Prop slip 4 or 5 blade
 

Last years setup I really didnt get to any prop testing. I ran a 28 B1 up to 6300 rpm with a 1.5 ratio and was seeing 83.9 on two different GPS's. it had more in it the motor should have gone to 6700rpm's but I was fighting dirt in the fuel filter and no seat time in the boat... With the 28 B1 the only thing the boat did well was plane and mid rpm blasts heading straight forward. It would not even make a slight turn with any throttle without blowing out. While running the boat flat with very little trim the stern lifts up and starts to fish tale not chine walk but fish tale this all happens in the mid 70's. If I trim the drive pretty high the fish tale goes away but the attitude of the boat sucks for running in big water when it goes air born the bow goes way up in the air and the landing sucks. The funny thing is the prop I was running on this boat I also ran on my Baja and on two completely different hulls they both chine walked at exactly 80. I mean you could literally run 79 mph all day long no problems but just bump the throttle a little and they start chine walking. I've read posts of the previous owner and he ran a 30 pitch B1 and would have the same kind of fish tailing. So, for this year i decided to add another 250hp but which way do you go with a prop? I'm thinking 5 blade

Is the 28 B1 stock or has it been worked on. Has there been any repairs done to the propeller?
Do you happen to know how deep your prop shaft is in relation to the bottom of the boat?

Brett

Brett it looks like the 28 is bone stock I did measure it from tip to tip and came up with 15" don't know if that means anything. Prop shaft is 4-1/2" from the bottom. I know the slip # is pretty high but honestly in the mid range the boat was like a rocket and would set you back in the seat. Even at high rpm the boat pulled hard. But what i really don't like is the fish tail effect. And trying to turn even a little with the prop blow out the way it does is almost embarrassing.

sounds like the drive Is TOO deep.

5 blade propellers create more stern lift than 4 blade props. Adding the correct tip cupping amount in the correct location and putting a slight bend in the blades will allow the prop to leverage the stern more and decrease the loose transom at speed. This will also reduce the venting in turns.
We do have 5 blade props for testing if you desire.
I'm not sold on the prop shaft being too low. Your slip % is almost 23% and that is too high. Theoretically, raising the depth of the prop shaft will make matters worse with slip and venting in turns with the prop as it is now.
28 Bravo 1 props are only 15" or a touch less in diameter.

Does the boat react at all to trim?

Brett

Brett the boat does respond to trim and never loosens up no matter how far you trim it. The best performance from the hull comes from a 2 foot rooster tail shooting way off to the port side anything more than that the boat doesn't handle big water very well and that's what I boat in 99% of the time unless you get one of those dead calm days. This is the first boat I've owned that has me on pins and needles when I'm driving cause it is a handful and has been flipped twice. I've seen videos of the boat running in the 70's and at that speed there is little if any boat in the water. So, what do you do? I have access to a 28&30 herring 5 blade also a 32 b1. Ill try thoose out and get with u Brett on something more tailored to my old hoppty unless you think there is something better to start with? Don't want to spend the summer prop testing/ explaining to the wife why I have to put the boat back on the trailor after running it for 5 minutes.

Test all the props you can taking good data.
Thank we should discuss the results.

Brett

Had the boat out last weekend and I think i discovered where most of the quirks were coming from. I had the steering rams rebuilt and its like I bought a different boat. With new power boat ran 91mph @ 6500 rpm no more fish tailing or chine walk with the same 28 b1 prop as b4. Slip is still really high. My question is this do I go down in prop size and spin it faster or up and spin it slower? What will get the slip down? Or is it trial and error...

Stiffer pitch can reduce slip but more blade area and cup adjustments are a better route.
Are the 28's truly box stock?

Brett

Box stock other than a little low tide blade thinning for about a mile or so...