Engine Mounting height on 10" setback bracket

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Author Topic:   Engine Mounting height on 10" setback bracket

Buckda posted 05-08-2006 05:17 PM ET (US)
Over 110 miles on the boat with the new engines, and I'm still racheting the engines up for each outing, trying to get maximal performance for speed and operation in "normal conditions" (about 1-4' Lake Michigan/Huron chop).
What I mean is, I'm trying to get the best speed, but also have the engines running well and consistently "planted" when running through 1-2 foot waves at cruise (about 24-30 MPH).
Here's some background:
The boat: 18' Outrage
Power: Twin 90 HP 20" shaft Evinrude E-TEC engines
Current Props: BRP 13.2"x19" aluminum props. Starboard prop has a small nick in it (already!)
The setup: Engines mounted 10" aft on Rite-Hite jackplates.
Fuel: 63 gallons aboard, and burning fuel to current level - about 40 gallons (estimated) in the tank.
Here's the question:
The anti-ventilation plates are approximately even with the bottom of the hull (perhaps 1/2 inch below), and I'm unable to beat 5,200 rpm without feeling like I've got the engines trimmed out too far (I'm worried about not giving them enough water for the cooling system...since I don't have a water PSI guage, I'm unable to really know what they're getting).
I've not had an opportunity to run in really calm conditions yet, but so far the top speed has been around 45 MPH running through 1 to 1 1/2 foot chop. In the test runs on the detroit river with these props, we were able to see over 50 mph...perhaps Douglas (the mechanic) had the engines trimmed way out to get there? I just worry about getting the engines proper cooling! The props are not blowing out on a regular basis, (other than when the boat launches off the waves)...so do I go even higher?!

Dave
Tom W Clark posted 05-08-2006 05:41 PM ET (US)
Dave,
You can go up...way up. You do not need to worry about the water pickups.
As a point of comparison, Rob Schmidt has his E-Tec 90's AV plate 2-7/8" ABOVE the keel of his Montauk. If your AV plates are 1/2" below the hull, you are way to low.
Teak Oil posted 05-08-2006 05:49 PM ET (US)
Just remember whatever height you discover is optimal for the aluminum props will be too low if you get high rake stanless props. I can run my Raker much higher than my OMC aluminum.
In my experience with my jackplate and water pressure gauge, I can not trim the motor high enough to lose cooling pressure. The prop cavitates way before the water pressure drops below 30 psi. Since your engines are offset to the sides, they probably have an even higher safety zone than mine does as far as cooling capacity.
I would jack the engines up an inch and try again. Just remember if you adjust for tip top speed on glassy water, go down about a 1/2" from there so the props dont blow out when you go out in four footers
ratherwhalering posted 05-08-2006 06:04 PM ET (US)
Dave, remember the rule of thumb that water rises 1-inch for every 12-inches of set-back (on plane). In addition, you have a 14-degree transom angle, so when you run those engines flat with the bottom of the hull (not in parallell to the transom) your about 1 inch too low if they are even with the keel. I'd say you need to raise them at least 1.5 inches. Then, they'll be about even with the respective keel points, and go up from there. I think those aluminum props will cavitate way before you lose cooling.
Also, take a gander at your water intakes on the E-TEC 90. They are basically at the top of the lower end's hub, and quite small. They look to be about 4 inches below the cavitation plate, so I don't think raising the engine up will influence your cooling system. With a different engine, this might be a concern, but I'm running mine DARN high, like 3-inches above the lowest transom point, and I still get good water pressure at all speeds.
Buckda posted 05-08-2006 06:27 PM ET (US)
Okay...
When I look at the picture here : http://continuouswave.com/whaler/cetacea/cetaceaPage81.html - reference image #12, I get worried that it's high enough already. Given that the water seems to be very aerated back there already.
The other concern is that the water pickup is only on one side of the gearcase, meaning that the engine with the pickup facing the keel will lose water pressure faster than the one that has the pickup facing the gunwale (due to the deadrise).
Dont' get me wrong - the setup is plenty fast already and performs well...I just want to be sure the engines are operating at a level where they can be maxed out on RPMs for the appropriate "excercise" that they need.
I'm running between 2800 and 3200 for comfortable cruising up to 30 or so MPH...this is definitely a good combination on the hull.
I'm estimating about 5 MPG economy overall (with mixed use - idling, etc) and about 2.5-2.75 MPG at cruise.
These are rough estimates based on fuel flow meter readings vs GPS speed indications, and will be confirmed when I eventually have to buy some gas.
The engines seem to sip that oil too.
Dave
Tom W Clark posted 05-08-2006 06:53 PM ET (US)
Dave,
Don't worry, be happy...and raise those motors. The water pickup is well below the AV plate. You will NOT have any trouble with water pickup even if you raise your motors another 2-3 inches. The propellers will ventilate long before the motors stop drawing water.
As it is now it appears the AV plate is running BELOW the surface of the water. No way you want that. It should be ABOVE the surface of the water.
ratherwhalering posted 05-08-2006 07:01 PM ET (US)
I agree with Tom...I agree with Tom...I agree with Tom...
Man, I feel like a puppy dog lately.
bsmotril posted 05-09-2006 03:24 PM ET (US)
In my experience of running Mercs and OMC, you can trim up to the point of prop ventilation before you lose any cooling capability. You'll see rpms rise with no more speed increase when you're at this threshold.
BillS
The Judge posted 05-09-2006 04:19 PM ET (US)
What is too high...depends on the setup. My 19' right now is jacked up 5"...yes 5" and I am going to lower it down an inch or so. My Montauk was jacked up 4+" and ran great, so does the 19 but I am not getting enough trim to raise the bow enough.
Level with the keel....with a 10" setback, go up 3-4" and start from there, I am only running a 6" setback.
Teak Oil posted 05-09-2006 08:39 PM ET (US)
JACK IT UP, MAN!
Sal DiMercurio posted 05-09-2006 08:59 PM ET (US)
Even without the jack plate, your engines are to low.
I'm with the rest of the guys, jack em up at least 3-4" & go from there.
Your rpms will also go where they need to, & that up with the up of the engines.
You might also consider a pair of Stilettos because they can be run much higher than those aluminums will stay hooked up when most other props have vented.
Sal
ratherwhalering posted 05-10-2006 01:31 AM ET (US)
Dave, I gave it some thought, and if you are worried about those inboard water intakes, get a flat board and run it along the bottom of the hull to mimic the waterflow at plane. When the top of the board is at the water intakes, you should not go any higher.
Caveat: This applies to an engine with a set back only, because the water will rise to about 1 inch above the inboard water intakes. Even then I'd be a little concerned.
The Judge posted 05-10-2006 12:24 PM ET (US)
That is why God invented overheat alarms....aint gonna need them though.
Binkie posted 05-10-2006 01:39 PM ET (US)
Everyone`s giving you the same good advice, just do it. You need to max the rpms at wot with the motor pretty close to vertical. Don`t worry about the water intakes, the engineers knew where to put them. Your not running an odd-ball configutation, they they hadn`t thought of.
Rich
Buckda posted 05-15-2006 06:11 PM ET (US)
A/V plates are now 1/2 inch above the hull bottom, was able to hit 5,500 RPM and 50 MPH sustained on GPS with engines trimmed out. (This on a calm, i.e., no waves, river..54 MPH Speed over ground(SOG)downstream, 47 MPH (SOG)upstream due to the rather strong current from our recent rain).
I LOVE WOT with these engines....the sound is awesome...they really "scream and fly".
Interesting note: when running WOT, both engines are at 5,500 RPM, but for running at below WOT, the throttles require slightly different settings to keep RPM's synched. I'm wondering if that has to do with trim settings being different?
This with 13.2 X 19 inch BRP Aluminum props, shelter, flying top, windshield and side curtains set, two flags on the mast and both 8' antennas up on the arch. Temperature was below 45 degrees and humid (what's going on with the weather this month?!)....oh, and a little more than 1/2 tank of fuel.
I think maybe I'll jack it up further and see what happens at Memorial Day on Spring Lake. I think that will be a good time to really tweak with the jackplates and burn some gas!
Solid three footers on the big lake, so I wasn't able to go very fast at all...about 15-22 mph out there, but the props stayed pretty well planted for the kind of seas I was running into....I guess it can go even higher.
Buckda posted 05-15-2006 10:07 PM ET (US)
Other note on economy.
With the 150 Mercury 2-stroke, I always calculated 120 mile range, and enjoyed 150 miles or so per tank.
I'm now at 147 miles travelled (GPS) on the first tank of gas, and I still have more than half a tank.
That's good news...
Dave
Boatplans posted 05-15-2006 11:26 PM ET (US)
There is an APBA racing class requiring stock gear cases on a tunnel boat. Can't remember the class name. Because the gear cases must be stock, the water intake must also be stock, yet it is run in a surface pearcing mode, meaning only the skeg and bottom third of the prop is in the water. Despite this, the intake is about 5 inches above the water!!! I could not believe this when I saw it. I was told there is enough water splashing up there to cool the engine. I don't know whether to believe this our not but I checked out the setup very closely. I would be using a water pressure guage in that boat. In fact, I would recommend using a water pressure guage on both those 90 hp engines. They are simple to install and useful. What if you get a plastic bag caught on your engine?
BlackMax posted 05-16-2006 11:08 AM ET (US)
Ihave never seen 19" aluminum props, running through 2.0 gearing at 5500 RPM produce 50.5 MPH. Pretty much impossible even with those CW wonder machines you are running. 45-46MPH would be more like it. You would have to be turning up 21" props to get that kind of TRUE speed. Your GPS is not accurate.
Tom W Clark posted 05-16-2006 11:23 AM ET (US)
Larry,
I suspect Dave's GPS is perfectly accurate. Many propellers have more effective pitch than their nominal specification. That is how propellers like the Stiletto Advantage series can run with theoretical negative slip numbers. This is fairly common.
Dave,
That is awesome, especially given you had your canvas up. I really think you should jack those motors up even more. With a pair of 19" Advantage Is or 20" Lightspeeds, I now think it is possible you will see 52-53 MPH.
Buckda posted 05-16-2006 11:24 AM ET (US)
Blackmax -
Do you have Garmin Blue Chart software? I can send you the file that I downloaded from my GPS.
Dave
Buckda posted 05-16-2006 11:35 AM ET (US)
I don't think we have a lot of experience (royal "we") on these new props from BRP. They appear to have a bit of cupping in them as well, which may help. I don't know enough about props to make that determination.
I do know that they are new props from BRP, designed to be a "new product" with their new E-TEC engines.
Engines howling, flags snapping and wind noise on the canvas rumbling....not much boat is in the water at that speed. Navigating a turn is an interesting thing...don't catch a chine!

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Author	Topic: Engine Mounting height on 10" setback bracket
Buckda	posted 05-08-2006 05:17 PM ET (US) Over 110 miles on the boat with the new engines, and I'm still racheting the engines up for each outing, trying to get maximal performance for speed and operation in "normal conditions" (about 1-4' Lake Michigan/Huron chop). What I mean is, I'm trying to get the best speed, but also have the engines running well and consistently "planted" when running through 1-2 foot waves at cruise (about 24-30 MPH). Here's some background: The boat: 18' Outrage Power: Twin 90 HP 20" shaft Evinrude E-TEC engines Current Props: BRP 13.2"x19" aluminum props. Starboard prop has a small nick in it (already!) The setup: Engines mounted 10" aft on Rite-Hite jackplates. Fuel: 63 gallons aboard, and burning fuel to current level - about 40 gallons (estimated) in the tank. Here's the question: The anti-ventilation plates are approximately even with the bottom of the hull (perhaps 1/2 inch below), and I'm unable to beat 5,200 rpm without feeling like I've got the engines trimmed out too far (I'm worried about not giving them enough water for the cooling system...since I don't have a water PSI guage, I'm unable to really know what they're getting). I've not had an opportunity to run in really calm conditions yet, but so far the top speed has been around 45 MPH running through 1 to 1 1/2 foot chop. In the test runs on the detroit river with these props, we were able to see over 50 mph...perhaps Douglas (the mechanic) had the engines trimmed way out to get there? I just worry about getting the engines proper cooling! The props are not blowing out on a regular basis, (other than when the boat launches off the waves)...so do I go even higher?! Dave
Tom W Clark	posted 05-08-2006 05:41 PM ET (US) Dave, You can go up...way up. You do not need to worry about the water pickups. As a point of comparison, Rob Schmidt has his E-Tec 90's AV plate 2-7/8" ABOVE the keel of his Montauk. If your AV plates are 1/2" below the hull, you are way to low.
Teak Oil	posted 05-08-2006 05:49 PM ET (US) Just remember whatever height you discover is optimal for the aluminum props will be too low if you get high rake stanless props. I can run my Raker much higher than my OMC aluminum. In my experience with my jackplate and water pressure gauge, I can not trim the motor high enough to lose cooling pressure. The prop cavitates way before the water pressure drops below 30 psi. Since your engines are offset to the sides, they probably have an even higher safety zone than mine does as far as cooling capacity. I would jack the engines up an inch and try again. Just remember if you adjust for tip top speed on glassy water, go down about a 1/2" from there so the props dont blow out when you go out in four footers
ratherwhalering	posted 05-08-2006 06:04 PM ET (US) Dave, remember the rule of thumb that water rises 1-inch for every 12-inches of set-back (on plane). In addition, you have a 14-degree transom angle, so when you run those engines flat with the bottom of the hull (not in parallell to the transom) your about 1 inch too low if they are even with the keel. I'd say you need to raise them at least 1.5 inches. Then, they'll be about even with the respective keel points, and go up from there. I think those aluminum props will cavitate way before you lose cooling. Also, take a gander at your water intakes on the E-TEC 90. They are basically at the top of the lower end's hub, and quite small. They look to be about 4 inches below the cavitation plate, so I don't think raising the engine up will influence your cooling system. With a different engine, this might be a concern, but I'm running mine DARN high, like 3-inches above the lowest transom point, and I still get good water pressure at all speeds.
Buckda	posted 05-08-2006 06:27 PM ET (US) Okay... When I look at the picture here : http://continuouswave.com/whaler/cetacea/cetaceaPage81.html - reference image #12, I get worried that it's high enough already. Given that the water seems to be very aerated back there already. The other concern is that the water pickup is only on one side of the gearcase, meaning that the engine with the pickup facing the keel will lose water pressure faster than the one that has the pickup facing the gunwale (due to the deadrise). Dont' get me wrong - the setup is plenty fast already and performs well...I just want to be sure the engines are operating at a level where they can be maxed out on RPMs for the appropriate "excercise" that they need. I'm running between 2800 and 3200 for comfortable cruising up to 30 or so MPH...this is definitely a good combination on the hull. I'm estimating about 5 MPG economy overall (with mixed use - idling, etc) and about 2.5-2.75 MPG at cruise. These are rough estimates based on fuel flow meter readings vs GPS speed indications, and will be confirmed when I eventually have to buy some gas. The engines seem to sip that oil too. Dave
Tom W Clark	posted 05-08-2006 06:53 PM ET (US) Dave, Don't worry, be happy...and raise those motors. The water pickup is well below the AV plate. You will NOT have any trouble with water pickup even if you raise your motors another 2-3 inches. The propellers will ventilate long before the motors stop drawing water. As it is now it appears the AV plate is running BELOW the surface of the water. No way you want that. It should be ABOVE the surface of the water.
ratherwhalering	posted 05-08-2006 07:01 PM ET (US) I agree with Tom...I agree with Tom...I agree with Tom... Man, I feel like a puppy dog lately.
bsmotril	posted 05-09-2006 03:24 PM ET (US) In my experience of running Mercs and OMC, you can trim up to the point of prop ventilation before you lose any cooling capability. You'll see rpms rise with no more speed increase when you're at this threshold. BillS
The Judge	posted 05-09-2006 04:19 PM ET (US) What is too high...depends on the setup. My 19' right now is jacked up 5"...yes 5" and I am going to lower it down an inch or so. My Montauk was jacked up 4+" and ran great, so does the 19 but I am not getting enough trim to raise the bow enough. Level with the keel....with a 10" setback, go up 3-4" and start from there, I am only running a 6" setback.
Teak Oil	posted 05-09-2006 08:39 PM ET (US) JACK IT UP, MAN!
Sal DiMercurio	posted 05-09-2006 08:59 PM ET (US) Even without the jack plate, your engines are to low. I'm with the rest of the guys, jack em up at least 3-4" & go from there. Your rpms will also go where they need to, & that up with the up of the engines. You might also consider a pair of Stilettos because they can be run much higher than those aluminums will stay hooked up when most other props have vented. Sal
ratherwhalering	posted 05-10-2006 01:31 AM ET (US) Dave, I gave it some thought, and if you are worried about those inboard water intakes, get a flat board and run it along the bottom of the hull to mimic the waterflow at plane. When the top of the board is at the water intakes, you should not go any higher. Caveat: This applies to an engine with a set back only, because the water will rise to about 1 inch above the inboard water intakes. Even then I'd be a little concerned.
The Judge	posted 05-10-2006 12:24 PM ET (US) That is why God invented overheat alarms....aint gonna need them though.
Binkie	posted 05-10-2006 01:39 PM ET (US) Everyone`s giving you the same good advice, just do it. You need to max the rpms at wot with the motor pretty close to vertical. Don`t worry about the water intakes, the engineers knew where to put them. Your not running an odd-ball configutation, they they hadn`t thought of. Rich
Buckda	posted 05-15-2006 06:11 PM ET (US) A/V plates are now 1/2 inch above the hull bottom, was able to hit 5,500 RPM and 50 MPH sustained on GPS with engines trimmed out. (This on a calm, i.e., no waves, river..54 MPH Speed over ground(SOG)downstream, 47 MPH (SOG)upstream due to the rather strong current from our recent rain). I LOVE WOT with these engines....the sound is awesome...they really "scream and fly". Interesting note: when running WOT, both engines are at 5,500 RPM, but for running at below WOT, the throttles require slightly different settings to keep RPM's synched. I'm wondering if that has to do with trim settings being different? This with 13.2 X 19 inch BRP Aluminum props, shelter, flying top, windshield and side curtains set, two flags on the mast and both 8' antennas up on the arch. Temperature was below 45 degrees and humid (what's going on with the weather this month?!)....oh, and a little more than 1/2 tank of fuel. I think maybe I'll jack it up further and see what happens at Memorial Day on Spring Lake. I think that will be a good time to really tweak with the jackplates and burn some gas! Solid three footers on the big lake, so I wasn't able to go very fast at all...about 15-22 mph out there, but the props stayed pretty well planted for the kind of seas I was running into....I guess it can go even higher.
Buckda	posted 05-15-2006 10:07 PM ET (US) Other note on economy. With the 150 Mercury 2-stroke, I always calculated 120 mile range, and enjoyed 150 miles or so per tank. I'm now at 147 miles travelled (GPS) on the first tank of gas, and I still have more than half a tank. That's good news... Dave
Boatplans	posted 05-15-2006 11:26 PM ET (US) There is an APBA racing class requiring stock gear cases on a tunnel boat. Can't remember the class name. Because the gear cases must be stock, the water intake must also be stock, yet it is run in a surface pearcing mode, meaning only the skeg and bottom third of the prop is in the water. Despite this, the intake is about 5 inches above the water!!! I could not believe this when I saw it. I was told there is enough water splashing up there to cool the engine. I don't know whether to believe this our not but I checked out the setup very closely. I would be using a water pressure guage in that boat. In fact, I would recommend using a water pressure guage on both those 90 hp engines. They are simple to install and useful. What if you get a plastic bag caught on your engine?
BlackMax	posted 05-16-2006 11:08 AM ET (US) Ihave never seen 19" aluminum props, running through 2.0 gearing at 5500 RPM produce 50.5 MPH. Pretty much impossible even with those CW wonder machines you are running. 45-46MPH would be more like it. You would have to be turning up 21" props to get that kind of TRUE speed. Your GPS is not accurate.
Tom W Clark	posted 05-16-2006 11:23 AM ET (US) Larry, I suspect Dave's GPS is perfectly accurate. Many propellers have more effective pitch than their nominal specification. That is how propellers like the Stiletto Advantage series can run with theoretical negative slip numbers. This is fairly common. Dave, That is awesome, especially given you had your canvas up. I really think you should jack those motors up even more. With a pair of 19" Advantage Is or 20" Lightspeeds, I now think it is possible you will see 52-53 MPH.
Buckda	posted 05-16-2006 11:24 AM ET (US) Blackmax - Do you have Garmin Blue Chart software? I can send you the file that I downloaded from my GPS. Dave
Buckda	posted 05-16-2006 11:35 AM ET (US) I don't think we have a lot of experience (royal "we") on these new props from BRP. They appear to have a bit of cupping in them as well, which may help. I don't know enough about props to make that determination. I do know that they are new props from BRP, designed to be a "new product" with their new E-TEC engines. Engines howling, flags snapping and wind noise on the canvas rumbling....not much boat is in the water at that speed. Navigating a turn is an interesting thing...don't catch a chine!