1985 SeaRay Amberjack Prop Questions

[blkzoe]

Am in the process of restoring a 1985 SeaRay Amberjack; twin 170's (470's) on Alpha 1's. New transom (I'm scarred for life); 1 total rebulid on the starboard engine; new interior and seating. You understand my sickness.......... Anyway, the original props on the AJ were Black Max QA1912X; 15 x 17, 3 blade aluminum. I purchased replacement props based upon what I removed from the boat. Now I come to find out that SeaRay recommended 14 x 19 on this model.

Currently my AJ behaves as follows:
hole shot - like a bat out of hell;
planeing - up on plane in a heartbeat;
speed @ 4000 rpm - 27 mpr via GPS; (NOTE: This boat weighs in at 4900 lbs.)
throttle left @ 4000 rpm - plenty; WOT - chickened out approaching 4600 rpm (upper rpm limit for 470's).


THE QUESTION: If I swap out the 15x17 props for the 14x19; what can I expect relative to performance? Any input appreciated. Thanks to all.

 

[steelespike]

Re: 1985 SeaRay Amberjack Prop Questions

Is the rebuilt motor broken in?
It does appear you are underpropped.It won't hurt to take healthy motors over the redline momentarily to get a wot rpm. and speed.
If a 19" prop is suggested its certainly a safe number.Is the 19 suggested for a twin installation?
Usually a 2" increase will reduce rpm about 300 to 400 rpm.This number may be slightly different as a twin installation suffers
with extra weight and drag compared to a single installation of the same total hp.

 

[blkzoe]

Re: 1985 SeaRay Amberjack Prop Questions

Is the rebuilt motor broken in?
It does appear you are underpropped.It won't hurt to take healthy motors over the redline momentarily to get a wot rpm. and speed.
If a 19" prop is suggested its certainly a safe number.Is the 19 suggested for a twin installation?
Usually a 2" increase will reduce rpm about 300 to 400 rpm.This number may be slightly different as a twin installation suffers
with extra weight and drag compared to a single installation of the same total hp.

After receiving many valid comments from a variety of knowlegable folks; I'm going w/ the 14.5 x 19 Quicksilver QA1916X (Aluminum). Would have loved to have gone w/ SS, but cost is an issue. My slip calculation was 23% for my current props (ouch). I noticed my old 15 x 17's were shot around the blade edges. Cavitation damage from being underproped at 15 x 17? Saw some enlightening pics that looked very similar. I feel good about the selection (and price). Thanks for the input.