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Place diverters, educate me

Blackmagic94

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ok so yesterday was the maiden flight of the botë with the new Xcelerator drive from JbP


My question is. What is nominally the optimal position of trim for maximum speed. It’s not like a prop where higher trim shows higher rpm.


Oh and big shout out to Tom JBP for all the help. The boat picked up an honest 4.4mph at a high altitude lake while running 650 less rpm
 

Mandelon

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Nothing about a jet boat is optimal. LOL

The roost is for show mostly, not so much for go.

Use your GPS and experiment where you gain the most mph.
 

wzuber

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View attachment 802777 View attachment 802778 ok so yesterday was the maiden flight of the botë with the new Xcelerator drive from JbP


My question is. What is nominally the optimal position of trim for maximum speed. It’s not like a prop where higher trim shows higher rpm.


Oh and big shout out to Tom JBP for all the help. The boat picked up an honest 4.4mph at a high altitude lake while running 650 less rpm
with a good hull pump combo typically you will feel the hull accelerate without additional throttle input at low to mid rpm range. At full throttle you would typically trim slightly above that. Every hull is different and you have to feel/find it's "sweet spot". You should have good steering input/control but the hull is as lose as can be without porpoising. The least wetted bottom surface area (aka drag) the faster the hull will go. A simple visual tell/tale is the rooster tail is approx. 2'-4' tall at speed. What rpm are you turning and what impeller size?
 

coolchange

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The nozzle controls your line of thrust.
Is your thrust vector below the center of mass, through it, or above it.
Most stock pumps point down, which leads to the jet boat condition of driving the bow over.
That's why a droop snoot works.
Seems the fast jet boats never have a roost of more than 4 or 5 ft.
Congrats on the pump swap, sounds like it worked great.
 

wzuber

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I would say in general the roost in your 1st photo is too high for max speed.
 

King295

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Can't speak to your pump setup as I have no direct experience but with a Berkeley / Place Diverter setup on a 19' BBC with modest power the sweet spot was about a 5' tail behind the boat. Seat time and RPMs will tell you the most.
 

mash on it

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I use the diverter for ride quality, about a 2 to 3' roost. But I have a heavy azz day cruiser.
Comp jets are limited to about 4' roost.

Dan'l
 

Devilman

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with a good hull pump combo typically you will feel the hull accelerate without additional throttle input at low to mid rpm range. At full throttle you would typically trim slightly above that. Every hull is different and you have to feel/find it's "sweet spot". You should have good steering input/control but the hull is as lose as can be without porpoising. The least wetted bottom surface area (aka drag) the faster the hull will go. A simple visual tell/tale is the rooster tail is approx. 2'-3' tall at speed. What rpm are you turning and what impeller size?
This is pretty much exactly what I would've said, saved me the typing haha. :thumbs up emoji here: :D

I know on mine it's 3 or 4 clicks from the bottom, depending on water conditions. Go over it and you'll feel the boat slow down. Anything higher than that "sweet spot" is just for show... :cool:... or hitting tubers... :p
 

Blackmagic94

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Ok great info.


Yeah that pic was all the way up for pics


I think I was one click up from middle when I recorded the run on the phone gps


Also I noticed that if I chopped the throttle shut hard at a full wot run it would torque steer or just straight pull left.


Could this be an issue of having a rudder installed. If so I’m ditching it
 

Blackmagic94

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The nozzle controls your line of thrust.
Is your thrust vector below the center of mass, through it, or above it.
Most stock pumps point down, which leads to the jet boat condition of driving the bow over.
That's why a droop snoot works.
Seems the fast jet boats never have a roost of more than 4 or 5 ft.
Congrats on the pump swap, sounds like it worked great.
The nozzle controls your line of thrust.
Is your thrust vector below the center of mass, through it, or above it.
Most stock pumps point down, which leads to the jet boat condition of driving the bow over.
That's why a droop snoot works.
Seems the fast jet boats never have a roost of more than 4 or 5 ft.
Congrats on the pump swap, sounds like it worked great.

it has a drop. I haven’t measured the ride plate angle yet like Tom has asked me to check but it was installed in the same notches as the panther before it was
 

mash on it

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The rudder is for slow speed maneuvering, and doesn't help top end numbers.

Dan'l
 

wzuber

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Also I noticed that if I chopped the throttle shut hard at a full wot run it would torque steer or just straight pull left
torque steer and veering upon hard shut down are two different things. Torque steer is during acceleration. Veering one same direction on hard (chop throttle) shut down could be just from weight imbalance side to side and the hull is rolling off the keel to the heavier side and decelerating quickly. I've had it where the intake adapter is not parallel to the center line of the KEEL so the thrust angle is slightly askew to the center line of the keel, but that typically shows up at least slightly upon acceleration as well. Does your veer or go straight when the steering wheel is centered/straight and you stab the throttle?
 

Hallett Dave

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The nozzle controls your line of thrust.
Is your thrust vector below the center of mass, through it, or above it.
Most stock pumps point down, which leads to the jet boat condition of driving the bow over.
That's why a droop snoot works.
Seems the fast jet boats never have a roost of more than 4 or 5 ft.
Congrats on the pump swap, sounds like it worked great.
Droop snoots don't necessarily work for every hull and engine configuration.
Talk to Dwayne at http://www.hi-techperformance.com/
Enjoy your boat. :)
 

Blackmagic94

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torque steer and veering upon hard shut down are two different things. Torque steer is during acceleration. Veering one same direction on hard (chop throttle) shut down could be just from weight imbalance side to side and the hull is rolling off the keel to the heavier side and decelerating quickly. I've had it where the intake adapter is not parallel to the center line of the KEEL so the thrust angle is slightly askew to the center line of the keel, but that typically shows up at least slightly upon acceleration as well. Does your veer or go straight when the steering wheel is centered/straight and you stab the throttle?

Go straight all the time unless it was max rpm then violent chop off throttle


Accelerate or partial accel and lifting no issues at all.

also it was windy and I might have been steering into the wind to be straight on those passes. But i didn’t really feel like the rudder helped low speed all that much so I’m gonna remove it
 

wzuber

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violent chop off throttle
Just a mention..this can get you and your passengers wet real quick..as in pitched out or spinning out etc. best to avoid this and roll off the throttle. If you are just testing to have an idea of the boats characteristics in the worst case scenario then I understand. Water/weather conditions can certainly effect how the hull responds under many different conditions. If you were steering into the wind then yes that could have caused or at least exacerbated an existing hull condition. Put a straight on the bottom and see if there is a significant amount of hook in the hull especially on the side it's pulling to. Can you get the hull off the trailer onto a dolly or blocks to give you clear access to the whole bottom area?
 

Hallett Dave

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Go straight all the time unless it was max rpm then violent chop off throttle


Accelerate or partial accel and lifting no issues at all.

also it was windy and I might have been steering into the wind to be straight on those passes. But i didn’t really feel like the rudder helped low speed all that much so I’m gonna remove it
Great idea removing the bolt on rudder.
If the rudder is even slightly bent it can cause the boat to pull.
Remember water is about a thousand times denser than air.
 

Blackmagic94

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Just a mention..this can get you and your passengers wet real quick..as in pitched out or spinning out etc. best to avoid this and roll off the throttle. If you are just testing to have an idea of the boats characteristics in the worst case scenario then I understand. Water/weather conditions can certainly effect how the hull responds under many different conditions. If you were steering into the wind then yes that could have caused or at least exacerbated an existing hull condition. Put a straight on the bottom and see if there is a significant amount of hook in the hull especially on the side it's pulling to. Can you get the hull off the trailer onto a dolly or blocks to give you clear access to the whole bottom area?
Never did this before with the stock drive that did not have a rudder.
 

wzuber

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Never did this before with the stock drive that did not have a rudder.
interesting....well if the rudder is not parallel or in line with the center line of the keel then this could be causing/contributing to the problem. Typically the rudders aren't considered very effective at speed as the pump thrust is so strong but in chop T. mode it could be a factor. It essentially starts the mis-direction and then as the hull rapidly decelerates, wets out, and goes toward a bow steer type conditions it get magnified?
When installing that kit onto the Jacuzzi I.A. how is the bolt pattern alignment established between the suction piece and the I.A.?
 

mash on it

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interesting....well if the rudder is not parallel or in line with the center line of the keel then this could be causing/contributing to the problem. Typically the rudders aren't considered very effective at speed as the pump thrust is so strong but in chop T. mode it could be a factor. It essentially starts the mis-direction and then as the hull rapidly decelerates, wets out, and goes toward a bow steer type conditions it get magnified?
When installing that kit onto the Jacuzzi I.A. how is the bolt pattern alignment established between the suction piece and the I.A.?
It was a panther pump intake assembly, done by Tom and Josh at JBP.

Dan'l
 

mash on it

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The ride plate should be about 2° up to start. Approximately 5/16" up. ( calculations based upon a 9" ride plate, if I remember right)

Dan'l
 

coolchange

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Just a quick point about chopping the throttle with headers and water. Depending on the camshaft can cause reversion and be pulling water into the cylinder.
 

wzuber

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I just looked back at previous posts and see you had a panther before and not a jacuzzi. With that setup you have extended the thrust line of the pump back a significant distance as well as added some speed. Is it possible that this is why the issue is showing up now as opposed to before?
With this new pump configuration you have created a whole new animal and everything it did before may no longer be relevant. Do you have any hardware hanging below the keel line? Loader grate etc? One change at a time. Remove rudder and run. If no change get the hull up so you have complete access to the bottom and straight edge the bottom and look for hook with a rigid 6' straight edge. Block at each transom corner and up front on the keel forward of the dash, so three points. Also while accessible, locate the center line of the HULL and mark on the keel from the transom forward 6' with tape and sharpie. Then pull a string line out past the back of the boat to the end of the pump at the reverse port. Mark on bowl and reverse port/gate etc. Verify that the pump is centered in and in line with the hull, keel etc. Aren't projects fun? haha
 

Blackmagic94

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I just looked back at previous posts and see you had a panther before and not a jacuzzi. With that setup you have extended the thrust line of the pump back a significant distance as well as added some speed. Is it possible that this is why the issue is showing up now as opposed to before?
With this new pump configuration you have created a whole new animal and everything it did before may no longer be relevant. Do you have any hardware hanging below the keel line? Loader grate etc? One change at a time. Remove rudder and run. If no change get the hull up so you have complete access to the bottom and straight edge the bottom and look for hook with a rigid 6' straight edge. Block at each transom corner and up front on the keel forward of the dash, so three points. Also while accessible, locate the center line of the HULL and mark on the keel from the transom forward 6' with tape and sharpie. Then pull a string line out past the back of the boat to the end of the pump at the reverse port. Mark on bowl and reverse port/gate etc. Verify that the pump is centered in and in line with the hull, keel etc. Aren't projects fun? haha

I have forklifts how would you recommend I lift the boat. Straps?

So if it’s not straight how do you correct. And if it has hook how do you correct
 

wzuber

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. Straps?
yes...that will make things much easier.
how exactly to correct depends on the specific conditions of the hook but generally involves grinding gel/glass etc. and filling or removing material to straighten out the bottom of the hull. Are you familiar with what hook is in boat bottom terms?
 

Blackmagic94

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yes...that will make things much easier.
how exactly to correct depends on the specific conditions of the hook but generally involves grinding gel/glass etc. and filling or removing material to straighten out the bottom of the hull

Who does that work in Az. This is blue printing a hull correct? Any ballparks on what those jobs can run.
 

coolchange

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When it comes to the bottom you need to be checking out hornets. Seems to me the race boats had a fin on them. They would just turn stupid.
Probably somebody in the comp jet class that knows.
 

nganga

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Who does that work in Az. This is blue printing a hull correct? Any ballparks on what those jobs can run.
You might try Dan Nelson, Jett Performance Marine.
 

Flying_Lavey

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Go straight all the time unless it was max rpm then violent chop off throttle


Accelerate or partial accel and lifting no issues at all.

also it was windy and I might have been steering into the wind to be straight on those passes. But i didn’t really feel like the rudder helped low speed all that much so I’m gonna remove it
Maybe it's the drastic elimination of rotational force from the engine? Maybe with the new pump set-up you're hull is running substantially drier so there isn't as much hull in the water to absorb that force so now you're feeling it as to before it wouldn't make a difference?

I'm not a jet guy but that's what I'm thinking based upon what forces are at work at that time and situation.

Sent from my LM-G710VM using Tapatalk
 

wzuber

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Who does that work in Az. This is blue printing a hull correct? Any ballparks on what those jobs can run.
Blue printing would be a generic term for it, yes. Costs are dependent upon degree of specific conditions, desired result and tolerance for financial pain. haha
In my opinion, for your boat to be all it can be, and while it's apart and getting "Blue printed" (straightened) anyway I would recommend removing the glassed Panther insert portion of the hull (recessed notch) , install a fully machined I.A. with adjustable hardware like a standard berk. or lo-pro type intake adapter, suction housing etc. and use as much of your current pump parts available to build a fully adjustable, use-able berk type pump configuration and installation.
I would recommend myself (tho I'm not in havi) Tom Petersen (sorry, I'm blanking on the name of his business), or Harold Bruce at R&D Marine.
 

FreeBird236

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Just a mention..this can get you and your passengers wet real quick..as in pitched out or spinning out etc. best to avoid this and roll off the throttle. If you are just testing to have an idea of the boats characteristics in the worst case scenario then I understand. Water/weather conditions can certainly effect how the hull responds under many different conditions. If you were steering into the wind then yes that could have caused or at least exacerbated an existing hull condition. Put a straight on the bottom and see if there is a significant amount of hook in the hull especially on the side it's pulling to. Can you get the hull off the trailer onto a dolly or blocks to give you clear access to the whole bottom area?
You obviously know a lot about this, even though most jets are fairly flat, couldn't it be bow steer? I know my sterndrive which isn't a very steep V will hook the nose if I chop the throttles depending on trim.
 

wzuber

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Is this hull a hornet or a carrera? I was under the impression it was the latter.
 

wzuber

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You obviously know a lot about this, even though most jets are fairly flat, couldn't it be bow steer? I know my sterndrive which isn't a very steep V will hook the nose if I chop the throttles depending on trim.
yes it could be generic bow steer type condition but typically B.S. it goes either way depending on how the hull falls/lands in the water. So far he may not have enough experiences with this current set up configuration to know if it goes both ways under diff. conditions or only wants to go left as I understand it at this point in time.
 

namba860

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Rule of thumb is the rooster tail should be about as high as your head when sitting in the driver seat under way.
 

namba860

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My sons Spectra will bow steer a little with the divertor in some of the negative trim levels once the boat frees up you can let go of the wheel. Remember a jet has no steering torque like a propeller driven boat.
 

Blackmagic94

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My sons Spectra will bow steer a little with the divertor in some of the negative trim levels once the boat frees up you can let go of the wheel. Remember a jet has no steering torque like a propeller driven boat.

The trim was 3/4 the way up or more I think.
 

jetboatperformance

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Thanks for the good words, Our JBP XLerator conversion has been a very succesfull program.. essential we only re use the suction housing and build a "mixed flow" jet into it, have countless sales no and always good feeback .... In reviewing the pictures I can see the ride plate needs to be adjusted way up , in its current sate it will very likley force the bow in and create bow steer or bow hunting , needs to be at minimum 2* to 4* up , also like we spoke the ride plate looks slightly distorted and as you know it has repaired cracks , suggest a new style ride plate with the deeper fins Tom
 

wzuber

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My sons Spectra will bow steer a little with the divertor in some of the negative trim
@namba860 ....this is occurring while at speed underway correct? His situation at hand is under a "chop throttle" condition and the boat goes from full lift to falling into the water under rapid deceleration.
 

namba860

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Don't know why he is chopping the throttle?????
 

Blackmagic94

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Thanks for the good words, Our JBP XLerator conversion has been a very succesfull program.. essential we only re use the suction housing and build a "mixed flow" jet into it, have countless sales no and always good feeback .... In reviewing the pictures I can see the ride plate needs to be adjusted way up , in its current sate it will very likley force the bow in and create bow steer or bow hunting , needs to be at minimum 2* to 4* up , also like we spoke the ride plate looks slightly distorted and as you know it has repaired cracks , suggest a new style ride plate with the deeper fins Tom


Yeah I need to go get my angle finder and check it today. Do you have pics of the deep fin variant you suggested
 
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