Proper Performance Engineering
 

The Good, Bad, and Ugly:
Quote from Mercury Marine:
........ " How do I obtain horsepower curves, torque curves, or fuel consumption data?

Horsepower and torque curves are not published because they are considered confidential company information. Fuel consumption data is not published because it is affected by factors beyond our control, such as boat hull type, temperature, humidity, altitude, gear ratios, propeller, etc. In some cases, fuel consumption or other performance data is available from your boat manufacturer for a specific boat/engine combination."

What absolute nonsense, keeping torque diagrams secret. Did not know marine engineers were required to be all wet!-(

Anyway: to properly determine best props (wheels), throttle settings, etc. one NEEDS to know the engine dynamics and torque curves.

For instance, one post read recently said there was NO delta between 2 stroke and 4 stroke engines, ah but I beg to differ: and the difference is readily distinguishable when the torque curves are shown.

Some two-strokes are notorious for their icicle (stalagmite) power curves where there is hardly any power until a certain high point of RPMs and the power multiplies so rapidly it totally changes the engines personality.

Who here can at least help with engine RPM stats, High, low, and cruise (typically 75%).

The engine I'm working with is the Mercruiser GM I-6 165 I/O. Knowing the proper throttle / RPM settings (again, the POWER is a direct function of engine design, volumetric efficiency and RPM) and the planing speeds for the SeaCraft hull we should be able to compute the proper - theoretical - pitch and diameter. Once the design P & D are determined things like harmonics, slip, etc. would play into the final determination. Right now I find the five blade Hill <http://www.hillmarine.com/> interesting.

Thanks, HBH
Oh yes, the craft is a lovely 1976 SeaCraft SF20

Re: Proper Performance Engineering
 

hp = torque * RPM / 5252

Re: Proper Performance Engineering
 

Am familiar with this relationship.
Note that it requires knowledge of one or more performance values for the specific engine.
It does little for analyzing the best performance from a given engine.

For instance, a rule of thumb is that engines are generally most efficient at their 75% power settings. That 75% position is NOT linear.

Several things are known about vessel throttle/power management - whether aircraft or planing boat - the amount of power needed to get `on step' (and that phrase applies to a hull without a geometric step, as it does to an aircraft wing) is greater than the amount of power required to keep it there. The skilled pilot will back off throttle while monitoring speed as will the skilled helmsman. Advancing throttle(s) after getting `on step' may increase speed but disproportionately increases fuel consumption.
It is a given that aircraft manuals provide extensive information on the powerplant. It is a shame on the boating industry that these same standards are ignored.

Am wondering if some power boaters add engine instrumentation; vacuum, manifold pressure, fuel flow. I know that on my Snowgoose Motor-Sailer I found the fuel flow meter (costly because for diesels a return line is required) VERY useful.

Here's a question then: What kinds of engine instruments are some of you using, and how. BTW, had full manual from Volvo and it was excellent. Guess I'm as much a Volvo fan as I am a Merc' denigrator!-)

HBH

Re: Proper Performance Engineering
 

put a 21 pitch old style Mirage on that boat, get it to turn 4400, and you should be right where you need to be. Theres no reason to complicate a simple setup

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Raw speed holds less interest for me than efficiency. For me the challenge is to return to base with more fuel left than anyone else.

Read your comment - elsewhere - on hull distortion from improper trailering, can you explain more?
HBH
BTW: the manual suggests 19 pitch, would tend to go with your recommendations as the impression is you go beyond basics.

Re: Proper Performance Engineering
 

The only thing the prop will change is the efficiency of your setup. Laser has nice thin blades, smaller diameter, and is a fast prop. I personally like the mirage plus because of the stern lifting characteristics, but folks here will run both. You've got a 20ft CC with a heavy I/O. The 20cc is light in the bow to begin with . . . without the 600+ lbs of motor/outdrive. But if you're truely after efficiency, get the Diesel, have someone blueprint the hull, have the prop labbed and be done with it.

Page 1 has the torque diagram for the cummins diesel.

http://www.cmdmarine.com/PDFs/4081824_1104.pdf

Have you ever bought parts for a Volvo??

Re: Proper Performance Engineering
 

thought i had edited my post earlier, must not have taken, Last nite, after thought, the 19 pitch Mirage is probably a better prop for your set up, its a large blade surface wheel with much lift, either bow or stern, this prop is extremlly efficient, i had a customer that had one on a performance boat, we calculated it was within 7% slip at 101 MPH, that type of efficency is allmost unheard of. We ran 21( it had been worked on) pitch on my old roommates boat, it had a 3.7l Mercuiser 4 cylinder, it was rated at 165 hp and has simular torque band as the I-6 250 GM engine you have, we got that 4 cylinder pushing a 17 ft boat to 52 mph( on radar), not bad for a 4 cylinder. The original Mirage had too much blade surface for an outboard( Mercury only recomended its use on the 3.4L 275), it was designed for the 454 sterndrives. most smallblocks wont even turn like it needs to be, but some engines, due to gear ratio in the drive( I-6 like yours, I-4)and their low rpm torque curves are able to make use of this prop. Some of the go fast crowd(Fountain for one) was trimming 1/4 inch of diameter to get a little less bite, to allow their engine to turn up in the rpm band they wanted it to be in, Mercury saw what they were doing and applied some fine tuning to the Mirage, allowing a litle less bite, making it an excellent prop for outboards.

Mercury has a prop selector on their web site, i have never used it, but several people i know have and have had excellent results with it.

Improperlly set up trailers can ruin a boat, they can warp the hull ( especially if it has set a long time), putting in excessive hook or pockets. This keeps the boat wet, it won't let the hull lift like it was designed to, roller trailers will do the same thing, just not one hook or pocket but several, at each place a roller contacts the hull. Of course it depends on how good of a hull you're talking about, there are some old trihulls out ther that you could'nt warp if you parked a truck on them.

As far as Volvo goes, they make the best sterndrive availble, they also have some of the most expensive( yamaha may have them beat), hard to find parts around. they now offer 2 day deliverd parts out of the wharehouse in Chesapeke anywhere in the continental US, it just seems the parts i order are allways nla

Was down at the ramp where Cummins Mercruiser test their boats, they have a new 150 hp Diesel that looks good

Re: Proper Performance Engineering
 

I've heard the horror stories!-) Truth is in over ten years of living aboard and cruising the Atlantic and The Mediterranean all I needed was the usual spare impellers, a consumable anyway.

Props are another story: I carry an inventory to select for range versus maneuverability - the SnowGoose had a sterndrive as well - but they were not terribly expensive.

As to diesel, there is a weight consideration in a planing craft, and while us blown boaters prefer the safety of diesel inboards, like the idea of keeping the SeaCraft original as possible.

On safety, do all of you with inboards make a practice of waiting while your bilge blowers run a while before turning the key?
When my sister got her first cabin cruiser, gas not diesel, silly girl, I gave her a key ring timer for the ignition keys, instructing she and her crew to wait, after starting the blowers, till the 5 minute timer had rung before starting engines.
HBH

Re: Proper Performance Engineering
 

Man . . Phnx you're one difficult complex dude. I'll bet that diesel is lighter than your setup now. You'll get better range and similar performance . . . especially if your 1976 motor is getting a little tired. I had a great time trying different props on my boat to find the right one. Each prop was very different and caused the boat to handle differently. Personally I really liked the Highfive, so if you try out one of the five blade hillmarine props I'd be interested to hear how you like it. The high five was super super smooth and I could turn the boat sideways at 45mph and still hold water. Where are you located?

Re: Proper Performance Engineering
 

Have set much store by your info, has the `ring' of knowledge and veracity to it. Wasn't it you recommended the Hill 5-blade which I find very interesting.
Another thing mentioned that has our attention is the stern lift factor you and others have pointed out.

If we assume the Seacraft, properly trimmed, is run at best power of 3-3200 RPM through the 1.65 drive and gets on step at just around 30 mph or better, and that little is gained by adding much power beyond that except raw speed in exchange for raw fuel consumption, than I find myself leaning toward a 21" pitch.

Trim will have to be changed of course when returning with 600 pounds of fish!-)

On the Outer Banks of North Carolina, Kitty Hawk Landing, plenty of dock space should you want to drop by and tie up.

Re: Proper Performance Engineering
 

my experiance with the five blades have been for a different purpose, the High Five was advertised for hole shot, several outboard powered ski boats came with them, these props were deisgned to be a semi surfacing prop at higher speeds( simular to cleavers). i have used them to crutch fix boats that were too stern heavy for pulling skiers. Theh downside of these props( in my experiance) has been unless you're running at elevated heights( ie: outboard on a jackplate) they tend to have a high slippage, we allways went up to the next pitch when replacing a standard prop with these. Fourblades tend to be a better comprimise between slippage and stern lift.

On the topic of diesels, check out the Steyer, they advertise the best weight to power ratio of the smaller engines, they are marketed to sterndrive engine replacement, and they operate at a simular rpm range to the engine you have now, so you wont have to change gear ratios

Re: Proper Performance Engineering
 

Man wonderful!
Nothing better than learning - never stops as long you're alive!-)

What is/are:
.. "semi surfacing prop "
.. "cleavers"

Never to coddle superficial friendship:
.. "simular"
Dammit `spares' you are WAY above average intelligence and you owe it to yourself to be accurate in your spelling. However much contemporary PC government education condones poor grammar someone of your ability needs to get it right.

HBH

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Oh brother here we go again...http://www.clicksmilies.com/s1106/wu...smiley-003.gif

Re: Proper Performance Engineering
 

We are NOT going to have a repeat of the last thread that
got closed by the Head Cheese.
Stay to the point, and keep the BS out of it.
This section is on my watch. And I'm on it.

See ya, Ken

Re: Proper Performance Engineering
 

dus "gag me with a friggin spoon" work with spellcheck ?

Re: Proper Performance Engineering
 

phnx when u decide to learn the other side of boating besides power curves and complaining about the fastest motor on the water go to screamandfly.com. u can see how to properly replace ur prop and engine posistion to break the water plan and enter air space. i am willing to sacrafice fuel economy to out run that ( enter rival boat brand here) back to the dock when the weather is turning into the perfect storm anyday. clever, chopper and other surface piercing props do just that they run with some or most of the prop out of the water due to the engine hight related to the transom. if u run a suface piercing prop it is highly recomended that u also run a low water pickup because the factory water pickup could be as high as 4-6 " out of the water. some of the cat hulls have to assist stearing with two foot throttles due to the engines being so high out of the water they do not turn the boat at speed. pretty cool huh.

Re: Proper Performance Engineering
 

nevermind

Re: Proper Performance Engineering
 

Thanks Rusty:
The getting away from weather is an important benefit of speed.
Listening to a skilled sport fisherman and boat builder, Paul Mann, talk about running in heavy weather - he was the first to call me blow boater, so I take it as a bit of a compliment I became aware of how much there is to learn there. Think a thread on heavy weather handling - very different on a high power boat than on a `blown' boat - could be a good thing.

Look guys, I meant no disrespect when I brought the misspelling to spare's attention, although maybe I should have done it off list.

Fact is, in my circles constructive criticism is an act of friendship, and that's how it was intended.
Careless spelling CAN stunt a career when you head to the top office.

As to that other thread, unless you're indulging cronyism you will note that spider started it and there was no way I would back off and give him satisfaction.

Finally, have nothing against speed, love it in fact, but outside the good points made by Rusty, think efficiency and reliability far more important, even for fisherman, and especially for offshore >20 NM fisherman.

HBH

Re: Proper Performance Engineering
 

If anyone is thinking diesel i/o then you need to check out this rig. Its not a seacraft but a very very sweet ride none-the-less.

http://www.thehulltruth.com/forums/t...ighlightmode=1

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thats one hot little bertram. sorry to address your question spare. as for the spelling thing phnx i cant spell never could but im alittle argumentitive or atleast my wife tells me i am along with a severe smart a.. i have a bad habbit of saying what i think even to the ceo of the company that i contract for offshore. my boss gives me that look.. (ya know the dont open your mouth look) every time i speek up @ our company wide saftey meetings. im like ron white the comic. i have the right to remain silent...... i just don't have the ability... :)

Re: Proper Performance Engineering
 

Sounds like we'd get along just fine. Had to form my own company cause the only time people would put up with me is when I paid them to!-)
Guess with tyme we'll git over the speling thing?
Hope you all (I'm in the South now) had a great thanksgiving.
HBH

Re: Proper Performance Engineering
 

Phnx - I was just reading about the 1957 Mercury Mark 75 (first 6 cylinder outboard and first mercury tested at Lake X).

In 1957 that motor set the world endurance record propelling a runabout over 50,000 miles in 68 3/4 days of continuous day and night running. Refueling on the run . . . the boat maintained an average speed of 30.3 miles per hour.

Re: Proper Performance Engineering
 

Tim,

That's impressive esepcially considering it was 1957. If my math is correct, that is about 1,632 engine hours, no?

I wonder if a modern day 4 stroke or maybe the ETEC could run constantly for 68 days?

-Ed-

Re: Proper Performance Engineering
 

They were twins 60hp Mark 75's pushing a decent size boat 30.2mph. I am guessing that they were running it continuously above 70% throttle to average 30+ mph over 68 3/4 days. The drivers had to eat meals, go to the bathroom, rotate staff, pickup fuel, etc. So 1632 hours is remarkable for that kind of load on a two stroke.

Re: Proper Performance Engineering
 

Ed - What's more impressive is that the motors ran 1600+ continuous hours (50,000 miles) WITHOUT changing water pumps, fuel pumps, gear oil, decarbing the motor, or any of the other routine maintenance items.

Re: Proper Performance Engineering
 

the truth to that feat was reveiled in a magazine article a while back( Powerboat, I think), apparently they did swap out lower units( with water pumps) on a regular basis, they were also allowed to change plugs and decarbon the engine. Due to the fact there were no spray decarbonizers available at the time, the were allowed to pull the head and scrape the chambers, because this took some time to do, they would install another stand by power head to continue while the other one was being serviced so the event could go on. There was some speculation that the decarboned powerhead that was returned wasn't even the same one that was removed. Fred Kekifer was a marketing genuis. During the test, one of the test drivers fell asleep and was killed when he ran into the trees, they decided to continue with the marathon, changing drivers more regularlly. I wish I could remember exactly which magazine it was in, the article was great, explaining some of the wars and compitition between Mercury and OMC, with the industry greats trying to one up each other.

Re: Proper Performance Engineering
 

Funny how that information doesn't make it into the film or the merc site. To me running continously means "continously". In the film they show them stop at 25,000 miles and disassemble the motors (check the specs) and state that it was reassemble using all the same parts. I wondered about the miracle water pump, plugs, lower unit gear oil, lack of carbon build up, etc.



************************************************** *********
In 1957, the company began operations at a 1,400-acre undeveloped Florida lake - a new testing area away from prying eyes. To keep the location a secret, Carl Kiekhaefer referred to it as "Lake X" when speaking with outsiders, and the name stuck.

" That same year, the Mark 75 was introduced, the industry's first six-cylinder, 60-hp outboard. At Lake X, two Mark 75s set a world endurance record, each propelling a family-sized runabout over 50,000 miles in 68 3/4 days of continuous night-and-day running. Refueling on the run, they maintained an average speed of 30.3 miles per hour."

Spares - If you find that article . . . let me know what issue it was in . . . I'd love to read it.

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i wish I could find it, it was a great article, had a lot of other stories about the early days at Lake X, had some great photos.It must have been about a year and a half ago, could have been trailer boat, boating, or yachting( they are the magazines we get at the office)

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hmmm, well, returning to the core of this post...

As most Mercruiser IO powerplants are GM, I would bet you could get the torque / horsepower / rpm curves from them - I know in my old hot-rodding days these numbers were available - and often were published in the factory shop manuals (not the owners manual), but the last set I have of those is for old Ford V-8's (think Boss 302.... yeah, I'm an old fart)

quite true on horsepower to get to plane, vs horsepower to maintain - same with a car, what it takes to accelerate to 60mph, vs, what it takes to cruise at 60mph - much lower.

Phnyx, sounds like you have heavy aircraft background - safety requirements called for many more guages to monitor in-flight condition of engine - on small, pleasure type boats you will mostly see fuel flow, maybe voltage, temp, oil pres if an inboard or IO - but would probably get more involved on a big bucks sportfish with diesels. My experience on manifold pressure, is only on piston engine aircraft, and military / commercial vehicles, with turbo or superchargers (and hot-rods with same)- so the boost point kick-in, and max pressure, could be monitored. Any other old farts out there, with any Army experience, remember the M551 Sheridan light tank - had a 6V53 Detroit Diesel, with twin turbos, and a supercharger - on full boost it was quick - I worked on that puppy at the Detroit Tank Arsenal.

stray thoughts...

Bill

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Bigshrimpin, for what its worth, i just changed out a set of impellers on the water taxi, twin 150 four stroke Yamahas, 2005 model, 1900 hours, they were worn, but they were still pumpin'