Ways to increase M/P/G without repowering?

[fowl intent]

I have a 2001 SeaSport 2540 powered by a 2001 Merc 225 EFI. Hull weight approx. 3600 lbs, 135 gal fuel capacity, Michigan Wheel 14 1/4 x 19 SS Rampage prop, 5200 RPM and 42 M/P/H at WOT. I get between 1 to 1.25 M/P/G, which seems fairly low (especially when told it would get between 2-3 M/P/G by seller) Any way to enhance fuel efficiency without repowering with a 4 stroke? How much more M/P/G could I expect if I did bite the bullet and put a 225 4 stroke on her?

 

[DJ]

Re: Ways to increase M/P/G without repowering?

Two opinions.<br /><br />1. Your engine is overpropped. It should be capapble of turning up higher rpms at wide open throttle. You are lugging it.<br /><br />2. Think about installing trim tabs. They will allow you to plane at lower speeds and trim out for more efficient running. Bennets are my favorite. Customer support is second to none.

 

[fowl intent]

Re: Ways to increase M/P/G without repowering?

I have Bennett tabs, and the 5200 rpm is max at all possible trim settings. Sounds like I need to look at a prop with less pitch to increase rpms. Will that necessarily increase fuel efficiency? This stuff gets complicated....

 

[rickdb1boat]

Re: Ways to increase M/P/G without repowering?

As Dj said, your lugging the engine and that's ineficient. Think of it as a car with a standard transmission going up a long hill in 4th gear. You would have to press the pedal all the way down to make it, therfore pumping alot of fuel while doing it. Shift to a lower gear and less throttle is nessesary. Same priciple as a lower pitched prop. More efficient and saves fuel. Prop for 5500-5700 for best performance..

 

[gss036]

Re: Ways to increase M/P/G without repowering?

Maybe if you contact the mfg at www.Seasportboats.com , they could give you a little help. The other part of the business is BoonDock boat & motors. That boat is mfg about 3 miles from me so there are lots of them around here. We don't see too many with outboards unless they have a bracket. Being very familiar with that boat, all truth be known, I think you are a little under powered because of the design and weight. That is a very heavy hull. I have a friend with the same boat and he runs the old Evenrude V8 on his. Also have a friend w/ a Volvo Diesel i/o. I would check to make sure you don't have any CUP in the prop. I would suggest you try a 141/2X17 prop. 5500/5600 would be idel top end WOT.

 

[fowl intent]

Re: Ways to increase M/P/G without repowering?

gss,<br /><br />Thanks for the response, but this boat is manufactured by United Marine in Illinois, just happens to go by the same name "SeaSport". I will try to give them a call next week for their advice.

 

[Boatist]

Re: Ways to increase M/P/G without repowering?

Fowl Intent<br />Better fuel mileage is a goal for most. To start make sure the hull is clean. Next lighten your load. For best MPG you need to run at a speed just above the speed where you reach a clean plane. Trim the bow up to reduce hull drag. I love my Bennett trim tabs but in general they cost you a little fuel mileage. They will save you fuel mileage if you are running below planing speed or plowing and useing trim tabs will get you on plane. If adjusted for best fuel mileage then I do not think you could messure the difference without some controlled test conditions. With trim tab you find planing speed you want to run and trim the boat with tabs then trim engine for best speed.<br /><br />Going to a lower pitch prop will cost you speed and miles per gallon. I belive your engines WOT RPM range is 5000 to 5800 RPMS. If you go to a lower pitch it is like taking your car out of overdrive back to high or from 4th gear back to 3rd gear. That will give you more power but cost your fuel mileage and top speed. You get faster starts but less MPGs.<br /><br />My boat is a 21 foot runabout with a 4 cyl I/O four stroke. I have two props both 3 blade cupped and with in 1/8 of an inch in diameter. I fish the same fishing banks in the ocean as offten as weather permits. I go From Bodega bay to Cordell Banks 26 miles out and back. This round trip mileage with both my depthfinder odometor and my GPS's trip log for a will be very close to 70 miles. Now some of these miles will be from drift fishing so not under power.<br /><br />With my 17 pitch prop I have a top speed of 35 mph at 4600 RPMS, my engines MAX WOT RPM. On a fishing trip to Cordell Banks I burn 18 gallons of fuel or I get 3.88 MPG.<br /><br />With my 19 pitch prop I have a top speed of 38 MPH at 4200 RPMS the low end of my engine WOT RPM range. On a fishing trip to Cordell Banks I burn 15 gallons of fuel or I get 4.66 MPG.<br /><br />Most I/O engines will get their best fuel mileage around 2500 to 3000 RPMS. Of course each boat and each engine changes a little. At full Throttle expect no more than half the MPG.<br /><br />Actuall most get their best MPG at idle speed.

 

[WillyBWright]

Re: Ways to increase M/P/G without repowering?

Four-strokes run significantly more efficiently at low end than 2-stroke EFIs. If that's where you are running, you'd notice a major improvement in mileage with a 4-stroke. You'd also do much better with a direct injected OptiMax. They rival 4-strokes in economy and power. In fact in most categories, they do slightly better. But it takes about the same amount of fuel to achieve 225Hp at top end. Doesn't matter if it has a carb, EFI, OptiMax, or 4-stroke.

 

[DJ]

Re: Ways to increase M/P/G without repowering?

It's a 2-stroke. You've got to get your wide open throttle rpm's up. This will allow the engine to run "easier" in all rpm ranges.<br /><br />Besides, lugging the engine is not good for it's overall health.<br /><br />Glad to hear about the tabs.

 

[rickdb1boat]

Re: Ways to increase M/P/G without repowering?

True Boatist ,<br /><br />But any motor that is overproped will be inefficient. 2-stroke or 4-stroke. I agree that the 4-strokes tend to get better milage qt lower RPM's, as they are in their powerband. But I still stick to the proper prop to attain this. A prop turning 5700 RPM's WOT can still be run in it's optimum powerband at a lower speed and get better milage than lugging along being overpropped. You have to figure out where the engine powerband is most efficent before you can prop correctly. Also, losing some weight carried, or moving it around can have an effect on performance. And I would do away with that Michigan prop, too.

 

[fowl intent]

Re: Ways to increase M/P/G without repowering?

Thanks for all the input guys. I have about decided that I can fish in the gulf stream as rigged once I:<br /><br />1. install a fuel flow sensor/computer<br />2. drop down to a 17 pitch prop<br />3. pull back a hair on the throttle<br />4. eliminate excess weight (although my significant other may resent being left on the dock)<br /><br />Thanks again, its been a great help.

 

[AW]

Re: Ways to increase M/P/G without repowering?

I am curious what speed your MPG reading is at.

 

[Tabman II]

Re: Ways to increase M/P/G without repowering?

fowl intent,<br /><br />I am Thomas and I work for Bennett Marine in the Client Service Department.<br /><br />Please let us know the size of the trim tabs you current have installed, since our General Sizing Guidelines would like to see 30 x 9's on a 25' vessel. You most likely have smaller than this, like 18 x 12's, but knowing the size will help all of us to better understand your situation and to provide some suggestions on how to help you improve your overall performance.<br /><br />I look forward to your reply.<br /><br />Sincerely,<br />MJ Thomas<br />Bennett Marine, Inc.<br />Client Services<br />trimtabs@earthlink.net<br />www.bennetttrimtabs.com

 

[airman]

Re: Ways to increase M/P/G without repowering?

Go to www.boattest.com You should be able to find a very similar boat to your own to get a good comparison of speed and mpg.