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Set back or not?

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That Rogers Guy

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« on: December 31, 2014, 01:21:59 PM »
So what's the advantages of a set back pump? I'm redoing a 77 hallet bubble deck and I'm trying to decide if it worth all the work to set it back. I know it will give me more interior room but what the pros and cons performance wise? Is it worth it?



capogniracing

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« Reply #1 on: December 31, 2014, 01:29:24 PM »

So what's the advantages of a set back pump? I'm redoing a 77 hallet bubble deck and I'm trying to decide if it worth all the work to set it back. I know it will give me more interior room but what the pros and cons performance wise? Is it worth it?
Tell them what your plans are for power.


"RTCP"

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« Reply #2 on: December 31, 2014, 01:36:23 PM »
True, I guess I should say I'm think of running a blower motor pump gas deal. I'm not sure of horsepower but I'm thinking on a conservative side like 650-700 hp. But I also want to know if a guy was going to run a smaller hp motor is it still a good choice?

herrhauptman

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« Reply #3 on: January 04, 2015, 06:20:41 AM »
I would that the whole purpose of a set back pump is to get your weight further aft. This in turn lets the bow rise, and reduces wetted surface which will give you more speed.  Also, it moves the hand hole outside the boat, so if you ever had to remove it while in the water, you can do that without the boat sinking.

GT Jets

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« Reply #4 on: January 04, 2015, 10:41:58 AM »
I would that the whole purpose of a set back pump is to get your weight further aft. This in turn lets the bow rise, and reduces wetted surface which will give you more speed.  Also, it moves the hand hole outside the boat, so if you ever had to remove it while in the water, you can do that without the boat sinking.

Not entirely accurate, but there is some good information there nonetheless.

The entire idea behind setting back the pump is to move the intake hole to the rear of the hull, so when the hull does fly and there is just a small surface  area in the water the pump does not lose a good load.

So it's not necessarily about moving the weight aft either. You also don't always have more room if the hull design wants the center of gravity more forward. Or if you have a fairly large transom deck.

Hope I don't seem like I am running over you here, just though more information was needed.

Something to keep in the back if your mind while designing your build. A blower motor is quite heavy, especially an iron headed, inter-cooled, big block. That much weight too far back will lower the freeboard at the transom making the hull prone to swamping. You may find with a heavier motor you will need to keep the motor in its original location, to much weight that far back can cause undesirable handling and an increased chance of blow over.

I would recommend finding someone with a set back Hallet or a hull very similar and talk to them about it. Take your time, do it once.

Good luck.

GT

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« Last Edit: January 04, 2015, 11:11:07 AM by GT Jets »
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

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Ray

GT Jets

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« Reply #5 on: January 04, 2015, 10:50:36 AM »
A set back pump also takes away a little of the turning capability, in case you were thinking about racing pin to pin to pin.

GT

Sent from my SM-G900V using SoCal Jet Boats mobile app

  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray


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« Reply #6 on: January 04, 2015, 11:15:21 AM »
The setback provides greater leverage on the thrust point which provides more lift and less drag.

I did this one a few months ago.  It was designed to handle both big power and less.  The pump was set back as far as possible without cutting through the transom.  An inch of keel was left just in front of the wood transom.  The rear flange of the intake was shortened to half-way through the last two intake bolts that attach through the fiberglass.  The intake was pushed back until the back of the ramp of the short turn radius just touched the wood for the transom cutout.  We feel it should have had a full setback which places the hand hole cover fully outside of the transom, but the owner wanted the extra rigidity to prevent the epoxy from cracking.  For this setback, a box was machined out of aluminum to seal around the inside of the hand hole cover, which is removable from the outside.

The engine was moved forward so that the @$$ wouldn't drag, providing better balance.  It will be a tight fit, but the original upholstery will be retained. The Jet-a-way is there for ease of disconnecting the drive line for running the engine while on the trailer and a longer drive line is used.

On mine, I do not have the room to move the engine forward.  I don't want to cut the floor or give up space around the back seats.  There should be enough room to leave the engine in its original location and do a full setback to where I can squeeze in a Jet-a-way and have the hand hole cover completely outside of the transom should I want to install a blow-off valve.

Cheers,

Joe
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

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« Reply #7 on: January 04, 2015, 11:26:26 AM »
The setback provides greater leverage on the thrust point which provides more lift and less drag.


Joe

Can you elaborate on this statement?

You can determine the thrust point with a properly selected droop, at the same time, keeping the original intake location and preventing the bowl from impeding the water plane.

Not calling BS, just wanting to see if I am missing something. Always up to be schooled.

A set back pump, in my opinion, does NOT provide lift by itself, it makes more lift possible by keeping the intake hole on the pressure point. You can do the same exact thing with a spoon....

On the rock dodger boats, we actually "dropped" the intake by about 1/2" (give or take, it was a secret) and created a dome just in front of the transition.

Love reading your posts Joe....  :thumbup:

GT
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

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« Reply #8 on: January 04, 2015, 11:40:06 AM »
...You can determine the thrust point with a properly selected droop, at the same time, keeping the original intake location and preventing the bowl from impeding the water plane...

GT

Or you could do both.

(Pic from b1_racing instagram)
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

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« Reply #9 on: January 04, 2015, 11:49:41 AM »
Or you could do both.

(Pic from b1_racing instagram)

You almost always have to do both... Like I stated earlier, just setting the pump back does very little to create more lift or change much in the way of thrust line. A proper setback with lower the thrust line (X dimension) about an inch with a 3 intake and a typical setback is approximately 3-4"... A short droop does the same exact thing, bringing the intake hole back allows way more trim "up" before you suck air.... I guess that is the only point I was trying to make.


Setting back a JC bowl is pretty much a futile process, mainly because of the work involved...

That set up is slick. Can you run a filler hand hole plug with that little box? or just a standard? That is almost exactly where my pump is, it's a bitch trying to get the TA to work out right.

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

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« Reply #10 on: January 04, 2015, 11:50:08 AM »
Cool thread BTW
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

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Ray

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« Reply #11 on: January 04, 2015, 11:50:20 AM »
The general rule of thumb is that you probably wont notice much difference unless you move the intake back at least two inches.  It is a lot of work for little to no gain.

Also, if the biting edge off the shoe gets too close to the transom line, the jet can suck air in a hard turn.
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

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« Reply #12 on: January 04, 2015, 11:59:19 AM »
The general rule of thumb is that you probably wont notice much difference unless you move the intake back at least two inches.  It is a lot of work for little to no gain.

Also, if the biting edge off the shoe gets too close to the transom line, the jet can suck air in a hard turn.

10-4. I have seen extended intake fins on some applications and it netted mostly positive results. If you are setting back a pump, just plan on Dodge Omni-like handling in the corners...LOL

Some have gotten it to work, but it is not the norm to retain cornering with a moderate setback.

A Sprint boat (the New Zealand form) has the intake waaaaaayyyy forward with those mile long Scott Pumps, they defy almost all forms of what seems more common...

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

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« Reply #13 on: January 04, 2015, 12:24:01 PM »
That set up is slick. Can you run a filler hand hole plug with that little box? or just a standard?

GT

This one uses the stock Berkeley hand hole cover, but you could make it to fit anything.
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

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« Reply #14 on: January 04, 2015, 01:10:49 PM »
10-4. I have seen extended intake fins on some applications and it netted mostly positive results. If you are setting back a pump, just plan on Dodge Omni-like handling in the corners...LOL

Some have gotten it to work, but it is not the norm to retain cornering with a moderate setback.

A Sprint boat (the New Zealand form) has the intake waaaaaayyyy forward with those mile long Scott Pumps, they defy almost all forms of what seems more common...

GT

Does the addition of trim plates help this?
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

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« Reply #15 on: January 04, 2015, 01:16:34 PM »
Does the addition of trim plates help this?

I am certain it can't hurt. The plates would have to be full width and/or installed very close to the pump ride plate. To really get it to pivot, I would say having a foot operated over ride pedal and favor the out side plate.... Mind you not proven, just my thinking out loud.

The big issue is the hull no longer has anything to "rotate" off of. Making a turning fin absolutely necessary.

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray


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