Gary864

I will be trying a set of shorty drives on my 34 Phantom in about 2 weeks. I currently have 29 Hydromotives 4 blade ( not labbed) running 5800 to 6000 rpm. With the shorter drive drive and the same 1.50 ratio any ideas on where to start and keep my Rpm the same or a little lower say 5600? I would like to reduce the learning curve if possible.

throttleup

I think potentially that you will need at least an inch taller pitch...but it really depends on how the efficiency changes. Post you results so we can take a look.

Julie

Gary864

Thanks Julie. I have access to Bravo's and currently run Hydromotive. I am now running a 29 Hydro should I start with a 32 Bravo?

throttleup

I would recommend baselining all the props that you have, so we can determine what is performing best to acheive your goals.

Julie

PatriYacht

I tried -2" shorties on my Black Thunder. It already had extension boxes and had propshafts about 6" below the bottom of the boat. The boat gets on plane fine and runs with good slip, 75mph at 51-5200 with 26 pitch Bravo 1's. It won't stay on plane, however, below 3000 rpm and it slips badly until about 3400. Also I'd like to spin a couple hundred more rpm, what can be done?

Gary864

Thanks again for your help. I have a local race team that has a array of props and was looking for a starting point. I think I will start with the 32 Bravos 4 blade labbed.

bbladesprops

Gary,

32 B1's are a good place to start since you are looking to decrease your rpm 200. With the drive height rise, you will acquire another 200 + rpm. Potentially you will need to drop 400 rpm total. The 32 B1 will run about 400 rpm less than your Hydro. Now the issue is the Lab process that has been done on it. Depending on how and where it was done, the rpm's could be anywhere. A box stock set would be better to gain the base line.

PatriYaught,

Tough combo. You can go to lower pitch larger diameter 5bl props or space the drive down and work with other 4 and 5 blade configurations.

Gary864

THANKS BBlades they props were labbed direst from Mercury as I remember.

KAAMA

Just FYI, my 32' A/T is a conventional V-hull without any steps, no notched transom, running Stellings extension boxes, Bravo XR drives with 1.5 gears. I went from a stock length Merc lower with no nosecone to some -2" IMCO shorties (propshaft centerline is now approx 2 inches below the hull directly in front of the drives). With the -2 shorties and 32" Bravo One 4-blade props I could hardly get on plane and I lost about 7-10mph in the midrange cruising speed and MAYBE (that's a BIG MAYBE) gained ONE-1mph on top---which is pretty poor results in my opinion! However, I do really like the way the boat rides---sits up on top of the water nicely and rides flatter.

I was told by Julie at Throttleup and Todd at Hydromotive I needed P5X 5-bladed props. All Hydro had in stock at the time were some stock (non-labed) 28 inchers in the 5 blades...I tried them and they popped me right up on plane, BUT midrange still sucks---still about lost 8-10mph in midrange cruise and gained 1-2mph on top and I still LOVE the ride! Hydro has just sent me a set of 30" P5X 5-blades. If they bring back all or most of my midrange crusing speed I will keep the -2 IMCO shorties otherwise, they will be removed and I'll put them up for sale.

LFarr

Kaama,

My situation is different from yours but I went from -2 Imco Shortie with 26p B1, to -3 and 26p Maximus 15 5/8 diameter had big increases everywhere AND top speed increased from 75 to 77 gps.

I think the hydro's are 15 1/4 diameter?

The extra diameter of Maximus might make a difference....just a thought before you give-up on shorties.

Brett at BBlades has all the info..........they have s sweet demo program.