porpoising-prop, ballast, or ???
 

I've got a 1990-91 Baja Bandit 223. It's beautiful and fast, but a shallow hull, so rough ride. But anyway, due to hull design oversights it's got a pretty significant porpoising issue, probably due to weight distribution. It's got a 454 mag, with a Bravo 1, both just slightly beyond stock. It's 25' long, 33" draft, 15 degree deadrise, about 3600#.

I started out with a standard Mirage 23p, and then tried a 23 plus, but didn't notice any changes in the boat. She'll do 70+ in the right conditions, but getting her there is difficult, as it goes into porpoise mode quite often. Seem to always have to drag the tabs, which prevents top speed of course. A little light on the fuel load seems to help a wee bit, but there is no way to "drive out of it" or past it for that matter, as I've driven it in every possible manner and trim configuration to prevent the onset of the porpoise.

So what's the next step? I guess I could try a 4 blade, but what size? What about configuring some sort of ballast system?

This boat looks and runs like a 4 year old boat, not a 20 year old boat, so I'm not ready to give up on her just yet.

Suggestions?
Thanks.

Sounds like you have a stern heavy hull with a decent amount of power. (BTW, I kind of doubt you're drafting 33" of water. Freeboard maybe?) The Mirage has a decent amount of bow lift. I'd suggest trying a prop with more stern lift - which most 4 blades have. One call to Brett a Bblades should give you more than enough correct information.

Thanks for the reply. Absolutely more stern lift, the mirage plus with more cupping was "supposed" to add some, but it did nothing. The 33" draft is a factory spec, bottom of the skeg maybe with a bunch of fat asses on board?

Now, what 4 blade should I shoot for? Buddy's got an Eliminator of the same size and relative power, and he's got a 28 4 blade. Granted, much better hull design, but has no trimming issues and doesn't appear to sacrifice any speed.

I did contact bblades last year and I think a got a "general" response. "Need more cupping" and "the 4 blade will slow you down". But I'll see when I can schedule a test period with a 4 blade with them.

I don't think you can spin a 28" 4 blade (very fast) you'll need a 22"-26". Have you checked the bottom to see if there is a Hook on the running surface? everything you described sounds like a hook.

The hull is like new, no hook. It's a design issue. That's why they added tabs at the factory after the first year of production. All of these hulls (produced by Sunsation) had the same problem. I agree, 28 sounds a little big, but I'm running close to 400hp essentially on a big ass bass boat (shallow hull). Once on plane, she takes off like a rocket ship, but I do sense a lot of slip and occassionally blow out on low speed turns and such. So 22-26" on a 4 blade, what should I try?

Thanks.

the 22" 4 blade is going to have rpm similar to the 23" 3 blade.

You should start with a stock 22" Bravo 1 4 blade.

Right. Hmm.............well, the 23 revs her up pretty good, that is, if I can handle the boat up to terminal velocity, but I think I've got a decent slip ratio in there as well. I guess if I try a 24 4 blade I can move up or down. Thanks to all for your input.............decisions, decisions, decisions........

Look to the bottom. I am fixing a velocity 22 that was impossible to drive

You'll need to clarify that a bit. that is "bottom of the boat" or "bottom number on props". It's not impossible to drive, it's just a game of chance whether or not she'll porpoise, and the research shows all of these hulls had the same issue. I can get her beyond 60, but not without dragging some tab, and in a windless and waveless condition, I shouldn't have to do that. But everyone's input here is going to finally resolve the issue, and maybe I'll sink her, maybe I won't.