Converted Cat from single to twins, now which prop?

[RuntheraceAMC]

I converted my DFE 36 from a single Leo 4092 1730kv to twin 4074's 1800kv on 5 and 6s. Running twin raider 150 esc's

Right off the bat I know this set up is pulling way less amps. I use to get 4 mins tops on 5000 MAH batteries (on a 647 prop) now I am getting 10-12 mins and Still at 3.7-3.8 volts.

Right now I am running 442 props but I am disappointed that I am not over 60 Mph. Temps are 70-80 F even lower for the motor but water temp is in the 40's. I think I need to be running 44mm-47mm props with 1.6-1.7 pitch.

On my single set up I could not use anything more aggressive than a 647 without heating things up, but on a twin I think it's clear I am pulling way less amps.

Any thoughts on the right setup?IMG_4233.jpg

[srislash]

Well, I think you should be good with 45mm at 1.6 pitch for sure on 6s. Now which props is the deal. ABC or 'other'. The 17* ABC's will likely get it a little light on the nose compared to the 442's(BTW, just shy of 60 is probably about right at that RPM with the 442's). You can get the batteries forward or dial some Neg in to get them tuned. Other options would be CNC or 'custom' Octura's.
You could try some 447's and just watch temps but you are probably good at those water temps. You will just have to settle it down in the summer. Likely 1815@17*rake would work too.

Shawn

[RuntheraceAMC]

Thanks for the advice

[dasboata]

I do have the 1815/17* in stock if you need 1 custom finished PM me if interested thanks Chris

[RuntheraceAMC]

I am interested but I need a reversed prop too since it's a twin setup

[fweasel]

Now I know why your wife wanted to restrict you to the 24" plastic hull...

[RuntheraceAMC]

It's bad man

[dasboata]

I am interested but I need a reversed prop too since it's a twin setup

I have some sets of 1914/17* I will make work for you

[RuntheraceAMC]

I bought a 43 mm CNC prop with a 1.7 pitch and am getting a bit better results. 50 mph on 5s (vs 45 on the 442) and 6s I am running 56mph (vs 53 before on 442). Still seems to be under achieving. No sign of anything heating up but with water temps in the low 40's I am scared of being deceived.

I just think the prop load behaves completely different in a twin with half of the prop out of the water since it sits directly behind the sponsons vs getting clean water thru the tunnel on a single. Maybe I'm wrong but it seems to need more prop. I don't think I am under powered. You would think a change from 1.4 pitch to 1.7 pitch would yield a bigger speed jump than I am witnessing but if a significant portion of the blade is not in the water than any pitch changes would be muted any way.

What do you guys think is going on? Picture of the strut angle to follow but the prop end is angled very slightly up.

[boredom.is.me]

The water flowing through the tunnel isn't going to be any higher than the water flowing off of the sponsons when on plane. At least not to a major degree. Your props probably just aren't in the water enough. Angling up isn't something you see on struts and stingers.

[RuntheraceAMC]

. Angling up isn't something you see on struts and stingers.[/QUOTE]

Not sure what you meant by this....

[boredom.is.me]

You said your strut is angled up (positive). Neutral to negative is the norm along with a rearward cg. Having to go positive would mean that your trying to get the bow up.

How stable is it?

[RuntheraceAMC]

Porpoises at low speed (only in the turns). Super stable at high speed with the occasional nose bob where it starts to look like a blow over is possible.

Just really surprised but the speed. Back to my original question tho: Does it make sense to prop up a twin more than you would on a single motor set up.

It should pull as many amps as a single so I should have room to prop up????

[srislash]

You can totally prop up a twin. Put simply it takes X amount of watts(power) to push a boat at a given speed. By going twin you share that power making it easier on each system. If a single pulled 300 amps to do say 90mph than a twin would pull 150 per side given the same Kv is used in both setups. A set of 45's is not a too big setup for that boat given its size.

BTW those numbers given are fictional, your twin setup is likely pulling 70 amps per side.

At what height off the bottom of the keel is the prop centreline?
1/2", 5/8"?

[RuntheraceAMC]

IMG_4301.jpg

Looks like a half inch