Stability

[pete]

Just done a float test on the almost completed hull of Talisman.
With batteries/motors and radio gear, needs about 3 lbs ballast to bring to waterline.
With the ballast on the floor of the hull, I notice that the roll rate is rather fast, although it rights itself perfectly.
Would it be advisable to fit some of this ballast below the hull, as is done with model yachts, as this might slow the roll rate?

[steamboatmodel]

If by "the roll rate is rather fast,"you are referring to the hull coming back to an upright position fast, this can be a good thing in models. Remember if you haven't completed the superstructure ti will slow down the roll rate. It all has to do with the center of gravity and the center of area ( metacenter center?). Thelower the center of gravity the faster the hull will become upright. You need to keep the center of gravity below the Mercantile center. This web site explains it better than I can:  http://www.uh.edu/engines/epi1854.htm ,
 http://www.johnsboatstuff.com/Articles/estimati.htm ,
It is for full size boats, but the same principle applies.
Regards,
Gerald

[Talisman]

In very lay terms keep the ballast as close and as low as possible to the centre line (along the length of the hull) and it will do pretty much the same job as a keel. (make sure it cant shift )
To put ballast on the underside of the hull will be more effective but will detract from the look of your model.
As mentioned in a previous post a gangway with a strip of lead on the underneath side is great as ballast for fine trim of the boat .

I would wait until the model is complete (remembering to make all items above the waterline as light as possible. then worry about the ballast.
Hope this helps
Kim

[Talisman]

Would be nice to see some pics of the build

[Talisman]

Another tip.
When you build your paddle boxes fill the voids with closed cell foam them you have extra bouyancy and no space for water to fill reducing the chances of a capsize / sinking.

[pete]

Thanks for your help. Found the articles v.interesting. I'll sort out the ballast when I've built the superstructure.
 

[derekwarner_decoy]

Hi PD's.....& Pete..just try a PD's search  on the word 'stability' you will find enough to keep you  for weeks...Derek

[amdaylight]

On my Mount Washington which from what I have read suffers from a stability problem, narrow, wide and tall so I went with a removable keel that mounts under the boat when in the pond, when on the shelf the keel stays in my float box. About 80% of the total weight is in the keel the rest is spread through out the hull as needed to achieve a good balance. The other paddler that uses a removable keel is the Mississippi River steamer that I am building, more on this one so it does not blow sideways rather than stability.

Heck I don't what model boaters call the tool box that they take to the pond but in the RC airplane world the tool box you take to the flying field is called a "Flight Box" so I call mine a "Float Box". This is where I keep the transmitter / receiver battery charger, the expanded scale volt meter, tools, glue, bug repellent,  and a small first aid kit ( never needed it yet  ) again a left over from my Airplane days.

Andre
over yonder in Portland Oregon