Correct prop size is always

[cyclops2]

The one that under any load, light or heavy, allows the motor to reach maximum ...RATED rpm... Hopefully your motor has a R P M Limiter.

Other wise, you need to have a GOOD hearing memory, of the correct R P Ms. That means using a temporary tachometer to memorize the pitch.

 

[45Auto]

Re: Correct prop size is always

Max recommended RPM range on my boat is 4400-4800 RPM. It has a 23" pitch prop.

With me and 1/4 tank of gas it will do 4800 RPM on the 23" pitch prop.

With me and a full tank it will only do 4750 RPM.

With 2 adults and a full tank it will only do 4700 RPM.

With 2 adults, 3 kids and a full tank it will only do 4600 RPM.

With 7 adults, 3 coolers, and a full tank it will only do 4500 RPM.

I've read that reducing prop pitch by 1" will raise RPM about 100 RPM.

Do I need a 23", a 22.5", a 21", a 20", and a 19" pitch prop to have the correct prop for my boat?

Do I need to change props as the fuel level drops so I have the correct prop on my boat?

What happens if I don't have the correct prop to reach MAX recommended RPM? Will my engine blow up?

 

[cyclops2]

Re: Correct prop size is always

You are perfect.

Range IS 4400 to 4800.................IDEAL range under all conditions. Your boat / motor loads are within the required range of 4400 to 4800 rpm.

Perfect for long life. Enjoy the daylights out of it.

 

[Texasmark]

Re: Correct prop size is always

Max recommended RPM range on my boat is 4400-4800 RPM. It has a 23" pitch prop.

With me and 1/4 tank of gas it will do 4800 RPM on the 23" pitch prop.

With me and a full tank it will only do 4750 RPM.

With 2 adults and a full tank it will only do 4700 RPM.

With 2 adults, 3 kids and a full tank it will only do 4600 RPM.

With 7 adults, 3 coolers, and a full tank it will only do 4500 RPM.

I've read that reducing prop pitch by 1" will raise RPM about 100 RPM.

Do I need a 23", a 22.5", a 21", a 20", and a 19" pitch prop to have the correct prop for my boat?

Do I need to change props as the fuel level drops so I have the correct prop on my boat?

What happens if I don't have the correct prop to reach MAX recommended RPM? Will my engine blow up?

Come on 45....give the guy a break. He's a newbie. Grin

Mark

 

[cyclops2]

Re: Correct prop size is always

Who is the newbe ?

I always assume the poster needs help or he would not waste his time & try to confuse others.

 

[Texasmark]

Re: Correct prop size is always

The one that under any load, light or heavy, allows the motor to reach maximum ...RATED rpm... Hopefully your motor has a R P M Limiter.

Other wise, you need to have a GOOD hearing memory, of the correct R P Ms. That means using a temporary tachometer to memorize the pitch.

The big guns on here recommend the upper end of the rpm range with the normal load. I have been running 500 rpms above the upper limit on my Mercs. since about '84. Yet to blow one or tear one up and usually keep them a long time....till I get tired of one boat and want to try something different. Actually they seem to love it as I have very few if any problems with them.

Mark

 

[NetDoc]

Re: Correct prop size is always

I am a newbie and will be launching my boat for the first time in the not too distant future. How do I find the following:

1. Recommended RPM (3.0L Mercruiser)
2. Max Allowable Load (1968 Fibra, 20')
3. Prop Size
4. Prop Pitch

 

[Bondo]

Re: Correct prop size is always

I am a newbie and will be launching my boat for the first time in the not too distant future. How do I find the following:

1. Recommended RPM (3.0L Mercruiser)
2. Max Allowable Load (1968 Fibra, 20')
3. Prop Size
4. Prop Pitch

Ayuh,... The 3.0l is usually 4400 to 4800rpms, though yer oldy might be 4200 to 4600rpms...

Max load for the boat, ain't a prop question, 'n the prop questions can be answered after ya read the Read This 1st stickies at the top of this forum...
And of course, after you start a thread of yer own, rather than hy-jackin' this 1.....

 

[NetDoc]

Re: Correct prop size is always

I'm sorry you see these questions as a hijacking, but the OP makes a statement that references these follow up questions. While I would love to know my own answers (thanks), I was hoping for more of a generic answer on how to discover these values to validate the OP's conditions. Heck, I don't even know IF I have a problem yet, so I am not asking for a solution... just trying to better understand that OP so I'll know IF I have a problem if I ever get in the water.

 

[cyclops2]

Re: Correct prop size is always

Hopefully you get the owners manual with the boat & the engine manual for the engine that is in the boat.

If they are NOT included.

Write down the make & model of the Boat & the engine. Go to a dealer that sells them. He will / should / hopefully give you the correct answers.

Rick, the owner of my marina is CONSTANTLY stopping me from doing NEEDLESS parts & labor "" improvements "" to my boat after I read those monthly magazine " experts " suggestions. Rick is a highly respected person by a lot of very boat savvy people.

 

[cyclops2]

Re: Correct prop size is always

Hi Bond-o

We spend the summer eating at the Blue Heron. Great people & place. You might be old enough to buy me & the wife a drink sometime.

Love that Meatloaf. I can down it in 2 minutes. Big as a loaf of Bond-bread.

 

[Bondo]

Re: Correct prop size is always

Hi Bond-o

We spend the summer eating at the Blue Heron. Great people & place. You might be old enough to buy me & the wife a drink sometime.

Love that Meatloaf. I can down it in 2 minutes. Big as a loaf of Bond-bread.

Ayuh,.... I'm plenty old enough to buy ya a drink or 2,....
though I quit drinkin' 'bout 15 years ago, My Love still enjoys...
We're seen at the Duck dinner for breakfast most Sundays, or at the grange hall, if they're servin'....

I own the houseboat ya see drivin' over the bridge, 'n the 2 houses behind it....

I take it you summer in the area,..?? Where's yer winter home,..??

 

[cyclops2]

Re: Correct prop size is always

We are in Frenchtown, N J on the Delaware River. Big kid loves play in the water. Mother used say I could come home with muddy shoes in the desert.
I am 73 & retired.
Help a couple of old racing hydroplane guys keep their boats safe & ready to run. Took a guys boat having a fire that singed his ankle to believe me when I kept harping about a fire in the old boats.
Now ALL of the old boats have extingushers.
Now after them to do pull tests on all the hardware screwed or bolted into that old gasoline & or oil soaked wood.

Always time for a mechanic to tune up the motor. Short of time to check out all other part of the boats. Hoping we get a close enough call to get safety to be as important as the engine. Engines & boats are replaceable. People are not replaceable parts.