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View Full Version : prop/perf data for 22, need guidance



boatnut
08-12-2005, 05:33 PM
I finally got a chance to run the boat with a GPS and gather some data. The boat is a '97 22 with the 7.4L/Bravo 1 pkg, 300HP I believe, carb, the prop is a Bravo 1 4 blade 28P (which seems like way too much for 300HP?). Two people in boat, 7/8 tank of fuel, altitude 1326 ft, freshwater of course.
Tach accuracy ??. Motor rated 4200-4600 max rpm.
With trim all the way in and tabs up:
3000 = 37.8mph
3500 = 45.0
4000 = 51.3
4100 = 52.2 (WOT)
trimmed
4000 = 54.5
4400 = 60.4

Below about 3500 the boat has a tendancy to porpoise, certain water conditions will result in continuous porpoise.
As an example of tab use, at 3000 rpm:
no tab, trimmed in = 37.8 mph
tabs down to stop porpoise, trimmed in = 36.0 mph
tabs down with some trim =37 mph (tabs down allow some trimming,
with tabs up any trim results in too much porpoise.

I am surprised that the motor will turn 4400 with the 28P 4 blade (as said I do not know how accurate the dash tach is). Any suggestions on a better prop for this boat? Several have mentioned the Turbo props, what model turbo do you suggest? I would think that 26 would be a better pitch although I see similar boats with 25 or less pitch Mirage props? I would like better all around handling (less porpoise etc.) than absolute top speed, however it would be nice to be able to see 60mph (the person that sold me the boat thought it was doing close to 70--the typical 10-20 percent wishful thinking factor). Thanks guys for the guidance, I know you get lots of requests for similar help. Ed

KFLB143
08-12-2005, 05:53 PM
I finally got a chance to run the boat with a GPS and gather some data. The boat is a '97 22 with the 7.4L/Bravo 1 pkg, 300HP I believe, carb, the prop is a Bravo 1 4 blade 28P (which seems like way too much for 300HP?). Two people in boat, 7/8 tank of fuel, altitude 1326 ft, freshwater of course.
Tach accuracy ??. Motor rated 4200-4600 max rpm.
With trim all the way in and tabs up:
3000 = 37.8mph
3500 = 45.0
4000 = 51.3
4100 = 52.2 (WOT)
trimmed
4000 = 54.5
4400 = 60.4

Below about 3500 the boat has a tendancy to porpoise, certain water conditions will result in continuous porpoise.
As an example of tab use, at 3000 rpm:
no tab, trimmed in = 37.8 mph
tabs down to stop porpoise, trimmed in = 36.0 mph
tabs down with some trim =37 mph (tabs down allow some trimming,
with tabs up any trim results in too much porpoise.

I am surprised that the motor will turn 4400 with the 28P 4 blade (as said I do not know how accurate the dash tach is). Any suggestions on a better prop for this boat? Several have mentioned the Turbo props, what model turbo do you suggest? I would think that 26 would be a better pitch although I see similar boats with 25 or less pitch Mirage props? I would like better all around handling (less porpoise etc.) than absolute top speed, however it would be nice to be able to see 60mph (the person that sold me the boat thought it was doing close to 70--the typical 10-20 percent wishful thinking factor). Thanks guys for the guidance, I know you get lots of requests for similar help. Ed

I just posted that i use a Mirage 24" 4 blade on my 69 21gt. Runs well.

I do not have a porpoise problem. I run the trim out until I loose speed and gain rpm. Slight tab to keep the nose down.

Great mid-range performance and MPG.

I run a 454 MAG 365.

Bravo 1

LD

Dr. Dan
08-12-2005, 06:18 PM
:biggrin.: Turbo 23 ...get it from Poodle... or pay more from others.

Doc :wavey:

knots2u
08-12-2005, 06:59 PM
Hate to rob this post but what would be the recommended prop for a 22 with a carb 502ci/502 crank HP with a 1.5:1 Bravo?

ChromeGorilla
08-12-2005, 07:08 PM
Hate to rob this post but what would be the recommended prop for a 22 with a carb 502ci/502 crank HP with a 1.5:1 Bravo?



26P Hydro QIV.... :yes:

boatnut
08-12-2005, 07:16 PM
:biggrin.: Turbo 23 ...get it from Poodle... or pay more from others.

Doc :wavey:
how much rpm increase would you get going from a 4 blade 28 to a 3 blade 23? I am getting 4400 hundred now, wouldn't 5" reduction in pitch get me over the 4200 - 4600 redline of the Merc 7.4 motor? What type of Turbo, they have several different styles? Thks, Ed

MOP
08-12-2005, 07:20 PM
Roughly 200RPM per inch of reduction, with the same amount of blades. A 4 blade will usualy be an inch less then a 3 for about the same RPM. Was'nt the 454 carb a 330HP in 92.

Phil

RedDog
08-12-2005, 07:27 PM
trust the Doc

28 is way too much for your HP. I run a 25 Turbo but spin it 5000+ with a 502 Mag. something in the 23 to 24 should be in the range you want.

Wouldn't 4800 rpm be ok for the 7.4L Merc? I'd push it with a smaller prop to have better acceleration - you only run WOT intermitently anyway (or at least I do)

boldts
08-12-2005, 08:04 PM
I'm thinking the 23" Turbo 1 might be a bit small, but alot depends on how your planning to use the boat. If your pulling skiers or water toys, then a smaller pitched prop may be just what you need. You said speed wasn't tops on your list of wants. How-ever, you may find that all aspects of your boats performance will improve with a different prop on the boat. One thing you'll notice about the Turbo 1 prop is that while being a smaller diameter than the Mirage prop, because of the better slip ratio the prop offers, you may need less pitch than a same size Mirage. In my case, I was running a 23" Mirage at 4600 rpms. I ordered a 23" Turbo 1 and found that the rpms stayed almost the same, but speed increased plus 3 mph. My drive also was running a higher I believe ratio. (prop turned less per engine rpm) I ended up running a 22" Turbo 1. Rpms were at 48-4900 trimed out. So, with a 1.50 Bravo1 drive and currently running a 4 blade 28" prop, I'd start with a 24" or 25" Turbo 1. The nice thing about the Turbo brand props is that you can order them in 1" increments rather than have to send the prop to a shop to have the pitch changed. If you start with a 25" and find your rpms are still low, you should be able to simply exchange the 25" for a 24" and be right where you need to be. I'll bet you get better speed, fuel economy and you'll notice much better handling. Most or all of your porposing should be gone. I used to have to run mine trimmed all the way in also. Any trim and my 22 porposed badly. Wasn't much fun to drive and it wasn't my driving style as I had other more experienced boat drivers drive my boat with the same results.

Sorry to be so long. The Turbo 1 worked on my 22 Classic set-up. I think it deserves a try. The new prop by Precission is the TXP. I haven't read a report on this prop by someone running a stock drive height or stock engine, but I know one person running a non stock set-up that has given the prop thumbs up ratings.

boatnut
08-12-2005, 08:45 PM
Thanks to all for the detailed responses, I really appreciate it. To answer a few questions (the drive is a 1.5 ratio which I don't think I mentioned). According to the documentation I have the 1997 motor I have is 300HP, not 330. It is called a 7.4L Bravo and the Merc model number is "MCM 7.4 litre/Bravo". They state the wot rpm should be in the range of 4200-4600 and yes as someone stated I would only be wide open for short periods of time but I think I should not target the rpm to be over 4600. On the Turbo website they state the Turbo Vector was designed specifically for the Bravo 1 drive. Does anyone have experience with this prop. I assume from the posts that when all of you mention Turbo you mean Turbo 1 as Scot stated.
Thanks again, I am going to try something as the handling of this boat is more of a chore than my 18 or a 1982 22 I had with a 330 TRS 454 with a cleaver prop. It sounds like the Turbo is the way to go. My Bravo 1 28P is literally new, been used a few hours and no nicks --- if anyone is interested it will be available soon. Ed

MOP
08-13-2005, 07:24 AM
Qoute MP: I wouldnt go any higher then a 21 on that combo.

I am with Poodle on a 21 maybe 22, try to borrow a prop or two before you plunk down your dollar. I am going through propping my 22 right now, a inch one way or the other can make a lot of difference overall. As far as worrying about the 4,600 at top I would not, I would prop the boat to be able to run 4400 WOT with a full load IE: full fuel and 4 people, light you may hit 48-5000 @WOT but how often. There are more big blocks running up into the 5's and better then you can imagine with no troubles. Most WOT runs are pretty short, once the GPS stops climbing or you got by another boat thats it does anyone hold it there more then 20-30 seconds not many, 90% of all running is done in the mid 3's some up to 4. Yeah it is nice to hit a high number but I think many will agree mid range performance is far more important.

Phil

boatnut
08-13-2005, 10:05 AM
The nice thing about the Turbo brand props is that you can order them in 1" increments rather than have to send the prop to a shop to have the pitch changed. If you start with a 25" and find your rpms are still low, you should be able to simply exchange the 25" for a 24" and be right where you need to be. .

Scott, does someone have a program where you can buy a prop and exchange it within a short time (assuming no nicks etc.) for a different pitch?
That would be ideal. I am getting valuable advise from what I consider to be a team of experts but it is difficult for me to drop 6 inches in pitch when I am turning 4400 now. I am convinced the Turbo 1 is the prop to try as I am more focused on full range characteristics than another mile an hour or so on the top end. The question is what pitch to try 22", 23", 24",25"?
thks again to all, Ed

boldts
08-13-2005, 01:18 PM
Ed,

When I bought my Turbo 1, I bought from a company up in Michigan. Dan's prop shop I believe was the name. Since then, one of our own Scott Baxter (Madpoodle) has begun selling these props to the public. Scott is a great guy and won't do you wrong. Send him an private message or e-mail and talk with him.

As for which pitch to start with, it's kind of a trial and error type of thing. Your running the 1.5 Bravo1 yet you want your rpms to top out at 4600. I had a baseline 3 blade Mirage prop to work from when I started. So, knowing what that 3 blade prop topped out at speed and rpms wise, gave me the feeling that since the Turbo 1 had a smaller diameter than the Mirage, if I ran a 23" Turbo 1, I should gain some rpms and speed. Turned out though due to the efficency of the Turbo 1, rpms stayed the same at 4600. So, I returned my 23" for a 22" Turbo 1 and hit my set-up right on the money. Some prop shops charge a restocking fee, but as long as there is no damage to the prop, they'll exchange for a different pitch. Talk to Mr. Baxter. He can tell you better what he can and can't do in that matter.

Now, your running a 28" 4 blade at 4600 wot right? Most of the time when you switch from a 3 blade to a 4 blade prop, like MOP said, you go 1 or maybe even 2" less in pitch. With your current results, that would mean a 29 or 30" pitch 3 blade. Personally, if you go with a prop that big in a 3 blade, I think it will really hurt your out of the hole and midrange cruising performance. Like everyone else has said, how long do we really run our boats at wot? I think personally, I'd start with a 25" Turbo 1. Get a good baseline. Find out just how high your wot rpms go up to unless it gets up past 5500. I don't think it will, but obviously, if it did, you'll need more pitch than 25". If the rpms top out at 4900 or 5000, I wouldn't change pitch at all. Now, lets say the engine tops out at 46 or 4700. Then, I would decrease the pitch to keep your engine in a better midrange placement. I'd try a 23" next and test again with all conditions as close to the same as possiblem. Remember what your after. You want good midrange with-out the boat porposing.

Just curious. Are you sure the diameter of your 4 blade has not been changed? That really seems like a lot of pitch for your set-up, but maybe not. Hope my advice is usefull to you. Jerry Eisele is testing my 22" Turbo 1 right now, but if Jerry doesn't think it is what he needs, I'd be willing to let you test my prop. I'm still thinking it is a bit small for the 1.5 drive, but maybe not considering what your wanting out of your package.

MOP
08-13-2005, 02:10 PM
Scott not real sure but I think I am making more torque then his 300, I am spinning a 1.5 Bravo with a 23 on it. No trim tucked in I turn 60.9 trimmed to what I think is full 65.1 51-5200, the prop is a cleaver which I think is a bit easier to spin then a round ear.
I have a hunch his 28 has been down pitched along the way or his ratio is 1.62, even the 22'S with 454HO won't turn a 28 4 blade as high as he is turning it.

I just did a tour through the Hot Donzi section, it sheds a lot of light on what should be a starting point, higher HP 22C's are running 23's!

boatnut go there do some home work to form a better opinion, many posts on 22's most with HP, ratio and prop size. All the lower powered ones fall into the same 1-2" category, you can PM some guys with darn near the same package as you have to closer to nailing things down.

Phil

Pismo
08-14-2005, 07:29 AM
MOP,

I agree, something is clearly wrong, 4000rpm with a MPlus 25" (which acts more like a 26") and a 1.5 drive yields around 60mph in a 22 Classic, so 51.3mph at 4000 rpm with a 28" prop and a 1.5 is even higher, like 63-64mph. Not a true 28" or the drive is a different ratio. I'll bet on ratio. Maybe huge slippage because so over propped, but at 29% slip I doubt it. Even with a 1.62 drive it is 21% slip. A 1.81 yields 12% slip which is getting back in the ballpark. Sounds like a 1.81ish drive or a lower pitch prop.

boatnut
08-14-2005, 09:22 AM
Scott/Phil, thanks for the time spent on responding to this. Shortly before I bought the boat (weeks before) the outdrive was stolen from the dry storage racks along with three other Bravo-1 drives (the thieves knew what they wanted). The Bravo drive is therefore new and the labels on it indicate it is a 1.5 ratio. At the time, being they took the prop also, the owner and his mechanic said the previous prop was turning too many revs so they ordered the Bravo 1 4-blade prop (p/n on it is 48-831916 28P) and from what I was told it was not repitched or cut down. The motor is supposedly completely stock and looks and sounds that way?? I completely agree with both of your doubts about how this power/boat pkg could be turning that prop at that speed based on all the other data on like boats and engines in the forum. Some thoughts and things I will check on:
1) I turned about 4100 hundred trimmed in and 4400 hundred trimmed out, maybe the prop was slipping more trimmed out although I got a +7 or 8 mph when trimmed.
2) maybe the tach is not accurate -- it seems to be OK at idle but I do not have anything to compare its readings on the high end??
3) I will try to contact the previous owner and see if I can find out what prop was removed and what rpm's they were turning with it.
4) I will try to measure the diameter of the prop I have

Is the rpm at wot with the drive trimmed all the way in a meaningful measurement?? I was getting 4000-4100. Thanks again, Ed

boldts
08-14-2005, 12:02 PM
Ed,

When looking for the top rpms a prop will turn, usually I tried to run the boat with about half a tank of fuel, just me, tabs up and drive trimed up until you see the rpms go higher, but the boat doesn't go faster. Then just a tap of the down trim button. You'll feel the boat grab and go faster again. This is known as the sweet spot and should give you your best wot rpm reading. Since this is the max rpms you can run the boat at with the prop currently on the boat, it is the reading you want to use when setting up the prop to the application. It is also the lightest you will run the boat except for fuel weight which would decrease as more fuel is burned off, but half a tank is a good average for testing purposes. Inportant thing here is that you test each different prop you try under the same conditions. Always start with the same amount of fuel so that your results can be compared side by side. In most cases, different props will change the numbers being read. Sometimes, the prop will even change the amount of trim used to find that sweet spot.

Pismo
08-14-2005, 04:56 PM
At 60.4mph and 10% slip on a 1.5 drive and 28" prop yields 3800rpm. So maybe the tach is off but I would think you would hear the difference. Regardless, 310hp in a 22 with a 28" prop and a 1.5 drive is very overpitched. The max speed should be around 62-65mph hopefully at 4500-4600rpm indicating about a 23" prop at 8-10% slip. Good luck. Try an external tach or borrow a 23" MPlus and try it.

boatnut
08-15-2005, 10:49 AM
I contacted the previous owner and he said the prior prop that was on the boat was a 4 blade also but he didn't think it was a Bravo 1 (seemed to have thinner blade ends), he thinks it was a 24P and it turned 5400 and 63 (not a GPS reading so ??). I am going to try and determine if the boat has the Thunderbolt V system and a rev limiter which would be a vote for incorrect tach readings I think as I assume the limiter wouldn't let it run 5400. I have an older (70's era) service tach/dwell unit, if I can hook it up I may be able to confirm the tach readings?? Although with this solid state ignition I am not sure how to do that at this time---any suggestions in this area. Ed

MOP
08-15-2005, 12:35 PM
You can hookup back at the engine to the gray on the coil or If you look under the dash at the back of the tach you will see the gray wire, disconnect it then attach your meter to it and ground tape over your connection to the gray so it does not contact any other terminals under the dash while bouncing around. To do running checks the dash is better, you can lay the meter on the floor while you run. If your tach is off look on the back to see if there is either a switch to change cylinder numbers or an adjusting screw, either or should be cycled (moved) back and forth a few times this can clean the contact surfaces and get it reading right again

Phil

boatnut
08-15-2005, 02:31 PM
Thanks Phil, I will try attaching it per your advice. I just realized my dwell/tach unit is at my son's house in Sacramento so it will not get checked for a week or two. I did check and I think I have the thunderbolt V ignition system (at least I have two modules attached to the dist which looks like the picture in the merc shop manual). Therefore, I don't think the previous owner should have been able to run at 5400 -- I would assume the rev limiter is set to 4700 or 4800 being they suggest max wot 4200-4600. It is looking more and more like I should try a Turbo 23 as several have suggested?? I would like to check the tach soon though. Ed