Original prop size for 1976 starcraft chieftain mk Iv 25 foot with 165 merc

[robertsavorgnan]

I'm in need of original prop size for 1976 starcraft chieftain mk Iv 25 foot with 165 merc.
can anyone help me out?
just picked up this beauty but only getting 29mph indicated at 3000rpm at WOT. rpm should be between 3900 and 4300rpm

 

[Bondo]

I'm in need of original prop size for 1976 starcraft chieftain mk Iv 25 foot with 165 merc.
can anyone help me out?
just picked up this beauty but only getting 29mph indicated at 3000rpm at WOT. rpm should be between 3900 and 4300rpm

Ayuh,.... Welcome Aboard,..... That question can't be answered,....
But,..... Tell us the size of the prop on it now, 'n we can give you guidance on which way to go,.....

 

[robertsavorgnan]

Ayuh,.... Welcome Aboard,..... That question can't be answered,....
But,..... Tell us the size of the prop on it now, 'n we can give you guidance on which way to go,.....

I can do that in a few days as I'm back at the farm for a bit.

 

[Scott06]

I can do that in a few days as I'm back at the farm for a bit.

Also would verify the tach is accurate vs shop tach so you don't make pitch changes off a bad rpm number.

 

[robertsavorgnan]

Old prop is an old merc 15.75 x 19.
Got a beat up 15.75 x 17 on now. Will try when the wind dies down.
Was told at a boat shop that it should net me a 400 to 500 rpm gain. That will bring me up to 3500 rpm. Motor is rated for 3900 to 4300 rpm WOT.
May be looking for another test prop soon.

 

[Bondo]

Ayuh,..... Sounds like ya need a 15" prop,....

Oughta cross check yer tach,....

 

[robertsavorgnan]

Ayuh,..... Sounds like ya need a 15" prop,....

Oughta cross check yer tach,....

Tach was accurate when tuning. At least up to 1500 rpm. I will hook it up and check it at a higher rpm.

 

[robertsavorgnan]

Hooked up a digital tac this morning. Boat tac was out by 500rpm. A new 15.75 x 17 prop is bang on 3900rpm at WOT.
The 15.75 x 19 should come in at 3500 to 3700rpm.
Considering the manual said 3900 to 4300rpm what do you think about using the 19 pitch prop and running a few rpm lower for longevity and load on motor?

 

[Bondo]

Hooked up a digital tac this morning. Boat tac was out by 500rpm. A new 15.75 x 17 prop is bang on 3900rpm at WOT.
The 15.75 x 19 should come in at 3500 to 3700rpm.
Considering the manual said 3900 to 4300rpm what do you think about using the 19 pitch prop and running a few rpm lower for longevity and load on motor?

Ayuh,...... That's luggin' the motor, which leads to burnin' holes in pistons,......

I'd consider runnin' a 15" to get up higher in the rpm ban,...

 

[airshot]

Also make sure your engine is running properly !! Have saw numerous people change props only to find their engine was not up to par and having to start over after a good tuneup !!

 

[robertsavorgnan]

Also make sure your engine is running properly !! Have saw numerous people change props only to find their engine was not up to par and having to start over after a good tuneup !!

 

[robertsavorgnan]

Next door neighbor is an ag equipment mechanic. He did the tune-up and I helped, should be good.

 

[airshot]

Compression good along with good ignition and no carb issues ?? Only questioning because you said " should" be ok... My 22' Islander had the 140 hp 3.0 and it did 34 mph at 4500 rpm with full tank and two guys with fishing gear....I know yours will be a heavier boat.....

 

[robertsavorgnan]

Compression good along with good ignition and no carb issues ?? Only questioning because you said " should" be ok... My 22' Islander had the 140 hp 3.0 and it did 34 mph at 4500 rpm with full tank and two guys with fishing gear....I know yours will be a heavier boat.....

The prop I have on is the 15.75 x 17 and it's not in the best of shape. Bent, chunks missing, and welded on. I actually used a rock and picnic bench to straight it sum. Found a next to new old stock prop in the good old USA. Should be here 2nd week of Sept. Lesser Slave lake Alberta Canada.

 

[robertsavorgnan]

The prop I have on is the 15.75 x 17 and it's not in the best of shape. Bent, chunks missing, and welded on. I actually used a rock and picnic bench to straight it sum. Found a next to new old stock prop in the good old USA. Should be here 2nd week of Sept. Lesser Slave lake Alberta Canada.

I got 31.8mph today on flat water.

 

[robertsavorgnan]

This prop looks interesting. What's your take in this.
16x16. Should add 150, 200rpm.

 

[Scott06]

Ayuh,...... That's luggin' the motor, which leads to burnin' holes in pistons,......

I'd consider runnin' a 15" to get up higher in the rpm ban,...

This is the best advice here, best to prop it so you can hit the upper end of rpm spec. Not that you have run it that rpm, just will be a more lively boat if its pitched correctly. What ever you do don’t put the 19” back on it as it will put more strain on the engine lugging it.

 

[robertsavorgnan]

This is the best advice here, best to prop it so you can hit the upper end of rpm spec. Not that you have run it that rpm, just will be a more lively boat if its pitched correctly. What ever you do don’t put the 19” back on it as it will put more strain on the engine lugging it.

Ordered a Solas 15.8 x 15 aluminum part #1511-158-15
Hopefully this will do the job.