Promax cavitation on breakover with SHO

[Marshfly]

I am running a 24" Promax with no vent holes and the Promax exhaust ring on my SHO. I get bad cavitation on breakover while coming on plane. For comparison, I get zero cavitation with a 23" Turbo TXP OT4. I'd really like to get the Promax working better as the midrange acceleration, fuel economy, lift, and top speed are all considerably better than the OT4.

Is the cavitation something that the prop can be worked to improve?

Will a foil from Chris Bailey help some? I'm thinking of adding one to help with my bow rise when I use my huge livewell in the rear deck. It's like 45 gallons so it adds serious weight.

[Marshfly]

I guess no one has any suggestions for this.

[Bullet 20cc]

Compare cup size and diameter of the 2 props against each other. Larger diameter and more cup will help on breakover. Not really sure how much that exhaust ring is helping either... might be hurting you right there. Stick a Bravo 1 on there if you get a chance to and you might be totally amazed in several areas of preformance compared to your current props. That prop does everything very well... Though the TPX OT4 is no slouch either. Promax prop is a little bit of a slouch in my opinion...

[Marshfly]

Compare cup size and diameter of the 2 props against each other. Larger diameter and more cup will help on breakover. Not really sure how much that exhaust ring is helping either... might be hurting you right there. Stick a Bravo 1 on there if you get a chance to and you might be totally amazed in several areas of preformance compared to your current props. That prop does everything very well... Though the TPX OT4 is no slouch either. Promax prop is a little bit of a slouch in my opinion...

The Bravo 1's are too fragile for how we run in the shallow marsh here. I've heard they would do well on this hull but I need the thick blades of the OT4 or Promax to keep it running well. The exhaust ring definitely helped. I do have a 25" OT4 that hasn't been run since I had it brought back to stock configuration. I managed to ding it when I tried to run it before I even got on plane and it had virtually no bow lift. I guess what I need to do it run everything I have back to back and then bring them all to Brian at Holeshot Propellor and have him make a recommendation.

[Bullet 20cc]

There's about 14 different models of Bravo 1 out now (slight exaggeration)...not just one. Some of them do have serious blade thickness on them. Bravo FS and unlabbed original Bravo are 2 of the off the top of my head but there are more. They are pretty stout props...way too thick for me. Good luck on it!

[Marshfly]

There's about 14 different models of Bravo 1 out now (slight exaggeration)...not just one. Some of them do have serious blade thickness on them. Bravo FS and unlabbed original Bravo are 2 of the off the top of my head but there are more. They are pretty stout props...way too thick for me. Good luck on it!

I thought that the FS was thin like the XS. Good to know that it's thicker. I know that would work. How does the pitch compare to the stiff Promax and OT4?

[Bullet 20cc]

They are a little short of advertised pitch if you ask me. I run a 30 that feels like a 29+... I think the promax is a tad higher than advertised. No idea on the OT4...

[Marshfly]

I've been thinking to start with a 26 FS and tweak from there. Now to find one in the classifieds.

[Bullet 20cc]

OT4 and Bravo compare...I think the Bravo is better everywhere except for 1-2 mph on the big end...

[Bullet 20cc]

I've been thinking to start with a 26 FS and tweak from there. Now to find one in the classifieds.

You might be thanking me later...and I do take personal checks too!

[Marshfly]

You might be thanking me later...and I do take personal checks too!

How about a fishing trip where we end up with redfish, speckled trout, and bass in the livewell all at the same time? Thanks a ton for the advice.

[Bullet 20cc]

How about a fishing trip where we end up with redfish, speckled trout, and bass in the livewell all at the same time? Thanks a ton for the advice.

Hell yeah brother! Can catch em out of the same water here too. Kinda determines whether you went saltwater or freshwater by looking in the wells at the end of the day...

[John Jackson]

IF you are worried about hitting things, Bravo's also run and holeshot better when ran higher.

[Garfish]

I have no experience with 4/s engines, however I would think a 250 anything could swing more prop than a 23 or 24 pitch. What rpm are you turning WOT? I have owned and run BravoI's in 28 pitch and for clean deep water was the best all around fishing prop ever. I've run other 4 blades but have been dissatisfied until I bought a Croxton Razor 4XL in 28 pitch. I really wanted to buy a 28 ProMax but couldn't make a deal and wound up with Marks. First time out of the hole with all 8 PVS holes open it was a dud of course and had to feather it forever to get on plane. Next trip I closed the 1st set of holes and it came out of the hole with two on board, half tank of gas and no live wells at 4,700 4pm and NO blow out. It pulls like a rented mule, carves like a skate board, great mid range and so far tops out at 60+ @ 5,000 rpm. I just haven't tried to go over 5,000 rpm but have plenty of petal left. I'm just now dialing it in. Calmer conditions with less wind I'll go for 6,000. I run about 2" below pad with a 8" a Detwiler Hyd plate. I fish a lot of skinny water and wanted a beefy Mud bug type of prop and could see that in the ProMax all the others are just to thin. You could almost shave with my Bravos but they were to fragile. Fastest prop I ever ran was a Croxton prepared 27p TXP lightning with PVS holes at 79.1 GPS.

[Marshfly]

I have no experience with 4/s engines, however I would think a 250 anything could swing more prop than a 23 or 24 pitch. What rpm are you turning WOT? I have owned and run BravoI's in 28 pitch and for clean deep water was the best all around fishing prop ever. I've run other 4 blades but have been dissatisfied until I bought a Croxton Razor 4XL in 28 pitch. I really wanted to buy a 28 ProMax but couldn't make a deal and wound up with Marks. First time out of the hole with all 8 PVS holes open it was a dud of course and had to feather it forever to get on plane. Next trip I closed the 1st set of holes and it came out of the hole with two on board, half tank of gas and no live wells at 4,700 4pm and NO blow out. It pulls like a rented mule, carves like a skate board, great mid range and so far tops out at 60+ @ 5,000 rpm. I just haven't tried to go over 5,000 rpm but have plenty of petal left. I'm just now dialing it in. Calmer conditions with less wind I'll go for 6,000. I run about 2" below pad with a 8" a Detwiler Hyd plate. I fish a lot of skinny water and wanted a beefy Mud bug type of prop and could see that in the ProMax all the others are just to thin. You could almost shave with my Bravos but they were to fragile. Fastest prop I ever ran was a Croxton prepared 27p TXP lightning with PVS holes at 79.1 GPS.

My boat is a 22ft long bay boat with a V pad and 12 degrees of dead rise. I can stand up at the console comfortably and it's big enough to flush mount a 16" GPS so it has considerably more wind resistance than a bass boat. I think 72mph is pretty darn good while turning 6100. haha. I run all my props to turn right at 6000-6100 at full throttle. On the SHO, redline is 6000 and 6250 is the rev limiter.

So the Razer 4XL runs same pitch as the Bravo?

Just FYI here is a boat like mine. The backrest is all the way across for three people so it has a good amount of drag and I run an HDS9 and Terrova on the bow.

[mdtritn21]

Bravos run lite on pitch which is why Mercury tells you to run 2" pitch higher than the tempest or fury you run. The 4XL runs a little stiffer than a Bravo. If you call Mark Croxton since he sells the 4XL he can tell you what pitch to buy from him and if it's not right he'll fix it or replace it. I'd get the Pro max drilled with at least four PVS holes too.

[Garfish]

If you have propped the engine to turn the ProMax 6,000+ WOT I think you could benefit with the adjustability of PVS holes and plugs, but the over ventilation at break over also may be corrected with a bit of cupping. As stated on the holeshot with hotfoot on the floor my 28 Razor XL turns up 4700 rpm without blowing out. This weekend I'll be trying a little different arrangement of plugs hoping to reduce my initial rpm on the hit to 3900-4000 rpm. If not I can live with 4700 rpm, love the sound but it make the engine use more oil for that short period of time, I'm told. I'm happy with the purchase so far, if it needs tweaking Mark will take care of that.

[Marshfly]

If you have propped the engine to turn the ProMax 6,000+ WOT I think you could benefit with the adjustability of PVS holes and plugs, but the over ventilation at break over also may be corrected with a bit of cupping. As stated on the holeshot with hotfoot on the floor my 28 Razor XL turns up 4700 rpm without blowing out. This weekend I'll be trying a little different arrangement of plugs hoping to reduce my initial rpm on the hit to 3900-4000 rpm. If not I can live with 4700 rpm, love the sound but it make the engine use more oil for that short period of time, I'm told. I'm happy with the purchase so far, if it needs tweaking Mark will take care of that.

I can't think of a single 4 stroke Yamaha that ever needed PVS holes in a prop. They just don't. I was able to run a 25" Tempest on my last boat with an F150 and the hole shot was still impressive on an 18'6" boat. Regardless, more venting is only going to make the slipping worse, not better. The OT4 doesn't slip at all. Zero noticeable slip on takeoff. I'm going to run my 25" OT4 in the morning to see what it turns up at WOT and then call Croxton for some advice.

[Bullet 20cc]

I can't think of a single 4 stroke Yamaha that ever needed PVS holes in a prop. They just don't. I was able to run a 25" Tempest on my last boat with an F150 and the hole shot was still impressive on an 18'6" boat.

I agree with you about PVS holes on your size (pitch) props...shouldn't need them at all on pitches that low. Prop really doesn't take a very big bite of the water at all compared to higher pitches and doesn't need any additional assistance. PCS holes only really necessary starting at 25-26 pitch and higher in my opinion...and the holes would get bigger as pitch increased.

[Marshfly]

I was washing the boat today and just for kicks I measured the Propshaft to pad and setback to compare to what I see other guys posting on here.

With the 10" Bobs Action Jacker I have 26" of setback from the end of the pad to the bottom rear corner of the jackplate. With the jackplate on 3 which seems to be best for top speed I measure the propshaft at 1" below the V-pad. The cavitation plate is 7.5" above the pad at that height.

No wonder this boat is tricky to set up.