17' Chaparral / 3.0 Mercruiser - New Prop?

Okay, I am a relative newbie to boating and prop selection is a bit of a mystery but I think I am catching on. Here is the lowdown on what I have -

1988 Chaparral 178XL - 17' bowrider.
3.0 Mercruiser @ 130 hp.
2bbl. carb / original configuration.
Alpha 1 outdrive, no clue as to ratio but can check tomorrow.
Speedometer doesn't work.
Tach works, still have more throttle to go when I hit 4000 RPM's, so I haven't run it at WOT.
Running a Merc Aluminum 3-blade, 17" Pitch, 15" diameter.

We like to load up the boat with friends, so running with 6 people total plus a bit of gear. I am looking to get a good hole shot (enough to bring up a 225# skier with a loaded boat), and decent speed. I still want a bit of wake for tubing and my wife wants to get into wakeboarding. I know that I probably need more hp and a bit larger boat, but I need to make the best out of what I have.

What is the suggestion? I would like to increase the pitch so that I could run WOT without redlining. What is the redline/optimal rpm for the Mercruiser 3.0?

Thanks!

AG

Re: 17' Chaparral / 3.0 Mercruiser - New Prop?

ashleygoodin said:

Okay, I am a relative newbie to boating and prop selection is a bit of a mystery but I think I am catching on. Here is the lowdown on what I have -

1988 Chaparral 178XL - 17' bowrider.
3.0 Mercruiser @ 130 hp.
2bbl. carb / original configuration.
Alpha 1 outdrive, no clue as to ratio but can check tomorrow.
Speedometer doesn't work.
Tach works, still have more throttle to go when I hit 4000 RPM's, so I haven't run it at WOT.
Running a Merc Aluminum 3-blade, 17" Pitch, 15" diameter.

We like to load up the boat with friends, so running with 6 people total plus a bit of gear. I am looking to get a good hole shot (enough to bring up a 225# skier with a loaded boat), and decent speed. I still want a bit of wake for tubing and my wife wants to get into wakeboarding. I know that I probably need more hp and a bit larger boat, but I need to make the best out of what I have.

What is the suggestion? I would like to increase the pitch so that I could run WOT without redlining. What is the redline/optimal rpm for the Mercruiser 3.0?

Thanks!

AG

Click to expand...

I will add that I am running at about 1000ft above see level, probably just a bit less.

I would estimate the fully loaded weight of the boat, people, fuel, and gear to be around 2100lbs.

The tach has a painted red line, which I assumed to be put there by someone knowledgeable but that could be a bold assumption at 4100 rpms.

Re: 17' Chaparral / 3.0 Mercruiser - New Prop?

Ashley, in my opinion that is an assumption, as that motor is supposed to be able to turn 4,800 RPM at max WOT. If the motor is healthy then it needs to have a prop that will let it reach that 4,800 RPM at WOT in order to not be lugging the motor at all RPM ranges. You need to borrow a hand held GPS or even some phones have GPS built in, and take the boat out and run it at WOT and give us the WOT RPM and speed so we have real numbers to work with. I would turn the switch on the back of the tach 6 or 8 times to help clean the contacts before I ran it though, because sometimes the contacts get corrosion and do not show the true RPM.

If you will fill this form out I will help you as much as I can.

Iboats Boat and Motor Info

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the maximum recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make. manufacturer and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing then do the same thing on the flywheel and turn the motor until the tape lines up with each other on the prop, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a board under the keel and stiking out to the anti ventilation plate for a referene
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch, number of blades and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a digital tachometer and hour meter here: http://cgi.ebay.com/ebaymotors/Tacho...Q5fAccessories
RPM ___________ Speed ___________ No. of people ____________ Gal. Gas ________
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.



H