Trying to get rid of porpoising
 

I have a 28 Pantera with 425hp 454's and number III drives. Right now it has 4 blade 28 pitch props on it. It will only turn those to around 4200 rpm's and it porpoises bad. I was wondering if going to a set of 3 blade 27 pitch props would help it out? I have only used the boat for one weekend so far and the water was smooth so I don't know how bad the porpois is in rougher water.

Sorry they are 26 pitch 4 blades right now.

You have too much prop for one. What shape are the ears on the current props? Does your boat have tabs? If so , at what deployment do they alleviate the porpoise?

I think the 23-24 P will be close. If you can't find a set to test with, BBlades has a nice loan/swap program.

K planes need to be about 3 to stop it and it does not run free at all, you can feel the bow being held down. Which props are better for porpoising 3 or 4 blade? The boat used to have 600 plus hp and ran in the 80's with these drives and props. The guy I bought it from put these 425 hp motors in it. Will weight in the bow help, you think?

What diameter are your props now? If they are under 16 I would say try A larger diameter and down in Pitch.

My 33 fountain had III's on it and I had the same problem. I went up in diameter and down in pitch. I had 26x16.5 and I picked up 8 mph. Felt like a different boat. I also tried some 29 x 17 three blades and they ran the same top end but lost some on the cruise.

I think they are 15 3/8 x 26 now.

So more diameter would increase transom lift, correct? Is that what I need to stop the porpoising, transom lift? Do I need to get 16 or bigger, or would a 15 3/4 3 blade be better than what I have?

Excaliber, did you also have the same rpm problem or were you always able to turn around 5000? How many hp you have?

You need more bow lift that is why your getting the porpose.It can't carry the bow and it falls it's better in rough water and worse in flat right? You can try to spin the drives in that might help. I would try to find a set of 16.5 x 25 or 24 three blades that would probably work. It's going to be hard to find props in the smaller pitch sizes in the 3's they are just getting hard to come by.

Which would be better to 4 blades or 3?

Would the 4 blades carry the bow better? Would 16 X24 4 blades be better than 16.5 X 25 3 blades?

Depends on the prop, they are all designed for different lift, bow/stern/neutral. I personally would try the 4 blades first, depending on what they are. I am running 3 blades, and get a bit of porpise at slower speed because they cant quite carry the bow and it falls on its face. Throttling up past that point makes it go away. I was told 4 blades would help a lot (Bravo 1's)

I have a 271 sr-1 Formula that I'm going through the same stuff right now I have a labbed 24 B1 4 blade that does no porpose and a 25p Mirage that is porposing and I just Overreacts to trim in the rough stuff. Top speed is better w/ 3 blade but overall I like the 24p Bravo One. IMHO

you want the biggest diameter the boat will allow meaning that you want to keep in increasing the diameter until the boat starts to chine walk or act stupid. when it does this, it means the stern is lifting to much. i will explain more later, have to run...

The only problem I think your going to have is if you can't spin the 26 x 15 3/8 over 4200 your definitely not going to be able to spin a 24 x 16.5 5,000. I think you might have a 1.3 gear ratio.

have you called pantera yet???? those guys have been around longer than almot anyone in the business and im sure they can help you out....

Try one of the prop companies... BBlades or ThrottleUp.

I do have the 1.3 ratio. Is that what you have to excal?

Yeah i had them sold them and did bravo's. You should see if someone would trade you for 1.5's . Then you would be able to find more props. Try to call bblades or cobra power or murphy's prop shop. They might have something for you.

+1 for Brett @ BBlades

NEED.....MORE......POWER :party-smiley-004:

I warned you it was going to have a bad purpoise....... I would try redistributing some weight with sand bags first, but I think you will be stuck with it no matter what you do. I have read several testimony's from owners about 28 panteras with twin big blocks having a bad porpoise and I have riden in one so I can verfiy. Most don't realize just how bad it really is. Generally, it should ride much better in rough water, but could also lead to a nasty stuff.

Now were are all those pantera owners that said 28 pantera's with twin big blocks don't have a bad porpoise?

His pantera has number III's totally different animal than a bravo boat.I actually was going to buy that boat. Taked to the guy and was on my way down but I got such a good deal on this fountain could not pass it up.That was a good deal you got and a nice boat.I read here some where that there was weight in the front of the boat.

Like Excal said totally different boat. I had a 99 twin bigblock 28 and it did not have this problem so I know. Sooner or later I will get it right, got to find some props to try, and some day like RT said MORE POWER:drink::drink::drink:

Excal you had me worried when you was looking at it and then you had me relieved when you got the fountain, I was happy. I have been talking to the owner for 2 1/2 to 3 years about this Pantera before he finally came close to my offer. I love this boat like it is, it is different, just have to get it riding as good as possible. Good thing that I have a life time to do it, LOL.

I have a 89 with twin big blocks and I have NO porpoise. I have trs drives with 2" spacers and the props turning in.

bb28, check your xdim... you may need to get deeper.
There is a thread in the cig forum similar to this, it may be of help.

The right props can most likely fix the problem. Putting the drives deeper is an easier and cheaper way but you will also scrub speed. It may mean trying about 20 different props but I can almost bet you will find some that straighten it out.

You might want to check the bottom of the boat to make sure it's straight. From the transom to about 6 ft. up. Also I agree with the more power thing. I bet over 70 it would smooth out.:evilb:

Storm, the shafts are about 4" below the hull and Jo said that is about right.

It does get better the faster you go. I just need to get a 40-50 mph cruise without the crazy porpois and not have to use any trim and alot of tab. I don't like the stuck in the water feeling.

My boat was thw same way and it sucked to get on plane too. It also felt like i was draging an anchor but I tried some props and that was it.There was a set of 17x24 four blades on here in the swap shop that might be the ticket.

I will check for those props or if you know where they are let me know. I checked on a few that I found on here and they were all sold.