41" Cat HELP

[Alfa Spirit]

Hi,
A top speed with your 41'' cat will need more than 6S or 2 motors or 8S for two combos with 1300kV motors

[TristanJones]

Anyone want to recommend a steering servo that will handle a 60mph genesis?
I have 7kg but I dont think its up to it. Should I be using something more like a 15kg?

[iamandrew]

Tristan,
Let me tell you somthing important.
the Genesis is not a 100Kmph boat.
Its not built for 100, and it will not withstand many crashes at that speed.
Yes you will be able to get it to go 100, but if you can afford to loose the whole thing, then thats your decision.
a 7KG steering servo would be ok as long as you have a direct pushrod to the rudder, e.g. one without the bend in it

[drwayne]

@iamandrew,
no boat will do 100kmph out of the box..even 'brand name' hulls need extras to approach 100 000mph without damage.
Read post11 for Tristan's extras for 100kmh.

@tristan. IMO 7->11Kg metal gear are fine for this.
You'll break the servo from it's mount, before it falters.

[TristanJones]

Thanks heaps guys, as I said I'm not trying to do it daily, once or twice (ever) @ 100+km/h (62+mph) will keep me happy as larry as thats the goal for this hull. Then its back down to 4s for fun and the occasional run on 5s for a bit of a thrill when the waters glassy. Id say I will need to be @ 6s to get my 100kmh (if).

I have a 7kg metal gear in it now, I'll upgrade to 3mm SS threaded rod for the steering arm and side mount the rudder, hopefully then I can wind on some throttle without it going apeshiz on me, start to dial the boat in, and hopefully start heading towards my goal.

I have been toying with the idea of adding a brace inside the hull from sponson to sponson IE: a bulkhead just forward of the hatch opening to add strength but I can see it backfiring and creating weak points around it, also, adding rigidity can cause issues with cracking as you loose some flex.
Would you guys recommend any further strengthening mods to what Ive done to help it out? I've got plenty of FG matt and resin here.....

[keithbradley]

Thanks heaps guys, as I said I'm not trying to do it daily, once or twice (ever) @ 100+km/h (62+mph) will keep me happy as larry as thats the goal for this hull. Then its back down to 4s for fun and the occasional run on 5s for a bit of a thrill when the waters glassy. Id say I will need to be @ 6s to get my 100kmh (if).

I have a 7kg metal gear in it now, I'll upgrade to 3mm SS threaded rod for the steering arm and side mount the rudder, hopefully then I can wind on some throttle without it going apeshiz on me, start to dial the boat in, and hopefully start heading towards my goal.

I have been toying with the idea of adding a brace inside the hull from sponson to sponson IE: a bulkhead just forward of the hatch opening to add strength but I can see it backfiring and creating weak points around it, also, adding rigidity can cause issues with cracking as you loose some flex.
Would you guys recommend any further strengthening mods to what Ive done to help it out? I've got plenty of FG matt and resin here.....

Tristan,
You're way off in my opinion. You should be well over your goal on 5s with that motor. 6s will not be needed. That's a 4s motor in a single setup and a 5s motor with twins. I say save your money, make it a twin, and run over 70mph all day long.

[TristanJones]

Tristan,
You're way off in my opinion. You should be well over your goal on 5s with that motor. 6s will not be needed. That's a 4s motor in a single setup and a 5s motor with twins. I say save your money, make it a twin, and run over 70mph all day long.

Now sir this is what I want to hear! FWIW I have been into drag racing (full scale) for a long time now and Im used to being very cautious with my speed estimates. LOL (just quietly Im pretty confident this will do what I want it to on 5s also)

Why do you say 4s single motor and 5s twin motor set up?? more rpm required for twins?? why sir??

[rhengst22]

Whoever said the genesis is 37" is wrong..maybe they have a 37" but mine is 1045mm which is 41"

[Rocstar]

Whoever said the genesis is 37" is wrong..maybe they have a 37" but mine is 1045mm which is 41"

No one is "wrong", HK is including the rudder in it's measurement. The boat is 37''.

[TristanJones]

so HK is wrong.....

[Rumdog]

Nope. Overall length is not Hull length.

[keithbradley]

Now sir this is what I want to hear! FWIW I have been into drag racing (full scale) for a long time now and Im used to being very cautious with my speed estimates. LOL (just quietly Im pretty confident this will do what I want it to on 5s also)

Why do you say 4s single motor and 5s twin motor set up?? more rpm required for twins?? why sir??

Higher RPM causes an exponential increase in power consumption. Besides the fact that you are increasing voltage, your setup will also draw significantly more current, as the higher RPM also results in a higher load. In a single motor setup, your current spikes and overall load placed on the motor will be quite high on 5s if you're spinning a decent sized prop. In a twin, the props/motors/ESCs share the load, so you can run a higher RPM and still keep load at a reasonable level.
I also find it easier to setup twin cats to go fast. Most of the cats I build start at 70mph and go up from there. 70mph is relatively easy to keep on the water once you get your setup right with a twin cat.

[gb tiggycat]

gb tiggycat

That Graupner PX-1 is the same hull as the MHZ Isiklar http://www.mhz-powerboats.com/Hulls/...---42-71-.html
You can use their drives and might not cost as much as the ones you speak of. You want the drives for their 44" Mystic. Which are in this link http://www.mhz-powerboats.com/catego...m---44-8-.html I am building a 41" myself and if I do single a TP 4092 1450kv on 6S with a ABC 3 blade prop 1.6P 45.72mm will get you low 60s but on 8S should put you at 80.

Hi ElectricOnly

Thanks very much for the info

[keithbradley]

Hi ElectricOnly

Thanks very much for the info

gb are you already familiar with the MTC drives for this cat?

[gb tiggycat]

gb are you already familiar with the MTC drives for this cat?

Hi Keith,

These were the ones that I was referring to in my original post. Actually I made a bit of a miscalcualtion when converting the Euro cost to GB pounds. They work out at about the equivalent of $150 for a pair of stingers + the cost of flexis etc, not too bad at all. These are almost certainly the way to go.

Thank you for pointing these out to me