Fuel economy sacrificed with bigger and bigger engines?

[dloop]

Hi folks,

I'm new. I've been lurking for a while as I've been trying my best to research the R25 on my own. This is a great forum with tons of good info and I have learned a lot by reading through your many excellent posts. Thank you for sharing.

In reality I'm probably not going to be able to get a new boat for a while as I have kids (plural) in college. But I see the light at the end of the tunnel, and I really feel that the R25 would be a perfect fit for my wife and me.

I do have a question. Fuel economy is one thing that really attracts me to this boat. If anything the recent years have taught us is that we, as a country, don't have independent control of over the prices we pay for the fuel we consume. I don't want to get into a situation where I have a beautiful boat, but can't afford the fuel to actually use it. (been there, done that 🙁 ).

I read a post by Jeff from a while ago where he mentioned that the R25 was originally designed around the Yanmar 75HP, and that the 75HP provided more than enough power for the boat. Later the 110HP became the standard, and now it's the 150HP.

Has fuel economy fallen with the bigger engines? Can you still get a 75HP instead of the 150? Would you recommend against it? Why, or Why not?

Thanks,


dave

 

[Ram]

My observation (and I'm sure there are others who have a lot more direct experience with diesels than I) is that it has more to do with top end and engine longevity than fuel economy. I've compared the performance curves of all the engines Ranger has used in the R25's, and they generally get about the same fuel consumption at the same rev's.

The differtence is that a bigger engine will allow you to go faster. You'll burn a lot more fuel in the process, but that's the tradeoff. My Yanmar 125 probably uses 3 times as much fuel cruising at 12 knots as it does at 8 knots. 50% increase in speed, 200% increase in fuel consumption. That's because of the amount of water being pushed out of the way, which is going to be the same for any engine.

There's also the argument that diesel's last longest when run moderately hot. So if you get a big engine and run it slow all the time to save money on fuel, you may lose money on the life of the engine (not to mention the original cost and the replacement cost).

Like anything in boating, it's a tradeoff. You'd best think about where you'll be cruising and how fast you'll want to go, then get an engine that best fits that profile. The fact that Ranger has hept increasing the size of the engine, to me says more about the human mind (ours, not theirs) than it does about the boats.

 

[captd]

Todays run stats...........On Flathead Lake , Montana Running south from Big Fork to Wild Horse Island, where we are now anchored for the night. The lake is like glass and just as clear. Sun is setting in the west. A full tummy of burgers on the barbie. 😀

Running at 8.3 miles an hour, we were burning 2 gph. The nice thing about the little bigger engine is......If I am in a hurry to get out of some crappy weather i can run up to 20 miles an hour. Depending on load of course. Dropping down to hull speed, 6 and better is possible. One boat I had before the C-Dory i would burn about 25 gals an hour. With a 600 gal tank, you do the math. How about a $2500 fill up in the bahamas, now over $3000. Once there you had a nice place to live, but you did not cruise around for fun.

If you want to spend time living aboard and still see some neat places cruising. The Ranger would be agood one for you and Wife.

captd

 

[rt11002003]

Displacement and semi-displacement hulls tend to move a lot of water. That takes energy, in our case diesel fuel driving the vessel. The faster one goes the more water is moved, requiring more energy/fuel.

There are three interesting articles in the Sept. issue of MotorBoating. It swallowed up Power Cruisingto which I had subscribed.

One was written by an experienced captain; his subject was sudden bad weather (squalls). He made two interesting points. He doesn't always agree with the idea that one "needs" a faster boat in order to outrun bad weather. It may work if one is close to a shelter, but that isn't usually the case. Second, he reminds us that when running from weather, with the waves, and it gets rough, one should go slower than the speed of the waves.

Another article concerned fuel flow computers. The point was made that small power (throttle) adjustments can make big differences in fuel consumption and that the only way to detect some of these adjustments is to know real time fuel flow.

The last article I'll mention is one where the editor writes of a trip with his daughter on a Grand Banks 36. He compares that vessel to an older model that he once owned. One of his topics had to do with the difference in power and the resulting change in speed and fuel consumption. He made a point of remarking about motoring along at a higher speed than he did in his former vessel and finally looked at his wake, which was huge. He then realized that a displacement hull was always a displacement hull and all he was doing was moving large amounts of water with very little increase in speed.


Gene

 

[SlackwaterJack]

Hi,

first of all, what kind of hull does the R25 have? If displacement it can't exceed its hull speed even if you put a jet engine on it, If its a semi - displacement it will lift a bit and allow a little more speed but it can take a lot of power to achieve any real difference over 30% of its displacement speed, planeing hulls are designed to allow the boat to almost leave the water and can be very fast because if it, but again lots of power is needed to climb the displacement "bow wave".... but once on plane usually the power need drops somewhat and she can be throttled back to "settle" it.
I may be wrong (happens) but I can't imagine that an R25 could get on plane, and wasn't designed to...does the factory offer a waveboard tower option? The original engine size was plenty , after all it isn't a big boat.
My old Albin 25 (lighter boat) came with a 21 hp diesel and later models had up to 30 hp. and also had a semi displ. hull it couldn't achieve more than around 9 knots. Later models came with 30 hp and the performance didn't change. I know of one fellow in BC that re-powered with 80 hp and says he manages to make 12 knots. The main difference is ability to maintain the max speed against high wind and waves and more power will give you that ability.

To sum up.......... ya, it's an ego thing.

Check out my photo gallery (page 4) to see how a Ranger R-21 can achieve speeds in excess of 12 knots with a stock engine

Alex
"Slackwater Jack"
Lewiston, ID

 

[Tom Ray]

Hi,

first of all, what kind of hull does the R25 have? If displacement it can't exceed its hull speed even if you put a jet engine on it

A common misperception. Sailboats exceed hull speed under sail all the time. When a boat is going faster than hull speed, it is attempting to climb its own bow wave. That's hard, but possible. It's a bow wave, not a bow wall. As you go faster and try to climb higher and higher on the bow wave, it gets increasingly difficult, requiring more and more power. It doesn't take much power to drive any displacement hull to hull speed, and it takes a lot to drive it beyond hull speed, but it happens all the time. I have had a 17' Com-Pac Sun Cat sustaining 6 knots. Hull speed on that boat is 5.19 knots.

Getting back to your original question, the sacrifice in fuel economy below hull speed is negligible. At a little under 7 knots, the R-25/150 burns a gallon an hour, which is about the same as an R-25/75 would burn at that speed. Increase speed by one knot, double your fuel consumption.

 

[dloop]

Thank you for all your responses. You've given me more to ponder.

 

[terraplane]

I have a 2008 Ranger 25, yanmar 110.

I run usually at 6-8 knots..often burning about 1.6 gal per hour.
I have been operating on the Chesapeake for 37 years..been caught out maybe 4 times in bad storms...in each case a faster boat would not have helped me at all. I check weather and am very careful about when i go out.

I chose the Yanmar 110 because my mechanic friends here say it is relatively simple to service, has a proven record, and less high tech specs. It has worked flawlessly.

 

[dloop]

There's also the argument that diesel's last longest when run moderately hot. So if you get a big engine and run it slow all the time to save money on fuel, you may lose money on the life of the engine (not to mention the original cost and the replacement cost).

Here is an interesting artice I found that talks about what you wrote about Ram.

http://www.oceannavigator.com/ME2/d...91&tier=4&id=0CFEBC2E279B497DB69BDDBE438A619F

Here is the pertinent part:

Various studies done over the years have demonstrated that as power utilization starts to fall below 50 percent of the available power, the fuel efficiency on diesel engines begins to decline. Once power utilization falls below 20 percent, fuel efficiency can decline dramatically to the point that the amount of fuel burned per horsepower hour of energy produced (i.e. the fuel burned per hp of energy used by the propellor) can easily be double, triple or even six times what it is at the most efficient fuel burn rates (which generally occur somewhere around two thirds of maximum speed).

This is one of the reasons why it is such a bad idea to run diesel engines lightly loaded for extended periods of time (such as when battery charging or refrigerating at anchor, or when using an AC generator for light loads). The excess fuel being burned results in a good deal of carbon formation that fouls piston rings, valves and exhaust systems, and can, in a worst-case situation, wreck an engine in less than 1,000 running hours.

 

[Levitation]

The findings of decreased fuel efficiency, carbon buildup, smoking and wet stacking, at low RPM and light loads, come from the era of mechanically injected diesel engines... Those engines barely managed to have the proper fuel to air ratio at 60% of rated HP/load and up... At lower RPM and light loads they ran rich on the mixture causing smoking and carbon buildup and lowered mileage/efficiency...

The new, common rail, electronically injected engines maintain the proper fuel to air ratio from WOT right down to idle... I do not see even a trace of black exhaust from cold start and idle right up to WOT with the QSD 2.0 - 150hp engine... There is no penalty for having more HP with these engines as they run happily at part throttle...

The computer on Levitation says she has averaged 3.4 MPG over the nearly 150 gallons of fuel the engine has burned..

denny-o

 

[commander bill]

I believe I have the only 75 hp Yanmar in my Ranger 25. I am limited to about 10 kts. The 75 hp and 110 hp are really the same engine with a smaller turbo on 75 hp. As such I would guess fuel economy at 6-7 kts would likely be identical between the 2 engines. I usually cruise between 5-6 kts and take engine up to WOT about 5 min/hr. Last season I put 80 hours on engine and burned 60 gallons of fuel. Most of the boats comparable in size to a ranger 25 that I know at my marina can burn that much fuel in one weekend. As such the owners spend their weekend partys at the dock. Reliability is very important to me & I am very glad that I have an "old tech" type mechanical controlled engine. I have operated these type engines for many years & I have never known a "well maintained" engine to let you down. I have a more modern design in my F250 Ford diesel truck. Works great but I stay awake at night worring about it having a problem.

There is a very nice older 36 foot Grand Banks nearby at my marina. According to owner it only has a single 125 hp diesel and gets excellent economy. More modern models have dual/larger engines. It also is not capable of any speed records. That boat is nice & I would love to have it. Problem is that owner feels the same way.

 

[dloop]

I believe I have the only 75 hp Yanmar in my Ranger 25.

Hi commander bill, I was wondering if anyone had stayed with the 75 and not optioned-up. If you were to do it all over again, would you still get the 75, or would you go with the 110?

dave

 

[baz]

I believe I have the only 75 hp Yanmar in my Ranger 25. ...snip...

What size fuel tank do you have in your 75 HP Yanmar R25 ?

 

[commander bill]

To address both above questions my boat has same fuel system, filters & fuel tank as others (75 gallons). I am more than pleased with my 75 hp Yanmar. It has never required more than a nanosecond to start and performs much better than I expected. I am constantly surprised when I see posts that discuss how fast their boat will go and yet all admit they cruise at about 6 kts. Again the 75 hp is the same basic engine as 110hp, but with less boost (turbo) that means less stress over the life. Both engines have same weight and use same replacement parts. I would not expect there to be any difference between 2 engines in fuel useage if driven below "hull speed". My boat will only reach 10 kts so if that is too slow buy something else. Prior to delivery Mark took my boat out & held a sea trials and reached 12 kts (GPS memory shows this as accurate) however, the boat got bottom paint before I took delivery. Additionally, I keep it heavily loaded (fuel, water, much junk) and usually go out with 4 or more people so under ideal conditions 12 kts could be expected. I know speed is important to many of you but to me the journey is more important than the destination. If I was trying to get there in a hurry I would call Delta airlines.

 

[bbrh842]

I agree with Commander Bill.
If you are in a hurry, get on an airplane.
With 110 Yanmar, I typically cruise at 2000 RPM, which yields about 7.2 knots.

Also, F.Y.I.
That same basic engine block comes in four HP ratings.
54 HP, no turbo, no intercooler.
75 HP, turbo, no intercooler.
110 HP, turbo and intercooler.
125, bigger turbo, intercooler.

If I had to re-engine my R-25, I would seriously consider the 54 HP.
All the turbo and intercooler hardware, and plumbing, on the 110 HP, make it nearly impossible to get to the water pump to change the impeller.
All that stuff is going to cause an expensive problem someday, when it needs to be replaced.

 

[commander bill]

The original order for my boat was to include the 50 hp engine. However, once Ranger got to the engine installation stage they found that the 50 hp version came with a differnt transmission configuration and would not fit without significant redesign. The 75 hp comes configured the same as the 110 hp so it would drop right in. Ranger contacted me and we decided to upgrade to 75 hp engine. Apparently, although designed for the 75 hp engine none had been built until mine (hull 67). As mentioned above 75 hp version does not have an intercooler and access to waterpump may be somewhat easier on my engine

 

[Levitation]

Every choice has consequences... However, I am less concerned about the turbo (assuming you let the engine idle at least 3 minutes by the clock to cool the bearings before shut down) needing service and costing big bucks, than I am about the water cooled muffler... These things are always a problem after they age a bit...
There is a reason the commercial fishermen use a dry stack exhaust - they know what works long term...

denny-o

 

[doke01]

I usually cruise at around 3000-3200 RPM at 10 knots. I top out at around 15 knots at 3600 RPM or so. I have gotten up to 18-19 knots or so when conditions are perfect (wind and tide at my back, half full tank, no water, etc). I have the Yanmar 125 HP. I have found in extended cruising that I get about 2.5-3 gph (compared to my old Maxum Express Cruiser 2400 SCR that averaged around 11 gph at cruising speed). I boat usually on the weekends with one or two boating vacations per year so I have to move a little to get there and back. At 3000-3200 RPM the boat performs beautifully and is not struggling at all. With my experience with my prior boats I've found it better to get the bigger engine. It's easier to slow down with a smaller or bigger engine but a whole lot more difficult to speed up when the engine is small. Especially if you want to bring a bunch of people along (I've had 11 people on the boat comfortably for a day out). Since I came from the power boat side, 125 HP seems tiny but it does the job really well.

Doug
Nauti Dream