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TC 255 Hull Speed?
- Thread starter peterbrownell
- Start date
GulfSailor
New member
Doryman":2szlcnq2 said:That sounds like what I was getting a couple of years ago. Now I am getting about 14.x GPH. :crookDiscovery":2szlcnq2 said:At 4000 RPM the Floscan's show a combined flow of around 9 GPH. In flat seas we will usually be going around 22 MPH at that RPM, or better than 2 MPG
Warren
From what you said earlier it sounds as though you've lightened the boat and you're not dragging a forest of plant life around on the submerged portion of the hulls.
That makes it likely that it's an engine problem of one sort or another, and if so then it would be unusual for both engines to develop the same malady at the same time that would cause them both to consume more fuel.
If you have somewhere you could do a controlled test over a couple of miles you might consider running with just one engine over a set course, then repeating the same course with the other engine, then comparing the fuel burn for each engine.
If one engine is using significantly more then the other then you have to determine whether it's a fault with that engine (leaky injector or bad sensor causing it to run rich, whatever), or if it's working harder than the other one which is under performing.
Captains Cat
New member
"Seriously thinking about a Tomcat 255"
You really need a TomCat, then you could become our research ship!! Lots of good ideas... You sound like my spousal unit...."Let's cut the grass".... She doesn't mean she's gonna helpl!! But
:love :hug :lips :hug2 45 years almost and counting!!
Charlie
You really need a TomCat, then you could become our research ship!! Lots of good ideas... You sound like my spousal unit...."Let's cut the grass".... She doesn't mean she's gonna helpl!! But
:love :hug :lips :hug2 45 years almost and counting!!
Charlie
billtwymank
New member
***
all great input......
and thanks for taking time to provide all the good information.
Lady KC is usually running at about 4000--4200rpm, always going from Point-A to Point-B
and my estimates always seem to be about 10gph,
(no flow meters)
after the reworked aluminum props
were put back on the Honda 135's
***
all great input......
and thanks for taking time to provide all the good information.
Lady KC is usually running at about 4000--4200rpm, always going from Point-A to Point-B
and my estimates always seem to be about 10gph,
(no flow meters)
after the reworked aluminum props
were put back on the Honda 135's
***
Good suggestions, thanks! The currents here will make setting up a repeatable test tricky, but it would be worth doing.GulfSailor":7zf584uk said:From what you said earlier it sounds as though you've lightened the boat and you're not dragging a forest of plant life around on the submerged portion of the hulls.
That makes it likely that it's an engine problem of one sort or another, and if so then it would be unusual for both engines to develop the same malady at the same time that would cause them both to consume more fuel.
If you have somewhere you could do a controlled test over a couple of miles you might consider running with just one engine over a set course, then repeating the same course with the other engine, then comparing the fuel burn for each engine.
If one engine is using significantly more then the other then you have to determine whether it's a fault with that engine (leaky injector or bad sensor causing it to run rich, whatever), or if it's working harder than the other one which is under performing.
Warren
A couple observations . I am by no means an expert ,I just get to think about and deal with boats and manufacturers constantly , have lots of interactions with boaters and have a little tech background .Just enough to be dangerous yet hopefully helpful.A researcher I am not .An observer is a better description.
Number one thing is ethanol amounts are not consistent from location to location or from day to day . That would have a definite effect on fuel economy readings from the perspective of available energy in the fuel.
Engine tune and performance matters as well , injection systems are sensitive,and water and dirt wreak havoc on marine engines, propping is another wild card.
Condition of bottom makes a huge difference as many will point out.
The Yamaha fuel management gauges on Warren's boat , I believe are "paddle wheel type" and distance is calculated by pitot tube speedometer/odometer .That's not speed over ground , but is speed through the water . The NMEA 2000 data bus fuel monitors are driven by the engine computer and interfaced with GPS data . NMEA data bus is probably more accurate across the rpm spectrum than the inline paddle wheels of the Floscan, Navman, or early Yamaha fuel management systems.
All modern systems are now NMEA .
There is not a huge difference in efficiency of modern power plants . It takes X amount of energy to move X amount of load through the water . There is some different design philosophies to get the same end result .
For instance small displacement ,lots of programming , valve timing and things like supercharging; I.E Merc and Honda .
Another design style is the "no replacement for displacement " school . Suzuki and Yamaha have subscribed to that in their mid size offerings , another is the dangerously lean and mean 2 stroke philosophy of Evinrude , Merc Opti and Tohatsu TLDI.and its all changing all the time .
The conquest of efficiency should not overshadow the pleasure of simply being on a boat that starts,runs , gets you where you want to go and brings you the satisfaction and lifestyle that we all love .
Number one thing is ethanol amounts are not consistent from location to location or from day to day . That would have a definite effect on fuel economy readings from the perspective of available energy in the fuel.
Engine tune and performance matters as well , injection systems are sensitive,and water and dirt wreak havoc on marine engines, propping is another wild card.
Condition of bottom makes a huge difference as many will point out.
The Yamaha fuel management gauges on Warren's boat , I believe are "paddle wheel type" and distance is calculated by pitot tube speedometer/odometer .That's not speed over ground , but is speed through the water . The NMEA 2000 data bus fuel monitors are driven by the engine computer and interfaced with GPS data . NMEA data bus is probably more accurate across the rpm spectrum than the inline paddle wheels of the Floscan, Navman, or early Yamaha fuel management systems.
All modern systems are now NMEA .
There is not a huge difference in efficiency of modern power plants . It takes X amount of energy to move X amount of load through the water . There is some different design philosophies to get the same end result .
For instance small displacement ,lots of programming , valve timing and things like supercharging; I.E Merc and Honda .
Another design style is the "no replacement for displacement " school . Suzuki and Yamaha have subscribed to that in their mid size offerings , another is the dangerously lean and mean 2 stroke philosophy of Evinrude , Merc Opti and Tohatsu TLDI.and its all changing all the time .
The conquest of efficiency should not overshadow the pleasure of simply being on a boat that starts,runs , gets you where you want to go and brings you the satisfaction and lifestyle that we all love .
Actually, my Yamaha calculates distance using the GPS, and it is NMEA 2000. I installed a paddlewheel sensor separately to get speed through the water, and that information is displayed on my Raymarine E-80 but is not interfaced to the Yamaha Command Link system. The paddlewheel is not very accurate and gets gummed up too frequently.Wefings":12zizkfi said:The Yamaha fuel management gauges on Warren's boat , I believe are "paddle wheel type" and distance is calculated by pitot tube speedometer/odometer .That's not speed over ground , but is speed through the water . The NMEA 2000 data bus fuel monitors are driven by the engine computer and interfaced with GPS data . NMEA data bus is probably more accurate across the rpm spectrum than the inline paddle wheels of the Floscan, Navman, or early Yamaha fuel management systems.
It will be interesting to see the condition of the bottom when the boat comes out of the water at the end of the season. It has new non-copper bottom paint.
I have a feeling that one of my engines is performing suboptimally because now that I think about it, one side uses more gas than the other, as measured at refuel time.
Warren
Peter,
I think we have very similar Tomcats so maybe I could collect some data for you. Mine has the Suzuki SMIS gauges so I have very accurate gph numbers from the engine electronics. My gph numbers seem to be quite good up to about 7 mph, then at planing speeds of 26-29mph. I do have 16X23" props so I think that might move my efficient planing speed up a bit. I have actually been using the fuel flow instead of rpms to balance the engines since I like the idea of using equal amounts out of each tank. My best mpg at a plane is at 4.75-5.75gph where I am getting 2.4-2.6 smpg. This is with full fuel and water tanks, plastic tender on top and three on board. I'll have to look to see what the rpm's are there.
With this engine and prop combination, it really does not like to go 15-20mph. It takes a lot of throttle to get on a plane, but once there, it wants to go at least 22. I keep the motors trimmed to about 39deg (also on the SMIS gauges) where it seems to get very light in the water at 24mph and higher speeds.
I did try to get on a plane with one motor and couldn't do it.
I think we have very similar Tomcats so maybe I could collect some data for you. Mine has the Suzuki SMIS gauges so I have very accurate gph numbers from the engine electronics. My gph numbers seem to be quite good up to about 7 mph, then at planing speeds of 26-29mph. I do have 16X23" props so I think that might move my efficient planing speed up a bit. I have actually been using the fuel flow instead of rpms to balance the engines since I like the idea of using equal amounts out of each tank. My best mpg at a plane is at 4.75-5.75gph where I am getting 2.4-2.6 smpg. This is with full fuel and water tanks, plastic tender on top and three on board. I'll have to look to see what the rpm's are there.
With this engine and prop combination, it really does not like to go 15-20mph. It takes a lot of throttle to get on a plane, but once there, it wants to go at least 22. I keep the motors trimmed to about 39deg (also on the SMIS gauges) where it seems to get very light in the water at 24mph and higher speeds.
I did try to get on a plane with one motor and couldn't do it.
From the ECM.Wefings":3tvz9ila said:But does it get its fuel data from a padlle wheel in the fuel line or from the ECM?
Warren
Brian:
Interesting observations and numbers--the difference in our boats--is that you have a 175 hp Suzuki and a 23" pitch; I have a 150 and a 21.5" pitch (if I am correct-the boat is not here right now). I jump right onto a plane, the boat runs fine at lower planing speeds (Permatrims), and I seem to get slightly lower mileage. The 175 developes it greater HP at high RPM--so that with the higher pitch prop may account for the reason you don't get on a plane rapidly (although I am surprised).
Interesting observations and numbers--the difference in our boats--is that you have a 175 hp Suzuki and a 23" pitch; I have a 150 and a 21.5" pitch (if I am correct-the boat is not here right now). I jump right onto a plane, the boat runs fine at lower planing speeds (Permatrims), and I seem to get slightly lower mileage. The 175 developes it greater HP at high RPM--so that with the higher pitch prop may account for the reason you don't get on a plane rapidly (although I am surprised).
thataway":2xd0hkhg said:Brian:
Interesting observations and numbers--the difference in our boats--is that you have a 175 hp Suzuki and a 23" pitch; I have a 150 and a 21.5" pitch (if I am correct-the boat is not here right now). I jump right onto a plane, the boat runs fine at lower planing speeds (Permatrims), and I seem to get slightly lower mileage. The 175 developes it greater HP at high RPM--so that with the higher pitch prop may account for the reason you don't get on a plane rapidly (although I am surprised).
Hi Bob,
I didn't mean to say that it doesn't get on a plane rapidly, it definitely does that, but it needs near full throttle to get there when heavily loaded. Last weekend at Seafair, we had close to full tanks and six on board and it took 3/4 or better throttle to get planed but then I could pull back to my magic 4.75-5.75gph and it would fly along at 25-30mph. I think I am feeling the effect of the 23" props like I'm starting out in a car in second gear. I'm not sure if the electronic throttles are part of this but they are very sensitive and with just a little movement it will drop off of plane or go 35mph or better. I have had the Glendinning rep help me a couple of times already and I think I will have him adjust the throttle curve again.
I suspect that a lot of this is the throttle settings. There will be quite a difference in feel between the electronic throttles and manual. I like to tweek the throttles so that RPM are same (but if you have a synchronizer, that is not necessary, and both throttles will come up equally--and advantage of the Glendinning. You should be able to gradually move from 20 to 40 knots as you want--and not over shoot etc.
I would be surprised if your RPM went up to a high level, and that you had prop slip.
It is hard to compare boat weights, due to amount of cruising gear--but we rarely have 6 aboard--on the other hand, we have had a lot of "stuff"...
I would be surprised if your RPM went up to a high level, and that you had prop slip.
It is hard to compare boat weights, due to amount of cruising gear--but we rarely have 6 aboard--on the other hand, we have had a lot of "stuff"...