Set back on a 18' Kachina
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Set back on a 18' Kachina

  1. #1
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    Default Set back on a 18' Kachina

    Does anyone have any experience with a set back pump on an 1985 18' kachina custom?
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    Glendale Arizona Squirtcha?'s Avatar
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    I had a 76 Kachina with a setback pump and a buddy of mine has one now (79 I believe). We both had em done by a Jett Performance Marine here in Phoenix in the same season and both had the same amount of setback. About 1 1/2" of fiberglass left between the intake and transom. Total setback was about 3" or so (rough guesstimates). Mine was the yellow/orange one on the left and the other setback is the blue/black one in the middle. The white/blue one is stock.

    Although I've done quite a bit of glass work, I didn't trust myself to get the intake in properly so paid to have it done. That's the extent of my experience.
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    Last edited by Squirtcha?; 08-19-2014 at 08:34 AM.

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    How much of a difference in performance and handling did you notice?
    Last edited by Kachinajoe; 08-19-2014 at 11:23 AM.

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    Default Set Back

    Quote Originally Posted by Squirtcha? View Post
    I had a 76 Kachina with a setback pump and a buddy of mine has one now (79 I believe). We both had em done by a Jett Performance Marine here in Phoenix in the same season and both had the same amount of setback. About 1 1/2" of fiberglass left between the intake and transom. Total setback was about 3" or so (rough guesstimates). Mine was the yellow/orange one on the left and the other setback is the blue/black one in the middle. The white/blue one is stock.

    Although I've done quite a bit of glass work, I didn't trust myself to get the intake in properly so paid to have it done. That's the extent of my experience.
    Did you have the same power when you put the boat back together if so how much difference did it make? Were there any other mods made. Straighten the bottom,pump mods,engine mods?

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    Senior Member 67weiman's Avatar
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    The bigger question would be what do you want out of the boat? How much hp?

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    The bottom has not been work on, but I plan on it. Themotor will be release with a 540 BBC 12.5-13:1 comp. I’m hoping to be around arealistic 700-750 hp. The pump hasn’t been rebuilt in years that are the planfor winter. I figured since I have it torn apart that far, I might as well seeif I could benefit from a set-back pump. I'm hoping to have a pertty quick lake boat that I could still ski behind.

  9. #7
    Glendale Arizona Squirtcha?'s Avatar
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    Quote Originally Posted by Kachinajoe View Post
    How much of a difference in performance and handling did you notice?
    Quote Originally Posted by greg shoemaker View Post
    Did you have the same power when you put the boat back together if so how much difference did it make? Were there any other mods made. Straighten the bottom,pump mods,engine mods?
    Lots of changes were going on about this time. While the intake was out it was machined for a shoe and rideplate. Spent a good amount of time on setup to get the ride right. Also ended up going to a straight snoot. The boat would top out at about 78 mph with 450hp and a 100hp shot of N02 prior to the setback and setup work. bumped the nitrous up to a 150 shot for a total of 600hp. After everything was all said and done it was pretty consistently in the mid-80's.

    Handling was very good at speed and the boat was not at all sketchy. A year or two later the bottom delam'd on it. I stripped and flipped it and spent hours fixing and straightening out the bottom. Had it dead nuts straight and after that it would porpoise like crazy. Couldn't get rid of it for anything. After a season of trying, ended up having to put a set of fixed cav plates on it to settle it down. It rode o.k. after that but never like it did prior to straightening out the bottom. I sold it and went to the gullwing after that.

    It might have just been me, but I have heard of others having porpoise issues after straightening out the bottom on their Kachinas, Challengers, Southwinds. Had I known prior, I would've just fixed the damage and not tried to blueprint/straighten it.

    Watch the bottom area adjacent to your motor/stringers for delamination both inside and out. Saw a number of these come apart in that same area. Seems like it was a problem, at least potentially.

    If you want to do 90mph or better you might want to start thinking about another platform/hull to do it with. My buddy is real close to that with his (blue/black one), but he's on the ragged edge.
    Last edited by Squirtcha?; 08-20-2014 at 07:52 AM.

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    Default Straight bottoms

    Quote Originally Posted by Squirtcha? View Post
    Lots of changes were going on about this time. While the intake was out it was machined for a shoe and rideplate. Spent a good amount of time on setup to get the ride right. Also ended up going to a straight snoot. The boat would top out at about 78 mph with 450hp and a 100hp shot of N02 prior to the setback and setup work. bumped the nitrous up to a 150 shot for a total of 600hp. After everything was all said and done it was pretty consistently in the mid-80's.

    Handling was very good at speed and the boat was not at all sketchy. A year or two later the bottom delam'd on it. I stripped and flipped it and spent hours fixing and straightening out the bottom. Had it dead nuts straight and after that it would porpoise like crazy. Couldn't get rid of it for anything. After a season of trying, ended up having to put a set of fixed cav plates on it to settle it down. It rode o.k. after that but never like it did prior to straightening out the bottom. I sold it and went to the gullwing after that.

    It might have just been me, but I have heard of others having porpoise issues after straightening out the bottom on their Kachinas, Challengers, Southwinds. Had I known prior, I would've just fixed the damage and not tried to blueprint/straighten it.

    Watch the bottom area adjacent to your motor/stringers for delamination both inside and out. Saw a number of these come apart in that same area. Seems like it was a problem, at least potentially.

    If you want to do 90mph or better you might want to start thinking about another platform/hull to do it with. My buddy is real close to that with his (blue/black one), but he's on the ragged edge.
    A lot of times guys will straighten the bottoms of there boats and end up having a porpoise problem. What they fail to realize is that a lot of mfg's would put a lot of lift in the bottoms of there boats to generate a lot of speed with low HP. The problem is that once the bottom has been straightened and you set back the pump now you are really making a lot of lift because of the original bottom. One of the reasons the CP's run so well is that they have small lifting strakes. When we do a bottom you have to take this into consideration so if the strakes are to big we will make the strake design a lot smaller. If you experience this problem the only way to correct this is to add a small set of non adjustable cavatation plates and adjust accordingly to take the porpoise out of the boat. The best way to avoid this problem is to make the mods to the bottom so this does not occur.

  11. #9
    Glendale Arizona Squirtcha?'s Avatar
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    I could have used that info about 5 years ago Greg

    That's exactly what happened with mine. Hopefully the OP will see this and learn from my mistakes.
    Last edited by Squirtcha?; 08-21-2014 at 08:22 AM.

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