I need some help on picking the right prop!!

[bvprice]

Hey all!!!<br />I need a little advice. I recently purchased a 1996 Bayliner Ciera 2855 with a 280 horse Mercruiser 350(5.7)and an Alpha One Gen. II drive. She is 30' 3" long and has a dry weight of about 6900 lbs, so she's big. I am having some prop issues. I bought the boat in Chicago (It was ran on the great lakes.) and trailered it to Wyoming. The prop that it has now is a 15P Aluminum. The guy I bought the boat from said he got 25 to 30 mph cruising and about 35 top speed out of her. She had a new engine put in her in 2000. It has about 200 hours on it. I realize that elevation has an effect on what prop to use. (Chicago is about sea level and it's about 5000 ft above sea level where I live.) I took her out for the first time a couple of weeks ago, and realized I need to re-jet the carb. The boat has trim tabs, which I'm learning how to use, but I could only get about 17 mph out of her at 3500 rpm's. I want a good top cruising speed, but also plan to pull tubers and maybe a kneeboarder or two, so I still need some hole-shot and a little low end torque. Can anyone suggest an option or direct me to a website with some info? I was thinking maybe a 17 or 18P? What about 4 and 5 blade props? What is the suggested rpm's for cruising and top speed? Any help is appreciated!

 

[luckydog49]

Re: I need some help on picking the right prop!!

I had a 28 bayliner that we moved to Lake <br />Tahoe, about 6000ft elevation. You lose about 3-4percent of your power per 1000 feet, so at 5000 feet you are down as much as 20percent, our boat had a very hard time planning until we ran the fuel tanks to one-half, the boat would top out at 28mph at sea level, but only about 21 at the higher elevation, that was after going down 2 degrees of pitch (from 15 to 13), the boat is heavy and a 5.7 motor at elevation is too small. Our friend has the same boat with the 7.4 and doesn't have any problems. Ro

 

[Boatist]

Re: I need some help on picking the right prop!!

Unless you find a lot more power there is no way you can turn a 17 or 18 pitch prop even a 3 blade. With what your have right now you are looking at a 11 or 9 pitch prop to get your RPMs up where they should be. 4 and 5 blade props are really design for light fast boats like a bass boat. Unless you find more power you will be lucky to get that boat to reach a clean natural plane. Your engine WOT RPMS should 4400 o 4800 rpms. If you get it up on plane then you should pick up some speed. Do you know what speed your boat reaches a natural plane? Most boats about 19 to 21 MPH. After you rejet the carb and adjust the timing for your elevation you may be able to get on plane. If you can reach a clean natural plane then I would recheck your speed and rpms. <br />Check things to reduce drag of the boat in the water. Clean the hull, reduce weight. Do not fill the fuel and water tanks. Loose weight, Throw the Wife Kids and Guest overboard.<br /><br />Hard to tell what pitch prop you need until you get the boat on plane but it will be 13 or less. <br /><br />In my opinion you would be better off to buy a second boat or PWC to pull tuber and boards.

 

[bvprice]

Re: I need some help on picking the right prop!!

Originally posted by Boatist:<br /> Unless you find a lot more power there is no way you can turn a 17 or 18 pitch prop even a 3 blade. With what your have right now you are looking at a 11 or 9 pitch prop to get your RPMs up where they should be. 4 and 5 blade props are really design for light fast boats like a bass boat. Unless you find more power you will be lucky to get that boat to reach a clean natural plane. Your engine WOT RPMS should 4400 o 4800 rpms. If you get it up on plane then you should pick up some speed. Do you know what speed your boat reaches a natural plane? Most boats about 19 to 21 MPH. After you rejet the carb and adjust the timing for your elevation you may be able to get on plane. If you can reach a clean natural plane then I would recheck your speed and rpms. <br />Check things to reduce drag of the boat in the water. Clean the hull, reduce weight. Do not fill the fuel and water tanks. Loose weight, Throw the Wife Kids and Guest overboard.<br /><br />Hard to tell what pitch prop you need until you get the boat on plane but it will be 13 or less. <br /><br />In my opinion you would be better off to buy a second boat or PWC to pull tuber and boards.

Thanks for the responses. I have a hard time beleiving I'm just "screwed", though! What I'm hearing is that I spent a lot of my hard earned money on a fancy floating log? I realize that she's a lot of boat for a 350, but it has 280 hp where as the 454 only has 310 hp and a little more low end torque. It's hard for me to believe that 30 hp is the difference between a boat that "does fine" and one that doesn't. I had a heavy 1986 22ft cuddy with the same motor prior to this boat and I ran a 21P prop for a top speed of 50 mph. I realize the current boat is heavier, but it seems I should hope for more than barely reaching natural plane and a top speed of 21 mph!! More thoughts on this would be greatly appreciated!!!

 

[walleyehed]

Re: I need some help on picking the right prop!!

27-28MPH will be the fastest speed you could possibly attain at your elevation but it's gonna take some work to get there. Max timing is going to above recommended, the carb is going to need set-up for 6000ft, and most likely, you will need to vent the prop to get any hole-shot.<br />We run a 350 on a wellcraft 21-1/2ft'r at 4000+ elevation and it does best with a 19 for cruise...a 17 is required for skis or tubes.<br />1" pitch reduction for every 1500ft is about as close to a rule of thumb you can get...<br />As Boatist said a 13 or lower...<br />I believe a 13 will put you in the bottom of your RPM range with no load, an 11P should be real close to the prop you need.<br />To top it off, the engine must be in perfect working order and set-up for high altitude operation by someone who truely understands what it takes to make it work there.

 

[Boatist]

Re: I need some help on picking the right prop!!

Titan<br />I hope I am wrong but that is a big heavy boat and at 5000 foot you are not going to get 280HP. I really feel you need to do everything you can to reduce weight so you can get boat on plane. Once boat comes up on plane with out trim tabs you will gain speed at that point you can get a better reading on your WOT RPMS and determine which prop you need.<br /><br />You might also want to check post in this fourm,<br />"Engine Size / Searching for 1ST Boat by Sharelove"<br /><br />Most boats out here your size have Twin 5.7 or they just run at hull diaplacement speed.<br /><br />Good Luck I wish you the very best.

 

[QC]

Re: I need some help on picking the right prop!!

BTW, was there ever a 280 rating on the 5.7? I thought they jumped from the 250 TBI to the 350 Mag at 300 in 1996. Not sure. Maybe somebody else is? They rate the carbureted 5.7s now at 250 prop shaft which is about 280 at the flywheel. Maybe that is what you've got.<br /><br />Boatist is right too. No matter what it was originally rated at, it is not making 280 at 5000 ft.<br /><br />This has to get back to a tachometer discussion. Everything else is just crap without a good WOT reading. And with your boat I would prop to the higher end of the WOT range like Kenny is pointing you. This would give the best possible hole shot.<br /><br />I wouldn't give it up for driftwood just yet. Worse case sell it to somebody that boats at sea level and try again. Just depends on your priorities . . .