How much of a pitch change do I need?

[Scott Danforth]

I use a photo tach on the flywheel to verify the dash tach. I verify at a few different RPM's in a barrel on outboards. I use the same photo tach on the damper to verify tachs in I/O's

 

[Sea Rider]

Definitely, thanks. We're currently working with Yam and Tohatsu motors. Know both animals very well and the transom height they love to work at. Like doing transom and prop maximizations with both motor brands at my boating Club to get the max out of any combo. Later will post some pic suggestions that will be helpful to try to follow.

Will need to check if current tach is doing it's homework right, would preffer to install a induction tach, will know elapsed working run hours, rpm at different throttle settings, maintenance services, etc.

Happy Boating

 

[Sea Rider]

Ir order to know if the motor woks at the sweet transom height will need to determine that by a visual inspection :

Parameters:

-Must test combo on flat calm, no wind water condition.
-Motor must be trimmed to neutral position beforehand.
-Deck load must be evenly distributed.
-Go for a wot run.
-Have a lighter boater to "visually" check pulling head to side of motor to check at which lower leg height is water flow passing by ? This is of extreme importance for the equation.
-If passing over the yellow line will have back water splashes, will need to raise motor 1-2 holes ? till that condition is completely canceled.
-Ideal motor installations for Yamies is when flow skims right under the yellow line, that's right under the upper splash plate as shown in modified picture.



Check what's happening at back transom and report your findings, to know what adjustment needs to be done to the motor, if all is good that combo only needs a spot-on prop maximization to a lower prop pitch and voila.

Happy Boating

 

[Faztbullet]

Tis a tad low ..raise one hole and loose the whale tail ...too much drag.

 

[Faztbullet]

That not right right Sea Rider. This is from a 2016 Yamaha manual so its not Jurassic.....

 

[WesNewell]

It appears to me it's at least 2" low. Assuming the holes are each the standard .75" apart, I'd start by raising it 2 holes. And loose the whale tail for sure. Once at the proper height, you won't need it. Just throw it in the trash. That's all they are good for.

 

[Sea Rider]

Hey folks, a dry installation is one scenario which says nothing, when the hull rides over water it's a different scenario. For what I see you guys don't care at all at which lower leg height will water flow pass at plane/speed mostly because no one looks what's happening at back transom while combo runs full hammer down.

You have to dial a top lower leg height in order for the prop to work at its max trust in all water conditions, that's from flat to choppy ones... Why don't we all relax and let the OP test what's pic suggested, report his findings and go from there if that's OK with the OP and you guys...

Forgot to mention that if the doel fin does not ride parallel to water level once combo is on plane with deck weight well distributed will achieve a free extra water drag in the fin which will slow combo down. Doesl fins are huge garbage collectors, only good for swimmers to step out of the water from transom side...

Happy Boating

 

[Elkins45]

It appears to me it's at least 2" low. Assuming the holes are each the standard .75" apart, I'd start by raising it 2 holes. And loose the whale tail for sure. Once at the proper height, you won't need it. Just throw it in the trash. That's all they are good for.

I've used it with and without the whale tail and it does seem to make a difference in terms of the trim position at plane. With the tail attached I can get a little higher out of the water. But that might be because the mounting height is wrong.

 

[WesNewell]

Most of the whale tails I've seen installed were to counteract porpoising, and they would do that. But in reality the porpoising was caused because the engine was mounted too low in the first place causing the bow to rise when the engine was trimmed up to off set the low mounting. Then when the trim was raised the trust angle was pointed downward causing the bow to rise. Once the bow is raised, and engine trust iss more parallel to the waterline, the bow drops and the porpoising cycle begins. With a properly mounted engine you don't have that action and trimming should be minimal. I went through all this when setting up my new boat after the boat manufacturer had mounted the engine too low. My brother bought a 2019 crestliner with a 60hp 4s just like mine and couldn't keep up with me even though he boat weighed only 670# compared to mine at 995#. He had water coming into the boat right in front of the engine because the engine was mounted too low from the dealer. After he raised it, that was eliminated and he gained a lot of speed and got a smoother ride. All of the new aluminum model boats with 20" transoms I've seen have the engine mounted too low from the factory as of last year. I never paid much attention to this until I bought my last boat in 2017 and let the dealer talk me into not getting a bigger engine. And I've owned bass boats since the 1960's. So long ago I don't even remember the name of my first one. It was a 16' glass trihull with a 70hp rude.

 

[Sea Rider]

Is porpoising the continued up-down movement the hull experiences when al plane ? If, so you need to shift more weight towards bow along an excellent transom/motor height match.

Happy Boating

 

[Sea Rider]

That not right right Sea Rider. This is from a 2016 Yamaha manual so its not Jurassic.....

My friend, doesn't matter if being a Jurassic or newer model motors, all Owner's Manual states the same BS and I have read them all. You usually sit a motor on transom to be flushed with it, from there need to go for a wot run in order to check whatever you want to achieve or better regarding water performance. Will know if in need to raise or lower the motor if being a bolt on motor, raising or chopping down the transom if it were a clamp motor model. To each his own boating prefference...

Happy Boating

 

[WesNewell]

Is porpoising the continued up-down movement the hull experiences when al plane ? If, so you need to shift more weight towards bow along an excellent transom/motor height match.

bow/stern weight can't be changed on most boats. At least not enough to matter when there's only one or 2 people and designated places for everything by design. Get the engine mounted right and it won't be problem. This guys engine is just mounted too low. It's that simple.

 

[Faztbullet]

all Owner's Manual states the same BS and I have read them all.​

Maybe you need to go to work for a engine manufacturer as you seem to know more than the engineers that design and test these....Owner manuals,service manuals,Google and YouTube must be all wrong. WOW !! Guess I set all my satisfied customers and my play boats up wrong all these years....

 

[Sea Rider]

Hey Fuz, why don't we end this useless stupid discussion between parts, as said before you can go per your expert parameters, I'll go with mine, as both parameters works spot on for both of us let's live in peace and harmony in the forums...

Let the OP test the Yam given lower leg paremeters and repor his findings...

Happy Boating

 

[flyingscott]

Check.your tach. I ran a similar setup with the same motor. Your speed sounds about right as does the prop pitch.

 

[Faztbullet]

Remove the whale tail, raise 1 hole and check RPM at WOT and trimmed out. Looking over stern you should see something like this, if not its to deep.

 

[Elkins45]

I figure if I’m going to go to the trouble to raise it then I might as well come up two holes. I ordered an induction tachometer that will be here tomorrow so I will be able to get an accurate rev number, but my feeling is that my tach is accurate. I know what 5000 rpm sounds like and this isn’t it.

 

[Sea Rider]

Before taking the trouble of raising the motor, visually check as posted pic, at which lower leg height is water flow passing by at speed. Combo must be riding on plane at full wot rpm with trim set to neutral and deck load well distributed. Preferably test on flat calm water cond as early in the morning. Report your findigs...

Happy Boating

 

[Elkins45]

I figured discretion is the better part of valor so I only raised it one hole. It will be a couple of weeks before it's on the water again so I will report back then.

 

[Elkins45]

I spent the week on the water after raising my engine one hole. I did gain a couple hundred RPM and 1.5 mph but at the expense of blowing out while cornering. When I trim the motor down enough to prevent blowouts I’m back to exactly the same RPM and actually lower speed because the boat has to be trimmed so more of the pad is in the water. It appears the issue wasn’t motor height after all and I really do need a different prop.

I’m going to lower it back to where it was.