Prop KV and amp draw help

[fweasel]

i'm not sure i even know which hull you're talking running those electronics in.

[Jimmypooh]

That makes 2 of us. I don't know what the hull is other than looking at it.the pictures are up in the thread.

[srislash]

i'm not sure i even know which hull you're talking running those electronics in.

We are talking the 48” cat hull Ryan.
Jimmy, I think I’d be more in the 50mm range on props, perhaps 47mm. I don’t think id worry about the amp draw with 6s on 1250kv. You should be good there. I think 75 amps is where I’m at with 447’s and 1700kv Motors. Might even be less.

A few things to add to Ryan’s comments,
#1: I think the silicone would work fine in this situation. I did it on my little boat WITH flood tube when I started having sealing issues. Two years and no issues.
#4: I haven’t done the ‘annaeling’ process as I find the bends usually gentle and can be gently worked into shape. One size over and under tubing helps to get leverage.

And I was looking at the pics you posted and you’ll have to glass up that hatch but then I think that lid should seal pretty well. Bit of foam tape perhaps.

[srislash]

Jimmy, do you have a pic of the stinger you speak of? Perhaps a strut would be better.

[Jimmypooh]

Thanks for the prop size recommendation. Given your setup with higher kv, you're probably right I need something like x450. I think I'll try that first.

I'm definitely glassing the hatch. It likely won't look pretty for now since I don't have a ton of time, but I'll get her sealed up.

I don't have pictures of the stingers since they are in the mail. But these are what I ordered. I don't want to do a strut simple because I've done that before and wanted to try stingers.

https://www.ebay.com/itm/3-16-left-r...-/142314976890

[srislash]

Ok yeah Promise hobby is good to deal with. The tubes I usually run the tube just inside the stinger. Enough to go inside but allow the stinger to move up and down a little. Should only need a few degrees of travel positive/negative.

You shouldn’t really need to move the brass tube up and down within the hull.

CNC for 50mm props. I just got some from RCboat bitz I believe.

[Jimmypooh]

Those are fairly expensive compared to Octura for $12. Is it just because they are already balanced? Since I'm still not sure on the size I might go with cheaper props until I know what size I'm going to stick with. I'll still balance and sharpen though.

[srislash]

Those are fairly expensive compared to Octura for $12. Is it just because they are already balanced? Since I'm still not sure on the size I might go with cheaper props until I know what size I'm going to stick with. I'll still balance and sharpen though.

Oh I guess you are looking at plastic ones. Yeah they would be fine too as your not spinning 40k

[Jimmypooh]

Sorry looks like that correct size is $15 from here on OSE site: https://www.offshoreelectrics.com/pr...?prod=oct-x450

I don't mean to be too cheap, but in the next couple months I'll be buying at least 4, maybe more.

[Jimmypooh]

IMG_20190720_142054.jpg

First boat is complete. This is a fiberglass 32 inch Dumas Deep V 40 that someone made from a plug of my Grandfather's wood version. It's far too heavy because the fiberglass was laid too thick which is why it was given to me for free years ago. I call it the tank.

It weighs 4.3kg (10lb) all up and uses a 4074 2000kv Goolrc motor with a Seal 130a esc and Banggood special 40 x 1.9 prop with 2p 5000mah batteries. It draws 55amps peak jumping in and out of waves. My guess is that it does about 30mph, but I will clock it later using my 1:1 boat. The speed is about perfect for the rough conditions I plan on running it in. I may go up in prop diameter while going down in pitch, but this prop did fine.

For my test run I taped some plastic to waterproof it, but now that I know the boat works I need something more permanent. I'm open to suggestions for simple cowl materials. The tough part will be dealing with that weird front and back lip.

[Jimmypooh]

I'm getting close to finishing the 48 inch Cat. I just ordered x447 props (right and left handed). Here are the specs. Can anyone see any glaring issues?

All Up Weight: 18.5 lbs
Dual 4092 1250kv SSS motors
Seal 130a 6S ESCs
x447 Props
10,000mah 6S battery
CG at 30% from the transom

[srislash]

All looks good to start. Just watch the startups with that heavy of a boat and only 130amp ESC’s. It’s gonna takes bit to get it up and moving. Hopefully 447’s are up to the task

[Jimmypooh]

Thanks. It's getting cold here now, so I might not get a chance to run this boat until next year.

[Jimmypooh]

Quick update and a couple questions in case anyone is still watching this thread.

The black mono has been doing great. With 10Ah 3S battery, it has a long run time. I made a cowl for it out of plexi, but it's cracking where the thumbs screws hold it down. I'm going to have to come up with a better design.

The big twin cat is complete and I've put 4 sets of batteries through it. It's a riot in rough water and pretty fast. The question I'm having is that I can't seem to get the nose up high enough. I have the stinger trimmed all the way up, and the weight as far back as I can make it. Should I put some washers on the bottom bolts of the stinger to get some more angle out of it? I think there is a lot more I can get out of it if I can pull the nose up some more. Below is a video of it running.

[srislash]

It definitely sounds like it is working at it a little hard. If you balance the boat (Loaded ready time run with hatch on) on a dowel or something Where is the balance point in relation to the back of the transom? It should be about 30% of the length.