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Brad @ SCJB

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Flat Keel Vs Round Keel
« on: June 02, 2015, 08:48:54 pm »
What is the pros or con's of either?
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More2LifeThanMPG

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Re: Flat Keel Vs Round Keel
« Reply #1 on: June 02, 2015, 08:50:55 pm »
Thank you, I have been wondering the same thing...


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GT Jets

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Re: Flat Keel Vs Round Keel
« Reply #2 on: June 02, 2015, 08:52:34 pm »
What is the pros or con's of either?

I am going to go out on a limb and assume your are speaking of a delta pad?

GT

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Ray

Brad @ SCJB

  • Karma: +255/-0
Re: Flat Keel Vs Round Keel
« Reply #3 on: June 02, 2015, 08:55:38 pm »
I am going to go out on a limb and assume your are speaking of a delta pad?

GT

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Ok so that raises another question... Is there a difference between a flat keel and a delta pad? Or are they the same thing and just the proper name for it is delta pad? Why is it called a delta pad?

I'm just looking to get learned ;)
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81sprint

  • Karma: +18/-0
Re: Flat Keel Vs Round Keel
« Reply #4 on: June 02, 2015, 08:59:34 pm »
Thank you, I have been wondering the same thing...


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Same here. Hear all kinds of stuff back and forth about the two
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mobboss

  • Karma: +15/-0
Re: Flat Keel Vs Round Keel
« Reply #5 on: June 02, 2015, 09:02:48 pm »
Come on GT schools in session and your teachin!!!


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JordanDangerfield

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Re: Flat Keel Vs Round Keel
« Reply #6 on: June 02, 2015, 09:13:08 pm »
*Legal pad in hand, ready to take notes*


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GT Jets

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Re: Flat Keel Vs Round Keel
« Reply #7 on: June 02, 2015, 09:19:17 pm »
It's really pretty simple.

To answer the second question first.  A flat keel, typically tapered from about the last third of the length of the hull to the stern, is a delta pad.

The "what it does" is basically vertical lift.  You would either have wide flats on the strakes or a delta bottom. It would be rare to have both.

The delta pad offers a couple different advantages over a rounded keel.

The first advantage is the ability to plane at a lower hull speed. As a side benefit, quicker planing times from dead stop to plane.

The second benefit is a higher riding attitude at speed. It mimics a lower "x" dimension. This creates bow lift and a higher attainable top speed with moderate hp.

It also makes the boat more stable up to certain speeds. Unfortunately, once that speed is exceeded, makes it unstable, it can "step off" and create a dangerous hook to either direction.

Another drawback is they can sometimes cause odd intake flows on a jet. Necessitating creative "spoons" and shoes to keep the pump loaded properly.

It's not until the lower 70 mph ranges that any of this comes into play in my experience.

They also don't turn nearly as well as a rounded keel,  I feel it is that "step off" that causes a strange transition entering a turn.

I like delta pad hulls for the family ride that occasionally gets flogged on the weekend.

Up to about 75mph I don't think the negatives can be realized. The positives are far more beneficial for the average schmoe.

They also very seldom experience a porpoise problem and the hooks on these hulls are typically very slight.

GT

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« Last Edit: June 02, 2015, 09:30:32 pm by GT Jets »
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81sprint

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Re: Flat Keel Vs Round Keel
« Reply #8 on: June 02, 2015, 09:27:12 pm »
So would putting a rounded keel on a delta bottom that is running over 75 be beneficial?


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Re: Flat Keel Vs Round Keel
« Reply #9 on: June 02, 2015, 09:34:35 pm »
So would putting a rounded keel on a delta bottom that is running over 75 be beneficial?


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Depends on a bunch of different aspects, but the short answer is probably yes.

The 75 mph number I threw out there is just my opinion. If straight line speed is what you are after, I would think a delta pad with a properly set up shoe, ride plate and loader would kick ass. I would definitely install a turning fin just ahead of the pad though.

This is all just my personal theory.

GT
« Last Edit: June 02, 2015, 10:20:24 pm by GT Jets »
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mobboss

  • Karma: +15/-0
Re: Flat Keel Vs Round Keel
« Reply #10 on: June 02, 2015, 09:36:11 pm »
Ok GT so you have answered there questions !!! Here's mine , why is it better to have the bottom of the hull ruff and both smooth. And why we're on the subject why does it help load the jet to put a dome in front of the loader ???


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Re: Flat Keel Vs Round Keel
« Reply #11 on: June 02, 2015, 09:43:17 pm »
Ok GT so you have answered there questions !!! Here's mine , why is it better to have the bottom of the hull ruff and both smooth. And why we're on the subject why does it help load the jet to put a dome in front of the loader ???


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Hahaha!

What is this? Science class?

Ok, here's what I know.

For the surface question,  micro bubbles are "slippery" and a rough surface promotes those bubbles.  A smooth surface, especially a waxed surface, has too much surface tension and "is one" with the water.

As for the dome question. As it was explained to me,  a low pressure creates a higher pressure. Basically you are effectively "turning" the path of flow.

Look up Bernoulli theory.

It is the same exact thinking.

GT
« Last Edit: June 02, 2015, 10:21:21 pm by GT Jets »
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Brad @ SCJB

  • Karma: +255/-0
Re: Flat Keel Vs Round Keel
« Reply #12 on: June 02, 2015, 09:43:18 pm »
Ok GT so you have answered there questions !!! Here's mine , why is it better to have the bottom of the hull ruff and both smooth. And why we're on the subject why does it help load the jet to put a dome in front of the loader ???


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The idea of putting a 'hump' or otherwise known as a spoon in front of the intake is to bend the water into the intake. Take a spoon and put it into running water from your faucet like this.
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mobboss

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Re: Flat Keel Vs Round Keel
« Reply #13 on: June 02, 2015, 09:44:55 pm »
Very cool!!! Thank you.


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Re: Flat Keel Vs Round Keel
« Reply #14 on: June 02, 2015, 09:46:31 pm »
The idea of putting a 'hump' or otherwise known as a spoon in front of the intake is to bend the water into the intake. Take a spoon and put it into running water from your faucet like this.

Perfect example.

Bernoulli.
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mobboss

  • Karma: +15/-0
Re: Flat Keel Vs Round Keel
« Reply #15 on: June 02, 2015, 09:47:18 pm »
Ok what are each one worth?? As in speed how much do they add?? I'm sure it's been tested???


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Brad @ SCJB

  • Karma: +255/-0
Re: Flat Keel Vs Round Keel
« Reply #16 on: June 02, 2015, 09:50:27 pm »
So Glenn,

I picked up this Eliminator Sprint project from Rhino here on the boards. (yeah, I needed another boat project like I needed a hole in my head  :banghead: :screwy: ) I have been back n forth on what to do with the bottom of it. Part of me is just leave it. Other part of me is to convert it to a rounded keel. The intake is cut for a ride plate but no shoe.

The idea I have for this is to create a mild gale banks turbo 454. I dont plan on sawing anyone off, just want to do something a little different, still turn key, but has some balls when I wanna jab it.





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Re: Flat Keel Vs Round Keel
« Reply #17 on: June 02, 2015, 10:03:28 pm »
Do you see where the strakes end? That would be a major deal killer for me to round off the keel. Reason being is I would want to extend rearward the middle (second) strakes to keep the lift potential. The center strakes would be fine imho.

If it was mine, I would keep the delta and add a shimmable shoe and maybe a 3/8" (very modest) spoon.
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Ray

81sprint

  • Karma: +18/-0
Re: Flat Keel Vs Round Keel
« Reply #18 on: June 02, 2015, 10:11:50 pm »
Very good info. Thanks GT 👍


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Re: Flat Keel Vs Round Keel
« Reply #19 on: June 02, 2015, 10:43:54 pm »
Very good info. Thanks GT 👍


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Truly my pleasure.

8)
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Blue2184

  • Karma: +4/-0
Re: Flat Keel Vs Round Keel
« Reply #20 on: June 03, 2015, 05:52:14 am »
Gt witch bottom does my boat have? Good? Bad? I have only had the boat in the mid 70's? But fixing to throw about another 300hp at it? Thanks Jason




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Re: Flat Keel Vs Round Keel
« Reply #21 on: June 03, 2015, 05:59:50 am »
Gt witch bottom does my boat have? Good? Bad? I have only had the boat in the mid 70's? But fixing to throw about another 300hp at it? Thanks Jason




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That's a great bottom for going fast.

Very wide stakes for lift and if you look at these as compared to the ones on Brad's, they are perfectly straight.

About the only concern on this type of bottom design is chine walk.

Looking at just the phone as far as the picture, it looks like a Southwind bottom.

GT

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Blue2184

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Re: Flat Keel Vs Round Keel
« Reply #22 on: June 03, 2015, 06:13:32 am »
So? It would be considered a rounded keel? Thanks aging gt!!


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Re: Flat Keel Vs Round Keel
« Reply #23 on: June 03, 2015, 06:22:43 am »
So? It would be considered a rounded keel? Thanks aging gt!!


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Yep. Textbook rounded keel.

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mobboss

  • Karma: +15/-0
Re: Flat Keel Vs Round Keel
« Reply #24 on: June 03, 2015, 07:24:10 am »
That is what the bottom of My kona looks like! Ok what is chin walking???

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philofab

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Re: Flat Keel Vs Round Keel
« Reply #25 on: June 03, 2015, 07:52:11 am »
That is what the bottom of My kona looks like! Ok what is chin walking???

Chine walking is when the boat starts rocking left and right. It's uncomfortable and if it walks too far the side of the hull will grab and make the boat turn. It usually happens when the boat gets too far out of the water.
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philofab

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Re: Flat Keel Vs Round Keel
« Reply #26 on: June 03, 2015, 07:54:37 am »
I'll add my own question in the mix. I got this Hondo Pantera hull with a trailer last week. It has a slot cut in the center of the keel aprox 1-2' in front of the intake. I assume this was for a turning fin to help the boat turn rather than slide?

How are these fins attached? Where does one buy one or is it something you just build yourself out of stainless or aluminum plate?
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steves86ta

  • Karma: +41/-0
Re: Flat Keel Vs Round Keel
« Reply #27 on: June 03, 2015, 08:05:01 am »
I'll add my own question in the mix. I got this Hondo Pantera hull with a trailer last week. It has a slot cut in the center of the keel aprox 1-2' in front of the intake. I assume this was for a turning fin to help the boat turn rather than slide?

How are these fins attached? Where does one buy one or is it something you just build yourself out of stainless or aluminum plate?

All of the ones i have seen bolt through the floor
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GT Jets

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Re: Flat Keel Vs Round Keel
« Reply #28 on: June 03, 2015, 08:30:51 am »
That is what the bottom of My kona looks like! Ok what is chine walking???

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Chine walking;  adjective,  to determine how big and hard ones balls are by how l long the driver keeps his/her foot on the gas.



Sort of a skipping, sideways,  crab walking left to right rock. Mostly identified by how tight your ass cheeks grab for vinyl in the seat.

Not a good thing.

GT

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« Last Edit: June 03, 2015, 12:06:53 pm by GT Jets »
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GT Jets

  • Karma: +192/-0
Re: Flat Keel Vs Round Keel
« Reply #29 on: June 03, 2015, 08:32:33 am »
I'll add my own question in the mix. I got this Hondo Pantera hull with a trailer last week. It has a slot cut in the center of the keel aprox 1-2' in front of the intake. I assume this was for a turning fin to help the boat turn rather than slide?

How are these fins attached? Where does one buy one or is it something you just build yourself out of stainless or aluminum plate?

That is a drop through fin slot.

You might check Glenwood Marine to see if you can come up with a matching replacement.

GT

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mobboss

  • Karma: +15/-0
Re: Flat Keel Vs Round Keel
« Reply #30 on: June 03, 2015, 08:35:06 am »
Nice!!! By the way probably just big and hard enough to get into trouble!!😀

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philofab

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Re: Flat Keel Vs Round Keel
« Reply #31 on: June 03, 2015, 08:36:06 am »
That is a drop through fin slot.

Wow. That seems like an awesome way to rip a hole in the bottom of the boat if you ever hit something in low water.
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Undersoul02

  • Karma: +16/-0
Re: Flat Keel Vs Round Keel
« Reply #32 on: June 03, 2015, 11:13:29 am »
Chine walking;  adjective,  to determine how big and hard ones balls are by how l long the driver keeps his/her foot on the gas.



Sort of a skipping, sideways,  crab walking left to right rock. Mostly identified by how tight your ass checks grab for vinyl in the seat.

Not a good thing.

GT

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LOL Thank you for this! I lost my coffee on that one!
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steves86ta

  • Karma: +41/-0
Re: Flat Keel Vs Round Keel
« Reply #33 on: June 03, 2015, 11:33:13 am »
chine walking SUCKS!

The bahner is really bad about it. Starts right around 65-70 or so it can get pretty violent if you keep it aired out.

Though, ive noticed with the new motor and the extra power it doesnt do it nearly as badly... Maybe im not airing out as much to get to the same speed?

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HONDO_JET

  • Karma: +2/-0
Re: Flat Keel Vs Round Keel
« Reply #34 on: June 03, 2015, 12:08:13 pm »
Wow. That seems like an awesome way to rip a hole in the bottom of the boat if you ever hit something in low water.

They are pretty tough, I've bent mine twice, but those hull bottoms are layed up heavy,
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Re: Flat Keel Vs Round Keel
« Reply #35 on: June 03, 2015, 12:09:52 pm »
chine walking SUCKS!

The bahner is really bad about it. Starts right around 65-70 or so it can get pretty violent if you keep it aired out.

Though, ive noticed with the new motor and the extra power it doesnt do it nearly as badly... Maybe im not airing out as much to get to the same speed?

Your Bahner is a delta bottom, is it not?

And more ponies does typically help.

GT

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crazyjim

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Re: Flat Keel Vs Round Keel
« Reply #36 on: June 03, 2015, 12:23:18 pm »
Wow. That seems like an awesome way to rip a hole in the bottom of the boat if you ever hit something in low water.


It helps prevent this kinda thing Philo...

  1:00 in for the action. EEK!

I have one on the bottom of my Spectra, it's been hit and bent, I'll replace it over the off season I think, but wouldn't want to remove it.
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steves86ta

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Re: Flat Keel Vs Round Keel
« Reply #37 on: June 03, 2015, 12:30:05 pm »
Your Bahner is a delta bottom, is it not?

And more ponies does typically help.

GT

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Nope V hull with an outdrive
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Re: Flat Keel Vs Round Keel
« Reply #38 on: June 03, 2015, 12:37:42 pm »
Nope V hull with an outdrive

What drive? Bravo?

Make sure the cav plate on the lower unit is at the keel line. Not above. You must have a day cruiser.

GT

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Undersoul02

  • Karma: +16/-0
Re: Flat Keel Vs Round Keel
« Reply #39 on: June 03, 2015, 12:49:48 pm »
Your Bahner is a delta bottom, is it not?

And more ponies does typically help.

GT

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GT, I recently bought a Bahner with a delta pad. It has what I'm assuming is a stock berkeley JG with a stock nozzle on it. I'm going to be ordering a place diverter in the next few days and was wondering if I should add a droop snoot now or see how it handles before I do? Are there any negatives to adding a droop on a delta pad? Benefits? The set up right now runs 63 on GPS. It has a harman marine 454 (previous owner told me it's the 405 kit?) with 415 - 430 hp (again this is per previous owner) This is my first Jet so I'm reading and learning as much as I can. Thanks
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steves86ta

  • Karma: +41/-0
Re: Flat Keel Vs Round Keel
« Reply #40 on: June 03, 2015, 01:08:38 pm »
What drive? Bravo?

Make sure the cav plate on the lower unit is at the keel line. Not above. You must have a day cruiser.

GT

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Nope.... Alpha...

Yeah its below the keel line. Actually this drive is pretty damn deep.

Its a mini day
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1980 Bahner 21' Mini Day
1968 Rogers project

GT Jets

  • Karma: +192/-0
Re: Flat Keel Vs Round Keel
« Reply #41 on: June 03, 2015, 02:18:08 pm »
Nope.... Alpha...

Yeah its below the keel line. Actually this drive is pretty damn deep.

Its a mini day


Too deep is actually bad too. It does make them ride better,but can get funky at speed.

What prop are you running?

If you have the ponies, I would consider looking into a chopper.

GT

Sent from my SCH-I545 using SoCal Jet Boats mobile app

  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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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

GT Jets

  • Karma: +192/-0
Re: Flat Keel Vs Round Keel New
« Reply #42 on: June 03, 2015, 02:22:11 pm »
GT, I recently bought a Bahner with a delta pad. It has what I'm assuming is a stock berkeley JG with a stock nozzle on it. I'm going to be ordering a place diverter in the next few days and was wondering if I should add a droop snoot now or see how it handles before I do? Are there any negatives to adding a droop on a delta pad? Benefits? The set up right now runs 63 on GPS. It has a harman marine 454 (previous owner told me it's the 405 kit?) with 415 - 430 hp (again this is per previous owner) This is my first Jet so I'm reading and learning as much as I can. Thanks

If you have the patience and can hold off, I would drive it first.

The droop on a delta can be too much lift. With the Horsepower you have now I think the Diverter will be plenty. If you do decide to go with a droop, I would highly recommend having the intake fit with a shoe and ride plate.

Jmho

GT

Sent from my SCH-I545 using SoCal Jet Boats mobile app
« Last Edit: June 03, 2015, 06:14:57 pm by GT Jets »
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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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

steves86ta

  • Karma: +41/-0
Re: Flat Keel Vs Round Keel
« Reply #43 on: June 03, 2015, 02:37:48 pm »
Too deep is actually bad too. It does make them ride better,but can get funky at speed.

What prop are you running?

If you have the ponies, I would consider looking into a chopper.

GT

Sent from my SCH-I545 using SoCal Jet Boats mobile app

Yeah... this is the family boat so not gonna mess with the setup to awful much. Now that my Weiman is almost done.

Current prop is one of 2, i have a no name stainless 3 blade 19 pitch that i use most of the time. It came with the boat and if it gets screwed up i dont care. Rpm's are decent at cruise speed but its really nice for skiing or tubing, something we do often. But you stab the throttle and itll see 6k plus with this one and pretty much right now. Has great bite though

The other prop is a Mirage Plus 21 pitch, its really nice. For the life of me i cant remember if its been on this engine or not. Only have had it out about 3 times. But with the last engine we could swing it 5200-5400 and it worked well. Nice cruising at 3500rpm at 40-45 mph. (again if memory serves correctly somewhere in that neighborhood)

I really think that i could spin a 23 to about 5k or so with the new engine. But again its the family boat supposed to be fun for watersports and just cruising.

Ive always felt that with the lift built into the hull, the trim on the drive, and most if not all of the props i have being considered (bow lifting) props that this was part of if not the problem. Just to many things helping get its big ass out of the water. And that it does. Trimmed out under heavy throttle its riding on the rear foot maybe less maybe a little bit more. But not much hull is in the water at all.

Its funny you say that, I did buy a chopper for it a 21 pitch. Stainless won it on ebay for 25 bucks. Though it was ugly as sin figured try it out. If it helped straighten this thing out then we could spend the money on a nicer one..

threw it on the boat at home. Took boat to the lake. yeah damn prop was reverse rotation. that was nice and embarrassing.

Actually now that the jet boat is almost done, considering dropping the cam down a couple notches in the bahner. Its the family boat doesnt need to see 6k. 60 or so is plenty fast enough for it.
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Undersoul02

  • Karma: +16/-0
Re: Flat Keel Vs Round Keel
« Reply #44 on: June 03, 2015, 02:46:14 pm »
Of you have the patience and can hold off, I would drive it first.

The droop on a delta can be too much lift. With the Horsepower you have now I think the Diverter will be plenty. If you do decide to go with a droop, I would highly recommend having the intake fit with a shoe and ride plate.

Jmho

GT

Sent from my SCH-I545 using SoCal Jet Boats mobile app

Thank you and I can wait.
  • Boat #1: 1981 Bahner
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