plugging water intake holes for jackplate?

[wrestler20]

Hope someone can help me with a few questions about this. How exactly does this work? Does the motor overheat at idle for long periods of time? How do you know how many to plug? Will the ol' trial and error method work using good old duck tape to find the right combination? Sorry for so many qestions, but i don't want to risk overheating the motor or damaging anything. steve

 

[Gold Bear]

Re: plugging water intake holes for jackplate?

wrestler20 <br /><br />I am assuming that you are talking about installing a jackplate, then raising the engine as far as you can for maximum performance? <br /><br />On engines that have the water intake holes located above the propshaft, the idea is to plug the highest holes, so they will not "suck air" when the engine is raised so high.<br /><br />First you must have a water pressure gage so you know for a fact the water pump pressure. If you raise the engine to high you will fry it!!!<br /><br />Plugging the upper most holes allow you the raise the engine a bit higher. The trade off is that the more holes you plug, the less intake "size" you have. (Another reason you must have a water pressure gage).<br /><br />Some engines have "low water" intakes to get around this problem.<br /><br />Let us know what engine we are talking about, and others will chime in on this subject.<br /><br />Regards, Gold Bear

 

[wrestler20]

Re: plugging water intake holes for jackplate?

My motor is a 92 200 Johnson gt. Tee jackplate is a 10 inch hydraulic jackplate. my water pressure guage i see is in the "T" on the overboard indicator, which i have now found out is wrong on the loop charged v6 models. I am not sure where exactly is the correct spot and have spent much time using the search feature to try to figure it out. Is there a plug to remove to put a fitting in, or do i have to drill into the water jacket somewhere? I haven't really used the jackplate because i want to make sure everything is right before i risk screwing it up by raising the motor too high. THnks for any help you can give.<br /><br />Steve

 

[ob]

Re: plugging water intake holes for jackplate?

In all likelyhood your prop will cavitate before your water intake is sucking wind.Jackplates are widely used on outboards on the gulf coastal flats and I have never seen anyone that plugged upper holes on a water intake.At most you would gain maybe a 1/2 inch and run the risk of overheat.

 

[fishfinder221]

Re: plugging water intake holes for jackplate?

On the 92 loopers there is a hose coming from the base right by the pisser. It runs to a pressure switch hooked to the throttle arm. then the hose runs to the top of the engine. The water pressure guage hose should be teed in between the sensor and the outlet in the base. If there is hardly no pressure there, spray the water hose down the base end. This runs directly to the water pump. It does not go through the engine. You should read about 8 to 10 psi. there.Thats about as much pressure you will get with those year loopers.

 

[fishfinder221]

Re: plugging water intake holes for jackplate?

I have a 1991 exinrude 225xp which is basically the same engine. I run a cmc hyd. jackplate w/ a 7" setback on a 20'5" stratos bass boat. I have the motor set at the highest level on the jackplate. I usually jack up about 2 1/2" before my water pressure drops and i start to cavitate. Omc made their lower unit housings bigger than the competion for reasons no one knows, so the units create more drag in the water. I know a few people who have plugged off top holes on their outboards, but unless you go with a low water pickup lower unit. the trouble you go through is really not worth it. But...to each his own.

 

[Dhadley]

Re: plugging water intake holes for jackplate?

You didn't mention if the plate is manual or hydraulic so lets start at the begining. The guys are right - the water pressure gauge will T into the hose coming from the adaptor housing to the throttle controlled water valve on the starboard side of the block. Run the boat with the motor at a relative low setting to establish a baseline.<br /><br />Many times we have plugged the top one or two holes on an E/J and even drilled one more at the bottom and plugged the top 3. Testing will tell you what to do. Sometimes we add scoops to the bottom 2 to increase water flow. You can buy scoops from any Evinrude / Johnson dealer depending on which style gearcase you have.<br /><br />It's not unusual these days to have a prop that will still "bite" even when the motor will no longer pick up water even with the modified water pick ups. At this point we go to a low water pick up. Heres where you get into rigging for performance. If you install a nose cone with low water pick up it can slow you down if you are not approaching blow out speed. Once you are near blow out speed the nose cone will allow you to go faster. <br /><br />Get the water pressure gauge working properly, establish a baseline and we'll go from there. Tell us more about your rig. What prop you are running (that will ultimately determine your X dimension) at what speed and rpm. Manual or hydraulic plate? Let us know.<br /><br />Good luck!

 

[wrestler20]

Re: plugging water intake holes for jackplate?

Thanks for all of the info guys, This forum has been a life-saver. <br /><br />Dhadley, The jackplate has 10 inches of setback and is a hydraulic jack. The boat is a 20 foot 91 Astro fsx. the prop that seems to run best so far has been a 24 pitch raker. I am running 5500 rpm at wot and running 52 mph (GPS). I know that seems really slow for 5500, but i have not been able to decrease my sip % no matter what i do. <br /><br />Thanks,<br />Steve

 

[Dhadley]

Re: plugging water intake holes for jackplate?

That's about 23% slip. I would set the rig up to turn 5800 with an average load if it were mine. The 3 blade 24 Raker has good lift as long as it has not been reconditioned improperly. Many, many times a Raker gets reconditioned and loses lift. Has yours been reconditioned? I would lean toward setting it up with something like a 4 blade Turbo since you have the ultimate in jackplates with hydraulic. <br /><br />How about the pad? Is it straight?<br /><br />Let us know!

 

[Waterbugtoo]

Re: plugging water intake holes for jackplate?

Why not install a nose cone with low water pickup and permanently rid yourself of worrying about it, and at the same time add another couple of MPH.<br /><br />

 

[wrestler20]

Re: plugging water intake holes for jackplate?

dhadley,<br /> The raker was purchased new in august, so that shouldn't be a problem. I have even taken the boat to a repair shop to have them take a look at the stringers and to see if the pad was okay and they said everthing was true and is running properly. I have though about the 4 blade turbo, but i just wanted to make sure i had the jackplate set up properly before getting a prop that wants to run that high in the water. If i go to a 4 blade renegade or turbo, should i start with the same pitch, or lower the pitch some?<br />Waterbugtoo, The nosecone and low water pickup are a definite possibility, i have almost purchased one before, it would be great if i don't need one though because i do so much running in the Mississippi river and am a bit afraid of running into a muck or sand bottom and screwing up the low water intake. I have also wondered about what some of the other guys said about a nose cone slowing you down if your boat is not approaching blow out speed, which i am not even remotely close.<br /><br />Again, thanks guys for all of the help here, setting up this boat has been a real pain in the rear. <br />Steve

 

[Dhadley]

Re: plugging water intake holes for jackplate?

Thats most likely where we will end up Waterbugtoo but we need to establish a good baseline now. We need to get the water pressure gauge working properly and look at the basics first. At 52 mph the additional drag of a nosecone (longer gearcase) may in fact hurt us. <br /><br />Once we get a number on the water pressure we can utilize the plate to gain rpm and speed by reducing drag. It may or may not be with that prop.

 

[Dhadley]

Re: plugging water intake holes for jackplate?

Did you get the water pressure gauge hooked up correctly? If so lets run it as is and get a baseline on the pressure reading. See how high you can run it before the pressure drops. Dont worry too much about the prop losing bite right now. Also get a "feel" for your steering. Thats great that the Raker has not been rebuilt. That will give us solid info. <br /><br />Put a 4' straight edge on the pad and see how much hook it has from the very stern forward. It should be at the very back if any at all. <br /><br />Good luck!

 

[wrestler20]

Re: plugging water intake holes for jackplate?

dhadley,<br /><br />I just took my boat to the repair shop on saturday, so i will have to wait for it to get back before i can test things out. Hopefully i can still find enough open water to test everything out. Gettin a bit cold up here. When i get it back and fix the water pressure gage i'll refresh this post. Thank you for all of help. I don't mean to sound ignorant, but what exactly do you mean by hook? <br /><br />Steve

 

[Waterbugtoo]

Re: plugging water intake holes for jackplate?

Dhadley,<br /><br />Excuse me? "Additional drag of a nosecone"? What do you think nosecones are for?<br /><br />wrestler20,<br /><br />You can always get the nosecone, weld up the existing intake holes, and cut new intake holes higher up the nosecone. This would relieve your fear of sucking up muck, but still retain enough water intake depth that you would never have to worry about running out of water no matter how high you ran the motor.

 

[Dhadley]

Re: plugging water intake holes for jackplate?

Hook is built into the running surface to assist the boat getting on plane. Since your boat has a pad, lay a straight edge on it from the back to about 4' forward. Right at the back you may see the surface dip down slightly leaving a small space between the pad and the straight edge. It may be 1/8" near the rear and taper back to flat 6" to a foot forward. Some pads are perfectly flat and the hook is in the lifting strakes and the bottom away from the pad. If the hook is excessive it will keep the nose from rising at speed. Ideally you want to use as little positive trim as possible to raise the bow at speed to reduce the wetted surface. This reduces hull drag while (in a perfect world) keeping propeller thrust going forward. Excessive hook could help explain your high slip factor.<br /><br />And yes, I do know what a nosecone does. I also know that there are many kinds or water pick ups and not all have to be in a nosecone. I also realize that at 52 mph the additional square area of wetted surface creates more drag, not to mention additional side load stress. We still need to get the all-important baseline established which includes water pressure at this X dimension. Most likely a nose cone with low water pickup (or the Sportsman or Grassmaster style) will be helpful. Maybe we can use one of the other systems. If we approach blowout speed then we will definately need a longer case (nosecone). Right now thats better than 20 mph away. <br /><br />Keep us informed when you test!

 

[Waterbugtoo]

Re: plugging water intake holes for jackplate?

Dont mean to argue, but how do you figure more "wetted area" is increased drag vs. a blunt factory nose bullet?<br /><br />If its only getting 52 (assuming speedo is even close to correct) out of a 200 horse on a 20 footer, theres definately a problem. I've never been a fan of Raker's, but thats not saying there is something wrong with the prop, its not saying theres not either. Jack plate and good prop should push that boat close to low 70's without much strain. Even a 4 blade would run close to that speed. No one knows exactly how high the motor is right now. That may be the whole factor. Its anyones guess without seeing it with own eyes.