Time to change size of props????

[Redhook98]

I am at my wits end. Ever since I bought the boat almost 2 years ago, I can not get past 3600-3700 RPM with either motor. (I have been cruising at 3100 RPM at 22-23 MPH. 36-3700 RPM will only bring me 27-28 MPH.) The 454's had 120 hours on them when I got the boat (207 now) and have always ran perfect. I have cleaned the tanks, replaced the entire ignition system on both motors (caps, rotors, wires, plugs, ignition sensors, ignition modules, and distributers), cleaned the spark arresters, checked fuel pressure, new carbs (Q-jets), etc etc...... Compression is perfect in every cylinder and all are within 5% of each other, for both motors.

I still cannot reach full WOT (4200-4400 according to specs).

I am thinking a re-prop may be in order now. The props were last reconditioned in 1999 and are the factory sized 17 x 17 props. The PO installed an elaborate 3/4 tower structure of aluminum, and an electronics box. Combine this with the fact that I may have water somewhere hiding in the hull, usually a full water tank and gas tanks, and a good supply of tools on board..... It seems to me to be a weight issue at this point.... Not sure if props go bad over time or not... ???

I have a set of 16 x 16 props I could try. Theoretically I would pick up 600 RPM with those props over my 17 x 17's. (400 RPM for the decrease in diameter, and 200 for the reduced pitch).

What do you guys think? Anyone with an older SR experience similar?

 

[Redhook98]

Nobody? Really?

 

[Half Fast]

If you already have the props in hand, why not give it a shot?

If its been this way for multiple seasons and you have ruled out engine problems, I think you've already answered your own question.

Swap em and report back.

 

[Getaway]

It sounds like the 17x17 may be too big for what you are doing. The 16x16's sound like the answer, however, be careful reving those BB's too high. Their sweet spot is right around the 3100-3300 r's. Any higher and you start to shorten the life of those girls.

Dropping down to the 16x16's may cause your boat to fall off plane at lower speeds. The bigger dia props help keep those heavy boats on plane at low speeds/r's but you do lose some top end.

I jumped up to a 16x16 on my 268 and now she stays on plane at 18-20 mph, but she don't go 37 anymore. Now she tops out around 30-31mph. That was a small sacrifice to pay to stay on plane at 20mph, 2700r's. Lake Michigan and Huron get pretty choppy and it's pretty rare to be able to travel at a high rate of speed anyway.

 

[JVM225]

I changed the props on my boat before the start of the 2010 season and it was the best money I ever spent on the boat.
Talk to a good prop guy and tell him what you have, and what you would like to see the boat do. He should be able to recommend something to you.

 

[390x]

Whether or not he cruises his boat at higher rpm's, those big blocks are meant to wind out to 4200-4400 RPM's. If they don't wind up that high, you definitely need a change. I'd try the 16x16's, lugging the motors like you are is harder on them than winding them up. You do want to aim for a cruise in the 31-35 range, but I'm sure you know that.

I wish Sea Ray's didn't have prop pockets, and used more reduction so you could spin a big diameter prop. I hate how much I have to spin mine to maintain any speed. My dad has a 38 Carver with basically the same drivetrain and he's swinging 24x24's compared to my 19x17's, and his top speed is just about the same. We won't even get into how much better his handles.

 

[Redhook98]

Whether or not he cruises his boat at higher rpm's, those big blocks are meant to wind out to 4200-4400 RPM's. If they don't wind up that high, you definitely need a change. I'd try the 16x16's, lugging the motors like you are is harder on them than winding them up. You do want to aim for a cruise in the 31-35 range, but I'm sure you know that.

I wish Sea Ray's didn't have prop pockets, and used more reduction so you could spin a big diameter prop. I hate how much I have to spin mine to maintain any speed. My dad has a 38 Carver with basically the same drivetrain and he's swinging 24x24's compared to my 19x17's, and his top speed is just about the same. We won't even get into how much better his handles.

Yeah, I will try the 16 x 16's first and see how I like em. With the 17 x 17's off, I may get them retuned to 17 x 15's. Not sure yet. I try and cruise in the 3200RPM range and get about 22-23 MPH. That is more then enough for me. I hope the change in props wont slow that down to badly.....