Wattle by Ikcdab - 1:24 - Steam Tug - my first scratchbuild

[Ikcdab]

Hi all, well this is my first post for my first ever scratchbuild for my first boat. The plan is to build a 1:24 model of the steamtug Wattle. I have just received three sheets of plans and there is a comprehensive article in the winter 2013 Model Boats special edition, so I am ready to go.

 

My background is that I am a lifetime railway modeller (https://www.rmweb.co.uk/forums/topic/157222-charlton-bridge-4mm-brs/#comment-4078299) and i have scratchbuilt much of that. So although this is my first boat build, I am fairly confident about what I am doing.

 

I am based in Somerset, UK.

 

The article suggests 3mm ply for the frames overlaid with 3mm balsa planks that are then sheathed with fibreglass sheet. i have a 3d printer and i think that i should be able to 3d print various fittings etc - eg the rudder looks ideal for 3d printing as do portholes and deck fittings.

 

My first step is to copy the drawings, print out the frame plans, stick them to the ply so that they can be cut out. I need to get over to the local model shop to buy ply and basswood (for the keel). Then I need to source some 3mm balsa so that i can cut planks.

 

So my first basic question is about sticking the printouts to the ply. Its got to be stuck down well enough so that the frames can be shaped, but i guess loose enough so that the paper can be removed afterwards...and soaking in water to release glue doesnt seem a good idea! Whats the best approach for this?

 

All other comments are welcome!

 

Ian

[Roger Pellett]

Welcome to MSW and to the scratch build forum in particular.  An ambitious project like this is a major investment of your time.  Cost, on the other hand is amortized over a long period of time.  It therefore pays to invest in top quality materials that will not cause problems as you proceed.

 

Most experienced modelers do not consider balsa to be suitable for high quality ship models.  It is too soft and weak.  You might want to see what other woods are available locally.  Many British ship modelers prefer Lime wood, not to be confused with the tropical fruit, but similar to our American Basswood. 

 

Roger

[Ikcdab]

37 minutes ago, Roger Pellett said:

Welcome to MSW and to the scratch build forum in particular.  An ambitious project like this is a major investment of your time.  Cost, on the other hand is amortized over a long period of time.  It therefore pays to invest in top quality materials that will not cause problems as you proceed.

 

Most experienced modelers do not consider balsa to be suitable for high quality ship models.  It is too soft and weak.  You might want to see what other woods are available locally.  Many British ship modelers prefer Lime wood, not to be confused with the tropical fruit, but similar to our American Basswood. 

 

Roger

Hi Roger thanks for that and I appreciate your comments. As a beginner to boat building, I am open to all advice.

The model was designed by someone who i believe to be reputable. I had the same thoughts about balsa planking, but I was reassured by the fact that the planking is sheathed on the inside by a single layer of 200gsm chopped strand mat cut to fit between the frames then on the outside first a layer of 185gsm cloth, then a layer of 85gsm cloth followed by a coat of straight resin as a sanding filler. It seems to me that this should give a strong and light hull. Clearly this is a decision i need to make soon and I would welcome further comments.

Ian

[GrandpaPhil]

I use Elmer’s glue sticks to glue down patterns to wood or other materials.

 

It is generally sticky enough to hold for a bit, but then it can usually be removed relatively easily by just peeling it off.  Some scraping may be required to remove all of it.

[KeithAug]

On 1/10/2024 at 2:10 PM, Ikcdab said:

So my first basic question is about sticking the printouts to the ply.

Hello Ian - welcome to MSW - I use Pritt Stick - and then peel / sand it off.

 

I would suggest basswood for planking. You may find 3mm balsa planks are a bit too fragile when it comes to shaping - particularly if the frames are widely spaced (as they tend to be on Model Boats plans). If the spacing is wide balsa planks will tend to "straighten" between the frames producing a series of flats.

 

Have a look here for wood. https://www.slecuk.com/allcategories - Decent service and reasonable cost.

 

I had a look at your railway model link. You shouldn't find ship modelling too much of a transition.

 

Keep asking questions, MSW is a friendly and helpful place.

 

Good luck.

[Ikcdab]

1 hour ago, KeithAug said:

Hello Ian - welcome to MSW - I use Pritt Stick - and then peel / sand it off.

 

I would suggest basswood for planking. You may find 3mm balsa planks are a bit too fragile when it comes to shaping - particularly if the frames are widely spaced (as they tend to be on Model Boats plans). If the spacing is wide balsa planks will tend to "straighten" between the frames producing a series of flats.

 

Have a look here for wood. https://www.slecuk.com/allcategories - Decent service and reasonable cost.

 

I had a look at your railway model link. You shouldn't find ship modelling too much of a transition.

 

Keep asking questions, MSW is a friendly and helpful place.

 

Good luck.

Hi Keith, thanks and thats very helpful. Pritt it is then, i use a lot of it on the railway in building construction.

I have received several replies and each is against balsa and none support it. Although it is the material used by the designer, he is far more experienced than me and so can probably cope with the problems you mention. So i should take that advice and choose an alternative.

Bearing in mind that the hull will be sheathed in two layers of fibreglass cloth, is there any reason why i cannot use 3mm ply for the planks? I can easily cut these from ply sheet, so i can get the exact width required for a whole number of planks?

 

[KeithAug]

Ian, ply is more difficult to sand than basswood but in principle there is no reason why it can't be used. I assume you don't have the means of cutting your own planks from basswood? You are going to find that the planks will need to tapered to fit on the frames - wider at the middle of the boat and narrower at stem and stern. Also to get smooth curve round the hull the need to be relatively narrow - probably no wider than 5mm. Some may need to be even narrower.

[Keith Black]

Ian, welcome to MSW. I'll be following your build, wishing you great success.  

[Ikcdab]

7 hours ago, KeithAug said:

Ian, ply is more difficult to sand than basswood but in principle there is no reason why it can't be used. I assume you don't have the means of cutting your own planks from basswood? You are going to find that the planks will need to tapered to fit on the frames - wider at the middle of the boat and narrower at stem and stern. Also to get smooth curve round the hull the need to be relatively narrow - probably no wider than 5mm.  Some may need to be even narrower.

Hi Keith, i can cut any type of wood on the table saw. It's only that my local model shop (whom i like to support) doesn't list basswood on its website and I've not seen it in the store. Maybe i should go in and ask. I also read that basswood is "furry" - several quotes of this!

Edited January 12 by Ikcdab

[KeithAug]

7 hours ago, Ikcdab said:

basswood is "furry"

Ian - it is quite soft but no where near as soft or furry as balsa.  An alternative would be Lime. Both would work reasonably well as a foundation for fibreglass.

You can look here http://modelshipworldforum.com/resources/materials_and_tools/Modelling_Woods.pdf on the MSW web site for recommended woods and their uses. However the best approach is to do what you are comfortable with in the knowledge that if it doesn't work you can always rip it off ant try something else.

 

Basswood 

 

[Roger Pellett]

Since you are glassing inboard and outboard I assume that this will be a working (RC) Model.  Correct?

 

Roger

[Jim Lad]

Is this the Brisbane steam tug 'Wattle'?

 

John

[Ikcdab]

11 hours ago, Roger Pellett said:

Since you are glassing inboard and outboard I assume that this will be a working (RC) Model.  Correct?

 

Roger

Yes!

[Ikcdab]

11 hours ago, Jim Lad said:

Is this the Brisbane steam tug 'Wattle'?

 

John

Hi there John, it's the one currently based in Melbourne. https://baysteamersmaritimemuseum.org.au/5present.php

 

[Ikcdab]

Well, my first purchase.  Whilst I plan to make most of the parts myself, I thought that the prop would be beyond me.  So now I am the proud owner of this

A bronze 90mm M5 prop.  

I know I haven't even started on the hull yet, but thought I needed these things to get me started.

Ian

 

[Jim Lad]

She looks a fine little tug, mate.

 

By the way, I hate to be picky, but unless it's a trick of the light that looks like a left-handed propeller - like almost all single screw ships, 'Wattle' had a right-handed propeller.

 

John

[Ikcdab]

21 minutes ago, Jim Lad said:

She looks a fine little tug, mate.

 

By the way, I hate to be picky, but unless it's a trick of the light that looks like a left-handed propeller - like almost all single screw ships, 'Wattle' had a right-handed propeller.

 

John

Hi Jim yes it's a LH prop.  I bought that as it was recommended by the designer. Apart from prototypical accuracy, does it make a difference?

[Jim Lad]

Won't make any difference on the model. On the full size ship, it would make the stern swing in the opposite direction to the usual when going astern.

 

John

[bricklayer]

A further note on wood for hull planking.

I`d go for fir or spruce as it`s commonly available, cheap, flexible, strong and soft. Not too soft, if coated with fibres and epoxy.

Of course it dents easily. The same about lime and basswood in particular.

These species are lightweight and can be machined easily.

 

Finally it`s your choice.

 

Michael

 

[Ikcdab]

So I already have a motor in stock. It claims you be high torque, with the following specs:

Rated Voltage: 12-24V

Rated Current: 0.32 A

Rated Speed: 3500-10000 RPM (15000 RPM MAX)

Rated Power: 60W

 

I tested it this morning. Several wallwarts that were rated at 12v failed to shift it.  Even though they claim to output 1amp or more.  All I got was a couple of rotations, then a stall, then a few rotations etc.

 

I then connected up my beefy 12v old rheostat railway controller, rated at 1.5 amps.  Motor ran perfectly, controllable and smooth.

I guess that the wall warts, even though claiming 1 amp current aren't up to the job...my electrical theory is letting me down.

 

But the real question is, how on earth do I choose a battery pack? I am told lipos are difficult to manage and I should steer clear of lead-acid.  So that leads me back to NiMH.

what sort of rating do I need to get a decent run time?

 

YOu may think I am getting ahead of myself, but I need to know now what size of equipment the hull is going to have to accommodate so that I can make space as I cut the bulkheads.

 

 

Edited January 18 by Ikcdab

[FreekS]

Nice build!  
 

you will find (or calculate) that you will need quite a bit of ballast. Then lead-acid is fine provided it’s a sealed unit.

 

looks like you don’t need much current. If 1,5A works (test in bath for waves produced with that prop, the 5Ah would give you three hours of run time.

As there is no benefit for low weight and high currents of Lipo, stay away from them. I use them in subs where space is a premium.
I also successfully used 2x10 eneloop AAA to get 12-14V. Big advantage (these are a special type of NiMH) is that these have no memory and hold charge perfectly over storage.

Finally, Li-ion also has lots of very good cells (3.7V 5000mAh).
If you make sure you speed controller has a low battery alarm than these are widely available and cheap. 

something you do need to research is the match of the motor to the prop. 90mm props will put a lot of torque on the motor. For brushed motors rule of thumb is that diameter of motor should be about same as that of prop. For brushless that does not hold, the have massive power.

Edited January 18 by FreekS

[Roger Pellett]

I agree with Bricklayer.  Spruce is a great choice for planking your model.

 

Why?  Plans directed at model makers often do not space bulkheads close enough.  This can make it hard for you to produce a “fair” hull; one without knuckles and flat spots where you don’t want them.  Spruce is known for its ability to bend easily in a fair curve.  I have a stash that I rip into splines for drawing lines drawings.  It is also the lightest of the family of softwoods (those woods cut from coniferous trees.)

 

In addition to differences in the King’s English and American English, lumber can have it’s own nomenclature.  If you do plan to use spruce, make sure that you’re buying the real thing.

 

Roger

[Ikcdab]

2 hours ago, FreekS said:

Nice build!  
 

you will find (or calculate) that you will need quite a bit of ballast. Then lead-acid is fine provided it’s a sealed unit.

 

looks like you don’t need much current. If 1,5A works (test in bath for waves produced with that prop, the 5Ah would give you three hours of run time.

As there is no benefit for low weight and high currents of Lipo, stay away from them. I use them in subs where space is a premium.
I also successfully used 2x10 eneloop AAA to get 12-14V. Big advantage (these are a special type of NiMH) is that these have no memory and hold charge perfectly over storage.

Finally, Li-ion also has lots of very good cells (3.7V 5000mAh).
If you make sure you speed controller has a low battery alarm than these are widely available and cheap. 

something you do need to research is the match of the motor to the prop. 90mm props will put a lot of torque on the motor. For brushed motors rule of thumb is that diameter of motor should be about same as that of prop. For brushless that does not hold, the have massive power.

Hi there thanks for the reply. My motor is 43mm diameter, so only half the diameter of the prop. I fear that a motor 90mm in diameter would be rather large!

[FreekS]

I’m not an expert on tugs but I estimate yours will be 1 meter long and weigh maybe 7 kg? (99 tonnes/24^3).  I think that prop will provide massive power at under 5000rpm.
 

Then you might consider a gearbox or drivebelt with a 1:3 reduction. Takes more space and risk of noise if not done well. 
 

you will need an electronic speed controller (with reverse!) and that unit and the motor can get really hot if prop and motor (and voltage) are poorly matched. You can cool them but that is wasting power. When you have the speed controller and a cheap servotester you can test the current draw and heat generation in a bath or sink.

 

Alternatively you can buy a brushless motor which are much smaller for the torque (but take care that they need a different type of speed controller)

 

sorry, this sounds difficult (or different from trains), but testing the voltage/current/motor/prop combination before building them into your ship is worthwhile.

[Roger Pellett]

You’re probably going to have to make some calculations but I suspect that anything in the 1000’s of RPMs is way too fast.  The RPM for the full sized tugboat would be something in the neighborhood of 75-90RPM.   You need to consider the whole drive train including the motor’s speed torque curve with the propeller’s geometry and the resistance of the hull at various speeds.  It wouldn’t surprise me if that prop stalls the motor.

 

Roger

[Ikcdab]

7 hours ago, Roger Pellett said:

You’re probably going to have to make some calculations but I suspect that anything in the 1000’s of RPMs is way too fast.  The RPM for the full sized tugboat would be something in the neighborhood of 75-90RPM.   You need to consider the whole drive train including the motor’s speed torque curve with the propeller’s geometry and the resistance of the hull at various speeds.  It wouldn’t surprise me if that prop stalls the motor.

 

Roger

Hi Roger thanks, I am not familiar with any of those sort of calculations and i know nothing about the motor's torque curve, the prop geometry or the hull resistance. Do people really make all of those sort of calculations for a model boat? if so, where do i find the info?

Bearing in mind its a 12v motor, if i link it up to 7.2v NiMH 5ampere batteries, then that should give slower revs and a reasonable duration?

[FreekS]

We all struggle with these calculations!

there are some formulas that convert prop rpm and pitch into speed, and like roger I suspect at a few 1000 rpm the prop will deliver the max speed that hull can reach. The hard calculation is if the motor can deliver the torque to the prop under load. I suspect your motor can only do that if you use a gearbox (dropping Reva for more torque). Dropping the voltage on a brushed motor will drop torque. Brushed motors like to run at their rated rpm. but on a brushless motor which typically has ample torque that is exactly what you do. These have kV indications, being rpm per volt, so a 1000kV brushless motor at 12 volt delivers 12000 rpm (too much) so you could run that at lower voltage. You likely would need a 300-700kV brushless motor.

 

I would couple a shaft and prop to your motor in a test rig, hook it up to a ESC and test if it runs and does not get too hot (and how much power it draws).

[Roger Pellett]

I do not build working models.  The ones that I build spend their lives in glass cases.   FreekS’ post appears to provide you with good information about the small electric motors involved in model ship propulsion.

 

Screw propellers work by taking advantage of Newton’s Third Law;  Action- Equal and opposite reaction.  In this case the action is a slug of fluid pushed aft by the propeller.  The reaction is the equal and opposite force pushing the ship or aircraft forward.  Aircraft propellers turning at high speeds act on a very low density fluid- air.  Ship propellers act on a much more dense fluid, water and turn much more slowly, requiring high torque.  I agree with FeekS that you will probably need a gear box.

 

Roger

[KeithAug]

Ian - this might provide some guidance. https://www.building-model-boats.com/model-boat-motor.html

[Ikcdab]

So some progress.

I think I can 3d print many of the fittings for the boat. I very much enjoy using fusion360 and I have used this to design a number of features.  I have now printed some.

 

Below are the double bollards:

 

 

And here are engine room hatches with portholes built in.

 

And a failure.  This is the rudder, but it has warped while printing.  So I now need to reprint it, bit with additional supports to keep it true. The bend you see is not an optical illusion...

 

I have also designed funnel, portholes, skylight, vents etc.  But not printed them yet.

More to came later.

Ian

 

Edited January 24 by Ikcdab