Jeremy_H

Are your flips only occurring on throttle off?

crispyspa

Off throttle most of the time. I've flipped at full throttle though. Mostly because of rough water.

arcdude

I would agree on not using polyester resin on any wood substrate, vastly inferior unless a thinning method is used. One method that may help is to place paper towels over the suspected contaminated area and saturate with Methyl Hydrate, it has a wicking effect and will draw foreign oils, wax and so on to the surface to be absorbed by the paper towel.
Cheers,

1QwkSport2.5r

Keep in mind the forces involved when you have 25-30lbs of wood going 70mph on smooth water. Now add the G-forces in a flip at 70mph of forward motion. That's a lot.

Kurt - you might need a Gyro or three on that pig!!

St.Marek

Hello.
I suggest to make hull from balsa and cover bottom of it with laminate, secure top of the model with clear coat. By this hull will be lighter and faster. Simply slim down it.

Jeremy_H

I reckon the damaged is being caused by the rear of the boat flexing the deck around a hinge point created by your deck stiffener, the sponsons are seeing huge tensile loads on the adhesive joint as the force, which could have exceeded the bond of the ply itself, pry's the sponson away from the deck. I believe your stiffening should run fore and aft, and to stop putting it in that position rig a simple brake off a Y off the throttle channel, set so that it contacts the water at 1/4 throttle or something. It strikes me that it's the classic race airboat problem where the removal of prop force to keep the bow down on throttle off allows the air pressure to win and flip it.

I think

crispyspa

When you put it that way, it takes on whole new look.

That's exactly what happened this last time.

I have a video and a still frame from the video I want to share. Thoughts?
It looks to me the rear is bouncing as well as the sponsons flopping while the top deck is flexing.

http://youtu.be/9A9GxmJZ3ew

1QwkSport2.5r

I think the bounce is an easy fix by adjusting your CG. The transom end is likely a LOT lighter without a big bulky engine and fuel tank so your CG will need to compensate for that. You'll never get rid of the bounce completely just due to the water surface is likely rarely ever like glass. Minimizing it might require doing a motor stand edit or adding ballast?

I think you or one of the other veteran SI3 builder/operators said the overall known speed limit for these boats (speaking of the smaller .20 & .60 sizes) is in the 65mph realm... Could it be that they just aren't stable enough to handle that kind of speed even though they're built incredibly strong? What thickness is the top deck of the 1/4 scale? Another thought is to biscuit joint the sponsons to the top deck. Doing a blind butt joint, fiberglass or not, is riding on a prayer in a high stress environment. This is where I would be going into "stupidly overbuild" mode and super build the sponsons. I went simple on my SI3 mini originally and narrowly averted a disaster with a skin failure. The re-do is 200% stronger. But keep in mind, I only know how to overbuild... Every one of my projects exceeded my planned RTR weights by 20% or more. The SI3 mini was supposed to be 3-3.5lbs but ended up at almost 5. After the last couple runs with that boat, I doubt it will see 60.

Jeremy_H

Looks like it's just basic lift to me. So I guess it's either adding weight, sorting some down force via wings, or changing the angle of attack of the deck. I'd go for the latter, by adding some depth to the rear of the tub's planing surface perhaps.

crispyspa

I've kinda been thinking about it and I think I can cure 3 birds with one stone by adding a wing behind the motor pylons so it helps lift the back end out of the water.
Bird 1 being the bouncing, bird 2 being the tendency to flip at speed and bird 3 being reducing the drag to gain speed.


Only two drawbacks. It might not work and it will be destroyed should the boat blow over.

I thought about adding a couple of ride pads like Jeremy suggested and I may try that first. I did try it on my Big gasser SI "Overbite" but I didn't ever get enough speed to overcome the drag and lift the back out of the water.

crispyspa

Time for an update on this boat. I started out this year with a feedback glitch in the Castle 200a ESC. The motor would glitch out when steering was applied....I have no idea why, and the guys at Castle have drawn a blank also. Funny thing is, it only does it with the giant scale servo and not a standard. I tried 3 of them and got the same result.
https://www.youtube.com/watch?v=sHkvcsAEtr8 Anyway...I relegated the castle to another boat project and ordered a Swordfish 300a speed control. I'll be damned if that thing wasn't defective too.

https://www.youtube.com/watch?v=-2qRkwsNqew I'm still waiting for the replacement from Hifei electronics in China. The Swordfish will allow me to add a couple of more cells to the battery pack an finally break that 70mph barrier that's been eluding me for so long. 14 cells puts me over the motor rated capacity of 11 cells by 8ish volts but as the good Lord as my witness, I will make 70 mph..maybe 80?

pinky_d_brain

Nice to see you back at it Crispspa
Sounds like your larger servo is pulling to many amps and browning out the system or something. basically puling all the power to it and not providing the receiver with enough power casing a disconnect and then reconnect. With a smaller servo this would not happen. If your ESC allows you to increase voltage to the receiver that may fix the problem.

crispyspa

I have actually tested the high draw theory by placing two 1600mah 6v packs in parallel on a "Y" connector. The big servos don't actually pull their power through the receiver, they use a "y" harness and power the Rx through the BEC circuit. So in effect, I had 6V @ 3200Mah powering

All that still doesn't explain why it worked fine last fall.
Anyway, I blew the capacitors and went to replace them and look what I found.


https://www.youtube.com/watch?v=CogLiEV9EeQ

crispyspa

Got the new Swordfish today...Now just to find a day to run.
https://www.youtube.com/watch?v=f2qTDMKjVlw

1QwkSport2.5r

Yeah baby! I'd love to see that thing run 70+! Fall rendezvous perhaps? LoL.

asmithnc

Make it Happen Crispy Guy!

crispyspa

Found out why it was cutting out. One of the 5 cell batteries has a dead cell so all the others were carrying the dead one and when power was applied there was a big enough voltage sag to sen the ESC into LVC.
I've ordered new batteries and removed the dead cell from the one pack to make a 4 cell, so I wont have to cobble together 4 or 5 packs to make 14 cells, just 3 packs. Two 5 cell and the one 4 cell. Less resistance because less wire.

I have another video of it with 14 cells hooked up. It tries to lift the back of the boat up. According to the prop calc, this set up on 14 cells should have just over 30 lbs of static thrust @ 13000 rpm with a speed of 106mph It requires 10+ hp, to run it 7.62 kw.


Video.
http://youtu.be/yvbcy4nNiXo

1QwkSport2.5r

That is just sickening, Kurt. Sick I tell you. LoL!

Like the old days... Wall climb! Wall climb! (Chants... Wall climb wall climb!)

or the Empire State Building.... ?

crispyspa

LOL! A wall climb would be super scary. I am genuinely nervous about running it. Got knots in the gut just thinking about it.

1QwkSport2.5r

But it'd be so much fun!! Hooty did it!

Id be scared too. You have a LOT to lose if she goes south. You're pushing a LOT of power to that poor little motor...

crispyspa

Tried again today, I think the sponson gussets are causing the bounce in the stern.

http://youtu.be/F9VoIPxo1Ig

hooty301

Awesome run!
Be persistant, I know the feeling....when you said always a problem.
After the NC meet in 08 I tried every chance I could get to better my speed but the gps kept coming back dead, It was frustrating too say the least.
I finally got the gps problems sorted out, took it for another run and lost radio contact, smacked into a dock pylon at 73. It was a rough week following.Spent the winter rebuilding.

I also feel ya when said these electrics are scary. I guess were just used too predictable fuel engines,
running these high powered electric setups they can have a mind of there own if something's not right on start up.

I know I'm a little scared of mine and it's only half the size of your beast.

hooty301

Watching yours makes me wanna dust off mine, and hit the water again.

That is some awesome speed, especially for a boat that size!

hooty301

....delete double post....

crispyspa

Thanks.

Do it! Dust it off and get out there.

You have any thoughts on the sponson strut theory?