Prop pitch ?

[rjwoodrome]

Good evening fellow members, Same old question here? I have an 1985 2.5L omc with a 13 3/8x17 prop metal not aluminum, on a 18' Penn Yan enclosed bow. unsure of the weight, but the boat is rather small 61" wide, hole shot is great top end is only 37mph. @ 4100rpm. I would like to know if changing the pitch to 20 or 21 is asking to much of a 2.5L.

 

[Bondo]

Re: Prop pitch ?

Ayuh,... At 4100rpms at WOT,... That motor can barely turn the 17" prop...

No Way it'll turn anything Bigger...

 

[steelespike]

Re: Prop pitch ?

Tried to look up the boat in NADA.85 and 86 has no listing.
Only guessing but I think your 2.5 would be about 120 hp.
and capable of about 40 mph.Is the motor in excellent tune,good compression,throttle opening all the way,bottom clean,prop in excellent shape.Looking at your boat To me it isn't a typical Penn Yan model seems sporty not what you would call a practical design.I would think intended for speed not ultimate deep V luxury ride.??61" wide is very narrow.Is that the actual widest beam outside to outside?There are 14ft aluminum fishing boats wider than that.Perhaps 61" is at the chine?

 

[a70eliminator]

Re: Prop pitch ?

The difference between 37mph and 40mph can be full tank and a 10mph headwind vs a close to empty tank and 10 mph tailwind. If your operating WOT's on the high end of the RPM range than lifes good.

 

[rjwoodrome]

Re: Prop pitch ?

I think I have given the wrong info on boat spec. the 2.5L is tuned. 120hp good compression on all 4 cyl. Hull is clean and waxed. prop is metal magnet sticks to it no blems. prop pitch 17 prop. dia. 13 3/8ths. boat actual width is 70". from the stern end bottom to the top is 36" as far as wot I was only throttled up to 4100 it will go to 5500 but the speed didnt increase. also I generally only cruse at 3200. and its not a typical penn yann I cant find another one like it. It isnt even listed on the penn yann site. its actual registeration name is a
"tornado II" enclosed... Prototype? LoL any who I dont want to increase the diamater just the bite.

 

[APPALOOSA2]

Re: Prop pitch ?

15 x19

5500 and you will blow that 120 up. You are turning too small a prop.

Max is 4400.

 

[rjwoodrome]

Re: Prop pitch ?

yup I agree 5500 will detonate the poor thing... 4200 is a more comfortable rpm on the high end by the sound. 15"diax19p EBAY here we go! thanks
ps. just went out and measured from center of the shaft for clearance.
14 1/8th is the distance. max.

 

[steelespike]

Re: Prop pitch ?

Normally diameter is simply a product of the prop design and not a primary consideration except to be sure it clears on the motor.You need to drop at least 1,000 rpm off. That would put you at about a 21" or 22" pitch.This makes more sense with your setup.This will make a big change in rpm through the performance range and will reduce the hole shot but will most likely improve your mileage and top end.To obtain the most predictable rpm change its best to try to stick with same brand and material.Your ideal cruising speed could could be anywhere above just on plane just picking a speed you like could waste gas.Experimenting or a flow meter is the only way to figure the best speed.