Avg. Fuel Consumption on my twin 8.1S Mercs

I've only this boat a couple of months and I'm also adjusting to the increased fuel consumption. I used to get about 1.3 MPG out of my 300DA and now I get about .7 MPG. That's about half! Anyway, our boat is a lot closer to places we may want to go so that helps. I don't count the time idling away from the dock or in no wake zones.

I agree with Alex D, "that's what it takes to run this boat."
 
GHP on a 8.1s

Hello Alex,
I got a question about your numbers I have a 2004 34 with 8.1s and my average GHP is 28 to 29 total at 3400 where are you coming up with 15 ghp, please tell me that one engine.
if it is I am sorry for being stupid.

Steve04 javascript:emoticon(':smt017')
javascript:emoticon(':smt017')
 
Just Ran Palm Beach, Fl to Panama City, Fl, almost 700 miles, on between 7 and 800 gallons - I just got here, and haven't done the math yet.

We generally ran at about 3500 RPM which yielded 25.0 knots. The fuel flow indicated right at 30 gph. In smooth water, we ran 3250 RPM, 25 gph, and got 21.5 knots. We tried running at that speed in the Gulf, but with 5 foot seas, it would slow to 19.5 Knots SOG, so I pushed it up, and it stayed between 23.5 and 25.5, which was a better plane.

2005 340 Da with 8.1's.

I personally scrubbed the bottom for 3 hours with ther boat on dry dock to save gas.
 
Re: GHP on a 8.1s

Steve04 said:
Hello Alex,
I got a question about your numbers I have a 2004 34 with 8.1s and my average GHP is 28 to 29 total at 3400 where are you coming up with 15 ghp, please tell me that one engine.
if it is I am sorry for being stupid.

Steve04 javascript:emoticon(':smt017')
javascript:emoticon(':smt017')
Click to expand...

Hey Steve ... I thought it was covered in this thread how I arrived at this number ... my objective was to determine avg. fuel consumption for budgeting. We boat about 60 - 80 engine hours per year. So I did an accurate fuel measure over the hours mentioned. This is an average per engine hour, incl. genny hours and comes up to 15 gal./hr. This includes warm up time, idling in and out of the marina. Maneuvering around docks, running on plane, etc., etc.
15.3 gal./hr. is the true average of that. Running on plane consumption is higher, prolly around a true 28 - 32 gal./hr.
 
We do whay Alex does too. Though it's nice to know your burn rate at cruising speed, unless you crusie 100% of the time this really does not give you a measure of your average burn rate.

We have no wake zones, idle time, docking time, fidling time, etc. All of this will reduce your gph and give you your true average.
 
A lot of that will reduce your mpg, but the no-wake zones don't seem to, unless you're up and down on the throttles a lot.

At 1200 RPM, my fuel burn was around 5 GPH total (or less), and the boat was getting over 6 knots, so the mpg went up at slow, no wake speeds as compared to cruise.
 
Just to add more confusion on the subject. I have a 2002 340DA with the 8.1s. I was not happy with the cruise speed nor the way it "squatted" in the water. I had the original 3-blade props that searay shipped with the boat. After consulting several boat reviews with performance specs, I was convinced that my boat was not configured for an optimal cruise speed. I e-mailed searay for an opinion and they responded with "whatever the boat shipped with is what we recomend" :smt021 .

So then I started looking at the specs for the newer 340DAs, and noticed that all later models, with the same motors came with 4-blade props. After weeks of working with my prop guy (and moving cinder blocks all over my boat), running my boat ip and down in the shipping channel, I put on some 4-blade props.

The result is a brand new boat. This thing moves out of the water smoothly at almost any RPMs. I am in the Bahamas now doing most of my cruising at 3400 RPMS running about 24-25knots. It does not seem like the motors are working at all, AND I am LOADED down. I have a dinghy on my swim platform with gas tank and a motor, as well as beer and wine for the trip (that is a lot of weight).

I am not sure about the consumption, but I will start to figure it out when I have time. I can't wait to see what this thing will do without all the weight. :thumbsup:

BTW, my top end got better as well by 2 MPH.
 
brimanst said:
Just to add more confusion on the subject. I have a 2002 340DA with the 8.1s. I was not happy with the cruise speed nor the way it "squatted" in the water. I had the original 3-blade props that searay shipped with the boat. After consulting several boat reviews with performance specs, I was convinced that my boat was not configured for an optimal cruise speed. I e-mailed searay for an opinion and they responded with "whatever the boat shipped with is what we recomend" :smt021 .

So then I started looking at the specs for the newer 340DAs, and noticed that all later models, with the same motors came with 4-blade props. After weeks of working with my prop guy (and moving cinder blocks all over my boat), running my boat ip and down in the shipping channel, I put on some 4-blade props.

The result is a brand new boat. This thing moves out of the water smoothly at almost any RPMs. I am in the Bahamas now doing most of my cruising at 3400 RPMS running about 24-25knots. It does not seem like the motors are working at all, AND I am LOADED down. I have a dinghy on my swim platform with gas tank and a motor, as well as beer and wine for the trip (that is a lot of weight).

I am not sure about the consumption, but I will start to figure it out when I have time. I can't wait to see what this thing will do without all the weight. :thumbsup:

BTW, my top end got better as well by 2 MPH.
Click to expand...

Can you post what brand, style, pitch and size props you put on your boat?? I still have the factory 3 blade props on mine, not bad but if teh 4-blades are so much better, I'd be interested.
 
Ya mon, no problem. My original props were 18x22 3-blade Nibral. I still had a problem with "squatting", so I had him put a cup in these and there was some remarkable gains. Much less bow rise and the ability to plane at lower RPMS. Armed with this knowledge and trial runs for Speed vs RPMS, we decide to go with a 4 blade prop. The current models are using a 18x21 4-blade, so that is what we chose. Because of the great gains adding the cup in the 3-blade we cupped the 4 blades as well. I am still able to hit 4600WOT, but the best part is I can cruise comfortably at 3200RPM if I want with control and no bow rise to speak of.

Searay puts their prop charts on their website. You can look at each model and year. This is where I saw that all newer models came with 4-blades. The 2002 model is the first they started putting the 8.1s in, so I think there is some learning curves that had to be made. My only dissappointment, is they do not pass on the lessons learned to existing boat owners.

I can't complain too much, though, it took me to the Bahamas :grin:
 
Mine are 4-blade. From idle, I increase the power up to about 2800 RPM (tabs left in place from previous cruise) and it comes up and settles in at 3250 RPM and 21.5 knots. I can set about 3000 initially, and it settles in at 3500 RPM and 24.5 knots.

After it's planing, I make minor adjustments to the tabs. Generally, the tabs are full up, with one slightly down to lower the bow on one side or the other to compensate for weight or winds. No wind, both of us on the right, I need a little left tab down. Throw in a little left cross wind, and no tabs required. Moderate left cross, and left one's up and right one's down just a tick.

Generally, I'm idling on the hull and planing on the hull plus a touch of one tab. (On the hull = tabs full up and not affecting running.)
 
perfect .. where did you buy them and what was the cost if i may ask ... pm me if you'd like ... thanks !! :thumbsup:

engune rpm and speeds seem to be the same. my 02 340 runs about 26.5 to28 mph at 3400 rpm
 
Alex,

If you're asking me, they came with the boat. Maybe you can get a part number from a SR service center/parts department. Mine is a 2005 340 Da with 8.1 Horizon's.
 
Was asking brimanst since he has the same boat and year I do and had the three blade props from the factory. They changed it for 2004 with the new 340 to 4 blades. So I wonder where he bought them and how much they cost ..
 
I bought mine from a local prop guy. He was able to take my data from numerous speed vs RPM tests and somewhat calculate the efficiency of the props. As I said before, Searay was less than helpful on this issue. I opted for the bronze props because of cost. I paid around 650.00 eac vs >900.00 for the Nibral. Searay ships theiir newer boats with Nibral and it is better, but I could not justify the costs since I was re-propping. These costs do not include the time and prop change outs. I live in the Charleston area so I decided to support the local economy. I think Michigan Wheel is chaeper, but then they also did not have the support that I had analyzing all the data. With that said, I would think that you could benefit from my work and shop on-line for the best price. I also checked with Searay and pretended I had an 05 340DA to see if they were in line, and they quoted me over 1000 a prop. Hope this helps.
 
Guys with my old 03 340 I was very unhappy with my cruise speed @ 3400 -3600 Rpm. I run with two other 34's. I wrtoe down all the info at different RPm's gave it to the local prop shop and he gave me some new props... Boat kicked butt... I cruised at 3450 rpm buring 34 gph at 30-32 mph Depending on current and wind. 3 exact sameboats all ran at different speeds same rpm.... dealers reasons are numerous...

:smt021 So i took matters into my own hands.



Rob
 
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