Step hull help....

[Bryan Rose]

After this weekend of running 50 gallons of fuel throught this thing I have some questions.
Boat 1997 Donzi 27 ZX twin step, with a HP 500 EFI 24 inch Bravo one prop.
Can spin it to 5500 68.5 GPS......Too much slip!
1 I took some pictures from another boat and it seems to run flatter than I figured it would be.....Looks like it needs some bow lift and trimming it out does not get it done, Is this a trait of twin step boats?
2 I can blow the prop out at will between 3000-4000 with just the throttle, even trimmed down... What the hell is going on here. If I am easy on it it will hold, but even at around 3000 it will blow out and run fine just not as fast. Do I need more Prop?
I am thinking I need to get a prop with a ton of bow lift in the 26 inch range....Any suggestions? I need Help
I will post pics of the boat running if it will help.
Bryan

[Havasu Hangin']

What diameter is the prop? :idea:

[Bryan Rose]

What diameter is the prop? :idea:
Dont know I assume that it is 15 something? maybe .....as far as I know it is stock?
Bryan

[Havasu Hangin']

Dont know I assume that it is 15 something? maybe .....as far as I know it is stock?
Bryan
Where is the propshaft in relation to the bottom of the boat? :idea:

[FASTERDAMITT]

If you have a rubber hub prop, it's probably slipping.

[Bryan Rose]

If you have a rubber hub prop, it's probably slipping.
Solid hub prop, not slipping. As far as the X dimention I am assuming it is stock but I will meassure it today and get back with you.
What about the Bow lift issue?
Bryan

[TPI]

With the information you have provided, you are at approx 17% slip. If you were running 115 mph in your boat, I would say that 17% would probably be close in your v-bottom, but not at 68 mph, more like 11-13% slip. Assuming your boat does not have any problems such as: Spun motor coupler, or too high of an X dimension, it sounds like you just need the right prop. If that 500 of yours is a stock 1997 carb motor with gil exhaust it was not designed to RPM like that. Even though it obviously does it. These motors run very well between 5100-5200. That being said, if you try a Merc 15 1/4 26 and are able to turn it 5200+ you should be in the 75 mph ballpark with about 13% slip. I have recently been running some tests on the new Hydromotive P5X 5 blade. They do have some bow lift and V bottoms seem to LOVE them. They are non labbed and about $1000/ea. Just food for thought, good luck.

[hotlavey]

With the information you have provided, you are at approx 17% slip. If you were running 115 mph in your boat, I would say that 17% would probably be close in your v-bottom, but not at 68 mph, more like 11-13% slip. Assuming your boat does not have any problems such as: Spun motor coupler, or too high of an X dimension, it sounds like you just need the right prop. If that 500 of yours is a stock 1997 carb motor with gil exhaust it was not designed to RPM like that. Even though it obviously does it. These motors run very well between 5100-5200. That being said, if you try a Merc 15 1/4 26 and are able to turn it 5200+ you should be in the 75 mph ballpark with about 13% slip. I have recently been running some tests on the new Hydromotive P5X 5 blade. They do have some bow lift and V bottoms seem to LOVE them. They are non labbed and about $1000/ea. Just food for thought, good luck.
I have a Lavey 2750, twin step ventilated, HP500EFI with a Whipple. I tried a 26 P5X and hated it. Major porpoising problems and over torqueing(had to run left tab down all the time to correct it). Bravo 28 labbed works much better and I'm thinking of going to a 30 Bravo as I am turning the 28 around 55-5600 rpms at 80 mph.

[TPI]

I have not tried a p5X on a lavey, but thats good to know. I would imagine a 30 lab would be a good choice for yours. There definately is a prop out there for every kind of boat. I really think the Donzi in this thread needs a different prop.

[Bryan Rose]

I have not tried a p5X on a lavey, but thats good to know. I would imagine a 30 lab would be a good choice for yours. There definately is a prop out there for every kind of boat. I really think the Donzi in this thread needs a different prop.
Motor is a 2001 model EFI with stainless CMI Headers. Only took it to 5400-5500 once or twice trying to wring its neck. I spoke with Julie at Throttle Up and we are going to try a 27 Hydro motive quad 4X for some base line and go down from there. I would realy like to get this right, first big boat. I am ot so sure this is the right prop but people say it is the shit. Seems the Bravo I design is from 1991 with no improvements in that time. She did say that 26 inch and above got some attention but she said not enough to matter. The Hydro motive design is recent and should get it done. I do not want to give up on the cruise speed, this is where we all spend 90 % of our time.
Looks to be Bravo I VS Hydromotive Quad 4 X What is your opinion?
What about the Bow lift isue?
Bryan

[hotlavey]

I have not tried a p5X on a lavey, but thats good to know. I would imagine a 30 lab would be a good choice for yours. There definately is a prop out there for every kind of boat. I really think the Donzi in this thread needs a different prop.
That's going to be my next prop for a trial. I think the P5X did not have enough bow lift for my boat. What are your thoughts?

[TPI]

I would not be looking for bow lift, unless you are absolutely sure thats what you need. Go to the lake and try a few different ones(if you can) or Call the manufacturer of your boat and find out what works best. For most V's running under 85 mph the Bravo Lab works pretty well. Good luck

[hotlavey]

I was told the Bravo 1 has more bow lift then the P5X.
As the boat is much better with the Bravo I am assuming that the increased bow lift makes the difference. What do you think?

[nextel4u]

I have a Hallett 270 Step with the 500 efi. I had the 24 prop on for quite awhile, the boat would hit the rev limiter alot and it liked to sway side to side at about 60 mph. I just put on a brand new stock Mercury 26 pitch 15 and 1/4 diam and it made a huge difference. The side to side swaying is gone and the boat seems to cut the water better. The only downer is that I have lost some rpm's and some speed. I used to get the boat up to about 74 at 5100 rpm's, now I cannot get passed 4600 rpm and I am doing 66 mph. I am taking the prop to a shop here in Vegas, I have been told I can get some more RPM's out of it and still keep the ride that I like. Hope this info helps
John