Hydroplane build dimensions around 3670 BLDC

Hi y'all,

First post here .. (please let me know if there's something wrong)

I have a 3670 inrunner 2150Kv and a 60A ESC that's been lying around for some time, and I'm considering an hydroplane build around it .. (Just in case it matters, I live in france so I don't mean to race the boat in any category, this will be a pure hobby/fun build).

Since I have access to a big 3d printer my plan is to print the boat thin and glass/epoxy it to make it watertight before painting.

So far I have a base design for the boat, basically a kind of brain dump after having watched countless hydroplane pictures for a while, not intended to match any particular historic boat :

Attachment 166663

Attachment 166670

Attachment 166671

Attachment 166669 Attachment 166672

I'm very new to RC boats and BLDCs so I could use some help, especially with the boat dimensioning size, weight, propeller, lipos etc..

I'd like to design the powertrain in order to push a 1/10 or 1/8 scale boat if that's feasible, would you be kind enough to help solving the equation ?

If possible :
1/8 hull ~31" [GROSS WEIGHT ?] >> [LIPO 4/6/8s ?] >> [BLDC 3670/2150Kv] >> [PROP Diam/Pitch ?]

If more realistic :
1/10 hull ~27" [GROSS WEIGHT ?] >> [LIPO 4/6/8s ?] >> [BLDC 3670/2150Kv] >> [PROP Diam/Pitch ?]

I'm assuming 1/10 to 1/8 to be OK with the motor but feel free to suggest any size weight combo variation that would work (make the boat fun to sail) ...

I'm also welcoming any constructive criticism about the hull / boat design ;)

Thanks for any input ...

Lorenzo.

Hi oxomoxo.
Welcome to the forums.

The length of the boats compared to the scales that you mention don't seem quite right.
The original boats were around 28' in length.

1/8 scale is about 42" long'.
1/10 scale is about 34" long.
1/12 scale is about 28" long.

The motor you have is best on 4s with that kv of 2150. 6s & 8s are not options in my opinion.

It will definitely suit the 1/12 scale and the 1/10 scale, but the 1/8 scale is too big for that motor.

Initial props for testing would be an x445, then x447. Moving up from there if the temps are ok.

Cheers.

Quote:

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Originally Posted by 785boats

Hi oxomoxo.
Welcome to the forums.

The length of the boats compared to the scales that you mention don't seem quite right.
The original boats were around 28' in length.

1/8 scale is about 42" long'.
1/10 scale is about 34" long.
1/12 scale is about 28" long.

The motor you have is best on 4s with that kv of 2150. 6s & 8s are not options in my opinion.

It will definitely suit the 1/12 scale and the 1/10 scale, but the 1/8 scale is too big for that motor.

Initial props for testing would be an x445, then x447. Moving up from there if the temps are ok.

Cheers.

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Hi 785boats,

Sorry for the long delay in replying, I got caught in my last exams session that I had to attend (good new is : I passed !)

And thanks a lot for the infos, this is exactly the kind of basics I'm in need of :D

So apparently my model is more 1/10 (~31" from nose to transom) than 1/8 as I thought, so far I was estimating the length (eyeballed from pics) to about 6.5m which appears to be is a little short ...

I'll be checking the diameter/pitch of the props you suggested, IIRC they are 2 blades props, what about a 3 blade prop ? I read that they tend to push smoother because one blade is always in the water, is there a notable drawback to be aware of, such that everyone uses 2 blades props ?

About the motor, 4S is somewhat a good news since I'm considering a two pack (serial) lateral arrangement to balance loads, and I've seen two pack 2S LIPOs are quite affordable.

As I mentioned I'm considering 3D printing the hull + frame + deck in one piece and a detachable cowling / cover. But I'm not completely sure this is a good idea, or even feasible : plastic is not so lightweight ... it could be printed thin, but not too much, water is hard at speed. In the software I use for printing I can get a good weight estimate of the material used so I can budget and do trade offs (shell thickness, infill etc.). So comes my next question : what does a good riding 1/10 boat weights about ? And how much weight grows in glassing the shell ?

I'm trying to get the CAD model as close as I can to the definitive thing and plan for hardware, putting some thicknesses for strut, rudder and fin, a mount for the servo etc. My understanding is that rudder and turn fin go on opposite sides of the boat, with the rudder on the outside and turn fin on the inside, is that correct ?

BTW I'm not sure why the rudder is offset from the strut .. what is the rationale ?

Thanks for any hints :D

Lo.

Congrats on passing the exams.

1/10 scale can be anywhere between 34" to 37" or so. Some of the original boats were 30' in length.

Someone else will have to answer the question on 3 blade & 2 blade props, & the use on different types of hulls. All I can say personally is that I mainly use 2 blade on hydros, & 3 blade on monos & cats.

The main reason for offsetting the rudder is to keep it out of the prop wash. The accelerated water over the rudder creates mare drag than if the rudder is in clear water.
It can also create handling problems in the prop wash, by causing some flutter. That can make the boat wiggle in a straight line & need corrective rudder input, which is even more drag.

Here are some plans in different scales that will help you with the dimensions & relative proportions for your design. They might be of some help.

http://www.rumrunnerracing.com/plans.html

Cheers.