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GEB

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Posts: 2,054
Reply with quote  #16 
Hi,
FYI. More re importance of correct engine mounting height that I found buried in the old posts

Quote
The reason that getting the mounting height right, (ie the Anti Ventilation plate just above the water’s surface when on the plane and correctly trimmed out), is so important is that when the A/V plate is under water it is trying to lift hundreds of kilograms of boat which creates a lot of drag thereby robbing the engine of a lot of horsepower.
You want the boat to carry the motor, not the other way around.

Cheers
GEB
Note, the Anti Ventilation (A/V) plate is commonly incorrectly referred to as the CAV plate.






Source
http://www.etecownersgroup.com/post/show_single_post?pid=37330295&postcount=34&forum=136485

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Stacer 389 Territory Striker
Model No.E25DTSLAFC
Serial No. 5503333
Mid North Coast
New South Wales
Australia 
The learner will not shear the rams.

rickmcd53

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Reply with quote  #17 
Gavin, thanks for all the work as our resident "reference librarian".
GEB

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Posts: 2,054
Reply with quote  #18 
Hi Rick,
Thanks. I’ve been out of action for a while but now back again. Actually in this instance I was trying to understand for myself just why an engine mounted too low would create some much drag. After all the LU / gearcase is fairly streamlined which IMO wouldn’t create much drag but when I found that old post and read about the effect of the A/V when it’s buried under water the “light bulb” finally came on.
The OP’s (ghind) comment “A cav plate that is trying to lift hundreds of kilograms of boat will do worse. You want the boat to carry the motor, not the other way around.”
Says it all in a nutshell. and Amazing what I find buried in the old posts
Cheers
Gavin

__________________
Stacer 389 Territory Striker
Model No.E25DTSLAFC
Serial No. 5503333
Mid North Coast
New South Wales
Australia 
The learner will not shear the rams.

rnovak

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Posts: 12
Reply with quote  #19 
Thank You for the Info. Great Forum.
PhilH12

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Reply with quote  #20 
YES, the very BEST ETEC forum!  [smile]

Except that I interpret the AV plate much differently when it's buried.  Trimming out the motor points the AV plate downward.  If it's underwater, it's trying to drag the stern down lower, and at the very least it's more like a bucket on a rope over the stern.  Rather than trying to lift anything, it's more like your hand out the car window - turn it more "flat" against the wind and see if your arm doesn't bend a bit.  [wink]  If the AV plate were trying to "Lift" anything, you'd have to be Trimmed In - not Out.

EDIT:  Also, to me, Anti Ventilation suggests that the "plate" is really there to direct the prop and hull spray back down to the prop itself.  Keep the prop in as much water as possible - not to provide either Lift or Drag.  Easier to cut through "air" or "spray" than "solid water", though dragging even some bottom growth has caused a few questions about mph and rpm's on here.

Sorry, Gavin.  Just my view from Under the Shade Tree.  [biggrin]

Phil

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Always check the Easy Stuff First!
20' Weeres fishing pontoon
90 HP E-Tec E90DPLSUM  05184332
Lake Tawakoni, TX - Catfish Capital of Texas
GEB

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Posts: 2,054
Reply with quote  #21 
Hi Phil,
Nothing to be sorry about. I actually agree with you because IMO we’re both saying the same thing but looking at it from a different point of view. You’re looking at the “stern dragged down” while I’m looking at the “bow pushed up”.
When the stern is being dragged down then the bow is being forced / lifted up. Whichever way you look at it it’s all robbing horsepower. As you say “like dragging a bucket on a rope”.
I know that even with my engine height / propping correct, when I’ve forgotten to trim in / down, if I try to plane off like that, with the motor trimmed up /out, the drag from the A/V will bury the stern, digging a deeper and deeper hole in the water to the point where, if I didn’t back off the throttle, I’d have water coming in over the Transom while at the same time the bow is pointing at the sky. Unlike the “boat wheel standing “example below I don’t have enough HP to dig myself out of the hole and up onto plane.
While this video below is about Nauticus Smart Tabs,
about 35 seconds into the video there’s a good explanation of how the “Axis Point” of a boat moves and which ties in with what you’re saying, “ stern dragged /pushed down” and what I’m saying about “bow lifted pushed up”.

Also (just for laughs) another extreme example, boat wheel standing, of just how much force the A/V plate can exert on a boat. Note that the motors are trimmed up / out before he advances the throttle and how that forces the stern down / bow up.

Your understanding of what an Anti Ventilation Plate does is correct.
Quote.
Most outboard and stern-drive engines have anti-ventilation plates made onto the lower unit housing directly above the propeller. Many people mistakenly call them cavitation plates or possibly anti-cavitation plates, but that is incorrect.

The anti-ventilation plate does not stop or help prevent cavitation. Its sole purpose is to prevent surface air from being sucked into the negative pressure side of the propeller blades.

End Quote

The Quote above is an extract from this article https://www.louisianasportsman.com/fishing/is-it-cavitation-or-ventilation/

Cheers
Gavin

__________________
Stacer 389 Territory Striker
Model No.E25DTSLAFC
Serial No. 5503333
Mid North Coast
New South Wales
Australia 
The learner will not shear the rams.

rnovak

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Posts: 12
Reply with quote  #22 
Ran the Mako to check WOT rpm's. I was close. It ran 4200 rpm and 32 mph.
When I bought the bought it was set up by the guy I bought it from's dealer when the 2012 Etec was installed on the 1992 hull. I assumed all this time it was done correctly.
Prop is Apollo x115. 993145-131/8x19.
Any suggestions?
PhilH12

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Posts: 2,936
Reply with quote  #23 
Height first - AV plate above solid water when on plane and trimmed?  Fix that first, if needed.  You may even gain several 100 rpm's just doing that if you're way low now.

Then the guys will chime in on some of the best props for your application.  No sense buying a prop to overcome motor height though.  You'll still be leaving performance and economy "at the dock".

EDIT: Also getting your exhaust valve to open at "correct" WOT rpm's will help a lot, too.

Phil

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Always check the Easy Stuff First!
20' Weeres fishing pontoon
90 HP E-Tec E90DPLSUM  05184332
Lake Tawakoni, TX - Catfish Capital of Texas
Tee2Sea

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Posts: 51
Reply with quote  #24 
Quote:
Originally Posted by rnovak
Ran the Mako to check WOT rpm's. I was close. It ran 4200 rpm and 32 mph.
When I bought the bought it was set up by the guy I bought it from's dealer when the 2012 Etec was installed on the 1992 hull. I assumed all this time it was done correctly.
Prop is Apollo x115. 993145-131/8x19.
Any suggestions?


I run a Hydra Sports 18'CC with a 115HO and use a Turning Point Stainless Steel 4 blade Hustler, 13.25 x 17  wot is 5700+ with speed around 35 mph.  I have the S2 gear case so  the ratio is 2.36:1.  My guess is you have a 2.00:1.

You should start with a 15" pitch, boat should jump on plane, and with more rpm's achieve the same or better speed, with less effort.  You will also notice the exhaust valve change,  will feel like a turbocharger.  While trying to be BRP loyal, very happy with the Turning Point.  Started with the aluminum 13.25 x 17 and the TP had better bite than the BRP, same specs.  The 4 blade SS gave me better mid range speed.  TP also has a pitch exchange program.  You can swap out for $35.  The BRP 4 blade rogue gave me the best speed and rpm, but not much change in cruise, and was 2x $$.   (and I did buy the TP from a local dealer, and did not internet shop$$).

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Tom W
115 HO  mfg 2018
A115SHLAFL    05530167
2003 Hydra Sports 180CC  TP13.25 17 Mach4
rnovak

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Reply with quote  #25 
Great info. Thanks Tom. Will check out the TP.
rnovak

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Reply with quote  #26 
Looking for more help. Previously explained how my 2012 115hp ETEC mounted on a 1992 Mako 181S Flats boat was only getting 4200 rpm wot. It appears that it is my exhaust valve not opening. Mobile mechanic determined it is locked up and probably has been for years.
Servo motor still working, software shows it opening and closing but the shaft will not turn. Tried heating it up, lubing it up but no luck. I am aware of the problems others have had with this motor and the exhaust valve and the after warranty fix with grease nipple but that only helps if it is freed up.
Questions:
1.Has anyone had success with ETEC sending parts n/c for an out of warranty motor ?
2. Any magic way to free up the shaft ?
3. Can the shaft be accessed from the lower unit and cut out? If so, any down side to this ?
I understand it is an expensive fix.
Any suggestions would be greatly appreciated.
Rnovak
Huey

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Reply with quote  #27 
1. Yes but you will get no luck dealing with a mobile guy, you would need to take to a certified tech. your chances will be better if you are the original owner, have good service history and the engine has been propped right so that you see around 5800RPM at WOT. 
2. Patience and heat.
3. No but you would be able to access it from the top with the powerhead removed. Preyy easy job and then you would also be able to soak it more to free up.
rnovak

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Posts: 12
Reply with quote  #28 
Thanks for your response. My mechanic is very qualified and also owns and loves Etec's.
To be clear, is it not possible to drop the lower unit and cut out the shaft from below ?
I am the second owner and do not have confidence in any of the Etec Dealers in my area.
I am going to call Evinrude regardless and see where I stand.
Thanks.
Russ
Huey

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Reply with quote  #29 
Anything is possible if one has the will power but it would be practically impossible and why I said no. From the top would be possible.
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