School me on props

Dirty_Oar

Dirty_Oar

Member
image.jpeg image.jpeg I have a 175 Johnson 2-stroke with a 4 blade prop. My buddy was telling me that I should put a stainless prop on it, that it would be better if I hit anything (chunk of wood etc). And that it would perform better. Thing is I don't know what the numbers on this prop I have mean? What prop would I need to replace this with (pitch etc) in a stainless that would be an upgrade? Would a 3 blade stainless be an upgrade over the 4 blade regular (aluminum?) prop? Here's pictures of the numbers on the prop I have. I dont even know what they mean.
 
no matter what prop you have use it as
a base line for testing and find out how
it performs at wide open throttle
(WOT) with a moderate max load.
if you are running close to max
rpm then the pitch is right.
if you are low subtract 1 in of pitch
for every 200 of rpm you want to gain.

what you have there in the pix is a 17 for top end and a 12 inch pitch prop for
pulling stumps...as far as the stainless
goes yes they are more durable and better
top end but if you hit something hard
you may do more internal damage
then its worth....your choice
 
There absolutely no predicting if the boat will perform better till you try a few different props. A stainless prop may give you better holeshot as the blades don't flex as much getting up on plane.

If you go offshore a lot a would recommend a stainless prop. That is because if you hit a minor chunk of wood you will still have a working prop if it's stainless. An aluminum deform easily if it hits a minor floater and will be unusable to get back from offshore with. Of course, If you hit a big log you may blow up your lower unit with a stainless prop. Better chances of the bottom end surviving that with an Ali prop as it shreds on impact at speed.

It took me trying at least 5 different props to find the right one for my boat. I settled on a 3 blade stainless that performs great. I was taking the boat offshore a fair bit so I felt I wanted stainless. See if you can find a prop shop that will let you exchange props if the first one isn't right for your boat.
 
1marko said:
no matter what prop you have use it as
a base line for testing and find out how
it performs at wide open throttle
(WOT) with a moderate max load.
if you are running close to max
rpm then the pitch is right.
if you are low subtract 1 in of pitch
for every 200 of rpm you want to gain.

what you have there in the pix is a 17 for top end and a 12 inch pitch prop for
pulling stumps...as far as the stainless
goes yes they are more durable and better
top end but if you hit something hard
you may do more internal damage
then its worth....your choice
Click to expand...

What should my RPM be at WOT? I think I'm maxing out at about 4600 right now but I get good snap out of the hole.
 
You have a 14.5 diameter by 17" pitch prop. And I believe the Rubex is a removable hub prop, similar and I believe interchangeable with Mercurys torq-flo system and other hub systems. WOT for the 175 is 4500 to 5500 so you are on the low end by still within spec. Going to a stainless 3 blade with the same pitch may give you a few more rpm but as others have said its best to test a few different props to find out what works best on your motor and boat combination.
 
How do I know what props would even fit my motor? Would this prop fit? And would it be a candidate to upgrade the one I have now? I like the holeshot that my boat has right now and it cruises at an acceptable speed for me. If I could cruise at near the same speed and save some fuel would be nice but I don't want t feel like a slug getting up to plane either. I am wondering if I even want to go stainless? I carry a spare aluminum prop so in the event I toast the one I have on I should be ok to get home. I don't like the thought of destroying my lower unit if its avoidable and I can sacrifice a prop instead.

https://comoxvalley.craigslist.ca/bpo/5778942041.html
 
I can't remember the site, but Google is your friend. There is a website with a prop pitch selector calculator. You enter your boat model, motor size and other stats and it spits out prop recommendations.

I would suggest going to iboats. com and doing a bunch of research on your model of motor. Their forums have tons of info. Look for posts with similar boats and motor to yours. Chances are someone has already done the trial and error for you and recommendations for the right prop will be there. Or you can make a post on their forum and ask, if you can't find the info. Search the site well first, the info is probably already there. There are far more boaters in the States than Canada, sometimes there forums are more helpful because of the sheer numbers of boaters.
 
As someone who has smoked a lot of props running in shallow water and at night for work, my choice is a mercury prop with a plastic hub. You get the benefits of the stainless but the hub is a sacrifice when you bend a prop and you save your gearcase.
Lots of people seem to carry a spare prop , but don't have the gear or spare hub to do a on the water change. Not a fun process hanging out on the transom trying to catch a prop nut while trying not to fall in. On most inboards a on the water change is not a option.
 
MY SPARE HAS A SPARE CASTLE NUT AND WASHER ZAP STRAPPED TO IT.. oops i yelled.
 
hmm, from a "boy scout, be prepared" perspective, a spare nut zapped to the spare prop is a good idea - going to have to steal that idea!
 
Floating prop wrench comes in handy if you don't have a kicker and "have" to change your prop on the water. It's not much fun, but with the right tools and spare parts you can get it done on the water.
 
Dirty_Oar said:
How do I know what props would even fit my motor? Would this prop fit? And would it be a candidate to upgrade the one I have now? I like the holeshot that my boat has right now and it cruises at an acceptable speed for me. If I could cruise at near the same speed and save some fuel would be nice but I don't want t feel like a slug getting up to plane either. I am wondering if I even want to go stainless? I carry a spare aluminum prop so in the event I toast the one I have on I should be ok to get home. I don't like the thought of destroying my lower unit if its avoidable and I can sacrifice a prop instead.

https://comoxvalley.craigslist.ca/bpo/5778942041.html
Click to expand...

If that prop fits it might be a good candidate. might bring your top end rpm's up a bit and still maintain holeshot having the four blade. your better to be propped so you can attain closer to max rpm than under. it's harder on your engine to be under max rpm's. kinda like using overdrive to climb a long 15% grade. your lugging the engine if you can't attain max rpm...
 
Not sure where your are dirty oar , but Mercury Marine in Victoria has a set of loaner props that you can use for the day. Great way to get the feel of a 4 vs 3 blade and different pitches.
 
Stainless is stronger, so the blade is thinner - you can usually go 1-2 more inches of pitch from where your AL prop is at. You can put more cupping on a stained prop - mount the motor higher for less drag but still get enough bite.

4 blade is smoother & more efficient at lower speed but 3 blade had a higher top speed.

All the above assume that your motor runs within the factory recommended RPM range.
 
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