SET BACK CHANGE TESTING RESULTS?? KINDA

[FLYING BUTCHER]

With all this talk of closer being better on set back (thanks to Randy for parts) I thought I would try it. It has been raining here EVERYDAY!!!! for well oveR 6 weeks!!! Had to drive 60 miles to find a back portion of the river where I could run. Even then it was rainging like hell. Here is my set up 2003 20" 280. With the 14 1/2" set back I could trim her so high I couldn't see the water over the windshield. I ran the jackplate as high as it would go and had the motor so high on the plate I could only have 4 bolts holding it to the plate. I always overtrimmed boat until I was flying then when she got light I would trim her down. When I put the smaller set back on it sure looked like the engine was sitting higher (this is where you are supposed to measure prop shaft!!). Took her out in the rain yesterday. First thing is the engine got hot, shut her down and lowered the jackplate. Thank God I had just started. Boat never did get light but I didn't expect it to. Before no matter how high I ran the jaackplate I always had 20-25 water pressure. I got her to 85 with 18 water pressure and she blew out!!! Black and blue leg and a little brown in the shorts!! I lowered the plate as low as it woud go but it was raining so hard I couldn't find sweet spot. Came home and NOW MEASURED the propshaft. The new plate had the engine sitting over an inch higher that the longer set back. Reset everything and if it ever stops rainging I will try her again. Very odd feeling not having the front end coming way up and boat getting real light. I am running the boat full but still need to have a few more runs. More to come later

 

[GPI Racing]

Bill,

Your going to need a height that is 1/4 to 3/8" below the same setting that you were at the long setting. The effective swing is more pronounced at a long set back and as your nose went up your gearcase went down. Now closer to the transom the effect is less so you'll need to be lower to start with. The gearcase running position will be the same even though you are lower using a straight edge. At 1" higher than you tested you effectively were 1 1/2 to 1 3/4" higher than your original set up.

Randy

 

[catfish123]

Please keep the information coming.......although I only have a 225X on mine I am tempted to try less setback. How much setback do you have now that you have shortened it up?? Thanks.

 

[Stace]

YES keep it comin' I've gone from 14.5" to 11.5" and so far love the diff. in holeshot. Was still working on speed runs but someone added Viagra to the water here in MI. :evil: Stace

 

[catfish123]

Stace........what boat/motor combination are you running? Thanks

 

[Stace]

96 XB 2003 , 225 PM Stace

 

[FLYING BUTCHER]

MORE TESTING

Put on a CLEAN pair of underwear!!!! set the propshaft 1/4" below pad and went back to the river this afternoon. Before I just read Randy's post. Guys when I tell you I am running loaded here is what I mean. Full tank of gas, trolling motor, all six of the front storage trays are full of fishing lures, two bucket seats, one fishing seat, one pedstal and stand up seat, three batteries, charger, extra prop, and both rear compartment FULL of tackle and rain geat etc. Anyway took her out again!!! Still feels strange not feeling the nose of the boat come way out of the water. Fells like I am running flat BUT (perhaps because of blowout yesterday) she feels real light. When I overtrim her now mother really seems to bring the nose up (not as high) but up a whole lot faster than ever before. Little pucker factor and trim her back down again. If I overtrim it it really feels like it is out of control. Well now for the good news!! THAT RANDY BOY KNOWS WHAT HE SPEAKETH OF!! When she is running flat (believe me I have absoultly no clue why) the engine turned 500!!!! more rpm!!! Like I said I have no clue where the extra rpm came from. Running unlimited ECM and everyhting else stock 280 turning 8100 with 28ET 99 mph. Maybe a little more there but I need more time at the wheel with this different set up. So different than the big set back. I am not sure how much power is used when pushing the entire boat out of the water then trimming down but I can relate to best mph I ever ran at the drags is when I didn't trim her out all the way and just found the sweet spot as I went down the track. Well ther you go boys longer isn't always better. I will put the engine a little lower and run her again sometime soon. My two cents

 

[jimmyb]

butcher, what length setback are you running now???

 

[GPI Racing]

Bill,

Now if you like it so far.....imagine how it will be when totally dialed. Usually your at 85-90% on the first try. Once you get the feel for the new things the boat is telling you you'll really like the whole package. The extra RPM is not having the gearcase bury when your trimmed out. The old set up would dive the gearcase as the nose went up, your new set up doesn't do that near as much. This is why I've been so one sided on my set up suggestions. The overall package gets better with the CG closer together.

Randy

 

[John Richied]

Sounds like you are having too much fun… “She blew out!!! Black and blue leg .

We have been brainwashed over the years with the idea that running more setback puts the prop in cleaner water.

Be safe Butch!

 

[2fast4mom]

There was also a "power argument" regarding setback. The rule of thumb being that the less power, the more setback required, up to some who-knows point. A leverage, load-carrying thing.

With the power at hand on the types of motors we have on this thread, the "power" factor should mean that this is one less variable to consider.

My 2003 began life with a 13" setback on a 225 promax SS. That was back when I couldn't drive it. I met another, experienced owner at Clear Lake with my boat in September of 2001. He could drive it faster than I could, but had lots of trouble over 80 and suggested we go to 14.5".

At that point, the boat seemed MUCH easier to drive. But maybe I was just learning how? Hard to know.

If you listen to the indoctrination of the bassboat mainstream on this topic, the "law" reads that more setback will allow you to carry a heavier load faster, with some sacrifice to holeshot.

If you think for yourself and consider the physics at work, as has been pointed out, it seems this "law" does not apply equally across the board. Especially with Allison hulls and the bottom features they have--many of which are patented. Some of which had the intended benefit of getting the boat up with less power. Darris and his efficiency thing.

What I'm hearing lately is, "more power...less pad lip...less setback." So far, the guys trying this have had impressive results. I'm hoping to do some of my own experimentation with setbacks & such in 2006.

 

[chad202]

Randy wrote:

The extra RPM is not having the gearcase bury when your trimmed out. The old set up would dive the gearcase as the nose went up, your new set up doesn't do that near as much

I need help with this. If you hit the trim switch and the nose rises, that tells me the propshaft stayed parrallel to the water and it still has good bite or leverage to lift the bow? Example: if you support the motor on the trailer so it couldn't move but undo all the straps holding the boat down, then hit the trim button, if the trim was strong enough, it would lift the boat? So as long as you bump the trim and the nose responds, doesnt this mean the propshaft is still parrallel. Now if you bump the trim and the nose doesn't rise, now you diving the gearcase.
Also, if with 14" of setback, you're at 1/4" above and with 10" you're at 1/4", if this puts the lu at the same height when running, should't one have to trim more because the leverage of bite on the water is the same but now with the motor closer, the fulcrum is further up.
If you were overtrimming with the 14" and not with the closer JP, why the more rpms now. I thought overtrimming ment rpms went up but no speed? I get more and more confused everyday. :lol:

 

[hack02]

I ran the numbers on the prop calc. ,added 1 inch for a cupped prop like it said , and it says 17% slip at 8100 and 99 mph. Thats alot of slip. Did I calculate it correctly?

 

[CDave]

I come up with 13.8% slip. + 1 pitch = 16.77

http://www.boatramp.com/prop_applet/PropAnalyzerAppletG.html

Seems high slip but he was runnin' a heavy load.

 

[GPI Racing]

Chad, Hack and CDave.

Slip numbers are irrelivant. Unless you know the EXACT pitch of the prop and not some number stamped on it, the slip calculator is worthless. The new merc props are 2 inches plus bigger than stamped. Some props are on the low side. Also what part of the prop is doing the work and what pitch is that part of the blade. The next thing guys get caught up in is that they want the smallest slip they can get. Slip is not bad. It is thrust. You must have slip to have forward motion. If an airplane had 5% slip it would fall out of the sky. Slip is reletive to the weight and drag of the object compared to the horsepower doing the work. More power/less weight = less slip required. Bill's boat is quite heavy the way he ran it. He would need at least 12% true slip just to move it. A 1000lb F1 boat has 10% so why would a 2000lb bass boat be any better.

As for the angle of attack. Think this way: when your on a teeter-totter back in the playground when one side goes up the other goes down. This is the same effect the gearcase has behind the boat. The farther back you go the more this happens. Your bow doesn't just go up and the gearcase stays put. The gearcase can't support that much weight unless Bill was going 135. So as the nose goes up the gearcase buries itself a little. Think about that...your bow goes up but the rear of the pad is in the same spot. If the gearcase was unmoved the back of the pad would be out of the water. This effect is lessened as you get closer to the boat. Because his gearcase is way higher (effectively) his RPM went up. Granted he needs to optimise the whole thing, think of the teeter-totter effect when you look at your total setup. Imagine one kid out on the end (the bow of the boat) and the other sliding his way toward the center. The closer he gets to the pivot point the less up and down motion he experiences.

Back to the slip thing. I have pitch gauges and the like, you'd be surprised how far some props are from what they are 'stamped". Different trim angles move the center of pressure across the blade and the faster a prop turns centrifical force moves the water out toward the tips. In 25 years of experimenting and learning what works on props and what doesn't I have found that it really is not a new science. The "black art" is understanding what works and why, then sticking with the basics.

Randy

 

[chad202]

This is all good stuff. If the gearcase is at the same position when running, where the 500 rpms come from? Is it because he had to trim more to get the lift?

 

[GotMyAlly]

Very interesting for sure. I think I'm gonna move mine in and try it in the next week or two. Since I have the adjustable plate, it'll only take a few minutes to move it in. It'll be interesting to see if the 225 can run with less setback like the 280 apparently can or if that HP breaking point is somewhere between 225 and 280.

Any other handling differences you noticed with less setback other than more responsive trim?

 

[GPI Racing]

Chad,

It is very important that you understand that the gearcase and prop are NOT at the same height or attitude when you trim and the bow comes up. Also watch your motor just sitting on the trailer and you'll see a ton of height change just trimming it in your driveway. Draw a picture of your boat and motor from the side and then pivot it on the bottom corner of the pad. You'll see the change from the engine and it's height. Compounding this is the change that the engine does when trimming. That is why I hang over the rear of the boat to observe the gearcase when on the water.

Too many variables right!! :?

Randy

 

[GotMyAlly]

I sure would have thought less setback would have hurt the load carrying abilities...but sounds like Flying Butcher had a pretty good load in the boat so it sound like that may not be the case.

 

[catfish123]

Neal, I'm really glad you are going to try this because your boat/motor, are the same as mine. I am all ready to order different spacers for my jackplate but I think I'll hold off to hear your results............and besides, my wife refuses to hang over the back of my boat at WOT to observe the gearcase in the water..............LOL............seriously though, I'm really interested in this whole topic. Let me know how you make out with it.