Paddle "dig-in"

[brian freegard]

Hello All,

I have just done some trials with my nearly complete "Confederate Blockade Runner", a free plan from Model Boats. Whilst ballasted down to the waterline with the paddle floats just immersed she floats on an even keel but with the slightest encouragement one paddle wheel seems to dig-in and then the ship will not regain an even keel. The ballast is as low as can be (screwed to the outside bottom) and she is statically balanced and will self right. With the wheels revolving there is always instability. Suggestions please!

I am considering a) A (much) deeper false keel or b) Reducing the vertical depth of each paddle float so as to reduce the thrust.

Thanks,
Brian Freegard

[Eddy Matthews]

Hi Brian,

Almost certainly the model is a little "top heavy" - Fitting a deeper false keel will certainly help. The Phantom is a small model, and these problems are exagerated in smaller models.

Before you go making drastic modifications, try a simple false keel held on with some double sided tape for testing. That way you can play around with the depth and the weight before you commit yourself to making a permanent change. Just remember that it won't stay there for long when immersed in water!

If that doesn't work you can then look at the depth of the blades in the water - It can also cause similar symptoms. And it may even take a combination of things to cure it...

Lastly, it can be caused by not having enough vents for the water to clear the paddleboxes, causing a sort of hydraulic lock - A couple of small holes drilled into the top of the paddleboxes will often cure that, and no-one will ever notice them unless you point them out!

I'd still look at a false keel first though, as that is the most likely thing.


Eddy

[Mercury]

Brian,

As Eddy states it's fairly common to get this problem. I don't know the model in question but another solution if you have sponson houses is to have the whole sponson open underneath rather than enclose the paddle in the paddle drum. This prevents the wheels sucking down into the water. I used this on my 1:48 Mercury and it worked a treat.

[Eddy Matthews]

Brian,

As Eddy states it's fairly common to get this problem. I don't know the model in question but another solution if you have sponson houses is to have the whole sponson open underneath rather than enclose the paddle in the paddle drum. This prevents the wheels sucking down into the water. I used this on my 1:48 Mercury and it worked a treat.

That's a trick I've not heard of before mercury, so I'll keep it in mind for future builds!

Regards
Eddy

[scotfriend]

Hi PD's,

i had the same problem with my "Mull of Kintyre" the Edwardian Paddle Steamer, what i did was as Eddy said before I've added some lead with doubletape to the outside of the hull underneath the keel, this helps a lot but the model is still instable when using the rudder or if there is the lightest breeze of wind like the fart of an ant In my opinion when you look at your model from the bow and the model is upright then will each paddle in an equal depth in the water and has the same power, when your model is leaning to one side the wheel who dig's deeper into the water has more power then the other and there is no way to go back until you has stop ed the motor to allow to go upright and then accelerate slowly till it happened again

regards Hans

[Harold H. Duncan]

any internal ballast added should also be on the centreline of the boat, not out near the edges of the hull
kiwi

[steamboatmodel]

I have seen one model where the builder incorporated a counter weight on a servo arm. When one side digs in he moves the weight over to the opposite side.
Regards,
Gerald.

[Hankwilliams]

Hi Brian,

I know the problem from my explorating steamer "Welf", she has also some toplast, when she is only still in water, the model is quite stabil.
When I drive with half power, she immediately gets a sloping position. Sometimes it will help to give countersteering, sometimes not. But this instability will disappear, when I give full power, in this state the paddlewheels must have a stabilising effect and then the boat sails in a very stabil position.

The paddleboxes are open at the outside, I don't think, that there a pressure of air and water is possibel.

The only solution from my sight is to fix some ballast unobtrusive at the deepest place in the hull or outside at the keel.

It's also possible, to make a stability tube at the water line, it's easy made of balsa in a model (some European paddlers like on Lake Constanz got this alterations in later years), but at a blockade runner this will be unsatisfactional, because it's far away from original.

Tom

[derekwarner_decoy]

Hi PD's...as Eddy has just previously mentioned [& appears in PDs' archives] ....with many paddlers we have ....issues with

Stability, top weight, low draft, high aspect ratio to windage ...so we can do the bath tank tests & all may appear OK...but get the vessel out on the water & what changes?

Yes 'mother nature' & even a gentle breeze x the square root of the scale = 'instability + top weight+ low draft + high aspect ratio to windage' & the potential for a wheel to 'dig in' ......Derek
 

[brian freegard]

Thanks for your interest. I tried lowering the ballast, which was on the outside of the hull, by about 1/2 inch. This certainly improved the situation. I am in the process of making a false keel/hull extension.

I hadn't thought of venting the paddle boxes although this semms to be the norm on the full size ships. Probable do that as well.

A fellow club member has also been through this loop with his "Waverley" and has made similar suggestions.

Thanks again, and I will report progress, as and when.

Brian Freegard

[andy]

Problem is the ventilation of the paddleboxes! I know from a model of mine, too.

Andreas

[brian freegard]

Hello All,

I have added a false keel 16mm square X 150 long with the lead ballast secured below it (about 600 gr) It looks absolutely terrible but has fixed the problem and doesn't show on the water.

The model is very tender in side winds but it seems to perfom pretty well on my private pond. It may be a different story in open water.

Anyway- it's a paddler. Done that!

Regards,
Brian

[Eddy Matthews]

I'm afraid that's one of the problems with smaller models of paddlers Brian, glad you eventually got a model that's stable at least!

Regards
Eddy

[kiwimodeller]

Even my large paddler had problems in side winds. I fixed most of the problem by fitting a skeg ahead of the rudder for about a third of the length of the hull and a small bilge keel on each side just inside the chines for about centre 50% of the hull length. Hope that makes sense, the keels are about 1/4" deep and run from 1/4 of the way along the hull to 3/4 of the length. Cheers, Ian.