WOT Performance Question

[KCLOST]

You will see what boat and motor I have below...<br /><br />Here is my question. When I'm running at wide open and tilt the engine out to a certain position, I often encounter the scary wiggle of the boat that frightens the hell out of me...<br />Is there something I can do to the height of the outboard, prop, anything that will help prevent this? At my current set-up I'm getting up to 58-60mph, at 5100 rpms safely. If I tilt out to gain a little more that's when the boat starts to rock/wiggle on me. <br /><br />The outboard has a 24 pitch prop on it (merc. 175), pushing a 18' Ranger. <br /><br />Thanks in advance.

 

[Walt T]

Re: WOT Performance Question

I think that's chine walking you are referring to. That basically means your hull is going too fast. <br />As the hull lifts out of the water the faster it goes the higher it lifts. The chines on the side of the hull stablize the hull. As the chines lift out of the water they no longer work. Because of the rounded shape of most hulls in the back the boat will roll back and forth from chine to chine rapidly. This is a very dangerous situation. <br />It means the hull is at the limits of its design.

 

[Jdeagro]

Re: WOT Performance Question

I agree, the boat is "chine walking". To little boat in the water to control the roll. This can be eliminated with MOBster Tabs which is a variation of Smart Tabs that we also make. MOBster Tabs (moto is "Steal the Hole") are designed primarily for high speed bass boats to improve the hole shot (accleration) and eliminate the chine walking common on these boats. See Smart Tabs on this site and go down to MOBster Tabs.

 

[Forktail]

Re: WOT Performance Question

An '88 371V is specd for a 175 HP, so I don't think you're over-powered. And these boats are known for doing well over 70 mph. It could be weight distribution, or you may want to have the hull and transom checked for problems by a professional. Be careful.

 

[LubeDude]

Re: WOT Performance Question

Do you have a Jack plate on this boat?? The engine is too low on the transom, Its lifting the pad out of the water and allowing the boat to rock side to side! (Chine walk)! This boat will do more but may need a Jack plate to acomplish it! If you do not have a jack plate, you can still lift the engine one hole at a time to see how this effects the performance! Go at it slow as the scare the he*l out of you feeling is telling you something! Dont think you can drive through it!

 

[KCLOST]

Re: WOT Performance Question

Thanks Everyone..<br /><br />LubeDude,<br />I do have a jack plate, and I agree that the motor is sitting low. I was planning on raising the engine a bit anyway, based on a conversation I hade with Ranger. I think it is diffinitely sitting too low, as the upper exhaust ports are nearly completely under water when at idle or no-wake speed. I just didn't realize that a low motor could cause "chine walking". But it makes complete sense. <br /><br />Another question, does a rooster tail indicate a good, fair, or potentially poor set-up in regards to motor position on the transom. The reason I ask is because right now, I don't have one at all even at WOT. I guess that goes along with a low motor position, correct????

 

[Dhadley]

Re: WOT Performance Question

Your engine is way too low. As you gain height you will find you dont need as much positive trim and the "tail" will not be as pronounced.<br /><br />Raise the jackplate and carefully test again. Watch your water pressure!!<br /><br />Good luck!

 

[LubeDude]

Re: WOT Performance Question

A rooster tail to a point is good, and you should have one to a point! After that its "All show and no go"!! Looks cool though!<br />My 1800SF Tracker with a High five prop when trimmed a little too far up throws a rooster tail about 50 Yards long, but I loose about 3 MPH to do it though! Impresive untill you blow your engine showing off!!

 

[WillyBWright]

Re: WOT Performance Question

I've found that running a 3-blade propeller contributes much more to chinewalking. 4-blades usually do better. You can generally run a 4-blade closer to the surface as well which reduces drag and gives you a bit more speed.

 

[LubeDude]

Re: WOT Performance Question

WillyBWright:<br /><br />I have not personally found this to be true!<br /><br />The best top speed is nearly always found with a 3 blade prop, However hole shot is always improved with a 4 or 5 blade prop!<br /><br />As to chinewalk, different strokes for different boats!!

 

[KCLOST]

Re: WOT Performance Question

You guys have been a great help....<br /><br />Up the motor will go,,, (a bit at a time)...<br /><br />Do you think I will see an increase in RPMs, with this adjustment? I'd like to see a 5500-5800 reading at WOT... Being at 5100 now, that seems like a hell of a jump... <br /><br />What do you think?

 

[DJ]

Re: WOT Performance Question

KCLOST,<br /><br />All you cn do at this point is carefully: test, test, test.<br /><br />You are now "dialing it in".<br /><br />Yes, as your engine is raised, you will notice an rpm jump-to a point. As Dhadley mentioned, keep a close eye on H2O pressure.

 

[Dhadley]

Re: WOT Performance Question

I too have found that 4 blade props are more stable. When set up correctly the 4 blade is usually a tad faster although the set up is different between the 3 and the 4. And we are comparing the same brand/type props. I wouldnt compare a 4 blade comp prop to a Turbo 3 blade. You have to compare apples to apples.<br /><br />Good luck!

 

[LubeDude]

Re: WOT Performance Question

Yes you are going to see a difference in RPM as you raise the engine! What do you think guys, 1-200 RPM per hole?? You may very well get to the desired RPM range you want by the time you are done!<br /><br />WalleyeHed has done a lot of this, I wonder where he is!!

 

[KCLOST]

Re: WOT Performance Question

Well that's good news....<br /><br />Right now I already have a 4-blade trophy on the motor. And it runs pretty stable until I get to that 58-60mph range and try to tilt out to gain more...<br /><br />Speed isn't my concern, safety (stable ride) and the all important optimal rpm range is what I'm looking for...<br />From what it sounds like, I know the test, test, testing of the motor height is where I should go forward. However, I don't have a Pressure gauge on this boat, I guess I should invest in one. Until then, I'll have to carefully look around my shoulder. (that will be fun)<br /> <br />Not to drag this thread out, but with an increase in rpm's of let's say,,,,, 4-500 can I expect a signifigant increase in engine temp, assuming the pump still gets optimal water flow to it? These motors like to run hot and my temp gauge always likes to read at the max at WOT...No alarm yet however. (water pump is new as well as the poppet & stats, replaced for assurance).????

 

[walleyehed]

Re: WOT Performance Question

Here I am.......<br />I got about 125 RPM rise with each hole up, and stability increased as well...<br />My testing with 3 and 4 blade props has produced best speed with 3-blade, and handling is great with the 4-blade with the biggest improvement being less torque, steering-wise, throughout the power band.<br />KC, you don't want to "tilt out" anymore, you need to raise the engine, I believe.

 

[VistaMan]

Re: WOT Performance Question

There are several other things you should be aware of. First if you don't have a water pressure gauge then get one! It is too easy to raise the motor too much and blow it for lack of water pressure. Second what kind of steering do you have? If it is a single cable then, at these speeds, you should realy get double cable to eliminate any free play. Also as you get up in speed the typical rubber motor mounts can cause problems with too much wobble. Many have replaced these with solid mounts. But above all have fun and be safe!

 

[KCLOST]

Re: WOT Performance Question

Steering is tight, very little if any play... Motor mount is solid.. No rubber mounts.... Bolts are tight on transom, jack plate and motor to plate... Transom is solid as well. I'm confident, as I checked them all... Good advice however..<br />Thanks....

 

[Dhadley]

Re: WOT Performance Question

A water pressure gauge kit is about 1/2 the cost of 1 piston.<br /><br />Food for thought..............

 

[KCLOST]

Re: WOT Performance Question

DHadley,<br /><br />Do you have a part# for the kit I need. Gauge, tubing, wiring, etc...?