Trying to size prop for 25 foot sea Ray

[CAPTKEV85]

Hey eveyone,
It's been a while since I've been on forum. I need some help with prop selection. I just put a new motor in my 1985 sea ray Seville. It is a 350 vortec small block with a 1409 eldelbrock carb. Hp at crank is 315 hp as per the previous 260 hp with old motor. Right now I have a turning point propellor 4 blade aluminum with a 14.5x17 wot at 4200-4400. My motor is rated at wot at 4800-5000. Max speed with this prop is 37 mph. I like to cruise with the boat not race it. At 3000 rpms it's speed is around 18 mph but it's semi plane. And 3200 I'm on plane at 22.5 mph. Now should I try a 14x19 pitch? Or leave it alone? Also I tried some 3 blades but felt I reved out to much. Would stainless help at all? Any info would be a great help thanks guys.

 

[Maclin]

What is the top RPM your new engine can get to now with that prop in that boat?

 

[CAPTKEV85]

4400 rpms

 

[Bondo]

4400 rpms

Ayuh,.... You need to go Down in pitch, to bring the rpms up,....

Goin' to a 19" will further lug the motor,.....

 

[Maclin]

What Bondo said.

Was this the same prop in use before the engine replacement? If so, what rpm did the 260hp engine hit with that prop? If the old engine was getting into the top of the rpm band with it then this new engine may not be quite up to that 315hp potential yet regarding the state of tune.

 

[CAPTKEV85]

Same prop on old motor as well. Problem was old motor was sucking sea water in back cylinders so wot was 3400 rpms motor was toast for two years. Does 4400 seem like a good wot? Motor does not sound like it's working hard at all. I guess what I'm trying to do is get my cruising speed up but rpms down. I like the prop I have now and I think I'm out of options.

 

[Maclin]

Only hitting 4200-4400 would be a concern for me. I think you need to get the top RPM's up to 4600 or 4800. The engine will like life better not being lugged down, and I bet the top speed would be the same. And by the way, Cruise speed up and RPM's down are opposing goals, and can be hard on an engine if it cannot rev freely to top RPM's even if you do not go "there" often.