Battery Position & Weight Distribution

[Queequeg QuintParticipant @queequegquint38270]

My triple-screw boat had quite a roll the other day while at full-throttle, in rough water. I would like some advice on weight-distribution to help address this. I made a video to explain what my situation is:

https://www.youtube.com/watch?v=4ubqHbCwxXg

[Tim RoweParticipant @timrowe83142]

Hello QQ

In your photo it shows your boat heeling in response to the wash from another boat ahead of it.  Effectively it is running on a piece of water that is not level so heeling is inevitable.  Any boat would behave in a similar fashion.

I have seen your desire to get the boat to go faster but I think you may be heading for ever diminishing returns. The design looks to be very much like what is called a semi-displacement boat.  These can operate at higher speed that is restricted normally by the waterline length.  This of course needs power but the boat may not be happy when try to push for full planing speeds.  If you look at planing type hulls they are almost without exception hard chine form of some sort and are designed to skim across the surface.  Stability is related to speed (up to a point) in a dynamic sense.

Your boat is round bilge and although it may be perfectly stable at rest and at reasonable speeds it could become unstable at higher speed due exactly to the hull form.

Some of the most notably seaworthy semi displacement full sized boats such as Nelsons and Halmatics have dangerous transitions to lack of stability if over powered and pushed too hard.

In any case it should improve stability and probably performance if you could shift the cg aft by putting the battery aft of the motors.  This is over the widest, flattest section of your hull. The boat may be a bit trimmed by the stern at rest but i should level out quite quickly when going a bit faster.  Easy to experiment with.

Hoe this helps a bit.

Tim

[Richard SimpsonParticipant @richardsimpson88330]

I suspect with such a set up a lot of it is going to be trial and error and there will probably be no definitive answer.  Interestingly the only performance related hull I have is an Aerokits RAF Fire tender and when I turn that one hard at speed it actually leans into the corner rather than leans out.

From what I can see of your set up above, the first thing I would try would be to place the battery longitudinally.  That would at least get the CoG a little bit lower as the battery will sit in the keel better.  I also think it might be worth trying moving the battery aft a little.  Is the hull supposed to be a planing hull?  If that is the case then I think moving the battery aft might help to get the bow out of the water a bit.  If it is not a planing hull then there is no harm in trying to get the battery lower.

In my RAF launch the battery is split into two banks, although they are connected together as a single battery.  This gets them as low as possible and they are a good bit further aft than yours are.

Just a couple of thoughts.

[Queequeg QuintParticipant @queequegquint38270]

Thanks for the advice. Here’s another video that shows how the boat handles at fast speeds in rough water.:

 

 

 

[Ray Wood 3Participant @raywood3]

Hi QQ

Completely agree with Tim and Richard, my only advice would be to retro fit some spray rails to the hull where the chine would be , she is just sending the water straight up her topsides and the rails would lift the bow enough to plane on the rear part of the hull which would also benefit from some rails like a Huntsman design, it will never corner like a deep vee hull or have the stability.

Regards Ray

[Richard SimpsonParticipant @richardsimpson88330]

My apologies, I didn’t pay enough attention and didn’t realise it was a rounded hull.  In which case both Tim and Ray are spot on.  As Ray suggests spray rails might help prevent the water flowing too far up the hull but, looking at your last video, it is easy to see the boat simply wants to roll around.  Spray rails at the point of where the hard chine would be might help or even a bilge keel.

Moving the battery back and lower may well help but, at the end of the day, you really want to stop the boat rolling and that hull shape makes that quite difficult.

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