Hydrospeed - getting the old girl back on the water

Hi, this was the boat I had as a kid... she worked rather well back then on the original Graupner motor and prop system with the then modern vario.

Now as she has stood up to the time rather well I am looking to get her back on the water, this time for my kids.

So I'm going to gut her and replace the broken rudder system by an aluminium prop/rudder a flex shaft, new prop, brushless motor (water cooled) and probably powered by a 3s lipo.

My question is what kv and prop to pick so I have a decent speed and a good run time.

PS the mah of the lipo battery will depend on the space I have left to fit the battery in the boat which will then also determine the run time.

Any advice welcome.

The boat is a Graupner Hydrospeed 60cm long.

A suggestion, TP3630 1500kv with an X442 or 445 on 4s would get you moving nicely. OSE Raider 150 esc is ample and 4000mah would do. This should give you at least the same performance and runtime the original setup did. A Seaking 120A esc would work fine as well and may fit better space wise.

Thx Peter for your response.
I'm glad one thing is now validated is the size of the motor, a 36 size. What I was less sure is the KV as I'm not too familiar on how to calculate the kv with the prop size as speed is not the priority, I am looking to have decent speed (but not too much) it is an old girl afterall and I've seen few others going over the top but the hull can't take too much speed. And I would value a good time on the water.

This is to get her back on the water for the kids... In paralell I'm looking for a second hand hull about btw 1 to 1.2m long for me.

I need to replace the prop system and the steering.
was looking to find a small in-line strut rudder system as place is very limited on the transom together with a flex and rudder shaft to work on it.

So for the motor was looking at these
https://hobbyking.com/en_us/turnigy-...ess-motor.html
https://hobbyking.com/en_us/turnigy-...-inrunner.html (with a water jacket)

and this for the ESC
https://hobbyking.com/en_us/hobbykin...c-3a-ubec.html
But you reckon I need to move up to a 150 Esc?

And the battery I don't know know either as it will depend on the size I have left as space is very limited. Not sure I'll be able to fit a 4S... maybe but would need to find a 4S pack that would fit hence I was looking more towards a 3S.

for the Prop setup I'm looking at a 3.18m flex in a 4mm shaft but haven't found a in-line rudder strut that will fit.
Looking at this https://www.ebay.ie/itm/Rudder-with-...wAAOSwBfJcuYei but then can't find a flex that would fit. Don't know the length of the strut length and the distance from the back of that axle to the rudder behind it.

Hydrospeed is a small ABS hull, a 3S setup should be fine with a 450H size outrunner motor (3300-3500kV)

Motor :
https://www.altitudehobbies.com/coll...-450-500-class


https://encrypted-tbn0.gstatic.com/i...FSwE2iLT2yW0tg

Alfa is right, this is a tiny boat by modern standards, 24” including the useless transom extensions, making the effective hull length about 22”. A 36mm motor on 4S would overpower it and give far far faster speeds than the original. And, it will weigh too much. Most modern conversions of the hull seem to use 3S, I’d install a 28mm inrunner or a small outrunner motor. And no, a 150 amp ESC is definitely not required, if it fits. There isn’t much room in there.

Attachment 165408

Remember that these hulls are over 30 years old and the ABS has become brittle. Too much stress and the hull will crack easily; the few ABS hulls of that vintage I had left broke apart in the move. Here is someone’s 3S brushed version, plenty fast for the OP’s kids.

https://www.youtube.com/watch?v=B72L...&feature=share


.

Thanks for your your input... that 450/500 motor looks good and at a good price too.
To Fluid's point yes the steering system is useless now and I need to replace it as it is broken but don't seem to find a place to buy a small in-line steering unit to replace the original plastic one. Any recommendation?

Yes I think 3s on lipo with a brushless will be plenty fast - so I think i have the spec I am going to get, with the ESC and lipo battery ... now I need to find the shaft and steering

Thinking of this for the steering and strut system https://www.offshoreelectrics.com/pr...prod=ose-80972