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MPR FAB
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Discussion Starter #1 (Edited)
I have a 18 ft southwind with a Berkeley jc and the intake is out of the hull.would it be worth it to set the pump back since the intake is out of the boat?Right now it has a stock BBC and i plan on building around a 500hp motor with in the next year or two.what would be the pros and cons of doing the set back now.I have a bad porpoise with the stock setup.would this help me or not?
 

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we recently set the pump back and blueprinted the bottom of that same model boat ,along with machining the intake for a ride plate and built the plate installed it , the boat runs very nice now and we picked up a bit on the mph side. the owner is running a healthy ford (sin) and at 6200ft adjusted elevation hes running 83.4 gps that's damn respectable at this altitude with a aspirated pump gas motor so yup id go for it
 

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I have a 18 ft southwind with a Berkeley jc and the intake is out of the hull.would it be worth it to set the pump back since the intake is out of the boat?Right now it has a stock BBC and i plan on building around a 500hp motor with in the next year or two.what would be the pros and cons of doing the set back now.I have a bad porpoise with the stock setup.would this help me or not?
DO-IT. I have done a few of the early 18 southwind v-bottoms and nothing wakes them up faster. I have gone 3" back and my son is building one as we speak and he went out the back with it. You HAVE TO set the bottom up correctly for it to work proper. M
 

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DO-IT. I have done a few of the early 18 southwind v-bottoms and nothing wakes them up faster. I have gone 3" back and my son is building one as we speak and he went out the back with it. You HAVE TO set the bottom up correctly for it to work proper. M
X2. I set the intake back 3" on my Kachina (very similar if not splashed I believe), and best mod to date. My Buddys boat on the other hand,with with same everything pump and similar HP and semi v hull, feels dangerous to me. He's got 3/4" hook the last 3 or 4 feet of hull. Not fun to drive, let alone ride in...:)bit

Edit: I just read futs' reply and reread OP - must've missed the porpoise statement. never had anything weird prior to set back in my deal...
 

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I have a 18 ft southwind with a Berkeley jc and the intake is out of the hull.would it be worth it to set the pump back since the intake is out of the boat?Right now it has a stock BBC and i plan on building around a 500hp motor with in the next year or two.what would be the pros and cons of doing the set back now.I have a bad porpoise with the stock setup.would this help me or not?
opening a big can of worms...........jmo
 

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I agree, can be made to work really well but you gotta be careful. Thing could be worse as far as porpoising goes.
With all due respect futs and cs that is why I stated the bottom must be set-up as well. Along with a ride plate,shoe and diverter. If he has the intake out now then do it now. Do it right the first time and be done underneath. M
 

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With all due respect futs and cs that is why I stated the bottom must be set-up as well. Along with a ride plate,shoe and diverter. If he has the intake out now then do it now. Do it right the first time and be done underneath. M
Could you elaborate on what you would do when you say " bottom set-up" Are you talking just make sure there's no hook, or do you need to create a Delta pad? Is there some sort of standard or starting point? What is the criteria when considering a set back pump? Inquiring minds are also curious.
 

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Could you elaborate on what you would do when you say " bottom set-up" Are you talking just make sure there's no hook, or do you need to create a Delta pad? Is there some sort of standard or starting point? What is the criteria when considering a set back pump? Inquiring minds are also curious.
Too much hook is very bad in my humble AZ experience...
 

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So are you guys looking at the rocker that was built into the boat? Some people place there straight edge right on the rocker and think, wow, this has a ton of hook because the straight edge has a 1/4" gap or more, when in fact that rocker needs to be there to let the boat roll over so to speak. I hear everyone talking about hook, do most not know about rocker?Set backs have a time and place. It can work well on one and do terriable things to the next. If this is a ski boat and your looking to enjoy it, just leave it alone. If its an all out max effort, well, then cut the intake for a shoe, move it back a few inches, and get the bottom done. Then let the headache start when you cant figure out how to hardware the thing and your wasting your time dicking with the boat rather than enjoying it.


Dont get me wrong here, Im all about performance, but when your taking a 1/4 stringer boat and seting the pump back, its going to do funky things to the bottom as far as structual integrity.

This is just my opinion. im not a know it all, just been around for awhile and seen some stuff....:))eek:))
 

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I have a 18 ft southwind with a Berkeley jc and the intake is out of the hull.would it be worth it to set the pump back since the intake is out of the boat?Right now it has a stock BBC and i plan on building around a 500hp motor with in the next year or two.what would be the pros and cons of doing the set back now.I have a bad porpoise with the stock setup.would this help me or not?
Agree with Tim , (potential "worm can" as you were advised above)not every boat will benefit from this , try to sort out and diagnose whats causing the porposing problems with the original setup vs making a huge and significant modification that will require a whole new set of changes and adjustments , pics will help (bottom ,intake area ,jet etc) could be something simple Tom
 

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MPR FAB
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Discussion Starter #12
What would be the cause of the porpoise with the stock set up? Also I will be replacing the 1/4 stringers with full stringers. Dose anyone have pic of there set up?I would like to see the difference from stock. Thank for all info.
 

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knew a guy many years ago that had a sw splash. would run 88 through the traps porpoising like a mother. he tried everything; droop, no droop, short plate, long plate, diverter, bottom blueprint, and everything in between. still porpoised. after exhausting everything he and others could think of, he finally added trim tabs, adjusted them once and the porpoise was gone. and then it would run over 90.
nobody really wants to add trim tabs. but it's a sure way to eliminate porpoise. sometimes ya just gotta do what ya gotta do...
 

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nobody really wants to add trim tabs. but it's a sure way to eliminate porpoise. sometimes ya just gotta do what ya gotta do...
what do i know,but tunnel tabs are mounted on top of tunnels and can affect handleing as well as trim tabs that are mounted level with bottom of boat..
 

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what do i know,but tunnel tabs are mounted on top of tunnels and can affect handleing as well as trim tabs that are mounted level with bottom of boat..
i know. most every swtunnel has 'em. but boat that didn't come with 'em, people are reluctant to add 'em. but they will kill a porpoise...
 

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Trim tabs are a negative force add on. May improve the condition however it is a band aid to the problem. If you have the ability to do glass work for fill in and restructure, You have a problem now existing anyway. Talk to others, plan it using good advice and do it. The set back changes your wet line as it allows you to dry up the hull (MPH) Not being aware of the bottom U will find a lot of good people who will offer direction. Find out the motor location setting's based on your HP. Due sound glass glass work, pull a center line before re-cutting your new location on the intake. Set shoe inside 1" or so, Inside the transom line. The hull will fill much larger and yet dry up over current. Good Luck with whatever you do. Dave Jones
 

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B1 Racing
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knew a guy many years ago that had a sw splash. would run 88 through the traps porpoising like a mother. he tried everything; droop, no droop, short plate, long plate, diverter, bottom blueprint, and everything in between. still porpoised. after exhausting everything he and others could think of, he finally added trim tabs, adjusted them once and the porpoise was gone. and then it would run over 90.
nobody really wants to add trim tabs. but it's a sure way to eliminate porpoise. sometimes ya just gotta do what ya gotta do...
Real common right here...

A little hook left in the bottom can be a good thing on one of these, you straighten the crap put of the bottom it will porpoise, guaranteed. Weight distribution meaning motor placement is huge, if it was a 2 seater and you could move things to where they should be the boats would work better IMO.

All the stuff is worth doing and it can be delt with but it will be alot of testing before it gets there.
 
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