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[zooma]

I bought a Relentless V2 some time ago just before HK stopped selling them as I thought it was a superb looking craft - and I wanted to have a change from my usual deep V boats and try a fast catamaran  - without spending too much on my first "fast cat" venture!


When the boat arrived I was really impressed with the decor and the finish, I think it looked really impressive, and I still do over a year later - but running it is another matter!


When I first put it into the water it just burbled away at fast revs kicking-up lots of spray, sounding good - but not really doing anything much speed wise for about half the length of our club lake - and then "BOOM" - without any warning it took off like a scalded cat!


Several repeat launches showed exactly the same situation - high revs - impressive sound - no real speed for some considerable time and then it just took off like it had been released from a high powered catapult!


Once the boat was eventually running at high speed it really was impressively fast, but most of each trip was spend waiting for the boat to decide to "get going".


I was advised that this situation (before take-off) is called cavitation when the propeller fails to "get a bite" and just buzzes away without pushing the boat forwards at any speed.


I tried applying the power fast, and then with a slow build-up (both as suggested by knowledgable onlookers) and then I made adjustments to the "stinger" (?) to try different angles of thrust - but absolutely nothing made any difference at all.


I ordered a couple of alternative M5 props from The Prop Shop and tested them.


This did improve (but not remove)the problem quite significantly, to the extent that much less time was spent waiting for the sudden thrust forwards and more time was spent appreciating the surprisingly high speed across our club lake!


Having achieved more time running fast,  I then spent a lot more time with my Relentless V2 upside-down in the water!


Constant adjustments (and even adding trim tabs) has failed to either cure the cavitation 100% or indeed do anything to prevent the boat preferring to flip up into the air and always land the wrong way up!


The aerobatic displays are as impressive as the top speed (when it arrives) - but I would prefer to keep the boat in the water (the right way up) and run fast  for longer... 


Does anyone know how to stop the cavitation on a Relentless V2, or how to stop it flipping over so often? 


Note:-  this same boat is also available as the Joysway US 2 - yellow coloured and not quite as pretty ( in my opinion at least!).

[canabus]

Hi Zooma

The flipping over is one or two things and maybe both !!!

1. The prop angle on the stringer, start with it parallel to the bottom of the boat.
2. CG of the hull at high speed, to far forward and the bow drop down.
To far to the stern and the bow goes up and the boat kites.
The middle section of the hull is basically like the wing of a plane.

Dropping the stringer down a bit may help your other problem.

Try one change at a time.

Canabus

[zooma]

Hi Zooma

The flipping over is one or two things and maybe both !!!

1. The prop angle on the stringer, start with it parallel to the bottom of the boat.
2. CG of the hull at high speed, to far forward and the bow drop down.
To far to the stern and the bow goes up and the boat kites.
The middle section of the hull is basically like the wing of a plane.

Dropping the stringer down a bit may help your other problem.

Try one change at a time.

Canabus

 


Thanks for your advice, it is appreciated, but I have already tried every one of your suggestions many times already over the last 12 month period with no really noticeable improvements.


The change of prop has made the biggest improvement by reducing the cavitation (but not curing it altogether), but the high speed flipping remains a problem that can only be resolved by driving more slowly!....not what I want from a high speed craft!


When the craft is flat out in a straight line on calm water I would still like it to act consistently without flipping at random and for no apparent reason.


I have the LiPo cells mounted on Velcro so shifting them to change the balance point is easy and this does effectively change the ride height of the bow.  I have also checked to make sure they are not shifting at all, but they remain secure and have not moved when the boat returns to shore - even after having to be recovered after a flip! 


I have also tested the full range of movement available in the stinger with various props and different battery positioning.


Only making one change at a time is the way to go, but having made so many I am now combining various options to see if I can find a recipe that works!

Maybe all Relentless V2 and Joysway US 2 owners have the same problem - but I am hoping that somebody somewhere has experienced these problems with their own similar models and have found solution for them faster than I have been able to achieve to date.

[martno1fan]

The thing with cats and other tunnel style  hulls is you need to launch them with some revs to avoid the cavitation,cavitation from a  standing start is unavoidable on most boats but especially cats and hydros etc . Give 1/4 throttle and launch with forward motion and off you go.As regards the boat flipping welcome to running cats lol, first thing to check is your COG where is it at ?, on cats usually it needs to be around 34% but the more power you have the further forward it will need to be etc .Also not just prop angle will change the boats running and handling the actual depth of the prop in relation to the sponson depth is critical . Start with it sat level when having the sponson transoms sat on the edge of a flat table top then adjust up from there keeping prop parallel to the bottom,many cats prefer the strut depth to be up from the sponson ride surface by around 4-5 maybe even 6 mm . Having it shallower allows the prop to free up a bit quicker so might help a bit with cavitation from a standing start but me personally i launch with revs and keep running never stopping until i need to that also helps your esc no end as your never overloading it .

[zooma]

The thing with cats and other tunnel style  hulls is you need to launch them with some revs to avoid the cavitation,cavitation from a  standing start is unavoidable on most boats but especially cats and hydros etc . Give 1/4 throttle and launch with forward motion and off you go.As regards the boat flipping welcome to running cats lol, first thing to check is your COG where is it at ?, on cats usually it needs to be around 34% but the more power you have the further forward it will need to be etc .Also not just prop angle will change the boats running and handling the actual depth of the prop in relation to the sponson depth is critical . Start with it sat level when having the sponson transoms sat on the edge of a flat table top then adjust up from there keeping prop parallel to the bottom,many cats prefer the strut depth to be up from the sponson ride surface by around 4-5 maybe even 6 mm . Having it shallower allows the prop to free up a bit quicker so might help a bit with cavitation from a standing start but me personally i launch with revs and keep running never stopping until i need to that also helps your esc no end as your never overloading it .

Thanks Mark,


At the moment I am stuck in Rossendale (lock-down) and the boat is in Southport!


As soon as I am able to get out again I will try everything you suggest and double check everything again.


I would love to see this good looking little cat running well - for a small craft it is very impressive when it really gets going.....until it flips!


Stay safe!


Bob.

[zooma]

Just to conclude this thread, I have just sold my Relentless to an overseas buyer as part of my clear-out of boats to make some more room in my workshop.
I needed to make some space as my current new builds and restorations need priority on the bench space so anything that I have not used (or even looked at) for some time have been found new homes.