Motor height - Merc 150 seapro

[Macdeep]

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?

Ya, it is trimmed all the way under when running without the foil because otherwise I get porpoising if I release the trim angle to get more speed etc. If I release the trim angle on the outboard, I have to use the trim tabs to fight the porpoising which adds drag and is counter productive...

 

[Macdeep]

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?

Yes, the model and specs of the prop are already posted above. Not interested in a SS prop. too $$. But would consider a 4 blade aluminum.

 

[Macdeep]

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.

Ya, I just have the one prop, but am in the market for a 4 blade ~14x19 or ~14x17. Already contacted NI props in Campbell, just waiting to see what they think for propping. But if there's a used one kicking about on the North half of VI, I'm back and forth between McNeill and Comox, Parksville and Qualicum regularly enough to make something work.

 

[SpringVelocity]

Ya, it is trimmed all the way under when running without the foil because otherwise I get porpoising if I release the trim angle to get more speed etc. If I release the trim angle on the outboard, I have to use the trim tabs to fight the porpoising which adds drag and is counter productive...

That isn't normal. Have you moved some of your weight forward. I am tending to think that extra 100 lbs is screwing you a bit.

On mine I moved my hali anchor...dr balls in the cuddy center in that cubby hole.

Also moved my batteries in back closer in towards centerline.

 

[SpringVelocity]

what is your leg gear ratio compared to his?

Mine 2.50:1

Seapro 1.92:1

 

[Pineapple Express]

Mine 2.50:1

Seapro 1.92:1

Nope. @Macdeep has posted a pic of his motor and the lower unit ratio is 2.08:1

 

[SpringVelocity]

I just grabbed if off website. Sorry didn't see that.

 

[Pineapple Express]

Ya, it is trimmed all the way under when running without the foil because otherwise I get porpoising if I release the trim angle to get more speed etc. If I release the trim angle on the outboard, I have to use the trim tabs to fight the porpoising which adds drag and is counter productive...

That is not normal. I think your mounting height may be close once you can trim the motor in a neutral position.

You've gotta address the weight issue. Shift weight forward. Look at lighter batteries. You can also experiment with ballast just to test how the boat responds to different centre of gravity.

Regarding the prop you're giving up a lot of performance by sticking with an aluminum prop. Mercury does make an aluminum 4-blade prop but the diameter is only 14" so you're giving up a lot of blade area with it being such a small diameter which defeats the purpose of going to a 4-blade prop.

 

[Max123]

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.

@chille51 - you are minimum 1 - 2. Don't bother to try new props until you get the mounting height right because that will change your prop pitch again. When you are mounted too low, you are dragging the lower unit through the water. Once the drag is eliminated, you can typically gain 1-2" of pitch.

Its an easy change if you have access to the mounting bolts. When you have the boat on the trailer, lower the unit all the way down and shim blocks of lumber underneath till the skeg is supported. Then go to the front of the trailer and raise the jack so the hitch rises, and the back drops a bit. Once the skeg is fully in contact with the block, go back and look at the mounting bolts. You should have 4 bolts, and the upper mounts should be individually drilled holes, and the lower holes should be a slot (or the other way around). Take out the bolts two bolts in the holes, then loosen the two in slots - have a buddy hold the engine steady. Then go to the jack and crank it up - this will raise drop the stern of the boat so you can get in line with the upper mounting bolts. reinstall the top two bolts at desired height, tighten bottom two bolts. Done

 

[Macdeep]

That is not normal. I think your mounting height may be close once you can trim the motor in a neutral position.

You've gotta address the weight issue. Shift weight forward. Look at lighter batteries. You can also experiment with ballast just to test how the boat responds to different centre of gravity.

Regarding the prop you're giving up a lot of performance by sticking with an aluminum prop. Mercury does make an aluminum 4-blade prop but the diameter is only 14" so you're giving up a lot of blade area with it being such a small diameter which defeats the purpose of going to a 4-blade prop.

View attachment 125602

Roger - sounds like I should try to re-balance the weight distribution before moving the motor up any further or getting into a new prop. Though I do need a second prop any way. Was hoping to get a 4 blade to run as my main and keep this 3 blade as my spare.

Will get all my jigs and Hali lead in the cuddy as well as my spare cannon balls.

My concern is that any re-balancing now will be a net zero once I put the downriggers on, unless I add another 100 or so pounds in addition to rebalancing. Moving the batteries doesn't seem like a feasible idea - there's no where for them to go unless I do some re-modeling and substantial plywood and glass work, as well as rewiring which will be a costly project.

The quickest way is for me to make a substantial rebalance is to ditch my 9.9 kicker, but then I'd have to get down to a 17 pitch prop to be able to troll. With the 19p, idle is already pushing me at 2.5 knots. And to troll effectively, I'd probably want the fancy digital mercury smart craft controls which is a couple G$s installed... so ya, stuck between options that might not work and ones that definitely cost more than I'm prepared to spend.

I guess this is where I'm at before I shell out another grand lol

Step 1: move the transducer, keep the foil off for now.
Step 2: rebalance the weight as best I can, and re-test with down riggers etc so I'm at my final fishing weight and distribution.
Step 3: get the second prop that I'm going to get any way, but get one that offers good stern lift - ie. 4 blade in a decent diameter to max lift.

Then if none of that makes enough improvement

Step 4: move the motor up one last notch...

Has anyone seen ideas about putting a flexible rubber or plastic splash guard off the back? Would a 4-6" splash guard help? Or is that just a silly idea?

 

[Max123]

@Macdeep - Fix the transducer since this is obviously throwing up a ton of spray. I generally agree that you are likely stern heavy, but why not start with raising the motor one more notch?

Here's what I see: In both photos of the anti-cav plate, you are still low. The entire plate should be skimming the surface - I can just see a little bit of it in one of the photos. Unless you are blowing out/venting the prop, motor is too low. Raise it one more, and see where you are at - you are close, but not quite there.

Once the motor is up, it will help the porpoising, but to really address you may need a stern lift prop (typically a 4-blade, but not always). The foils may also help lift the stern, but only if the foils are skimming the surface. If they are buried, it just makes the handling go completely wonky.

Your description of having to run with the motor fully trimmed down to avoid porpoising was exactly what I was dealing with on my etec. I had to raise it 2 holes and switch to a 4 blade. Its a learning experience for sure.

 

[Aquaholic]

@Macdeep - Fix the transducer since this is obviously throwing up a ton of spray. I generally agree that you are likely stern heavy, but why not start with raising the motor one more notch?

Here's what I see: In both photos of the anti-cav plate, you are still low. The entire plate should be skimming the surface - I can just see a little bit of it in one of the photos. Unless you are blowing out/venting the prop, motor is too low. Raise it one more, and see where you are at - you are close, but not quite there.

Once the motor is up, it will help the porpoising, but to really address you may need a stern lift prop (typically a 4-blade, but not always). The foils may also help lift the stern, but only if the foils are skimming the surface. If they are buried, it just makes the handling go completely wonky.

great points. These newer propellors do not have to be buried in the water for fear of ventilating in turns, they can run quite high relative to the water surface.

 

[Max123]

Changing props would be my last move. There is no substitute/fix for a badly mounted engine - that is step 1. Once the engine is mounted correctly, step 2 is decide on foils/no foils. Foils will give you a bit of stern lift. Step 3 is playing with weight, but realistically you don't have too much flexibility on this, and this is just to optimize. Step 4 - is fine tune the prop selection. Mainly you are just looking to get the pitch right so you don't lug the engine (do you get max rated rpms at full throttle with the boat loaded up the way you want it). You can select different prop types for slightly better grip or stern lift/bow lift - but at $1000/pop its an expensive learning curve. I wouldn't ditch a prop unless you are lugging the motor.

Most people seem to jump to step 4, which is a total waste if your problem is elsewhere. On my old Lifetimer the factory mounted Suzuki was mounted 2 holes too low. Both Lifetimer and the Suzuki mechanic suggested a foil, which did absolutely nothing and made the handling/speed worse. It literally felt like I was dragging something behind the boat. I raised the motor one hole at a time until I started to vent the prop, then dropped it back down. Once the engine was mounted correctly I was able to go up 2" in pitch and go way faster.

Same thing happened when I upgraded to my current boat. I raised that one 2 holes as well and now runs way better. Don't trust your mechanic on this - most are experts at fixing broken engines - not commissioning boats.

 

[chille51]

I only posted my situation to confirm what others are telling @Macdeep and give him a comparison/moral support, haha. I am well aware my motor is running low and needs to come up. It is being done next week, while I have the boat in for annual service. Unfortunately, I only have 1 more hole to go before I max out. Hopefully it is enough. Also aware of the trailer tongue lift trick @Max123 noted. I may have gone that route if I wasn't taking it in for other service too - but good info for those that may just need to play with mounting height.

Regarding the question for OP about raising it one hole or two now, I offer an alternative perspective: If you think you might need to go 2 holes, you can go all the way now. If it works, then you're done. If it is too much, you can come back down 1 hole. Someone told me that a year ago, but I thought I was playing it safe and only went up 1 hole. Now I'm going back to go up another hole. If I had just gone 2 to start with it would have been one less motor move.

 

[salmonkiller01]

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?

Did not realize you are already above the bottom of your boat already. Something ain’t right. Don’t go higher.

Are you noticing more bow rise when at cruising speed?

 

[BC Coast Pilot]

Yes, the model and specs of the prop are already posted above. Not interested in a SS prop. too $$. But would consider a 4 blade aluminum.

At this point I would give you a stainless REV4 just to prove the night and day difference between Aluminum and stainless. but I've suffered enough reading. You're reluctance to explore this is gonna cost ya in the long run, its like wheels on a car except more important Compare this to when you actually need quality ball joints but do tires. I spent 2k on Stainless props when I got my boat and they are paid for in spades. Zero Regrets. Prop is the most important piece on the boat. "Not interested in SS Too $$$" Now this all makes sense.... Thats all i can say.

 

[mikep]

I have a 15P mercury enertia prop that you can try if you want. If you are running a 19P aluminum right now it may be a little under pitched for the boat but is worth a shot. On my 18 outrage whaler I am running a 17P enertia on a 150 mercury. Works great. Stainless is worth it and you can usually get them 2nd hand for half of new or better.

 

[InterMechanico]

I have a 15P mercury enertia prop that you can try if you want. If you are running a 19P aluminum right now it may be a little under pitched for the boat but is worth a shot. On my 18 outrage whaler I am running a 17P enertia on a 150 mercury. Works great. Stainless is worth it and you can usually get them 2nd hand for half of new or better.

I have the same two props for my 18.5’ SS and they are super fantastic. I was super skeptical but I’d never go back to a turning point stainless or an aluminum prop