Prop help

this moay not be in the right spot but here it goes: i have a 1448 grizzly side console, the stock 10p prop works great with just me in the boat, however when i have another person in the boat the prop slips a little. i hammered a rocok in the river yesterday, even with a river runner it got banged up. blades not twisted but just the edges are chewed a little so here is my question, which pitch prop should i get? i would like to get one that would work better for two people. any help is much appreciated

What size motor?

What do you mean by slipping? Cavitation? Slipping on plane, on take off, when turning?

on take off, boat doesnt want to plane. with just me it comes right up on plane. added weight of a person, cooler gear. it plows, trimmed it wont go more than 12mph. so i was thinking lower pitch from 10 to 9 and should let motor get up to speed better

still didnt give us the motor size and another thing to determine prop size is rpm's what are you running at wide open throttle rpm's not speed.

2009 merc. longshaft, 20hp. cav plate is about 1/2" above bottom of boat, no tach, so no WOT rip'ems. sounds like it is bogging i.e not correct rpm too slow

the smaller the prop the higher the rpms so if it is bogging down might need to go smaller

awesome. it has a 9.25x10 so i was going to go with a 9.25x9

It will help. I kept two props on my old IO boat so I could pitch it lower for heavy load days. I'd take a file to your current prop too and keep it as a spare.

Jamie

Thanks! i did the file trick as soon as i got home i pulled it, checked the hub and shaft. then filed away. looks rough but worked fine to get us home.

20hp on a 1448 should pop right up on plane even with 2-3 people in it. Especially with that prop! I don't have anything to compare it to except my 1542 with a 25hp. I currently have a 12 pitch prop and pop up no problem even with over 750 lbs of people. Plus floors, front deck, 2 batteries, and cooler. Even before I trashed my 14 pitch prop it would still get up with all that in the boat and run 25mph, 30mph with two people and gear. I would think yours should pop right up no problem.

Sounds funny to me. Im still wondering about the "slipping"? Is it cavitating because you have people sitting up front and it raises the prop out of the water causing it to cavitate or "slip"?

Someone mentioned that those little motors will run pretty good on only 1 cylinder and you wont even know its not right untill you put a heavy load on it. Check your spark plugs. If one is really wet and the other is nice and golden brown that is your problem. If they are both wet and black replace both of them.

It does sound like you are plowing (low rpm), so lower pitch is the right direction. I've had that happen on shallow v boats where the load was just a little too much to get the motor into the powerband. Once on plane, it would be fine. On a flat bottom, I'd expect less of an issue planing. Is this a heavily modified jon, with lots of weight added to the hull to start with?

Comparing pitch between other motor brands or models is meaningless, unless you know the gear ratios are the same. The owners or service manual usually provides a standard prop comparison, for a range of boats. Where does you current prop fit in that range?

Trying to get enough understanding to determine if you really have a motor issue, or just a prop for current load issue.

I just had a conversation with a mech and shop owner about prop selection for my boat. he told me that a motor is rated by running it on a dyno and that the rating is the peak hp that the motor will put out at the optimum rpm range before it drops off. Lets say 40hp @ 5500 rpm. He said you want to run as big a prop as you can and still be within a certain range. Say 5200 to 5700 rpms for this example. If you run too low a pitch you will get up on plane quick but your motor will be screaming before you get to WOT and will never really put out the hp that its capable of. If you put too high a pitch you will get up on plane slowly (if at all) and may not reach your optimum rpm range of 5200 to 5700rpms. running a motor hard at low rpm or bogging it is hard on it. He said its acually harder on it than bouncing it off the rev limiter. You should be operating your motor in the optimum rpm range. Lugging it around also fouls plugs.

I used to race dirt bikes so he used this analogy to help me understand......Just like dirt bike 2 stroke motors, a 2 stroke outboard has a powerband that is at the upper end of the rpm range. You want to keep the motor in that powerband (in motocross we call it keepin it on the pipe). With 4 strokes you have a little wider powerband but the principle still holds true. If you had a corvette or mustang you wouldn't idle around in it would you?

I was using dirt bike and bicycle logic to try and figure out how big or how high a pitch prop I could run. I believed as long as me or the motor had enough Power to turn the gear (prop) I could just keep gearing up to get a higher top speed or gearing lower to get more low end torque such as in drag racing.

He said a lot of people try to look at a prop like a gear but there is more too it than that. Anyway with all that said maybe you should check and see what the factory prop pitch was for your motor and try that pitch. It will probably get you on plane provided the motor is ok.

Sorry for rambling.

reed thats awesome! i do the same thing. i used to race hare scrambles and still ride a KTM200exc 2 stroke. it is more than a gear there is a lot to a prop. i was thinking of the motor revving and comparing different props in my head using the DB as a reference like you said on the pipe and at what RPM would it be. i will give it a try this weekend with the smaller prop and 2 peeps and then try it with just me to see what difference it makes.


the current prop 9.25x10 will hop right up on plane with just me. no porposing. but with a passenger it takes for ever with weight rearranged it still doesn do well. i have one starting battery in the back with a 6 gallon fuel tank. not modified. just the weight of a storage box, an aluminum hatch the covers the fuel tank and battery. one trolling battery up front.
the cap

i did find a loose plug wire it wasnt off the plug but did "snap" onto the plug when i pushed on also........ but the motor wasnt misfiring. it did seem like it felt underpowered so i may have already fised my problem and wont find out until this weekend

max torque occurs at a rpm much lower than the peak hp rpm. If you are not on plane by max torque rpm, you will never see the max hp rpm range. Unfortunatly, none of the mfgs post max torque specs. How many people here water skied behind a 1950's 25-35hp E/J? Try that with a modern 25-35hp. Max torque follows the old rule "No replacement for displacement".

FuzzyGrub said:

How many people here water skied behind a 1950's 25-35hp E/J? Try that with a modern 25-35hp. ....".

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He he,,,oh ya buddy,,river raised with those old big twins. Some tweaking, mounted on a home made skip jack made from modified plans from modern mechanics mag,,,, unfortunately the prop making man was few and far between then.

LOL! funny you say that. there are pictures of my dad and uncle skiing behind a wooden jon boat with as my mom put it "that motor is too big, it is going to sink the boat...... big. she says they did it all the time with no problems. and if new prop doesnt get here before i get home tomorrow we will be running the dinged up stocker.

It wasn't a wooden boat for me, but a '67 alum starcraft that we still have.