JAE 67/84 build up

[MikeStewart]

Apparently, you never want a gap between ski and strut?

 

[dwilfong]

Well look real close at the video and tell me what you all see.
removing the gap did solve most of the problem..........
Like I said tell me what you see look real close at it.
I have more prop testing to do and some strut changes to try.
So tell me how do you get it to not blow out running over its own wake??????????????
Should be a hoot in race water with some X hydros...........................LOL

 

[MikeStewart]

So, it sounds like you put a round bottom strut. That would make the rear ride surface stop at the end of the ski, and allow the prop to get a bite in the water.

 

[dwilfong]

If you look close it is STABBING the front end.. that in turn pops the back up and unloads the prop.
Have bin bouncing this off my bud and we think it is that the end of the planing surface is to far forward of the CG.
I will build a new set of sponsons to test the next time out.
Adding weight to the bait box may help but this is just a band aid for the problem if it works.
Think of a see saw to much weight on one side and it plants it self.
Remember the pivot is the end of front planing surface.
Do not want to make the boat any heaver if any thing want it lighter.
Can not move the motor any more with out messing up the cowl.
Will move the tank as far back as I can to start.
It is funny the smaller lighter boats are less pron to this.
I am too deep into it to quit now.........I will figure this boat out to heat race............
So all you JAE Gurus what do you think???????

 

[mercguy]

Dave
Have you tried props with much less lift. Maybe try some with a lot of rake to hold onto the water longer. Maybe Eric and you have tried that but just a suggestion.
Bill Hoch

 

[Ray Sametz]

If you look close it is STABBING the front end.. that in turn pops the back up and unloads the prop.
Have bin bouncing this off my bud and we think it is that the end of the planing surface is to far forward of the CG.
I will build a new set of sponsons to test the next time out.
Adding weight to the bait box may help but this is just a band aid for the problem if it works.
Think of a see saw to much weight on one side and it plants it self.
Remember the pivot is the end of front planing surface.
Do not want to make the boat any heaver if any thing want it lighter.
Can not move the motor any more with out messing up the cowl.
Will move the tank as far back as I can to start.
It is funny the smaller lighter boats are less pron to this.
I am too deep into it to quit now.........I will figure this boat out to heat race............
So all you JAE Gurus what do you think???????

If you plan on heat racing this boat, adding weight to the bait box maybe a band aid that can be removed or added in increments.(wow big word, surprised myself.)

 

[dwilfong]

Dave
Have you tried props with much less lift. Maybe try some with a lot of rake to hold onto the water longer. Maybe Eric and you have tried that but just a suggestion.
Bill Hoch

I have a 3 blade 23 deg rake prop to test some more. will see what it dose.
I was asking for some High rake props in the prop forum before this build for just this reason.

 

[dwilfong]

If you plan on heat racing this boat, adding weight to the bait box maybe a band aid that can be removed or added in increments.(wow big word, surprised myself.)

I will try the weight in the box to start. easy to do and no effort involve in a rebuild.

 

[dwilfong]

The planing surface is WAY up front on this boat compared to other boats.
WHY?????????
inquiring minds want to KNOW!!!!!!!!!!

 

[David Murany]

Check the CG in relation to the afterplane. From what I remember it was supposed to be about 65/35. Then check the turn fin trailing edge.

 

[dwilfong]

Check the CG in relation to the afterplane. From what I remember it was supposed to be about 65/35. Then check the turn fin trailing edge.

65/35 so 65% to the prop and 35% from the back of the ride surface?
There is 34.5" from ride surface to prop.

 

[David Murany]

65/35 so 65% to the prop and 35% from the back of the ride surface?
There is 34.5" from ride surface to prop.

Yes that's the way we set them up. The next thing you may check is the CG dry and the CG wet and put the trailing edge of the turn fin in the middle of the 2

 

[dr gary turner]

So what is the optimum after plane length
for each hydro size. 21 45 67 F hydro and twin?

 

[dwilfong]

OK here is the new sponson I have in mind to test.
Top one is as is from the kit bottom is mine.
Have the foam cut out and getting them all squared to each other now.

 

[dr gary turner]

Decreasing the after plane?

How wide and what is the AOA?

 

[dwilfong]

Decreasing the after plane?

How wide and what is the AOA?

It has the same AOA I just moved the surface back 3 "making the after plane 31.5"from 34.5"
Also made the top flat with the same AOA .
Then cut 2" off the front now thy are even with the tub and changed the bottom front angle.
Just as wide 2" so it has the same planing surface.
No major changes just a few tweaks.

 

[dr gary turner]

The change in after plane is monumental

I think one of the problems with ski boats is there is no blow out.

My 21 ski boat has 1/4 blow out

 

[dwilfong]

The change in after plane is monumental

I think one of the problems with ski boats is there is no blow out.

My 21 ski boat has 1/4 blow out

What are you referring to when you say "blow out"

 

[DON MAHER]

Are you running 1-11/2 deg.strut angle? If you are I would try 0 deg. if you have not already.

 

[dr gary turner]

What are you referring to when you say "blow out"

Rocker in the bottom at the back of the tub.

BTW shortening the after plan may let you turn a bigger prop BUT more likely for the prop to unhook and hop.