Prop question

I have a 2014 mercury 150 4 stroke on my 175 alumacraft dominator. Currently running an aluminum 3 blade 14.5×19 prop.

I dinged a rock and took a chunk out, and im now borrowing a buddies 21 pitch, 4 blade stainless prop while mine goes in for repair.

With his stainless one, im getting great hole shot, but i lost about 8mph in top speed. The boat also runs super smooth and handles noticeably better with the stainless.

So im thinking of buying a stainless one now, but wondering if i want that top speed back, would i want to go back to a 14.5×19 3 blade like my aluminum one? Or should i be trying something else? I cant afford to just buy a bunch of different ones to test them all out.

On a side note, my lake has a lot of dead heads sticking up, just under the surface that are very hard to see. The main lake is fine and safe, but the bays can be loaded with them. Its how i damaged my current one. So my question is, at idle speeds, if i hit a deadhead with a stainless prop, will it damage my lower unit?

Thank you for any help as i am brand new to prop stuff.

Unfortunately there’s no straight forward solution to this prop thing. I tried multiple props several years ago to find the right combination of hole shot and top speed. What someone tells you at the prop shop may not be the actual result. The only way to solve this is with trial and error.

Always a trade off with aluminum vs SS props. Better overall performance with SS but any type of accident is more costly. I’d honestly probably go with an aluminum prop if there was a relatively reasonable risk of hitting an obstacle like in your case.

On a side note, my lake has a lot of dead heads sticking up, just under the surface that are very hard to see. The main lake is fine and safe, but the bays can be loaded with them. Its how i damaged my current one. So my question is, at idle speeds, if i hit a deadhead with a stainless prop, will it damage my lower unit?

Yup…

Ok, i wasnt sure if low speeds would still cause damage. I had someone twll me no, but didnt feel right about that answer…

You could go with an aluminum 4 blade 14.5x17p to be safe.
Is the 21p a 14.5″ also? if so you want a 14.5″ 17p SS then. What are you RPM’s at WOT? You want to be as close to Max RPM at WOT to get the most out of the motor prop combo.

bigcrappie wrote:

What are you RPM’s at WOT?

This is one of two very important factors. Also the motor mounting height.

But, max RPM when fully trimmed is a key to determine the correct prop. If you lost 8mph, then that is not the correct pitch. Also, equal pitch going from a 3 to a 4 blade is about the same as bumping to the next pitch. Prop diameter is also a factor.

If you wanted to go with a 4 blade, you’ll likely want to go to a 17″. I would assume whatever dealer rigged your boat, likely has a good idea what prop is needed since that’s a pretty common motor for that size of boat. So the 19″ prop is likely pretty close to where you want to stick with.

Going from the 19 to the 21 with a better hole shot and less top speed is baffling and a 4 blade would be more like a 22 or 23 pitch equivalent from what I have read and experienced. Was the diameter smaller? A 4 blade on it’s own will run smoother have a better hole shot and have better slow speed handling. I think you would have to be running at least 750 rpm slower or more to lose that much top end. Even then in my experience I. Went from a 15 pitch and 22 mph at 5000 rpm to a 13 pitch at 19 mph and 5500 rpm. But I am polish so my view of things is usually bass akwards.

I run strictly stainless I have hit bumped ran over numerous stuff rocks, logs, stumps, gravel, sand and have never taken out or damaged my lower unit.If I would of been running aluminum I would of replaced a bunch of them. One time took my skeg right off and the stainless had a few nicks lower unit was fine. Now if I strictly ran rocks yeah I think I would run a aluminum.

The boat type, hull design and weight distribution plays as much combined with the horsepower, then there is the question of 2 stroke or a 4.

I kid you not, I owned two Lund boats that were the same model (one an I/O and the other an outboard) they were 8 model years apart with identical hulls. I went through 8 stainless steel props and 2 aluminum to find the prop that belonged on the boat! Getting on plane, ability to trim once on plane, RPM’s (over/under), hole shot and top end were some of the issues with all of them til I found the one. A friend of mine has the same boat with only the rear seat configuration inside being different and what worked for him did not for me, close but no cigar!

Good luck! I have 2 ss props for sale that fits Merc one a 4 blade 23 pitch brand spanking new and the other a 21 pitch 13.5″ 5 blade used.

Stainless harming your LU is sort of a myth. If you have an older non sacrificial hub, then less it can, but with most prop hubs now, that will be the first thing to fail.
I run stainless on the MN and Miss rivers and have hit many of things with my stainless prop and everything is great. I would never go back to aluminum.

I would suggest checking out the X7 Spitfire prop for you boat. It’s kind of a all around great performer (holeshot, handling, top end speed).