Help Me Understand How My Boat's Planing

[rdj735]

I'm making plans to get my 190tx/115 Opti running as good as possible in terms of motor height/prop selection. During my year of owning it, I've been learning how it runs and handles, and what I'd like to change. However, there's one thing I've noticed that seems odd, and I don't understand the cause of it. The boat planes out quickly , and is out of the water substantially at about 30-35mph. However, when I go faster, the boat seems to dig a bit deeper into the water, no matter how I trim it. I would think the opposite should happen - it should come up more. Motor is currently in lowest setting with a stainless Laser II prop. I planned on changing both motor height and prop, but would like to understand the physics of what's currently happening, first.

[TOXIC]

If your motor is set too low on the jackplate or mounting bolts if you don’t have a jackplate, as your boat gets on pad the bow lift will put your motor too deep in the water and you will lose speed no matter how you trim. Trim is fine tuning, motor mounting is major factor.  The proper prop will give your  motor the correct rpms at wot which will maximize your speed without bogging or over reving  your motor.  You have considerations that will affect your prop choice like a 4 blade will give better bite/holeshot/rough water handling but will cost you speed.  A 3 blade will give you better top end.  Prop pitch and size will depend on what your motor can turn to achieve your goals and top end rpms.  

[S Hovanec]

Could there be a problem with the trim pump not actually trimming the motor while under load??

[rdj735]

1 hour ago, S Hovanec said:

Could there be a problem with the trim pump not actually trimming the motor while under load??

I don't believe so - I can trim the motor up at WOT to the point where I'm cavitating. 

Putting jackplates aside, is there only a "window" of speed where your boat is up high out of the water? Or can you do it from "X"mph to WOT? Is it possible that my motor, in its current location, just lifts the boat well at 30-ish mph, but going faster lifts too much, and the bow falls? Would moving the motor up cause the boat to lift better at a higher speed (and possibly not as well at 30)?

[GaryH]

Sounds like the motor is set to low. Allows for a good hole shot bud your not getting the proper lift at higher speeds. 

[TOXIC]

Just to add, I’m not totally familiar with fine tuning a tin hull vs a glass hull.  I am assuming that the tracker is a pad hull.  

[gm4511]

If not engine height, it could be there's a hook in your hull at the transom or bad welds that's preventing more lift.  

 

Has it always done this or just recently developed?

[Way2slow]

gm4511 said the first thing I would check.  Put a four foot straight edge on both sides of pad.  Start at the bottom of the V  with a couple inches sticking out the back and move it out to see if there's a hook and how much if there is. (a hook is section of the hull that's above the straight edge.

 

Next I would see if I could get my hands on a different prop, preferable a stainless, to try.

 

You might also try lowering the motor one or two holes. If the motor is too high, it can't maintain the leverage needed to hold the bow up.  Dropping it down will help create more leverage.  My 20 Javelin would drop the bow at WOT if the prop wasn't at least 5" below the pad.   

 

Another option is to have a prop custom tuned for that boat with some extra stern lift added.    I have no idea who a good tuner is, Bob Lipton used to do mine but that was more than a few years ago.  Don't know if he is still around or not.  

[rdj735]

Thanks for the info so far, folks. My hull does not have a pad. My motor is currently in the lowest possible position, so there's nowhere to go but up. I'm also already running a stainless prop (3-blade LaserII 22p). I've never checked for a hook in the hull - will have to do that soon. The thing about it is that it seems to come up really well at 30-ish, where I can see the wake off the side basically right beside where I'm sitting. But, no matter how I trim it, when I go faster, I see that wake move forward.

 

There is a reputable shop an hour away that does nothing but props. My fear is that, when I go there to test them, I won't be able to tell if any problems I have are related to motor height or prop.

 

Many 190 owners just say "raise motor up to third hole, and put a cupped 4-blade on." I just like understanding the physics of that before I start randomly hoisting the motor and buying $500 props.

 

[Way2slow]

I just said pad in reference to the running surface.  Yes' yours is just a "V", that's why I said start at the bottom of the V and go out checking for a hook.  

Owners of your same model boat is the best source of info.  No two hulls are the same and no one prop works best on all boats.  

While I have a lot of experience with go fast fiberglass boats/hulls and getting them setup, I have absolute no experience with aluminum hulls, and I mean "0" experience.

The reason they say to use a cupped four blade is it provides more stern lift.  The same thing a tuner would do.  You will want want to see what four blade most seem to like.  Again, there are all kinds of four blade.  The standard, general purpose four blade works good on heavier boats, a high rake like about 15 degrees works good on boats that do have a riser pad, because they hold the bow up more.  I think the Laser is a high rake prop and may be wrong for your boat.  Like I said, high rake provides a lot of bow lift, which is good on riser hulls, but on your hull, while trying to provide all that bow lift, it could pushing the stern down.   Having a prop shop put more cup and stern lift in your prop would probably make it worse and over load it at WOT.  As you add cup, it's kinda like adding more pitch and will reduce top rpm.  A 22" pitch sounds like a sounds like a lot of prop for a boat that's only suppose to run in the upper 40's.  I never like to have a motor prop'd in a way that it won't turn very close to the motors max rated rpm.  I had rather have mine within 100 rpm of max.

 

Forgot to mention:  Moving the motor up and down changes the leverage point on the hull to get it in the sweet spot when the motor pushes the boat most efficiently.  That's also the purpose of adding a jack plate to help find that sweet spot of ideal setback and engine height.  A side affect of that is drag, the higher the motor the less drag created, the lower the motor, the more drag, which means more or less speed.  However, you don't want to get too high and let is start sucking air in the water inlet.  You need to monitor you water pressure and make sure it's not dropping below about 16psi in turns.  

 

[TOXIC]

I’m not sure all of the setup and tweak suggestions even apply when your boat does not have a pad hull.  Everything suggested has been tips to get on pad and run on pad.  You might make some changes to get more speed by raising and lowering your motor and prop selection but if your running surface is not a pad then your hull is not set up for speed.  

[Way2slow]

Actually, prop design can make a big difference. 

I would not think High rake props are a good choice for non riser hulls that can.t  lift more of the hull out of the water or even under powered riser hulls, so that as it gets faster it can take advantage of the rakes bow lift. 

Since the lions share of my experience is with OMC powered boats, I know more about OMC props than Mercury.  I've seen a number of Stratos 201's with 200's on them run faster with a four blade Shooter prop, which has very little rake, than the 3 blade Raker prop that's a high rake prop.  Simply because the boat didn't have the speed it needed with a 200 to take advantage of the lift the prop was trying to give, making it run deeper in the water.

A prime example, several years back a friend had a 1993, 201 with a 200 Johnson. With a three blade Raker, the most he could get with two people, gear and live well full was 57 mph. I put a Shooter prop on it, without changing anything else and it ran 60.3 mph.   

I then modified his motor.  After which with a three blade Raker it ran 78.7 mph, and then with a shooter prop on it only ran 72 mph.  The boat had enough speed to get the riser hull up fully on the pad and take advantage of the high rake prop.

And yes, I don't think he ever did get the grin off his face every time he put it in the water going from 57mph to 78mph.

 

[rdj735]

Hah, yeah, 21mph is huge! I'm expecting something more modest - maybe the 4-6 range ? My smartest move may be to just go to the motor height and prop that many other 190/115hp folks are running so I can be in the general vicinity, then go from there.

[Way2slow]

Going from 200hp to over 300hp, does add a little extra speed on a hull that can take advantage of it.

 

Since stainless props are not cheap, I would try to find someone that has one setup right and see if they will meet you at the lake, or let you borrow theirs before dumping another $500 -$600 in another prop.  I know of a couple dealers that will let you try before you buy as long as you don't do any damage to it.  Might check around in your are and see if you have one that will.

[Bassattackr]

On 3/27/2021 at 2:29 PM, rdj735 said:

I don't believe so - I can trim the motor up at WOT to the point where I'm cavitating. 

Putting jackplates aside, is there only a "window" of speed where your boat is up high out of the water? Or can you do it from "X"mph to WOT? Is it possible that my motor, in its current location, just lifts the boat well at 30-ish mph, but going faster lifts too much, and the bow falls? Would moving the motor up cause the boat to lift better at a higher speed (and possibly not as well at 30)?

 

1) No defined "window" of speed where you get bow lift.  That is a function of motor height, setback, boat load, etc..

2) No, if the bow were to "fall" you would get porposing, not a steady "plow" thru the water.

3) Moving the motor UP, DECREASES bow lift.    Moving the motor down increases bow lift.

 

Questions for you:

- Do you have a jackplate on the boat, or is the motor directly mounted to the transom?

- Given your 22P prop, what are your RPMs at WOT?

[J Francho]

Trackers aren't known for performance.  Turn the key, stab 'em and steer.  I wouldn't do anything to try and customize the setup, beyond maybe trying a prop that was +1, but it's doubtful you'd improve things.  These boats are setup to go as is from the factory.  

 

Your focus should be gear arrangement and weight distribution with a fully loaded boat.

[Way2slow]

As you trim up, you should see an increase in speed, and the wake should move toward the back of the boat as you trim.  Once you hit the spot where you don't see and increase in speed, and the wake is no longer moving back, you have reached the end of you effective trim.  Trimming beyond that is just going to hurt performance.   Especially if you start seeing and increase in rpm but no increase in speed, then you have trimmed to the point of cavitation.  

[E-rude dude]

Most guys are running the newer Spitfire x7 on that motor. Smaller diameter much stronger blades. Find a dealer that will let you try it out first since you can get 1/2 pitch sizes to really tune in the best overall performance. The 1/2 pitch sizes are professionally modified, so around $600. Best to know before you buy.

https://www.boatpropellerwarehouse.com/category/8128/spitfire-x7

 

 

BUT FIRST

Contact Tracker. Ask them what hole the factory mounted motors are being mounted on. Some dealers are clueless unfortunately. I’m guessing you need to go up at least on hole.

[rdj735]

On 4/5/2021 at 11:25 AM, Bassattackr said:

 

1) No defined "window" of speed where you get bow lift.  That is a function of motor height, setback, boat load, etc..

2) No, if the bow were to "fall" you would get porposing, not a steady "plow" thru the water.

3) Moving the motor UP, DECREASES bow lift.    Moving the motor down increases bow lift.

 

Questions for you:

- Do you have a jackplate on the boat, or is the motor directly mounted to the transom?

- Given your 22P prop, what are your RPMs at WOT?

I do not have a jackplate - it is mounted directly. Also, I'm below max RPM at around 5.2k/43 mph. Your thoughts seem to support the recommendations I've been reading on the internet (19-20p 4-blade, motor raised). I currently can't trim high enough to porpoise, with a 22p LaserII, motor in lowest position. Changing to a 4-blade cupped would increase lift (possibly causing porpoising), so raising the motor one or two holes to offset that may get it to where it is lifted its best at WOT, but motor high enough that it may not porpoise. I think this is getting to what I'm trying to understand. Thanks!

 

12 hours ago, E-rude dude said:

Most guys are running the newer Spitfire x7 on that motor... I’m guessing you need to go up at least on hole.

Yep, that's what I've been reading on the interwebs. Thanks for the info - just trying to understand the effects of the changes I'll probably be making.

[Bassattackr]

16 hours ago, rdj735 said:

I do not have a jackplate - it is mounted directly. Also, I'm below max RPM at around 5.2k/43 mph. Your thoughts seem to support the recommendations I've been reading on the internet (19-20p 4-blade, motor raised). I currently can't trim high enough to porpoise, with a 22p LaserII, motor in lowest position. Changing to a 4-blade cupped would increase lift (possibly causing porpoising), so raising the motor one or two holes to offset that may get it to where it is lifted its best at WOT, but motor high enough that it may not porpoise. I think this is getting to what I'm trying to understand. Thanks!

 

You are 100% correct.  A 4 blade will give you more lift, but I would still raise one slot on the motor mount.  One hole up likely won't be enough to offset the lift you "created" with the 4 blade but it will help get RPMs up higher to where the motor needs to run at WOT.  As a second point to this recommendation, comparable 4 blade props like to run 1/4"-1/2" higher than 3 blades anyway.

 

You could also use trim extender tabs to get more lift with your current setup.   I had these put on an older champion and it helped extend the useable range of the trim if your boat is still plowing at full trim.

 

Your comment of your boat pushing more water the faster you go seems odd, I'm not sure how to interpret that.    There should be a trim "sweet spot" where your boat runs the fastest with a given load.    An aluminum boat typically only porpoises if it is over trimmed.  Which leads me to believe you don't have enough trim or lift for your setup because you can't get there, even at full trim.

 

If it were me, I would try the trim tabs first (budget solution), swap the prop next and lastly move the motor up one notch if your RPMs with the new prop are still a touch low.

 

Hope that helps.

[Way2slow]

You can't arbitrarily say a four blade give more lift.  The rake is what gives the lift.

Yes, a high rake four blade with the same rake as a three blade high rake prop will usually give motor lift.

High rake props give bow lift.

Low rake props have no where near the bow lift of high rake props.

Low rake props work better on boats that can't take advantage of the lift high rake props give.  It's wasted energy running high rake props on them.

 

[WRB]

115 Optimax usually performs 5800 rpm’s with 20 pitch Laser 2, 3 SST prop. My guess is 22 pitch is too much. What rpm’s are you turning?

Tom

[rdj735]

On 4/10/2021 at 2:42 PM, WRB said:

115 Optimax usually performs 5800 rpm’s with 20 pitch Laser 2, 3 SST prop. My guess is 22 pitch is too much. What rpm’s are you turning?

Tom

Yeah, definitely overpropped - only turning about 5200rpm with motor in lowest position. As I'd mentioned, I had some advice on how to get it running optimally, but most people's recommendations are based on the newer 4-stroke Mercs, which have a recommended max RPM a few hundred higher than mine, so I'm a bit nervous about blindly making that prop purchase. In a recent turn of events, however, I was making a long run in rough water during a tourney last weekend, and a submerged log wedged between the prop and cavitation plate, breaking the flange, dinging the prop, and (at least somewhat) spinning the hub. Insurance so far has seemed willing to compensate for all damages, so I may have several opportunities for change coming up soon.

[WRB]

You Most prop shops can repair SST props. Ask if they loan props to test,  most good shops have loner test props.

Tom

[Bassattackr]

On 4/15/2021 at 9:25 PM, rdj735 said:

Yeah, definitely overpropped - only turning about 5200rpm with motor in lowest position. 

 

Bingo, you're lugging the motor with your current setup.  Check on the motor mount what your max RPMs are for that motor (5600?).   All else equal, one pitch down equals a gain of 200 RPM at WOT.   You want to me close or at your max in winter (cold air, cold water).   

 

See if you can test a 20p and 21p and go from there.  Your boat will come alive, I wouldn't change anything else.   (Ignore my previous posts, I had assumed you had the right prop before..)

 

Good luck!

 

On 4/9/2021 at 9:16 AM, Way2slow said:

You can't arbitrarily say a four blade give more lift.  The rake is what gives the lift.

Yes, a high rake four blade with the same rake as a three blade high rake prop will usually give motor lift.

High rake props give bow lift.

Low rake props have no where near the bow lift of high rake props.

Low rake props work better on boats that can't take advantage of the lift high rake props give.  It's wasted energy running high rake props on them.

 

 

Fair enough.  I should have specified - four blades typically carry loads better resulting in better bow lift.