Props for shorty drives
 

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.

Re: Props for shorty drives
 

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

Re: Props for shorty drives
 

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?

Re: Props for shorty drives
 

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

Julie

Re: Props for shorty drives
 

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?

Re: Props for shorty drives
 

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.

Re: Props for shorty drives
 

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.

Re: Props for shorty drives
 

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

Re: Props for shorty drives
 

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.

Re: Props for shorty drives
 

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.

Re: Props for shorty drives
 

Well, this past weekend I tried the 30" P5X's and picked up most of my midrange back, but not all of it....still down about 2-3mph at some RPM ranges, but picked up about 3-4mph on top in calm water which isn't too bad. If the IMCO shorties didn't make boat handle better with a better ride, flatter angle of attack, etc I would probably take them off and go back to the stock length Merc lowers.....So, I guess I will hang on to the IMCO shorties for now.

LFarr, Perhaps I will try some Maximus props when I get a chance, but was told the Maximus 5-bladed props were not a very good prop compared to the Hydro P5X's-----but then I guess every boat is different.

Re: Props for shorty drives
 

I just went to a shortie running my B1 26 lab the pick up was wild but did slip a little getting on plane is longer but I have 380s for k planes :D didn't have a change to open it up but I think I hit 64gps at 4000rpms it was rough out, then I NAILED IT LATER AND BROKE A ROCKER STUD :eek: Iwill be back out the 27, so would a 5 blade be good for me. and before the 2''shortie the 26 would bogg down then pick up this is starting after being on plane at 2500or2800 then mashing it. last year it topped out at 76gps,

Re: Props for shorty drives
 

Ian,I just put a 1" drive spacer on last week and just tried it out,the porpoising,cavitation,blowout and crappy rough water drivability is GONE. You might need to experiment with some 1" spacers and different props to get a happy medium,Smitty

Re: Props for shorty drives
 

What did your boat do speed wise at 4000rpm (or where ever you cruise at) BEFORE you installed the -2" shorties??? Along with myself, I have found with people who have tried the -2" shorties that they have always suffered a significant loss in the midrange cruising speed.

A friend of mine has a 34' Scarab (no steps, no notched transom, no extension boxes) with stock length Bravo One drives with 4-bladed props where the propshaft centerlines would sit about 5 inches below the hull directly in front of the drives. He eventually installed some -2" IMCO shorties and his RPM has increased by about 200, and speed increased by only about 1.5mph @WOT (his boat runs in the high 70's on the GPS), but handling improved and gave the boat a much flatter ride as my boat has done however, his midrange crusing speed has suffered by about 4mph.

He's very happy how much better the boat handles with the shorties. He is still using the Bravo 4-bladed props because his propshafts still sit below the hull by about 3 inches, but he says he experiences a little more slip while coming on plane and would like to try some 5-blades to see what happens with coming on plane and his midrange cruising speed.

Re: Props for shorty drives
 

when it was stock at 4000rpms I IT WAS AROUND 60 GPS, Iwon't be back in the water until next weekend getting new nickerson 1050 :D so I hope see some more speed and maybe try a 5 blade