I need to be schooled

[Boat_Newb]

Hey everyone. Haven't done an intro thread yet, so a bit about the boat...
Atomik P1 KOS, within a few weeks of getting it off kijiji I blew up the stock 60A ESC, replaced it with a Dynamite 80A, then the magnets in the stock outrunner all let go, so I took the motor out of my truck and put it in the boat, new motor is a castle 1415 2400kv with a 5mm shaft upgrade. Its a torque monster IMO, I replaced it in the truck with a Tekin Pro4HD 2500kv and the magnets in it have NOTHING on the castle motor.

I'm still running the stock nylon prop 36mm x 1.4 pitch (50.4mm if my math is right) and 1/8" flex shaft, and I'm getting 35mph on a 4s battery. I am considering buying a 5s. The 1415 is only good up to 5s, the ESC is good for 6s.
I did a bunch of research about props a few nights ago before buying a new prop. My hobby shop can't get any replacement parts for the boat, the atomik part numbers don't come up in the great planes network, I tried to get the replacement aluminum one.

Thinking I knew what I was doing, I picked up an Aquacraft L40x57 (1.425 pitch?) metal prop.
Thinking that the metal would be an improvement in itself I tried to keep the pitch as close as I could.

When I got out to the water, running 4s, the boat couldn't even get up on plane!

I've read of other people putting octura props in their KOS's (x640 seems to be popular) but I don't know if my hobby shop can get them, and even if they do, I have NO clue about how to finish/balance them. The Aquacraft prop was in stock at my LHS and came finished.

Is it just too heavy? Or do I not understand prop pitch?
Sorry for the newbish question

Thanks!

[Skullcracken]

No no man. Pump the brakes. 2400 is maxed out on 4s. Ideal on 4s is 2200kv. Your stock motor was a 2000kv usually in a KOS P1. What you want is to prop up. Get an octura X440 or X442 2 blade prop. Just upping the prop size you should reach 45mph. The stock prop is too small. Definitely don't go up in cells. I use a 120amp esc just running 2200kv on 4s. Boats are not anything like trucks as far as matching cells a kv.
A quick generic "FE boats for dummies" cells/kv guide:
4s - 2200kv
5s - 2000kv
6s - 1600kv
8s - 1000kv

[Skullcracken]

Basically you wanna be 35,000 rpm range.
KV x cell volts = rpm
e.g. 2200kv x 14.8 volts (4s) = 32,560 rpm

[Skullcracken]

That prop didn't work because the pitch is way too much. Pitch is 2.2 on that GrimRacer prop. If you want to try out that prop. Have a friend toss the boat forward in the water and hit the throttle as it hits the water. The prop is cavitating. Not a good match for that boat.

[NativePaul]

That L40x57 you have is indeed 1.425 pitch, nowhere near 2.2, not sure where Skullcracken got that from. It is however a lifter prop more suitable for a hydro than a mono, you might be better off with a prop without the L preceding the numbers like the 40x53 or 40x55.
I believe the AQ props are not finished and are just tumble polished so they are nice and shiny in the packaging for sales reasons, they still need sharpening and balancing before use.

You should be able to get decent speeds without having to buy a new battery, 4s with the right prop will be plenty on 2400kv.

[martin]

The 1.425 is the pitch ratio, the 2.2 that Skullcracken refers to is the total pitch in inches ie 57mm = 2.2".

[detox]

If you go larger on the prop your 80A ESC may not live long. The simple Octura x442 will get on plane quick and go faster.

[NativePaul]

Ahh, thanks Martin, now it makes sense, sorry Skullcracken. I'm awkwardly too young to think in inches, I think in miles then meters, yards, feet and millimetres, although I can convert them if I think about it my brain doesn't naturally work in KM, feet, inches or CM.