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Old May 03, 2005, 08:03 PM
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Sydney, Australia
Joined Feb 2005
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Scratch building the Erreka tug in 1:32

Well here goes..

I was sent a copy of some plans for a tug from a friend in Portugal. The following photo is from the modelmakers website, so at least I have some idea what its supposed to look like when I finish.


The plans are from a 1:50 scale static plastic model that he found at a market. The kit was incomplete and he was going throw it when he remembered that I have built model boats from plans. He emailed me the plans as below.


After some initial discussion with the master Pat T and my new pan pal Martin in Spain I have made a start.

I scaled up the plans using the photocopier at work to 1:32. I then copied the cross section of the hull onto transparency so I could flip it over to produce the complete hull section.

I took multiple copies of this and cut out one for each of the sections on the plan.

I have some 4mm ply which I will use for the keel. I am not sure whether to use ply or balsa for the frames. Does anyone have any strong opinion here?

I also need some advice on motor size. Due to the hull shape (this is from a plastic static model remember) I will have to use a geardrive arrangement and I would like good bollard pull on this tug. The prop size scales off the drawing at about 42mm dia. I will probably use a 45mm prop as I can get one with the Kort nozzle from a shop nearby.

I welcome any feedback?

If anyone wants a copy of the plans, please PM me.

Cheers
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Last edited by Capt_Christo; May 30, 2005 at 08:18 PM.
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Old May 03, 2005, 10:22 PM
Useful Idiot
Asturias, Spain
Joined Mar 2001
3,545 Posts
Hi Chris, a motor like the mabuchi 545 geared to 3:1 or 4:1 should provide enough torque assuming a fairly low pitch prop and give good "throttle" response.
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Old May 10, 2005, 07:24 PM
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Sydney, Australia
Joined Feb 2005
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Here are the frames ready for cutting out. The board is 4mm construction ply. I will leave the three fore-most and rear-most frames whole. The others I will cut out the centre leaving 12mm at the sides, 25mm near the keel and 10mm under the deck.
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Last edited by Capt_Christo; May 30, 2005 at 08:22 PM.
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Old May 10, 2005, 07:54 PM
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Sydney, Australia
Joined Feb 2005
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A quick question

The first picture is the diagram showing where the propshaft runs (red line)


There is also a diagram showing the aft view


You will notice that the propshaft is wider than the timber used for the keel. How do I get around this..either

A. use thicker material for the keel,

or B. Build up the thickness in this area by glueing extra timber on eack side of the exposed skeg area,

or C. laying a strip of cloth along both sides of the tube with resin, before I start assembling the frames.

Otherwise this has the effect of cutting off the bottom of the keel.

Has anyone come up agianst this problem and how did you get around it?

Cheers
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Last edited by Capt_Christo; May 30, 2005 at 08:29 PM.
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Old May 10, 2005, 09:30 PM
Veni, Vidi, Feci
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Joined Dec 2004
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Yes, in a model you'll cut the keel to run the stuffing tube through, but keep in mind that the hull isn't a flat plate in that area, it quickly flares out providing lots of structure to strengthen the area. So yes, cut the keel and put some fish plates to either side to hold it all together until the planks are in place.
Picture of a single screw tanker- the real thing uses a mix of large castings and formed plates to build up this complex area.
Pat M
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Old May 10, 2005, 10:02 PM
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Sydney, Australia
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Thanks Patm,

I sort of came to the same conclusion after studying the first picture in this post. You can just see the bulge forward of the prop. I just wasn't sure how to go about it.

Thanks again for the guidance.

There's a lot to be said for having a big think about things before you hoe in...especially when building from scratch.
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Old May 15, 2005, 05:36 PM
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Sydney, Australia
Joined Feb 2005
382 Posts
Hi guys, I have run into a slight snag. I will use a 3:1 reduction gears, and where the prop shaft ends, I need to cut a notch in the keel for clearance for the gear wheel. This leaves the keel only 10mm deep at this point. Is this going to be a problem?

The other option is to angle the propshaft up slightly but I dont know if that will cause problems with the Kort nozzle.

PS I tried to take a photo but you cant see the pencil marks on the wood.

Cheers
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Last edited by Capt_Christo; May 15, 2005 at 06:03 PM.
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Old May 15, 2005, 11:18 PM
Useful Idiot
Asturias, Spain
Joined Mar 2001
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The main strength of the hull is going to come from the rigidity provided by the planks. It should be OK but you may feel better using a couple of ply doublers. Also taper down to the 10 mm thickness rather than a sudden step.
You could avoid the problem alltogether, using a planetary gearbox.
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Old May 16, 2005, 12:21 AM
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PDX, OR
Joined Dec 2002
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Christo,

If you put in a brass tube that is one size larger diameter than your stuffing tube, you can build the hull around that. After the hull is complete, you can put the actual stuffing tube assembly through the larger tube, and cut it to any length you need. This may allow you to put the motor farther forward or back, if required, to help you get clearance in the hull for the gears.

It might help to know, that I pull out the keels in most of my scratch builds once the hull is fiberglassed. I then come back on the inside, and lay a 2"(50mm) wide strip of fiberglass down the center line of the hull where the keel was removed.
Never had a problem with strength.
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Old May 16, 2005, 05:07 PM
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Thanks for the encouragement guys.

the build continues...
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Old May 30, 2005, 05:47 PM
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Sydney, Australia
Joined Feb 2005
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Finally got some model time.

the 1st picture below shows the completed keel with the embedded prop shaft. the second and 3rd photos are closer detail of the notch in the keel to accomodate the gears and the propeller end.

OH CRAP,... I just realised that I forgot to solder the breather tube to the prop tube. Oh well, it shouldn't be too hard to do it now.

The other problem that I have is the construction grade ply I was going to use for the frames is rubbish, it splinters like crazy when you try to cut it. I will revert to using balsa for the frames. Hopefully I will have them cut out by this weekend.

Cheers all
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Old May 30, 2005, 07:44 PM
Registered User
Monterey Bay California
Joined Feb 2004
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The driver of your Elise is taking the corners a bit fast isn't he Capt.?

Keel is looking good!
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Old Jun 10, 2005, 10:24 AM
Tinkerer in Training
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Guelph, ON
Joined Sep 2004
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Any updates?
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Old Jun 10, 2005, 01:07 PM
If it ain't broke, fix it
Cambridge
Joined Aug 2004
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looking good so far . keep up the work and the updates
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Old Jun 11, 2005, 06:21 PM
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Sydney, Australia
Joined Feb 2005
382 Posts
RL has been getting in my way. I work 6 days a week and ionly have Sunday for R&R so things progress slowly. I have 2 frames left to cut out but ran out of balsa.

Question: do you do the rudder tube the same way that you do the prop tube, ie cut through the frame? And when is the best time to do this?


BTW as Ray started this trend,I'll keep going

Cost so far (in A$)

Motor $18.00
gears $7.00
balsa $8.50
Prop shaft $10.00 (but enough for 3 shafts)
glues $8.75 (balsa and epoxy)
4mm ply for keel $4.00 (but enough material for several more keels)

Total $56.25
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Last edited by Capt_Christo; Jun 11, 2005 at 09:37 PM. Reason: added costs
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