Fuel economy query....282 Sailfish...

[Capnjim7]

I finally got my 05 282 Sailfish off shore twice in the past month for some bottom fishing... first trip totaled around 120 miles.; second around 100. 4 guys each trip full fuel and 100 lbs of ice. Moderate sea conditions both days. I have 225 Yamahas with Yam factory SS props. The very best fuel economy I achieved with motors trimmed and no tabs was around 1.6 MPG around 4600 RPM 5400 to 5800 was around 1.3. But less than 4200 was still only around 1.6 tops. Now...the one thing I waited to mention was that the props had previously been damaged and repaired. Before I take them in to have them tested for current pitch, however, I wanted to check with others to see what their numbers were like. Does this seem right to those with similar set ups? It seems like my 03 300 marlin with 225s was about the same performance. I was expecting 1.8 or better at optimal but maybe its already in line...any comps?? Thanks Jim

 

[seasick]

I would consider your results not bad for that load and hull. I am a bit surprised that the peak economy was at higher revs than I would expect.
I don't think you are at the point where you need the pitch checked. What speed are you getting at WOT and what are the WOT revs?
Also, did you happen to measure (by refilling the tank) how many gallons you actually used? Also, how did you measure the trip miles?

 

[Sharkbait282]

Yeah, in a moderate sea-state, 1.6 isn't bad. Our '02 282 with F225 definitely required dead flat conditions, clean bottom, and trimmed out to 3.5 - 4 bars of trim to see 1.8-1.9 with 15 1/4 x 19 SWII, so with lump and long distance it's certainly not averaging 1.8 mpg. Just check your WOT in flat calm conditions, you should hit 40 knots at 5900-6000rpm.

 

[Legend]

Yup - 1.6 to 1.7 matches mine with that type of load but with F250s. 6000 RPMs early in the season does about 45 knots

 

[seasick]

Yup - 1.6 to 1.7 matches mine with that type of load but with F250s. 6000 RPMs early in the season does about 45 knots

That's 52 MPH. Do you really make that speed?

 

[Lsquared]

3800 rpm will get me 1.6 with the 225s

 

[mleads310]

I posted the below paragraph on a similar thread recently:

"I recently switched my m-19's to a pair of the same props I had as spares, but had them refinished to compare numbers. I also did this while my boat was being worked on the other week, so clean painted bottom. I ran the new props in somewhat choppy weather, wind at 5-10kts, against the tide, 2 people, light gear, 80 gallons of gas. Good news was I was able to hit 5900 rpm, but still could only Max out at 45mph. Maybe because of wind and slight chop? Also good news I was able to cruise with much better efficiency, I believe I was around 3900-4100rpm, aprox 29mph, aprox 17-18gph. Which even in perfect conditions I don't believe I achieved with the other props (maybe those small dings really made a difference)?. Also for reference outboards mounted per Grady spec and second to top hole."

I'm going to end up taking a run soon on a calmer day and and trim up more to see if I can beat those numbers

 

[Capnjim7]

The weird thing is that even though my Yammie fuel gauges were reflectiing 1.3-1.6 MPG , I only ran a tad over 100 miles and ended up putting 103 gallons in the tank when i was expecting no more than 80-85. This happened twice in a month... math doesn't add up and I cant figure out the fuel use... I will pay more attention to my actual speed per RPM and recheck my maximum RPMs and GPS speed to see whether these props were inadvertently reconfigured when repaired.

 

[Capnjim7]

I would consider your results not bad for that load and hull. I am a bit surprised that the peak economy was at higher revs than I would expect.
I don't think you are at the point where you need the pitch checked. What speed are you getting at WOT and what are the WOT revs?
Also, did you happen to measure (by refilling the tank) how many gallons you actually used? Also, how did you measure the trip miles?

I measured my trip on the NSS12 gps... I refilled the tank after both trips to measure the exact fuel burned. Im not sure I have actually hit WOT....but at right about 5900 I was at 43 MPH ...I need to check that though as I do realize its significance in MPH to revs ...proper prop selection.

 

[amf282]

We had 250's on our 282 and the best fuel burn will be at the cruising at around 4200 rpms. You will get a little better at 4000, but not significant. Our typical burn was around 1.6. We just recently repowered her with Suzuki 300's and it appears we will get better fuel economy with those engines. In the early breakin period, we are seeing 1.8 at cruise. We will know more once we take offshore.

 

[Legend]

That's 52 MPH. Do you really make that speed?

Early in the season with 2 people and lite load. The boat is not made for that speed. The few time I cranked it we hit 51 and the canvas felt like it was going to blow of or shred. I am more than happy with an occasional 40! The speed was measured by the gauge not the GPS so not sure of the accuracy but it was crazy fast.

 

[seasick]

I am surprised;faster than I would expect. Do you know the prop pitch?
If I have the right numbers, your gear case is a 1.75. At 6000 revs that in a perfect word would equate to 51 mph with zero slip and a 15.7 pitch prop. Zero slip is basically impossible. If you had 10% slip, still a very good percentage, your props would have to be be 17.4 inch pitch to make that speed. Who knows, it could be..

 

[amf282]

We could only top out at around 48 mph with our 250's 15 1/4 x 19 3 blade props. 5900 rpms.

 

[Legend]

I am surprised;faster than I would expect. Do you know the prop pitch?
If I have the right numbers, your gear case is a 1.75. At 6000 revs that in a perfect word would equate to 51 mph with zero slip and a 15.7 pitch prop. Zero slip is basically impossible. If you had 10% slip, still a very good percentage, your props would have to be be 17.4 inch pitch to make that speed. Who knows, it could be..
[/QUOTE
props are 15 1/2 x 17

 

[seasick]

That pitch would put you are about 10% slip. That's very good performance.

 

[mleads310]

That's pretty interesting numbers considering two things.
1-grady white tested this boat with the Yamahas and the 15-1/4x19 why would they do that if they could get better numbers with a lower pitch?
2- I thought it would have lower pitch you would lose fuel economy? I bet that's one of the reasons why I never thought to drop down and pitch because I thought I would lose both top and speed and I would get worse fuel economy?

Again I'm just throwing thoughts out there but that's very surprising and at the same time encouraging that you're getting such excellent numbers with lower pitch props!

 

[seasick]

That's pretty interesting numbers considering two things.
1-grady white tested this boat with the Yamahas and the 15-1/4x19 why would they do that if they could get better numbers with a lower pitch?
2- I thought it would have lower pitch you would lose fuel economy? I bet that's one of the reasons why I never thought to drop down and pitch because I thought I would lose both top and speed and I would get worse fuel economy?

Again I'm just throwing thoughts out there but that's very surprising and at the same time encouraging that you're getting such excellent numbers with lower pitch props!

It's a bit more complicated I have to admit. First of we need to make sure we are comparing the same motors (actually that the motors have the same LU gear ratios. I used 1.75 because I think that what his motors are but they could be different and the motors in the Grady performance could be different.
On point 1, Grady probably wouldn't test with props that gave poorer fuel efficiency. They would though select props that let the package run WOT at the revs spec'd by the manufacturer and not higher Their hands are tied a bit forcing the selection of a prop that can operate at wot and perform at cruising speeds.
On point 2. Lower pitch doesn't automatically mean lower fuel economy. Too low a pitch could lead to excessive slip since it might not 'bite' enough water. Think of a prop with no pitch. It just spins but doesn't move water On the other hand think of a prop with really high pitch. Your motor may not be able to spin up to WOT dues to the drag.
My disclaimer: After much research and reading over the years about experiences with propping, I have come to the conclusion that I know very very little about prop selection. The prop gurus get their knowledge by experience and to gain that experience you need to have worked on a lot of hulls and motors.
So feel free to tell me I don't know what I am talking about. You may be correct!

 

[mleads310]

Lol I probably know much less than you about props if that helps any lol. It makes me question maybe I should try a set of lower pitched props to see if it helps with the fuel economy. Either way it's good to know that he is getting such great performance numbers with those props.

 

[amf282]

I honestly can't see how the 17" pitch would go faster. I would expect a higher WOT rpm and lower speed. I could be wrong, but 17" should have a little more bite out of the hole and slower top end for the very same motors and boat using the same diameter 15.25" prop. In the end it really doesn't matter as long as WOT is close to your RPM limit. The prop selection can be tricky and fuel consumption can be difficult due to many variables. I would be interested in what your numbers looked like with 19" pitch props.

 

[seasick]

If we are comparing the 19 in to the 17, you would be correct assuming the motor can't put out enough torque to spin the 19 to WOT. But in theory for same revs, the larger pitch will make more speed.