outboard motor height?

[vetstudent]

I was wondering if there were any guidelines on how high an outboard should be mounted. I have a 1996 tracker with a 40 hp merc on it. There are several holes in the mounting bracket and my motor is mounted at the "deepest" setting (factory I'm sure). Now If I was running in deep water all the time this would be fine, but I am usually on rivers where the depth can be shallow and underwater objects (logs) are readily found. I generally have to tilt the motor up a lot to get through shallow areas and this keeps me from being able to stay on plane.<br /><br />What I'm wondering is... How much can I raise the motor and not "suck air" when I'm in corners. I know this is somewhat subjective depending on load and boat size (17.5 tracker BTW). I'm assuming I can use a level under the bottom of the boat to see what the distance is from the top of the prop to the boat bottom... I just wouldn't know how to interpret it. I don't have any trim tabs or anything of that nature on the motor/boat if that makes a difference. <br /><br />Also, how hard is it to raise??? DO I just remove the four bolts, lift, and replace??? Are there other considerations? It looks like silicone squirted out from under the current mounting position.<br /><br />Thanks!<br /><br />Brent

 

[chuckz]

Re: outboard motor height?

As a starting point the cavitation plate should be even with the bottom of the hull.<br /><br />Do some searching of the forums and you'll find lots of information on motor height.<br /><br />Somebody who knows maore about your specific motor will have to chime in and tell you how to adjust the height on your set up.

 

[JB]

Re: outboard motor height?

Moving to Outboard Non-repair

 

[Dhadley]

Re: outboard motor height?

The final mounting height (X dimension) of the motor depends on a combination of hull design, prop design, gearcase configuration and set back (if any - none in your case) among other things.<br /><br />As a very basic rule of thumb, an OE ss prop will run a higher X dimension than an OE aluminum. Something like a Stiletto will run higher than most, not all, OE ss props. A Turbo will run higher yet. A 4 blade will run higher than the same technology type 3 blade. A large diameter prop will run higher than the same style prop with less diameter.<br /><br />Testing is the key. Aint this fun?

 

[vetstudent]

Re: outboard motor height?

So what you're saying is that prop type is a big differential. That brings me to another point... I'm in the market for a new prop. The one on it is the aluminum "stock prop" which is 13 pitch. It has found several of the underwater items in the river so it is in pretty bad shape. <br /><br />Any suggestions on a prop and pitch that will fit my uses. I understand the whole WOT RPM thing but other than that...? I was looking at a used stilleto triad II that was about $100 (they're $210 new) Is this a good prop? It's a 15 P which I think is a little higher than the majority of the props for my motor. Most are 13 P but range from 13-15. Are all stainless props created equal as far as durability???<br /><br />So it wouldn't hurt anything to just raise it up and go try it out... move it if not satisfied.<br /><br />Thanks<br /><br />Brent

 

[Dhadley]

Re: outboard motor height?

No, ss props are not all created equally. Not in durability, efficiency, technology or performance.<br /><br />The Stiletto Triad II is a very good prop. It will definately run higher than the prop you have now. $100.00 is a very good price as long as it has not been reworked and looks to be in decent shape. <br /><br />As far as the pitch goes, if your 13 is hitting the rpms you want then the 15 may be a bit too much. However as you raise the motor you will gain rpm (less drag). For that kind of money I'd be tempted to buy it and see. It'll still be worth the $100.00 as long as its in the same shape.

 

[imported_JD__]

Re: outboard motor height?

vetstudent,<br />I've owned 3 Tracker boats over the years and have asked the same question as you. I've tried raising and lowering my engines for increased performance but found that Tracker's recommended engine height setting is optimum. They were dead-on on all three of my boats. Call your dealer or Tracker customer service and give them your rig specifics. They will tell you what the best engine height is. <br /><br />I'm running a Stiletto ss on my current boat, very pleased. I don't see how you can go wrong for $100. It would make a great spare, if nothing else. I would check dimensions/measurements of the prop, call Stiletto and have them spec it. There's nothing wrong with a properly repaired prop but I've seen some good looking used props with the blades ground down to remove damage rather than being returned to spec. If you try the prop and find you're reaching the recommended RPM range but suffering on hole shot, you could try drilling some vent holes in it provided your engine exhausts through the prop. I had my Stiletto prepped for the Mercury pvs plugs. Works really well with my setup.

 

[vetstudent]

Re: outboard motor height?

Thanks!!!<br /><br />I really appreciate the help. My main concern was that the 15 pitch was going to be too high but you're right, for the money it's worth a try! It has to be better than my current one!!! If I were buying the one I have on it I wouldn't give $5 for it!!! If I think I'm not getting enough RPM's I'll look into the hole drilling. <br /><br />One more question: I've heard people talk about one pitch making a big difference on the way their boat ran. Is this generally true for all hp's and sizes of boats or would you see a greater difference in more "performance" and larger hp boats? Just curious.

 

[Dhadley]

Re: outboard motor height?

Your correct that differences depend on hull configuration. A hull like my old Dusky doesnt see as much difference between props but still some. However a pad bottom boat reacts to small changes. A tunnel boat really reacts.

 

[imported_JD__]

Re: outboard motor height?

vetstudent,<br />Let me clarify, drilling holes will ONLY help hole shot. Principle is that the holes will allow some of the exhaust gasses that normally go through the center of the prop hub to pass over the blades when you throttle up. This will partially ventilate the prop allowing it to slip/spin in the water which lets your engine rev up and develop horsepower. As you pick up speed, the force of the water rushing by becomes greater than the exhaust pressure at the vent holes, thereby sealing them. All the exhaust then travels through the prop hub as normal. If your current 13 P aluminum prop isn't allowing you to reach WOT, a 15 P will most probably kill what power you have. Don't be surprised to see a 300-500 drop in RPM. Is the current damage you have already holding you back? It doesn't take much. <br />Drilling holes in an already too large prop will just ruin the prop for your setup. If your engine really has a hard time turning the 15 P and you can't get close to WOT, drilling holes may keep you from planing out at all. You may just "sit-n-spin". <br />Remember me stating that I had my prop prepped for Mercury PVS plugs? I had to do that or weld the holes shut and re-drill. I had enlarged the pre-existing factory vent holes in my Stiletto several times making them too big. I was sitting-n-spinning.<br />JD

 

[vetstudent]

Re: outboard motor height?

JD:<br /><br />Thanks! That was a real good explanation. I think I'm getting about 5000 rpm's right now with my beat up aluminum prop. When I say beat up I mean "beat up" Every blade is wavy and dinged up from hitting many logs over the years... It's not that I'm a bad boat driver... I use it on a small river that constantly fluctuates water levels. Underwater logs are abundant and will be struck over time!<br /><br />I'm thinking that the better condition stainless prop will almost compenstate for the 2P increase. I think I'll give it a try anyway.<br /><br />By the way, does anyone know what RPM I should be getting at WOT. 97, 40hp merc tracker (4 cyl). I wish I had time to go out and try it. Finals have got me "holed up".<br /><br />Thanks<br /><br />Brent

 

[steelespike]

Re: outboard motor height?

If you are likely to be hitting things you may want to stick with an aluminum prop<br /> The stainless puts more stress on the drive line<br /> because of the weight.It also transmits more stress to the drive line if you strike something.<br /> Im no expert but if you are running proper rpm with a 13 now a stainless 15 may be too much.Youll lose hole shot and rpm may be too low.