need help in figuring out what prop i need from the pros ^_^

JOEjones31989

Seaman Apprentice
Joined
Jul 7, 2015
Messages
34
Ok so i ordered me a tach meter for my boat last week and it finally came in today. i always thought my boat wasnt getting no where close to the RPMs it should be at WOT. so as soon as i got home today i mounted the tach and hauled but to the water and after a few trial runs to get the tach on the correct settings it was confirmed my motor is only hitting 3500 RPMs at WOT. and i can tell she has alot more to give. but here is the information i have on my boat and motor and what i have done to it so far. maybe someone can help me with the formula to figure out the prop i should put on it to get my RPMs up where they need to be and help me get on a plane faster with more top end.

the boat is a 1972 doggett industries 16FT stick steer boat. model is champ. (see pics) no one can find any information on this boat. and i dont know the acually weight of the boat.

the motor is a 1972 evinrude 85 hp electric shift.

the prop is a 13 spline prop. and thats all i know i did find these numbers on it but that is all i know about it. (RL-1086-4P is on the bottom of the prop on some type of rubber gasket)

at 3500 rpms without my dolphin phin the boat will do 30-33 MPH at WOT..... but takes for ever to get on plane like 30 - 45 secs....... but with my dolphin fin at 3500 rpms i get 27 mph at WOT wich it takes less time to get on plane but a few extra seconds to get to 27 mph.......

i have 18 gallons of fuel on the boat but this run was about 12 gals left in it. and this test i also had myself and one other person in the boat wich averages out to about 350-400 lbs....... but with myself or someone else in the boat the speed is always the same. ive done the gps speed since day one of me getting the boat it is always on.

so if someone could help me i would really apreciate the input or if you need more info i will do my best to provide it for you. btw im wanting to also know would a 3 blade or 4 blade prop be better for me. thank you everyone in advance.
 

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SkiDad

Lieutenant Commander
Joined
Jul 18, 2010
Messages
1,518
I would take your current prop to a prop shop. They can tell you what it is pitch wise. Then drop at least 4" in pitch to get into the bottom of your range. I'm guessing by what you say that you have a 21p and that you need something like 17p. You might even need lower but it's hard to tell. A 17 might do more than normal jump in rpm bc you will be in a higher HP range. 3 blades are fine.
 

JOEjones31989

Seaman Apprentice
Joined
Jul 7, 2015
Messages
34
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ok i was off on the letterings on the bottom of the prop. here is the correct letters and some pics of the prop maybe this will help someone lol.

Lord Mfg Co Erie PA USA BJ-1086-4P ( thier is a one more part but i cant make it out if i had to guess i would say 7-78....... but not 100%)
 

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JOEjones31989

Seaman Apprentice
Joined
Jul 7, 2015
Messages
34
ok so i just got back from running around to 8 different boat shops around my town and near by areas. not one of them can measure my prop. so at one shop the guy was pretty cool and started lining up props next to mine to figure out the pitch. he said it is either a 21 or 22 pitch prop. i then asked about the diameter but he was already back working on a clients boat and his helper just told me that where i buy my prop from should tell me what diameter i need....... so as of now i think im going to run a 16p prop but not sure on the diameter any one have any tips/suggestions for that?
 

SkiDad

Lieutenant Commander
Joined
Jul 18, 2010
Messages
1,518
around 13-14" diameter - it depends on the manufacture.
 

JOEjones31989

Seaman Apprentice
Joined
Jul 7, 2015
Messages
34
ok so i got my prop ordered with the hardware i need. i had to go to a 17P cause the 16 only came in a SS prop for my motor. it should be in thurday/friday i will keep everyone informed on how it performs i hope it does awesome cant wait to try it out. thank you skidad for your input!
 

JOEjones31989

Seaman Apprentice
Joined
Jul 7, 2015
Messages
34
so had the boat out this weekend with the new prop. ^_^ i put her in the water and then hammered down on her and wow. it jumped up on a plane quick fast and in a hurry. boat was running around 35 - 36 MPH but then after about 10 mins of running it she started losing speed slowly down to 30 mph. i guess its time to dig into the motor some more but im happy with the props performance thank you for the info in picking my prop.
 
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