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?147996

[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... :laugh:

[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]

148242

Looks like a half inch

[srislash]

You should be good for 45mm. I am not sure how that hull will respond to a lot of pitch but I bet 1.6 would be fine.
Perhaps more on the CNC ones. But I think the suggested ABC 17-1815's would be the ticket.

[RuntheraceAMC]

Sweet! Ordering

[RuntheraceAMC]

Update: So I have been running CNC cleaver 46mm 1.6 props and have been in the 63-65mph range. I thought those results were very promising. Runs very stable at high speed.

I ran a bent shaft rather than replacing it and blew up on of my 4074's. So I am throwing my 4092 1730kv in there and ordering a matching one.

my temps have never really gone above 70F so I believe I can still prop up. Plus I should be able to swing more prop on the 4092. I can't find cleaver style props bigger than 46mm and 1.6 pitch that come in counter clockwise and clockwise directions.

So my question is: what about 3-blade props. I tried one when I was running a BJ24 and the results were terrible. Struggled to get on plane.

But this is a very different boat. Thoughts.

[srislash]

Ok so a three blade will draw another half amount the amps of a two blade( assuming the same pitch). Running a twin you will have less cavitation than you would as a single. Many things can contribute to cavitation like too much pitch and/or not enough blade area.

Which three blades did you have your eyes on?

[RuntheraceAMC]

Well since I wanted to go up to 48mm two blade props( can't find a counter-rotating set) I didn't back off the size of 3 blade much. I already ordered the 45mm 1.8 pitch CNC but now I'm thinking that was a mistake

[RuntheraceAMC]

New prop question. So I have both 4092's in and it's now running 68-70 mph on the 2 blade CNC 46mm 1.6 pitch prop. I tried a 3 blade CNC detounged 45mm 1.8 pitch on the new set up. They ran ok. Decent whole-shot and very little cavitation but weak on the top end. I only did 61 mph on the 3 blade. It seemed like the props just really weren't working. They were hooked up but perhaps props with that kind of pitch need to run higher Rpms?? Couldn't figure out the problem and so I don't know what to try next.

I know I can push my set up further than the 2 blade 46mm, and detounged props are performing better. I like the CNC props but am limited in my options. Some have suggested running an ABC 1417 or 1517 but I have a set of 42mm 1.7 pitch props. They get me to 62mph. I just don't think that's enough surface area to push my boat. Where to next?

[srislash]

Well certainly not 14-1517's 1816,1817, heck with 4092's I wouldn't worry about any of the 19 series either but you'll be pulling all of 250 amps.

On the higher pitch props you may need to shift the CG back as they lift the transom. I have a vid somewhere where I could show you in an obvious fashion, it really just pushes the nose in. You can see it. It starts out great and at some point just flat lines.
Now on the other hand those ABC props mentioned with high rake will do the exact opposite. So huge adjustment going from one extreme to the other.

You are limited to those ESC's so maybe consider the 17 or 18 series props. I have had awesome results with the 1815's and just experimenting in the higher pitches in those props now.

[RuntheraceAMC]

That's interesting stuff about moving the CG on high pitch props. I think 1816 and 1817's might be worth a shot. I have a 1917 I could try on one side just to see if it helps or hurts speed before ordering $90 worth of props.
I'll try moving the CG back on the 3 blade 45 1.8 props and let you know my results

[MarkF]

Your running to small a prop at 45mm. I would buy the 1914s Chris offered and try them as is. If they are not fast enough, he can put some pitch into them. I went 101 mph on 2300 kv motors and 6s with 50mm prop with 1.5 pitch. Cats don't like high pitch like riggers do. I would run 47 to 50mm props with 1.4 to 1.5 pitch.

Mark

[srislash]

So I awoke this morn to Mark's post and thought 'what was I missing'! Still not real awake but for one I was wrong about the amps as I missed the 1800 kv'ish motors. With 47,48, or even 50's you'll likely only be pulling 120'ish amps. He has sound advice.

Sorry about that KV thing, I've been helping a couple people with 2100kv setups.

But try what you have as it is how we learn.
Shawn

[MarkF]

I think the logical next step would be those 1914s from Chris or a pair of Octura 447s.

Mark

[RuntheraceAMC]

What 1914's are you referring to?

[MarkF]

Look at post # 8

Mark

[RuntheraceAMC]

Thought I would update you guys on my results. I've been experimenting with 2 and 3 blade detounged CNC props. On a two blade 48mm I am seeing 70-71mph. On 48mm 1.8 3 blades I am hitting 75 but I lose some hole shot. I've been wanting to try 50mm 2 blades but both reversed and regular props are never in stock.

The latest I've tried is 50mm 1.8 3 blades. I have hit 78mph but it requires a bit of tuning from the other props because these props really force the nose down. Had to adjust the strut angle and weight back. Also noticed I have to be careful backing off the throttle on the 3 blades. If I back all the way off the throttle it drags the back end and starts dancing around. However it does handle the corners better with the three blade.

[fweasel]

The latest I've tried is 50mm 1.8 3 blades. I have hit 78mph but it requires a bit of tuning from the other props because these props really force the nose down. Had to adjust the strut angle and weight back. Have you tried swapping sides with the props and cables and spin switch from CW to CCW or CCW to CW?

[RuntheraceAMC]

I have not. Should that make a big difference?? Currently the right side is CCW and the left side is CW

[fweasel]

It's prop and hull dependent, but switching from inward rotating prop pairs to outward rotating can change hull attitude characteristics.