115 Two Stroke Efficiency?

[adam7]

I just got a book on offshore fishing the other weekend from my in laws and was going through it since I couldn't be out on the boat that weekend. It had me wondering some things right off the bat. While I wouldn't plan on going more than say, 15 miles offshore, I'd still like to know my effective range. The book gives a rule of thumb as 1/3 of your fuel to head out, 1/3 to fish/come home, and 1/3 just in case. So I tried to think of what my 1/3 was.

I have a 2002 Key West 1900CC with a 2002 Mercury 115 ELPT Two stroke and a 60 gallon fuel tank. What can I expect on that motor at a reasonable cruising speed for fuel efficiency? I 'think' I'm using about 20 gallons a weekend, which is about 8-10 hours of boating with some considerable WOT. Then again, I could be way off.

 

[redjmp]

Re: 115 Two Stroke Efficiency?

I have an older inline 6 115hp that gets 2.45 km/l best cruise pushing a 15' cobra style boat.
My buddy has a newer 4 cylinder merc 115 pushing an aluminum 19' and he goes through twice as much gas as me but he doesn't have a fuel computer like me that tells him where the best economy is.
Mine works out to 5.75 mpg...
Running mine at wot cuts it down to 3 mpg.

 

[adam7]

Re: 115 Two Stroke Efficiency?

I'm seeing elsewhere that a rule of thumb is to divide HP by 10 to get GPH, which gives me 11.5gph, burning all 60 gallons of fuel in 5.21 hours (at WOT I assume). Assuming I'm doing, what, about 40mph? Thats a 208 mile range at WOT, maybe 400 miles cruising? Is that even close? I'm still digging through the forums to see if I can find anything...

 

[1fishbone]

Re: 115 Two Stroke Efficiency?

I have a 2002 Key West 1900CC with a 2002 Mercury 115 ELPT Two stroke and a 60 gallon fuel tank. What can I expect on that motor at a reasonable cruising speed for fuel efficiency? I 'think' I'm using about 20 gallons a weekend, which is about 8-10 hours of boating with some considerable WOT. Then again, I could be way off.

I had similar fuel consumption, 20' cuddy older 115 2 stroke.
That's how I figured my 'range'.

Don't forget tide and wind!!

Fishing the tide gave me awesome fuel mileage.
I could do an over night trip and burn 16 gallons of fuel averaging 10 to 15 hrs motoring...some WOT, (I'm conservative about speed/fuel)

Keep in mind, going off shore was different...morning wind/wave is minimal, but coming home has more wave/wind action.

I like to use the 1/4 rule...1/4 of my fuel out, a 1/4 to move around, and a 1/4 to get home...it leaves room for error!!

 

[adam7]

Re: 115 Two Stroke Efficiency?

So the next step is figuring out how fast my boat is. I don't have a dedicated GPS for it yet, but I could probably use the TomTom from my car to at least get lat/long coordinates while out there and measure speed, right?

Any assumptions I could make? Like 40mph WOT, 30mph cruising at 3,000 rpm? Anyone else have examples? I plan on measuring it all for real when I can get the boat out again, but now I'm just bummed its so cold out and want to think about boats.

 

[Robbabob]

Re: 115 Two Stroke Efficiency?

As pretty much identified, so many factors come into play with range. You have mentioned off-shore and being 15 miles out. I don't know if that is considered very far in a 19' cuddy (I assume that's what you have). I hope you have a marine gps and radio.

We mess around 20 to 30 miles up and down the river/lake, but we are never farther than 1/4 mile from a shore or 5 minutes from another boat seeing us (if we are in need of help).

As for your efficiency....... trial and error (testing) will give you what you're looking for. Tide, wind, waves, wake, _________ all depends on your throttle and conditions.

Good luck with your outings!

 

[adam7]

Re: 115 Two Stroke Efficiency?

The radio was the first thing I bought for the boat, but the GPS was out until next year as the rest of the boat money went to safety gear and fixes to get it up to speed after purchasing it. Its a center console.

I only say 15-20 miles because I don't know what's out there and I'd like to maintain radio contact with the shore at least at first.

The whole range/efficiency question is important to me because one of the first things I did with the boat was run out of gas (the fuel gauge stops at 1/3 a tank). I hope to learn from my mistake.

 

[adam7]

Re: 115 Two Stroke Efficiency?

Well I didn't get a GPS for christmas

But it looks like the weather should be clear this weekend (although a bit chilly), so I think I'm going to go out for a bit and bring the car GPS with me to see if I can get a speed measurement. That and my friend wants to try and get some oysters.

 

[Silvertip]

Re: 115 Two Stroke Efficiency?

Speed is sort of a non-factor since speed and time gives you MPG which varies greatly depending on load, speed, wind, currents, waves, etc. Your engine at WOT burns about 11 - 12 gallons of fuel per hour at WOT. At cruise it will burn 20% less. So at cruise (5/8 to 3/4 throttle) or so you would burn about 9 - 10 gallons/hour. So using that number and 1/3 out, 1/3 in, and 1/3 reserve, your range is based on 36 - 40 gallons of gas. That then translates to 4 to 5 hours run time AT CRUISE. You will not get anywhere near 400 miles (at cruise or otherwise) on 60 gallons of fuel with that engine/boat. So base your travel on fuel burn rate (gallons/hour) just like they do with airplanes. MPG is an average, and highly variable as I mentioned. In fact without a fuel flow monitor you cannot accurately tell what your MPG is until the trip is over and you refuel.

 

[Chris1956]

Re: 115 Two Stroke Efficiency?

Adam, 15 miles offshore is a long way in a 19' boat, IMHO. You need to head straight out for about 45 minutes running time, to get that far, in light seas. You will not see land after 13 miles or so, and may not have VHF radio contact, unless you have a powerful set and a tall antenna. Cell phone will not work....

The good news is that you will have plenty of fuel. You should burn about 9 gal out and 9 gal back, give or take a few gallons.

I am not sure of your weather patterns, however, if a storm comes off the land, and you are out 15 miles, that will be an issue. Watch the weather carefully

 

[adam7]

Re: 115 Two Stroke Efficiency?

Adam, 15 miles offshore is a long way in a 19' boat, IMHO. You need to head straight out for about 45 minutes running time, to get that far, in light seas. You will not see land after 13 miles or so, and may not have VHF radio contact, unless you have a powerful set and a tall antenna. Cell phone will not work....

The good news is that you will have plenty of fuel. You should burn about 9 gal out and 9 gal back, give or take a few gallons.

I am not sure of your weather patterns, however, if a storm comes off the land, and you are out 15 miles, that will be an issue. Watch the weather carefully

I don't want to push my limits, I just want to figure out what they are. This is the third time I'm typing this because I keep hitting the wrong button to post it, but basically, here is where I am:
http://www.charts.noaa.gov/OnLineViewer/11516.shtml

Leaving Port Royal it is roughly 6 miles to the tip of Parris Island, and another 4 from there to the open ocean (10 total). So really, I don't want to go much more than 5 miles out from there, 10 to 15 miles would be a stretch on a really nice day. In other words, I'm more or less confining myself to the bounds of that chart, and I'm perfectly comfortable with that right now.

 

[adam7]

Re: 115 Two Stroke Efficiency?

The Betsy Ross is a reef that everyone mentions locally when asked about going not too far off shore. I just checked on Google Earth and that is 16 miles from the mouth of Port Royal Sound, so it would be 26 miles from home, 10 of which would be relatively sheltered, but it can get harsh out there in the channel depending on the conditions.

Given ideal weather and water, a full tank of gas, and rounding it up to 30 miles each way, would you guys consider that trip a stretch, or easily doable?

 

[Chris1956]

Re: 115 Two Stroke Efficiency?

OK, 60 miles on 60 gallons. A bit tight for my comfort, especially if you have to plow water all the way in from the reef, due to a storm. Can you fill up just before you hit the ocean? That makes it 32 miles on 60 gal. More like the 1/3 out, 1/3 back and 1/3 in reserve fuel rule.

 

[adam7]

Re: 115 Two Stroke Efficiency?

Its possible I could find a place off Hilton Head to fuel up. I'll have to check for a marina around there.

edit: Using the path measuring tool in google earth it doesn't seem worth it. Going from my landing to the reef is a round trip of about 50 miles. Going from the closest marina in Hilton Head (which is up and inland some), assuming the trip starts there with a full tank of gas, going out to the reef, then straight home, it is about 47 miles. (and that doesn't include the time/gas it will take to get to the marina first. All the best pieces of land that would be good for fueling up before heading out are prime beach real estate, no marinas at all.

 

[BatDaddy1887]

Re: 115 Two Stroke Efficiency?

Adam,

Chris1956 said that you start to lose sight of land about 13 miles out.....if you can't see land when you return you might need a compass. Have fun!

 

[Chris1956]

Re: 115 Two Stroke Efficiency?

I guess I am being over cautious. You will probably have plenty of fuel, unless something really bad happens. I took my 19 footer from the dock to the inlet (10Mi), out 20 mi and back (60 mi total). It was an I/O and only burned 25gal. I had a 35 gal tankl and 12 gal more in emergency gas. There was gas avail at the inlet mouth, so I felt pretty safe.

However, I have been out 20 miles and suddenly encountered 8' waves, with no storm, just a bit more breeze than normal. Luckily I was in a 35 footer vs my 19 footer. We burned a ton of fuel getting back, but made it. Most of the cruisers out there that day had to plow along at 4-6 knots, as it was too rough from them to plane. That turns a 45 min triip to a 4+ hour trip, and really sucks the fuel up.

 

[adam7]

Re: 115 Two Stroke Efficiency?

I understand. I'm going to take it in baby steps.

I have a compass btw.

 

[cps22]

Re: 115 Two Stroke Efficiency?

I have a 2005 Merc 115 on my 18' Tracker. My wife and I cruise throughout the big TVA lakes and rivers throughout the South. We often put on 500 boat miles per week while on these cruises.
Anyway, I mentioned that because we monitor our gas consumption closely with GPS and paper logs. When cruising between 3000~4000 RPM we average about 3.8MPG. The 3000~4000 range seems to be a sweet spot, fairly quiet, runs well, fairly efficient.
CPS22

 

[adam7]

Re: 115 Two Stroke Efficiency?

Over the weekend we took the boat out for some oysters. The gps on my phone had us at 36 mph top speed with about 30 gallons of fuel and two people on board. Later, with 60 gallons I was hitting 33-34mph but in slightly rougher seas.