Motor height - Merc 150 seapro

[Macdeep]

So I repowered over the winter from a 115 Merc 4S to a 1 year old Merc 150 Seapro. I always used one of those SE300 hydrofoils, made a world of difference being underpowered, but didnt solve all my problems, hence the repowering.

Had the new 150 mounted at the same height as the previous motor (which never had spray or cavitation issues), and had spray issues so bad. Back seats were soaked within minutes and was starting to get a wet back. That, and even when trimmed all the way under, I had porpoising issues that could only be stopped by using the trim tabs, which isnt what I want. Took it back in and had it raised another notch.

Spray is improved but not eliminated, especially for the dang transducer, but I can move that around easy enough.

Ran it with a hydrofoil first, and then without. Found I was still getting a more spray than I wanted with the hydrofoil, but I had great trim control with just the outboard and no porpoising. Did a second run without the hydrofoil and while it was much cleaner (less spray etc), I had to have the motor trimmed all the way under to prevent porpoising, and even had to use the trim tabs if there were small waves that I used to just cut through with the old 115 and the foil.

Any way, attached some photos of the differences. I think I want to keep using the foil. But mostly I want all my future passengers to stay dry lol, and to have better trim control with the outboard and not have dang porpoising issues.

My mechanic is not 100% sure that moving it up one more notch is the answer, but I dont have cavitation issues with or without the foil whether in turns or taking off, or even in rougher water. Had it out in 2-4ft chop the other day and honestly, it performed best in the rougher conditions...

Any way, did some reading on the old google, and it was suggested that with the Seapro's having a larger gear case the push more water than the regular merc 150 and can have more spray, so tend to need to be a notch or two higher than one might think.

So ya, photo shoot time. Without the foil, the water is a lot cleaner. Seems like the foil is touching the water too much when on plane, and causing a lot more wash etc.

Running a 3 blade 15.3 x 19 prop. Hits the top end of WOT with a medium load (2 ppl, full fuel, basic gear but not downriggers, rods.)
Pics are ~4000rmp hitting ~25knots. She planes happily enough at ~18knots at just under 3500RMP, and WOTTED out at 5200RMP for 35 knots. WOT range that I understand is 4800-5300.


And then ya, the foil is clearly in the water still. But without it, the cav plate seems to be just about the surface of the water? Maybe still a little deep?

Transducer spray was a mess.


Thoughts?

- Throw more money at it an move it up another notch?
- Throw more money at it and get a 4 or 5 blade prop for more stern lift?
- Run it as it is without the foil and just use the trim tabs to keep the porpoises at bay?
- Run it as is with the foil and make my kids and friends wear rain gear lol?

Never had this issue with the 115. Same 25" leg. Both mercury 4 strokes. Used the foil on the 115 with no spray issues, not even from the transducer... But the 150 is about 100lb heavier which I think is also a factor in this equation.

Edit - adding photo of motor height. Cav plate is 2" above hull line.



Prop: Rubex/Solas 3plus 15.3x19
Boat: Malibu 182 (2009 model I think)
Motor: 2025 Merc Seapro. 4.75" gear case, 2.08 gear ratio.

 

[BC Coast Pilot]

I don't or won't run hydrofoils.
Like to get to root of problem.
Your water flow looks really clean in all the no hydrofoil pics.
The 100lbs could be shifted with a weight if you would like to check that box off, add a 100 lbs or more to the bow locker.
What model of prop are you running for the baseline?
Switching to a Rev4 or another stern lifting prop may be your saviour
Or an Enertia series 3 blade, so much science and research goes into this.
The props are a game changer, gotta stick with the Merc props.
Can you run the Mercury prop selector?

I like the clean water with the no foil 3rd hole as a base line. If you're porpoising now, I would stop there with height, it looks good on the cav plate.
Once you get motor and prop right, then go after the transducer, different problems which the foil will complicate with interaction.
My opinion, from experience

 

[Squire]

The 100 lb gain in weight from the 115 to the 150 Seapro could definitely be contributing to your issues. It’s all at the end of the fulcrum relative to your center of gravity and you may not ever completely eliminate porpoising, especially at lower speeds. As BC Coast Pilot already said, I would look at moving some weight forward and optimizing your prop. A good four-blade stern-lifting prop would be my next tweak. I’m another that believes hydrofoils are only warranted on underpowered rigs.
I have learned to accept that my factory boat bracket is simply not optimum on my boat with my outboard and I’ll always need some trim to counteract porpoising at lower speeds, even after moving the motor up, shifting some weight up to the cuddy, and getting a Powertech OFS4 prop of the right pitch.

 

[Marko]

I do not recognize that transom. Which boat is this? What HP is it rated for?

In my opinion, mechanics are better at wrenching engines than setting engine height, but of course there are exceptions. Your experience running the boat will be most valuable in optimizing the new power.

With the RPM and speed you’re getting, it seems like enough power for the hull so I would discard the foil.

The running image of your cavitation plate to me looks a little bit low so I would raise the engine at least one set of holes and then retest. When the boat is on the trailer and the cavitation plate trimmed parallel/aligned with the keel, it should typically be a bit higher than the keel. How much depends upon the boat, but for my old 22 Whaler, it needs to be about an inch and a half above.

Random image from THT:


As others have suggested, a prop change might be worthwhile too, but it will be most helpful here to first know what boat you’re pushing with that 150.

The ECU in my 2023 Mercury 200 Fourstroke will not allow the engine to over rev… I suspect your 150 will have the same technology, though I am not certain. Confirm this before propeller testing.

 

[chille51]

Not to hijack, but I've been battling a similar issue in my boat. I've pretty much arrived at the conclusion I need to move my motor up to the top hole (its on the 3rd now). Here is a photo to compare - that is not the cav plate that is visible there, it's the one above it.

This is the 3rd prop and otherwise the best performer - a Solas 4 blade.
Honda 100hp on a Arima 17', that sits stern heavy due to main, kicker, fuel tank, and dual batteries all at the stern. Common downside to these hulls. I run with my front freshwater tank full for ballast, and keep all my rigger balls, anchor and other gear up in the cuddy.

 

[Pineapple Express]

There are typically two causes of porpoising:
1. too much weight too far aft
2. motor too low.

In my opinion your motor (and @chille51 ) is too low. Ideally you want the anti-ventilation plate visible just skimming the water when trimmed normally. Look at the setup photo @Marko posted too. I bet you'll find your motor is lower than what is pictured.


My suggestions in order of action:

1. Ditch the foil thing.
2. Raise the motor
3. Adjust weight distribution
4. Test alternative props

 

[Macdeep]

Thanks for all the replies.

Motor Height: I am tending to agree that moving it up one more hole is likely the sweet spot. Will likely get that done and test again both with and without the foil. Currently the cav plate is at least 1.5" above the bottom of the hull. I'll get a photo of it this week when I look at the transducer placement.

Hydrofoil: I'm not married to the foil, but I like what it offers for trim control, especially in west coast and afternoon conditions to keep the nose down and manage forward/aft trim better. But in the end, I also want clean water behind the boat. Will see if I sacrifice trim control for dry passengers lol.

Weight distribution: yes, I can add 100lb to the bow locker. As it is, when the photos were taken I have 50+ lb in there that never used to be there as a full time thing - I now have both my hali anchor and smaller beach anchor as well as chain and 100ft rope up there. I keep my hali rope in a bucket in the shed as it's a bulky item that needs to dry out. I'll see about adding weight to the bow.

Boat type: Malibu 182, 2009 hull I think.
Prop: Rubex/Solas 3plus 15.3x19 which was recommended to me by a prop shop in Campbell River. I would like to try a 4 blade for stern lift and likely keep this one as a spare.

Yes, I have run the Mercury prop selector as well as a few other online ones, and talked to merc dealers. Results vary but the ball park seems to be a 14.5x19 give or take.

RMP data from my first test prior to the photos being taken:
3500 = 20knots
4000 = 25knots
4500 = 30knots
5200 = 35knots and is Max WOT with two adults, full fuel but no bigger anchors in the bow and minimal gear besides safety and first aid stuff. I often run with 4 people and another ~150lb of fishing gear, coolers, beer etc.

 

[Macdeep]

Not to hijack, but I've been battling a similar issue in my boat. I've pretty much arrived at the conclusion I need to move my motor up to the top hole (its on the 3rd now). Here is a photo to compare - that is not the cav plate that is visible there, it's the one above it.

This is the 3rd prop and otherwise the best performer - a Solas 4 blade.
Honda 100hp on a Arima 17', that sits stern heavy due to main, kicker, fuel tank, and dual batteries all at the stern. Common downside to these hulls. I run with my front freshwater tank full for ballast, and keep all my rigger balls, anchor and other gear up in the cuddy.

View attachment 125587

Looks a lot too low. Cant even see the cav plate, and I bet looking back you have the classic V-spray.

 

[Pineapple Express]

On the topic of weight distribution, I wasn't suggesting to add any ballast...rather look at shifting the weight that's already onboard the boat. Like repositioning batteries, change where you carry cannonballs and other heavy items.

 

[Aquaholic]

If your old Merc 115 was not a CT version, the much bigger gearcase and prop on the Sea Pro puts you in a different world where you are starting from zero, none of your data from before will carry over. Playing with props and heights will be a trial and error event, as you have found.

Do you have the ability to go one hole higher?

Are the legs the exact same length on the 115 and the 150? (basic, I know)

 

[salmonkiller01]

You need to come up 2 more holes I would say. Should see cavitation plate on plane
The pic is almost right could come up one hole

150 is heavier causing engine to be deeper, swapping props will not fix 100%. Need to come up, 2 holes and you will stop porpoising
Your rpm are good. Raise it

 

[Macdeep]

On the topic of weight distribution, I wasn't suggesting to add any ballast...rather look at shifting the weight that's already onboard the boat. Like repositioning batteries, change where you carry cannonballs and other heavy items.

Oh roger, ya I dont have much opportunity to shift weight forward. I already have all the heavy stuff in the bow (anchors x2, chain, rope, spare canon balls). I'm not big on moving the batteries to the front due to the cost of the work, and I'm concerned that batteries in the bow will experience more shaking and pounding through chop and lead/acid batteries dont like that as a rule. Seems like my easiest option for weight redistribution is to find something heavy to add to the bow - rubber floor mat, more anchor chain, all my hali lead etc. That, or get rid of my kicker which I'm not keen to do yet.

 

[Macdeep]

If your old Merc 115 was not a CT version, the much bigger gearcase and prop on the Sea Pro puts you in a different world where you are starting from zero, none of your data from before will carry over. Playing with props and heights will be a trial and error event, as you have found.

Do you have the ability to go one hole higher?

Are the legs the exact same length on the 115 and the 150? (basic, I know)

I'm pretty sure they are the same length - same nominal length at least @ 25". I have three holes to go higher. But ya, definitely feels like I'm starting from scratch. But all this fiddling is adding up with shop time...

 

[Macdeep]

You need to come up 2 more holes I would say. Should see cavitation plate on plane
The pic is almost right could come up one hole

150 is heavier causing engine to be deeper, swapping props will not fix 100%. Need to come up, 2 holes and you will stop porpoising
Your rpm are good. Raise it

Not sure if all this is for me or the honda guy. 2 holes up seems like a lot for my Merc? Was only thinking of coming up 1 hole at a time?

 

[Macdeep]

The cavitation plate is 2" above the bottom of the hull to add context to whether I should go up yet another hole or stop where I'm at and just move the transducer to a better height or location, and run without the foil which is cleaner. But I think ideally, I would raise it another hole or two and still use the foil?

 

[Aquaholic]

Do you have a 4-blade you can try? Adds lift at the stern. I do hope you get 90% there without the foil or 4-blade, and then they make it perfect.

 

[SpringVelocity]

Always love these threads.

Thanks for all the replies.

Motor Height: I am tending to agree that moving it up one more hole is likely the sweet spot. Will likely get that done and test again both with and without the foil. Currently the cav plate is at least 1.5" above the bottom of the hull. I'll get a photo of it this week when I look at the transducer placement.

Hydrofoil: I'm not married to the foil, but I like what it offers for trim control, especially in west coast and afternoon conditions to keep the nose down and manage forward/aft trim better. But in the end, I also want clean water behind the boat. Will see if I sacrifice trim control for dry passengers lol.

Weight distribution: yes, I can add 100lb to the bow locker. As it is, when the photos were taken I have 50+ lb in there that never used to be there as a full time thing - I now have both my hali anchor and smaller beach anchor as well as chain and 100ft rope up there. I keep my hali rope in a bucket in the shed as it's a bulky item that needs to dry out. I'll see about adding weight to the bow.

Boat type: Malibu 182, 2009 hull I think.
Prop: Rubex/Solas 3plus 15.3x19 which was recommended to me by a prop shop in Campbell River. I would like to try a 4 blade for stern lift and likely keep this one as a spare.

Yes, I have run the Mercury prop selector as well as a few other online ones, and talked to merc dealers. Results vary but the ball park seems to be a 14.5x19 give or take.

RMP data from my first test prior to the photos being taken:
3500 = 20knots
4000 = 25knots
4500 = 30knots
5200 = 35knots and is Max WOT with two adults, full fuel but no bigger anchors in the bow and minimal gear besides safety and first aid stuff. I often run with 4 people and another ~150lb of fishing gear, coolers, beer etc.

Been through this....lololol

I have a 185 podded. Your numbers are close to mine with a 150 suzuki. Your top end is a bit low.

I get 5700 on mine WOT a little faster I think 37knots.

I like the hydrofoil on mine personally especially on the design of boat.

The prop I use is a 3x15.25x19R three blade SS.

I will see if I can find that photo where my cavitation plate was relation bottom of hull.

 

[Pineapple Express]

View attachment 125599
The cavitation plate is 2" above the bottom of the hull to add context to whether I should go up yet another hole or stop where I'm at and just move the transducer to a better height or location, and run without the foil which is cleaner. But I think ideally, I would raise it another hole or two and still use the foil?

Your mounting height looks better than I imagined. I think that your height might be in the right range as-is. The other thing I noticed in your original pics is that you're running the motor trimmed very far down. I think that once you trim the motor a bit more neutral you'll see the anti-ventilation plate visible when running (considered ideal).

That looks like a basic aluminum prop. I think you will see better performance with a good quality stainless prop. Do you know the exact brand/model/specs of the prop you have now?

 

[SpringVelocity]

Always love these threads.

Been through this....lololol

I have a 185 podded. Your numbers are close to mine with a 150 suzuki. Your top end is a bit low.

I get 5700 on mine WOT a little faster I think 37knots.

I like the hydrofoil on mine personally especially on the design of boat.

The prop I use is a 3x15.25x19R three blade SS.

I will see if I can find that photo where my cavitation plate was relation bottom of hull.

This was my mounting height and what it looked like vs bottom hull extension.

Looking at your photo we look fairly close in height.

 

[Aquaholic]

Always love these threads.

Been through this....lololol

I have a 185 podded. Your numbers are close to mine with a 150 suzuki. Your top end is a bit low.

I get 5700 on mine WOT a little faster I think 37knots.

I like the hydrofoil on mine personally especially on the design of boat.

The prop I use is a 3x15.25x19R three blade SS.

I will see if I can find that photo where my cavitation plate was relation bottom of hull.

what is your leg gear ratio compared to his?