I normally run 26P bravos at around 5000 rpm's in my 31 Sonic with 502 MPI's. Apparently Powerboat ran this same setup with 26P hydromotives at 74 mph. I tried some 26P hydros today and kept blowing them out while trying to get on plane. After finally getting on plane, I easily reached 5200 rpm's without trimming out nearly as much as I do with my bravo's and the boat ran more level.

I like the way the boat rides with the hydros and I might be able to try a set of 28P hydros. My question is - will the 28's be any better getting on plane or will they blow out like the 26's?

I'm thinking that if I can spin 28 hydro's at or about the same rpm's as my 26 bravo's, then I should see more top end speed??

you ran 200 rpm higher with a 5 blade over your old bravo 4 blade???? I thought hydros where 5 blades.....am I wrong? if they are 5 blades and you want to get rid of them let me know.
Tony

i'm running 25p hydros on my 35. mine have diffusers welded on them. I never had problems with blow out......until I had the labbed. Are yours labbed ? do you have diffusers ?

I would always put drives all the way in and put tabs fully down to plane off. now with the blow out problems, I found that putting down the tabs all the way is dropping the bow too quickly causing the blow out. So now I put tabs down 1/4 - halfway (leaving the bow high and the stern in the water) and blow out is gone. it does take a little longer to plane with the tabs only 1/4 - halfway, but no more blow out.

hydros come in 3, 4, and 5 blades.

My hydro's are 4 blade Q IV's. They do not have diffusers on them and I don't think they were labbed, but they look like somone brushed the blades.

thank you

As was said, you probably need diffuser rings.

And/or 5 blades.

Chris

I had the same problem with Hydro Q-IV on a 575 SCi 29 Fountain Fever. As soon as the bow started to break over, it would blow out, hit the rev limiter, and the boat would squat back into the water. Tried tabs all the way up, part of the way up, all the way down, and none of that worked. Also tried getting up on plane slowly by very slowly increasing throttle until it seemed reasonable to put it up on plane by applying enough throttle to get the nose over, and that didn't work either. Also fooled around with drive trim setting to see if that would help, but it didn't. Had several Hydro's to try, a couple of different pitches and LH and RH props. None ever worked. Was sure that if we could get it on plane, top end numbers would have been better than with B1 prop and with much less slip (running more efficiently). Came to the conclusion that the X was too high for the standard Q-IV prop. On previous boats, always had some degree of blow-out when cornering with Hydo Q-IV props. Didn't have that same issue with the Bravo One props. I think it had to do with the Hydro being a semi-cleaver prop versus the bravo one round ear props. I think Hydro later came out with a round ear prop, too. Think they called it a "P" or PX series (not sure on the designation).