311...porpoise...
 

My 89 311 has 330hp and I bought a set of hydromotive 24 pitch 4 blades and put them on before I ever ran the boat. So wide open full of fuel it only turns 4000 rpm...but once it gets lighter on fuel I can turn the motors too around 4200. Problem is once I start trimming out it had a horrible porpoise...I guess either the boat just isn't fast enough to run through the bouncing or the props are causing it. Who has ran bravos on their boat? Any issues with them? Also boat only runs 60mph wide open. Thinking I may need to drop to a 22 pitch. Problem is I love the cruise speed with the 24s and it comes on plane with no issues...

If you porpoise while trimming out, I would just trim back in a bit until it stops . . .

You also might be a little over propped, since your RPM is not quite up to spec.

It will start to hop at like 2-3 on the indicators..

My 292 does the same thing. I just tested some hydro 24's on mine so see if I would lose the porpoise but nope- same as the bravo's. The Mirages porpoised the least of all the props I've tested. Now the big difference is I've got 1300 hp now, so once I hit 55 I start trimming up. Then the boat gets loose and really feels great. At 60 the boat is just starting to come to life. find a set of 23 Mirages and test them out. Get a set of non-pluses. Your hull will like them better than the Mirage Plus props. That should allow to you get close to the 4500 rpm mark. You are over propped now.

I feel like the boat needs way more tail lift then a 3 blade can provide. It rides bow high now with 4 blades and still drags the tail..

Try the 22's ... how many hrs on the 330's? Those motors aren't real strong to begin with ...

They do have 700hrs on them. But the fact that it still runs 60 turning 24s they still seem strong...

Try the 23's as stated ....you need to be at 4600-4800 ... my 89 311 came with 23's...

Most everyone likes the cruise speed of props that are too big.

It's like overdrive in a car, but issue is boats won't kick down a gear or two.

Not good for the motors or drives ....

Your boat with 330's should run 63 mph. You are down on power, I'd start thinking about a refresh. If it was my boat, I would start saving and find a nice set of 502's. With stock 502's you will have a 70 mph boat and a great platform to build on in the future.

As for props- I've run Mirages, Bravos, Rev 4's, Hydromotive Q IV's. The QIV's will give you the best stern lift, but in my opinion the best overall prop is the Bravo. Again- I would start thinking about new engines, your boat should be faster than 60 GPS.

Im running 25 mirage plus with the 420's with 900 hrs on them. She runs right at 68 with no porpoising. I trim up past the indicators until I start to lose speed then put them back in the water a touch. It only starts to porpoise if i back off throttle before sinking the drives.

You are overpropped. The 23 Mirages were stock, so you are lugging the motors with the extra inch pitch and the extra blade. You might get away with going to 22" Hydromotives, though.

So you think a 24 bravo would be better since its 1" smaller diameter then the hydromotive? Does everyone agree that they need 4 blades on these boats to get the tail up outta the water? Or am I totally wrong? The 3 blades I have heard blow out bad on these boats?

How far can you trim say at 3500 rpm's?

The biggest issue in my opinion is that your engines are tired and need to be refreshed. My boat would turn a 24 hydro QIV to 4600 rpm and 63 mph with 330's. 311's and 292's run the same speeds with the same power. So your two options are to reduce your pitch or rebuild your engines. Reducing your pitch will get your engines in the correct RPM range but I doubt your will gain any speed. With my new engines I went from 30P Bravo's to 26P Bravos and I gained maybe 1 mph and 700 RPMs. Yes it was fun cruising 50 at under around 2500 RPM's, but it sure wasn't good for the motor to be lugging it like that. Don't get hung up on prop pitch, run what the boat likes and forget about the number.

Not to sound like a broken record but I would sell the 330's. My boat was slug with those engines. Since I bought my boat I've had 3 different 454 builds (330, 420, 450 hp) and now 509's (650 hp). There was a big difference the way the boat ran going from 330's to 420's. Yes it's even faster now with twin 650's but the boat really comes alive with 400+ hp. Again- at a minimum rebuild what you have.

I know what your saying about the motors are tired. But you had to turn your 330s to 4600 rpm to run 63...I can run 60 at 4000 rpm. I know that everyone says 292 and 311s run the same. But there still is a weight difference between the two boats. So mine is heavier too.

I think if I'm going to pull motors again, I might just sell the boat...

Just gotta decide what too do.
Thanks for the input, btw how does your boat like the extension boxes?

I run both 23 and 25 mirage plus and have no issue with porpoise. At 3k I'm around 2 on the indicator and wide open I am up around 7 to 8. Boat runs mid 70s.

The extension boxes are nice. They really tightened up the steering and it's a really clean instal compared to the typical external steering set up. The issue I have is, while I went with -2 sportmasters to raise the prop shafts the 7" set back of the box does't give me full advantage of this. What I mean is that while my shafts went from 7" below the hull to now 5" below the hull, the water comes back up once it leaves the transom. I have no idea how much it comes up within the 7" of extra setback but I'm guessing around .75 to 1". So I'm really not seeing the improvement I should have seen with the shorter lower. With 1300 hp, I'm currently at 80-81 mph. I can gain another 1.5 +/- by trimming the extra long skeg down, but I feel I should be closer to upper 80's with this kind of power.

This summer I did a lot of prop testing. When it came down to it, as posted above, the best prop was a BBlades labbed 26P Bravo. Now I need to work on my exhaust. I know my Gil's are not matched to the exhaust ports on my heads. I'm sure this is part of the reason that I'm not seeing the speed I should with these engines. I know that you don't even want to think about pulling your engines, but in time you will be able to do it with your eyes closed, and do it quickly. I don't even know how many times I've had mine in and out over the past 6 years. Ha- too many, I do know that.

Mr. Maine- what engines are you running to see mid 70's? Do you have some modded 502's? If so, what kind of power are they making?

Oh pulling the motors are no issue...already had them out and back in...30 mins tops per motor. I see where you think you should be in the upper 80s, but I think the straight bottom and hull design of our boats are going to be limiting you. Also I believe the use of ext boxes is more for the fact of moving weight further back off the transom of the boat for weight transfer and also to get the prop in cleaner water, as well as moving the prop shaft (x demsion) up. I know it be a lot of work but you should try it with no boxes and see what mph ya run then.

My engines were 420s. 40 over 454s with 308 darts, 9.2:1 comp., custom roller cams, 454-r Victor Jr, QF 850s, gil exhaust, all good components.

Haven't dynoed yet so not sure on the power

Ha- no way I'm pulling the boxes to test, if I do that I also lose my steering. It's not as simple as just installing standard transom assemblies. I'm looking to try out a set of IMCO -3's. That is the easier way to go. My issue is I'm still to deep in the water.

If you dig around in here you can find a lot of good info. Somewhere there is a topic from a guy that used to set up race boats. He said in the mid-90's they finally figured out where the X- dimension needed to be and that combined with the new props, that they were seeing big speed increases. He said the stepped bottoms were good for 3 mph +/- but the real increases were coming from x-dimention and prop changes. Also you need a large boat for them to really work. At 29' my boat is just big enough that you may start seeing advantages of a step bottom. Either way, at some point I'm going to try -3's. There are still a few things I can do to gain another 3 mph, but I really would like to get this old boat to 85 mph. If I can get there, I'll be satisfied.