I am trying to replace my prop and need help

[Chris_94_Sprint_TX]

I bought my Sea Ray used and don't know much about it but I am learning more every day (mostly on here). Everything is original as far as I know. Its a 1984 Sea Ray Seville 5.6 (I think, I know its a Seville and I know its 18.5ft) open bow, its 18.5 feet long. It has the Mercruiser 3.0L 4 cyl and I think its 140 horsepower (if I am wrong please correct me), I don't know which drive it has but I would guess its an alpha 1 (again if I am wrong pleas correct me). It has a 19 pitch prop now (best I can figure) that is aluminum and missing some chunks on some of the blades and if the tach is right its running at 5k plus at WOT and should only be running at 4600 at WOT. I would like to change to a prop for a little more speed as the boat only hits about 32mph right now. The following numbers were written down from the inside of the prop and match the outside of the prop somewhat. Inside says 48-78120 19 and the outside says 48 78120 A40 19P. I would like to upgrade to a stainless steel prop for durability reasons. I am a fulltime student and don't have lots of money and would like to stay as inexpensive as possible. Sorry for all the noobish questions and thank you all for taking the time to read and offer help.

Chris

 

[90stingray]

Re: I am trying to replace my prop and need help

Sticking with aluminum will help keep costs down. Its hard to judge what prop might work best because your numbers are a little skewed.... due to the damaged blades I would guess. I would find a buddy with a 3 blade aluminum 19p and throw it on and get some better numbers. Your local marina might have an exchange prop program to where you can try before you buy. Maybe a prop shop might be able to rework your current prop for cheap. I like to search craigslist for good deals too. And if you have to break down and buy new... then try here on iboats! Prices are really great and they usually are running sales/promos. I hope I helped you some... Have fun with your "new" ride this summer.

 

[jestor68]

Re: I am trying to replace my prop and need help

The WOT rpm range for your 1984 140 is 4400-4800 rpm. The 4200-4600 range is for the 120.

Be more specific on your current WOT rpm. Saying it does 5000+ means what?

For more speed, the next step up would be the 21 pitch. Expect this pitch to drop your WOT about 400 rpm and pick up several mph.

A quality aluminum prop, such as Solas or Turning point will provide performance rivaling some SS props for a third the cost.

Your current high slip numbers are likely being caused be your prop being damaged.

 

[fishrdan]

Re: I am trying to replace my prop and need help

Those numbers don't seem right. A Mercruiser 140 turning 5K RPM(+?) with a 19P prop, only going 32 MPH? That's around 30% prop slip?!? It should be up into the high 30's pushing 40 with those numbers. Bad prop causing excessive slip, tach off, inaccurate speed? Was the speed by speedo or GPS?

I agree with stingray, try to beg or borrow a good prop to get good baseline numbers (along with GPS speed), then select an aluminum prop based on the "good" numbers.

My heavily loaded 18' aluminum fishing boat with a Mercruiser 140 turning 4500-4600RPM with an 18P aluminum 4 blade prop goes 34-35MPH GPS. Less RPM, less pitch, probably higher load, yet more speed? It's just a comparison, though comparing my boat to yours could be like comparing an apple to a tangerine due to different hull designs, loads, props, etc.......

 

[Chris_94_Sprint_TX]

Re: I am trying to replace my prop and need help

I saw 5200 or so and imediately backed off the throttle to avoid over revving the motor. Both readings are from the original boat guages. How do I know which prop will work with my drive? I will try a few places this afternoon to see about a prop exchange program or prepair. THanks guys for all the help.

Chris

 

[Chris_94_Sprint_TX]

Re: I am trying to replace my prop and need help

I will post a picture of the prop later when I get home for y'all to see. Maybe somebody can tell me if it can be repaired.

Chris

 

[Maclin]

Re: I am trying to replace my prop and need help

If the prop is missing a lot of blade then it will rev higher but go slower, lots of slip, goes along with 90Stingray's and other's posts. I would get a good 19p (see if a prop shop can fix yours ) on there and see what it does. A (good) 19p should be just about right for your setup.

 

[Chris_94_Sprint_TX]

Re: I am trying to replace my prop and need help

What size gear case would the alpha 1 drive have for my year? I have been looking at the West Marine website since I have one fairly close to me and I can go pick it up instead of shipping and waiting. I want to buy a buy and have a spare so I will see if a shop can repair mine as well. When replacing it should I replace the washers and nut as well? I figure it would be a good idea considering the age of the boat but if I were to buy extra props at different pitches do I need to change those items everytime?

Chris

 

[90stingray]

Re: I am trying to replace my prop and need help

Gear case is 4 3/4." You do not need to change thrust washer every time. Just make sure the prop does not rub the case once installed... they make thicker or thinner thrust washers. But I would bet you will be fine. The locking tab under the nut has 6 wings and you only use 3 to lock it down. These do take several removal and reinstallations pretty well before requiring replacement. And the nut is usable as long as the nylon still provides friction when spinning it on.... basically if you can hand thread it all the way down, nylon is worn and you need new. But buying a new nut and locking tab to start you off would be a good thing. Then you can keep the original as a spare.

 

[Chris_94_Sprint_TX]

Re: I am trying to replace my prop and need help

That's kind of what I was thinking but being an auto tech and always being told when replacing certain things always replace the nut made me second guess so I figured I ask those who know more than I do.

Chris

 

[Chris_94_Sprint_TX]

Re: I am trying to replace my prop and need help

Took these today. this is my current prop.

Chris

 

[Grub54891]

Re: I am trying to replace my prop and need help

Yup ya need a prop,its slipping/cavatating through the water.there are places that rebuild props,get a new one,use that for a spare.
Grub

 

[Chris_94_Sprint_TX]

Re: I am trying to replace my prop and need help

Found a repair actually its an automotive shop but they work on boats as well and he says he has a few props laying around that He will let me borrow and try out, I just have to get with him tomorrow afternoon. Hopefully I can find a good combination of performance with one of them.

Chris