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biggiefl
08-24-2011, 04:07 PM
Anyone have a copy I could see?

Pismo
08-24-2011, 06:01 PM
You have great fleet, two whalers and a donzi...nice

biggiefl
08-24-2011, 10:48 PM
Actually 4 Whalers, Donzi, and an aluminum boat :confused:

Carl C
08-25-2011, 07:40 AM
I think I have the article. I know these are archived somewhere but if no one finds it I will post it later. It's not dated but is a review of a yellow stripe OMC 454/King Cobra.

Pismo
08-25-2011, 09:43 AM
Actually 4 Whalers, Donzi, and an aluminum boat :confused:


even better..a 16' duranautic?

biggiefl
08-25-2011, 01:05 PM
Found it... http://www.donzi.org/forum/showthread.php/992-Donzi-22-Classic-Boat-Tests

No offense but I can not understand how it does 55 @ 4k (55@4k) and at 4600 it only does 56....something aint right there. Lastly my 1991 brochure states a 270 350 or 330 or 370hp 454, not 275 & 310. 275hp from a 454...what is the the President Ford era? I know they started rating them at the prop later on and the 330 went to a 300 or 310 and the 365/370 went to a 340 or 350 depending on exhaust and then you had the 385MPI I think.

Carl C
08-25-2011, 01:55 PM
Found it... http://www.donzi.org/forum/showthread.php/992-Donzi-22-Classic-Boat-Tests

No offense but I can not understand how it does 55 @ 4k and at 4600 it only does 56....something aint right there. Lastly my 1991 brochure states a 270 350 or 330 or 370hp 454, not 275 & 310. 275hp from a 454...what is the the President Ford era? I know they started rating them at the prop later on and the 330 went to a 300 or 310 and the 365/370 went to a 340 or 350 depending on exhaust and then you had the 385MPI I think.

It takes special skill and experience to drive these boats and the guys at Powerboat just don't (didn't) have it! In the other test they drove a 2002 with a HP500EFI engine and only got it to almost 75 mph. That package is easily capable of 79-80 mph. They also said it was overpowered and dangerous. :)

RickSE
08-25-2011, 03:30 PM
...they drove a 2002 with a HP500EFI engine and only got it to almost 75 mph. That package is easily capable of 79-80 mph. They also said it was overpowered and dangerous. :)

They were driving boat #1 in the test. From what I heard Donzi was dissappointed with the performance of boat #1 with the stock X-Dim. After this they decided to raise the X-Dim's on boats #2 & #3.

Carl C
08-25-2011, 04:25 PM
They were driving boat #1 in the test. From what I heard Donzi was dissappointed with the performance of boat #1 with the stock X-Dim. After this they decided to raise the X-Dim's on boats #2 & #3.

Interesting. I hadn't heard about that. The higher X really helped my boat too.

biggiefl
08-25-2011, 09:10 PM
If Teague or Norskog can't drive a frigging 22 Donzi.....well I guess that is why Powerboat Mag went bust....pussies!

4000k is about right...4600 is about 8-10mph faster!

biggiefl
08-25-2011, 09:13 PM
Lastly the 22 is "rated" for 425hp max. The fact that they put a 500 in it and it was 5mph SLOWER than a 496HO.....HELLO!

My 1994 with a 330/310? runs a 23" Mirage 1:50 and I have seen 66-67 on the speedo but at 50 my GPS was almost dead on with the GPS. I will have to try and get a GPS reading....a 425 in the brochure says an 80mph ride....500 EFI should be SICK!!!!

BUIZILLA
08-25-2011, 09:26 PM
My 1994 with a 330/310? runs a 23" Mirage 1:50 and I have SEEN 66-67 on th GPS really? thats the fastest 330 on earth. ;).....


a 425 is an easy 80mph ride.... actually, it's not, figure 72-74, 76 if a fluke..

Carl C
08-25-2011, 09:45 PM
Lastly the 22 is "rated" for 425hp max. The fact that they put a 500 in it and it was 5mph SLOWER than a 496HO.....HELLO!

My 1994 with a 330/310? runs a 23" Mirage 1:50 and I have SEEN 66-67 on th GPS....a 425 is an easy 80mph ride....500 EFI should be SICK!!!!

really? thats the fastest 330 on earth. ;).....

actually, it's not, figure 72-74, 76 if a fluke..

496HO (425HP) runs about 73, They can hit 75 with all things being perfect. HP500EFIs seem to be just bumping 80. HP525EFI runs low 80s to 85. 66-67 with 330 HP, well, I don't know, I guess with a perfect set-up..............

biggiefl
08-25-2011, 10:29 PM
Ok...I calibrated the speedo with my GPS up to about 50. It was within 1mph through ALL the ranges. I have seen 65 with 2 people and 2/3rd's fuel and 62 with 4 and 1/4. I really don't give a poop as 60 is fast enough for me. Lastly I REALLY don't know WHAT engine I actually have except I have oval port heads so I assume a 330. PO said he has seen 70...I highly doubt that but I think 65 is probably....maybe more on a "Good" day!. A 1:50 with a 23" Mirage @ 4900 is 65ish or more.

My 1987 Baja 240 sport with 375-400hp would do 63-65 on a good day(60 with the 330) and she weighed 4000 dry and carried 100 gals of fuel and had a 8' beam.

According to Powerboat Mag the 22' Cougar weighs the same, has the same dimensions and runs 67+ with the same engine/drive/prop. Who knows....who cares!

Who has REAL numbers on a 22? I just bought mine last week so...................

biggiefl
08-25-2011, 10:33 PM
Lastly...2009 brochures say 80+ with a 425....what gives?

silverghost
08-25-2011, 10:53 PM
The 330 HP Merc engine had small oval "Peanut Port" heads.
I have a lightly used 330 core engine sitting as my spare on an engine stand here.

BUIZILLA
08-26-2011, 08:08 AM
The 330 HP Merc engine had small oval "Peanut Port" heads.
I have a lightly used 330 core engine sitting as my spare on an engine stand here. actually, the 330 had the reguler and not so bad oval's.... the 310 had the stupid small and really bad oval's... i've owned different boats with both setups

mattyboy
08-26-2011, 09:01 AM
one thing to take into account too is all 22's are not created equally. some left the mold better off then others, some were built to withstand an onslaught of abuse, some were built light to be fast with small block power. 92-93 were the years that Chris Craft were making the 22s in Indiana. the reversed chine was added so was a heavier build than previous early OMC era 22s. I think Dr Dan's boat was running about the same speeds as posted in the article with a cobra and 454 his is a 93 omc boat it's not a 50 mph boat anymore !!!!!. let's see an 88 with a 300 hp sb and alpha is a 60 mph boat and a 92 with 300 + hp BB and cobra is a mid 50 mph boat wonder why???? is the alpha that much faster??? is the BB that much heavier??? umm maybe , how bout the 88 is some 600 to 700 pounds lighter(dry) according to the brochures. and when they leave the factory they are all propped perfectly :rolleyes:

Pismo
08-26-2011, 09:10 AM
1996 22 502 stock, 75.5 GPS with a labbed 27" MPlus, 74.3 GPS with a standard 25" MPlus. multiple runs with both, not a one time fluke, pre ethanol gas.

biggiefl
08-26-2011, 09:54 AM
Have they changed the hull since the 90's or the X-Dim? If the brochure says 80+ with 425hp I bet they have to stand behind that.

Again everything I can read shows a 3500lb boat 22-24' with a BBC pushing a B1 1.50 w/23" mirage is a 65-69mph ride depending on 4700-5000 redline, one hit 5400 and 74. I will GPS it but I don't think 65-67 is unobtainable with my setup. When was out she was reading 50 on the speedo and my gps said like 48.9. I can't hold the gps and drive 65mph at the same time just yet...these do have a learning curve that takes a little time.:hyper:

BUIZILLA
08-26-2011, 09:58 AM
If the brochure says 80+ with 425hp I bet they have to stand behind that. wouldn't hold your breath on that ever happening..


Again everything I can read shows a 3500lb boat 22-24' with a BBC pushing a B1 1.50 w/23" mirage is a 65-69mph ride depending on 4700-5000 redline, one hit 5400 and 74. I will GPS it but I don't think 65-67 is unobtainable with my setup. When was out she was reading 50 on the speedo and my gps said like 48.9. I can't hold the gps and drive 65mph at the same time just yet...these do have a learning curve that takes a little time.:hyper: put it in your lap, or fix mount it, and hit MAX SPEED recall at the end of each run

biggiefl
08-26-2011, 10:03 AM
Not sure if mine has that feature. I have 2 handhelds so I will check. Thanks for the insight(s). Had a tad too many cocktails last night and had to do some editing. I think I got excited about ??? something.:bonk:

RickSE
08-26-2011, 10:56 AM
Lastly the 22 is "rated" for 425hp max. The fact that they put a 500 in it and it was 5mph SLOWER than a 496HO.....HELLO!!...

One thing that hurts the 22SE's is that they are about 300 lbs heavier then a regular 22C due to the layup and hardware. From what I was told my SE with a 1.50" raised X-Dim left the factory running 82 or 83 MPH. I believe at the time most of the regular HO 22C's were in the mid 70's. The speeds on the regular 22's didn't approach 80 until Donzi raised the X-Dim 2" and started running 27P props on the Shelby's & 009's.

silverghost
08-26-2011, 12:08 PM
actually, the 330 had the reguler and not so bad oval's.... the 310 had the stupid small and really bad oval's... i've owned different boats with both setups

Jim~
I was always under the impression that the 330 HP used the very small oval "Peanut Port" heads.
The 365 HP used the standard large oval port heads.
Both these engines make their horsepower at lower RPMs with tons of torque.

The large Rectangular port heads were not used on very many boat engines ; and were for all out high speed RPMs & full out racing engines & blown supercharged race engines.

If I am wrong~
I stand corrected.

mattyboy
08-26-2011, 12:21 PM
One thing that hurts the 22SE's is that they are about 300 lbs heavier then a regular 22C due to the layup and hardware. From what I was told my SE with a 1.50" raised X-Dim left the factory running 82 or 83 MPH. I believe at the time most of the regular HO 22C's were in the mid 70's. The speeds on the regular 22's didn't approach 80 until Donzi raised the X-Dim 2" and started running 27P props on the Shelby's & 009's.

very true, each boat and setup is just a bit different.

biggiefl
08-26-2011, 01:41 PM
The 330' s just had oval ports. The 400, 420, 440's of the day and the 502's have the rectangular port heads. I had a stock 502 Alum intake & carb on my 454 Baja. I am not sure about the 365-385's but probably the rectangular. You can tell just by looking at the intake. Oval has a flat intake, rectangular is more high rise like you see on a stock 350. 330's are basicallky truck engines and have amazing low end torque and durability and hence why I like them. Just keep the revs under 5k if you want it bulletproof. I can "squeek" 4900 but with more than 1/4 tank it is basically pegged at 4800 trimmed and throwing a tail....no tabs. again I have no idea what 454 I have or if anything has been done to it internally. All I know is it has oval port heads and the carb cover just says 7.4L. It does however impressme no matter what the deal is. I bet in 5 years I will have about 2 minutes total at WFO. Don't get many opportunities around here to run too fast for very long. Damn Jimmy Buffett put up too many Manatee zones. You now pretty much have to be in Tamp Bay to run and Tampa Bay is RARELY calm enough for a 22C at 60+

roadtrip se
08-26-2011, 01:50 PM
One thing that hurts the 22SE's is that they are about 300 lbs heavier then a regular 22C due to the layup and hardware. From what I was told my SE with a 1.50" raised X-Dim left the factory running 82 or 83 MPH. I believe at the time most of the regular HO 22C's were in the mid 70's. The speeds on the regular 22's didn't approach 80 until Donzi raised the X-Dim 2" and started running 27P props on the Shelby's & 009's.

Carl, you didn't change your x-dim, but you did change your prop shaft height with the shorty. Big difference.

When Donzi started messing around with x-dims of the special edition 496 boats, they made some significant wild leaps with the CG
and handling of these boats. I haven't seen one yet that could run at 80 and do it under control. They can be settled down, but it takes
significant rigging changes, that most won't make the investment to do. Most 496 HO boats that I have seen run low 70's and I have
run with a bunch of them.

My 502 ran 68-70. My stock 500 EFI boat ran 78-81 with a shorty. On a miracle day, 83-84, but not on demand. It runs much better now,
and it has most of the 500 SE style upgrades and I certainly wouldn't be running the HP that I do without all of the other structural and rigging
changes. FWIW, it really isn't about the number, at least to me, it's about doing it safely and any time you want on demand.

biggiefl
08-26-2011, 02:07 PM
I agree about the number thing, just bragging rights for most. When I bought this I was happy to see 60 but I am happier it goes faster...for bragging rights.:tongue:
I have been boating all my life and at 42 this is my 3rd go-fast so it is not my first rodeo. around here you can't do much more than 60 anyway. I will however say that if it did not do at least 60 I doubt I would buy it. I would hate to be passed by a V6 sweet 16.

Carl C
08-26-2011, 03:41 PM
There is the thrill factor too. For me the 496 and 73 mph was close but not there. The HP525 EFI gives me the low 80's and acceleration that I wanted. It's a whole different boat now and an absolute blast to drive. Like Todd said though, I did a lot more than just drop in a bigger motor.

gcarter
08-26-2011, 04:19 PM
let's see an 88 with a 300 hp sb and alpha is a 60 mph boat and a 92 with 300 + hp BB and cobra is a mid 50 mph boat wonder why???? is the alpha that much faster??? is the BB that much heavier??? umm maybe , how bout the 88 is some 600 to 700 pounds lighter(dry) according to the brochures. and when they leave the factory they are all propped perfectly :rolleyes:

Matty, MOP started out w/a 300 HP SBC and an Alpha, then changed to a B1.
I think he found the Alpha to be about 3 MPH faster. His boat seems to be well balanced and handle very well.
I would like to see a high HP SBC in a lightish 22. I think it would be an interesting boat.

Ghost
08-26-2011, 06:51 PM
Found it... http://www.donzi.org/forum/showthread.php/992-Donzi-22-Classic-Boat-Tests

No offense but I can not understand how it does 55 @ 4k and at 4600 it only does 56....something aint right there. Lastly my 1991 brochure states a 270 350 or 330 or 370hp 454, not 275 & 310. 275hp from a 454...what is the the President Ford era? I know they started rating them at the prop later on and the 330 went to a 300 or 310 and the 365/370 went to a 340 or 350 depending on exhaust and then you had the 385MPI I think.

If Teague or Norskog can't drive a frigging 22 Donzi.....well I guess that is why Powerboat Mag went bust....pussies!

4000k is about right...4600 is about 8-10mph faster!

Late to the dance and apologize if I missed someone else's clarification in my skim of this thread.

That said, when I open the PDF for the 22 with the OMC plant, the summary table shows 56 MPH at 4000 RPM. And 56 MPH again at 4500 RPM. The text of the article says 55 MPH at 4000 RPM, and 56 MPH at 4500 RPM. This has to be some sort of typo/confusion. Those numbers:
can't possibly be right
don't even agree with each other
That said, it all seems to be an amazing, compound-error mess. If you run through the specs on the motor, gears and prop, what would make sense to me is something like:

3000 RPM, 38 MPH, roughly 10% slip
4000 RPM, 49 MPH, roughly 10% slip
4500 RPM, 56 MPH, roughly 11 % slip

I'm guessing they had a couple of typos.

BTW, these numbers seemed slow to me for a 454, but apparently this was a 275HP 454 OMC motor? Seems like a LOT of cubes for 275 HP. I thought my old 310HP 454 was about as low as they went, but I guess not. Still, if it really was a 275 horse, those numbers (above) strike me as reasonable. Am I off base on this?

Mike

biggiefl
08-26-2011, 09:01 PM
Again...4000 @ 55 and 56 at 4600 makes NO sense to me. I would think 4600 would be more like 62+. Mine pulls like a freight train between 4000-4800 and is a whole lot different than 1mph. I will try and GPS my lowly 330?hp tomorrow. My 21 Scarab with a 260hp alpha with a 23 Laser2 did over 60 at 5k.....that review is skewed in my opinion.

Ghost
08-26-2011, 10:24 PM
Again...4000 @ 55 and 56 at 4600 makes NO sense to me. I would think 4600 would be more like 62+. Mine pulls like a freight train between 4000-4800 and is a whole lot different than 1mph. I will try and GPS my lowly 330?hp tomorrow. My 21 Scarab with a 260hp alpha with a 23 Laser2 did over 60 at 5k.....that review is skewed in my opinion.

I agree completely that 55 @ 4000 AND 56 at 4500 (I believe it was 4500 in the article, not 4600, but the concept is the same) makes no sense. That's what I was saying in item 1 in my post ("can't possibly be right").

However, unless I botched the math in my spreadsheet, with the 1.42 drive and 21 inch prop pitch spec'd in the article, your gress of 62+ MPH would require less than 2% prop slip. Which is clearly unrealistic. So, it is theoretically possible that something was wrong with the boat, trim. motor, whatever. Such that the boat, dialed in properly, would run 62+. But it would only do so, with that drive and prop, by revving a LOT higher. Like 5000 RPM. And I've never seen a stock 454 that was supposed to rev that high. 4500 RPM is smack in the middle of the prescribed RPM range for the low-HP 454s I have seen.

So, if the drive ratio, prop pitch, and RPM numbers are right, their observed top end of 56 MPH seems about right, as one would think 10 or 11 percent slip might be about right. And thus the number they completely botched was the speed when running at 4000 RPM. That speed should be around 49 MPH, not up at 55 (as the text in the article listed) or 56 (as the summary table in the article listed).

Put another way, I think you're right that the speeds at 4000 and 4500 CAN'T be the same, or one MPH apart. One of those speeds is wrong. But the speed number they typo'd isn't the WOT speed, it's the 4000 RPM speed. The 4000 RPM speed of 55/56, with the drive ratio and pitch they give, would require NEGATIVE slip. 56 MPH is 3 MPH faster than the theoretical maximum for that drive and prop at 4000 RPM. If they correctly listed the drive ratio and prop pitch, we KNOW that 55 or 56 MPH is simply impossible at 4000 RPM.

Regards, apologies if I botched the math, but I don't think so.

Mike

biggiefl
08-27-2011, 01:25 AM
I am bringing out 2 GPS' tomorrow. I will let you know what I REALLY run.

biggiefl
08-27-2011, 01:34 AM
http://continuouswave.com/cgi-bin/propcalc.pl

Crouches says a 1.5 ratio with a 23" spinning 4900 is 65mph roughly with 10% slip. Why are so many here against that?

roadtrip se
08-27-2011, 09:48 AM
http://continuouswave.com/cgi-bin/propcalc.pl

Crouches says a 1.5 ratio with a 23" spinning 4900 is 65mph roughly with 10% slip. Why are so many here against that?

Record your GPS numbers together with a tach reading. I think you might find that slip number a little optimistic. I have to run a five blade to get that kind of number. But, as said here, every boat is different. Have fun.

Ghost
08-27-2011, 09:56 AM
I am bringing out 2 GPS' tomorrow. I will let you know what I REALLY run.

Cool, always good to have more data. (Don't know if you already posted your drive ratio and prop specs, those will help too.)


http://continuouswave.com/cgi-bin/propcalc.pl

Crouches says a 1.5 ratio with a 23" spinning 4900 is 65mph roughly with 10% slip. Why are so many here against that?

I don't know that anyone is against that--I certainly am not against it. I skimmed the thread but read the article, so I don't know all of what others claimed. That said, the reason I posted was to:
clarify the numbers that the article stated, BOTH in the text and in the summary table, which differed from the text. (In the thread here these numbers were misquoted, which could only add confusion.)
show that some numbers in both the text and the summary table HAD to be wrong. I was agreeing with you on this, that a 1 MPH change with a 500 RPM increase was ridiculous.
show that the 4000 RPM speed was inconsistent with the 3000 and 4500 RPM speeds, but the 3000 and 4500 RPM speeds seemed consistent with each other.
show that if the drive ratio and prop pitch and RPM measurements were correct, that the 4500 RPM speed of 56 MPH made perfect sense.
show that if the drive ratio and prop pitch and RPM measurements were correct, a 4500 RPM speed of 62+ was impossible.
Similarly, Crouches says a 1.42 ratio with a 21" prop spinning 4500 at 10% slip is 56 MPH. Their math agrees with mine exactly.

Regards, apologies for any confusion,

Mike

biggiefl
08-27-2011, 10:36 AM
I should have put that into the calculator as well. Interesting that the Cobra did not do too well. Even Mercury's speed calc said 57 with the Cobra setup. I would expect that from a 260hp SBC.

Ghost
08-27-2011, 10:55 AM
I should have put that into the calculator as well. Interesting that the Cobra did not do too well. Even Mercury's speed calc said 57 with the Cobra setup. I would expect that from a 260hp SBC.

Agreed. I don't know, but I'm not sure an alpha 260hp SBC wouldn't be in that ball park, just as you say. I was surprised at how low the HP was (275) in that 454. That's what, 2-3 hundred pounds of extra weight from the engine and drive? With some people talking about big block boats getting significant extra weight in glass also. All only offset by 15 HP in this case. Not sure a 260 Merc wouldn't outrun the big block cobra in that case. Your expectation here makes sense to me. It certainly doesn't seem far off if it's off at all.

(All that said, I bet that cobra with its low-tuned 454 might run 50 years between rebuilds, with just basic, proper maintenance.)

Mike

mattyboy
08-27-2011, 02:37 PM
the numbers you posted are not roughly 10% they are more like 8%.
one thing you guys are taken as a given is a constant slip rate thru out the rpm range. Coming from the old volvo world some props get less efficient the faster they spin. so a gain in 600 rpm from 4000 to 4600 might not see any noticible speed gain as the prop goes from 12-13% to 14-15% slip . To think the OMC factory would have a 22 leave the factory with a prop that would be at 8% slip is VERY DOUBTFUL they probably had prop that was used on all of their drives for boats ranging from 17 feet to 29 feet or more from the like of 4 winns larson. we all know the classic hull is very prop sensitive.


George I would also think MOP's 22 is one with the lighter weight, there were rumors the X might also be up on that era 22 but I have no first hand knowledge of that.

Ghost
08-27-2011, 03:30 PM
the numbers you posted are not roughly 10% they are more like 8%.

Matty,

I agree that slip is not constant, but before that: what numbers that who posted are "more like 8%"? Or is it possible you missed the drive ratio, which the article listed as 1.42, and used something something more conventional like 1.47?

I posted these (see list below, updated in parens with precise calculations). I ran them in Excel myself, and also in the web link BiggieFL posted, which agreed.

1.42 (that's Four Two) drive, 21 inch prop pitch:

3000 RPM, 38 MPH, roughly 10% slip (more precisely, 9.56%)
4000 RPM, 49 MPH, roughly 10% slip (more precisely,12.52%, and I see now where I goofed, rounding the wrong direction in my head from the nearest spreadsheet entry. I should have picked 50 MPH instead of 49.)
4500 RPM, 56 MPH, roughly 11 % slip (more precisely, 11.14% slip)

But we're nowhere near 8%. Virtually dead on, except for my noted goof, which means higher, not lower slip. I'm guessing you are using 1.47--I ran one example of that and it pushed almost exactly down to 8%.

Regards,

Mike

biggiefl
08-28-2011, 12:42 PM
Why is this site so slow and buggered up?

When you use the Mercury speed calc it asks for ratio, pitch, & slip and then it calculates speed. I am putting in 10% slip. The Mirage plus is an aggressive prop ublike the OMC prop they used. Thier prop would be equiv to a 1" less pitch on the Mirage. Put 4 21" props on the same boat and you will get 4 different performance numbers not to mention handling characteristics. Hell I tried 3 different 17" SST's on my Whaler and got 3 different numbers. A 23" laser 2 is WAAAAYY different than a 23" Mirage although both made by Mercury.

mattyboy
08-30-2011, 12:34 PM
http://continuouswave.com/cgi-bin/propcalc.pl

Crouches says a 1.5 ratio with a 23" spinning 4900 is 65mph roughly with 10% slip. Why are so many here against that?


ghost not the numbers you posted but the numbers biggie posted above

these are the numbers that don't add up I get .086% on those numbers you find a prop with .086% slip buy it hell buy 2

I know 10% is the base line for a good prop most run higher in slip than that.


the numbers on an omc powered 454 don't seem out of line with the OMC boats I have seen in person with that kind of power.

http://www.rbbi.com/folders/prop/propcalc.htm

biggiefl
08-30-2011, 02:45 PM
Matty if Crouches and Mercury's prop calculator are saying 10% slip(which is what I put in), how do you get less than 1%?

Again..you put in slip(10%), Ratio(1.50), RPM(4900), and pitch(23") and both give 64-65mph. If I put in .86% slip It would be in the 71mph.

http://www.mercuryracing.com/propellers/propslipcalculator.php

Ghost
08-30-2011, 05:19 PM
I think where Matty wrote ".086%" slip it was an accident, and he meant to type either ".086" or "8.6%" which are the same. But I don't think he actually intended to discuss anything under 1%.

Worth noting that the slip numbers are are pretty sensitive to a difference as small as 1 MPH. For instance:

4900 RPM, 1.5 ratio, 23" pitch, 64 MPH --> 10.05 % slip
4900 RPM, 1.5 ratio, 23" pitch, 65 MPH --> 8.64 % slip

So I agree that something really good, like 7% slip, is rare and thus unlikely. But it's probably worth noting that it only takes 2 MPH difference to get from 10% down to 7. So, in a discussion like this, to roughly estimate on paper what a particular boat/drivetrain might do, somebody saying "no way" to 65 might well say "sure" to a goal of 63 or even 64.

However, getting back to the discussion prior to some confusion about slip math itself, I will say I don't buy that a boat running at say, 55 MPH at 4000 RPM, could be cranked all the way up to 4500 or 4600 and only see one MPH of increase, to 56 MPH. While I agree that slip percentages change over the RPM/speed range, I don't believe anything is going to create a near brick wall on speed like this example. Not in a sterndrive boat with a hull of this shape that has otherwise been near-linear in its planing speed vs. RPM relationship. I don't buy it.

I DO buy that the boat could tail off in efficiency, measured by slip. But the change just HAS TO be more gradual than "fat dumb and happy, with nearly proportional speed vs RPM" all the way to 4000 RPM, and then suddenly a massive loss of efficiency the minute you go above 4000, such that you can crank it up 500 or 600 more but only gain one MPH. If you graphed it, it would make for a SHARP turn in a nearly linear relationship, with an even HUGER jolt in the second derivative. That kind of sharp change makes sense when you are changing modes, as on the cusp of wallowing just below plane, then getting out of the hole. But I can't imagine it making sense up near WOT on a fast, planing hull, with a sterndrive. At least, not on any of the gear I've ever driven. Not unless the prop spun out. :)

Sure, I can see stuff tapering off, but just not that quickly.

Which means, in the context of the article, this is where it was clear to me that given the data points for 3000 RPM (38 MPH), 4000 RPM (55 MPH), and 4500 RPM (56MPH):
the numbers simply CAN'T be right, as Biggie had pointed out. There's a goof in there somewhere.
the number that was most likely the goof was the SPEED when the boat was at 4000 RPM
Mike

mattyboy
08-30-2011, 06:10 PM
yes sorry I use the rbbi calc it uses decimal points/places the calc i posted is what crouches used as a base for theirs

8.6 % or .086
10% or .10

biggiefl
08-30-2011, 09:57 PM
OK...so why is 4900 with 1.5 ratio, 10% slip and a 23" Mirage plus not a 64+mph boat as that is what I have(on paper)? The ONLY thing I have not done is GPS the 64+ which I will do as soon as I can. Again I am happy with 60 but I have owned 2 others that have GPS'd pretty much what the Mercury site predicted and I honestly feel she is a 64+ boat. Again my bad is I don't really know what is under the hood except a 454 with oval ports. No matter the numbers "should" be close or Mercury needs a new website. Nobody thought my 21 Scarab was a 62mph boat due to Powerboats review of 55....sorry powerboat.

mattyboy
08-30-2011, 10:17 PM
biggie,

my point was that finding the right prop is the key on the classic. that 10% is a hard number to reach. 12% or higher is common not to mention the handling quirks some props have. I struggled with props on my volvo 16 it took some time to dial it in with good handling and top end all in one prop. Once it was propped right my wot speed went up 3-5 mph.
the 22 guys should have some suggestions for a merc setup.

Ghost
08-30-2011, 10:25 PM
OK...so why is 4900 with 1.5 ratio, 10% slip and a 23" Mirage plus not a 64+mph boat as that is what I have(on paper)? The ONLY thing I have not done is GPS the 64+ which I will do as soon as I can...

Let me be up front that I don't know if she is or isn't a 64+ boat. If I understand you correctly, those are the drivetrain specs AND the max RPM you are getting, wide open, is 4900.

So, if I have that right, my instinct is that if you have things dialed in, you might be getting 64. You might be getting 63. 64 would be 10% slip, which is pretty good. 63 would be about 11.5. If you were reaching 65, that'd be down at 8.64% slip. Possible, I guess, but less likely. 66 would be down to almost 7%. Possible? Maybe, I think Osur866 and a few others may have gotten that low, but it's even rarer. So, I think you see the sort of math going on here. No "answer", just probabilities.

Further, who says whether a "23" inch prop is exactly 23"? Dunno, but the math we're doing is extremely sensitive to that spec. Almost never see a prop spec'd out at anything but an even inch increment. So, I suppose they might be off as much as half an inch from what we'd use on paper. If your prop was almost 23.5 inches, 66 MPH would be about 9.2 % slip. How about the guys we've seen who are down at 7%? Are they really there, or are they running props that are somewhere north of the pitch spec, giving them artificially low slip calculations? Again, don't know without someone putting the prop in a lab for analysis. Then there's wind, current, Coriolis effect, nepotism...

Thus, estimating 63 or 64 for you on paper as a best prediction makes sense to me. Whereas arguing on paper that you can't reach 65 because you can't do 8% slip, but saying you can get to 64 because that's at almost 10%, in my view is getting beyond the limits of the paper analysis. To be contrasted with telling you that 71% is out of reach because 2% slip is unattainable, which is almost certainly the case.

But getting right to the hairy edge like 8 vs 10 %, who knows? Doubt we know the true pitch of the prop all that accurately. The drive ratio is probably pretty accurate. I suspect the tach is too, but when do you even hear anyone cite a number that's more accurate than the nearest 100 RPM? And how good a look do you even get when running wide open, to see where it really peaks?

Anyhow, I hope that's useful in pondering the limits of paper analysis, at least as I see it. Beyond a certain point, you have to just run the boat, and measure the speed, right? People can lay their bets down, and then we all see. However, after all this discussion, I REALLY want to know what your GPS tells you. :)

And, just to make ya really nuts, I have seen readings from GPS speedos as far apart as 2 mph...

Mike

P.S. All of which runs the risk of getting lost in MPH Crazy Land. My new toy probably won't get over 44 yet, but I have one he11 of a good time running the boat. I can think of another owner around here who has a REALLY cool old 18 that I *think* runs under 50, down there not too far from me. And it still puts a smile on everyone's face. So, I don't consider speed all that important unless it can double me up. ;)

biggiefl
08-30-2011, 10:30 PM
Amen brother...my point exactly! 1-2mph is ??? but it is obtainable.:popcorn:

biggiefl
08-30-2011, 10:37 PM
Lastly a 23 Laser might be 15% slip where a 23" Mirage or Stiletto might be 8-10%. Just because a prop says 23" does NOT mean it is 23" or even close. A 21 OMC SST today is equiv to most 18-19" stainless props. In the days it was the goods! My 22" Stiletto is made by the same company that makes many OEM props and I think "might" be owned by Yamaha in the states. Again a Mirage 23" against a Hydromotive 23" could be night and day. The Mirage again could be night an d day against a BRP prop....nobody knows until they TEST.

Barry Eller
09-02-2011, 07:32 AM
Well, my old post of the review has brought some interesting conversations. My 1993 22 Donzi by Chris Craft came with the 454 HO engine and King Cobra drive. The 454 HO had rectangular port heads and a 850 CFM Holley 4150 carb. The stock prop was the OMC Viper 21" 3 blade prop. It was a 62 to 65 MPH boat at best. My current 502 (HP 500 clone) is a 75 MPH boat with a 25" Turbo 1. I have bumped 78 MPH with a tweeked Ballistic 25" with a nearly empty gas tank and only me in the boat. My 23" Hydromotive 4 blade is a 72 MPH prop. My RPMs are 5000 with the Hydro, 4900 with the Ballistic and 4800 with the Turbo. King Cobra drive ratio is 1.42