WOT, RPM's and Prop size

[jmatteo1]

1978 Wellcraft 196 Sunhatch, 198 H.P. Mercruiser, Pre-Alpha outdrive.<br /> <br />Lake Erie cooperated yesterday and I was finally able to run WOT. I was able to run 5000 RPM, and according to my fishfinder I was going 40 MPH. My prop is stamped "15 3/4 R 17". The boat has trim tabs and I get on plane easily using them. <br /><br />Two questions; 1) Are the RPM'S and MPH are in the right range? 2)Does the prop seem like it's the correct one? <br /><br />Thanks, Joe

 

[TilliamWe]

Re: WOT, RPM's and Prop size

I guess it would plane pretty quick! You are underpropped, if your RPMs are correct. While I do not Know the correct rpms of a 1978 Mercruiser 198 (is that a Ford 302 or Chevy 305?), I can say that 5000 is too much. I would think wot rpm range should be 4200-4600.

 

[TilliamWe]

Re: WOT, RPM's and Prop size

I now know it's a 305 Chevy, I went to yuor picture site. I am really quite certain that 4600 would be the max rpm. I say that cause we had a 1984 260 (350) and it's range was 4200-4600. We propped it to run at 4400 rpm wot & it did everything well.

 

[jmatteo1]

Re: WOT, RPM's and Prop size

Anyone have any suggestions for a different prop? I'm assuming I should go to a larger diameter? The boat is used for cruising, fishing, and watersports.

 

[TilliamWe]

Re: WOT, RPM's and Prop size

Don't worry about diameter too much. In your case you need more pitch & maybe more blades. Get Trailer Boats Magazine's July issue & read the article on props. Should tell you everything you never wanted to know about props.

 

[rbezdon]

Re: WOT, RPM's and Prop size

Definately go bigger pitch and not diameter. The rule of thumb of 200 rmp per inch says that a 19 pitch of the same dia should get you down to the recommended rpm range

 

[1979SeaRay]

Re: WOT, RPM's and Prop size

jmatteo1 I have the same engine in my 21.5 ft Sea Ray. I know the recommended RPM range for my boat is 3800-4200rpm at WOT.

 

[f_inscreenname]

Re: WOT, RPM's and Prop size

You may want to play with this. http://www.boatramp.com/prop_applet/PropAnalyzerAppletG.html

 

[ibncolorado]

Re: WOT, RPM's and Prop size

Hello--I have a 19 ft Sea Ray Bowrider with 5.7 Litre and Alpha One--cant find the right prop-have tried 19,21,23,24. 23p works best so far but I only get 4100 rpm @ wot and about 42mph max speed. I am at high altitude in Colorado-4000 ft above sea level-but, gotta get those rpms up and should get at least 50 mph I think. Any thoughts ? I may try a 22 next-21 doesnt work right. thanks

 

[Don S]

Re: WOT, RPM's and Prop size

OLD 2005 Post
Welcome to iboats ibn
Best to start your own thread, and in the correct forum.
Please repost in the Prop Questions and Topics forum and start a new thread