I need a new prop, but the more I read up, the less I seem to know.

[beilwing]

Hey gang,
To start I am currently running an 04 chaparral 210 ssi, approx 21.5 feet long, equipped with the carburated 5.0 mercruiser rated at 220 hp. I have a 19 pitch prop and I can make out the 14 but not what follows it for diameter. It is an aluminium 3 blade prop that may have been refurbished but maybe not. It came with the boat. I think I have read that 4800 is max rpm for my set up but I tend to "chicken out" around 4500. I am seeing speeds of about 46 with just the admiral and I on board. I'd like that to be over 50. I know I'm not far off and I'm only at top speed a few times a year, but for those times, I want 50+.

Now we get to the questions:
Do I need more pitch if I go more blades, or more like how much more pitch per blade? I have read that more blades help with hole shot but hurt top speed due to drag. So if I went to a 4 blade but jumped to a 21 pitch s.s. prop, would the extra blade cancel out the extra pitch?

If I do go to a stainless prop and do hit a rock (it's has happened once it the 6 years I have been a boater) and the rock doesn't give, and the prop doesn't give, wouldn't that mean trouble for the internals of the out drive?


T.I.A.

 

[steelespike]

Re: I need a new prop, but the more I read up, the less I seem to know.

Prop sizes are written diameter X pitch i.e.: 14 X 19.Usually can be found near the base of the blades or under the prop nut.To tell how your setup works we need your prop size,wot rpm and gps speed.
you need to try to get it too its fastest rpm and speed using the trim.The motor is designed to a operate for extended periods at 4800 rpm but will hold up better when operated at a slightly reduced rpm which most people run at.
It won't hurt to run beyond the red line long enough to establish your performance numbers if necessary.
While a 5.0 is able to make 50 easily a speed change of over 5 mph at that speed isn't likely unless the boat is poorly setup to begin with. You prop to get the best speed within the motors rpm range.
Very basically adding blades usually slows top end.Increasing pitch "may" increase speed at the expense of hole shot and load ability.
Reducing pitch improves hole shot and load ability usually at the expense of top speed.
These generalities depend on present prop size and performance.

 

[callen369]

Re: I need a new prop, but the more I read up, the less I seem to know.

Hey gang,
I have a 19 pitch prop and I can make out the 14 but not what follows it for diameter. It is an aluminium 3 blade prop Do I need more pitch if I go more blades, or more like how much more pitch per blade? I have read that more blades help with hole shot but hurt top speed due to drag. So if I went to a 4 blade but jumped to a 21 pitch s.s. prop, would the extra blade cancel out the extra pitch?

If I do go to a stainless prop and do hit a rock (it's has happened once it the 6 years I have been a boater) and the rock doesn't give, and the prop doesn't give, wouldn't that mean trouble for the internals of the out drive?


T.I.A.

If you are sure it is a 19 pitch, and you can see a 14 on it, then it is most likely a 14 inch diameter by 19 pitch prop. Which sounds about right for that motor. Would depend also on the outdrive gear ratio, which can be found stamped on the side if it's a merc. I think the V8 motors usually have something like a 1.67 ratio, but don't qoute me on that, look at the drive. Easy to measure diameter, measure from center of prop to outside edge of a blade and times by 2. You'd probably be right at 50+ at 4800 RPM, which you should not be "chicken" of hitting, just don't run it there all day long. You'll hit rev limiter if it goes too high, but it it passes it when running, pull throttle back and keep it there.

For any more speed, you would normally go up in pitch. However, simply switching to a high performance 3 blade stainless in the same diameter/pitch will probably put you in the mid 50s, and you will still have great hole shot and acceleration.

Unless you are pulling a lot of skiers at once, or a couple on slalom, you should be good with a 3 blade. If you switch to a 4 blade and go up in pitch, your WOT Rpm's may be too low and could be bad for the motor. If you stay 3 blade and go to 21 pitch, you will probably lose 2-300 RPM off the top.

Stainless prop strikes could really damage your outdrive, best to know the water where you are boating if running stainless, and carry the aluminum as a spare to switch out if checking out new waters.