Catamaran riding nose high and flipping

[tlandauer]

Ideally, when one raises or lowers the strut, it should go up and down in a straight line assuming the axis is already parallel or as close to parallel ( neutral)as possible. I think it is better to view the axis of the strut in a right angle in relationship to the transom. But in the real would this will not be the case, the stuffing tube is fixed at one end and so your path will be more of an arch than a straight line. Experienced builders anticipate this and they set the curve so it can accommodate the up and down of the strut without having the attitude of the thrust being too much either way. Factory RTR's sometimes have a curve already biased towards "positive" so if you raise the strut it will make the arch path more pronounced and eventhough your strut height may be correct, your thrust angke can be wrong.
Hope that clears it.

[jester_s1]

ron1950- No, I wouldn't want to start putting significant money into upgrading the boat. I can see spending money on the hobby, but not on tweaking a $200 boat that is probably too small to ever handle the waves really well. If I can make some tweaks to the stock setup and improve it, then great. If not, I'll just relegate it to a calm day boat for making hot straight runs with.

If I understand the process of reshaping the tube, I just need to be sure nothing changes right at the spot where the tube exits the hull? What makes that area so sensitive? To get less positive angle and be able to raise the strut, I'll have to take some arch out of the tube at the middle and put more in at the front near where it comes out of the hull. Is there anything else to watch out for when I do that?

[tlandauer]

Any undue movement on the floor will weaken the seal. It is just a matter of seeing how the floor flexes when you wiggle the tube. So I try to immobilize it with one hand while doing this reshaping.
You may not need to have a serious reshaping, proceed with caution and if indeed you don't need to, then there is no such concern, like I said, good luck!

[kfxguy]

Look. Honestly rtr's are usually not the best quality nor the best design, we know that. But, if you like the boat, then it's worth upgrading. They may not make bolt on upgrades for it, but you can easily modify things to make them work. A hull is a hull and you can do anything you like to it. It will be a learning experience, which to me is valuable on itself. I started out this boating stuff a year ago. Started out with a plastic hull, 26" proboat shockwave. Man I thought it was pretty badass with my mamba minter setup I put in it. It was a rush because that little hull could not handle much speed without it flipping. Then I moved "up" to a miss geico thinking it's world's better than the Shockwave. Well it was, but I had no idea how far behind I still was compared to "real" hobby grade boats....I was in for a surprise. But, I did learn a ton before jumping into building my first boat. I was lucky enough to have bought a almost completed "real hobby grade" boat and was able to see how it was assembled. That helped alot. Now here I am, building really nice boats for myself that I had never imagined. What's my point? Continue on and do what you need to, to fix your boat and make it run right....it will help you out in the long run. Now.....to answer your question....

Your prop looks like its angled up. When the prop is angled up, like said above, it brings the nose up. It's really a balancing act to get it right. I was running my 26" cat earlier today and noticed it was running nose up. It kept coming out the water. I just knew it was going to blow over...and it did. I didn't have the tools with me to change anything with the strut so I moved the batteries about 2" forward. Well, that did the trick. When I got home I checked the strut and the prop had a slight angle to it. With most cats, you want the strut (prop shaft) level to the sponsons. I'm sure there's a little more to this if your tuning to break records, but since we arent, level is a good starting point. Here's how mine was when I checked it...

(Note, boat is sitting flat on table, strut is too high I believe)



And this is how it was running before battery movement (it never flipped again after moving the batts)

[jester_s1]

kfxguy- Mine isn't running even as flat as yours was there, so if your nose was too high then mine definitely is. I'll try moving the battery first. I guess having the CG a bit more forward than recommended won't hurt anything else, will it?

So now you guys have me thinking, what is a true hobby grade boat in this size? If I can stick with using these 3 cell 2200 batteries that would be a plus since I have 4 of them that I also use with park flyer planes and my helicopter.

[kfxguy]

How fast are you looking to go or what are you wanting out of it? To step into a much higher realm, you'd need to build it yourself. If you want an rtr with potential, there are a few models out there.

[jester_s1]

I want it to handle well on the water and not flip over. This Desperado Jr is fast enough, at least for now. It's actually my wife's boat. I'm in the planes and cars, and she got a wild hair that she wanted to buy this boat that she saw at the hobby shop when I had asked her to pick up an aileron extension for me. She might go for a building project later on, depending on how involved it will be. Are we talking about a plywood kit that you have to assemble and paint, or are we talking about a fiberglass hull that you have to put all the electronics in?

[Luck as a Constant]

If I were to do anything I would re drill the strut mounting holes higher and shim it so the prop is more neutral. Probably need to re shape the stuffing tube for your shaft.

[jester_s1]

I reshaped the stuffing tube last night (this thing is made of some really tough thick wall aluminum!) and raised up the strut. I've gone from about 3/16 inch below the sponsons to a tick less than 1/8 inch above. I also got the strut as close to parallel to the sponsons as I could. CG is still at 30% because I'll have to move the battery connection outside of the little box that's in the hull and seal it up then make a battery mount. What running characteristics am I looking for to tell me if I have the prop high enough and at the right angle? I can shoot a video if I need to in the next few days.

IMAG0578.jpg

I tested the boat at the lake this morning, and it's improved. It doesn't try to flip end over end now when I apply full throttle, and it does run a bit flatter. But I'm still getting a lot of bounce and it is still pretty bouncy. I flipped it once when it started bouncing on the transom at 1/2 throttle and I didn't slow it down in time. Winds were 8-10 mph.

So I watched a video about blueprinting the sponsons. Is that commonly done on these blow molded hulls? I can't sand material off from this thin plastic, but I can add epoxy putty to it. My concern would be though that this plastic must flex more than a fiberglass hull does, so will a blueprinting job actually last? If it would help, I have some 2 oz glass and could put a couple of layers on and blueprint that. Also, the shape of the sponsons on this boat aren't nearly as wide or flat as I'm seeing on some of the hobby grade catamarans. If you guys will have a look at the picture, can I reasonably expect to see an improvement with these as much as they probably stay down in the water?

IMAG0579.jpg

[grsboats]

I don't think a blueprint will help too much in this case.Depending on thickness of plastic you will have to make reinforcement inside the boat with light cloth and epoxy resin before sand it If the boat still bounces there is something wrong with the set up; can be wrong strut angle or wrong CG.If possible move the CG little forward to help to keep the nose low and go test till get it flat all the time .Gill

[kfxguy]

My rivercat would Bob up and down at half throttle when the prop was barely angled up. Level, no more bobbing

[jester_s1]

At full throttle I was out of the water more than I was in. We're talking 2 foot jumps completely out of the water, and this isn't a crazy fast boat. It probably tops out around 30 mph I guess? I'll try moving the CG forward a bit and see what happens with it.

On the blueprinting topic, I didn't mean to add glass to the inside and then sand the hull away. I meant adding glass on the outside to have some material to sand back down to be flat. But if it's a waste on this hull shape, I'd certainly rather not spend the time on it.

[jester_s1]

I did some experimenting today with a CG change. I put some lead weights on the nose (just for quick testing purposes) and got the CG to 35%. The water was a little bumpy today, so here's how it did.

http://youtu.be/gA2ro3GvBTQ

It was very prone to snapping loose (that's what I'd call it if it was a car anyway) in a fast turn, so I figured the nose was digging in to the water too much. Am I right about that? I took some lead off which took the CG to 33%. It turned better then, but is still pretty bouncy.

http://youtu.be/J5leIb3CLmY

Then the wind died down, and I was able to make a run and really see how the hull sits in the water. From what I can tell, the sponsons are touching the water at roughly the 1/3 point from the front. It looks like other catamarans sit farther back from there, don't they? It also felt a little slower too than it has been. If that's the compromise I have to make in order to have a boat that is driveable, then so be it. But then just after this video was taken, the boat dug in to a small wave and flipped again. I realize this one is kinda far away, but when you're working with a 6 year old videographer, you get what you get.

http://youtu.be/6jzLn_rz944

At this point, full throttle turns still result in bad bouncing and sometimes flipping, and the boat is still a bit bouncy in a straight run. So, do you guys see anything in the way the boat runs, especially in the third video, that indicates where I can make improvements now? I understand that having the hull sit right in the water is a combination of CG and thrust angle, but what I don't know is how to diagnose which one needs tweaking if either.