Porpoising reduction advice please

[Robbie Racer]

This has been an ongoing frustration issue for me for the past 21 months that I have had my Carrera 257 cat. burningm Initially when I complained to my rigger (Greg Shoemaker at G.S. Marine) he said it might be a lack of horsepower thing. He thought the 598" blower motor that I had him install (built by a Lake Havasu builder) may not be putting out the 1100 hp that I was told it put out. Greg figured that the lack of power might be causing the porpoise problem. (I still have a problem with grasping that concept. I can see this type of a boat going slower because of a lack of power but not causing a porpoise situation). Anyway, Greg was right about that motor not having 1100 hp, but he was not right about it causing the porpoise problem. I now have a for sure 1180 hp motor and it goes faster but it still porpoises on smooth water. Now, it's even more scary when it porpoises at a higher speed. eek! The only way that I have been able to get the porpoise to go away is to add excessive trim (7-8 on the Bluewater scale which is about 6 or 7 degrees angle of "out" trim as compared with the sponson angle. At that angle the porpoise will almost always go away BUT, now I get between 18% prop slip with a WPM nose coned lower, to 25% prop slip with a Bravo Shop nose coned lower unit. I talked to Dean at the Bravo Shop today and he says something is drastically wrong for me to have to go to that much out trim to eliminate the porpoise. He says I shouldn't be more than 1 to 2% out trim (compared to the sponson angle) and that my prop slip numbers should be in the 8 to 10% range. My frustration level is increasing and I don't know any experts other than you guys to turn to. Any suggestions other than maybe trying tunnel tabs? Thanks, R/R

[hboldno7]

badblown572 will be able to answer any questions for you on the 257. He's not on the boards very often but shoot him a pm and im sure he would be more than happy to give you some advise

[HeavyHitter]

Have you tried different props? My boat's best speed is with a heavily cupped prop but is does porpoise a bit at speed. I run right around 1 degree of trim with that prop. If I change to a 3 blade cleaver it lifts the stern so much that I have to trim up around 3 degrees. Slip numbers aren't that bad but then again that prop is 16 1/2" in diameter. Put a 4 blade cleaver on and it's all I can do to hang on to the wheel to keep it from turning and I've got a full hydraulic setup. When I talked to John at Mazco (cupped prop) he suggests I lower the drive 1/2-1 inch to help keep the prop loaded. I know that's not easy to do with a bravo. I added a cavitaion plate to the center pod at step level to help get on plan and slow speed cruising. It helped at the top end as well. I've got to get some reference number before I add the spacer to see what it does to my speed. I'll let you know.

[gmnhra]

the solution to my 25 daytonas porpoise was to install dana marines hydraulic sponson tabs...
there is absolutly no porpoise at any speed and getting on plane is easy....
a bit on the pricey side but they worked....

[Bling Bling]

Robbie Racer:
This has been an ongoing frustration issue for me for the past 21 months that I have had my Carrera 257 cat. burningm Initially when I complained to my rigger (Greg Shoemaker at G.S. Marine) he said it might be a lack of horsepower thing. He thought the 598" blower motor that I had him install (built by a Lake Havasu builder) may not be putting out the 1100 hp that I was told it put out. Greg figured that the lack of power might be causing the porpoise problem. (I still have a problem with grasping that concept. I can see this type of a boat going slower because of a lack of power but not causing a porpoise situation). Anyway, Greg was right about that motor not having 1100 hp, but he was not right about it causing the porpoise problem. I now have a for sure 1180 hp motor and it goes faster but it still porpoises on smooth water. Now, it's even more scary when it porpoises at a higher speed. eek! The only way that I have been able to get the porpoise to go away is to add excessive trim (7-8 on the Bluewater scale which is about 6 or 7 degrees angle of "out" trim as compared with the sponson angle. At that angle the porpoise will almost always go away BUT, now I get between 18% prop slip with a WPM nose coned lower, to 25% prop slip with a Bravo Shop nose coned lower unit. I talked to Dean at the Bravo Shop today and he says something is drastically wrong for me to have to go to that much out trim to eliminate the porpoise. He says I shouldn't be more than 1 to 2% out trim (compared to the sponson angle) and that my prop slip numbers should be in the 8 to 10% range. My frustration level is increasing and I don't know any experts other than you guys to turn to. Any suggestions other than maybe trying tunnel tabs? Thanks, R/R Hey R.R.,
Sorry to hear your frustration. Porpousing sucks Ive dealt with this on a few boats before, quite surprised to hear that Carrera has a porposing problem at all. If you havn't done this yet..
try this, find out the correct X dimension of your boat and ask Carrera what it should be.
If its off try and correct it. Unfortunatley that means possibly changing the drive cut out in the transom depending which way you need to go. If your lucky just try drive spacers. If this helps out then start working with a good prop guy. Easiest way, find a person with same boat as you that is riding good and measure it.
Another suggestion get with someone who knows bottoms and check how the center pod is loading the drive with water. If you do decide to try a ride plate or some type of trim tab I've found that the full hydrallic adjustables are way better. Good luck.

[cjordan]

Robbie;
My Carrera had a very high X, so high that the only prop I could plane with was a Bravo. I would get porpose on flat water in that 70-85 transition, but could always drive right through it. A little trim never hurt. I never have experienced any porpose from 85-110 though. Late last season I put on a box and the boat did not porpose at any speed. (very limited test time) Before the boat needed little trim (ran near flat) now it definately like a little more. Its difficult to make Carrera's fly, they tend to run very flat.

[Robbie Racer]

Thanks for the feedback guys. I appreciate the response.
hboldno7: That's a good idea. I will send BB572 a PM.
HeavyHitter: I have tried a few different props but almost all of them have been Mercury Bravo 15.25" diameter 4 blades. (30 lab, 30 cupped, 32 lab and 34 lab). I also tried a Hydromotive 31 four blade. I had trouble getting the boat on plane with the Hydromotive and the Bravo lab 34. That's interesting about the experience you had with the 4 blade cleaver prop and the cavitation plate addition. Are you able to run 1 degree of trim with the 4 blade props even at WOT? I can run 1 degree up to about 75 mph, then it will start to porpoise on smooth water. That's when I have to accelerate hard while moving the trim out to 6-7 degrees to get it to stop porpoising.
gmnhra: Thanks for the info on the Dana sponson tabs. Did that addition affect your top speed at all?
Bling Bling: I did take the boat to Carrera and Dennis took a look at the drive (B-max) installation. We walked back to Bill Auberlins 257 that happened to be in the shop at that time and both looked to be the same. He said that Bills' boat doesn't have any porpoise at all. Bill's boat has a little different C/G as he has an open bow model and it is a heavier lay up. I had mine built with a light layup so that may be part of the porpoise problem. I did meet with another owner in Havasu with a light layup to see if he had this problem too. We have similar power with the main difference in that he is running a XZ drive. Our X dimensions are almost identical. He says he doesn't have a porpoise problem. That might be due to possibly rougher water at Havasu. I didn't have a problem there either. I do know a good bottom guy (Jeff Bennett)who used to help me with bottom work on my drag boat. I may contact him for help on this project too. Thanks for the suggestion.
Corey: Thanks for the info on the box. The 75 to 90 transition seems to be the worst part of the porpoise except for when after I have added all that trim and it has gone away and now we are flying along at 120 or so with a big rooster. At that point I try bumping the trim back down to reduce the prop cavitation. If I bump it more than a degree or two back down, it will start the porpoise again. At that speed it is a little scary when that happens. eek!
Thanks again for the great feedback. R/R

[midmagic]

Keith, what did I tell ya'? Tunnel tabs! Careful with the hydraulic tabs. They can get you in to big trouble quickly if you aren't aware!

[Robbie Racer]

Thanks Bill. It sounds like both the tunnel tabs that you have and the sponson tabs that gmnhra has will both help the problem. What are the pro's and con's of one of these solutions over the other? R/R

[midmagic]

Once you have set the fixed tabs in their final adjustment setting, you no longer have to deal with them. I have been told, and advised, not to run the hydraulic tabs due to the possibility of over/under adjustment at high speeds that could result in a VERY ill handling boat. They sound like a great idea, and boy did I want them, but was advised against them. Remember, you only crash one of these boats once at high speeds!!!

[gmnhra]

i suggest you call dana at dana marine and/or jerry may at eliminator regarding setups with hydraulic tabs in cats...
having the ability to adjust the setup without monkeying with turnbuckles, etc. is a plus...the concern for high speed mistake is a good one.. personally, i have setpoints on the bluewater that i aim for after getting on plane and don't touch the hydraulics after that....maybe a little drive trim here and there but not the tabs...too many other things to worry about!!!!
good luck
[ May 13, 2003, 03:03 PM: Message edited by: gmnhra ]

[jm2drvr]

everyone is right when saying be careful with trim tabs on a cat...after I installed them on my old cat, I would very rarely let anyone else drive it. With the tabs set incorrectly, it was a very scary ride!!!

[HeavyHitter]

RR, I run 1 degree at any speed above 50 with the 4 blade cupped prop. The cleavers lift the stern so they require more trim. The 4 blades are all long shaft so they also paddle wheel but then there aren't too many single engine offshore boats. A real drawback to having a speedmaster. I want to try a Hoss offshore 4 blade prop. Dave Bostic seems to know what he's talking about but the 16.5" 4 blade round ear is $2700. The same as a new 4 blade cleaver from Mercruiser.

[jlnorthrup122]

It sounds like you have your problem solved. When you swaped out your motor did you go with a lighter motor than your original? The reason I asked is that if your new motor is lighter than the original motor you would be moving you "Weight Center" Balance forward thus puting your teter in favor of the nose thus causing your boat to porpose with a longer wet surface @ plane. or vise versa frown
[ May 13, 2003, 08:41 PM: Message edited by: jlnorthrup122 ]

[Robbie Racer]

Thanks much for the additional info.
jlnorthrup122: to answer your question. The weight of both motors is within probably 50 lbs. of each other so I don't think that would have much effect on the C/G. That brings up another thought though. It doesn't seem to make much difference either if I have full gas tanks or mostly empty. That is about a 400 lb. difference. Since they are located in the back, you would think that would have a huge impact if this was a C/G issue. R/R

[SVO 540]

Robbie Racer,
If I were you, I would take the boat to Gary Teague of GT Performance and tell him to fix it.
He fixes all the ill handling Hallets and Eliminators. He is the guy the factories go to. Almost every time I am there, there is a boat in there that is being fixed for poor handling, set up, performance, etc.
You have been spending so much effort trying to fix this problem that it takes away from the enjoyment of your boat. Just take it to Gary, have him fix it and be done with it. It may cost you more that fixing it yourself, but I am sure you will be better off.

[Robbie Racer]

SVO, thank you for the excellent suggestion. What body of water does Gary normally take boats with handling problems to check them out? R/R

[gmnhra]

just for the record...svo540 is on the money...gary at gt is who did my dana sponson tabs...

[Robbie Racer]

gm: thanks for the feedback. I have never met Gary but I have heard only great things about him and his work on this forum. I will be contacting him. That does sound like the best way to go. Thanks again for all the suggestions, R/R

[midmagic]

gmnhra, what exactly are "sponson tabs"? Are they the same as tunnel tabs but just a different name? I am curious because I have never heard that term before. Thanks! :confused:

[cjordan]

I still think a box will solve your problems. Your boat will plane better and you can experiment with different drive heights. It will definately step over bigger water with less effect on ride quality.
[ May 16, 2003, 05:17 AM: Message edited by: cjordan ]

[Boatmaster]

Try taking the motor out and clipping some 300Xs on the back :D

[cjordan]

Eggbeaters.... :p :p are just wrong on a Carrera.

[Robbie Racer]

gm: I'm with Bill in that I would like to understand how sponson tabs work too. Corey, I think I will ask Gary Teague to take the boat for a ride and then ask him which solution he thinks would be the best one for my situation and go that direction. Boatmaster, I would consider a couple of clamp on's but my motor guy needs a job. :D

[gmnhra]

take a look at the dana marine website. there are some pics of thier sponson tabs and tunnel tabs...the sponson tabs are attached below the step on the outside of each sponson..they extend the running surface of the hull...tunnel tabs are attached above the tunnel portion of the hull...
the hows and whys are beyond me..all i know is the sponson tabs worked for me.....
gm

[SVO 540]

Robbie Racer,
You will be happy with your decision to contact Gary. His number is 909 982-8391
I know he is busy so you may want to call soon so he can get you into his schedule.
Gary tests at Lake Elsinore. You should suggest meeting him down there at a time when Gary will already be there testing another boat. This gives him a chance to go for a ride in your boat and he doesn't need to make a special trip for you. After his test ride you could then talk about your options.
I really think this is the best way to go, but it is only my opinion.
SVO 540 - OUT

[DogHouse]

So while we're on the subject of modifying a cat's manors, can anyone comment on the use of tabs or k-planes to get a cat to stay on plane and nose down at tubing/wakeboarding speeds? My boat doesn't have a porpoise problem, but when my kids get a little older I will be spending a lot of time dragging them around on water toys. I'm pretty sure that the boat won't be happy at that speed. Has anyone used some of the longer style tabs on the sponsons and noticed a difference in planing speed?
thanks,
-Brian

[gmnhra]

doghouse...
i put the sponson tabs on my daytona for two reasons..the porpoise issue discussed above and for the exact reason in your question..yes, my gt performance whippled 540 cat is also a wakeboard boat...with the tabs down all the way the boat planes easily at around 20 mph...
gotta keep the wife and kids happy...
gm

[Robbie Racer]

SVO: Thanks for the phone number for Gary. I just got off the phone with him. He thinks that based upon what I told him, that my X might be too high to carry the bow like it should and that is why I have to give it excessive trim. He suggested putting a 1" spacer in the drive and giving that a try before I drag the boat down to So. Calif. to meet with him. I will look into what parts I need to buy in order to do that. Thanks again and I will keep you posted. R/R

[andy01]

You can't go wrong with Gary! He rigged my boat and I love his work!
DogHouse you might call John West at Ultra about the big tabs. I know he has put some on a couple of his 27 Shadows for customers. Ask him what it does to the handling and what not of his boat, then call Gary to instale them. On another note I can drive my cat at 30 mph (GPS) and it stays on plain and handles fine, I know you are putting together a new motor for yours which means you will be running a big prop. You might not need anything at that point, some times everything changes with prop and motor changes.
Andy

[DogHouse]

Thanks for the tips. 30 is good, 25 gets mushy depending on load, 20 is out of the question unless you like that max fuel burn setting where half the water in the lake is getting drug along behind the boat, you know, that speed that newbies like to cruise through the no wake zones!
GMHRA that's pretty good that you can plane cleanly at 20 with the tabs. That's exactly what I'm hoping for.
RR, I will probably continue to run my 28p most of the time but may buy something bigger as a second prop for speed runs. The motor makes plenty of torque to hop on plane even with the 28, but I suppose something smaller would be more efficient at ski speed. That would just seem too strange to put a 22 or 24 on an 800 hp cat!

[roln 20s]

but when my kids get a little older I will be spending a lot of time dragging them around on water toys. I'm pretty sure that the boat won't be happy at that speed. Doghouse-
No need to worry. I have you covered. You should spend time getting your boat to go faster...and I will keep the Malibu ski boat handy for your kids when they are ready for a tow. Easy trade off-I don't mind towing them around (or you driving my boat) whenever they want to. My boat will plane at 14 mph, NO tabs :D
The offer for a free ski towing is open to all...and I challenge anyone wanting to Tube :D
Roln 20s

[DogHouse]

Cool, I'll just them over to "Uncle Roln's" house and they can pester you to go to the lake all the time, thanks!!! :D