Prop Advice for Merc EFI 115 on Malibu 182

[Macdeep]

Looking for advice on selecting the right prop to get better performance out of my Malibu 182 with a Merc EFI 115 on the back. Hull is rated for up to a 185 I think. Seems like most people put a 115 or a 150 on this hull. I know repowering to a 150 is the only real solution, but I'm not in a position to do that now and not for a few years. I've read enough threads with the usual advice to just repower...

Boat and motor weights that I found online - not sure if the hull weight is accurate
Hull 1750lb
115 motor 360lb
9.9 kicker ~100lb
130L of Fuel ~290lb
Total ~2500lb

Add beer, gear and 3 adults, we're just over 3000lb. I usually use the boat with myself plus two buddies or me plus wife and two young kids, so about the same load either way. I don't do water sports, just fishing and whale watching etc.

I have 3 props and have tested two:

13.75 x15 3 blade - no
13.5 x16 3 blade - yes
13.25 x17 3 blade - yes

The previous owner had the 13.5x16 on it. Sea trial with just myself on board and ~100lb of gear had a 6800rmp WOT on flat water. Holeshot was not stellar but acceptable. The boat struggles to hold plane under 4500rpm with trim tabs jacked down, and comfortable plane with trim tabs backed off is 5000rmp. This seems high. Specs from the manual suggest the motor should be propped to WOT closer to 5800-6200rpm.

Edit- manual says 5800-6400rpm…same same but different I guess…

I changed to the 13.25x17 for my first family outing of the season. 3 adults and 2 kids plus lunches and minimal fishing gear. WOT at 6400rpm. Holeshot was pretty bad but we eventually go up lol. Comfortable plane at 5000rmp that gets me 19-21 knots, can't hold plane under 4700rpm and she chugs down to ~15-16 knots on the GPS at this rpm. Planning to do a solo test this weekend to directly compare to the 13.5x16.

I'm guessing that the 13.75x15 would be best to reserve for tubing and watersports or super heavy loads. Probably gonna sell it at some point.


Questions - will a different prop solve anything or is the 13.5x16 my best bet?

I've read that a 4 blade prop might resolve the mediocre hole shot, help get the bow down/transom lifted and if pitched correctly could get my cruise RPM down to a more comfortable ~4500rpm, though I might sacrifice a bit of speed. But I dont need to hit logs much faster than 20 knots, so speed isnt my issue. Online prop selectors suggest a 13x15 or 13.5x15 in the 4 blade, and the same range of props I have available in the 3 blade.

I've also had good success with my previous underpowered boat (17ft aluminum with a 50hp and no trim tabs) by adding a hydrofoil to get on plane a much faster and hold a comfortable plane at ~200rpm lower while keeping the same speed ~16-18 knots. But I've also read that if you already have trim tabs, then a hydrofoil isn't needed. The only advantage I see in the hydrofoil is that it can make the footprint of the hull longer and eliminating cavitation risks, thus giving some performance gains, but I know other's disagree.

Other details - the motor seems to be mounted at the right height. Plate is ~1-2' above the bottom of the hull. Could go higher I guess, but not sure if necessary. Definitely does not show any of the tell tale signs of being mounted too low - v-spray etc.

Also note that I'm still getting used to using trim tabs... but I do jack them down to help hole shot, and to fight wandering when under low speeds around the marina. She wanders a lot at slow speeds around the marina if you let her lol. Tabs down, and trim up the motor and she straightens out phew So much to learn with a new boat!

Thanks.

 

[gone fishin]

I have a 115 pro and use a Mercury Stainless Eneriata 13.6 x 212P on a little lighter unit.
Go stainless, you will never regret it.
best to check with a dealer. They will know what is best suited for your rig.

 

[Macdeep]

I have a 115 pro and use a Mercury Stainless Eneriata 13.6 x 212P on a little lighter unit.
Go stainless, you will never regret it.
best to check with a dealer. They will know what is best suited for your rig.

Ya, I'd go stainless if prices wasnt an issue. Gonna be aluminum unless there's a deal out there on a used one.

But will consult with a dealer shortly, just figured I'd get some advice from the crowd before I talk to a sales person.

Cheers

 

[SpringVelocity]

I think your really going to be fighting with this one.

115hp on that hull is under powered (butt you now know) in my opinion if you want to load it up with people. My 185 I went with a 150hp. My old inboard was 135hp and that struggled a bit when I had more than one passenger onboard.

 

[Aquaholic]

Something is wrong if that motor was revving to 6800 RPM. Is your tachometer accurate? I would start there. For reference, I just went from a Merc 90 to a 115, and have tried a couple different propellers myself.

The rule of thumb for your situation is matching the maximum rpm by the manufacture, with a prop that get you there or slightly over that amount but you don’t run it in that range. eg…. maximum rpm of 6000 according to the manufacture, but the prop that works best will hit 6200, but you don’t run it there.

Do you know what the gear ratio is in your leg? Is it the command thrust version at 2.38 or the regular gear case version at 2.07?

Depending where you are, I have some propellers that you could try.

 

[Macdeep]

Something is wrong if that motor was revving to 6800 RPM. Is your tachometer accurate? I would start there. For reference, I just went from a Merc 90 to a 115, and have tried a couple different propellers myself.

The rule of thumb is matching the maximum rpm by the manufacture, with a prop that get you there or slightly over that amount but you don’t run it in that range. eg…. maximum rpm of 6000 according to the manufacture, but the prop that works best will hit 6200, but you don’t run it there.

Do you know what the gear ratio is in your leg? Is it the command thrust version at 2.38 or the regular gear case version at 2.07?

Depending where you are, I have some propellers that you could try.

I had the tach etc checked over by my mechanic last fall as part of purchasing the boat because of that exact concern you raised. My repurchase water test for WOT ran to 6800rpm with 2 ppl on board. Mechanic said all systems are good to go, likely just need a different prop.

For a 2012 115 EFI I'm pretty sure its 2.33:1 but google is suggesting it's 2.07:1. I can check my manual once I'm home.

But yes, I'm trying to find a way to get WOT down to around 6000rpm, or 6200rpm as you suggest and then run at a lower rpm for cruising, hopefully somewhere nearer 4500rpm for ~20-22knots.

I'm located in Port McNeill but do venture down island a few times a year during the boating season.

My concern is that if I change props to get my WOT rpm down by substantially increasing pitch, then the motor might be under a lot of strain and/or experience a lot of slippage to get out of the hole. And once on plane, might a still have a lot more strain and also issues with being able to sustain speeds when in chop or swell. I'd rather burn extra fuel and not blow up the motor by straining it too much by asking it to push too much load with too much prop.

I'm becoming more aware though that I won't be able to have it both ways - I'll either struggle to get out of the hole, but might eventually be able to cruise at ~4500rpm if I don't mind the engine straining for like 30sec to get me on plane, or I'll have to plane at 5000rpm with acceptable holeshot.

I'm not expecting much more than a small increment of improvement by changing props, but I want to get all I can out of her.

Anyone with experience with changing to a 4 blade prop to improve this sort of issue?

 

[Aquaholic]

"My repurchase water test for WOT ran to 6800rpm with 2 ppl on board".

They do make an XP version with a 6400 rpm range, not sure if in the year that your model is though.


"For a 2012 115 EFI I'm pretty sure its 2.33:1 but google is suggesting it's 2.07:1. I can check my manual once I'm home."
They did not have Command Thrust in 2012, so it will not be the 2.38 leg, my 2009 manual from my last motor says yours is a 2.07, as does the newer version they made a few years later. 2.33 was on the 75 and 90 hp.


"cruise at ~4500rpm if I don't mind the engine straining for like 30sec to get me on plane, or I'll have to plane at 5000rpm with acceptable holeshot".
The 5000 rpm plane with acceptable holeshot seems like what you will have to do. Can you ditch the kicker and troll off the main to save some lbs. at the stern? Hydrofoil will help too if you do not have one.


"Anyone with experience with changing to a 4 blade prop to improve this sort of issue"?
Yes, with my 90 (2.33 leg) the 17" 3 blade was good (6000 rpm max, plane at 4000 rpm) but I wanted to improve, so the Merc Spitfire 17" 4 blade prop was noticeably better, (pitch for pitch swap if your 3 blade is good for rpm etc) allowed me to plane faster, low speed wandering almost gone, and was 3600 rpm at plane, plus I added an SE 300 Hydrofoil from Harbour Chandler and that also made it pop up quicker with the added stern lift.

My newer 115 (2.07 leg) needed a 15" 4 blade to hit 6000rpm as recommended, as the 17" 4 blade was a bit low on rpm with identical boat, hydrofoil etc. after we tested it. Planing rpm is the same, 3600. I did go aftermarket (Turning Point) with the 15" 4 blade though, not a Merc Spitfire.

 

[Macdeep]

"My repurchase water test for WOT ran to 6800rpm with 2 ppl on board".

They do make an XP version with a 6400 rpm range, not sure if in the year that your model is though.


"For a 2012 115 EFI I'm pretty sure its 2.33:1 but google is suggesting it's 2.07:1. I can check my manual once I'm home."
They did not have Command Thrust in 2012, so it will not be the 2.38 leg, my 2009 manual from my last motor says yours is a 2.07, as does the newer version they made a few years later. 2.33 was on the 75 and 90 hp.


"cruise at ~4500rpm if I don't mind the engine straining for like 30sec to get me on plane, or I'll have to plane at 5000rpm with acceptable holeshot".
The 5000 rpm plane with acceptable holeshot seems like what you will have to do. Can you ditch the kicker and troll off the main to save some lbs. at the stern? Hydrofoil will help too if you do not have one.


"Anyone with experience with changing to a 4 blade prop to improve this sort of issue"?
Yes, with my 90 (2.33 leg) the 17" 3 blade was good (6000 rpm max, plane at 4000 rpm) but I wanted to improve, so the Merc Spitfire 17" 4 blade prop was noticeably better, (pitch for pitch swap if your 3 blade is good for rpm etc) allowed me to plane faster, low speed wandering almost gone, and was 3600 rpm at plane, plus I added an SE 300 Hydrofoil from Harbour Chandler and that also made it pop up quicker with the added stern lift.

My newer 115 (2.07 leg) needed a 15" 4 blade to hit 6000rpm as recommended, as the 17" 4 blade was a bit low on rpm with identical boat, hydrofoil etc. after we tested it. Planing rpm is the same, 3600. I did go aftermarket (Turning Point) with the 15" 4 blade though, not a Merc Spitfire.

Ya I dont have the XP version, and looks like the 2.07:1 gearbox.
** edit- manual says 2.33:1 gear box for the 115XL45 (2011, not 2012) and a max WOT 6400rpm

I could remove the kicker, but it's so much better on fuel, and the added insurance of a secondary power option for motoring home and also charging battery and keeping electronics alive in an emergency so probably wont' be ditching it.

Will look into a 4 blade prop for sure. Just emailed the Parksville Boat house these same questions so will see what they come up with.

And yes, despite all the groans I'll surely get from the peanut gallery, I just ordered the SE 300 hydrofoil. At the very least it might help with potential cavitation when underway in the swell, and reduce porpoising when I'm trying to fully trim it out for top speed. It worked so well on my last underpowered boat that I'm just a sucker for it hahaha. Another 100$ down the drain I guess

Will have to see what the options are to repower in a few years if I can't get a decent solution. But I'm happy to fiddle around with a few 100-500$ ideas rather than get into a several thousand dollar upgrade. By then I'll probably be wanting a 21ft boat and will make a point of making sure the package isnt underpowered this time lol.

I'm a sucker for an underpowered boat.


Cheers

 

[Aquaholic]

Many here know the hydrofoils do work in the right situation, so you will have supporters as well. I'm getting T shirts made up, what's your size?

 

[Macdeep]

Many here know the hydrofoils do work in the right situation, so you will have supporters as well. I'm getting T shirts made up, what's your size?

Hahahah, I'm that awkward in-between L and XL depending on the season and whether I get my beach body going, but so far this summer's beach bod isn't going to happen hahaha. Sign me up for an XL Perhaps if I lost 20-30lb my boat would go faster and get on plane better

 

[Aquaholic]

Hahahah, I'm that awkward in-between L and XL depending on the season and whether I get my beach body going, but so far this summer's beach bod isn't going to happen hahaha. Sign me up for an XL Perhaps if I lost 20-30lb my boat would go faster and get on plane better

I didn’t think you’d be a jockey anytime soon.

 

[brutus]

Just going to chip in lol, I also have an underpowered boat 25ft with a single 225, went from a 3x18 ss to a 4x15 ss, boat gets up quick, can plane at 14mpg 3800 rpm and still do 40 mph at wot, cruise at 25mph at 4200rpm and 28mph at 4500 and don’t burn to much gas, my Honda goes in Vtech mode after 4500 and sucks fuel like an alcoholic after work. With the 3 blade 3x18 it was slow to get on step and needed to stay in the 4500rpm to keep it there at 25 mph, top speed was the same. Also I fish solo 90% of the time

 

[Fishin]

I’m on my 3rd 115 4 stroke started with a 04 merc/yam on a 17’ hourston 13.25x17 was perfect 6k rpm at 39mph, went to a 2022 115 merc CT totally different animal 14.5x19 46mph at 6k rpm on the hourston bought a 2005 1802 trophy with a 2005 merc 115 similar to your set up 1925lbs (hull) the 05 Merc definitely had to work it was pitched down low to a 13p it worked but performance wasn’t great. I now have the 115 CT on the trophy I’m a big guy with 2 people 52gal of fuel and all our gear im 36mph wot only at 5400rpm Gonna drop to a 17p I think, I’m running the 14.5x19. based on my experience with these motors, I think a 17p 4 blade s.s might be alright for you to live with for now anyway maybe add a foil and check your motor height as well I’ve had really good luck with 4 blades in the past.

 

[MikePA]

Just going to chip in lol, I also have an underpowered boat 25ft with a single 225, went from a 3x18 ss to a 4x15 ss, boat gets up quick, can plane at 14mpg 3800 rpm and still do 40 mph at wot, cruise at 25mph at 4200rpm and 28mph at 4500 and don’t burn to much gas, my Honda goes in Vtech mode after 4500 and sucks fuel like an alcoholic after work. With the 3 blade 3x18 it was slow to get on step and needed to stay in the 4500rpm to keep it there at 25 mph, top speed was the same. Also I fish solo 90% of the time

Please tell me 14 mpg is a typo

 

[brutus]

Please tell me 14 mpg is a typo

Lol mph. I wish

 

[Aquaholic]

Knowing now that you have the 2.33 leg and 6400 redline, from my recent experience I would recommend the four blade Spitfire 15 or 17”. With your full weight I think the 15 but with the hydrofoil the 17 might be close. Merc dealers usually let you try one on an exchange basis but it has to be perfect when returning.

 

[Macdeep]

Knowing now that you have the 2.33 leg and 6400 redline, from my recent experience I would recommend the four blade Spitfire 15 or 17”. With your full weight I think the 15 but with the hydrofoil the 17 might be close. Merc dealers usually let you try one on an exchange basis but it has to be perfect when returning.

Sounds good, will definitely be looking at the 4 blade 15 and 17" pitches - what diameter are these ones you are referring to? or is the Spitfire all one standard daimeter?

The online prop selectors for 4 blade at 3000-3300lbs all suggest a 13x15 or a 13.5x15 depending on which prop selector and what variables I input besides weight and HP.

My hydrofoil arrives today or next Monday via Amazon

 

[InterMechanico]

Please tell me 14 mpg is a typo

Hahaha I think he's got the right prop

 

[Aquaholic]

The pre-determined diameter comes with the Spitfire pitch you choose, don't overthink this one.

SE SPORT 300 Hydrofoil

Harbour Chandler is a locally owned and operated business that has had its doors open to the public since 1985. What has made us so successful over the years is our well-stocked shelves, our fair prices and our efforts to find whatever it is that our customers are looking for.

harbourchandler.ca

This was my data below when going from a 3 blade 17" to the 4 blade 17", and you can see the highlighted Spitfire info. Again, Merc says pitch for pitch if you have the correct prop in 3 blade. (but obviously want the 4 blade improvements) Notice I was getting 5900 on a 6000 redline so it was propped well.

 

[Macdeep]

The pre-determined diameter comes with the Spitfire pitch you choose, don't overthink this one.

SE SPORT 300 Hydrofoil

Harbour Chandler is a locally owned and operated business that has had its doors open to the public since 1985. What has made us so successful over the years is our well-stocked shelves, our fair prices and our efforts to find whatever it is that our customers are looking for.

harbourchandler.ca

This was my data below when going from a 3 blade 17" to the 4 blade 17", and you can see the highlighted Spitfire info. Again, Merc says pitch for pitch if you have the correct prop in 3 blade. (but obviously want the 4 blade improvements) Notice I was getting 5900 on a 6000 redline so it was propped well.

View attachment 93004

Ok so then next step is to get an idea of the correct prop for my boat in a 3 blade and then make the jump to the 4 blade I guess.

Trouble is, my current props aren’t really doing the job and not sure I have a good understanding of the math to figure out a better 3 blade.

Seems like I gotta get answers from a merc dealer or a local marine shop… or do some more water testing?