TEMPTATION 2500: Twin Yamaha 200-HP Outboards: Fuel Consumption

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Author Topic:   TEMPTATION 2500: Twin Yamaha 200-HP Outboards: Fuel Consumption

DL posted 04-25-2006 10:06 AM ET (US)
I have a 25' Temptation with twin rebuilt '86 Yamaha 200's. I would like to run it to Bimini from Fort Lauderdale but I don't have a good feel for the fuel consumption. All of my running to date has been short distances with varying speeds and I don't have a fuel gage or a fuel consumption gage. Any opinions on what I should expect for distance running at 25- 30 mph? I will only go if it is flat. She does close to 50 flat out. (The temptation is an outrage hull with a small cuddy - a little heavier.)
WhalerAce posted 04-25-2006 02:22 PM ET (US)
DL,
If you can wait until next Monday I can give you an answer.
We have a 25' Temptation WD, twin '89 Yamaha 200s. We cruise about 3500 rpm, and seem to get about 2 mpg. Like you, most of our cruising has been short distances, or longer distances with lots of starts and stops.
This weekend, we are cruising from Charleston to Georgetown and back, about 60 miles each way. When I fill the boat back up Sunday afternoon, I will have a good idea of mileage, but so far, I have been pleasantly surprised with our mileage. It seems to have been better than our last boat, an '89 Outrage 22 WD, with twin Evinrude 120s.
We plan on doing the Bimini rendezvous this summer with the Temptation -- maybe see you then?
Again, will let you know soon!
WhalerAce
Tom W Clark posted 04-25-2006 03:04 PM ET (US)
At a cruise speed of 25-30 MPH you can expect to burn 15-16 gallons per hour.
DL posted 04-25-2006 03:28 PM ET (US)
Ace - Good to hear from you. Hope you are making good use of the Bimini top I sold you last year. My run to Bimini will also be about 60 miles each way. I am debating whether I need to fuel up (at $6.00 a gallon) or if I can safely run there and back. I have the same boat as you so let me know how your trip goes. I will look into the Bimini Rendevous and try to make it this year.
Tom - thanks for your input.
jimh posted 04-25-2006 09:25 PM ET (US)
[Moved]
jimh posted 04-25-2006 09:26 PM ET (US)
As a rough estimate, use the horsepower divided by ten as the fuel consumption in gallons per hour.
Tom W Clark posted 04-25-2006 09:37 PM ET (US)
Jim,
One would only do that if they cruised at full throttle, the throttle position where that rule of thumb works. I do not believe that DL is going to cruise from Fort Lauderdale to Bimini at full throttle ;-)
jimh posted 04-25-2006 09:58 PM ET (US)
I think it works at any throttle setting, but the problem is knowing the horsepower at less than full throttle. As another rule of thumb, I suggest using a horsepower that is proportional to the full throttle horsepower. For example:
If an engine is rated a 200-HP at 5,500-RPM, how much horsepower does it produce at 2,250-RPM?
HP = 200 x (2250/5500)
HP = 100
This implies about 10-gallons-per-hour at 2,250-RPM
Again, this is a very rough estimate. It will tend to produce estimates that are too high, but this is a safer way to plan a trip.
Plotman posted 04-26-2006 01:31 PM ET (US)
Why not use the crouch calculator to calculate your hull factor based on speed at WOT, and then figure the HP required to propel the boat at your normal cruise speed, and then use that HP/10 to guestimate fuel consumption in gph.
For my boat, this works pretty well - gives me a figure very close to what my navman fuel flow instruments indicate.
I'd be very interested to know how that works for other.
David
Tom W Clark posted 04-26-2006 01:35 PM ET (US)
David,
That was the response I was expecting Jim to give ;-)
jimh posted 04-26-2006 01:45 PM ET (US)
That is a grand idea, and another good use for the Crouch's Calculator. Prior to the invention of this calculator, it was a bit awkward to deduce the horsepower from the speed prediction equation.
andygere posted 04-26-2006 02:48 PM ET (US)

quote:
I will only go if it is flat
With all due respect, I think calculating your range based on various calculators with assumed inputs that work under ideal conditions is downright foolish. On a 60 mile crossing, you are likely to encounter weather and sea conditions that are vastly different than what is forcasted and what you experience when leaving port. Heavy seas can easily drop your fuel efficiency in half. Will you have enough to get back? What if you get part way across and have to return because of hazardous seas? Was is worth saving $2 per gallon on fuel?
I would invest in a fuel flow instrument such as a Flow Scan or Navman, and measure your fuel consumption in a variety of sea states, including some really lousy ones. With that data in hand, you will be able to determine your range over the spectrum of conditions that you might encounter during such a trip.
Tom W Clark posted 04-26-2006 04:24 PM ET (US)
I think that Andy offers DL excellent practical advice.
But ignoring this for a moment, and indulging my mathematical side, let's use David's suggestion and Jim's Crouch Calculator to see what figures we come up with for DL's fuel consumption at cruise speeds.
Temptation 25 with twin Yamaha 200 HP motors and a top speed of 50 MPH. According to Jim's rule of thumb we can expect this boat to burn approximately 40 gallons per hour at WOT. This I believe.
Using the Crouch Calculator we find that DL's boat has a hull factor of about 200. Using this hull factor and a speed of 25 MPH the Crouch Calculator tells us it takes 100 HP to propel this boat at this speed. Using Jim's rule of thumb again, that suggests it will burn 10 gallons per hour. Hmmm...
OK, what about at 30 MPH? The Crouch Calculator tells us it takes 144 HP to keep this boat going at this speed. Horsepower divided by ten: 14.4 Gallons per hour. Closer to reality.
Let's just split the difference and see what happens at 27.5 MPH. 120.9 HP or 12.9 gallons per hour. Too low. Not a conservative estimate at all, but it is simply a result of the simplistic inverse square relationship in Crouch's formula and illustrates the problem's with using simple rule of thumbs.
I stand by me estimate of 15-16 gallons per hour at this speed.
jimh posted 04-27-2006 01:43 AM ET (US)
Tom--Thanks for running the numbers. I was looking at some older data I had on speed and RPM, and was going to convert it to an estimate of horsepower. On the first pass, it seemed to be coming in low, that is, the estimated horsepower seemed lower than I would have thought.
On the other hand, I do have a fuel flow meter. Perhaps I could collect some more data of RPM, boat speed, and fuel flow. This would be another way to estimate the horsepower at different engine speeds.
As for making a long run with limited fuel, weather can really cause you to have problems. In 2003, LHG and I ran up a long inlet in British Columbia, about 45 miles up from the coast. We topped off our tanks at the last gas dock on the way inbound. We make the trip up the inlet in great weather, and we were on plane all the way at optimum cruise. We spent the night at the very head of the inlet. The next day we left in the late morning. The weather turned ugly, and soon we were running with "up-inlet winds" and a tide coming out. Those combinations made for some very ugly boat speed. We were down to about 10 to 12-MPH and on much higher fuel burn rates. Fortunately, we only had to weather about ten miles of that stuff, and then the course line made a 90-degree bend. We were out of the wind and waves
and back on plane. If we had to run the whole distance in that high-fuel burn mode, it would have been a race to make it out and back to the gas dock.
BOB KEMMLER JR posted 04-27-2006 05:39 PM ET (US)
Ace now that Merc has those new 300 Opti's out,that Temptation seems like the right candidate for them.
WhalerAce posted 04-30-2006 11:07 PM ET (US)
DL,
We really haven't used the Temptation since the Stuart event last year. In fact, I just put the top on about a month ago, and this weekend was the first time that we got to use it. And also, the Eisenglass was in great shape too. We thank you much for the top.
Now, as for the mileage. We went from Charleston to Georgetown, about seventy miles one way. We fought a twenty knot headwind and about two- to three-foot swells the whole way up. Ran about 3400 to 3800 rpm (don't have a speedometer I can rely on). The trip was three hours almost exactly, with no stops. Filled up before we left, and this morning we put 45 gallons in to retop before the ride back home. I have not put gas in it since we have gotten home, but the trip back was pretty much the same duration about two hours, forty-five minutes.
Not quite two MPG. I always figure about 1 MPG when I travel, and always the peace of mind of knowing I have started off with a full tank is important to me.
Hope this helps.
Ace
Tom W Clark posted 04-30-2006 11:21 PM ET (US)
Ace,
If I am reading you correctly, you burned 45 gallons in three hours of running time. That's 15 gallons per hour at a cruising speed of 23-24 MPH.
WhalerAce posted 05-08-2006 10:20 PM ET (US)
Tom, et al,
Is that good? We haven't really used the Temptation a whole lot, especially for long distances, so I have no idea if this is good or not.
15 GPH "translates" to about $45 per hour of run time. You can't really beat that price for the amount of fun we have running the boat.
I know these carbed two-strokes are not the most fuel efficient in the world, but I just cannot justify in my mind spending $22K for new "fuel efficient" engines.
Thanks in advance,
Ace
DL posted 05-12-2006 09:15 AM ET (US)
Ace, Tom, thanks for the advice and info. It looks like an over and back run would be pretty safe on 140 gallons with a couple of six gallon spare tanks. We were hoping to avoid the ordeal of going into town, clearing customs (which I hear is now $150.00) and buying gas at $6.00 a gallon, but as it turns out we are staying over so we have to do all that anyways. Will top off to be safe. Hope to see you in Bimini in July.

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Author	Topic: TEMPTATION 2500: Twin Yamaha 200-HP Outboards: Fuel Consumption
DL	posted 04-25-2006 10:06 AM ET (US) I have a 25' Temptation with twin rebuilt '86 Yamaha 200's. I would like to run it to Bimini from Fort Lauderdale but I don't have a good feel for the fuel consumption. All of my running to date has been short distances with varying speeds and I don't have a fuel gage or a fuel consumption gage. Any opinions on what I should expect for distance running at 25- 30 mph? I will only go if it is flat. She does close to 50 flat out. (The temptation is an outrage hull with a small cuddy - a little heavier.)
WhalerAce	posted 04-25-2006 02:22 PM ET (US) DL, If you can wait until next Monday I can give you an answer. We have a 25' Temptation WD, twin '89 Yamaha 200s. We cruise about 3500 rpm, and seem to get about 2 mpg. Like you, most of our cruising has been short distances, or longer distances with lots of starts and stops. This weekend, we are cruising from Charleston to Georgetown and back, about 60 miles each way. When I fill the boat back up Sunday afternoon, I will have a good idea of mileage, but so far, I have been pleasantly surprised with our mileage. It seems to have been better than our last boat, an '89 Outrage 22 WD, with twin Evinrude 120s. We plan on doing the Bimini rendezvous this summer with the Temptation -- maybe see you then? Again, will let you know soon! WhalerAce
Tom W Clark	posted 04-25-2006 03:04 PM ET (US) At a cruise speed of 25-30 MPH you can expect to burn 15-16 gallons per hour.
DL	posted 04-25-2006 03:28 PM ET (US) Ace - Good to hear from you. Hope you are making good use of the Bimini top I sold you last year. My run to Bimini will also be about 60 miles each way. I am debating whether I need to fuel up (at $6.00 a gallon) or if I can safely run there and back. I have the same boat as you so let me know how your trip goes. I will look into the Bimini Rendevous and try to make it this year. Tom - thanks for your input.
jimh	posted 04-25-2006 09:25 PM ET (US) [Moved]
jimh	posted 04-25-2006 09:26 PM ET (US) As a rough estimate, use the horsepower divided by ten as the fuel consumption in gallons per hour.
Tom W Clark	posted 04-25-2006 09:37 PM ET (US) Jim, One would only do that if they cruised at full throttle, the throttle position where that rule of thumb works. I do not believe that DL is going to cruise from Fort Lauderdale to Bimini at full throttle ;-)
jimh	posted 04-25-2006 09:58 PM ET (US) I think it works at any throttle setting, but the problem is knowing the horsepower at less than full throttle. As another rule of thumb, I suggest using a horsepower that is proportional to the full throttle horsepower. For example: If an engine is rated a 200-HP at 5,500-RPM, how much horsepower does it produce at 2,250-RPM? HP = 200 x (2250/5500) HP = 100 This implies about 10-gallons-per-hour at 2,250-RPM Again, this is a very rough estimate. It will tend to produce estimates that are too high, but this is a safer way to plan a trip.
Plotman	posted 04-26-2006 01:31 PM ET (US) Why not use the crouch calculator to calculate your hull factor based on speed at WOT, and then figure the HP required to propel the boat at your normal cruise speed, and then use that HP/10 to guestimate fuel consumption in gph. For my boat, this works pretty well - gives me a figure very close to what my navman fuel flow instruments indicate. I'd be very interested to know how that works for other. David
Tom W Clark	posted 04-26-2006 01:35 PM ET (US) David, That was the response I was expecting Jim to give ;-)
jimh	posted 04-26-2006 01:45 PM ET (US) That is a grand idea, and another good use for the Crouch's Calculator. Prior to the invention of this calculator, it was a bit awkward to deduce the horsepower from the speed prediction equation.
andygere	posted 04-26-2006 02:48 PM ET (US) quote: I will only go if it is flat With all due respect, I think calculating your range based on various calculators with assumed inputs that work under ideal conditions is downright foolish. On a 60 mile crossing, you are likely to encounter weather and sea conditions that are vastly different than what is forcasted and what you experience when leaving port. Heavy seas can easily drop your fuel efficiency in half. Will you have enough to get back? What if you get part way across and have to return because of hazardous seas? Was is worth saving $2 per gallon on fuel? I would invest in a fuel flow instrument such as a Flow Scan or Navman, and measure your fuel consumption in a variety of sea states, including some really lousy ones. With that data in hand, you will be able to determine your range over the spectrum of conditions that you might encounter during such a trip.
Tom W Clark	posted 04-26-2006 04:24 PM ET (US) I think that Andy offers DL excellent practical advice. But ignoring this for a moment, and indulging my mathematical side, let's use David's suggestion and Jim's Crouch Calculator to see what figures we come up with for DL's fuel consumption at cruise speeds. Temptation 25 with twin Yamaha 200 HP motors and a top speed of 50 MPH. According to Jim's rule of thumb we can expect this boat to burn approximately 40 gallons per hour at WOT. This I believe. Using the Crouch Calculator we find that DL's boat has a hull factor of about 200. Using this hull factor and a speed of 25 MPH the Crouch Calculator tells us it takes 100 HP to propel this boat at this speed. Using Jim's rule of thumb again, that suggests it will burn 10 gallons per hour. Hmmm... OK, what about at 30 MPH? The Crouch Calculator tells us it takes 144 HP to keep this boat going at this speed. Horsepower divided by ten: 14.4 Gallons per hour. Closer to reality. Let's just split the difference and see what happens at 27.5 MPH. 120.9 HP or 12.9 gallons per hour. Too low. Not a conservative estimate at all, but it is simply a result of the simplistic inverse square relationship in Crouch's formula and illustrates the problem's with using simple rule of thumbs. I stand by me estimate of 15-16 gallons per hour at this speed.
jimh	posted 04-27-2006 01:43 AM ET (US) Tom--Thanks for running the numbers. I was looking at some older data I had on speed and RPM, and was going to convert it to an estimate of horsepower. On the first pass, it seemed to be coming in low, that is, the estimated horsepower seemed lower than I would have thought. On the other hand, I do have a fuel flow meter. Perhaps I could collect some more data of RPM, boat speed, and fuel flow. This would be another way to estimate the horsepower at different engine speeds. As for making a long run with limited fuel, weather can really cause you to have problems. In 2003, LHG and I ran up a long inlet in British Columbia, about 45 miles up from the coast. We topped off our tanks at the last gas dock on the way inbound. We make the trip up the inlet in great weather, and we were on plane all the way at optimum cruise. We spent the night at the very head of the inlet. The next day we left in the late morning. The weather turned ugly, and soon we were running with "up-inlet winds" and a tide coming out. Those combinations made for some very ugly boat speed. We were down to about 10 to 12-MPH and on much higher fuel burn rates. Fortunately, we only had to weather about ten miles of that stuff, and then the course line made a 90-degree bend. We were out of the wind and waves and back on plane. If we had to run the whole distance in that high-fuel burn mode, it would have been a race to make it out and back to the gas dock.
BOB KEMMLER JR	posted 04-27-2006 05:39 PM ET (US) Ace now that Merc has those new 300 Opti's out,that Temptation seems like the right candidate for them.
WhalerAce	posted 04-30-2006 11:07 PM ET (US) DL, We really haven't used the Temptation since the Stuart event last year. In fact, I just put the top on about a month ago, and this weekend was the first time that we got to use it. And also, the Eisenglass was in great shape too. We thank you much for the top. Now, as for the mileage. We went from Charleston to Georgetown, about seventy miles one way. We fought a twenty knot headwind and about two- to three-foot swells the whole way up. Ran about 3400 to 3800 rpm (don't have a speedometer I can rely on). The trip was three hours almost exactly, with no stops. Filled up before we left, and this morning we put 45 gallons in to retop before the ride back home. I have not put gas in it since we have gotten home, but the trip back was pretty much the same duration about two hours, forty-five minutes. Not quite two MPG. I always figure about 1 MPG when I travel, and always the peace of mind of knowing I have started off with a full tank is important to me. Hope this helps. Ace
Tom W Clark	posted 04-30-2006 11:21 PM ET (US) Ace, If I am reading you correctly, you burned 45 gallons in three hours of running time. That's 15 gallons per hour at a cruising speed of 23-24 MPH.
WhalerAce	posted 05-08-2006 10:20 PM ET (US) Tom, et al, Is that good? We haven't really used the Temptation a whole lot, especially for long distances, so I have no idea if this is good or not. 15 GPH "translates" to about $45 per hour of run time. You can't really beat that price for the amount of fun we have running the boat. I know these carbed two-strokes are not the most fuel efficient in the world, but I just cannot justify in my mind spending $22K for new "fuel efficient" engines. Thanks in advance, Ace
DL	posted 05-12-2006 09:15 AM ET (US) Ace, Tom, thanks for the advice and info. It looks like an over and back run would be pretty safe on 140 gallons with a couple of six gallon spare tanks. We were hoping to avoid the ordeal of going into town, clearing customs (which I hear is now $150.00) and buying gas at $6.00 a gallon, but as it turns out we are staying over so we have to do all that anyways. Will top off to be safe. Hope to see you in Bimini in July.