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Author Topic:   How high is too high.
Airborne posted 06-10-2002 10:17 PM ET (US)   Profile for Airborne   Send Email to Airborne  
I have a 22 outrage sea drive with armstrong bracket and 250 Ram Ficht. I rose the motor one hole (she really goes now!!). I would like to raize it one more time to see what happens. How high is too high and how can one tell? Is there a water pressure and/or ventilation. What do I look for first?
I am keeping an eye on the RPMs.
kingfish posted 06-11-2002 08:18 AM ET (US)     Profile for kingfish  Send Email to kingfish     

My understanding (and the belief under which I am operating with my 22')is that if you are getting traction and holding traction, you are getting the cooling you need, so watch the tach.

Some of the real pros here on the site have this down more accurately than I do I'm sure, but in general I understand you should be able to set your cavitation plate 1" to 1 1/2" up from the keel if your motor is on the transom, and another 1" up for every 10" your motor is set back from the transom.


Bigshot posted 06-11-2002 10:58 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
1" for every 6" you go back, so most brackets can run 5-6" above the bottom. You will know when it is too high. It will drive like a slipping clutch when you come out of the hole. Will also sound like your exhaust is out of the water......because it is.
bsmotril posted 06-12-2002 03:45 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
A water pressure gauge is the only way to tell for sure on inland waters. They are standard on the shallow water boats running hydraulic jack plates around the TX coast. You'll see a drop in pressure before you start getting prop ventilation as you start raising the motor up. But if you run offshore in any type of seas over 2', then I would expect you'll see ventilation during turns out there before the water pressure drops off. Try some full lock to lock S turns in chop at cruise speed to see if you get prop ventilation. If not, you're likely OK.
lhg posted 06-12-2002 07:50 PM ET (US)     Profile for lhg    
You have to do two things to make sure you're not mounting your engine too high, or raising it too high with an adjustable bracket.

First, look at the distance the top of your water intakes are below the anti-cavitation plate. That is the absolute max height you can raise an engine without sucking air and burning the top pistons from inadequate water supply. Then, you have to look down at the anti-cavitation plate while underway at speed and properly trimmed. Be sure that the water flow is such that your intakes are not above water.

Generally, according to Mercury prop performance literature, a standard "elephant ear" aluminum or SS prop should not be run more than 1/2" high, which means for this discussion, the smooth flow of water coming off the boat bottom should be no more 1/2" BELOW the anti-cavitation plate. If your boat will do 45 and over, you can use more height, up to about 1 1/2" max (2 bolt holes on a standard transom), and for this you need a performance line SS prop for proper holding. This height is good for boats up to about 60 mph. For high performance boats like the go-fasts and performance bass, as much as 2 1/2" of elevation can be used, with something like a 4-blade Mercury Trophy Plus prop. At this height you are getting close to sucking in air. For engine mounting heights above 2 1/2", you have to have a special low water pickup conversion done, with the standard intakes plugged.

Remember, the position of the anti-cavitation plate relative to the hull bottom does not really apply when setback brackets are involved. Sighting this from behind with the boat on a trailer doesn't tell the story. You just have to check the water flow height under the anti-cavitation plate at speed.
That is the benefit of most setback brackets.
Because of the upward surge of the water as it leaves the transom bottom, the engine will in effect be running much higher, with less lower unit drag, but still keeping the water flow under the AC plate within limits.

On my 25 outrage with 26" setback bracket, the flow under the engines is only down about 3/4". But sighting this on the trailer shows that the engines are actually up about 4" above the hull bottom.

If your exhaust relief ports are showing a lot of steam at 3500RPM and higher, you are probably mounted too high.

larimore posted 06-15-2002 12:59 PM ET (US)     Profile for larimore  Send Email to larimore     
I raised mine 1 hole on my 22 OR and it made my boat run more bow down, not an improvement because I lost the range of trim I have from my trim tabs...
Bigshot posted 06-17-2002 02:17 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I can't see how it would change attitude of bow but i have not driven it. Usually the lower the engine the more the bow drags.
Airborne posted 06-27-2002 01:34 AM ET (US)     Profile for Airborne  Send Email to Airborne     
I did raise it one hole and noticed the bow ran a little lower. This is an improvement since the boat has always been a little stern heavy. I don't understand why but I think larimore is correct.

lhg posted 06-27-2002 01:58 AM ET (US)     Profile for lhg    
Often, raising an engine should be accompanied by a switch to a surfacing, bow lifting prop, such as an OMC Raker or Merc Laser II.
Airborne posted 06-28-2002 03:03 AM ET (US)     Profile for Airborne  Send Email to Airborne     
I'd love to pay someone to step out on the swim platform and see where the anti-cavitation plate is located, at speed.

The ports, so far, are slightly steaming after a stretching her legs but nothing excessive.

I'd like to raise her again although it'd be a drag if it was too high on a planned distant offshore trip. It's still digging in fine cornering in 2-4 foot chop.

What the hell, one more hole.

Bigshot posted 07-01-2002 10:13 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I raised my jackplate another 1/2 yesterday and it ran the same almost. It does not blow out in a holeshot and I can still bank a turn. For the first time it will blowout if I really wrench the wheel in a turn which is good. I am now almost 6" off my transom with a 5" setback plate. According to setup logic...I am way too high. according to my setup...I am about dialed in.
Wild Turkey posted 07-01-2002 11:38 AM ET (US)     Profile for Wild Turkey  Send Email to Wild Turkey     

I am in the same situation as you. Raised engine another 1/2" the weekend (about 5" above transom). No problems or blowouts. Prop makes a different sound when totally trimed out @ WOT. Buzzing sound almost... I guess the tips of the prop blades are coming close to the water surface.

I always check the confidence stream but, I am starting to wonder if I need a water pressure or temp gauge. Do you run one?


Bigshot posted 07-01-2002 02:29 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
No....but wondering as well. I just got the buzzing sound(kinda like something flapping) when I did the 1/2". I had my bud hold the wheel and I went back there and she was normal temp. the plate does not seem to be out of the water(at least with me back there)and everything seems ok. i have heard that they block off the 1st couple intake holes so the pump does not suck air but....if you look at a Suzuki the intake grate is right in the back of the lower, not the middle like Merc, OMC and yammie. Maybe this aids in cooling.
vdbgroup posted 07-04-2002 12:17 AM ET (US)     Profile for vdbgroup  Send Email to vdbgroup     
That sound is the prop catching air, ventilating.

I have played around with this setting on Montauk. If you really want to "jack" around with your engine height you need to match props.

For what its worth, I have not really noticed any significant performance gains on a Montauk. I raised my engine to before the prop ventilated. I also took prop in and re-cupped which made a big difference in performance. I subsequently swithced to a Michigan Rapture which has good cup, and this prop has perfomed 100% satisfactorily with my manual jack plate (4" setback CMC brand).

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