JAE 67/84 build up

[mercguy]

Doc
I agree that shortening the afterplane will create a lot more prop hop with the same AOA on the sponson. Will need a lot of rake in the prop. Sometime back a guy built a JAE but instead of using the ski he made rear sponsons. I never heard how that worked for him. Does anyone remember that?
Bill Hoch

 

[dr gary turner]

I am running rear sponsons with the ski on my JAE 101.

It improved heat racing.

 

[David Murany]

I am running rear sponsons with the ski on my JAE 101.

It improved heat racing.

How much downforce is built into these rear sponsons Doc? I wonder if some winglets like the SGX boats use would help stabilize it as well.

 

[mercguy]

Doc
Wow, I forgot you had all three on your boat. The one I was referring to didn't use the ski. The boat was white with black trim if I remember correctly.
Bill Hoch

 

[dwilfong]

I have tried some different strut angles.
the run in the vidio was the first run with the ski set back so the strut would sit on it.
I had the strut at 1.2 deg the same as the ski AOA
Tried 0 deg and even some positive.
I need to set the strut at 0 and leave the boat as built to start and find the right prop and pipe length first.
Then I can work on other things.
Do not want to chaise my tail yet.
The new sponsons can be put on in a few seconds at the pond just remove the outer clamps and slip them on.
This way I can test back to back with no other changes.
I will also make some rear sponsons to test and a new ski set up.

 

[dr gary turner]

I had 2 twins with ski’s. They have been removed. Rear sponsons are on them.

One twin has blow out and one is flat.

My twin 90 has JAE type sponsons longer after plane, blow out and rear sponsons.

The longer after plane really smoothed the boat out and handled the rough twin water.

It ran extremely well at Brandon this year.

 

[dr gary turner]

BTW the twin was black white and blue

 

[dr gary turner]

BTW I have a ski on my 21 hydro and does great

 

[dwilfong]

Yes the smaller boat run great but as soon as you step up bigger than the 45 thy are shall we say a hand full.

 

[MikeStewart]

Did you try moving the sponson's in?

 

[Buckshot]

Doc,
The “blow out” you are trying to describe is the same as a diffuser on race cars. In theory it speeds the air up as it exits the rear undertray and creates downforce on the rear. Same is true with our toy boats. I think the SGX boats had a rear diffuser with rears and center ski. Some boats benefit from a rear diffuser.

David,
Be careful about just simply extending the ride pad at the same angle and not adjusting the boom tube height. It will change the aoa of the tub.

 

[dwilfong]

Doc,
The “blow out” you are trying to describe is the same as a diffuser on race cars. In theory it speeds the air up as it exits the rear undertray and creates downforce on the rear. Same is true with our toy boats. I think the SGX boats had a rear diffuser with rears and center ski. Some boats benefit from a rear diffuser.

David,
Be careful about just simply extending the ride pad at the same angle and not adjusting the boom tube height. It will change the aoa of the tub.

It is at the same relation ship just moved back 3"

 

[dwilfong]

The thing is with this boat it turns perfect in flat water.
Look at the way it corners like it is on rails and dose not lose any speed.
Got to figure out how to maintain this and still run in race water.
I do not think that adding down force is the answer.
The ski will just react harder.
I think It will take a different ski set up and some stabilizing wings with no down force.
Did some testing with my SGX a few years ago and tried a different wing Andy made up.
Tried using it with nothing on the back but the wing and the blow out as you call it.
The boat was hard to launch but the props worked at almost 100% needed smaller props to get it going.
I may try this wing and the smaller old style SG center ski with less AOA and no re-curve (blow out)

 

[Jeff Lutz]

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???????

David, over the last 3 years I’ve worked on planing surface relation a lot, moving the planing surfaces forward etc etc. I was having a different issue on my twin in race water that I resolved. You do need to think about the CG for more than just turn fin location when boat designing. When the planing surface is further forward of the CG it is harder for the prop to over rotate. It also supports the front end better. Even if moving the front planing surface further back helps with chatter in the turns, it will be more prone to snap roll completely over. Also, moving the front planing surface further forward made the turnfin location better closer to the CG than I’ve ran in the past. I would increase AOA in the front sponsons some and play with props before building new fronts. It appears that you are running a lot of cup and LE pitch . Just to see how the boat reacts put a 1467 on it with cup and cut the tongues down a little. Hope you work it out, Jeff Lutz

 

[MikeStewart]

It looks like your rudder blade is in line with the side of the hull. What effect does this have compared to the rudder being behind the hull? (inside the width of the hull). Is the rudder running in clean water as you have it?

 

[dwilfong]

David, over the last 3 years I’ve worked on planing surface relation a lot, moving the planing surfaces forward etc etc. I was having a different issue on my twin in race water that I resolved. You do need to think about the CG for more than just turn fin location when boat designing. When the planing surface is further forward of the CG it is harder for the prop to over rotate. It also supports the front end better. Even if moving the front planing surface further back helps with chatter in the turns, it will be more prone to snap roll completely over. Also, moving the front planing surface further forward made the turnfin location better closer to the CG than I’ve ran in the past. I would increase AOA in the front sponsons some and play with props before building new fronts. It appears that you are running a lot of cup and LE pitch . Just to see how the boat reacts put a 1467 on it with cup and cut the tongues down a little. Hope you work it out, Jeff Lutz

Yes props will have a lot to do with it.
Will not make any more changes till I find the prop that will work best like it is built now.
I have a 2717 23 38 3 blade prop that I will cut down and remove some trailing edge cup.
Just have a feeling that high rake may work the best as the boat is built now.
Wish there where more high rake props out there to test with.

 

[dwilfong]

It looks like your rudder blade is in line with the side of the hull. What effect does this have compared to the rudder being behind the hull? (inside the width of the hull). Is the rudder running in clean water as you have it?

none.......
How would it be dirty running 1/4" more out side .
If any thing it would be cleaner away from the prop and ski.

 

[dwilfong]

OK well it is time to build my own hybrid of this boat.
I will start a new build tread her soon.
I decided to leave this boat as is so I can see the difference side by side.
Will gust have to swap the eng tank and cowl at the lake to run them both.
It will be a Zgull.................................
HOLD MY BEER>>>>>>>>>>>>>>>>>>>>>This will be a good one......LOL

 

[Terry Keeley]

Why $hit can this whole project when you haven't figured out what's going on? I've seen quite a few of these boats running super smooth so I'd bet it's something in your hardware/setup that causing it to hop.

You might build a whole new boat with the same set of problems.

BTW, I've tried many, many different aero "fixes" to try to correct the prop wanting to come out (hop) on my SAW boat. I made sponsons from 3 -8*, several different skis with different sizes and angles, tried winglets etc., etc. They all worked to some degree but the biggest improvements were with anything that was in or touched the water.

Was getting real close with my new props having only the tail come up slightly once or twice in a 500' run. Cut 1/4" off the rudder and it was absolutely smooth. Cut another 1/4" off and it no longer held the boat straight and needed left correction. Back to the hop...

 

[dr gary turner]

I would consider decreasing the height of the ski. Angle is important but the ski maybe too deep.

In setting up a non ski boat with rears we get the boat level on the fronts and the strut and put the rears on 1/8 inch off the table. Sooo maybe a level boat sitting on a ski and fronts maybe a prob.

Again I like some blow out