Hospital Hop...how to stop it?

[Capt. Crash]

Newbie question for all you hydroplane guru's.

My UL-1 starts a sponson to sponson wobble and sometimes gets worse and more violent until I have to let off. Some times it straightens itself out... but usually it doesn't.

What is the cause and cure for this condition?

Is this caused by being too light on the sponsons?

Do I need more weight forward or more prop depth?

BTW...I heard Darrel Waltrip (I think it was Darrel) talk about a car on the brakes too hard while getting into the corner too hot making the car hop up and out and hit the wall. He called this hop the "Hospital Hop" because that's where it lead too!

I call the sponson to sponson wobble the same thing cause that's where your boat is going to end up if you don't let up.

Thanks for the help guys...maybe I'll quit bugging ya someday....probably not though...cause we now have 3 of these new boats in the club and several more saying they are getting them....and nobody knows what there doing!

[Darin Jordan]

The first place on a Hydroplane that I suspect as being an issue is always the turn fin. Perhaps make yourself a STRAIGHT turn fin and give that a try. If the problem goes away, then you know where to start tweaking... Also make sure that it's aligned correctly, parallel to the centerline of the boat...

I'm not a big fan of curved turn-fins... They can work great, but can also be a REAL headache until you get them just right...

If that doesn't seem to cure it, then I'd look at the sponsons next... are they flat?? REALLY FLAT?? If you look at the pictures of my project boat, even though they appeared flat, a light sanding revealed some decent troughs down the center of the one sponson... This can cause the sponsons to suck down, then release, then such down, then release... Not good... MAKE THEM FLAT! Some block sanding and filler primer and block sanding again should take care of that for you... the other sponson on mine was REALLY flat, so just a little attention here needed... No need to go to the trouble of ride-pads if you don't mind taking the time to sand...

Just my $0.02...

[AndyKunz]

It could also be caused by an incorrect angle on the prop. You want the prop to push the nose down (but not too far down). If the angle is wrong, it's going to lift the bow and force air under the hull. The air has to come out somewhere, so the boat rocks left and right to let it blow out the sides. An air dam prevents the air from getting under there in the first place.

It could also be related to the design. If the air stays trapped under the hull too far back it will do the same thing. You need to allow the excess air to vent. This could be accomplished by removing the tunnel sides on the afterplane a little or by moving the sponson transom forward (that's the design solution, not the fix for something you already are driving).

Another possibility is that the angle on the forward portion of the tunnel is too steep. This lifts the bow. On my designs I use a shallow angle and run it farther down the boat, resulting in a lower pressure gradient and smoother operation.

Any chance you could get a video of it doing this? Some of it is normal - you might be seeing something normal and not realize it.

Hope this helps.

Andy

[Darin Jordan]

There I go, ignoring basic setup tweaks again!

I made the assumption that you had already tried various strut positions... Can't overlook the basics! (Like I seem to do from time to time... )

[Capt. Crash]

Any chance you could get a video of it doing this? Some of it is normal - you might be seeing something normal and not realize it.

Hope this helps.

Andy

We don't normally have anyone taking pics except me and I don't have a way to take video.

The "Hospital Hop" usually starts as a result of crossing my own wake from a previous pass. Once started...it usually, but not always, stays the same or gets more violent until I let off. When I ran with the air dam it still did it. The only difference I saw with the air dam was slightly slower speed...but this was a limited set of tests....3 runs with it on and 2 different props and strut settings. I will try it with the 40X57 prop 1/8" lower next run putting it at 1 1/8" from the bottom of the hull to the bottom of the strut measured with the boat on a flat surface, with out the dam.

At what speed do we need the air damn with this boat?

[Capt. Crash]

There I go, ignoring basic setup tweaks again!

I made the assumption that you had already tried various strut positions... Can't overlook the basics! (Like I seem to do from time to time... )

Yes...that's one of my questions above...will more prop depth fix this?

[Darin Jordan]

It's not just depth, but also angle... I haven't run mine yet so I can't give you good answers... I've read to the effect that 1 1/6" of depth with a 3-degree downward angle works... I think that was Tony's setting (Properchopper)...

[Capt. Crash]

It's not just depth, but also angle... I haven't run mine yet so I can't give you good answers... I've read to the effect that 1 1/6" of depth with a 3-degree downward angle works... I think that was Tony's setting (Properchopper)...

Oh boy...I must have missed the angle setting part of this adventure!

That poses new questions!

Which way is down? Prop wash shooting down?

What do you use to measure the angle?

How do you orient the boat and take the measurement?

Hey just how is this done?

[Darin Jordan]

Down means prop is thrusting downward... Front of strut is slightly higher that the back...

The way I set a strut initially is to remove the rudder and turn fin, then set the boat on a flat surface. I set everything from there... Set your depth (1 1/16"???), then adjust your angle (raise the front of the strut slightly until you get 2 or 3 degrees??)

To measure it... why not make yourself a shim from a piece of scrap wood... Sand it to the angle you want, then slid it up to the strut and set the angle...

I usually just eyeball it... until I get it where it runs well... Then I measure it after that with a protractor...

[Capt. Crash]

Thanks for all the great help here guys...one more question...if you had to guess...how far off the flat surface would the end of the strut (not propshaft) be @ 3 about degrees (in inches please)? or...how much air is there between the surface and the end of the strut....1/8" more...less?

[detox]

.030" max (front of strut to table) is what I have read. Going over this setting may cause stern (rear) to hop...unless you bend your prop.

[egneg]

This is what fluid said to do and I have about the same setup but at maybe 2 degrees down and no hop. When I was at 1" and 3 degrees I had some hop.

Fluid: My TP5000s weigh 9 ounces each, and I have no problems getting up on plane. Brian wasn't using light weight cells at the SAWs and his never subed. I suspect that the problem most guys are having is with the strut setting. Hydros are not like monos...
The bottom of my strut came 7/8" below the hull and angled at most 1 degree down at the prop end. If you are having trouble getting on plane you can simply flatten the strut. You do not want to angle the strut any more or you'll never get on plane! A flat strut is the default setting; if the bow flies then angle it down a bit at the prop end. It won't take much. If the boat runs too hard on the water raise the strut 1/8". Several guys have e-mailed me about problems getting up on plane, and in every case a minor strut adjustment was all it took regardless of the packs used.
Different props can cause trouble getting on plane too. Screw on a lifting prop combined with too much strut angle and you'll never get on plane. If you are using a lifting prop, flatten the strut. You may even need to run the strut up a degree at the prop end. "Best" all-around prop may be an m445 or K45. It will take some additional testing to find out for certain. The x442 is pretty small - doubt it has enough blade area to load the motor enough.
BTW all strut adjustments must be done on a flat surface like a table. The hydro should rest on the sponsons and the strut. The strut angle will be between the bottom of the strut and the tabletop. Don't try to do it "by eye", it won't work.

[detox]

Fealer gauge works great along with a flat piece of 3/4" MDF board. I attached three rubber non slip pads on the bottom of my 3/4 MDF setup board.

[Capt. Crash]

A feeler gauge I have...I must be getting tired...I dont know why I was thinking a gap at the back of the strut.

Ok...now I think I'm ready to go to the barn!

[detox]

Raptor has experimented with good success.

Hey guys, I finally got my hands on a computer.

The UL-1 really suprised me. I put an M445 on it for it's first pass, I flew it off and tumbled through the traps at 45mph. So I had a rough baseline. Next pass was with an M645 and 3/16" deeper on the strut, 52mph with a good ride attitude but still too light on the sponsons. 3rd pass was with a modified 2047 and a 1/2" deep tape air dam in the tunnel, 59mph pedaling it through the lights. Final pass was the same prop and air dam but 3/32" deeper on the strut, 65.7mph with a high 64mph return run. Temps on the final 2 passes were: motor 114F, ESC 126F, battery 109F (it had cooled down).

Stock motor/esc/hull. I didn't even touch the sponson bottoms. Total mods from out of the box: remove turn fin and vertical fins, tape air dam, strut adjustment and a fairly trick octura 2047. I did run my Futaba FASST 2.4G radio.

Then I put the turnfin back on with a 38x55 grimracer prop and ran 41mph for 8 minutes in rough water. I LIKE IT!!!

After the SAW passes