Sponson rock

[Gary]

Hey guys. I have a new problem with my Fun Boat. Its a Formula hydro , just like a miss bud or llumar and elam. Boat always ran great with a top speed of around 54-56mph. After a little tweaking of prop and hull it runs around 61-64 mph but the sponsons rock side to side as the boat is at top speed and just keeps getting worse. I moved prop all aroud but no good. Transom is fine...no hop

[Rumdog]

Usually on a hydro, too large of a prop will cause the prop walk you are seeing. Prop diameter that is. A little downward angle of the strut may help, but if not it's prob. the prop. Also, that hull wasn't designed for those speeds. Sponson mods or an air dam may be required to settle it down.

[Gary]

Its not prop walk. I know what that looks like and have delt with that on other boats. This is a FRONT side to side movement. It could be the hull but every now and then it will stay smooth......... Strange.

[Doby]

If its a Proboat conversion, Its fast enough in the high 50, low 60's....lets keep things in perspective...Whats your setup??

[properchopper]

Interesting situation, for sure. After trying everything I could think of to eliminate the hop from my UL-1 [ including exhausting my repetoire of Guatemalan Voodoo chants, and at Douggie's advice doing a Scottish Jig around the boat], I just added pads to reduce the AoA, and in a harebrained fit of desperate inspiration created some side vents channeled by air dam strakes to reduce the air-pack. Will test tomorrow & report. If the boat still does the death wobble after all this [ including packing weight inside the sponsons to reduce the roll] there will be a de-commissioning ceremony which will involve me wearing my heavy-duty engineer boots !

[Gary]

Propchopper you always make me laugh!!!!!!!Good luck tommorow. I will be testing at my big pond aswell with some adjustments and see what happens. Doby.....Combo is a 8xl,120 hydra x442 and 18 volt batts. you can see it in the video section under My Fun Boat. And Doby..Fast enough?....I never heard such foul language before !!!! LOL

[Gary]

Ok here is a video. You will see as it is coming towards me a couple times when the problem happens. It only went 60 but will do it a 55-70mph. http://www.youtube.com/watch?v=D03K_1rqUKU

[crabstick]

Hi Gary

is your turnfin straight or does it have a slight curve in it ?

[Gary]

Its a curved turn fin and its a pretty good curve to it aswell.

[tharmer]

I think it's the hydro version of chine walking. As too much air packs under the hull, one sponson lifts to dump air, then the other sponson lifts to dump air, the hull settles down again and again fills with too much air and the process repeats.

Try a slightly deeper strut, say 1/16 to 1/8". This reduces the amount of air under the hull by letting the transom ride higher, thereby reducing the AOA of the bottom plane.

-t

[Simon.O.]

I think it's the hydro version of chine walking. As too much air packs under the hull, one sponson lifts to dump air, then the other sponson lifts to dump air, the hull settles down again and again fills with too much air and the process repeats.

Try a slightly deeper strut, say 1/16 to 1/8". This reduces the amount of air under the hull by letting the transom ride higher, thereby reducing the AOA of the bottom plane.

-t

I have been down this path with one of my experimental hydro hulls. Lift the rear to reduce the AoA on the front, settle. Prop up and do it all again until it ploughs the sponsons. Drop the rear and dam the front tunnel entrance. Prop up or power up and do it all again until you realise that this is as fast as the hull will go.
This last bit takes a while to sink in.

Pushing hulls is a hoot. I especially enjoy the repair work when the blow off at 40+ mph and I get rebuild it stronger. This is for a 24" wooden hydro.

[crabstick]

Its a curved turn fin and its a pretty good curve to it aswell.

Just for giggles, Try putting a wee bit more of a curve in it, I find that can settle down a hydro that exhibits this behavior. Tylerm and I spent a day at the pond with his little 1/16 scale atlas van lines, running 4500mah 2s and an 8s fiegao. It was freaking fast but got its dance on once it was topping out. I put A nice gradual curve in the fin and settled it right down.. still fast, but not doing the hula on the sponsons.

[Gary]

Ok came back from lake again and fried motor.BUT found that putting in more than normal strut angled down and a little deeper made 90% of problem go away. Funny thing is boat still went a best of 63 mph so im happy with it.It was way off from where a normal seting would be. Oh and simon i know all about the "Rebuild " you speak of. When my SAW boat bows over at 100+ it tears the motor right out of the hull. One time it punched a hole on the top of the cowl. Good times!!!!!!!!!!!!!!!!!

[RandyatBBY]

Keep the strut flat to the setup table and drop the strut a 1/16 of an inch. You may need to drop it 1/8 but I dought it. You are just too loose. angling the strut will cause the rear or whole boat to hop.

[Ub Hauled]

I liked a few of these ideas... I went down that road as well, the thing is my boat was really happy on turns with the strut depth and angle, so I added weight in one sponson, problem solved... besides, she was getting a bit too light on the straights... two birds with one stone.

It is air packing most of the time, but it could very well be a turn fin issue.