catfish123
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10-4..................back door..................LOL
Effective setback on short-shaft motors
- Thread starter 2fast4mom
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one-fast-one
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I like all the technical post :? :? , but Baidbait's good common sense method seems to be best in setting up an allison :lol: :lol: :lol:
Later Dennis
Later Dennis
froggy
Active Member
Hey,
Old BadBait may just be onto something.
JR-I run 8.5" setback and the old GPS shows 68 MPH at 5000 rpm and 81 MPH at 6000 with a full fishin load. This is with a Merc 28 pitch Chopper II. I think that that is pretty efficient "cruisin" for an XB 2003 with short setback. Oh yah, I'm running .7" above the pad too---go figure.
froggy
Old BadBait may just be onto something.
JR-I run 8.5" setback and the old GPS shows 68 MPH at 5000 rpm and 81 MPH at 6000 with a full fishin load. This is with a Merc 28 pitch Chopper II. I think that that is pretty efficient "cruisin" for an XB 2003 with short setback. Oh yah, I'm running .7" above the pad too---go figure.
froggy
Froggy,
Do you have a short shaft or standard shaft motor? What hp?
Do you have a short shaft or standard shaft motor? What hp?
froggy
Active Member
Lou,
20" shaft, 280 HP with custom fuel curve and 8600 RPM limiter.
froggy
20" shaft, 280 HP with custom fuel curve and 8600 RPM limiter.
froggy
ziemer
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In order to determine the difference in "virtual" setback between a 20" and 15" we will need to measure the angle of the transom, in order to create a right triangle. From there we can figure the exact difference in setback between 20" and 15" at a specific propshaft height by comparing "like" triangles. The angle of the triangle would need to be figured like you would figure a slope on a roof. For example if the transom slopes rearward 2" for every vertical rise of 10" it would put the 15" mid 1" closer than the 20" mid at the point in which it bolts to the jackplate.
(All that makes sense in my head, so if it doesn't read clearly sorry. :grin: :grin: :grin: )
(All that makes sense in my head, so if it doesn't read clearly sorry. :grin: :grin: :grin: )
white03
Active Member
Hey RA,
I read with keen interest when you say "so the MOST I can run is 1/2" below"
After 9 years owning my Alli (and as a result of putting on a 280 and not getting the RPMs I thought I should), I just recently went out and tried to measure my prop shaft height. Seems to me that the best I can get is 1" below, given that the hydralic plate is all the way up and the set-back plate fixed in the position it is. By the way I have a 20" mid
Doesn't it makes sense that if 2 people have the same boat (XB2003) and the same motor (2.5 with sportmaster) and the same mid (15 or 20", pick-em) and the same set-back (14.5 inches - from the same hydralic jack plate and a setback plate that is adjusted using the same holes), that they should both have the same prop shaft height???
Can someone answer me this???
Bill
I read with keen interest when you say "so the MOST I can run is 1/2" below"
After 9 years owning my Alli (and as a result of putting on a 280 and not getting the RPMs I thought I should), I just recently went out and tried to measure my prop shaft height. Seems to me that the best I can get is 1" below, given that the hydralic plate is all the way up and the set-back plate fixed in the position it is. By the way I have a 20" mid
Doesn't it makes sense that if 2 people have the same boat (XB2003) and the same motor (2.5 with sportmaster) and the same mid (15 or 20", pick-em) and the same set-back (14.5 inches - from the same hydralic jack plate and a setback plate that is adjusted using the same holes), that they should both have the same prop shaft height???
Can someone answer me this???
Bill
Bill, if everything is equal between the two boats including the hole count where the motor is installed, they both should be real close, I would think. But there could be cumulative areas of uncertainty generated by manufacturing tolerances in the hole placement in the transom, brackets, plate, etc. that could add up to make some net difference.
If the highest you can get is 1/2" below the pad, or 1" below the pad, boy are you missing out on the top end. You're dragging case in the water. I have seen dramatic increases in top speed with my 03 running "even" with the pad; 1/4" below will be faster than 1/2" below too. Many run above the pad, but with my current setup, above the pad is NG.
Ziemer, the right triangle analogy is a good one.
Since all right triangles are similar (in geometric terminology), the triangle's base will be the same for a given amount of setback.
Once the angle of the XB-2003's transom is determined, this angle also will remain a constant.
The differences in the triangle with 20" and 15" motors will be the lengths of the vertical leg and the hypotenuse.
I suggest we use the forward edge of the propeller hub for the purpose of establishing a standard of setback measurement, instead of the nosecone tip, since the latter will be all over the map. Alternatively, the end of the propshaft could be used--this might be better. What do you think? We need to agree on a standard measuring point for the lower unit.
Let's agree that we call the triangle base measured from the center of the pad lip to the forward edge of the prop hub. Or propshaft tip. What say ye?
Once the above is decided, with geometry we can "extrapolate" setbacks for SS and standard-shaft motors at the same propshaft height (even with the pad, let's say).
Now, can someone come back with an accurate transom angle measurement for an XB-2003?
If the highest you can get is 1/2" below the pad, or 1" below the pad, boy are you missing out on the top end. You're dragging case in the water. I have seen dramatic increases in top speed with my 03 running "even" with the pad; 1/4" below will be faster than 1/2" below too. Many run above the pad, but with my current setup, above the pad is NG.
Ziemer, the right triangle analogy is a good one.
Since all right triangles are similar (in geometric terminology), the triangle's base will be the same for a given amount of setback.
Once the angle of the XB-2003's transom is determined, this angle also will remain a constant.
The differences in the triangle with 20" and 15" motors will be the lengths of the vertical leg and the hypotenuse.
I suggest we use the forward edge of the propeller hub for the purpose of establishing a standard of setback measurement, instead of the nosecone tip, since the latter will be all over the map. Alternatively, the end of the propshaft could be used--this might be better. What do you think? We need to agree on a standard measuring point for the lower unit.
Let's agree that we call the triangle base measured from the center of the pad lip to the forward edge of the prop hub. Or propshaft tip. What say ye?
Once the above is decided, with geometry we can "extrapolate" setbacks for SS and standard-shaft motors at the same propshaft height (even with the pad, let's say).
Now, can someone come back with an accurate transom angle measurement for an XB-2003?
white03
Active Member
I'm about 1" below, as best I can measure it. I used the method Kevin posted in Allison Owners stuff,....but the laser beam hits the rear most roller before it gets to the pad...so I can't be exactly sure of the measurement.
I agree I am missing a lot of rpms and speed. What got me to wondering is when I started running the same pitch prop as others with a 280 on an Xb2003 and I can't spin it up as high on RPMs...so something is wrong.
My thought is I need to go up on the mounting holes of the fixed set-back plate. But before I go to all that trouble I wanted to see other setups of guys that can do a good measurement.
Sometimes it's hard to understand what someone writes (me included) so I'm going to take pics tonight and see if I can get others with a 2.5, 20" mid and 14.5" setback and XB2003 to do the same.
I agree I am missing a lot of rpms and speed. What got me to wondering is when I started running the same pitch prop as others with a 280 on an Xb2003 and I can't spin it up as high on RPMs...so something is wrong.
My thought is I need to go up on the mounting holes of the fixed set-back plate. But before I go to all that trouble I wanted to see other setups of guys that can do a good measurement.
Sometimes it's hard to understand what someone writes (me included) so I'm going to take pics tonight and see if I can get others with a 2.5, 20" mid and 14.5" setback and XB2003 to do the same.
RedAllison
Well-Known Member
White yes it sounds like your motor is bolted low. I only have one more hole left on the engine mounting bracket. Sounds like yours might be all the way down or in the top two holes anyway.
Running a ProSport heavily loaded with above pad settings and a stock lip will make it awfully prone to swapping ends wont it? When Glenn Reynolds run my boat he got nearly 94 out of it (empty, just him but all the seats were in and the trolling motor was on) and when I ran 91 with Todd Bucknall and EVERYDAMNED thing including the sink was in it it was just as it sits now and I don't remember being all the way up either. I know when I was running 91 it seemed like it REALLY wanted to let go, I'm afraid running any higher while still loaded for a tournament would just make it want to sit down and we know what follows that when running over 90!!! :shock:
I might raise it that final notch but who knows,
RA
Running a ProSport heavily loaded with above pad settings and a stock lip will make it awfully prone to swapping ends wont it? When Glenn Reynolds run my boat he got nearly 94 out of it (empty, just him but all the seats were in and the trolling motor was on) and when I ran 91 with Todd Bucknall and EVERYDAMNED thing including the sink was in it it was just as it sits now and I don't remember being all the way up either. I know when I was running 91 it seemed like it REALLY wanted to let go, I'm afraid running any higher while still loaded for a tournament would just make it want to sit down and we know what follows that when running over 90!!! :shock:
I might raise it that final notch but who knows,
RA
cj707
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setback
Correct me if I'm wrong. Bolting a lighter motor 15" off the transom has the same effect as a heavy motor close to the transom. As far as leverage goes. To get the full benefit of a light motor, wouldn't you want it as close to the transom as possible? It sure improves holeshot and handling in rough water and top end! Not to mention the attitude of the boat at idle and at rest. If the hulls are so "efficient", why does Darris bolt an aluminum surf board on the new boats? Or hang the motor 15" off the older hulls?
Correct me if I'm wrong. Bolting a lighter motor 15" off the transom has the same effect as a heavy motor close to the transom. As far as leverage goes. To get the full benefit of a light motor, wouldn't you want it as close to the transom as possible? It sure improves holeshot and handling in rough water and top end! Not to mention the attitude of the boat at idle and at rest. If the hulls are so "efficient", why does Darris bolt an aluminum surf board on the new boats? Or hang the motor 15" off the older hulls?
GotMyAlly
Well-Known Member
RA....I sure woulda thought you coulda got more than 94 outta yours running light. I've ran mine 94 by myself loaded to fish and that was into the limiter.RedAllison said:
Lars when I saw the "aluminum surfboard" :shock: on the 21 footer, I thought the same thing. What is this thing and why couldn't or wouldn't it be just formed into the hull of the boat in the first place?
I don't know if it was an afterthought or not, but it IS patented....and usually the expense of patenting something is only justified if you believe that you (or more importantly, others) stand to make a lot of money off it.
About the weight thing, yes, but how much weight are we saving with the SS compared to the standard? The offshore-style single-ram bracket has to add some weight vs. the weight you lose from a smaller midsection...and with the SS, your "lever arm" is shorter from the point where the thrust is applied to the attachment point...right?
I don't know if it was an afterthought or not, but it IS patented....and usually the expense of patenting something is only justified if you believe that you (or more importantly, others) stand to make a lot of money off it.
About the weight thing, yes, but how much weight are we saving with the SS compared to the standard? The offshore-style single-ram bracket has to add some weight vs. the weight you lose from a smaller midsection...and with the SS, your "lever arm" is shorter from the point where the thrust is applied to the attachment point...right?
B
BP
Guest
None, the SS weighs more than a 20"2fast4mom said:
OK, wait a minute. I'm thinking out loud back to the "lever arm" concept.
If we assume the load being lifted by the "lever" is the boat, and the midsection length to the propshaft is the "lever", then the "fulcrum" must be....the WATER.
And since the force required to lift the boat is a function of the distance from the force (propeller) to the fulcrum (water), the length of the midsection should have NO EFFECT.
Prove that I am wrong. if I am. What if the midsection was five feet tall and had a bracket that came down low to attach to the transom? You are still going to be levering the boat up from water based on the position of that lower unit relative to the bottom of the boat. Right?
Wrong?
I must be wrong. There are more forces at work in the physics of this; I just can't visualize them right now.
If we assume the load being lifted by the "lever" is the boat, and the midsection length to the propshaft is the "lever", then the "fulcrum" must be....the WATER.
And since the force required to lift the boat is a function of the distance from the force (propeller) to the fulcrum (water), the length of the midsection should have NO EFFECT.
Prove that I am wrong. if I am. What if the midsection was five feet tall and had a bracket that came down low to attach to the transom? You are still going to be levering the boat up from water based on the position of that lower unit relative to the bottom of the boat. Right?
Wrong?
I must be wrong. There are more forces at work in the physics of this; I just can't visualize them right now.
J
John Richied
Guest
The only reason we would need to know exactly where our propshaft was in relation to the pad and exact setback was so that we could set our boats up identically.
If we were going to try to do that we would need to run the same prop, same load, same balance, have our batteries mounted in the same place, same gearcase, midsection, jackplate, etc… just a lot of variables.
If you want to get close that shouldn’t be a problem as long as both guys measure their propshaft height the same way. Like Bill (white03) said I found using the laser beam method it hits the rear roller on the trailer.
This method worked for me and I know others use it…
First the surface (cement flooring) from the pad area to the rear of the propshaft has to be a level surface. Check this with a level if the ground isn’t level then this measurement is not accurate.
Next level the pad of the boat. Put a level on the bottom of the pad just in front of the lip (from the second trailer roller to the rear of the pad, but not on the lip). Level the pad by adjusting the trailer jack wheel up or down as needed (watch your head on the trailer).
Then take the prop off and lay a level on your propshaft. Bump the trim up or down as needed. Now is a good time to mark you trim gauge for even/neutral trim.
Now measure the pad to the ground (an inch away from the lip to the ground.) Say its 12 5/8”
Then measure from the center of the propshaft to the ground. Adjust your jackplate up or down as needed so it’s the same as your pad measurement (say it’s 12 5/8”) to the ground measurement. Now you have the propshaft even with the pad, mark your jackplate or if you have a hydraulic jackplate mark the gauge.
When you find where even with the pad and the trim is level (neutral) make some marks on your jackplate and trim gauge and it’s a good reference point when trying new props, and just knowing where you are at on the fly.
Now lets deal with IF the 15” short-shaft is 5/8” closer with the 2”’s of built in setback then a 20” midsection. Is it interesting to know, yeah; will it make a difference in the performance of your 20” or 15” when you are comparing setback? Well I seriously doubt it. Originally and still today they say don’t add 2”’s to your setback calculation if you run a short shaft. So if you have a 10” setback plate with a short-shaft, then call it 10” of setback… 1” difference in setback won’t mean beans, so don’t sweat 5/8 of an inch of setback.
If we were going to try to do that we would need to run the same prop, same load, same balance, have our batteries mounted in the same place, same gearcase, midsection, jackplate, etc… just a lot of variables.
If you want to get close that shouldn’t be a problem as long as both guys measure their propshaft height the same way. Like Bill (white03) said I found using the laser beam method it hits the rear roller on the trailer.
This method worked for me and I know others use it…
First the surface (cement flooring) from the pad area to the rear of the propshaft has to be a level surface. Check this with a level if the ground isn’t level then this measurement is not accurate.
Next level the pad of the boat. Put a level on the bottom of the pad just in front of the lip (from the second trailer roller to the rear of the pad, but not on the lip). Level the pad by adjusting the trailer jack wheel up or down as needed (watch your head on the trailer).
Then take the prop off and lay a level on your propshaft. Bump the trim up or down as needed. Now is a good time to mark you trim gauge for even/neutral trim.
Now measure the pad to the ground (an inch away from the lip to the ground.) Say its 12 5/8”
Then measure from the center of the propshaft to the ground. Adjust your jackplate up or down as needed so it’s the same as your pad measurement (say it’s 12 5/8”) to the ground measurement. Now you have the propshaft even with the pad, mark your jackplate or if you have a hydraulic jackplate mark the gauge.
When you find where even with the pad and the trim is level (neutral) make some marks on your jackplate and trim gauge and it’s a good reference point when trying new props, and just knowing where you are at on the fly.
Now lets deal with IF the 15” short-shaft is 5/8” closer with the 2”’s of built in setback then a 20” midsection. Is it interesting to know, yeah; will it make a difference in the performance of your 20” or 15” when you are comparing setback? Well I seriously doubt it. Originally and still today they say don’t add 2”’s to your setback calculation if you run a short shaft. So if you have a 10” setback plate with a short-shaft, then call it 10” of setback… 1” difference in setback won’t mean beans, so don’t sweat 5/8 of an inch of setback.
RedAllison
Well-Known Member
Neal I wouldn't call what Glenn did "empty" as in strip it down and go for triple digit "empty". It still had the trolling motor on it and the back seat was in it. Darris and Glenn both told me that surprisingly having the top half of the back seat in the cockpit will cost you 1-1.5mph. (Obviously not weight, instead it effects air evacuation from the cockpit.)
Being yours is a centersteer it SHOULD run a spot or two better, some may argue that but I just feel that the boat balances better and will react more positively to the driver being in the center. The load I am talking about was VERY heavy (my 91). I literally had 18 rods and reels in the box and under the front deck (I took them out and counted them, couldn't believe I had that many) over 100#s of tackle, I had lawn chairs, and more food and drinks than you can imagine. Plus like I said, that was at over 1K ft elevation in June heat and it was raining so the humidity was off the chart.
Neal once we get the liquid steering in mine we'll take em both too Pickwick (hell we might even go too Clifton and run on that actual world record stretch of water) and we'll do the "empty em and run from a little battery" thing and see just what we can get out of them.
LLDoggg I think you is thinkin to hard! The fulcrum is the pad edge on the water is it not? As for the SS being "faster" my understanding was a theoretically stronger motor since 5" of less driveshaft is being turned (less driveline power loss) and the shorter leverage affect of having the powerhead 5"s lower than the 20". That "should" make for more quickness and better balance. But on lake boats and motors less than outright race engines, I think we are kiddin our selves. They are just "neater" and have that certain "that" about them (the SS').
RA
Being yours is a centersteer it SHOULD run a spot or two better, some may argue that but I just feel that the boat balances better and will react more positively to the driver being in the center. The load I am talking about was VERY heavy (my 91). I literally had 18 rods and reels in the box and under the front deck (I took them out and counted them, couldn't believe I had that many) over 100#s of tackle, I had lawn chairs, and more food and drinks than you can imagine. Plus like I said, that was at over 1K ft elevation in June heat and it was raining so the humidity was off the chart.
Neal once we get the liquid steering in mine we'll take em both too Pickwick (hell we might even go too Clifton and run on that actual world record stretch of water) and we'll do the "empty em and run from a little battery" thing and see just what we can get out of them.
LLDoggg I think you is thinkin to hard! The fulcrum is the pad edge on the water is it not? As for the SS being "faster" my understanding was a theoretically stronger motor since 5" of less driveshaft is being turned (less driveline power loss) and the shorter leverage affect of having the powerhead 5"s lower than the 20". That "should" make for more quickness and better balance. But on lake boats and motors less than outright race engines, I think we are kiddin our selves. They are just "neater" and have that certain "that" about them (the SS').
RA
cj707
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Lou, what I was talking about is the fact that were not supposed to be able to run a 3 ltr. motor on our hulls. Its ok to hang a 375 pound 2.5 15" off the back, but a 500 lb. 250 3" off won't work? I'm not talking ss vs. 20" mid. I'm talking about the argument that we need to run a light motor on the 20' hulls. What's the diff between 375 lbs 15" off, and 500 lbs 3" off? Yaamean thun
Red I like the SS motors becuz they look cooler and sound meaner.
The point is well-taken Lars and I am surprised to point of being shocked :shock: that ol' uncle Bill's XB-2003 gets out of the hole as fast as it does, has a high topend and from what have seen, there's really no tradeoff. That 250XS even with all the weight it's "not supposed to have" it works great. Well, except when he tries to slow down :lol: and he's workin on that part. :mrgreen:
I wish he would pull that rig to TN and show it off at the rally.
The point is well-taken Lars and I am surprised to point of being shocked :shock: that ol' uncle Bill's XB-2003 gets out of the hole as fast as it does, has a high topend and from what have seen, there's really no tradeoff. That 250XS even with all the weight it's "not supposed to have" it works great. Well, except when he tries to slow down :lol: and he's workin on that part. :mrgreen:
I wish he would pull that rig to TN and show it off at the rally.
RedAllison
Well-Known Member
YEP LLDoggg lookin and soundin meaner is that "that"!!!
RA
RA