need help prop in a celebrity 208

jpoisson

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Jun 29, 2015
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Okay here it goes have a celebrity 208 status. When I received the boat it hasn't ran in years. Long story short got her running like a top. Only problem is she has no speed. . Here is her specs:
Mercruiser alpha 1 5.7l motor
Mercruiser alpha 1 1.5 ratio leg
Prop on boat 14x19 aluminum in rough shape tested with this prop wot only 3800 rpm @ 58.9 km/h done with gps.
Changed to a 14x17 prop and now wot 4400 rpm @ 54.8 km/h with gps.
Timming of motor is 8 btdc@ 750 rpm and 28 btdc @ 3200 rpm.
Boat runs strong but only goes that 55 ish km/h which I think is kinda slow for a 5.7 motor. Oh ya the motor was new prior to me getting the boat. When I trimmed the boat with the 19 prop on it I could trim it almost to the stop without any cavitation but with the 17 prop I can only trim it a quarter then it starts to cavitat really bad. Is there anything I am missing? I know this is a big boat at almost 21 feet and 3700 lb's with fuel and passage but I feel it should do close to 80 km/h from what I have read with comparable boats. Any and all help is great fully appreciated.
 

Bondo

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Apr 17, 2002
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Changed to a 14x17 prop and now wot 4400 rpm
When I trimmed the boat with the 19 prop on it I could trim it almost to the stop without any cavitation but with the 17 prop I can only trim it a quarter then it starts to cavitat really bad.

Ayuh,..... Welcome Aboard,..... At 4400 rpms, yer pretty much at the bottom of the rev range,....

Addin' cup to the trailin' edges of the prop will help with the blow-out when trimmin', but will probably drop the rpms even More,......

Ya might need a 15" prop, with Alota cup beat into it,.....

Btw,.... I think 50 mph will be a pipe dream,.... mid/ high 40s probably,.....

Get yer rpms up, 'n build more horsepower,....
 

steelespike

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Apr 26, 2002
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19,069
What year? Is it a cuddy? A 250 hp 5.7 should turn a 19" up to about 4800, hole shot a little weak.
I think a 17 should threaten to over rev. Is the bottom clean and smooth no bulges or hollows.Does the throttle open all the way?
Maybe do a compression check.
 

jpoisson

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Jun 29, 2015
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It's a 1993 208 stratus and not a cuddy. Boat is nice and clean and has not been in the water for 10 yrs, stored inside so not water loged. Yes the throttle opens the butterflies wide open on both the primary and secondaries.
 

steelespike

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Apr 26, 2002
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If we assume your at the max power available your 17" prop has 28% slip based on your rpm.13% is more typical.
The tach is always suspect in these cases.Is the 17 a new prop?If the the tach is accurate and motor sound we have to look at the prop or the hull and setup
to find the reason for high slip I think the tach is a easier place to start.Perhaps you can borrow a shop tach. I'm thin king the rpm is actually lower than 4400.
While the boat was laid up for sometime the components are 22 years old.Been through thousands of hot and cold ambient temp cycles.
 

jpoisson

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Jun 29, 2015
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That is with a shop tack my tach was showing 4700 rpm. No the props both are used and are in kinda rough condition. I was wondering if a new prop would make the difference? Also would a stainless prop be a lot better as it won't flex as much. Just hate shelling out a bunch of dough for a prop that won't work. I also live like 400 miles from the closest marina so the option of trying different props is out.
 

Tail_Gunner

Admiral
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Jan 13, 2006
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6,237
Yes props in rough condition can effectively ruin performance, think of the thrust they create what appears small to you is magnified greatly under pressure. Post some pics let's see the little darlings.

As to stainless.....a 100 dollar 4 blade solas will drop that slip quite well and give you a foundation to pick a stainless if you so chose.
 
Last edited:

steelespike

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Apr 26, 2002
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19,069
So we are at 4400 with a 17' prop.
I agree an al. solas 4 blade is a good place to start.Being already a little low on rpm, 4400, I think you need to go down at least 1 " for the 4 blade maybe even 2 "
A 15" 4 blade may give you 4600 rpm possibly at about 13% slip.this calculates at about 37 mph 60 km.Should have a strong hole shot.
I still firmly believe there is a motor/drive train issue.
 

jpoisson

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Jun 29, 2015
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Thank you all for your replies. Here is what I did in the past week, put in a new set of spark plugs, rentals timed engine to 8 degrees btdc put a kit in the carb and bought a new 14.25X19 prop. Took her out to the lake on wed. New results 43 mph@ 4200 rpm thinking I should have bought a 17 pick prop now. Any suggestions on a diffrence carb maybe kinda partial to holley as I know how to set them up better than webber. Oh ya my engine is a 350 mag alpha 1993 model year. Thanks again for all responses.
 
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