Prop selection

[Brad Christy]

Guys,

My family has finally invested into the real boat world. I've been around powerboats all my life (I grew up on a 21' Nordic with a blown 454 V-Drive that would excede 80 MPH and pull FIVE sloloms from a wet start), but this is my first boat of my own:



Details:

Rinker 236 Sport Cuddy (approx 3800 lbs.), Mercruiser 454, Bravo One Sterndrive, engine warmed over by a very reputable local engine tuner, putting out 436 HP and almost 500 ft/lb of torque (according to the dyno readout). 22" pitch Bravo One 4 blade prop. Runs about 60 MPH.

60 isn't bad, but it seems a bit short compared to what I see similar boats running with similar or less HP, so I'm thinking the prop might not be right.

I've looked all over the internet and can't find a prop selector that will let me detail the HP. They all limit your answers to OEM engine options.

Does anybody have any experience with prop selection, or have access to an application tool that will help me out?

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

 

[Tom Foley]

Brad join Scream and Fly.com , Offshoreonly.com , thehulltruth.com you may find some answers there . Thats a big boat might be hard to get it going a whole lot faster but you never know . What RPM are you swinging the 22 ?

 

[HTV Boats]

Toms correct, Scream'n'Fly will have the info you want and a good section for buying ome used props. If your running 60 your doing well right now. In boats that size speed gets really expensive. I had a 30' Baja feeding 2 454's so I have knowledge of how fast you can drain your wallet above 60 mph. Reality to up say 10 mph for you would be more than difficult. Even finding the magic prop you can't air that much weight out enough to gain 2-5 mph. My friend with a single engine 25' performance hull went to a supercharger and from 425hp to about 700hp to go from 65 to 75. Tom's Allison does that midrange. Weight to HP is the key to performance and above 3000 to 4000 lbs your fighting an uphill battle.

Work around your 22 pitch and borrow every blade design from 23-25 pitch you can. Till you try a few different props you won't be sure what one may carry your hull to get speed. A tach and speedo will tell the tale. Many styles availiable these days. We have a dealer down here that loans props but those kind of guys are rare. He sells a lot of pairs to offshore guys though. Good luck and have fun but stay safe.

Mic

 

[AWaddle322]

Brad,

When those boats were made 3 blades where all that was available (or affordable). The forth blade will help with cruise speed but generally will hurt top end. we need to know your speed gps (and not from the dream a meter) and you rpm along with where your engine builder says the rpm should be limited or where the rev limiter is.

Other things to check: use a 4' straight edge at the back and bottom of the boat and look for a hook (rinker used to put one in from the mold as most boats where under powered and helped with plaining speed.

Couple of buddies had these with the 502 and the dream a meter would read about 70 (before gps were readily available).

Get the whale tale of the drive (good for nothing when trying to go fast)

Which drive and what gear ratio?

Allen

 

[Dan Hydro]

Brad,

Bravo one gear ratio are:

1.36:1 (standard)

1.50:1 (optional)

1.65:1 (high altitude)

what is your max RPM?

what is the year?

Dan.

 

[Brad Christy]

Guys,

Gear ratio - 1.5:1.

MAX RPM is about 4400 or so.

The GPS read 43-44 wound out, but we had 1000 lbs. of people in the boat.

We were told it ran about 60, which made sense considering the HP for this boat. It was dyno'd with a Holley 750 carb, but the engine was delivered with a Carter/Weber 650, which had been purchased for the engine, but had not arrived in time for the dyno run. I'm thinking we're not getting anything near the 436HP the dyno pull showed.

My dad has a 27' SeaRay with a stock 375HP 454. At 5500 lbs., it runs 52-53 MPH. This is one reason why I think this boat should do better than 60.

Allen,

The whale tail was gone before we ever got it to the water. I saw no need for it.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

 

[Dan Hydro]

Brad,

with the numbers you just gave, thats what the prop calculator gives me:

42.8 (30% slip),

48.9 (20% slip), and

55.0 (10% slip).

I agree with you, something is wrong.

Dan.

 

[AWaddle322]

Brad,

does you power trim work and do you know how to use it? something is bad wrong (slip numbers to high).Carb it definatley to little to. Post dyno print out to.

Allen

 

[Brad Christy]

Allen, others.....

Alright. A boat mechanic/friend of my dad's is going to swap us a Holley 750 for the weekend. He said the engine should turn about 5600 RPM and the boat should run mid to high 60's with this engine/prop combo. We're going to see if the carb helps. Pretty sure it can't hurt.

My question is this. I see (on eBay) LOTS of Holley 750 4bbl carbs. But which one? 4150 or 4160? Not sure abut the double pumper (always thought that was for drag strip holeshot), but I'm fairly certain I want the vacuum secondary (what we had on the blower motor I grew up skiing behind). Yes, no?

The distributor is not right, either. It's an automotive distributor with vacuum advance. We're looking into that as well.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

 

[Terry Flynn]

That carb is way to small for a 454. if it was bored out a little bit more compression I bet you could get a way running a 800 to 850 cfm.

Years ago I had a 1990 baja 250es with a 454 mag Trimed out loose I was running 5200rpms WOT with a 19x21 and 100 gal of fuel at 58mph if I had a boat load of people I had to drop down to a 19x19 or it would take forever to get it to plane out.

Also make sure that the Carb you get is a marine carb with the bowl vents going back

to the butterflys.

it a float sticks thats the last thing you need is a bildge full of fuel.

good luck

 

[moparbarn]

a few other things to add on carbs, get one with no gaskets below the fuel level. base/throttle plate & float/middle section are 1 piece. again, no fuel leaks at a gasket below the carb's fuel level . also, i'm not so sure you want vacuum secondaries. boats load an engine differently than a car, i would choose mechanical progressive secondaries. at least a 750 cfm, prolly larger. you're not worried about "driveability" around town, but rather feeding a big block at consistently higher rpm's than "street driving".

 

[Rigged]

But which one? 4150 or 4160?

4160's are easier to tune the 4150's. They dont use secondary metering blocks like 4150's... instead they have a metering plate with fixed jetting basicly (so if you need or want to make jet change on the secondaries for any reason with a 4160, you have to either drill the plate, or do block conversion).

750 is fine enough for a mild 454. Any bigger, you're likely to run into stumbling problems when getting on plain.

Holley # 0-9015-1 would be what you're lookin for. This is the Marine 4160 750.