Need Help With Phenomenon Build

[steve55340]

I have 3D printed a model of the quad-turbine boat Phenomenon. At least it resembles the boat, definitely not an exact copy. It is 72" long and 17" wide. I had to make it this big to try and fit four drives on it. I plan to have four motors, ESC's, batteries. I know, it's probably a stupid thing to do, but I like doing things out of the ordinary. So I want to build it and see how it runs. At worst (if it doesn't end up at the bottom of the lake) I'll have a bunch of stuff for more reasonable builds.

I have MHZ drives and a center rudder. The max diameter of the props can be slightly less than 47mm. I may try putting a larger prop on the outside drives and smaller on the inside. The inside drives will get a better bite, I think. I have been getting some info from a member in the UK and Using his input I decided to ask AI what I should use.

Here is what I'm thinking - SSS 4082 1850kv motors, Castle Hydra XLX2 200A ESC's (I'm open to using a cheaper ESC, but want data logging for sure), SMC Tru Spec Extreme 8S 8000mA 120C batteries, Octura X445/3 or X447/3 cut down to 46.5mm.

I know everybody has an opinion on what to use so I hope we can come up with a logical plan. This thing is going to be very expensive, and I can't be buying a bunch of stuff that won't work. I'm not looking to get max speed out of this thing, but I do want it to look impressive, big roost and maybe 80+ mph? Some of you guys with the larger boats may be able to figure out what adding more motors will do for this thing. Thanks in advance.

I tried adding pics to this thread a while back and lost the whole thing. I'll post this thread and post pics below in another thread.

[steve55340]

Pics of the boat - printed in 24 sections and many hours.Boat 1.jpgBoat 2.jpg

[Peter A]

Two drives, Big 56mm can motors, 500kv, 12s, 300A esc's, props start 65mm or so. It is a big boat. If you insist on 4 drives lower your kv anyway for 8s. 1100-1300 kv. Small high rpm props may not be very efficient on a boat that size. The only way to know is to try it though.

[fweasel]

That's a really cool looking model. Scale wise, the props we run are way oversized in comparison to the actual 1:1 hulls. With that said, running four drives and the logistics associated with them is going to be quite challenging, and would likely hurt the turning ability too. What does the bottom of the hull look like, specifically the rear where all 4 drives would be mounted.?

[steve55340]

Thanks for the input guys. Here are a couple pics of the bottom/drives. I have modified the hull so drives can be level with bottom or moved up/down a couple mm. Ended up with pretty large steps - hope it will be OK. I guess my main question is will the combination of electrics work well together? Will twice the normal props push the boat OK? It boils down to prop surface area, right?Drive Pic 3.jpgBottom 2.jpgAPR 10 Transom 3.jpg

[fweasel]

Those drive angles are still too "negative". The outboard drive specifically cannot be run neutral, or level with the hull bottom, based on the first picture. You can mill off some material on the black pedestal mount to provide a few additional mm of clearance before the stainless drive support bottoms out. That will get you closet to neutral, and hopefully allow a positive angle as well.

1850kv motors on 8S is WAY too much RPM, that's SAW territory for a boat in the 50" range. There is no magic equation to tell you what RPM, voltage motor size, and prop size to use. It's a combination of experience, copying other known successful builds, and general rules of thumb regarding RPM ranges, thrust cone size, current limits, etc... While I've never built a 72" quad drive cat, I'm fairly confident 45-47mm 3 blade props at any RPM won't have enough diameter to push that hull. They'll just cavitate.

[steve55340]

Thanks for the input fweasel. The pic of the drives are just where they happened to be sitting at the time - I printed many models of the stern section of the boat getting the height of the drive pedestals to where they could be adjusted both positive and negative trims from flat to the bottom.

Your opinion on the props and electrics worries me. Sounds like I better make this thing as light as possible to even have a chance of working - even using only two batteries will help. I posted this thread to find some of you guys who have the experience in all the options that are available in FE boats. I realize nobody has tried four motors and can give me exact details. I look at it as dividing the boat size and weight by four (or at least, by two) and having to run whatever is best for the size props I have to use.

If my choice of motors (using two of them) is good for a 50" boat, maybe four of them will be good for a 72" boat. I need to start somewhere and hope what I choose will be enough to at least get the thing to run halfway decent. Just don't want to pick a motor that will never work. There are so many motors to choose from that I don't know how you guys know what to use! I have to use the props I can fit on the boat so I should use the closest motor to match. If it won't even get up on plane, I'll have to make it a twin cat, I guess.

As far as ESC's - as long as I choose one that is large enough to handle the current, I should be OK, right? I figured getting the XLX2's as they should work if I make it a twin cat too, right? Thanks for your input. Anybody else have any recommendations about this boat?