What kind of propeller should I be using on my I/O boat?

Question

I have a 3.0 Mercruiser Alpha I (140 horsepower). We do alot of slalom skiing and I wish it had a little more power for getting the skier out of the water. After the skier is out it does great. It is a 3 blade prop (aluminum I think??) and I have no idea what pitch the prop is. What is the best pitched prop for pulling? Would a 4 or 5 blade be better or is that too much? Hopefully someone can help. The boat runs great so I don't want to mess around with the motor or carb, I think it's a prop thing. What is a shifting prop? Would that work for me? Any pros and cons to those? There are a couple of very small nicks in a couple of the blades, but nothing serious. How much of a nick is too much? Is it hard to change the prop, or can I do it myself? Alot of questions, but I know you guys can do it. Thanks in advance.

Answer 1

I am going to recommend a 4 blade or 5 blade with the best hole shot. Skiing requires the big hole shot, so prop to that and ignore the top end. Stay away from a shifting prop, it's a gimmick.



Small nicks in the prop are not that big a deal, but when you begin to lose weight from a blade on a balanced prop it will make a difference. If that shaft wiggles too much a seal could be compromised.



Changing a prop is easy, every boat owner should know how to do it. If you are not sure, grab somebody to help you the first time.



Edit: Arggghh, I have to edit because the answers I read were just crap. OK, start here, and this assumes you have a marina that will loan you props. 1. go to a four blade with the same pitch as your 3 blade. How's the hole shot? Is the WOT within recommended range? 2. Go to the five blade, how's the hole shot? Is the WOT within range. 3. Can either of these work for you. 4. Four blade not in range? change pitch to bring in range. Your marina can help you fine tune. 5. Five blade not in range, change the pitch. 6. Pick your favorite.



In the end it is a very involved, tedious process.

Answer 2

The prop is not hard to get off, bend out the three tabs on the washer behind the nut then remove the nut. Make sure not to loose the washer behind the prop, they tend to stick fast to the back of the prop if they are greasy. If you only need a little more bottom end power drop the pitch one number. Pitch runs in odd numbers so if you have a 19p go to a 17p. Size and pitch are normally stamped on the side of the prop or can be located behind the tab washer on the face of the prop. As a general rule any nick in the prop is too much, they will cause cavitation (small air bubbles) around the prop and reduce the bite it gets in the water. For a 3.0 stick with the 3 blade.

Answer 3

Here's what I know--Ive no professional-just a recreational boater but Ive talked to my local marine shop to discuss props pros & cons..



The pitch..is a # 18. 21. 25 etc...this number represents the length in inches the prop will travel in ONE revolution. 18 pitch prop will travel 18 inches when the prop spins 360 degress. Got it?



Ive been told the higher the pitch prop, the faster your boat will go at WIDE OPEN THROTTLE. a 25 pitch prop on the 3.0 merc wont do squat-no torque, just high end power with high RPMs.



The smaller the # pitch the more "pulling" power you will obtain--and increasing the # of blades on the prop. I think..that might be misleading-dont quote me on this one.



What to do? Call your local boat shop, tell them what you have and they will reccomend the best solution for your problem. I think the 5 blade stainless prop gives the best "holeshot" gets you onto plane much faster--but you lose a little at the higher range of RPM's



happy boating

Answer 4

Why isn't plain wood enough ? The ark only had to last 40 days in water ,If a shiplap joint was used ,and pitch was used to prevent gross water penetration of that joint then the problem is :How long would it take for the wood of the ark to absorb enough water so as to ultimately result in the ark achieving negative buoyancy ? What should be mentioned of course it that the objective would have been then as it is now to keep the amount of joints -and therefor potential leak -points at a minimum. Remember two other things are going on here 1)The water absorption is causing the wood to swell thereby making the joints more waterproof 2)The ark is getting potentially more buoyant daily due to 1/40th of the total mass of the on-board consumables be consumed.. The ark would therefor have to absorb water weight at a rate that exceeds the weight that is lost due to the depletion of consumables.

Answer 5

one that fits!