uncle

[miketsouth]

What is a back-cut shoe?
You see, now i got a boat with a shoe. Never had one before. It was my first inclination to mess with all of it, Shoe, rideplate, loader, even though i was told to leave it alone.
Motor tuning issues and time have put that stuff on the back burner so i am leaving it alone.
I am rather curious though. I crawled up under it and looked and thought and speculated and wondered. Then i realised i would have to seek advice from all that would lend it.
Here is what i did. I put a 350sbc in a cheyenne clone P/F. :eek:
Nothing special, a little cam. It has an AT B ss impeller, Droop, wedge plates, a loader of some kind and a 5/8" shoe and a rideplate. All this stuff works together, i can see that.
It had a sprayed regular old 454 in it before and would do almost 100. I saw the videos, it was fast. I still, contrary to ALMOST everyones advice, put a SBC in it. I am really pleased with it.
The gentleman that set it up initially mentioned to me that it was mentioned to him to try a backcut shoe in it.
He had all kinds of regular shoes of varying heights and cuts. By inspecting them i found that the shoe and rideplate are sort of a unit, and have to be mated to the intake of the pump. No problem. Back burner for now. Get engine mixture right and then play with shoes and stuff.
I still wonder what a backcut shoe is. I searched and found an explaination including "adds lift" I can only speculate that the leading edge is above the bottom of the shoe.
From the little time i have had to run it my feeling is that the pump is rather loaded for much higher HP and speed than my SBC is going to produce even when running at its top performance level. Slows down suddenly when you cut the engine. It should coast, i think.
Any suggestions. Right now, it takes rough water beautifully and never unloads the pump. My bubbledeck had a Jetovator and really needed it. This P/F dont need an up/down articulating nozzle contrary to my prejudice. Cruises with a very nice attitude at all speeds (0-60+mph)...i would not trade any mph for the stable platform it now presently has. I still think it can go faster. It has FTN. I have two to play with and more if i want. A 3 and a 3.125.
All i really want to know is what a backcut shoe is. I have not put the time in it to gain the experience necessary to accurately report facts to those willing to lead me the right way .
Sorry for being so long, but i am really happy with the boat and want it to do the best it can with the SBC i put into it. Math works.
A SHORT POOR VIDEO (http://mywebpages.comcast.net/rodajet/Picklepax.wmv)
mikeT

[BigBlockBaja]

Hey Mike,
Sorry Its not related to your question, but do you have the same video you put a link to in you sig without the movie? The motor sounded awesome, then the "music" started. :D :D

[miketsouth]

what happened is that that is the only portion of the video that you can hear the motor in, and then it stopped. The rest of the videos shot, one could only hear the chase boat and wind.
I had two sequences of the hole shot. One with sound, but very short. I overlapped them at as close to the same boat position and attitude as i could. I could have use better music, yes.
mikeT

[BrendellaJet]

I will try to explain this...If I say something wrong, im sure I will be corrected...
The shoe is used to adjust the biting edge of the intake. It is adjusted with shims. The intake needs to be milled to allow the use of a shoe. If you can look at the existing shoe, you will see this biting edge, shaped like a horse shoe-almost-not sure if thats where the name comes from...whatever, its U shaped. The bottom side is where the back cut is done. , a concave cut sloping back from the biting edge towards the ride plate, down towards the ground(5/8 of an inch for example) provides some lift. If you can imagine this, you will see how it will provide lift, hopefully that makes sense. If not, Ill take a pic of mine for you to see...

[UBFJ #454]

The Cheyenne hulls and properly done splashes are great jetboat hulls. If the layup you have weighs on the order of 500 to 600 or so #'s, I think you'll be quite happy with your choice of a SBC if your target is to max out at 60 to 75 mph in recreational use.
Just a couple of bits of advice now that you have all the "Gagets" on the hull to "Play With" ... DON'T ... Until you've researched and fully understand what each item does, how each interacts with the others and the hull and, how changes of any one component will change the boats overall running characteristics. Then when you have a grip on all that, make only very small changes, one at a time to see if you are benefiting from the direction you are going: You never want to make multiple, large changes all at one for that could be Catastrophic and Very UnHealthy.
Remember the Cheyenne Hull is a true air entrapment design and with the wrong hardware setup (especially in the case o the ride plate angle) and/or windy conditions, you could FLY The BOAT ...
Just a few very general Safety Minded Thoughts for you to consider.

[miketsouth]

Originally posted by BEAR_454PE
The Cheyenne hulls and properly done splashes are great jetboat hulls. If the layup you have weighs on the order of 500 to 600 or so #'s, I think you'll be quite happy with your choice of a SBC if your target is to max out at 60 to 75 mph in recreational use.
Just a couple of bits of advice now that you have all the "Gagets" on the hull to "Play With" ... DON'T ... Until you've researched and fully understand what each item does, how each interacts with the others and the hull and, how changes of any one component will change the boats overall running characteristics. Then when you have a grip on all that, make only very small changes, one at a time to see if you are benefiting from the direction you are going: You never want to make multiple, large changes all at one for that could be Catastrophic and Very UnHealthy.
Remember the Cheyenne Hull is a true air entrapment design and with the wrong hardware setup (especially in the case o the ride plate angle) and/or windy conditions, you could FLY The BOAT ...
Just a few very general Safety Minded Thoughts for you to consider.
I believe that is the best advice that one could get. I have read your posts before, and you ALWAYS have safety as the #1 item.
Small changes. That seems to be the story. I was told this hull weighed about 450lbs. It does not flex, and seems very rigid and seaworthy.
I posted here because upon examining the parts, i knew i just did not understand the relations. Loader depth vs shoe. Shoe depth vs rideplate angle. Then there is jet angle (droop/wedge). I saw them all. The boat feels GREAT at about 35-40mph, my normal recreational cruising speed (i was tired of getting beat up by the shallow V of the bubbledeck).
It will do 30 at 2500rpm or so. So economical and smooth.
I am trying to get a feel for what goes on here. I believe i understand the pump itself and its limitations. I beleive i understand HP/Q and pump cut.
I do not understand the intake side very well, and IMHO that is where it is all at. I like to know what i am doing and why. I like to play it safe. That is the hardest part, because it is the other traffic on the waterway that will most likely get one in trouble.
The air entrapment part. I am warned and guided by many. The boat feels stable but i know not to try to turn much at speed with this hull. So far it is a real pleasure to drive. I have done a great deal of research on the relationship here, at Banderlog, and RJB and everywhere else. Lots of the stuff is geared for high speeds (above 70). I dont plan to go there. Just 70max, and that is if it will remain stable, like it is now.
Thanks. I hear words of wisdom. They ring like a bell (sort of like the truth in a courtroom)
mikeT

[miketsouth]

Originally posted by BrendellaJet
I will try to explain this...If I say something wrong, im sure I will be corrected...
The shoe is used to adjust the biting edge of the intake. It is adjusted with shims. The intake needs to be milled to allow the use of a shoe. If you can look at the existing shoe, you will see this biting edge, shaped like a horse shoe-almost-not sure if thats where the name comes from...whatever, its U shaped. The bottom side is where the back cut is done. , a concave cut sloping back from the biting edge towards the ride plate, down towards the ground(5/8 of an inch for example) provides some lift. If you can imagine this, you will see how it will provide lift, hopefully that makes sense. If not, Ill take a pic of mine for you to see...
So that means that the biting edge is now not at the lowest part of the shoe, i suppose. The only other thing i could think of is that the "U" was frowning rather than smiling, but it did not make sense. I can see the water passing the bottom of the shoe, being shot down and causing lift at speed.
mikeT

[Ken F]

>I can see the water passing the bottom of the shoe, being shot down and causing lift at speed.<
Yes, exactly. The biting edge is NOT the lowest part of the shoe. The lowest part is where the rideplate attaches at the rear, and pushes the rear of the boat upwards. 5-10 thousandsth can make quite a difference at high speed. Possibly you just need a thinner shoe, or less shim under the shoe. Possibly installing an intake pressure guage might be a good idea?
Bears advice is sound. Take it. Learn what you are doing back there before you start to monkey around, or take it to someone who knows. Be careful on gusty days, and heading into the wind. If you look at the bottom of your boat from the front, you will notice that the air is "funneled" into the tunnels, causing the air in the rear where the boat rides to be compressed, or entrapped. you will see that there is a pretty large volume of air taken in at the front, and funneled into a much smaller space as it moves to the rear.
Ken F

[miketsouth]

The tunnel or air compression effect must take place at some speed, where it becomes a force to be reconed with.
My limited experience indicates this speed to be somewhere around 60-70mph, depending on the attitude or "angle of attack" of the boat relative to the water.
The greatest advantage at speeds that i plan on taking the boat (40mph, +-10) seems to be that the boat is up on the sponsons (i guess that is what they are called) and seem to cut thru the chop.
The only similar experience that i have is the difference between two skis and one. I'm getting a little older now and two skis would injure me. Too much bounce and too much drag. I can use one ski on its edge (constantly turning) and cut thru some rather rough chop without shaking my (overgrown in places) self to pieces.
What has been indicated to me is that once the boat is up on the sponsons, it does not respond well to thrust vectoring. That is to say that the jet will be way off to one side and the boat will still be going rather straight.
If, while trying to turn too sharp, the back comes unglued from the water, it wil flip. Makes sense. Im not going to test this, but rathrer keep it in mind.
Another thing i have not had to negotiate is the unavoidable big wake. It is common sense to slow down, but i have wondered what happens, even at a very slow speed if one buries the sponson in the wake. The bubbledeck was very forgiving. It would take more than i could. Shake your retina's loose.
Thanks again.
mikeT

[UBFJ #454]

Mike -
One of the most critical things about the adjustable hardware you have on your Cheyenne is the Ride Plate Angle ... Too High (Too much up angle) and the nose can come up too high making the boat more like a kite. Until you've got a better handle on your total setup I'd limit the up angle to no more than something like 2 degrees, 2.5 max. and I'd check its angle EVERY TIME BEFORE I PUT IT IN THE WATER (@ the Shore, just before backing in). Note the angle I'm refering to is the angle of the Ride Plate referrenced to the bottom of the boat ... At the transom, just off the shoe.

[miketsouth]

Originally posted by Ken F
Possibly installing an intake pressure guage might be a good idea?
Ken F
I ommited that. I got block pressure, fuel pressure, and all the usual gauges. The AT pump, if i am not mistaken, has a port just for the intake pressure. Yes, before changing anything, i need to get the intake pressure, for reference if nothing else.
YES!!!!
mikeT

[miketsouth]

Originally posted by BEAR_454PE
Mike -
One of the most critical things about the adjustable hardware you have on your Cheyenne is the Ride Plate Angle ... Too High (Too much up angle) and the nose can come up too high making the boat more like a kite. Until you've got a better handle on your total setup I'd limit the up angle to no more than something like 2 degrees, 2.5 max. and I'd check its angle EVERY TIME BEFORE I PUT IT IN THE WATER (@ the Shore, just before backing in). Note the angle I'm refering to is the angle of the Ride Plate referrenced to the bottom of the boat ... At the transom, just off the shoe.
I have measured it and it comes right about there. The shoe is at a different angle. Seems to be three angles.
Bottom plane, that part that is before the intake(reference)
Pump angle (- 4deg)
Shoe angle (i forgot, think it is in plane with boat bottom)
Rideplate angle (somewhere close to 2deg)
When i look at it, it all seems to have to work together. There are no shims under the shoe. The loader (funny 's' looking thing) is sitting about 1/2" (as i remember) up into the intake, (using as a reference the shoe and pump front) and its purpose seems to be to load the top of the pump.
Like i said, i have just begun to look up into the intake and note the parts and examine their interactions. Soon i will have exact measurements.
And as i will say again thankyou all very much.
"He who dont know and knows he dont know is a student"
mikeT

[miketsouth]

Originally posted by miketsouth
What is a back-cut shoe?
From the little time i have had to run it my feeling is that the pump is rather loaded for much higher HP and speed than my SBC is going to produce even when running at its top performance level. Slows down suddenly when you cut the engine. It should coast, i think.
mikeT
and here are some vids so you can see the way it rides on the water.
The first is about 55-60mph steady, shows ride attitude at speed.
The second is a slow motion video. What happens here is at about 20 seconds into the video i let off the throttle from about 45-50mph (one can hear it in the slo-mo but not in the original vid).
You can see that the boat immediately noses down and actually splashes the water. Close observation will expose some passenger reaction to deceleration. It is not uncomfortable, but noticible that it slows quickly and noses in.
For all i know thats the way it should be.
Notice the occupants of the P/F have good ski vests on.
.9meg AV
55-60mph attitude (http://mywebpages.comcast.net/rodajet/picklepax4.wmv)
1.2meg AV
Slow motion throttle cut (http://mywebpages.comcast.net/rodajet/picklepax4d.wmv)
The only change i made since these vids was to replace the 3.6"(?) nozzle with a 3.0" nozzle, but i didnt have a chance to open it up and it was runnin lean. Maybe Sunday.
mikeT

[BottleFedJet]

Rain again.........:mad: wish this shit would stop.

[miketsouth]

Originally posted by BottleFedJet
Rain again.........:mad: wish this shit would stop.
Mikey, the rain has done to me what it did to us last weekend. Looks like its getting a bowl pressure gauge, and probably no changes to the pump, with the exception of the nozzle, (like you said) until i get all the measurements exact, the motor right, and some more understanding of what is going on down there.
How bad is this rain gonna mess up the river above dam 4. Looks like as good a place as any. It has the required "upstream"
:D

[miketsouth]

Here are some simple diagrams. The top one is how i see most shoes cut. The bottom one is how i imagine backcut shoes to look.
Is this right? It would put the"bite" up, just like using a thinner shoe, but would thrust the water down and (maybe) provide lift.
http://www.***boat.com/image_center/data/502/1057baccut1-med.JPG

[UBFJ #454]

Mike - Your shoe profile diagrams are incorrect ... the biting edges of all shoes are internal to the shoe ... along the U you see in plan view ... In profile, the right edge is blunt on all shoes.
Using your profile diagrams ...
A Flat Shoe will be the same thickness from left to right,
A Tapered Shoe will be thinner on the left (the back of the shoe) than on the right (the front) ... Back of shoe to Front, shoe face slopes down,
A Back Cut Shoe will be thicker at the left (back) than on the right (shoe front) ... Back to Front, shoe face slopes up,
In both the Tapered and Back Cut Shoes, the slope of the lower shoe face relative to the upper horizontal plane of the shoe in degrees is what termed either the Taper Angle or Back Cut Angle, e.g.; a 1.5 Degree Tapered Shoe or a 1.0 Degree Back Cut Shoe.
Hope this helps.
Jak

[miketsouth]

Originally posted by BEAR_454PE
Mike - Your shoe profile diagrams are incorrect ... the biting edges of all shoes are internal to the shoe ... along the U you see in plan view ... In profile, the right edge is blunt on all shoes.
Using your profile diagrams ...
A Flat Shoe will be the same thickness from left to right,
A Tapered Shoe will be thinner on the left (the back of the shoe) than on the right (the front) ... Back of shoe to Front, shoe face slopes down,
A Back Cut Shoe will be thicker at the left (back) than on the right (shoe front) ... Back to Front, shoe face slopes up,
In both the Tapered and Back Cut Shoes, the slope of the lower shoe face relative to the upper horizontal plane of the shoe in degrees is what termed either the Taper Angle or Back Cut Angle, e.g.; a 1.5 Degree Tapered Shoe or a 1.0 Degree Back Cut Shoe.
Hope this helps.
Jak
It does more than just help. It explains exactly what a backcut shoe is.
I am not changeing anything until i get a better understanding of it (like you said), exact measurements (as Mr. Lee found for me, thanks to your asking) and an intake pressure gauge. Thanks Jak, again.
mikeT

[comin' unscrewed]

Lifted from MPD's site: (http://home.pacbell.net/jmcclure/)
http://home.pacbell.net/jmcclure/TshoeBCshoe1.jpg
Shoes can be made in any configuration. The 3 basic styles are Tapered (a 0.5 deg taper, left), Flat (not shown), and Backcut (a 2 deg backcut, right). The thickness, depth of biting edge, taper, backcut angle, plate pad angle, and length of opening are some of the variables.

[UBFJ #454]

Mike -
Glad we could help.
Some other Generalities ... To be taken just as that, for every boat is different and two identical hulls can have very different optimal setups ...
Back Cut Shoes give lift ... But ... also pushes the nose over, especially in a tunnel like the Cheyenne. This forces more air into the tunnels and lifts the back of the boat ... But this typically takes quite a bit of Hp to do this successfully & Too Much Back Cut can push the nose over Too Far ... Something that you don't want as among other things shut downs can be very Abrupt and one can get Pitched Out Over the Deck.
The faster race boats typically run Flat, or very slightly (less than 1.0 degree) Tapered Shoes.
In recreational boats Tapered Shoes are typically used to overcome lake/river chop conditions and help keep the pump loaded while running across the rough water surface.
Another point ... Before deciding to make, or have a shoe made, you have to factor in the angle the intake is set into the hull because it is the Net Angle that is important ... example, our intake is set at 0.5 degrees ... if we put a Flat Shoe in, we'd actually be running a 0.5 degree Taper Setup, if we put in a 0.5 Bacl Cut Shoe, we'd be running a Flat Setup and, so forth.

[miketsouth]

Ok, now i see even more. Thanks. I got a lot more to learn. I seen a BUNCH of rideplate configurations. Those look like they would bolt right on to my pump's intake (4 hole configuration).
mikeT

[miketsouth]

Originally posted by BEAR_454PE
Mike -
Glad we could help.
Some other Generalities ... To be taken just as that, for every boat is different and two identical hulls can have very different optimal setups ...
Back Cut Shoes give lift ... But ... also pushes the nose over, especially in a tunnel like the Cheyenne. This forces more air into the tunnels and lifts the back of the boat ... But this typically takes quite a bit of Hp to do this successfully & Too Much Back Cut can push the nose over Too Far ... Something that you don't want as among other things shut downs can be very Abrupt and one can get Pitched Out Over the Deck.
The faster race boats typically run Flat, or very slightly (less than 1.0 degree) Tapered Shoes.
In recreational boats Tapered Shoes are typically used to overcome lake/river chop conditions and help keep the pump loaded while running across the rough water surface.
Another point ... Before deciding to make, or have a shoe made, you have to factor in the angle the intake is set into the hull because it is the Net Angle that is important ... example, our intake is set at 0.5 degrees ... if we put a Flat Shoe in, we'd actually be running a 0.5 degree Taper Setup, if we put in a 0.5 Bacl Cut Shoe, we'd be running a Flat Setup and, so forth.
I saw that too: ANY change in one item means a probable change other things, just to keep the first change on an even "keel", but yet, only one change at a time, and little ones, based on good and accurate observation.
Next step, i suppose is to get those "generalities" such that an intelligent choice in change can be made. I am not targeting top speed. Good, safe, reliable performance is my direction, and the last couple of offerings and explainations have put me on a better track.
I still think it is mostly, or the greatest balance of performance/driveability is in the intake. It is the nature of the pump.
Thanks again.
mikeT

[UBFJ #454]

Hull CG, Hp, Intake, Shoe/Shims, Loader, Pump (Impeller), Ride Plate, Droop/Nozzle Angle are all interRelated ... Go Figure ..... It's The World of Jet Boats.
From what you've said, you appear to be on the right track ... Go to It.