Trying to learn size of prop and upgrades

[fmalott]

1983 Thundercraft Flamingo 470 merc 170hp it came with a I-R outdrive but i have replaced the I-R with a SE106 i think it's a alpha one i would have to dig out receipt to make sure but i'm sure it is. the prop size on the boat is what i'm trying to learn, i know the pitch is 21 because it's stamped on the prop but the diameter is not so this is my first time ever measuring the diameter i think i measured 13 3/4".
My first question: did i measure right for the 470 motor and outdrive with a 1.84 gear ratio

My second question: what other prop sizes can i use to improve performance, i'm not going to go top speed all the time i will be cruising more often then fast, probaly couple of times in a year i will be pulling a tube behind boat with 4-6 people on boat or just cruising with 4-6 in boat no tube. will the original size that came with boat is it good enough or upgrade?

 

[Bondo]

Re: Trying to learn size of prop and upgrades

Ayuh,.... Read the "Read This First" at the top of this forum, 'n answer those questions....

 

[steelespike]

Re: Trying to learn size of prop and upgrades

Is the gear ratio stamped on the drive?. We will need your base line numbers to evaluate your set up.
If it is a alpha one there are props available.

 

[Silvertip]

Re: Trying to learn size of prop and upgrades

You need the "right" prop regardless how you run the boat. Too much pitch lugs the engine whether at cruise or wide open throttle. Too little pitch burns more gas and causes higher revs than necessary. The right prop provides optimum top speed as well as comfortable cruising without lugging. We need wide open throttle rpm (observed) with what you consider an average load. You measure diameter of a prop by measureing from dead center on the prop shaft to the tip of one blade and then x2. On a four blade measure tip to tip on opposing blades. Also understand that as pitch goes up, diameter goes down a bit and vice versa. Use application charts to search for props and stop worrying about diameter. Buy a prop designed for your engine and diameter will take care of itself.

 

[fmalott]

Re: Trying to learn size of prop and upgrades

Is the gear ratio stamped on the drive?. We will need your base line numbers to evaluate your set up.
If it is a alpha one there are props available.

the SE106 outdrive was sold as a replacement for the I-R outdrive so yes it's a 1.84 ratio

 

[fmalott]

Re: Trying to learn size of prop and upgrades

You need the "right" prop regardless how you run the boat. Too much pitch lugs the engine whether at cruise or wide open throttle. Too little pitch burns more gas and causes higher revs than necessary. The right prop provides optimum top speed as well as comfortable cruising without lugging. We need wide open throttle rpm (observed) with what you consider an average load. You measure diameter of a prop by measureing from dead center on the prop shaft to the tip of one blade and then x2. On a four blade measure tip to tip on opposing blades. Also understand that as pitch goes up, diameter goes down a bit and vice versa. Use application charts to search for props and stop worrying about diameter. Buy a prop designed for your engine and diameter will take care of itself.

Thanks for reply Silvertip i ended up buyin from iboats.com a 14" dia. x 21" pitch with 4 blades. i figure since everyone says it important to keep the pitch the same i only went up 1/4" on the diameter and went to 4 blades, pitch i left the same. the original size that came from factory is 13 3/4" x 21 pitch 3 blades will this upgrade be ok?

 

[Silvertip]

Re: Trying to learn size of prop and upgrades

Thanks for reply Silvertip i ended up buyin from iboats.com a 14" dia. x 21" pitch with 4 blades. i figure since everyone says it important to keep the pitch the same i only went up 1/4" on the diameter and went to 4 blades, pitch i left the same. the original size that came from factory is 13 3/4" x 21 pitch 3 blades will this upgrade be ok?

We have no idea since YOU have no idea if the prop you have was correct for your application. There is no STOCK prop for any boat. Loading heavy requires a different prop than loading light. No numbers to work with -- we can't help you. The READ THIS FIRST sticky tells you why.

 

[steelespike]

Re: Trying to learn size of prop and upgrades

Not knowing your present performance no way to know if the prop will work.
It is within typical prop sizes.If it turns out to lug the motor you shouldn't use it for any extended time beyond fast no wake speed.