Not a trick question - top end speed

[2fast4mom]

OK, let's hear it from the professionals, experienced, or just the opinionated...

You're at a given setup and WOT going for the big number. You've seen this number before, last year, but now lacking it by 1-2 mph (or more) this year no matter what. Elevation and temperature and humidity are about the same as then.

You trim up as the boat asks for more. Finally you get to that wonderful spot where the boat is just beginning to lean to starboard--indication enough for me that's she's looking for a place to spit me out. Sometimes I can swing my left leg over to the left and it will go back to level flight, but I don't trim up anymore regardless.

Now to the question:

Is the best way to increase top end from here any of the following? Support your answer with the physics or observations that lead you to that conclusion.

1. Increase motor height. Will lessen drag.

2. Decrease motor height. You need more prop and skeg in the water.

3. Adjust setback. Which way?

4. Use a larger diameter prop. Allows for propshaft height even with the pad while maintaining bite.

5. Any other answer.

Any takers?

 

[chad202]

What I have found with the 03 and the lean your talking about is the faster you go the ballast needs change cause of the wind pushing down on the drivers side turtle shell in side the console. The weight that it took to balance the boat at 100 was less than it took at 103 which was less then it took at 105 and less at 107. The faster I went the more ballast I needed or I just had to move the ballast further towards the front.

 

[xb03fs]

I can agree with faster you go more ballast to the left needed. Also moving up in small increments like 1/8 or less at a time. The higher I have went typically the less trim needed.

Also sometimes just bumping the trim down once or twice will gain speed once the lean is achieved I think cause one up on the pad and air is packed, bumping the trim down improves aerodynamics netting a mph or two

 

[ziemer]

Time for a diet plan?

OK, let's hear it from the professionals, experienced, or just the opinionated...

You're at a given setup and WOT going for the big number. You've seen this number before, last year, but now lacking it by 1-2 mph (or more) this year no matter what. Elevation and temperature and humidity are about the same as then.

You trim up as the boat asks for more. Finally you get to that wonderful spot where the boat is just beginning to lean to starboard--indication enough for me that's she's looking for a place to spit me out. Sometimes I can swing my left leg over to the left and it will go back to level flight, but I don't trim up anymore regardless.

Now to the question:

Is the best way to increase top end from here any of the following? Support your answer with the physics or observations that lead you to that conclusion.

1. Increase motor height. Will lessen drag.

2. Decrease motor height. You need more prop and skeg in the water.

3. Adjust setback. Which way?

4. Use a larger diameter prop. Allows for propshaft height even with the pad while maintaining bite.

5. Any other answer.

Any takers?

 

[Alli-drenaline Rush]

I know next to nothing, but being the opinionated sort, and always willing to offer bravo sierra for the entertainment value, I'll say that you might consider re-building your motor..... might she just be tired from a year of running the river?

 

[Alli-drenaline Rush]

Alternatively, the gas that you're running now might not have the same energy content on a BTU per gallon basis as that which you ran in the past. Since power required increases with the square of changes in speed, 2 mph on the top end requires 4% more power. Easy to see changes in fuel formulation causing a 4% change. Summer vs winter gasoline blends, regional blend differences, fuel grade differences, % ethanol in the mix.... all could factor in here.

 

[rmills280]

I get small differences on back to back runs on diff parts of the river always figured it was current and wind.

 

[Bobalouie]

If your boat is responding well to trim, then raise the motor 1/8" and try again. If your running attitude is correct, there is no need to move the Jackplate, but if you were going to move it for more speed, you would increase setback, which in turn would allow for even more motor height due to being in cleaner water.

 

[GotMyAlly]

There's so many variables, I always accepted that repeating a number within 1-2 mph was an acceptable variance. Weather, water temp, fuel, weight, what I had for breakfast.....all change the equation.

Some of those you can control, to a degree. Others, not so much, without getting really scientific about it.

 

[Jr in Jax]

I agree that you might need to freshen your motor up. I was also able to buy non ethanol 93 octane at Lake Chatuge up there. My boat at 1000 MSL ran as good as it did at SL here in Jax. I can not buy 93 non-ethanol here in Jax or I would.

 

[ssv1761982]

I agree that you might need to freshen your motor up. I was also able to buy non ethanol 93 octane at Lake Chatuge up there. My boat at 1000 MSL ran as good as it did at SL here in Jax. I can not buy 93 non-ethanol here in Jax or I would.

What does that mean?

Fuel quality does make a difference. Trouble is that we can't really control it.

 

[biller31]

SL = Sea level.
You're on a current reservoir. Could be simple.

 

[whipper]

I would Q the lean. Q = question :] The fastest Ive ran was with no lean. If your leaning thats not going to help top speed since your creating more drag on the side your leaning. Could be motor to high not creating enough thrust to straighten you out. A little ballast re-arrangement. One more bump may have been needed? i've always used the rpm mph trick for max speed at any shaft hight providing the water is good enough and long enough to concentrate intensely enough. Ill trim up to reg speed almost to max it would seem. Then one bump wait one bump wait. when I do a bump and I see the gps loose so much as a point of a mph and or the tach goes up and zero mph Ill know theres no more. Every one bump should always be some sort of gain. When the gains start getting real small like .2 then that might be were I stop. With a helmet and safety boat near by and i feel like I dont care what happens im going for it ill always go till the tach goes up and mph looses. Then I will do the same thing over and over each time at different prop shaft heights. But no more than 1/4 above for me. Ive had more sketchy moments the higher i go past 1/2 above so I dont bother even trying it any more because there is actually a speed lose with most props any higher.

i know its unorthodox but after a pad repair i had to much material on one side. I could feel it. i was leaning and never leaned before I mucked with it. So that got me thinking and thats a bad thing some times as im very obsessive!! I took some emery cloth to the lake and a mask. I ditched 10 lbs of ballast then starting sanding on the one side little by little and each time taking a run until I had no lean. Now Ive center steered the seat base side ways and was able to loose another 20 lbs of ballast and she flys level as can be with no hands at 90 ish. Ive ran a 97 and a 98 once . Now I cant get past 95 it seems when I think everythings the same? Maybe the water is thick with algae or somthing creating more drag?? Maybe the stars aren't in line like they were those days. Or maybe the motor has 1000+ hours on her and she is just saying enough already.:big grin

If your getting around 1-2 mph of were you had her before I would be happy with that a year latter. The prop might not be as tuned as it was also. 1-2 mph could only be a bump away also if a bump never lost you speed yet?
ive accidently bumped once past the loss of speed point. Then seeing the bow dip a smidgen took 3 back. my spin outs have been broken prop,bad wave,over trimmed with a fat *** passenger and motor to high, or slowing down to fast a few times. Solo running in good water even with the pad not yet.:help

 

[2fast4mom]

Whipper is on to something and makes excellent points. I've had some experiences this week with another Allison (95 GSE) that we're counter intuitive to what I'd thought.

First though, the boat of this topic is a 1999 SS2000 comp running a stock 260. The fresh SM lower was destroyed last year, so I have a spare on --a 1996 "rode hard" 15" SM with the front bottom corner radiused by the former owner, possibly due to damage. This alone could account for the diff.

Secondly, the motor is 1/4" to 1/2" higher than last year. May lower it a tiny bit...Especially because of what I saw this week in the GSE,

A buddy of mine and I were doing long haul, fast river running (92 mile round trip). 200XS 15", 11" setback. Hydraulic jack plate with gauge and marks.

I usually run the GSE 1/4" to 1/2" below the pad. However with he and I up front it just wasn't getting it. I tried an experiment. Dropped the jack plate to where is was likely at least 1" below and all of a sudden we picked up 3 Mph on the big end!

Ziemer re the diet issue, the SS has always run faster on the top end with 2-3 people in the boat...so that ain't it...never hurts to lose a little though.

But now I've got a new damn gremlin in the 260. She intermittently shuts down at WOT approaching 100, then fails to idle just keeps stalling the lights up again fine.

I already replaced the whole stinking wiring harness on advice it could be the ignition switch. I don't know for sure but don't think this is a fuel issue. Brand new filters and full tank. Very intermittent problem which sucks.
Ideas on this problem anyone?

One thing for sure, good thing my setup is forgiving...with that damn motor shutting down at 98mph I'm lucky not to be taking a swim in this SS.

 

[Jr in Jax]

When my ECM went bad it did the same thing, shutting off power to the pump.
I switched to Tony's ACU
JR

 

[whipper]

When my ECM went bad it did the same thing, shutting off power to the pump.
I switched to Tony's ACU
JR

JR We did this about a month apart I recall calling you all the time trying to set mine up. :beer: That was years ago. I love Tonys ACU. Deep 6,s the tps also ,so theres again one less thing to go wrong. Once there dialed there dialed. Never had an issue pretty much ever again once i started using it also. i set mine up to feed more fuel not less. I may not get the best milage compared to some stock ecus but i have fuel were I want it buy choise.

2fast thats a scary thing to have in the back of your mind running knowing at around 100 somthing might shut off!!:shock: Hope you get it figured out. Ill bet if called tony he would have a unit for you to try first then buy if ya liked it maybe? Doesn't hurt to ask.

 

[David Shook]

Yall need to slow that chit down somebody is gonna get hurt !!!!!!
Shook

 

[Dave Hensley]

Yall need to slow that chit down somebody is gonna get hurt !!!!!!
Shook

David are you racing at Jasper? Would like to catch up with you and prove I don't look anything like Jimmy!!

 

[racerx]

Hey Hensley bring that yellow banana to jasper river run I put it on it with a Grand Sport full of beer and gas...lol

 

[FlatOutAlly]

Hey Hensley bring that yellow banana to jasper river run I put it on it with a Grand Sport full of beer and gas...lol

Now that's funny right there. I thought that gs was running down pontoons in PA now??? :beating dead horse