HK Princess

[Kev.WParticipant @kev-w]

[Kev.WParticipant @kev-w]

Can anyone tell me what diameter prop came fitted to the Hobbyking 'Princess please, I have tried Google, but not coming up with an answer.

[ashley needhamParticipant @ashleyneedham69188]

Cor. Is this the 1m Cabin cruiser/powerboat with a surface piercing prop on the back?? (Or that’s what it looks like).

Is it a dog drive or normal screw-on.

Ashley

[Kev.WParticipant @kev-w]

It certainly is Ashley, the prop is a 'dog drive' on a 4mm flexi-shaft.

[Chris FellowsParticipant @chrisfellows72943]

Hi Kev

Looking at the Hobbyking site photos and the motor size stated I'd guess it is around 40mm. I have a race boat which looks a similar size and that is a 37mm.

But there's a Japanese chap on Mayhem (sorry I can't provide the link using my tablet) who has one and will be able to tell you the actual size. His forum name is Backether and the Princess is on his post Model Boat Mahem/ Mess Deck:General Section/Model Boating/My Favourite RC Boating Scenes at Our Local Lake.

If you have a problem accessing I'll ask him for you.

Chris

Edited By Chris Fellows on 25/05/2021 22:04:35

[Kev.WParticipant @kev-w]

Thank you Chris, you have just about confirmed what a couple of lads told me down the pond, they said it was probably over propped, will get a plastic 40mm + a 45mm and try those, when the balance seems right, I will invest in an aluminium prop of the correct size.

At the moment, it has a 47mm ally prop, but as soon as I open the throttle, it tends to roll on to it's side with the prop torque, this is on a 4S, but I've seen videos of it on a 6S, and it is quite stable, just couldn't understand why it is going "loony tunes on a 4S.

I bought the boat secondhand, it's my first real foray into fast electrics, so am really a pure beginner .

[ashley needhamParticipant @ashleyneedham69188]

A three blade prop will reduce the torque. Also of course running it on 6s means more revs and this will allow a smaller prop to be used.

Does it have trim tabs? These can help reduce/manage torque-roll.

Ashley

[Kev.WParticipant @kev-w]

No trim tabs at present, don't want to add them if I can get it handling ok without.

Will try the prop adjustments first, change things a little at a time, that way I find out what is the cause of it's bad behavior, too many changes at once and I won't be any the wiser.

[Ray Wood 3Participant @raywood3]

Hi Kev,

May I suggest you follow your own advice to fellow forum member recently and apply moderation to the application of the throttle stick, and accelerate gently maybe less likely to roll ??

Regards Ray

[ashley needhamParticipant @ashleyneedham69188]

“Moderation to the application of the throttle”…this is not a term We are familiar with at Bushy Park.

At full throttle (the only sort) I think somethinG like this is bound to take a ‘set’ one way or the other, however a surface peircing prop will be larger than its underwater equivalent and exert more torque before it is correctly halfout the water.

The slower application of throttle initially may offset the roll?.

(Is that what you meant Ray?.)

Ashley

[Kev.WParticipant @kev-w]

I have tried the 'gently' method Ray, but it happens as the boat gets onto the plane, at which point, the motor sound changes, the boats acceleration increases very rapidly & that's when the torque roll starts, the boat then gets very twitchy.

The nearest thing I can equate it to, is a multi cylinder 2 stroke motorbike hitting it's power band.

[Chris FellowsParticipant @chrisfellows72943]

My race boat is the same Kev. It cavitates a lot and then takes off!

It seems a bit odd having a surface piercing prop and outrigger rudder on a boat like the Princess. You want some performance but not crazy!

Chris

[ashley needhamParticipant @ashleyneedham69188]

The sudden surge in performance is also noticeable on several items we have at the pond, and from observation may be due to water sticking to the hull and then just at the right speed it clears and whoosh! Off you go.

The Walrus and Hydroglisseur are like that. Hold 3/4 throttle and they gradually gather speed and then suddenly , on the same throttle, they zoom off.

On the Princess it may also have something to do with the operation of the prop itself. I converted a cat, originally fitted with an outboard, using a surface piercer on the end of a shaft sticking out the back, and this gurgles ferociously until it seems to “bite” and then off it goes.

Ashley

[Kev.WParticipant @kev-w]

'nail on head' Ashley, "shaft sticking out the back", maybe this is why it's called a 'Stinger'.

[Richard SimpsonModerator @richardsimpson88330]

Just an outsiders thoughts Kev, for what its worth, the propulsion system you have seems to be along the lines of a fairly serious racing system. In a hull designed for racing I suspect it would perform well.

Your hull however is more of a cabin cruiser design with more weight on top than most racers and simply not designed for the speeds that you are trying to get it to. Basically I think your propulsion system out performs the hull and the reason it becomes unstable at such speeds is simply because the hull is not designed to go to such speeds.

I'm not sure if you will ever be able to achieve the stability you want when you are pushing such a hull to its extremes. The real danger could be a split seconds loss of concentration or an odd little wave and you will suddenly see your model flip over and everything might be lost.

I really do believe that every hull has a limit beyond which you should not push it. Maybe it would be better to put a less powerful propulsion system in this one and enjoy the more stable characteristics and put the propulsion system into a racing hull.

As I said just a thought, I don't tend to have this problem in the steam world!

Interesting to see the old two stroke motorcycle analogy. I was always into four strokes when my brother once lent me his Yamaha RD 200 for a run in a car park. Being completely unused to 'power bands' when it did kick in it had me off the back. Plus, lets face it, how many of the old Japanese two strokes were vastly overpowered for the frame, suspension and, most importantly, the tyres?

[Kev.WParticipant @kev-w]

Thank you for your thoughts Richard, however, the boat is designed to run the factory supplied installation I have, with up to & including 6S LiPo power.

The prop had been 'swapped out' for a larger one by a previous owner & this was the main cause of the instability.

I removed the 47mm prop & fitted a 42mm & today I ran it on a pond with a few ripples, I started out with a 3S / 5amp LiPo, the boat performed well, but was still a little jittery so I removed the 3S & fitted a pair of 4S 6.2amp LiPo batteries either side of the motor, this gave the boat the weight it needed to stabilise it & by slowly inching the batteries forward I got the boat to a point where the balance was where it needed to be.

The boat now runs nice & stable using a steady thumb, so now in the process of making custom battery box to keep everything neat & tidy.

Edited By Kev.W on 30/05/2021 21:34:13

[Richard SimpsonModerator @richardsimpson88330]

Glad you got it sorted Kev. Watch out for the ducks!

[Kev.WParticipant @kev-w]

Thanks to all who put in their 'penny worth', all was noted & given due consideration & some is held for further review, should things not go quite as anticipated.

Advice is never ditched out of hand, it is always kept as something to be revisited, should things need to be tweaked, I always take the stance that 'no one knows it all', but some know more than others, so for the more experienced, I am listening, it's the only way forward.

Thank you, Kev.

 

Edited By Kev.W on 31/05/2021 23:19:18

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