270 islander MPG

[Fixit]

I just repowered my 2004 islander with twin 250 verados and my mpg isn't as good as I would have thought.

what's everyone getting for mpg at cruise/ wot mph and with what props etc

im currently getting 1.7Mpg at 30mph at 3800-4100rpm for best cruise when im light
WOT of 48mph at around 6000rpm trimmed up
and running enertia eco props (16x17P")

I figured that I should be getting low 50's mph
and was hoping that I would get better than my old F200 twin Yamahas that got 1.9mpg at the same speed

 

[Mustang65fbk]

Here's an article with some of the information you're looking for. I believe that the 270 Islander was discontinued after 2005, so you're likely not going to find a ton of information out there because of that. Depending on how many people respond to the thread here, I'd email or reach out to Grady White and see if they can send you the performance data sheet on a similar vintage boat to yours with twin 250's on it.

https://www.soundingsonline.com/boats/grady-white-270-islander

 

[Hookup1]

These are numbers I pulled from a boating magazine. Not sure I believe the numbers. See too high. I have a 268 Islander with twin F150's and 4-blade props. I'm a 28 knot cruise at 5000 rpm's with great midrange performance. Those 250HP V-6 blocks are heavy compared to the straight 6-cylinder engines. I suspect you would do better with prop tuning. Try PropGods.com .

 

[Fishtales]

Probably need to see a local prop expert to get some input. As stated above, not sure I trust print.

 

[family affair]

I just repowered my 2004 islander with twin 250 verados and my mpg isn't as good as I would have thought.

what's everyone getting for mpg at cruise/ wot mph and with what props etc

im currently getting 1.7Mpg at 30mph at 3800-4100rpm for best cruise when im light
WOT of 48mph at around 6000rpm trimmed up
and running enertia eco props (16x17P")

I figured that I should be getting low 50's mph
and was hoping that I would get better than my old F200 twin Yamahas that got 1.9mpg at the same speed

Looks like something is very wrong with your setup and/or props.
2023 df200 APs are on our boat with Mercury Eco Enertias 23 pitch. Here are some stats:

• I can hit 2 mpg + from 12 mph to 38.
• My best cruise number is 2.5 mpg @ 25 mph.
• Roughly from 22 mph thru 35 mph I can do 2.3 mpg
• WOT = 50 mph

My numbers are exceptional in part due to the props. If you are running v8 verados, you shouldn't be far off on MPG and your WOT should be around 55 mph. If you are running an older pair of blown verados, you still shouldn't be that far off @ WOT, and MPG should exceed 2.
With my old f150s the display would show 2.4 mpg, but I had been told the numbers were overly optimistic by the previous owner.
F225 270s were common. Their mpg wouldn't exceed 1.8-2. WOT 52 mph.
From what I've heard the VVT f250s exceeded 2 mpg.

 

[family affair]

These are numbers I pulled from a boating magazine. Not sure I believe the numbers. See too high. I have a 268 Islander with twin F150's and 4-blade props. I'm a 28 knot cruise at 5000 rpm's with great midrange performance. Those 250HP V-6 blocks are heavy compared to the straight 6-cylinder engines. I suspect you would do better with prop tuning. Try PropGods.com .

View attachment 31825

My experience was that these numbers were accurate. I had this exact setup and my flow numbers often exceeded this, but I had been told the numbers were a little optimistic. I never verified them.
No bottom paint BTW.

 

[Fixit]

thanks for the reply, I should add some more info
they are 2012 L6 verados, not the v8's and they have 850 hours on them
I do have some poor condition bottom paint on the boat with the odd barnacle im sure
maybe in should make a spread sheet RPM MPG GPH MPH as above.

FA - that is some impressive MPG your getting. I think the difference in the prop pitch between yours and mine is you have 2.5:1 gear case and I have 1.85:1 and I would guess the 2mph faster would be the difference between brand new and 10year /800hr old motors. although I do have 100 more HP than you.

 

[Sardinia306Canyon]

I do have some poor condition bottom paint on the boat with the odd barnacle im sure

Poor bottom conditions with barnacles reduce fuel efficiency in a incredible high way.
Before you do any further tests you should solve that first to get numbers to confront with others.

If the barnacles or zebra mussels are less than pin head size you may scrub them off while in the water, using snorkel or scuba gear, if bigger then pressure washer. I saw once a guy pressure washing while slipped but don't know how well it worked.
Ask the marina if there is a guy/company offering either scrubbing or pressure washing while in the water.
Chris

 

[family affair]

thanks for the reply, I should add some more info
they are 2012 L6 verados, not the v8's and they have 850 hours on them
I do have some poor condition bottom paint on the boat with the odd barnacle im sure
maybe in should make a spread sheet RPM MPG GPH MPH as above.

FA - that is some impressive MPG your getting. I think the difference in the prop pitch between yours and mine is you have 2.5:1 gear case and I have 1.85:1 and I would guess the 2mph faster would be the difference between brand new and 10year /800hr old motors. although I do have 100 more HP than you.

Yes, the prop pitch comp is apples to oranges due to gear ratios, but Eco Enertias are incredible with the Suzukis on this hull. I'm not sure if you would have the same luck with the Mercs with the appropriate pitch - as ironic as that might be.
Have you run a slip calculator? Your WOT slip should be in single digits. Midrange would be around 15% or so ideally but double check. Ken is an amazing resource for prop info.
Don't L6s rev out to 6200 rpm? What make/model prop are you running now?
850 hours for 250 L6s ain't squat for hours. You should have no issue hitting mid to upper 50s and much better mpg unless they were terribly maintained. L6s are efficient, quiet, and powerful. The weight and premium fuel requirements are really the only negatives about them. I think you either have a bottom issue, prop issue, or engine height or toe issue. FWIW, every recommendation from Ken was spot on.

 

[Fixit]

Yes, the prop pitch comp is apples to oranges due to gear ratios, but Eco Enertias are incredible with the Suzukis on this hull. I'm not sure if you would have the same luck with the Mercs with the appropriate pitch - as ironic as that might be.
Have you run a slip calculator? Your WOT slip should be in single digits. Midrange would be around 15% or so ideally but double check. Ken is an amazing resource for prop info.
Don't L6s rev out to 6200 rpm? What make/model prop are you running now?
850 hours for 250 L6s ain't squat for hours. You should have no issue hitting mid to upper 50s and much better mpg unless they were terribly maintained. L6s are efficient, quiet, and powerful. The weight and premium fuel requirements are really the only negatives about them. I think you either have a bottom issue, prop issue, or engine height or toe issue. FWIW, every recommendation from Ken was spot on.

im running brand new inertia eco 17"p.
they had a full 300hr service this spring.

checking the toe is something that's on my list, and I was contemplating raising the engines one hole. cav plate is at waterline while running but making heavy contact, if that makes sense.

slip numbers came out to 6% but that's with iffy rpm at wot (not completely certain).

I guess ill have to ensure the hull is spotless and go from there. there were ?30? barnacles on the bottom

 

[family affair]

I'm no expert, but I don't think toe would help in your case. I did it with mine to have more consistent bite. I was advised to bring the end of my prop shafts 3/4" closer from parallel. It definitely helped. The boat tracked a little more straight and the tachs were much more consistent when synced.