Powering with full ballast

[Dullboy]

Trying to pull a fat girl up slalom one time doesn't break an outboard crank. It was either a manufacturing defect, or the last straw in a long history of abuse(s), i.e. overpropping, underpropping, etc.

Your assertion seemed to be that the cause was due to "abuse" or where someone was a fault for doing something wrong. It could have been simply the "environment", normal usage, age as contributing factors.

As for "unfriendly environment", I would definitely classify salt water in that category.

[Dimitri-2000X-Tampa]

Trying to pull a fat girl up slalom one time doesn't break an outboard crank. It was either a manufacturing defect, or the last straw in a long history of abuse(s), i.e. overpropping, underpropping, etc.

Well, it certainly wasn't a new engine so perhaps the parts were already worn, cracked, etc., but there is no doubt that the specific waterski incident was what caused the crank to break..as I observed it with my own eyes and ears.

My original point was that this engine was most definitely straining (like flooring a motor which is on a boat attached to a dock) and I don't buy the fact that the prop will just slip away not causing enough strain on the motor to prematurely wear out the parts and possibly cause a failure. It is a question of how much load is on the engine.

[Moe]

Dimitri, you're taking my use of slip out of context, and exaggerating it with the boat tied to the dock example. My point is that, other things being equal, slip DOES increase with load and the resulting lower speed. As a result, the drop in engine rpm due to an increase in load is proportionally smaller than the drop in boat speed that occurs as a result of that (as Chip H said above). Here are some numbers Robert posted about his prop testing. I've added the slip percentage of each of these.

Suzuki DF50 2.27:1

Solas 4 X 11.8" X 9" aluminum

Ballast empty solo 20 mph 6800 rpm - 21.66% slip

Ballast full w/family 16.5 mph 6350 rpm - 30.79% slip


Solas 3 X 12.25" X 9" stainless

Ballast empty solo 21 mph 6800 rpm - 17.75% slip

Ballast full w/family 16.5 mph 6400 rpm - 31.33% slip

Get the point?

An engine is just a machine. It doesn't "strain." It performs work (torque, as in ft-lbs) over time (horsepower, as in ft-lbs per minute). While it doesn't "strain," it can be overloaded if not properly geared (and propped) for the load. The more work it performs, be that from more feet or more pounds, the faster it performs that work, and the overall time it performs it throughout it's life, all contribute to wear and sooner failure of some part in the system.

Given the limited change in rpm in Robert's reports above, and the likelihood there is little, if any, difference in horsepower at those rpms, his motor is doing the same work in the same time (the hour in mph, for example), whether unballasted and solo, or ballasted and with the family. That work (ft-lbs) is applied differently, with more feet (actually 20 or 21 miles) and fewer pounds unballasted, and fewer feet (actually 16.5 miles) and more pounds ballasted, both in the same time (the hour in mph). I would maintain there is little difference in wear here between WOT unballasted and WOT ballasted, and that's the crux of this thread.

Certainly, if you never make a 50HP motor produce more than 35HP by never using WOT, it should not wear as fast, or have as high a probability of failure at a given operating hour point, as one that is required to produce 50HP regularly. And if you only make a motor designed to produce 70HP over a similar life span produce 50HP, it should statistically have a longer life than the 50HP motor producing 50HP, perhaps like that of the 50HP motor only producing 35HP.

However, in the latter case, there's usually a weight penalty to be paid. Frank C chose the "big motor with longer life at the same lower output" route with his 358 lb Suzuki DF60, which is anywhere from 94 lbs (36%) heavier than a 264 lb Mercury 50 or 60HP BigFoot, to 153 lbs (75%) heavier than a 205 lb Honda BF50. For the 26X, Roger MacGregor originally chose the lightest possible motor solution that would do the job, the Tohatsu 50HP carbed two-stroke, which probably weighs under half Frank's solution, and much less than our 50 HP four-strokes or DFI two-strokes today.

Where performance and/or initial cost matter, longevity is often, if not usually, sacrificed for for lighter weight. That's certainly true of the rest of our Mac (and its trailer), from components operating at, or very near, their maximum rating, to the eggshell thin in places hull. The 50HP motor operating at or near maximum rating, when "going faster than hull speed" is part of that philosophy. Not everyone agrees with it. Certainly not Frank C WRT motors. Certainly not those who add at least some weight with heavier components. And certainly not those who add some weight reinforcing the hull.
--
Moe

[Mark Prouty]

Trying to pull a fat girl up slalom one time doesn't break an outboard crank.

What about a fat cat on two skis?

[Frank C]

. . . However, in the latter case, there's usually a weight penalty to be paid. Frank C chose the "big motor with longer life at the same lower output" . . . Where performance and/or initial cost matter, longevity is often, if not usually, sacrificed for for lighter weight.

Well said, Moe. I've adopted it as my mantra, but for the dozens of times I've posted it, many seem not to get it, or simply don't subscribe.

And to fully connect w/ the thread topic, I have NEVER driven my fully ballasted boat at WOT except on the smoothest water, and only for the briefest of minutes. Don't see any reason to do it, and many reasons not to. When ballasted in heavy conditions, I willingly drive the boat at prudent speeds, probably 4000 rpms & ~11 knots. If wave conditions punish the hull at that speed, I slow down. With my usual crew of 2 or 3, my boat (as loaded & equipped) absolutely does not need ballast to run safely in heavy conditions, and I'd prefer empty ballast. Speed is potentially higher, maneuverability is quicker, economy is better, ride is drier, and IMO, the hull suffers less.

I shopped this boat for over a year. During that time I developed my core criteria; EFI, 14" prop for QUIET mid-range cruising. Once we concluded that the hull would adequately support the extra weight, the larger (1300 cc) and heavier (quoted @ 335 in yr-2000) Suzuki offered many additional advantages.

Lowest in market gearing @ 2.42:1
Alternator @ 21 amps
Suzuki wty @ 6 years (soon to expire w/ nary a claim)
Gobs of torque (30% larger block than Bigfoot)
Great low speed maneuveability (prop size)
Lots of reserve power (for groups, higher altitudes or emergencies)

The risks were transom integrity and balance to the bootstripe. These proved trivial. The dealer reinforced the transom handsomely, and the factory's modified ballast tank easily balances the extra weight, at least when cockpit crew is only 2 or 3 persons. And, performance under sail is as good as any 26X I've ever read of.


P.S. If the true weight is the 360# now shown on Suzuki's webpage, and if the advertised weight of the Suzi 140 is true @ 410#, then it seems obvious that one could double the power and magnifiy cruise benefits for a small added weight penalty (right Billy? ... Mark?).

[Dimitri-2000X-Tampa]

Geez, sometimes I just like to argue with youz guys... (and me thinks Moe does too!)

Moe, now you are taking my use of the word "strain" out of context. Lets just stick with the word "load".

There is, however, an increase in piston, rod, bearing, and crank load due to the higher piston speed (compared to that at the torque peak rpm), as the piston is accelerated and decelerated. And wear goes up as well.

I don't fully agree with this because when the engine is under a greater load, the RPM (and piston speed) is definitely lower. On my boat, it can be as much as 600 RPM's lower under load. Although I do agree that wear goes up...and expect that it is due to higher torque on the crank (caused by higher load on pistons and rods).

And about slippage, I didn't say there was no slippage (nice figures though). My point was that the slippage would not be enough to significantly reduce the load (unless you are running the outboard in a barrel or something)

You may call it "overpropped" ... but in a practical sense, when I have full ballast and 7 people aboard and can only turn 5300 RPM, I'm not putting out max HP because I need to be between 5500-6000 for that. Next day, I go out by myself with no ballast and I can get up to 5900. I'm not about to switch props in the middle of those two days....as much as my uncle was going to switch props between 80# and 200# skiers. The lower RPM at load argument pretty much disproves the argument that you are putting out 50HP at load and 35HP when not at load, don't you think? Now, if you change that to higher torque at load (with lower RPM), I could buy that. Both yours and Chip's arguments indicate that the power is only proportional to the speed (RPM) but I am stating that power is proportional to both engine speed AND load. Load will increase as weight (and/or pitch) increases.

The main point here is that if my uncle hadn't tried to pull the fat slalom girl out that day, that motor could have lasted another 10 years. Can you agree with that??? Yes, I know you can make the point that maybe the motor would have broke on the next ski despite who was being pulled out...but that does this sound as likely? Afterall, we don't typically do high tech imaging on our crankshafts before and after an incident like this...so of course, it is hard to prove beyond all doubt. But if you (or other readers) do agree with me, then it proves the point that there is significant additional stress and wear on the motor when it is under high load.

I believe that both of these last two paragraphs prove that a fully ballasted boat being pushed around at WOT is more stressful to the "machine" than a light boat going at WOT...so, there is where I stand on this topic. I will agree with you that if you go with a lower pitch meant for full ballast, the wear will be less...but the force required to push the boat is still proportional to the weight so the difference is not zero. Talk to commercial barge folks who use outboards...they don't go fast, but they burn thru smaller motors pretty quick.

And finally, the fat slalom girl never got on top of the water causing tremendous drag...I suggest that the load on the motor was very similar if not identical to a moored boat at WOT...by the time you factor in the additional slippage and all.

[Dimitri-2000X-Tampa]

I have been reading the posts on larger engines on the Mac and one of the reasons stated for buying a bigger engine was to plane the boat with full ballast. It is stated in the manual that each 100LBs of weight in the boat reduces speed by one MPH. At 1400LBs of water in the ballast, a lot of power will be needed to move the boat at high speed. Also, I think the boat was never designed to carry a full ballast at high speed and could be a safety issue. I would check with Macgregor on this point as that is a lot of stress on the F/G. As far as I know we have never discussed this before and did not want it to get lost in 60 replies. Alot of money for something the boat was not designed to do.

My previous posts were in response to Chip and Moe stating that the higher loads of more weight did not stress a motor out additionally. But to get back to BK's original question, I can plane my boat with full ballast (and 6-7 people) with a 50HP bigfoot. Sure, it is just barely planing at about 14 mph but it is still planing. So therefore, I don't believe you need a bigger motor just to "plane" with full ballast.

And to fully connect w/ the thread topic, I have NEVER driven my fully ballasted boat at WOT except on the smoothest water, and only for the briefest of minutes. Don't see any reason to do it, and many reasons not to. When ballasted in heavy conditions, I willingly drive the boat at prudent speeds, probably 4000 rpms & ~11 knots. If wave conditions punish the hull at that speed, I slow down. With my usual crew of 2 or 3, my boat (as loaded & equipped) absolutely does not need ballast to run safely in heavy conditions, and I'd prefer empty ballast. Speed is potentially higher, maneuverability is quicker, economy is better, ride is drier, and IMO, the hull suffers less.

IMHO, Frank's statement also proves the point that you don't need a bigger engine to run with full ballast. I'm pretty much like him, although I don't run at full ballast in heavy conditions much more than 11 mph. Moe will probably know the exact number, but I expect my engine is turning what, 2-300 more RPM at that speed? Not a big deal IMO.

I've adopted it as my mantra, but for the dozens of times I've posted it, many seem not to get it, or simply don't subscribe.

So, would you say that you never run unballasted at WOT then? If so, I can understand your "mantra"...but if you do occasionally open her up and get that extra few mph over a 50, then what are you trying to get people to subscribe to? Also, I believe you bought a brand new boat and were already pushing Roger's design envelope in your mind at the time. You probably didn't have the benefit of Billy, Mark, Rolf, and other's BIG engine switches at the time. Begs the question of if your motor blew up tomorrow and you had to repower, would you go bigger than your current motor? And would you ever "open her up"? Or would you just enjoy that lower RPM cruise.

Personally, I run my Mac at all sorts of speeds, sometimes slow...sometimes medium...sometimes fast. The fact that you can get the same speed at 3800 than it takes us 50 Horser's 4000 RPM to achieve is not enough of a reason for me to undergo repowering with a larger motor. Otherwise, why didn't you get a 140 which you could probably run at 3000 to get the same speed with? It would be even quieter then.

Sure, I would enjoy the lower RPM when I'm in the medium speed range, but the main reason I would get a bigger motor is for faster top speed...the other thing would just be an added bonus.

[Moe]

There is, however, an increase in piston, rod, bearing, and crank load due to the higher piston speed (compared to that at the torque peak rpm), as the piston is accelerated and decelerated. And wear goes up as well.

I don't fully agree with this because when the engine is under a greater load, the RPM (and piston speed) is definitely lower. On my boat, it can be as much as 600 RPM's lower under load.

Yes, rpm at WOT heavily loaded is lower than WOT lightly loaded, but reread what you quote from me. I was referring to speed relative to the speed at the torque peak, which is much lower than either WOT speed.

Although I do agree that wear goes up...and expect that it is due to higher torque on the crank (caused by higher load on pistons and rods).

Under load, the engine applies torque to the drivetrain. The load is irrelevant. The most torque on the drivetrain is that which the engine is supplying. If it is greater than that required to pull the given load at the current speed, acceleration occurs, and vice versa. If the load goes up, deceleration occurs until the load (drag) decreases to match the torque, and vice versa. Under deceleration with engine braking, the load applies torque to the crank.

And about slippage, I didn't say there was no slippage (nice figures though). My point was that the slippage would not be enough to significantly reduce the load (unless you are running the outboard in a barrel or something)

What I wanted you to see is that it is possible (with the right prop), to narrow the rpm range between loaded and unloaded.

You may call it "overpropped" ... but in a practical sense, when I have full ballast and 7 people aboard and can only turn 5300 RPM, I'm not putting out max HP because I need to be between 5500-6000 for that.

I hate to break the quote here, but need to say that none of us, except the guys who run the motors on the dyno, know what the horsepower curve looks like in the last 1,000 rpm. Mercury's service manual says the EFI version gets peak HP at 5750, which is conveniently halfway between 5,500 and 6,000 rpm. For all we know, the horsepower may be within +/- one to two HP from 5,000 to 6,000 rpm, not just 5,500 to 6,000 rpm. My point is, you MAY have as much horsepower at 5,300 rpm as you do at 5,900 rpm.

Next day, I go out by myself with no ballast and I can get up to 5900. I'm not about to switch props in the middle of those two days....as much as my uncle was going to switch props between 80# and 200# skiers. The lower RPM at load argument pretty much disproves the argument that you are putting out 50HP at load and 35HP when not at load, don't you think?

Whoa! I never said that. In fact the opposite. My point was that in the last 1,000 rpm with two-valve engines of this size, the HP at the loaded and unloaded rpms is the same or very close. It was on that I based the high/low miles per hour. The 35HP had nothing to do with this.

Now, if you change that to higher torque at load (with lower RPM), I could buy that.

That's correct. At rpms above the torque peak, torque is decreasing as speed increases. If the torque is decreasing slower than rpm is rising, horsepower increases as speed goes up. If torque is falling the same speed as rpm is rising, horsepower remains level as speed increases. If torque is falling faster than rpm is rising, horsepower is falling.

Both yours and Chip's arguments indicate that the power is only proportional to the speed (RPM) but I am stating that power is proportional to both engine speed AND load. Load will increase as weight (and/or pitch) increases.

Then you are wrong. Power is proportional to both engine speed and TORQUE, which is supplied by the engine, not the LOAD. Increasing the load does not increase the engine's power output.

The main point here is that if my uncle hadn't tried to pull the fat slalom girl out that day, that motor could have lasted another 10 years. Can you agree with that??? Yes, I know you can make the point that maybe the motor would have broke on the next ski despite who was being pulled out...but that does this sound as likely?

Actually your extremes there sound equally unlikely. The motor might not've broken on the next pull, but it wasn't long for this world, certainly not another 10 years.

Afterall, we don't typically do high tech imaging on our crankshafts before and after an incident like this...so of course, it is hard to prove beyond all doubt. But if you (or other readers) do agree with me, then it proves the point that there is significant additional stress and wear on the motor when it is under high load.

Sorry... but it's an ancedotal childhood memory that doesn't prove anything.

I believe that both of these last two paragraphs prove that a fully ballasted boat being pushed around at WOT is more stressful to the "machine" than a light boat going at WOT...so, there is where I stand on this topic.

There's no doubt in my mind

I will agree with you that if you go with a lower pitch meant for full ballast, the wear will be less...but the force required to push the boat is still proportional to the weight so the difference is not zero.

If we say your horsepower at WOT 5,300 rpm is equal to the horsepower at WOT 5,900 rpm, the force required to push your boat to its top speed when heavily loaded is EXACTLY equal to that required to push it to its top speed when lightly loaded.

This is where it really gets good now. PAY ATTENTION! If we say your horsepower at WOT 5,300 rpm is LESS THAN the horsepower at WOT 5,900 rpm, then the force required to push your boat to its top speed when heavily loaded is LESS THAN that required to push it to its top speed when lightly loaded.

While you have a firm grasp that load increases with weight, you ignore the fact that load also increases with the speed that's obtainable with a lighter weight. That keeps you from understanding that the load is the same (or less) when WOT with a heavily loaded boat, as it is when WOT with the lightly loaded boat.

Talk to commercial barge folks who use outboards...they don't go fast, but they burn thru smaller motors pretty quick.

And in their short life, they've done as much or more work as "smaller motors" on lighter boats.

--
Moe

[Jeff S]

One thing is for sure- if you are ballasted you weigh more and will go slower at a given RPM. This will cause the motor to work longer to go the same distance, this will in the end cause more wear on the motor simply by operating longer.

Ok, that was my snipe from the grassy knoll- I have to stay out of this one, although it is interesting.

Frank, I prescribe to the idea to provide excess power and not have to run it at full capability (although available if needed). The whole trailer tow vehicle discussion has similar issues in terms of wear and tear on the tow vehicle (engine, transmission, brakes, shocks, drivetrain, etc.) which will affect the overall life of the tow vehicle- very similar to your engine ideology.

Now...I have a Tohatsu 50 because it came with the boat. It is a good engine I would love more power but I can't justify it yet. I sail most of the time-pretty much use the engine to get out to river (5-10 minutes tops) and back in, and run at WOT a high percentage of the time the engine is running. So this begs the question- is it easier on the engine to run say 4 hours at 3000rpm or 1 hour at WOT? Is there some type of generalized engine wear chart by RPM (fore example say it wears 10 times as fast at WOT as it does at 2000 RPM- that would be interesting to know.)

Jeff

[Dimitri-2000X-Tampa]

I think we are saying the same thing on some points, but differing on others....big time. I never meant to imply that there isn't additional force required at high speed....but that is only with constant mass. I fully understand that drag is related to speed, etc., but so is mass. Where I think you are wrong is by implying that load has nothing to do with power, although you do seem to agree that load is proportional to weight (mass).

This is where it really gets good now. PAY ATTENTION! If we say your horsepower at WOT 5,300 rpm is LESS THAN the horsepower at WOT 5,900 rpm, then the force required to push your boat to its top speed when heavily loaded is LESS THAN that required to push it to its top speed when lightly loaded.

This is where you are wrong and should pay attention. I may have been out of school for the better part of 2 decades but I do remember some Newtonian physics and can still do research and equations. Will you buy Newton's theories?

From Newton's theories, we know that Force = Mass x acceleration

But Linear momentum is defined as mass �velocity. So, in a simplistic manner, we can substitute velocity for acceleration and weight for mass. So, for my boat going 14 mph when it is weighing 5000# (1400# of ballast and 600# of extra people) versus going 17 mph when it is weighing in at 3000#, you would have the following force equations:

f1 = 14 X 5000 = 70,000
f2 = 17 X 3000 = 51,000

(I guess the units would be "mile pounds" ... probably divide by 5280 to get foot pounds)

Hence, it takes 37% more force to move my heavy boat at a slower speed than it takes to move the lighter boat at a faster speed. This is why my motor appears to be "straining" harder.

And in their short life, they've done as much or more work as "smaller motors" on lighter boats.

You seem to have acknowledged the fact that a small engine under greater load (a barge) works much harder than the same engine pushing a lighter load...isn't that my position in this debate???

Work = force x distance, right? Maybe not.

Newton's idea that work=force*distance is not logical. The definition of force as being any influence producing a linear change in the momentum of a body is wrong too. You can apply force to a stone and still not perform any work because of inertia. However, you did exert force. Exertion of force on an object does not depend on reaction of the object. Thats WORK! Work is the result of the force that you applied, not the force applied! Therefore you cannot use force in such equation. The equation for work is W=mass*distance. W=md. The inertia of the object can be calculated by subtracting force from work. The amount of work depends on mass and distance of displacement. It does not depend on friction or even inertia because it does not mater how much force or energy you lost. It matters how much work you have done. For the same reason it doesn't matter how much inertia have you defeated. Newton's equation for work contains "v," for velocity at which the mass is displaced. The velocity has no influence on the amount of performed work, therefore there is no place for it in such equation.

To illustrate my point, imagine two workers who are going to move your furniture. One of them may do it in 2 hours, the other in 4 hours, but they still will perform the same work The speed with which they will do work has nothing to do with the amount of work. It has to do with "power." It's easy to confuse "force" with "work" or "power" because not all their definitions in books are correct.

Old School (work done in one hour):

w1 = 70,000 X 14 = 980,000
w2 = 51,000 X 17 = 867,000

Or 13% more work to push the heavy boat slower

New School (work done in one hour):

w1 = 14 X 5000 = 70,000
w2 = 17 X 3000 = 51,000

Or same as the above equation for force, 37% more work done in one hour.

Either way, this proves that I am right and your engine is going to wear out faster when you use full ballast. Btw, this is further backed up by the fact that my boat will get much worse fuel mileage when powering the heavy load...I believe this is likely proportional to the work being done which in turn is proportional to the force required.

Sorry... but it's an ancedotal childhood memory that doesn't prove anything.

Everything I Need to Know I Learned in Kindergarten!

[Divecoz]

and the simple observations over time that two similar boats with similar motors but carrying vastly different amounts of weight. .. #1 lighter boat gets much better MPG and #2. lighter boats, motors last twice as long as heavy? overly worked boats motors. No Math required but more than a few beers downed a Lot more fun my way BTW

[Chip Hindes]

Force = Mass x acceleration...Linear momentum is defined as mass �velocity. So, in a simplistic manner, we can substitute velocity for acceleration and weight for mass.

Huh? In a single phrase, no you can't.

[Dimitri-2000X-Tampa]

Huh? In a single phrase, no you can't.

In a single phrase, prove it then!

(If you are going to correct me, back it up with some facts dude)

Even if you use a velocity squared function, it is still like 13% more force required to push the heavy boat around (which was the old school definition for work also). And since our boats don't operate in space, weight is equivalent to mass.

I'm sure that you can greatly complicate the equations by throwing in drag coefficients and other forces associated with fluid dynamics, but do you really think it will change the outcome much?

[Moe]

Dimitri, whether unballasted or ballasted, your motor is putting out all it can at WOT... about 50HP.

One horsepower is 33,000 ft-lbs per minute, so 50HP is 1,650,000 ft-lbs per minute X 60 minutes = 99,000,000 ft-lbs per hour, divided by 5,280 = 18,750 of your "mile-pounds" per hour (which you have to use if you're working with miles per HOUR). That's all of your "mile-pounds" per hour 50HP can supply.

18,750 "mpph" / 14 mph = 1339 lbs of load when ballasted
18,750 "mpph" / 17 mph = 1103 lbs of load when unballasted

If we say your motor only puts out 45 horsepower at 14 mph/5300 rpm when ballasted, that's:

16,875 "mpph" / 14 mph = 1205 lbs of load when ballasted

Why are these loads so much smaller than the boat weights? For the same reason you can load a 3,000-5,000 lb boat on the trailer with a 1200 lb winch... because the outboard doesn't have to lift the weight of the boat.

Just for grins, figure out how many horsepower it takes to supply your calculated mile-pounds per hour (that's 375 mpph per horsepower)
--
Moe

[Dimitri-2000X-Tampa]

I may have messed up some of the calculations, but it's still basic physics anyway you look at it. Takes more energy to push more weight around whether you are lifting it or not.

Your way of looking at it assumes the motor is putting out a constant amount of horsepower at a certain RPM, and that is probably not true if you put the engine on a dynamometer under different loads. More fuel burned equals more energy used hence more force applied for the greater weight.