Watersports: Which propeller do I get?

[dhdeanha]

Last year I posted a thread about my boat and finally took it out this week. Engine sounded much better and cooler so I'm assuming I'm within the recommended WOT rpm range. Well since I bought aluminum and I hit something again, I need another propeller. I previously had a 14 x 20 pitch 4 blade propeller and we are planning to buy another 14 x 20 pitch again. Now the question is:

Since I'm buying local and the seller has multiple listing for different sizes, they offer $140 for an aluminum prop and a SS highfive prop. The issue is that the 5 blade prop is 24 pitch and I think that it won't work for my boat while they claim that it is perfect for the boat. What are your thoughts?

If not I can just buy the aluminum 4 blade for $50 and leave the other prop alone.

Some history of the boat: initially bought for $4500. 1800 LSR, 4.3 L Mercruiser Alpha One 18 foot 190 HP. Replaced the 3 blade 21 pitch as the RPMs were too high with a 4 blade 21 pitch.

TL;DR

I go tubing and wake boarding with a heavier load than usual (around 9 adults on the boat).

1. What does adding a blade do in regards to RPM?

2. I know that adding pitch will decrease RPM, therefore if getting a 5 blade prop will add RPMs, should i add pitch as well?

3. Do I need to re-grease the shaft everytime I replace the propeller?

4. I'm planning to replace my 4 blade 20 pitch with a 4 blade 21 pitch, will that be okay for my boat?

5. Should I purchase the 5 blade prop if the pitch is 24?

Thank you.

 

[achris]

1. Will SLIGHTLY decrease top RPM and speed.
2. Adding blades and and keeping the same pitch adds a small amount of drag, which will drop the revs slightly.
3. As long as there's some grease on the shaft, you don't need to regrease. And if you are changing prop regularly, no problem.
4. As long as the revs don't drop out of the bottom of the recommended range, you'll be fine. 1" of pitch will drop you about 200rpm.
5. No. You'll drop 800rpm, roughly.

Chris.......

 

[Scott Danforth]

. Engine sounded much better and cooler so I'm assuming I'm within the recommended WOT rpm range. .

if you dont have a tach, get a shop tach. you cant pick a prop without knowing your RPM

for watersports you want less pitch for more low speed pull, not more pitch.

 

[Sea Rider]

My first thought would be to install a tach before dumping money into the deep blue buying props blindly. Need to prop engine right to rev between middle to max wot rpm range as loaded on current application.

What's the min-max wot rpm range factory stated for that engine ? Assuming you engine revs right by sound, is no indication that revs right at full throttlle, only a tach will tell..

If you would count with a tach right from the start would have known if current damged prop was a good performer so to buy new same or go for a prop maximization. Now you need to buy a starter prop and go from there...

Happy Boating

 

[SkiDad]

just buy the same prop again

 

[Sea Rider]

If plan buying same exact prop add a tach to check max wot revs as loaded, as no wot rpm was mentioned on the post assume there's no tach installed.

Happy Boating