golfcart. Jump in & see the bullet hole in the windshield from a golf ball. :clapsmiley:

I did that once, but the darn ball rode the club up, over and behind me.  Of course, I accidentally let the club go once it was sorta over my head.  Both the ball and club ended up behind me, back near a bunch of guys doubled up laughing.  I only ride now. 

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8 hours ago, brick said:

You will be consuming 10 to 12 GPH per motor at 3000 RPM cruise, if the boat is correctly propped to achieve full recommended WOT.

At WOT you will be gulping around 24 GPH per motor.

I agree with the WOT consumption but not the 3000rpm number. It won’t drink that much. I find the website below to be reasonably accurate and yes I know that there are a million factors but as you said, when propped for recommended RPM at WOT then you’re at a “typical” marine prop loading and these figures should be reasonable. It says about 7.5gph per engine. 

www.boat-fuel-economy.com

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Good one Curt.

We have a 19th  hole joke about Mr. Hole in One.  ( windshield )   No other golfers in the clubhouse know what really happened. 

The Mercury site & all others are done WITHOUT a stated boat & conditions. Real life should will be much higher. I use A boat test data when possible.

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Just don’t run her over 3500 rpms and you’ll be fine.  3000 rpms would be better.  WOT an o can see the needle moving in the wrong direction fast.  

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Doesn't really matter what boat you have, a 5.7 Mercruiser for the most part, burns the same fuel as any other 5.7 merc with the same HP at the same RPM. Yes, your fuel mileage will vary depending on what boat, but not GPH. Typical fuel burns at 3000 RPM is 7.5 - 8.5 GPH per engine. 3500 RPM will show burn around 9.5-10.5 GPH per engine.

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8 hours ago, cyclops2 said:

Size, shape & weight matter a great deal

On what? GPH or mileage?

A 5.7 at WOT on a 4000 lb boat burns the same fuel as a 5.7 at WOT on a 10,000 boat.....

The OP was asking about GPH.

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Millage of course (MPG) for a planing boat like an express cruiser. The hull size, shape, weight, load (people, gadgets, and fluids), and the prop type does matter.

The GPH is meaningless really unless one has a trawler that almost always floats at the constant speed of its displacement hull.

My boat can use from 0.9 to 23+ GPH when tested on the hard and going nowhere, and the same range while actually going somewhere at different speeds.

Not sure what the OP is going to learn here without injecting the miles traveled over time (MPH) number into that equation?

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He is asking about real world fuel consumption...………….. Not asking about a chart with no conditions specified.

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1 hour ago, TexasPilot71 said:

I know your question is more in regards to speed, but GPH can be found here:

https://www.boat-fuel-economy.com/mercury-mercruiser-3.0-181-fuel-consumption-us-gallons

I love that link!  Thanks for posting it also on the other thread as well.  It proved what I was looking at for fuel flow on my Smartcraft was not just right, but EXACTLY right once I watched the two together on the boat.  I got the exact same readings from both! 

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I just took a bunch of trips and always watch the Smart Craft I installed to my Raymarine. I payed close attention this time to see different GPH at different speeds. The Chap 330 Sig is extremely efficient hull design then many other boats which helps the fuel burn and also top speed . Several of my friends have other express cruisers like Formula and others and its the same or better then theres at speed. Here are some specs I got when cruising. There are variables like are you going into a head wind, against tide, trimmed down or up etc. But this gives you real world numbers from a week ago on my 2004 Chap 330 with 350 mag mpi and B3. 

 

3400 rpm 25.8 mph and 24.7 GPH

3600 rpm 29.3 mph and 27.8 GPH

3550 rpm 28.7 mph and 27.5 GPH

3750 rpm 31.5 mph and 29.2 GPH

 

As you can see some great numbers for a 35 foot boat running loaded up with 4 people. Good clean bottom, drive showers and motors running optimal. 

 

Happy Boating. 

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Also do not run the motors only at 3k rpms all the time. That is also not great and will build up carbon and eventually cause issues. You will find the optimal cruise speed on this boat with these engines is between 3300-3600. If run it at 3k most of the time just be sure to run it up into the higher rpms from time to time to clean it out. Too slow is also just as bad as running it WOT all the time. 

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