Donzi 73 inch

[Lefty20671]

I am building a Donzi 73 inch sport fisherman. Going to run dual counter-rotating motors and props. Any suggestions on brushless motor/esc? Not trying to set any speed records, just want a nice scale speed of about 30mph.

[fweasel]

That's a big hull, that will likely push a lot of water. While I have no experience building something that size, I would be starting with twin 56mm motors (TP5650 for example), lower kV (600ish), and higher voltage...10-12S.

[Lefty20671]

Thanks fweasel, I.m looking at the tp 56mm motor with 720kv. Would the ztw seal 200 amp esc be ok with those on 8s? Going to start small with the props and experiment with larger diameter. The real Donzi cruises in the mid 30's so I'd like this one to get on plane, and handle well. Thanks again.

[fweasel]

Yes, those ESC's will work on 8S at that kV, but they are the limiting power factor in the setup. You won't be able to go over 8S for battery voltage, and it you prop up, it may pull more current than those will deliver. If it's a budget issue, I would rather see you use water cooled MMX8S which have been known to punch above their weight, vs the 200A ZTW's. High voltage ESC's like the ZTW 300A G2 will give you plenty of current headroom, and allow you to run more than 8S voltage.

[Lefty20671]

So to water cool the mmx8s, just add a water cool plate, and leave the fan? Looks like they are out of stock as well.

[fweasel]

Stump Fab sells a water cooling plate and 3D printed cover to make the MMX8S a DIY conversion. You'll need a tube of thermal transfer paste as well. Sometimes they stock fully converted ESC's if you don't want to do it yourself.

Cooling plate (https://stumpfabrication.com/collections/fast-electric-fe-boat-parts/products/castle-creations-x8s-cooling-plate)
3D printed cover (https://stumpfabrication.com/collections/fast-electric-fe-boat-parts/products/x8s-cooling-plate-mounting-cover)
thermal paste (https://stumpfabrication.com/collections/fast-electric-fe-boat-parts/products/zinc-oxide-thermal-putty)

[Lefty20671]

Found it. Thanks fweasel, placed my order for the completed esc with Stump. I'll keep you up to date with the build.

[Peter A]

With submerged drives you will want some low kv. Depending on prop size, I'm guessing around 60mm 3 blade, You will want to keep your rpm under 10k. submerged drives will load the motor/esc a lot more than surface drives.
I am assuming that you are keeping with the scale thing in using submerged drives. Surface drives may not work too well or be very efficient at 30 mph.

Just as an example, the speed calc with a 60 x 1.4 pitch prop, 400kv on 10s and 80% efficiency shows 28 mph. That is for a surface drive mono. Playing around withprops and cell counts should get you where you want to be. Yes you have two drives and props also so should be more efficient and give you good run time. You could possibly use the ZTW 300 esc or even the 150A HV esc if your amp draw is kept quite low. I'm thinking you want to be in the 60A range per motor. On 10s that gives you around just under 6 hp equivalent hp.

[Lefty20671]

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[vvviivvv]

That's a beautiful hull,

Shame its a little late but a pair of out runners would of been perfect for this application.