switch to SS?

boatman37

Lieutenant
Joined
May 14, 2015
Messages
1,273
hey guys. 1986 Sundancer 250 with 5.7 alpha gen 1 1.47 ratio. i currently have a 14.5x17 aluminum prop on it. last year i could get to about 4000 RPM WOT and about 33-34 MPH (GPS) with 2 people and a 'normal' load of fuel and water. overall i'm ok with the performance but the RPMs are a little low. i also have a SS prop that the PO said is also a 14.5x17. the numbers on it are 48-88438A-4-17P, which looks like it is a 15 3/4 x 17? my main objective would be better fuel economy of the two. i would rarely ever see full throttle and i can plane out at about 2500 RPM at 23 MPH with the aluminum prop but that is barely on plane and should be considered as the minimum. i feel better at about 2700 and 25MPH.

another concern is the electrolysis with the SS prop. i boat on the ohio river and the boat is in the water for about 5 months.

so is it worth changing out to the SS prop? what differences will i see? most of my cruising will likely be at close to no wake speed. wife likes to cruise and sight see. but on plane occasionally and not concerned with top speed or WOT as long as i'm not lugging it
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Need to dial a prop that achieves middle to max wot rpm range for that I/B while loaded as stated, 4 K revs seems bit low towards lugging zone, if so, a less prop pitch whether alum or SS should pull revs up, when so, can go boating through your comfy rpm range along good fuel economy.

Happy Boating
 

Rick Stephens

Admiral
Joined
Aug 13, 2013
Messages
6,118
Like Sea Rider said, 4k is a little low. Prop down a little would be the normal recommendation. Since you already have the SS 17, what's the harm in testing it?
 

SkiDad

Lieutenant Commander
Joined
Jul 18, 2010
Messages
1,518
i think your rpm might go down with the stainless due to better grip - if i was you i might get the AL re-pitched to a 15 or sell the SS prop and get a new 15 p prop. I would shoot for 4400 rpm as a min.
 

boatman37

Lieutenant
Joined
May 14, 2015
Messages
1,273
thanks guys. if i remember correctly the factory recommended a 15x15 but not sure where i saw that
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Although factory recommends a 15 prop as a starter prop, need to wot tach it while lightly loaded and check achieved max rpm, ideal running middle to max rpm range. If family oriented, test same with family and check max wot rpm, can go from there maximizing a less prop pitch to pull revs up if needed.

Happy Boating
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Your slip is at about 20% .12% is closer to normal. Your heavy boat may also make higher slip.
I think the ss will improve the slip numbers but may lower rpm.A good prop shop can remove pitch add or remove cup etc.
 

Challenger84

Petty Officer 1st Class
Joined
May 9, 2010
Messages
341
Your rpm's is very low with your engine and prop combo....
I have a 5.0 with a 19 pitch prop.. With 4 people full tank of fuel and bbq grill and cooler I get way past 4k... I over rev with my 19 pitch. 5.4k.
I got a 23 SS prop but haven't had a chance to try it out yet..
Good luck !
 
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