John, I’m with Colin on this.  I wouldn’t get wrapped up in playing around with numbers as there are so many variables involved and so many assumptions that you can end up getting lost in it all.  For instance who is to say that 75% is a reasonable block coefficient for a tug hull?  At the end of the day putting the model in the bath and having a play is the only way to get somewhere near to where you want things.

I understand where you are coming from as you need a total ballast requirement if you are looking at using two totally different propulsion systems in the same hull.  Consequently I would play around in the bath by adding weights internally then putting the superstructure back on and see how she sits.  When you have her sitting correctly and she has a suitable righting moment then you know what weight you have available to play with. By suitable righting moment I mean you need to push the top of the mast over and see how quickly she returns to upright when you let go.

All the components you need to add for whichever propulsion system you are considering must then be weighed and subtracted from the total ballast to give you a ballast figure for each propulsion system.  I tend to then spread this ballast along the length of the hull, even sometimes just putting half at either end to prevent the ends bobbing up and down in an unrealistic manner.

As an example I have a 1/48th scale Graupner Corvette.  The instructions said it needed 6kg total ballast.  I got all the bits together I was going to put into it, receiver, smoke generator, 6v propulsion battery, 12v smoke generator battery etc, and weighed it all, which came to around 2kg.  These component were spread along the length and I put 2kg of lead shot in the bow and 2kg in the stern.  She sat perfectly in the bath and had a good righting moment so I fixed the shot with resin.

I would try a similar approach.

Yes I had that problem, ended up with a cheap paddling pool in the garden! I agree larger models look good on the pond but do pose practical problems.

One of the kit manufacturers I knew had a rule of not making a model that could not be fitted across the back seat of a standard car. Very sensible really.

Colin

I rather doubt if detaching the superstructure is going to be a practical solution given the amount of work and risk of damage but the boat is certainly going to be vulnerable to taking on water. Just raising the waterline a bit won’t be enough as a tug model moving through the water will create waves which will reach up to deck level along the hull.

There are a couple of ways you can mitigate things to some extent. It might be possible to establish a silicone gasket along the joint which, if not totally watertight, would significantly reduce the inevitable inflow. I think Ashley did this with one of his recent models.

Secondly, you could use some of that ballast weight to fit a miniature automatic bilge pump and a 12v gel cell battery. The outflow can be led through the side of the hull where it will be easily noticed.

I do find it difficult to understand how the original builder could have made such a serious design error which throws into serious doubt the viability of the boat as a working model. Maybe that is why it was never finished or run? It wouldn’t have worked without a rudder either and the design has made fitting one almost impossible as on this sort of  full size tug the rudder post would emerge on deck under the grating at the stern where it would be attached to a quadrant tiller. Chains from this would be led along the inside of the bulwarks and up into the wheelhouse. On a model it is sometimes possible to have a pushrod along the deck to a servo under the engine room skylight. But if you try to do this then you won’t be able to get the deck off without dismantling it all, not practical with a steam powered model at the pondside.

Your photos do not show the stern with the top off but the only possibility to fit a rudder in the circumstances would be to excavate the solid wood underneath the deck sufficiently to install a rudder tube with a tiller which can be connected to a servo placed further forward in the hull. This would be similar to what I am doing on my current liner model – see photo.

Having looked the the photos in more detail I’m not a all sure that you can turn this into a working model even if it was the original intention of the builder.

Colin

Very glad to see you have fixed the rudder issue, a neat solution and exactly what I had in mind.. You may find that the size is OK as it is directly behind the prop. Some people who have rudder problems have made ‘slip on’ extensions which can be removed when the boat is out of the water. If made with transparent plastic they are pretty much invisible when the model is afloat too.

I have messaged Ashley Needham to have a look at this topic to see if his ‘made to measure’ gasket idea would work for you. Could be more effective and less messy than your wax/epoxy idea.

Colin

Just adding a couple of thoughts to the mix to either chew over or spit out!

First I have to say your rudder connection is beautifully done and such a perfect example of how a ca

refully thought out and well executed solution can be used to solve a problem.

OK, the challenges, I’ve seen sticky backed closed cell foam edging used as a seal in the past.  They type that used to be used to seal poorly fitting doors and windows before everything went double glazing. Not elegant but fairly successful depending on the gap.  It needs compressing though.  I’ve also seen a smear of Vaseline used, again it depends on the size of the gap.

I just want to put a couple of probably more controversial thoughts out there.  First up I built a steam model over a twenty year period, see Model Boat Magazine Boiler Room articles in Editions Nov and Dec ’24 and Jan ’25, and had to come to the conclusion that it simply wasn’t seaworthy enough to risk it on the water.  She sits at the correct waterline, which is too low for a scale model, and contains a huge amount of expensive plant.  Not to mention the time, effort and love that has gone into its creation.  Consequently I am simply not prepared to take the risk and she now sits in a glass cabinet.  I saw it as a failure for some time, as did a number of friends who said I should give it “just one outing”, but I knew it was a risk I didn’t want to take.  To get the weight down would be a major disassembly and rebuild, which I am also not prepared to take on.  Now however I don’t see it quite so much as a failure, more of a big part of my own learning curve as a modeller.  I enjoy seeing it in the glass case and it will now outlast me, god knows where.  The only point being, it is an option to decide not to sail the model.

Having said that I also have a Model Slipway Envoy Class tug.  She sits very low aft and has a more normal arrangement of a sealed deck edge and access hatches over coamings.  Even with a very low aft freeboard I get very little water on deck as a result of only using it in appropriate conditions, i.e. flat calm day and take it out when the lifeboats go on the water!

The final thought I can offer is the fact that I’ve only ever had one model sink on me.  Yes, it was my Caldercraft Joffre.  Luckily I retrieved it, refurbished it, repainted it and still use it but it is a reminder that it can happen.  I did read somewhere that she was conscripted into navy service at one point so I went for a RN colour scheme.

Extra question, what keeps the top secured to the hull so that it doesn’t get knocked off?

Colin

Looking at the latest photos I would agree that Ashley’s method is more likely to compensate for the irregularities. It’s a mystery why the original builder chose this method of construction as tugs are popular subjects for steam power because it is relatively easy to incorporate large hatches with coamings under the superstructure and engine room skylights to facilitate access to the interior. A permanently attached deck also greatly strengthens the structure.

Colin

Having tried both I am nowadays firmly of the opinion that steam plants are infinitely easier to build, maintain and operate in an open hull.  Plus you get to see it all operating!

I’m not sure that steam models are invariably open launches, over many years I have seen plenty of models where this is not the case and the steam plant is below decks. Inevitably this introduces more complexity but this is not always a problem if the model is designed with adequate on deck access to the power plant at the outset and has sufficient ventilation. Not necessarily ‘difficult’, just a matter of choice and getting the initial design right.

As Richard says, open launches are more straightforward and easier to build, plus have you have the bonus of seeing it all operating and that is a big attraction to both modellers and observers. With enclosed steam plants you just see the plume from the funnel. Horses for courses really. It’s always great to watch a steam engine in action whether it is in a model or full size as in a preserved pumping station or a paddle steamer like ps Waverley.

It has been said that a steam engine is the closest thing man has created to a living and breathing object.

Colin

It was Len who suggested the High Modulus sealant..i had never heard of it before. You have to look at all the technical specs of various silicone sealants and it should state there what they are.

Marine silicone might be another source, from a boatyard. These are much tougher than kitchen types…I have used two lots over the years. One of them was used to stick the top and bottom bits of my MFA Fantome together.

Ashley