*THE HULL TRUTH is the world's largest FREE network for the discussion of Boating & Fishing. Whether you're researching a new boat, or are a seasoned Captain, you'll find The Hull Truth Boating & Fishing Message Forum contains a wealth of information from Boaters and Sportfishermen around the world.
Welcome to the updated THT!
If you are having trouble signing in, please email feedback@thehulltruth.com with your username and we will help you. We thank you for your patience as we help you access the new site!
Random Quote: The fishing was slow.......and then it tapered off
i think we are making some progress, but not quite there yet.
Quote:
Originally Posted by Inlander
...When that diesel boat starts at full throttle there is sufficient torque to enable the engines to get into peak torque range immediately....
wrong. the reason is that it is has sufficient power, not sufficient torque. now, in order to get sufficient power it needs a sufficient combination of torque and rpm. furthermore, at idle you could argue that there is insufficient rpm to make up for insufficient torque and therfore need more than sufficient torque at this insufficient rpm to make sufficient power.
however, from what combination of rpm & torque this power is made is of no consequence when considering how a boat (or any other motorized vehicle) will accelerate.
because different engines are so different on so many different levels (and not just at what rpm they make their power), i think comparing an engine to itself makes the point the clearest:
forget, for a minute, diesel vs. gas, peaky vs. smooth, etc.
consider that we all have available to us a very very very easy way to quadruple the torque of any eninge on the market. put it through a 1:4 reducing gear. i am not saying this to be funny, i am saying it to make a point. properly prop an engine with a straight through 1:1 gear, measure performance. take the same engine and put it through a 1:4 reducing gear and re-prop. you will have QUADRUPLED THE TORQUE of the motor/tranny package.
assuming both props perform the same (slip), what have you done to the performance? NOTHING!!
why? because you haven't changed the POWER of engine/tranny package.
now, it is unrealistic to think that a prop w/4x the pitch of another prop would perform the same but it is beside the point here. the performance of a boat at a given speed is independent on the torque of the motor but rather the torque AND rpm (i.e. POWER) of the motor.
Torque has nothing whatsoever to do with moving a boat. Or moving anything for that matter. Torque is simply a twisting moment. You can have torque without any movement at all.
where you high when you wrote this ? torque is a measurement of applied force. Please explain how you can have torque without movement
Quote:
Put a three foot long lug nut wrench on one of the lug nuts on your truck. Stand on the end of the lug nut wrench. If you are 200 pounds in weight you are no applying a torque of 600 foot pounds (three times 200) to the nut. Is the nut, the wheel or the truck going anywhere? I don't think so.
again , what the hell are you talking about. You give me a breaker bar 3 foot long on a lug nut, i'll move the f*ck out of that car.
Quote:
HP is the measurement of work being done. Work as in moving a boat of many thousand pounds at some velocity over a period of time.
no HP is the overall measuremeant of torque over a given speed (rpm)
I don't think the gas inboards would have a higher cruise speed..2 factors. 1) Typical gas cruise rpm is maybe 60% of wide open throttle. 2) The LOAD factor, percentage of "wide open throttle" at cruise is heavily weighted in favor of diesels.
Can we please get back on topic, we know you have plenty of torque in your diesel. Lets get back to the 2 stroke vs the 4 stroke banter. I will get it started, if you need an excellent hole shot to get your big CC out get A.................
__________________ My Suzuki 200's have tons of Torque, please no more lame talk about having to change the oil. Fish On...
For every action there is an equal and opposite reaction. You can't apply torque without something reacting to it. The lug nut..if the brake isn't on, you're gonna move the truck, since the center of rotation is different from the center of the axle. The old summation of forces thing.
torque on props..more complicated. The more torque applied, the more blade area required to "push" against the water. Speed is now affected by..blade friction!
Again, torque is measured, horsepower is computed, and all these values are rated at FULL throttle.
i think we are making some progress, but not quite there yet.
wrong. the reason is that it is has sufficient power, not sufficient torque. now, in order to get sufficient power it needs a sufficient combination of torque and rpm. furthermore, at idle you could argue that there is insufficient rpm to make up for insufficient torque and therfore need more than sufficient torque at this insufficient rpm to make sufficient power.
however, from what combination of rpm & torque this power is made is of no consequence when considering how a boat (or any other motorized vehicle) will accelerate.
because different engines are so different on so many different levels (and not just at what rpm they make their power), i think comparing an engine to itself makes the point the clearest:
forget, for a minute, diesel vs. gas, peaky vs. smooth, etc.
consider that we all have available to us a very very very easy way to quadruple the torque of any eninge on the market. put it through a 1:4 reducing gear. i am not saying this to be funny, i am saying it to make a point. properly prop an engine with a straight through 1:1 gear, measure performance. take the same engine and put it through a 1:4 reducing gear and re-prop. you will have QUADRUPLED THE TORQUE of the motor/tranny package.
assuming both props perform the same (slip), what have you done to the performance? NOTHING!!
why? because you haven't changed the POWER of engine/tranny package.
now, it is unrealistic to think that a prop w/4x the pitch of another prop would perform the same but it is beside the point here. the performance of a boat at a given speed is independent on the torque of the motor but rather the torque AND rpm (i.e. POWER) of the motor.
although your correct about gear reduction being a multiplier as I stated earlier in this post,
the rest of it is wrong. If that was the case electric motors which have a HIGH flat torque curve wouldn't have a purpose, but that not the case. They are almost 98% efficient when compared to diesels 40% and gassers 25%. There are TOO many variable that can be added and non engine builders really don't take into account. How about the volumetric efficiency of a engine, camshaft profiles, crankshaft stroke, intake runner length, theese are some of the things that added together that will give an engine of the same cubic inch different characteristic from another engine of the same CI.
You dont have to believe me, i'll post another reference like i did before. You don't have to believe that either.
Speed, without seeing torque plotted out, I'd guess the 4 strokes have a much broader torque curve. Many use variable valve timing and adjustable intake runners. 2 strokes are historically pretty peaky.
[quote=chainsaw42;2616884]i think we are making some progress, but not quite there yet.
however, from what combination of rpm & torque this power is made is of no consequence when considering how a boat (or any other motorized vehicle) will accelerate.
Wrong!
The amount of torque available at a given RPM has everything to do about acceleration.
Another way to look at it would be to imagine a car with a stick shift and going 15mph in 5th gear. An engine with low torque available at low rpm would lug badly. An engine with high torque at low rpm would perform better when accelerating. The car analogy is exactly what happens when accelerating with a boat from low speed.
i think we are making some progress, but not quite there yet.
however, from what combination of rpm & torque this power is made is of no consequence when considering how a boat (or any other motorized vehicle) will accelerate.
Wrong!
The amount of torque available at a given RPM has everything to do about acceleration.
Another way to look at it would be to imagine a car with a stick shift and going 15mph in 5th gear. An engine with low torque available at low rpm would lug badly. An engine with high torque at low rpm would perform better when accelerating. The car analogy is exactly what happens when accelerating with a boat from low speed.
for a second i thought it was falling on deaf ears, just to add to your car analogy when comparing to a boat think of that car with flat tires, thats because there is that much more drag on the hull then the rolling resistance of a car on pavement. Without torque to get the boat on plane and keep it there, we never get passed hull speed.
Somebody needs to make a variable pitch prop, and a lot of these issues will be solved.
You should have a dial by your thottles that controls your pitch... like an airplane. Then you could set your RPMS at the best torge to RPM and then adjust the pitch to move the boat.
Years ago i had a 18' speed boat w/ a 350 mag with a variable pitch prop.... have no idea who made it.
It would come out the hole w/ a 18 pitch than switch to a 24 pitch once it hit 4k RPM's.
It had a spring system that you could adjust to pick your RPM to switch.
You would think they would advance this technology to adjust at your controls.
Has anyone tried something like this on outboards?
Somebody needs to make a variable pitch prop, and a lot of these issues will be solved.
You should have a dial by your thottles that controls your pitch... like an airplane. Then you could set your RPMS at the best torge to RPM and then adjust the pitch to move the boat.
Years ago i had a 18' speed boat w/ a 350 mag with a variable pitch prop.... have no idea who made it.
It would come out the hole w/ a 18 pitch than switch to a 24 pitch once it hit 4k RPM's.
It had a spring system that you could adjust to pick your RPM to switch.
You would think they would advance this technology to adjust at your controls.
Has anyone tried something like this on outboards?
another company yellowfin(not the boat builders) has a variable pitched surface drive. Its still beta, not on the market. ZF make a 2 speed transmission.
[quote=RumRunner21;2616998]Somebody needs to make a variable pitch prop, and a lot of these issues will be solved.
If there is ever going to be a variable gear ratio applied to a boat, I think it would be in the form a 2 speed gear case.
The inherent problem with a variable pitch prop, is that the mechanics of such a prop would be very susceptable to damage. Unlike an airplane prop, a boat prop takes a lot of abuse and would not withstand the environment. A variable geared gearcase, on the other hand, has the potential to be stout enough to withstand impacts encountered in the marine environment.
Variable pitch props have been around for decades. They are more suited to displacement speed vessels, and are rather expensive. You do save the cost of a marine transmission though.
where you high when you wrote this ? torque is a measurement of applied force. Please explain how you can have torque without movement
I will try one more time. Torque is simple a twisting moment.
Take a torque wrench for instance. Set it to some value, let's say 40 foot pounds.
Put a socket on the torque wrench and then put the socket on a prop nut. Tighten the nut until it reaches 40 foot pounds. The applied torque will be 40 foot pounds. The nut is tight and is not moving. It still has the twisting moment (known as torque) being applied to it.
In a rotating power plant torque does come into play. But it is just one part of the equation. The end result of the equation is power, as in horse power. HP is a measurement of work.
Horse Power gets you there and Torque keeps you there.
My 460CID , I had to give it some good throttle to pull my boat up the ramp .
My 5.9L Cummins [ 360CID ], don't touch the throttle , just ease off the clutch and she walks right up the ramp and the motor never changes pitch.
There are no comparisons between ANY of the motors in this thread , Gas Diesel, electric, 2 stroke and 4 stroke.
One just has to pick the best motor for his application and go with it .
I picked a 4S motor for my Alloy boat because my hull has a 18* DR and it's lighter than glass and I wanted to cruise [ Read low RPM's ]at a comfortable speed with great MPG.
__________________ F350 4x4/ Dodge 2500HD 5.9L Cummins
Leaving the Picture of the Ford cuz I miss it
Pacific 2325 cc
Honda bf225
aluminumalloyboats.com
"'So explain to me...
My express has 355 hp diesel engines. Quick to plane, cruises 22 knots.
The same boat with 350 hp gas engines would barely be able to get out of it's own way.""
His diesels are probably operating at just under 3000 rpm at cruise and have a top speed of maybe 28 knots at just over 3000. And they are probably putting out 300hp at cruise. If you geared and propped the gas engine to turn the same prop at an engine speed of 4500rpm at 28 knots it would perform similarly. The gas engine wouldn't last very long though. Diesel engines, near their rated torque/hp/rpm are available for continuous use. Gas engines are not.
Read a remedial physics book and then don't talk to me.
you obviously haven't taken your own advise. Apparently you have not read any references posted here. Your rebuttal is worthless, you have no supporting data.
"The power exerted by a rotating object is the torque it exerts multiplied by
the speed at which it rotates. In standard English units, this would be
foot-pounds multiplied by radians/second. It is a special property of
radians that allows this product to be foot-pounds/second: a radian is a
distance around an arc divided by the length of the radius (feet per foot).
We start with 1 horsepower. We want to get to (foot-pounds)x(rpm).
1 hp = 550 ft-lbs/sec = 550 (ft-lbs)x(rad/sec)
1 rad/sec = 60 rad/min
= 33,000 (ft-lbs)x(rad/min)
1 revolution=2(pi)radians
