Prop Advice

Fish Assassin

Crew Member
Got a 14.5X19 alloy non ported Mercury Black Max prop on my new 115. Trims out nice but when I back off the throttle say 1000-1500rpm the back end drops quickly and I start porpoising.

Empty 6000rpm 42mph
Loaded 5700-5800rpm 38.5-40mph
MAX RPM 6000rmp

Would a 4 blade prop fix my quick drop on the arse end. Keep it up there at lower RPM when it's already up on plane.

I think I am going to try a 14X19 alloy ported 4 blade Turning Point Prop. So Id add a blade and drop a 1/2 inch diameter.

Any sugestions?
 
you could try a doel-fin, are your fuel tank and batteries aft? maybe too much weight aft. have your friends sit up front to distribute the weight and see if it stll does it as much, it could simply be weight distribution. you should still be planing fine if you do 27 at 4000 rpm. I would think a 4 blade would help a bit for sure. I'm still mucking a bit getting the right prop for my new motor, the original one they gave me was a wee bit too small, I was 300 over max rpm and climbing at over 40mph so had to back off lol.
 
There's a couple of options, some guys swear by the add on planing plate to your outboard makes a big difference. I do believe 4 blade props do help no first hand experience how ever I went from Mirages to Enertia's and it made a significant difference lower planing speed, better fuel economy and for the twins they synced nicer plus with the same pitch prop I gained 350 rpm.
 
4 blade do lift stern boat how about your outboard mounting height if it's tow low it can porpoise I don't like adding hydrofoil or dolphin fins because I don't like the idea of drilling holes in outboard. Trim tabs can will do the trick also
 
At say 4000 rpm and planing everything is normal..... I am a bit slower then my old 2stroke at popping up but I figured that was the joy of a 4 stroke.

2 stroke prop'd right instant
4 stroke as it is 2-3 seconds

But 5500-6000rpm trimmed out this sucker flys. Drop 1000rmp instant proposing. I have to trim down before pulling back on the throttle or else some many find it scary.
 
Check your engine height. Much spray comming from your motor at speed? Never had a 4 blade do anything for porposing but they do get you out of the whole quicker.
 
4 blade do lift stern boat how about your outboard mounting height if it's tow low it can porpoise I don't like adding hydrofoil or dolphin fins because I don't like the idea of drilling holes in outboard. Trim tabs can will do the trick also
My cav plate in a neutral position say on a trailer is perfectly in line with the bottom of the haul. When tucked right in my motor would be 11-12 degrees under, based by the slope of my tramsom. It's only in that position for takeoff.

I had a hydrofoil on the last motor on this boat. It came that way. Maybe it was the fix for the previous owner.

If a 4 blade eliminates the 2-3 second lag and keeps my arse end up when dropping the rpm Id be a happy camper.

Dont get me wrong the boat and motor are awesome. Really happy with every change its has gone thru this last year. I am just trying to reach perfection, something that may never happen. But I ain't going to stop trying :) LOL
 
Got a 14.5X19 alloy non ported Mercury Black Max prop on my new 115. Trims out nice but when I back off the throttle say 1000-1500rpm the back end drops quickly and I start porpoising.

Empty 6000rpm 42mph
Loaded 5700-5800rpm 38.5-40mph
MAX RPM 6000rmp

Would a 4 blade prop fix my quick drop on the arse end. Keep it up there at lower RPM when it's already up on plane.

I think I am going to try a 14X19 alloy ported 4 blade Turning Point Prop. So Id add a blade and drop a 1/2 inch diameter.

Any sugestions?
Porpoising I generally related to too much engine trim I believe. It certainly is on my boat. But I swear by that turning point hustler 4 blade. Back to back on my last boat and current one against the 3 blade was a no brainier. Better accel, smoother running and when you look at it, it's pretty beefy. And they are dirt cheap. Got one last fall at steveston marine(yeah,I know) for 130 bucks.
 
I have found 1 to 2 inches above bottom of the boat when the engine is on a hull with a extended transom or pod.
 
Owen. I think you may find that you will need to drop a couple inches of pitch in order to keep your WOT Rpms. That was my experience wen going from 3 - 4 blade.
 
Last edited by a moderator:
Owen. I think you may find that you will need to drop a couple inches of pitch in order to keep your WOT Rpms. That was my experience wen going from 3 - 4 blade.

That seems to be the general consensus but this hustler prop is pretty unique. It has 2 totally different pairs of blades. They say most applications you can stay with same pitch. Worked that way for me.
 
I vote for the tabs as well, however you may want to try the foil for less money.
I think there's one you can get that doesn't require drilling the cav plate
 
I vote for the tabs as well, however you may want to try the foil for less money.
I think there's one you can get that doesn't require drilling the cav plate
 
You get out often, so you have time to experiment. My whaler heavy in the stern, but stops porpoising when I have 5 or 6 cannonballs in the bow locker.
 
hydro foil on cav plate should help and some more weight in the bow.. my ol overpowered trophy did this...three bags of concrete up in the cuddy and a foil fixt it...
 
sounds like how my boat is running.

went from a 4.3 to a 5.7 and alpha to bravo leg.... she sits 2" lower in the water now at the back.

running wot at 4800rpm/50mph its dead flat and stable as anything
drop it back to 3000rpm/30mph and with any chop the proposeing starts. even trimmed fully in/down

my solution is going to be tabs.



i have read that some props specify more/better stern lift than others, maybe that would help, or get more weight forwards?
 
Back
Top