Powering with full ballast

[Moe]

You posted this at 1:41PM,

Where is that fellow Frank Mighetto? I'm sure he could add something to your debate

and two minutes later:

http://macgregorsailors.com/phpBB/viewt ... 8&start=15

Mark's right...


--
Moe

[Terry Chiccino]

Sorry Moe, I'll shut up!

[Dimitri-2000X-Tampa]

The prop is no different and takes no more time to change than a hanked foresail.

Uhhh, my boat is in a wet slip with the prop over water, you sure about that?

[waternwaves]

Dimitri

wearing my harness. and reversing the clip to the back, I changed the prop while hanging out over the motor in less than 5 minutes...

and suprisingly since I had the harness tethered to both rear cleats and around the backstay..... even in moderate seas it felt safer than standing on the foredeck..... but not as secure as kneeling in the front hatch changing sail..

and I still have my unbroken record of only dropping wrenches (dont ask how many) when attaching the forestay..lol (god I hate evey pin I have tried and used..., HAve gone to installing threaded stainless link rings in the back stay to make that job quicker( back in the days when I did not have tethers on the sockets..

suffice to say, changing props is easy and relatively dry. with the tether and harness......

[Moe]

Uhhh, my boat is in a wet slip with the prop over water, you sure about that?

What a whiner!

80-90 degree water, not to mention all the sandbars, and you can't change a prop in the water?

--
Moe

[Dimitri-2000X-Tampa]

Not quite...try 55-68 degree water for the next 3 months. You guys are nuts, I'm not gonna spend my time hiking out over the engine in a harness with a pocket full of prop nuts cussing as I drop wrenches in the water (can't really see anyone doing that frankly) I'm going sailing..and if I wanna hike out over something, I'll buy a hobie or dust off my windsurfer.

[Moe]

Not quite...try 55-68 degree water...

We do... every summer!

[richandlori]

Ok....When is Heath going to step in and end this sucker?

[waternwaves]

Dimitri!!

A vertically oriented bobbing log off of texada island necessitated the on the water change and inspection....lol..... Honest, I dont go out of my way too often to expand the envelope.. and practice my gymnastics..... Tho all those years of climbing does come in handy gear wise sometimes.

And right about now....68 deg. water is sounding pretty good......lol

even in a hobie....!!! Trap time.....lol
I'm jealous of all those hobbies of mine you can do down there...

At least I could go to a thinner wetsuit.
Now, to get back to the eternal quest of the best prop on that merc 50 BigFoot.... Solas anyone??

[Bill at BOATS 4 SAIL]

Was that fat water skiier wearing a white swimming suit or a blue swimming suit?

[Mark Prouty]

Everybody completly ignors the fat cat question!!



You guys need a vacation.

[Rolf]

Dimitri,
back to my simplistic answer (it may very well be but I'm just trying to UNDERSTAND) about the weight of the boat and/or size of the prop not affecting the wear and tear on motor (wear and tear only relate to how long and hard the motor is running, although with different props and boat weight the wear and tear will go up/down corresponding to how much hp is being used.) If a car is going up a steep hill with the pedal floored, the hp used to push it is up is exactly the same as the hp used to push it down the hill with the pedal floored as well. The motor wears at exactly the same rate, the only difference is obviously the speed going downhill would be mucho faster. Of course the wear and tear on the transmission, brakes, etc will be affected differently. Does this analogy fit? Am I on the right track here, or do I need to retake high school science(skipped it for most part in college) ?
Rolf

[Dimitri-2000X-Tampa]

Rolf, I'm certainly not trying to impede your understanding. Its just that this whole discussion is about a full ballast (additional weight/mass) and how it affects the operation of the boat/engine. What started the whole slew of posts to begin with was that I was disagreeing with some statements that implied that weight (and manifold pressure) has nothing to do with it. After a zillion posts, what I think some of the things are that we've agreed upon:

1. Mathematical equations are used to represent physical relationships
- Forces can be mathematically represented
2. Mass/weight is related to force and velocity
3. Prop size/pitch on a motor boat is similar to the transmission of a car
4. Time is a factor
5. Dimitri and Moe like to argue and can type pretty fast

What I think the disposition is can be related to using multiple props (gears) and how much power (energy) is really being used in various situations where you keep a variable (such as prop size) constant. I agree that wear is related to distance travelled (by virtue of time) but I also think that wear goes up on an engine when proportionately more of the power produced is coming from combustion versus the momentum and inertia of the moving parts in an engine (RPM). Moe would call this an over-propped situation. You could also say that this has something to do with the efficiency of the power generated. So, any way you look at it, adding more weight is going to make fuel consumption and wear increase when you look at the total picture (speed versus time versus power). There is a ton of stuff written about airplanes but perhaps not so much about boats. You look at an article like this to realize that we are all oversimplifying the matter. I was going to say that you could factor altitude out of it, and then remembered that we have trailer sailors on this board who operate at multiple altitudes.

Although a boat engine doesn't convert chemical energy (fuel) to altitude, it does convert it to speed. Speed on a boat is further complicated by the laws of fluid dynamics that govern drag (planing versus plowing and all that good stuff - btw Moe/Duane, who did the overwhelming majority of board users agree with on that issue???) Here is another interesting article I found regarding this subject on airplanes, much of it applies to boat engines too obviously (it also brings up a topic we hadn't even introduced yet about engine operating temperature and how that can reduce efficiency):

The engine is is used to convert fuel energy to airspeed and/or altitude. The rate at which it works to convert energy is power.
Conversion of fuel to airspeed includes paying for drag to maintain airspeed, which is also what allows an airplane to maintain altitude. There are three things that a pilot can use to control the rate at which altitude and/or airspeed are gained and drag is paid for: the engine, the propeller, and the control surfaces. Engine management is concerned about the first two. Here are the main jobs of engine management:

1. Controlling the engine power output
2. Keeping the engine in good condition
3. Controlling the rate of fuel consumption

Every control related to managing the engine must have something to do with engine condition or how to convert that fuel into altitude and/or airspeed. The throttle is one of the primary controls for all three of the above jobs. In fact, throttle can often be considered to be the main control for engine power output, but it would be a mistake to think that it is the only one that matters! It would seem that there is no end to a pilot's woes.

In fact, throttle is only the main control as long as certain other conditions are fulfilled. To understand what is important for engine management, let's look at what engine power output basically is. Everybody, even your flight instructor, knows that an engine produces power by applying a torque to a rotating shaft. As it turns out, the expression of that power is directly dependent on the torque and rotational speed of the engine, measured in revolutions per minute (rpm):

Power = Torque �rpm �6.28

Torque is the force applied by the pistons at a distance around the shaft, and is provided by combustion in the engine cylinders. As a result, the torque is influenced by all factors having to do with combustion. In your airplane, rpm is influenced by the propeller, engine controls and airspeed. The rpm is important because power is a measurement of work over time, that is, it is a rate. (The 6.28 in the equation represents 2�i and is there because we prefer rpm instead of angular velocity.) If the engine moves the pistons with the same torque but at a faster rate, anyone (yes, even your flight instructor) can see that more work is being done per minute. The happy result is that you will fly or climb faster, but of course there is a price.

Throttle can have an impact on both torque and rpm, but it is clear to see that any other factor that influences torque or rpm has to be considered and controlled.

What is the throttle?

So what does moving the throttle lever actually do? In most combustion engines, all it actually does is move a little stop that blocks to a greater or lesser degree the intake manifold of the engine. The intake manifold allows the pistons to suck air into the combustion chamber. Opening the throttle (pushing the control forward, away from 0% in FB) causes the stop to block the intake less, thus allowing the pistons to suck more air. Closing the throttle blocks the intake more, hindering the air flow into the engine. So with the engine running, the engine can simply suck more air the less it is blocked. To put it simply, the more air that the engine can suck, the more torque it can deliver for the production of power. It has already mentioned that this is limited by other factors, but the important thing here is that by manipulating the throttle lever you are just telling the engine how much air it can have.

Let's have a quick peek at the other factors that influence torque and rpm. The fuel has to be burned explosively in the right way, so the mixture of fuel and air must be in the right ratio. The mixture control helps this at higher altitudes, where the second stage of the supercharger (if present) also crams more air and fuel in. The engine works best in a certain temperature range, so if it is too cool or too hot you won't get the best performance. (If things get too hot, you can also kill the engine.) The engine has the job of turning the propeller, and this is what actually converts the engine output power into altitude and/or airspeed. The propeller pitch can load or unload the engine, allowing it turn faster or slower, and this also changes the power. These are the main controls besides throttle, and although they may be considered secondary, they are unquestionably necessary in their own way.

Using throttle

It seems that for many pilots in IL-2 and FB, throttle control is simply a matter of setting the engine either at full throttle or at some point at which they know the engine won't overheat. Although this is a valid approach and certainly the fastest way to build energy and maintain high speeds, it isn't always tactically sound. It is important to have a reserve of higher engine output at critical moments. Part of this reserve comes in the form of engine temperature: keeping your engine cool enough prior to an engagment that in a pinch you can have maximum power output for a short time. You might therefore consider how to use throttle in conjunction with radiator flaps and lower rpms to keep a temperature reserve. In fact, during combat it is a good idea to look for opportunities to cool your engine quickly, even if only a little bit. It's not all that different from finding the right time to reload your weapon during a gunfight, or refuel a car during a race.

Because of the short distances involved in the Eastern Front and the lack of realistic supply shortage in the simulation, fuel economy is an underappreciated aspect of flying in IL-2 and FB. Still, if you are on a long mission, starting with low fuel or for any reason find you need to conserve fuel, throttle and rpm control are the critical controls to get maxiumum fuel economy. More on this later.

Throttle is the primary control for making power changes, especially quick ones. Situations in which throttle control requires special consideration is during takeoff, landing, and various maneuvers, especially dives, loops and low-speed, high-angle-of-attack maneuvers.

Good reading
For more information on energy in aviation, see chapter 1 of See How it Flies, by J. S. Denker.
For a more enlightening presentation of piston engines, EPI Inc. has a good and easy to understand presentation of the fundamental physical concepts.
For a fun and informative read on manifold pressure and how throttle works, see the AVWeb article Manifold Pressure Sucks! by J. Deakin.

[Frank C]

"Although a boat engine doesn't convert chemical energy (fuel) to altitude, it does convert it to speed. Speed on a boat is further complicated by the laws of fluid dynamics that govern drag (planing versus plowing and all that good stuff - btw Moe/Duane, who did the overwhelming majority of board users agree with on that issue???) Here is another interesting article I found regarding this subject on airplanes, much of it applies to boat engines too . . . "

See, just like this one. I'm learnin' stuff I didn't even know that I didn't know!

[Moe]

The propeller pitch can load or unload the engine, allowing it turn faster or slower, and this also changes the power.

The load on the engine does change the rpm. Whether that changes the power depends on where on the horsepower curve you are operating.

Here's a comparison of two WOT dyno runs I did on small two-valve (like the Merc BigFoot) Harleys. The red run is with milder cams and the stock ignition module, while the blue run is with slightly hotter cams and an ignition module with identical advance curve as stock, but higher rev limit. In both cases, the peak HP occurs at 5,600-5,800 rpm, but the point is, the horsepower produced isn't appreciably different from 5,000 - 6,800 rpm. I can vary the load the dyno applies on the engine at WOT (or any other given throttle setting) to put the engine at pretty much any RPM (until detonation occurs).



As you can see, any change in load that varies the maximum rpm near the horsepower peak makes little difference in the horsepower produced. There's simply a trade-off between torque and rpm.

OTOH, at lower engine speeds, a change in load that changes RPM, WILL change the amount of power produced. However, since this is WOT, there is NO CHANGE in manifold pressure. It is ambient with WOT or near to that, and doesn't change with load at WOT.

If I had the load dialed down where the engine was operating at 3,500 rpm at 1/3 throttle (typical 70 mph cruise on these bikes), the torque and horsepower lines would be lower, but similarly shaped in that rpm range. If I then cranked the load up (like increasing the pitch on a prop or adding ballast to a Mac), the rpm will drop. As a result of the increase in load, the engine moves back (lower rpm) and down on the horsepower curve. And, as a result of the lower rpm, there are fewer intake cycles drawing air through the same throttle setting, and manifold absolute pressure (the static pressure) rises (manifold vacuum falls).

I'm not theorizing here... I'm telling you what actually happens in an instrumented real-world situation.
--
Moe