Logo

Prop Problems

tobyj

New member
"I have a 21' Chris Craft

"I have a 21' Chris Craft Bowrider Limited 205HP 4.3L V6LX Mercruiser.
I have a 14 1/2 " X 19 aluminum prop and it is not getting me up on plane fast enough. But I am almost at my top RPM range which is 4400 -4800. Alao with this prop I am having either ventilation or cavitation problems, not sure which. When I turn, RPM's go up and boat speed goes down. If I trim it up a little, same thing, RPM goes up speed decreases. I had this prop on a 19' bowrider and it worked perfect. Everybody said 19 pitch is the best all around for that size boat. That does not seem to be the case for this boat. And no one can tell me what the perfect pitch is for the 21' chris craft.
Can anyone help?"
 
"First, is the prop in good sh

"First, is the prop in good shape, no serious nicks, bent blades? Bad blades increase the odds of cavitation.

How many blades? Two, three, four? More blades increase the low rpm bite for improved acceleration and pulling skiers up, and decrease odds of cavitation. Also reduce left/right turning differences in performance.

When turning if you detect cavitation, it usually means you need to trim it down (in) for a better bite.

A stainless steel cupped 4-blade is probably a better choice. Work with a good prop shop that will allow you (or their tech) to actually try several props on your boat to select the best one for you - do not just buy what the salesman says with no return privilege or guarantee. Good prop shops work with you, not just sell props.

Perfect pitch - 19" ?? Depending on the diversity of activities desired, some people need two different props to cover their needs. Number of passengers, weight of fuel, number of toys, weight of boat, design of hull -- ALL affect the pitch requirements. A 17" pitch may be better choice for your needs. It would improve acceleration, bite better in turns, etc. Depending on load you could even get better top speed. Just do not let engine run above its rpm range. All this is why I strongly recommend good prop shops."
 
A SS 19P will take care of the

A SS 19P will take care of the issue since your alum. is near top WOT.
 
"Toby

I'd say the probl


"Toby

I'd say the problem that you have is ventilation and not cavitation. Ventilation is the prop being able to suck in outside air and get it mixed in with the water around the prop. RPM's go up, but boat slows down. Cavitation is low pessure areas occuring aound the prop and boiling the air out of the water. Not that any of this really matters. What does matter is that you have a problem. My 19.5 ft Tahoe with 4.3 pops right out of the water using an aluminum 23 pitch. Thats pulling 2 tubes, 3-4 people in the boat and 25 gallons of gas. So that works for me, but probably not for you. David has it right on alot of different points. My old ski boat worked perfectly with a 17 pitch stainless, but laboured with a 19 pitch stainless. Go figure. Guy is saying to try a stainless 19 pitch. This will take the flex out of the blades and usually improves perf. Aluminum blades flex and flatten out during acceleration, where stainless won't do this.

Wrench"
 
Back
Top