Please Help

[roy898]

Hi,
I have a small problem with a model my late father built of PS Sandown, and was hoping someone here could possibly point me in the right direction towards fixing it, the problem is that when ever Sandown turns then whichever paddlewheel is on the outside will drop down to the water, (as it will do) but it will not come back up again even if turned in the opposite direction. I have a theory on why this is happening and maybe someone here can confirm this; the model has independantly controlled paddles (which i have heard should never be attempted) is this the root cause of the problem???

[Eddy Matthews]

The basic problem is almost certainly because the model is too top heavy..... And to correct it now could mean a lot of work!

Independent paddles don't cause this problem generally, though if you removed one motor and did a single motor setup it might allow you to get a bit more lead low down in the hull. which may help - Though I have doubts about it!

Sorry to be so negative, but without a lot of work rebuilding the upperworks I cannot see that it will ever be a successful model

Regards
Eddy

[roy898]

Hi Eddy,
thanks for your reply and i'm grateful for your help but lightening the upperworks really isn't an option anymore, rebuilding wouldn't have been a problem to me had my late father not already done a major rebuild to lighten her superstructure/fittings to the point of taking off components and weighing them on Mum's kitchen scales then finding lighter materials to reconstruct them, as it may not be my theory of independdant paddles then i may have to look into other options, still it makes a fine static model until a viable solution can be found

[Eddy Matthews]

If rebuilding isn't an option, you can always fit a small drop keel, like those used on yachts but only about 4"-5" deep - That is providing you can remove some of the internal ballast to allow as much weight down on the keel as possible....

Regards
Eddy

[steamboatmodel]

Are the paddle boxes closed or do they have vents?
One fellow around here has a Mt. Washington which he had that problem with, he installed a weight on a swing arm on a servo. When running normal the weight is positioned on the center line, when he goes into a turn he swings the weight to the high side of the turn, this stops the low side from digging in and staying low.
Regards,
Gerald.

[derekwarner_decoy]

Hi PD's ......& welcome Roy..... ....all is not necessarily lost....but you have a few tasks to complete

1. Inclination test... ...place the [COMPLETE] vessel in the bath & force down one side of the hull to say 15 degrees ....then release the pressure ...
2. What happens?...does the hull return to level trim in one motion or does it rock from side to side for a period of time?
3. Consider the weighty contents in the hull......what type & orientation is the battery?
4. A vessels hull when immersed water displays a metacentric point of balance & the resultant of a very low MPOB will create a slow pendulem effect on a hull when subjected to pressure/force, a high MPOB will create a more continual rocking motion 
5.The MPOB rules actually work against any initial thought....a low MPOB will have a far greater potential to self wright, where as a high MPOB has the potential to eliminate any self wrighting action which is similar to what you are experiencing

Post a few photographs of the vessel with & without the superstructure  ...we need to see inside the hull

Be assured......if there is a resolution  one of the world wide group of PD members will point you in the correct direction.....Derek

[andy]

Hi,

I had the same problerm on my paddler Zaehringen. The problem is not the static of the hull but a vaccum effect, coming to the paddlebox which is not ventilated. So the paddleboy, whem coming to the water surface will be sucked and the force of the hulls weight and dynamic movements will not be enough to bring it upright.

I suppose, a hole of about 10-15mm in an unseen area of the paddleboxes will be enough.

have a look to the original ships, usually they have ventilations at the outer side of the paddle boxes. Made as embellishers, but ventilations.

Andreas

[Stuart Badger]

I do not profess to be correct on all issues regarding model paddle steamer behaviour on the water - but here are the problems and possible solutions as I see them - if anyone knows better PLEASE contribute!

The first thing to appreciate is the general misunderstanding for the term 'stability' - this does NOT mean a vessel that shows little tendancy to roll, heel or pitch. It describes a vessel that RECOVERS from roll, heel or pitch quickly and effectively. A 'stable' vessel can in fact be a very uncomfortable ship to travel on.

There are many reasons for unreliable performance while manouvering a model paddler. In no particular order they are (with possible solutions) ;

1. A high centre of gravity (basically too much top weight). The effect this has is to reduce the natural leverage of the model neccessary to right itself, either because the upperworks are too heavy or that there is not enough depth of hull to get the ballast low enough.

SOLUTIONS: When building keep the upper works REALLY light and or increase the hull depth to ensure a low centre of gravity. For an already constructed model see if there is a possibility of putting the ballast lower in the hull or remove the ballast from inside the hull and substitute an external weighted keel.

2. Flat bottomed hulls. The hull shape underwater affects stability remarkably powerfuly. A flat bottomed hull is MORE stable when inclined than when upright. This is because the angle between the side and bottom of the hull forms an artificial 'keel' when under way. The problem is exaggerated because flat bottomed hulls tend to be ballasted across their entire width and not just in the centre.

SOLUTIONS: When building increase hull depth and ensure any required ballast is in the centre of the hull and NOT towards the outer beams of the vessel. If already constructed try to move the ballast towards the centre or, again, fit an external keel/weight. Also if possible try to fit the scale external keel or skeg - this decreases the tendancy to heel remarkably.

3. Paddle box 'vacuuming' and surface tension. However carefully set up model paddle wheels lift a certain amount of water. If the paddle box is unventilated and or there is insufficiant clearance between the box and the wheel the lifted water will form a sort of 'mound' that adheres through surface tension to the inside of the paddle box and the hull. The result of this is that once heeled the model cannot recover. This is excerbated by the opposit paddle to the direction of the heel lifting LESS water because it is higher than the opposite one.Clearance of the paddle wheel to the hull is important too. If insufficiant the surface tension will drag that side of the hull down and hold it heeled once tipped onto its side.

SOLUTIONS: ensure that there is adequate clearance between the wheels and the inner surfaces of the paddle box and between the wheels and the hull. Ventilate the paddle boxes as suggested in the post above.

4. Cavitation. When the paddle rotates it can aerate the water. Aerated water is LESS BOUYANT than un-aerated water. The result is for there to be less bouyancey during a turn because the outer wheel will be lower in the water and mix more air with the water - again resulting in an inability to recover from a heeling moment.

SOLUTIONS: Reduce the paddle wheel speed (a higher speed will result in greater cavitation0 If possible use feathering, rather than fixed floats. Chamfer the rear edges of the paddle floats to reduce the cavitation on entry and egress to the water. Reduce the size of the floats.

5. Gyroscopic effects. A rotating shaft will tend to try to align itself with the earth's axis - no really! especially if spinning at high speed (the greater the speed the greater the effect). This will tend to make the model heel EVEN WHEN TRAVELLING IN A STRAIGHT LINE!

SOLUTION: reduce shaft speed to the minimum neccessary and try not to use high speed electric motors.

6. Model speed. the higher the speed of a vessel the more it will heel in a turn. most models travel at far too high a speed.

SOLUTIONS: reduce power and or paddle speed - increase paddle gearing.

7. Sponson drag. If the model's sponsonsare untidy underneath or cannot shed water quickly they will tend to add weight and drag to the immersed side of the model.

SOLUTIONS: Ensure that the sponsons are clean underneath and do not tend to trap water - adding a small amount of bouyancy in the form of a foam 'float' under the sponson may help.

8. Vessel is naturally 'tender'. Some models are just naturally inclined to heel - especially those with a high length to beam ratio.

SOLUTIONS: One method (actually used on the real thing in the past) is to have a travelling weight that moves to the high side of the vessel during a turn - this can be accomplished by putting a weight designed to move across the hull in the opposite drection to the rudder movement whenever the rudder is actuated.

9. 'Top hamper' some vessels carry an awfull lot of superstructure above deck level. This will naturally provide drag in windy conditions, and beam on to the wind will induce heeling.

SOLUTIONS: Don't go there! build something different!

Hope this helps - if you have any other ideas PLEASE let us all know!

All the best

Stuart

[roy898]

Hi all and thanks for advice/ assistance gonna try and answer some of the Q's raised,
Derek,
3. Consider the weighty contents in the hull......what type & orientation is the battery?
I think the battery is a lead/acid drycell 6v and positioned in the centre (i've not looked inside for a while now)

Stuart,
2. She is flat bottomed
3. Paddleboxes are ventilated as per real vessel
4. Paddlewheels are not feathered
7. Sponsons have foam 'floats' fitted and highly polished underneath

I will get some pics for those that asked when i can
thanks again to all who have suggested solutions/advice
regards
roy898

[mjt60a]

Just out of interest then, which of the following does everyone think would be best...
(just a roughly drawn example, not drawn to scale, hull would be deep enough that in every case the weights are below the waterline)
I've gone for the first one - low as possible - but it seems not everyone would agree?

[PeeWee]

I too would go with option 1 as it also spreads the weight accross the bottom thereby reducing roll as weight would have to be lifted rather than just pivot. 

thats me and usual cavets apply and people can ignor acordingly.

[sandystrone]

Get rid of the independent paddles and just have a through shaft like the real vessel

[Ivor Bittle]

Paddle wheels
I spotted this thread the other day and noted that no one had made any comment on why paddle wheels "dig in". It is indisputable that this does happen on paddle wheels of all sizes.

The digging-in must be the result of a downwards force generated by the wheels in addition to the horizontal force produced to drive the boat.

I can offer an explanation. Suppose that a model has wheels on a common shaft and is making way on an even keel. If it is disturbed by a wake from another boat one wheel might dip more deeply and its downward force increase. If at the same time the other wheel comes up out of the water the upward force that it generated might be reduced. This leads to an upsetting couple that can cause a model of marginal stability to heel and remain heeled. One paddle wheel has appeared to dig in. If the wheels are powered independently there will be no need to wait for a wash to upset it.

If digging-in is to be avoided it must be done at the design stage and not as a fix. We can attempt to do two things. The first is to fit a weighted drop keel to do two jobs. If it is weighted it can give adequate stability to permit the fitting of scale or scalish top works and have sufficient stability to minimise the effect of digging in. If it is made with an aerodynamic profile, eg NACA 0012-64, it can be given sufficient area to produce a small turning circle. (It won't work with a board rounded off at front and back.) The second is that, if the wheels are to feather, the feathering mechanism can be designed for the blades to enter and leave the water cleanly and give an advantage in terms of efficiency and, in doing so, reduce the downwards force produced by the wheels. (I do not know anything about wheels with fixed blades.)

I did all this on my steam-powered paddler and that turns in the designed radius and runs without digging-in. I once forgot to fit the keel and went afloat. The boat is stable but tender in this condition and under power a wheel dug in and stayed there.

We know nothing about the wheels on the boat that is in trouble.

[bill stafford]

have you considered fitting a yacht type of keel under the hull??
remove any ballast and put it under the hull, say 100/150mm below
i also saw a bloke in MB who fitted a external keel below the hull , made of lead , to fix a small tender hull.
 i know its not scale ,but its better than scrapeing a tender model , food for thought