Prop pitch

M

Maxz695

Guest
not much on specs yet I have a 40 hp 2 cyl 2 stroker with a 12 pitch. The boat i,m running is a 1750 procraft bass boat on sarasota inland wtaerway, salt water, I get to just under 5000 rpm i,m good at the lowest setting with my manuel jackplate and can relatively turn ok but not to far before it losses grip and revs up. I don,t normally take anyone out and carry very litlle, and it has a fuel tank in the rear 15 or 20 gal usually about half full. It,s not bad for a 40 hp pushing this big long boat 17 and a half feet, but i was told a 10 pitch would be beter but my thinking was to try to get a prop with more pitch for speed. up to a 17 pitch the prop is onlt 10 inch to 11 in diamiter would less pitch or more pitch help me here? I have no problem on exceleration and a prety good hole shot as it is. Cavitation is my main issue here advise please
 
M

Maxz695

Guest
Re: Prop pitch

now remember im on the lowest setting for tilt and it,s worse on the second notch but i like the bow up a little to handle them big wakes of them monster boats out here keep afloat. (save the bilge pump lol)jackplate is as low as it can go without turning the motor to lift it up without turning it you see my delema
 
M

Maxz695

Guest
Re: Prop pitch

the other day when I was stuck dead in the water halfway home a scarabb big as a city was going by but i,m not worried the wake isn,t that bad at all what bothers me is them damn deisels there wake is like a sunami
 
jerryjerry05

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
18,185
Re: Prop pitch

The small motor on a 17.The rpm should be about 5300-5500rpm.The way to increase to the opyimum is go down in pitch.Say from a 12 to an 11.You should get better gas mileage.Going up in pitch will maybe give you a better hole shot but the fuel economy will go.
Not a bigger boat but a bigger motor.J
 
M

Maxz695

Guest
Re: Prop pitch

Thanks for the info fuel mialage is aready great. i,m not concerend with that so an 11 pitch will prevent cavtation on sharper turns then correct?
jerryjerry05 said:
The small motor on a 17.The rpm should be about 5300-5500rpm.The way to increase to the opyimum is go down in pitch.Say from a 12 to an 11.You should get better gas mileage.Going up in pitch will maybe give you a better hole shot but the fuel economy will go.
Not a bigger boat but a bigger motor.J
Click to expand...
 
Silvertip

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
Re: Prop pitch

Wow -- you posted the first message at 12:32 and apparently were surprised that by 12:46 you didn't have a response. You have a couple of unrelated problems. Less pitch raises engine rpm at the same speed so you are placing less stress on the engine. Ventilation is a totally different problem and less pitch will NOT likely solve that. Where is the AV plate in relation to the bottom of the boat? To ventilate a 40 HP motor suggests you have a short shaft motor on a long shaft transom although the jack plate should allow lowering the motor to avoid ventilation. Trimming up too high in a turn can cause ventilation in turns. Going up in pitch will NOT help hole shot as indicated earlier. It hurts hole shot since you are in effect starting out in high gear to use your car as an example. It also LOWERS engine rpm so it would lug the engine even more than it is. It sounds like that boat could use a "Big Foot" lower unit. That lower unit has 2.34:1 gears and can use a 13-1/4 inch diameter prop. That lower unit is basically the same as the 75 & 90 HP three cylinder Mercs.
 
M

Maxz695

Guest
Re: Prop pitch

That lower unit has 2.34:1 gears Meaning my stoke lower unit on the 40 hp 2 cylce and you say if can tak up the 13-1/4 inch diameter prop? or the bugfoot which might be something i,m interested in. as for the post it was late and i spent hours on the forum here was just tierd
Silvertip said:
Wow -- you posted the first message at 12:32 and apparently were surprised that by 12:46 you didn't have a response. You have a couple of unrelated problems. Less pitch raises engine rpm at the same speed so you are placing less stress on the engine. Ventilation is a totally different problem and less pitch will NOT likely solve that. Where is the AV plate in relation to the bottom of the boat? To ventilate a 40 HP motor suggests you have a short shaft motor on a long shaft transom although the jack plate should allow lowering the motor to avoid ventilation. Trimming up too high in a turn can cause ventilation in turns. Going up in pitch will NOT help hole shot as indicated earlier. It hurts hole shot since you are in effect starting out in high gear to use your car as an example. It also LOWERS engine rpm so it would lug the engine even more than it is. It sounds like that boat could use a "Big Foot" lower unit. That lower unit has 2.34:1 gears and can use a 13-1/4 inch diameter prop. That lower unit is basically the same as the 75 & 90 HP three cylinder Mercs.
Click to expand...
 
M

Maxz695

Guest
Re: Prop pitch

i,m looking into 2 props a 12 X 11 and a 13 1/4 X 14 wouldn,t the 13 1/4 X14 strain the engine more ?
 
Last edited:
Silvertip

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
Re: Prop pitch

I need to correct the Big Foot situation since your engine is older and very different than either the 40/50/60 HP three cylinder Big Foot as well as the 75/90 HP three cylinder engines. I don't know off hand what gear ratio that engine has but going to a 13 inch prop would likely make the boat a complete hog. It takes power to twist bigger props. Even with the same HP, gearing needs to change to swing that prop. It also appears that the engine height is set too high (jack plate too high). The AV plate the flat plate just above the prop. With the engine perfectly vertical, a starting point for height adjustment (not trim) is to have that plate flush with or just and inch or so above the keel. Any higher than that and you risk blowout (ventilation).
 
M

Maxz695

Guest
Re: Prop pitch

I C but me going to a 12 x 11 Rather than th 11 x 12 should grab more water give me more RPM and strain the engine less I can drop the Jackplate but then I would have to turn the engine to lift it without it hitting the transome, or drill a new hole in the steering arm coming off the engine and cut off some of the arm to allow it to come up without turning the engine no big deal there but just looking for the right solution not nesecarily the easiest one also I run in shallow water in the inland waterway here in Sarasota FL. dropping the engine would get me evn more stuck than i already get lol. I agree with lowering the jackplate to stop cavitation. is this a short shaft engine with the measurments on the shaft I gave? getting another housing and shaft wouldn,t be beyond my means in time. Let me say this at full throttle the force shoots way out barely coming out on top of the water. My speedo is broke so i just go by RPM.shouldn,t the tail of the forced wake be somewhat above the water considerably? Maybe because it,s on the lowest seting this is happening. lower the jack plate and move to second tilt hole right? Remember this is a bass boat very wide It doesn,t sit way down in the water displacement is much greater on this boat. therefore the weight of the boat is less plowing through the water due to displacment and a bigger prop wouldn,t nessecarily make it a lug in the water. I hardly ever just gun the throttle I gradually let the boat pick up speed to about 3/4 throotle as not to dammage the bearings or break the shaft even though this little work horse can handle it, so bigger prop more pitch more speed more stain on the engine. bigger prop less pitch grab more water. get more RPM less starin on the little buger 40 HP. Heck it almost keeps up with a 115 for some time before they start to fade away. My oly other alternative after I get my new waterpump complete installed and drop the jackplate test with this 11 x 12 is the 12 x11 or MERCURY 25-60 HP 11 5/8 x 11" VENGEANCE STAINLESS PROP
 
Last edited:
M

Maxz695

Guest
Re: Prop pitch

Thanks to all for the reply,s and the input. We learn as we go. Have a great weekend Happy Boating !!
 
You must log in or register to reply here.
Top