Motor Mounting Height

[fishnowworknever]

How high (or low) do you have your motor mounted?  I'm trying to dial mine in as I believe mine is way too low.

 

I know it can be a huge difference between a flat bottom and V, I'm working with a V and am experiencing a lot of excess spray off to the left and right when on plane.  I need to trim up to the max trim angle to get rid of that spray but at that point I'm rooster tailing as well.  As it sits now I'm about 1.5" above the keel since I have just raised it up the last hole on the motor.  At this height I haven't been able to test it yet, but hope to in the next day or two.

Edited May 5, 2016 by fishnowworknever

[delcecchi]

My question would be how a guy can tell if the motor is at the right height. 

[fishingstar]

most motors cavitation plate should sit 1 to 2 inches below the transom.

My son's 8 hp yamaha is set at 1" my boat 75 hp is closer to 2".

[fishnowworknever]

I've been told to have the cavitation plate visible when on plane at cruising speed (not WOT), if it's too low where you can't see it it needs to get moved up.  The pic below is at a good starting point, from there it could move up or down all depending on where the cavitation plate is when under way.

 

fishingstar, I think that was the way dealers used to and still do mount the motors.  People have reported an increase in RPM and top end speed from moving their motors up.

Found a couple pics of some good examples

 

This is the correct height:

 

Edited May 6, 2016 by fishnowworknever

[delcecchi]

It is an anti-ventilation plate, not cavitation.  It is there  to keep the prop from sucking air.  So, is it a trial and error thing to tell when the motor is the right height?  Sort of painful for those of us without jackplates. 

[fishnowworknever]

Del you're right...Yep I mis-spoke there.  Anti ventilation plate.

Trial and error yes, it sure is a PITA because you're supposed to raise your motor until you get a blow out then go back down one hole.  BUT it could really gain you some extra performance in speed and gas.  Everything I've been reading has said that raising your motor 1 hole = approx between 100 - 300 RPM

[fishnowworknever]

The other issue is you need someone else to be driving the boat while you hang over the back to check out the anti ventilation plate.

 

 

(I almost typed anti-cavitation plate again)

[RebelSS]

2 minutes ago, fishnowworknever said:

The other issue is you need someone else to be driving the boat while you hang over the back to check out the anti ventilation plate.

 

 

(I almost typed anti-cavitation plate again)

Without falling in.    Lifejackets on!

[delcecchi]

A guy would think the boat or motor companies would make some recommendations...

[h8go4s]

10 hours ago, delcecchi said:

A guy would think the boat or motor companies would make some recommendations...

Yamaha, for one, does. Although I've often wondered what exactly "mounting hole position #2" means.

http://yamahaoutboards.com/sites/default/files/bulletins/bulletin_4stroke_midthrustjetport_al_alm_classic165tiller_f50tlr_2011-05-26_alm.pdf

[fishingstar]

when I bought my sons Yamaha the mounting height was in the  owners  manual.

when we first got it I put it even with keel and it was spraying water out both sides out the motor.

We found a manual on line, set the height 1" below the keel and the spraying went away.

Keep in mind  that this is a 12 ft boat with a 8hp motor. 

[delcecchi]

I'm guessing however that Suzuki won't have how to mount a 2011 motor on a 1998 lund.   Although I am sure Lund still sells that hull as something.

[fishnowworknever]

On 5/7/2016 at 7:28 AM, fishingstar said:

when I bought my sons Yamaha the mounting height was in the  owners  manual.

when we first got it I put it even with keel and it was spraying water out both sides out the motor.

We found a manual on line, set the height 1" below the keel and the spraying went away.

Keep in mind  that this is a 12 ft boat with a 8hp motor. 

That's interesting because I was experiencing the same thing with the spray off both sides of the motor.  Just goes to show you each motor/hull act differently than the next.

I raised my motor up to the highest position it would go, originally it was in the #2 hole (Yamaha) and previously I raised it to the 3rd hole.   I picked up 200 RPM and 2MPH on the top end, with an aluminum prop.

I'm now at 5600 RPM which is over the MAX RPM of 5500.  Looking to get a stainless prop and hopefully improve a bit more.  The spray is also gone when on plane and trimmed correctly.  That alone was worth the trouble.

Edited May 9, 2016 by fishnowworknever

[BoxMN]

FWIW, it is a combination of hull type, motor hp, prop type, prop size, prop pitch and weight of hull, load weight and position, what type of handling you want, all along with motor height

Can make it as easy or complicated as you want. We tested a bunch or props, at different heights, with different weights in the boats, to get what we wanted. We used a floor jack and elbow grease on our 50, 60, and 90, but had our dealer do our 150 (need a eye ring to screw into top). 

 

I would not worry about 100 rpm over, as now the water and air is cold and about the best conditions, it will slow down as heat hits, dropping you to right range. Also as you add weight... Going to a SS prop is going to change things huge for you, though. What motor and boat hull? If you are in the 150 hp range, on a 17-18' walleye styled boat, hard to beat a 19" Tempest Plus  

Others I have no idea, other than Tempests (3 big but tapered blades) are awesome for handling and speed and holeshot combo. Hi-5 (five blade) best handling hands down, but slow and no reverse power. Trophies (4 blade high rake) decent for heavy bass boats, Laser (3 thin blade) good for light fast hulls but suck for walleye style boats. All I know are merc props, and I have not tried the Vengeance but heard good stuff about them. Have a 4 blade Spitfire on pontoon and it has some serious power teamed with a Bigfoot.

I have found that dealer typically mount motors one hole to deep. I even raised my pontoon motor from the dealers location. Eake out all the performance that you can, even on a toon, I say!!! haha! Good luck!