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Hey all. Was just trying to pick some brains here. I have a '06 247 genesis with a 496 HO runnin I belive a 4 blade 24p prop. I have 30 hours on the motor and I have gotten the boat up to 78mph on the speedo.( save it I know this is off because a regular speedo isn't accurate.) I was at 75mph before at about 20hrs. Is this thing gonna wake up even more? Oh by the way the way I am hitting 4800 rpm trimmed out. Oh the other question. If I changed out props what would give me better top speed? and what does labbing do. and what does it mean? thanks in advance. One more question. If Merc says that the optimal rpm range is 4600 to 5000 does that mean that I cannot exceed this range?.....thanks again.
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I have an Ultra 247 with an HO and run a 26.5P labbed Bravo 4 blade. I run 79 mph on GPS. But, I do need the trim tabs when going that fast.
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I have an Ultra 247 with an HO and run a 26.5P labbed Bravo 4 blade. I run 79 mph on GPS. But, I do need the trim tabs when going that fast.
thor I wasn't quite sure. But is the 247 genesis the mold form Ultra? I know they aquired it from someone just wasn't sure exactly who. What are you rpm wise. And what did it cost ya for the prop? When you ran that fast what where the boat conditions. Alone? gas at what level?...I know what you mean. When i ran that fast the boat started to walk on me. Was thinking about gettin some tabs from Eddies marine.
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It's not possible to go over 73mph with a 24 pitch prop at 4800rpm. That is the max speed with 0% prop slip.
At 10% prop slip your speed would be 66mph at 4800 rpm's.
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It's not possible to go over 73mph with a 24 pitch prop at 4800rpm. That is the max speed with 0% prop slip.
At 10% prop slip your speed would be 66mph at 4800 rpm's.
So the speedo is that far off? I swear the damn thing said 78. at 4800 rpm. Sorry for the ignorance but what is prop slip?
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Sorry for the ignorance but what is prop slip?
Here:
http://sites.mercurymarine.com/porta..._schema=PORTAL
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So the speedo is that far off? I swear the damn thing said 78. at 4800 rpm. Sorry for the ignorance but what is prop slip?
I don't know all the calculations for prop slip and all that. If you do a search you should find it. What I do know is you may be mistaken about your RPM or you got a bum deal and paid for an HO and only got a 496 Mag. Max RPM on the 496 Mag is 4800 whereas the HO max RPM is 5300 I believe.
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So the speedo is that far off? I swear the damn thing said 78. at 4800 rpm. Sorry for the ignorance but what is prop slip?
In a perfect world for every revolution of your prop your boat will move forward 24 inches. That doesn't happen. Your prop will slip and you won't move forward a full 24 inches. The less slip, the more effecient your prop and set up is. Mathematically your boat can only go so fast at a given rpm with different sized props.
Unless your speedo is gps it could have very well said 78. :D
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I don't know all the calculations for prop slip and all that. If you do a search you should find it. What I do know is you may be mistaken about your RPM or you got a bum deal and paid for an HO and only got a 496 Mag. Max RPM on the 496 Mag is 4800 whereas the HO max RPM is 5300 I believe.
I think the HO is 5150.
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Nice link.
:cool: I figured it would be alot less typing this way.
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Moving a full 24 inches forward without some slip could hurt someone.
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Okay thanks for the info guys great work. Lemme throw one more at ya. How can I tell if my boat will handle a 26p?
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I think the HO is 5150.
Giving an average prop slip of 40% then he would have a max speed of 70.22 mph
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Okay thanks for the info guys great work. Lemme throw one more at ya. How can I tell if my boat will handle a 26p?
Easy. If you are at 4800 out of 5150 RPM. You are overpropped already. I was in the same boat (no joke intended) as mine came with a 24 on it. I was at 4850-4900. Went to a 22 prop and went right to 5100 and up a few mph. Try a 22. If you hit the limiter (5150) then you need a labbed 24.
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I am gonna check I might have been mistaken with the 4800 rpm thing. I am gonna run it this memorial and see what happens. Find out what the rpm truly is at. Boat load won't affect RPM correct? If I am at 4800 I will need to go down in prop if I am hitting 5150 then I will need to go to a 24p??
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I am gonna check I might have been mistaken with the 4800 rpm thing. I am gonna run it this memorial and see what happens. Find out what the rpm truly is at. Boat load won't affect RPM correct? If I am at 4800 I will need to go down in prop if I am hitting 5150 then I will need to go to a 24p??
Yeah, a heavy load will knock a little RPM off. Load the boat like you are going to run it, though. Don't cheat by leaving only enough fuel for one run and leaving everyone standing on the dock.
WOT and trim it up until the RPM raises a little. You will feel the boat "air-out" and run a little smoother. Let it settle a few seconds and see what the RPM levels out at.
If you HAVE A 24 NOW, and you are stable at 4800 - you could either have it labbed down to a 23-ish or just go with a stock 22. Although a stock 22 would probably put you into the limiter or right at it.
If you HAVE A 26 NOW, then you would need a labbed 26 down to 25 or so. Or just a stock 24.
I kept my 24 after buying the 22. Gives me an extra prop just in case, and also if I add a few more HP, the 24 would be just right and I could keep my 22 for high altitude or just that nice bottom end punch.
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Giving an average prop slip of 40% then he would have a max speed of 70.22 mph
You must mean 4%
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You must mean 4%
OR maybe 14 on the high end? Maybe 40% if it's tied to the dock
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I am gonna check I might have been mistaken with the 4800 rpm thing. I am gonna run it this memorial and see what happens. Find out what the rpm truly is at. Boat load won't affect RPM correct? If I am at 4800 I will need to go down in prop if I am hitting 5150 then I will need to go to a 24p??
Do you have a Smartcraft gauge on your HO? My Livorsi tach reads 300RPM higher than the Smartcraft at WOT. I'm not sure which one is correct, but the rev limiter is tied to the the computer/Smartcraft. When I was figuring out prop slip, best prop, etc. I used the Smartcraft, my GPS speedo and a handheld GPS to dial it all in. If you don't have a Smartcraft, a lot of shops have a hand held gauge that plugs into the cannon plug on the top of the engine. IMHO it is the best way to get an accurate reading on RPM vs. speed.
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Mine hits about 5000-5100 rpm. My lab job cost me about $300. I took him a stock 26P and he took out some cup and pitched the prop up one pitch to make it almost a 27P. My boat ran 79 when it was me and a buddy with no gear and about 10-15 gallons of fuel I am guessing.
The prop calcs are pretty good estimates for how fast you should be going, but they dont take into consideration the hull type, weight, x dimension etc. So, like I said, it is an estimate.
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Try this calculator. Again, it's an estimate, but this one takes into account hull length and weight.
http://www.boatpropellers.com/
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Do you have a Smartcraft gauge on your HO? My Livorsi tach reads 300RPM higher than the Smartcraft at WOT. I'm not sure which one is correct, but the rev limiter is tied to the the computer/Smartcraft. When I was figuring out prop slip, best prop, etc. I used the Smartcraft, my GPS speedo and a handheld GPS to dial it all in. If you don't have a Smartcraft, a lot of shops have a hand held gauge that plugs into the cannon plug on the top of the engine. IMHO it is the best way to get an accurate reading on RPM vs. speed.
No. I am running Faria Guages. I was thinking about a GPS speedo..but the guage. $140 + the receiver $200. For that price I was considering getting just a handheld with maps for the same price.
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You must mean 4%
Nevermind me. It is the angle of attack that is 40. I was reading and started computing stuff and it seemed to work. I was all happy to figure it out and now I realize I'm a dumba$$.
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No. I am running Faria Guages. I was thinking about a GPS speedo...Handheld GPSs work great. Mine and the one in the dash are always in agreement. Any MAG or MAG/HO (or Blue motor) can be purchased with the big expensive Smartcraft display or a small, much more economical digital gauge. It tells you water temp, water psi, oil psi, oil temp, RPM, gallons/hr, trouble codes, etc., etc. You may think about adding it at some point. It's obviously not as easy to see as a dial gauge, but is a valuable tuning tool.
A Smartcraft 1000 looks like this:
http://www.***boat.com/image_center/...2442SC1000.gif
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Try this calculator. Again, it's an estimate, but this one takes into account hull length and weight.
http://www.boatpropellers.com/
The weight and length does not effect that calculator. I tried different weights and length and it still gave me the same speed? Must be a gimmick to make you think it is different than the rest.
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The weight and length does not effect that calculator. I tried different weights and length and it still gave me the same speed? Must be a gimmick to make you think it is different than the rest.
You are exactly right. Prop calculator neglect the weight and type of hull. Those two things just so happen to be some of the most important factors. Prop calcs suck in general.
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You are exactly right. Prop calculator neglect the weight and type of hull. Those two things just so happen to be some of the most important factors. Prop calcs suck in general.
But if you are going faster than your theoretical speed, you know you have a problem. :)
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But if you are going faster than your theoretical speed, you know you have a problem. :)
On GPS, I have done 79.8 mph with a 27P Bravo labbed.
I have many problems, my prop is just one of them. :cool:
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On GPS, I have done 79.8 mph with a 27P Bravo labbed.
I have many problems, my prop is just one of them. :cool:
Were you throwing the GPS towards the front of the boat when you got these #'s. :)
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On GPS, I have done 79.8 mph with a 27P Bravo labbed.
I have many problems, my prop is just one of them. :cool:
With 1.5 gears and 5000rpm your theoretical speed would be 85mph so I see no problems here. :)
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Were you throwing the GPS towards the front of the boat when you got these #'s. :)
I never said the boat was running nor did I say it was off of the trailer when I got those speeds.
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Okay so to put this to the test I just purchased a Garmin handheld Etrex. with top speed and all that. This should make my tests accurate this weekend. I will post some results and do a confirmed check on my RPM's. Then maybe with yer help i can make a better prop decision. Thanks guys. oh anyone use a Garmin Etrex? This should be fine and accurate right?
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Sweet, keep this going and post what you get this weekend. I have a 24' cat with an HO. I've only been out a couple times and had a 4-blade 26 on it. I have a 24 I want to try but haven't yet. Best speed I saw was 59-60 and I have no idea what my RPM's were at the time. I'd like to see what you come up with
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Okay Guys, here is the final results. i was running 64.9 MPH on the HH GPS. I had 7 people aboard and a full tank of gas and gear. I am running a 24P at 4800 rpm's. I took a few poeple out and at half fuel i was running 69 flat. This was with 4 people in it and about half tank of gas with about 5000 rpm's. last run was with 3 people and i was able to hit 72.3 with just under half fuel. and i was at 5050 rpm's. I haven't ran it with myself solo or just one other, because i would never run by myself. Hopefully. Okay so once again i am wondering. Which way do i need to go with the prop? do I drop down a blade? do i need to Lab the prop? I get onto plane pretty fast and so i would like to pick up as much top end as possible. Any suggestions? Thanks again for all your help.
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3 people w/ half a tank and at 5050 rpms is damn good. I would lab it and take some cup out. That is just me though.
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Thanks Thor. Do I just lab my 24? Anyone else? recommendations?
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RI , weigh your boat minus the trailer . I do my calculations based on a close approximate weight and the speed came out very close compared to my GPS . > calculations = 74.64 , my reading last saturday out >http://www3.telus.net/spectrasonly/Gaffrig
Genesis' website is off here on ***boat to check the dry weight of your boat .
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York in Placentia is the man. He is the only one I trust.
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http://www.rbbi.com/folders/prop/propcalc.htm
Here is another speed calc that just has the needed variables. I have found these formulas to be highly accurate.