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Porpoising
I'm running a Active Thunder Tantrum with a 500 HP. Bravo 1 drive with a labbed 28 pitch Bravo 1 prop. Mercury racing did the work. At 5250 rpm I'm running 75 mph on gps. The boat wants to porpoise starting around 65 mph mark. I also see some chime walking as well but this was reduced a little after i placed the 28 pitch that Mercury racing worked on for me.
When I purchased the boat it was running a Bravo 1 26 pitch and running at the 5300 rpm range and hitting 74 mph. This prop porpoised bad. I have no idea what was done originally to the prop other then the probably added some cup to get the rpm down. What can be done when it comes to props to eliminate porpoising and gain top end? Thanks in advance, Mike |
Re: Porpoising
Mike,
I have calculated your slip with the 28P Lab Bravo I and you have 16% slip. This is a little Higher than I would like to see for your boat. You have 14% with the stock 26P Bravo I propeller, which falls into the acceptable range of 10-14%. So with this I think that you should consider working the 28P Bravo I Lab propeller and increase the cup to see if you can take the edge off of the porpoising. It is also possible that a 5B propeller may assist in decreasing the behaviors as well. They will create more lift and require a different amount of trim, possibly affecting the behavoirs....not sure how though. Testing is key in your situation, hopefully finding a propeller to take the edge off. Julie |
Re: Porpoising
throttle up-
does the cupping of a prop inprove a porpoise problem? assuming that the hull is flat on the bottom......what is actually going on when a boat does porpoise? kevin |
Re: Porpoising
If the 28 Bravo 1 decreased the porpoising after the Lab Finishing, I wouldn't add more cup to it. You stated the 26 porpoised worse. The 26 would have more cup than the 28 since it wasn't Labbed. Also the slip % on a Labbed prop can be higher than a box stock prop. A 5 blade is going to lift the stern more and if the prop can't hold the bow now, 5 blades may be worse. Be sure to try a 5 blade before you purchase one.
Have you inspected the bottom of your boat to make sure the running surface is true? Also how deep is the prop? |
Re: Porpoising
EYEBURN
I started to write the last post and had to walk away so it got posted without seeing your post. Porpoising can be caused by numerous reasons. Boat bottom hooks and rockers are key factors. Prop depth and prop choice can be a large factor too. The propeller attempts to raise the bow by leveraging the stern. As the weight increases the prop looses its ability to support the bow and down it comes only to start the process over again and again. |
Re: Porpoising
I was told by Mercury Racing that shorting the prop barrel that it would create more stern lift and possibly decrease the porpoising.
Your thoughts? |
Re: Porpoising
Originally Posted by bbladesprops
If the 28 Bravo 1 decreased the porpoising after the Lab Finishing, I wouldn't add more cup to it. You stated the 26 porpoised worse. The 26 would have more cup than the 28 since it wasn't Labbed. Also the slip % on a Labbed prop can be higher than a box stock prop. A 5 blade is going to lift the stern more and if the prop can't hold the bow now, 5 blades may be worse. Be sure to try a 5 blade before you purchase one.
Have you inspected the bottom of your boat to make sure the running surface is true? Also how deep is the prop? I missed your last question when I read your reply. My boat was built by active thunder for Smith Brothers Race Team. It was raced in the F1 series in it's first year. Not sure what was done with the hull. I know that it has no hook, might have a touch of rocker. Are you referring to my X dimension when asking about my prop depth? Not defendant on how to measure that. |
Re: Porpoising
Who at Merc Racing told you that about the barrel? Scott or Ron?
If you have the chance, give me a call. I can't give away all the trade secrets on this board. It's obvious by some peoples comments on other threads, I'm already giving away too many secrets. Hehehe. (just kidding, I know this forum is here to help and we all do the best we can.) |
Re: Porpoising
Will a rocker cause a boat to chine walk?? My Powerquest has what I would call two rockers, one on each side at the transom right where my tabs are located.
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Re: Porpoising
Okay if we are talking porpoise, here's my question. I have a Formula 311 running 502 MPIs through Bravos. It spins stock 26 Bravo 4 blades to 4600 rpm light at 70 mph. BUT I have to run tabs to about 6 in any but the smoothest water or it constantly porpoises. So, do I need more or less bow lift and should I think about maybe a 24 or labbing the 26's? Props are turning out right now.
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Re: Porpoising
1 Attachment(s)
Well here's a a pic of what I refer to as a rocker. Would I be correct? Also I would assume that it only helps out when coming on plane and after that I would think has no effect being its out of the water?
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Re: Porpoising
Originally Posted by Fast Forward
Well here's a a pic of what I refer to as a rocker. Would I be correct? Also I would assume that it only helps out when coming on plane and after that I would think has no effect being its out of the water?
do you mean the tabs?? rocker is- curve in the boat hull. ie. think of a rocking horse. front to back. hook- is just the opposite. ie. same rocking horse with the rails on upside-down. Hook (noun): The shape of the hull where the bottom is concave, rather than at or near the transom. Opposite of a Rocker. A hook can be caused by insufficient support from the Trailer, failure of the Hull, or actually designed into the hull Rocker: The shape of the hull where, rather than being flat it takes on a convex shape. Opposite of Hook. Can be caused by insufficient support from the trailer or failure of the hull. Almost never an intentional design characteristic of the hull. |
Re: Porpoising
Originally Posted by bbladesprops
Who at Merc Racing told you that about the barrel? Scott or Ron?
If you have the chance, give me a call. I can't give away all the trade secrets on this board. It's obvious by some peoples comments on other threads, I'm already giving away too many secrets. Hehehe. (just kidding, I know this forum is here to help and we all do the best we can.) It was Ron that I have been dealing with. If I get a chance Friday I give you a call. Thanks, Mike |
Re: Porpoising
If you look closly at the hull right behind the tabs about a foot foward you'll see that the chine starts to get smaller as it goes back to the transom.
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Re: Porpoising
Active Mike, ok call when you have a chance.
insptech, I would try turning them in as an experiment. Then I would Lab Finish the 26's. |
Re: Porpoising
Originally Posted by bbladesprops
Active Mike, ok call when you have a chance.
insptech, I would try turning them in as an experiment. Then I would Lab Finish the 26's. I didn't forget about you. I have been swamped during the week and have had no time to call. Can you be contacted on weekends? Thanks in advance, Mike |
Re: Porpoising
Originally Posted by biginches
ff,
do you mean the tabs?? rocker is- curve in the boat hull. ie. think of a rocking horse. front to back. hook- is just the opposite. ie. same rocking horse with the rails on upside-down. Hook (noun): The shape of the hull where the bottom is concave, rather than at or near the transom. Opposite of a Rocker. A hook can be caused by insufficient support from the Trailer, failure of the Hull, or actually designed into the hull Rocker: The shape of the hull where, rather than being flat it takes on a convex shape. Opposite of Hook. Can be caused by insufficient support from the trailer or failure of the hull. Almost never an intentional design characteristic of the hull. |
Re: Porpoising
i don't know for sure, but it's not usual that the manfacturer puts a rocker in the hull.
sometimes they intensionally put a hook (convex) in a boat to keep the bow down. you can take a straight edge 4' to 6' long and hold it to the bottom of the hull.the straight edge needs to be very true, because anything more than a 1/4 gap between the straight edge and hull is a hook. |
Re: Porpoising
Active Mike,
No problem. Call whenever you get the chance. Saturdays are mostly spent on the water. However this time of the year it gets cold around here. Try anytime and if we don't answer, we'll get right back to you! |
Re: Porpoising
Originally Posted by bbladesprops
Active Mike,
No problem. Call whenever you get the chance. Saturdays are mostly spent on the water. However this time of the year it gets cold around here. Try anytime and if we don't answer, we'll get right back to you! I'll see how the week goes. If not I'll try this weekend. I want to pick your brain a little on this prop. Thanks, Mike |
Re: Porpoising
My Kevlar Top Gun was like flipper under 70mph in any kind of water even with negative trim and also required 7 plus on trim tabs.
We tried every prop known to man, no change. We finally lowered the drives 1/2" which brought us to 4 or 5 on the tab scale, still not good enough. It wasn't until my motor guy's at Diamond Performance filled in a hook that I couldn't see,even with a 6' level that my problem was solved completely. I would have some one look at your hull,i'm glad I did, other than to keep my boat tight in the rough we now require zero tab and she will take positive trim at cruise speeds or less. Good Luck! |
Re: Porpoising
Originally Posted by WildWarrior
My Kevlar Top Gun was like flipper under 70mph in any kind of water even with negative trim and also required 7 plus on trim tabs.
We tried every prop known to man, no change. We finally lowered the drives 1/2" which brought us to 4 or 5 on the tab scale, still not good enough. It wasn't until my motor guy's at Diamond Performance filled in a hook that I couldn't see,even with a 6' level that my problem was solved completely. I would have some one look at your hull,i'm glad I did, other than to keep my boat tight in the rough we now require zero tab and she will take positive trim at cruise speeds or less. Good Luck! Did the hook drop your top end at all? |
Re: Porpoising
Originally Posted by Active Mike
Wildwarrior,
Did the hook drop your top end at all? More important to us than the extra speed, now with the hook removed our boat just handles way better at any speed, and know longer rides like flipper with out a ton of tab! Good luck! |
Re: Porpoising
Originally Posted by WildWarrior
We found 6 mph or so in the hull alone ,and i,m not talking a total blue print job.
More important to us than the extra speed, now with the hook removed our boat just handles way better at any speed, and know longer rides like flipper with out a ton of tab! Good luck! I thought having hook would prevent porpoising not removing it? You said that you had it filled correct? The shop that you had do the work are the experienced at this? Also you live in Pa? Thanks, Mike |
Re: Porpoising
Originally Posted by Active Mike
WildWarrior,
I thought having hook would prevent porpoising not removing it? You said that you had it filled correct? The shop that you had do the work are the experienced at this? Also you live in Pa? Thanks, Mike |
Re: Porpoising
Mike, I'm gonna take a guess that his hook was acting like a see-saw. The hook was trying to lift his stern, and force the nose down, and the props are trying to sink the stern, and lift the bow. When the hook was removed it allowed the props to lift the bow, sink the stern and help keep the props loaded.
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Re: Porpoising
Mike,
Our boat runs better with her drives 1/2" lower than stock and others perform better with shorties. I quess what i'm saying is that there are know exact clear cures for your problem. I was told the same thing in regards to my hook,however in conjunction with the other steps ,lower drives,more power and hook removal we have solved the issue on our hull. Rudy & Bill @ Diamond Boat Performance in Wilmington DE do all my work, blower motors, rigging etc. The important thing is finding a blue print guy that already knows your specific hull and set up. Manufactures all have subtle differences in their designs to help them plane out etc. Good luck and if you need some phone numbers feel free to pm me.! Glen |
Re: Porpoising
WildWarrior,
Thanks for the follow up. I may take you up on those numbers. I live in about center Pa area so if I have to look for some one that is good at working on hulls I would prefer to use some one with a good track record. Monkey Spanker, I wasn't really looking at it that way but I guess that could be very possible as well. I would guess that you ran that 23' Rinker in the Susquehanna river? |
Re: Porpoising
Yup, thats me.
I've been bouncing a few ideas around on here to see if, or how much, more power I wan't to stick in the thing. I have to tear the Chevelle motor down to drop the compression, so I thought I'd put the heads and Dominator on the boat motor. It should throw it well over 600 hp and let me chase down a certain Pachanga!!!!!! The other option is a blower, but with 9.2 comp I'd be boost limited. I talked to artic friends,(Smitty) about his bottom on his Baja, and he's going 92 on a stock bottom, which I think is as close to my hull as any. The only real limiting factor is the drive, everybody always asks, how much power will a stock bravo handle................Wally. |
Re: Porpoising
Originally Posted by Monkey Spanker
Yup, thats me.
I've been bouncing a few ideas around on here to see if, or how much, more power I wan't to stick in the thing. I have to tear the Chevelle motor down to drop the compression, so I thought I'd put the heads and Dominator on the boat motor. It should throw it well over 600 hp and let me chase down a certain Pachanga!!!!!! The other option is a blower, but with 9.2 comp I'd be boost limited. I talked to artic friends,(Smitty) about his bottom on his Baja, and he's going 92 on a stock bottom, which I think is as close to my hull as any. The only real limiting factor is the drive, everybody always asks, how much power will a stock bravo handle................Wally. Also what kind of speeds are you seeing out of your 23' on GPS now? Do you run the river every week? Just trying to figure out what boat you are. The rumor is that the bravo's are good for 600 hp range but a lot of it is how you run it and I know that there is larger horses put on them. Mike |
Re: Porpoising
There are two Pachangas on the river and the same guy owned them both. He sold one with a 454 in it, and got another with a 502. We(Mike with the Scarab and I) already got the 454 one, but I'd like to catch the other. Only because these things seem to have some VOODOO ledgend about how fast they are. I have a 496 now with 521 hp on the dyno, but so far 68.9 on the river(69.8 down by the bay at sea level). I still run through the mufflers, and havn't had the prop labbed yet. I'm going to dump the mufflers this winter and put a crossover on. That and the prop should get me 73-74, if I add the top end off my car, with a little luck....80 ???????? I bought the boat last fall from the insurance company after it sunk at the guys dock, so far I only have about $11,000 in it.
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Re: Porpoising
Originally Posted by Monkey Spanker
There are two Pachangas on the river and the same guy owned them both. He sold one with a 454 in it, and got another with a 502. We(Mike with the Scarab and I) already got the 454 one, but I'd like to catch the other. Only because these things seem to have some VOODOO ledgend about how fast they are. I have a 496 now with 521 hp on the dyno, but so far 68.9 on the river(69.8 down by the bay at sea level). I still run through the mufflers, and havn't had the prop labbed yet. I'm going to dump the mufflers this winter and put a crossover on. That and the prop should get me 73-74, if I add the top end off my car, with a little luck....80 ???????? I bought the boat last fall from the insurance company after it sunk at the guys dock, so far I only have about $11,000 in it.
I'm presently setting on 75 mph now and looking for more myself. I'm trying to dial out some porpoising that I get over 60 to 65 mph. Not sure if I have seen one of these Pachangas, what does it look like? |
Re: Porpoising
Yes it was local, if you haven't put yours away for the winter, your more than welcome to try my 25 mirage plus and 25 Rev 4 to see if it helps your porpoising. There is a pachanga on ebay right now, they're made by Sea Ray.
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Re: Porpoising
Originally Posted by Monkey Spanker
Yes it was local, if you haven't put yours away for the winter, your more than welcome to try my 25 mirage plus and 25 Rev 4 to see if it helps your porpoising. There is a pachanga on ebay right now, they're made by Sea Ray.
She's already put away and setting in her heated home. I have a 26 Bravo 1 with a lot of cup added to it so that I'm not over spinning it and a 28 Bravo 1 that was labbed and that puts me right at the 5300 that I'm looking for. Thanks for the offer. I'll have to check out these Pachanga's. Thanks again, Mike |
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