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Author Topic:   Fuel economy: 2-stroke vs. 4-stroke...
whalersailer posted 08-12-2002 01:54 PM ET (US)   Profile for whalersailer   Send Email to whalersailer  
Hi all,

I'm wondering what the fuel usage difference is between a 60-70 hp 4 stroke and a 70 hp 2 stroke. Boat is a 15' striper. I just bought the boat a few weeks ago (though it's my 3rd Whaler), and this past weekend finally had a chance to run it quite a bit. I knew she would be thirsty, and she uses about what I figured (roughly 3MPG). I saw a couple of other boats with 4 strokes go by and got to thinking...

Has anyone done a similar repowering, and if so, how do the fuel usages compare?


Bigshot posted 08-12-2002 03:34 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Spoke to a bloke yesterday with a 15CC with a 50 Yamaha 4 stroke 38mph. so i assume a 60 might do 41 or so which is not the 45+ you are with the 70. Nobody makes a 70 light enough to put on a 15 yet. My 70 Zuki 4 stroke averages about 1.4gph per tank. My 70 2 stroke was about 3 or so. The 70 burns about 2.5gph at 4k rpms vs about 3.5-4 for a 2 stroke. The nice thing is at 1000 rpm's it only burns .2gph that is why my avg is so low. At upper rpm's it is not as fuel efficient, if a 2 stroke burns 7gph wot then a 4 stroke might burn 6. It is in the slow-4500 range that makes the difference.
David Jenkins posted 08-12-2002 03:50 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     

Please ask your friend to drop me a line at . I am curious how fast that 4-stroke 50 will push a fully-loaded 15'.

In , lakesidelou says that he gets a top speed of only 30 mph with his Merc 60 EFI Bigfoot. I realize that his 150 is a lot heavier than my 1977 sport 15, but I still thought that he would have a higher top speed. Maybe the problem is the "Bigfoot." Anyway, I have a 42 gallon fuel tank and am worried about having too much weight in the stern. I would much rather use a light-weight Yamaha or Honda 50 over the Merc 60 if they would both be able to get me on a plane carrying 1000 pounds. And if the power is the same and the weight is the same, I believe that I would chose the Suzuki 50 over the Merc 60. But will I be underpowered, that is my big concern. The 1987 Nissan 70 (which I just sold) had fabulous top-end speed but with a heavy load, it did not have enough power to get me up on a plane.

David Ratusnik posted 08-12-2002 04:26 PM ET (US)     Profile for David Ratusnik  Send Email to David Ratusnik     
Whalersailer- (and others) This gas consumption thing re: 2 stroke dfi, 4 stroke and I'll throw in 2 stroke carb engines is a point that comes up from time to time. kBottomline- your hours of engine use per year and to a certain extent how you push the engine (e.g. watersports use gas more than puttering around with the wife) drives consumption quite abit. Point, you've got to factor in HOW and HOW MUCH you intend to use the engine before tyou can make an intelligent decision on the BEST/correct engine for you. A carb engine bought right and used occasionally is probably the best way to go for most boaters. .03 David
jimh posted 08-13-2002 03:02 PM ET (US)     Profile for jimh  Send Email to jimh     
Mercury's engine catalogue states that 4-stroke fuel economy is "up to 39 percent better than comparable 2-strokes."

When you calculate fuel costs, allow for the use of TCW-III oil in the 2-stroke engine. Also allow for the cost of crankcase lub oil and filter changes in the 4-stroke engine. Factor in lost time while making the oil changes, and the cost of service if you have it done for you.

Bigshot posted 08-13-2002 03:58 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Highwater...I mean David.....why on earth do you have a 42 gallon tank on a 15'? I could drive to Keywest on my 27 pate. If a 70 Nissan was 4 stroke will compare.....sorry.
David Jenkins posted 08-14-2002 08:50 AM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     

Why does it bother you that I have changed my username?

We like to take long trips and I do not want to run out of fuel. On my last trip, I launched at Biloxi, Mississippi and took the boat 75 miles south to Breton Sound, Louisiana. The nearest fuel dock was 30 miles away at Venice, LA. Fortunately, I did not need to refuel. I was able to return to Biloxi on one tank. But I was on empty when I returned. I got about 150/40 = 3.5 miles per gallon, most of it at about 4500 rpm. I was hoping that the 4-stroke would do better than that.

The 1987 Nissan 70 had good speed at WOT carrying a light load, but I could not get on a plane carrying 1000 pounds. I was hoping that the 4-stroke, with its different torque, might perform better than this.

So, are you saying that I cannot expect better performance with a new engine?

whalersailer posted 08-14-2002 09:04 AM ET (US)     Profile for whalersailer  Send Email to whalersailer     

are you counting your 42 gallons of fuel (250 lbs) in your 1000 lb. load, or is your load really 1250lbs?

Bigshot posted 08-14-2002 11:14 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Name change does not bother me a bit....just ribbing you:)

What kind of weight do you carry? Yes it has a different torque curve but it is slower out of the hole than a 2stroke. If it was me and the trips are not all the time, I would carry a few jerry jugs so I could disperse the weight forward or stop and refuel. If I was running that kind of weight all the time I would buy a 17'. I hate driving a boat loaded down, they handle like crap. I do not like to run long distances in my Montauk with more than 4 people, prefer 2 or 3. I am sorry that I sound sarcastic but your situation is not exactly the norm. You can move any weight with the right prop and maybe you need to carry 2. 1 for full tank and then swap when it gets to half, etc. The economy on the 4 stroke will almost double your range so therefore you should not need a 42. My Montauk can go at least 9 hours on a 27pate at cruise so about 250 miles or about 9mpg. I can not understand how a 70 gets that poor mileage. My Baja with a 454 gets 3-3.5mpg at cruise.

David Jenkins posted 08-14-2002 11:20 AM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
That is an excellent question and may deserve to be the title of a thread: "How do you define weight capacity?"

Here is my weight situation:

I weigh 200 pounds. Together, my wife and two children weigh 300 pounds. Sometimes we bring a friend or relative. Let's say they weigh 200 pounds. That's a total of 700 pounds of human weight.

My Pate fuel tank fully loaded with gasoline weighs a bit more than 300 pounds. Now we are up to 1000 pounds.

I have six comfortable but heavy seats mounted on 5/4" mahogany boards. The console and seats and battery probably weigh a total of 300 pounds.

Then I have a 8' stainless steel Bimini top that is not light, and it offers substantial wind resistance.

The 1987 Nissan 70 weighed 212 ponds, so with it I had about 1500 pounds of weight, in addition to the weight of the bare hull.

I'm thinking of getting either the Honda 50 at 212 pounds or the Mercury 60 EFI Bigfoot at 260 pounds. What I'd really like to do is to get Nick on good terms with me so that he can set me up with a year 2000 Suzuki DF 70 for $4200 :) As long as I can keep much of the weight forward, 75 extra pounds may not be that big of a deal. I wish I knew what to do....

Bigshot posted 08-14-2002 11:25 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
PS it is difficult to do mileage when you are using MPG instead of GPH. GPH is the way to do it on boats...this is why: On a boat at cruise if you burn 3GPH at say 25MPH then you know with 12 gallons of gas you roughly have a range of 100 miles. There is no odometer on a boat and therefore hard to tell how far you have gone. It is more imortant to know how far you can go. So if it took 2 hours to burn the first 6 gallon tank, you better get gas within the next 2 hours or you are SOL. My engine burns less than 3GPH so with 27 gallons I have rougly 9 hours of run time at 25mph. At 6mph I have roughly 100+ hours of runtime or 600+ miles....slow miles. Does this make sense? With my 15' and a 70 OMC I would burn roughly 4GPH at 30+MPH so I had a range of 90 miles with 12gallons. With your setup I figure 10 hours run time & 300-350 mi range. Even with a load about 250 miles. Therefore I am confused on why you would run out in 150. Are you sure you have a 42 gallon tank? If so are you sure you are not running WOT more?
Bigshot posted 08-14-2002 11:28 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Where do you put a 42 gallon pate? It would take up half the boat.

We are on good terms and when I post these engines here....write down the number and call them. I aint the UPS guy either:)

David Jenkins posted 08-14-2002 11:34 AM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
I have the Pate J42. Most of it fits under my raised rear seat. I love it.

The engine ran rough at mid-speed but smoothed out at or above 4200-4500 RPM (the RPM is an estimate as I do not have a tachometer). I had the carborators cleaned but not by a Nissan-certified mechanic. So maybe I got poor fuel mileage because the carbs were dirty. I tried everything else: new fuel tank, new OMC bulb & fuel line, new fittings on the fuel line. Anyway, someone offered me $1400 for the engine and before my wife even knew what I had done, that engine was loaded in the back of the guy's pickup truck and was heading south. So now I am without an engine :(

whalersailer posted 08-14-2002 11:39 AM ET (US)     Profile for whalersailer  Send Email to whalersailer     
I'm running a 70 Johnson VRO on mine, and based on what I have seen so far, it seems like I'm burning more like 5-7 gph @ 4,500 rpm's (low 30's) with about 700 lbs (not including motor). I must admit, though, that I didn't keep as close track as I should to have real numbers. This weekend, I will run it with the stop watch and chartplotter (WAAS) so that the numbers are much more accurate. Though I will say that I carry 19 gallons of fuel, and the thought of running the 70 miles to reach the Apostles is kinda scary based on what I have observed so far...I'll see how things go this weekend and post results next week. (If anyone actually cares!)
Bigshot posted 08-14-2002 12:09 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Guys it is easy to figure out. Run 3 gallons in a tank and see how long it taks to run out at cruise. If it takes 1/2 hour you burn 6gph, etc. No way does a 70 burn 7 gph at cruise. My 225 only burns 11 and my 1984 60(2cyl) only burned 3. Both at 4k. My 70 Johnson on my 15' would take about 1.3-1.5 hours per 6 gal tank at cruise.
Bigshot posted 08-14-2002 12:31 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I had a Pate 15 on my 15' and it stuck out from under my seat. A 42 gallon pate is 43"wide x 24" deep x 11.25" tall. I would like to see pics of that thing on a 15'.

Now that we are getting the whole picture here. A 15' with 2-3 adults and 2 children. A 18 gallon pate and a 50-60hp 4 stroke will be fine. Your range will be roughly 150 miles at 25mph if you burn 3GPH. You can either add some fuel on the way or bring another 5 gallon jug.

David Jenkins posted 08-14-2002 12:39 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
Well I have already purchased and installed the J42 so it is a done deal, even if it is a bit overkill. Anyway, I like the convenience of never having to worry about running out of fuel. Will send pics as soon as I get everything back together. While I have no engine, I am working on re-gelcoating the interior, so it will be a couple of weeks (at least) before I am ready to hang a new engine on the stern.

I have been going through the old posts, Bigshot, and I can't find where you mentioned the name or number of that dealer in FL that had new 200 DF70s for sale. If by chance, you happen upon it again, please post it.

If I had just sold my WorldCom stock a last year (instead of buying more), I would not have to worry about trying to get a good deal on a new engine. Or maybe I should follow the advice of Greg (Boston Marine), who would say: if someone buys it then it must be a good deal.

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