Prop change question...

[Travis71]

I have a 20' runabout with a 5.0L V8 engine. Manufacturer's shop manual says WOT should be 4000-4400 RPM. I am currently running a 14-1/2 x 19 prop, WOT is 4200, and top speed is 40 MPH. So everything looks good on those numbers as far as I can tell. Had it out on the water with the wife and kids (5 total people) and it seemed ok, but I am concerned about acceleration when trying to pull a skier out of the water.

I have a stainless steel 15x17 prop that I can put on this boat. What kind of differences can I expect in:
acceleration?
rpm at WOT?

 

[WesNewell]

You can expect better acceleration pulling a skier. Also wot rpm will probably go up 200-600 rpm with normal to light load. Use the 17p when pulling and the 19p when not, or just watch your max rpm with the 17p not to exceed max rpm. Up to you how often you want to change props.

 

[harringtondav]

^^ What he said.

I use one prop for water sports, and keep my cruising prop on board as a spare. I rarely change to the higher prop. I just use my right hand rev limiter. With my hole shot prop I can still go 44 mph and stay in safe rpms. That's fast enough for me.

 

[Sea Rider]

Bad idea, or you go boating with passengers as stated or skiing with driver and a spotter only if mandatory, the rest of the passengers will need to stay in terra firme, too much stress lugging the motor boating and skiing at same time with same prop. Personally deslike changing props for same day boating at both scenarios.Pulling a skier depending on its weight will be adding 1-2 more boaters to the equation.

Just for the record, when boating and skiing at same time with current installed prop, what's the max rpm achieved once boat is on plane ? The only way to know exact acceleration and wot rpm with a 15 x 17 prop will be testing it at both boating scenarios.

Happy Boating

 

[QBhoy]

That’s quite a low rpm rating. I thought a 1989 OMC 5.0 might be the same as the 89 mercruiser and VP 5.0 at 4400-4800 ? Weird one.

 

[Travis71]

That’s quite a low rpm rating. I thought a 1989 OMC 5.0 might be the same as the 89 mercruiser and VP 5.0 at 4400-4800 ? Weird one.

I double checked my book and that is the rating it lists.

 

[Travis71]

Bad idea, or you go boating with passengers as stated or skiing with driver and a spotter only if mandatory, the rest of the passengers will need to stay in terra firme, too much stress lugging the motor boating and skiing at same time with same prop. Personally deslike changing props for same day boating at both scenarios.Pulling a skier depending on its weight will be adding 1-2 more boaters to the equation.

Just for the record, when boating and skiing at same time with current installed prop, what's the max rpm achieved once boat is on plane ? The only way to know exact acceleration and wot rpm with a 15 x 17 prop will be testing it at both boating scenarios.

Happy Boating

I'll have to get back to you on those statistics. I just got the boat and water isn't warm enough for skiing yet.