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[Darren81]

Hi All,

I've been on the forum for a while just loitering, reading and learning. I'm planning to scratch build an anchor handler but having never built a model boat before I thought I'd start with something simpler and cheaper for a practice run, so a modified springer tug seems a good place to start!  I'm also hoping it'll be a relatively quick build too to get out on the water...

I've decided to alter the lines slightly, going for 600mm length and a section of flat bottom, 250mm beam, 150mm depth plus a 50mm raised focsle to be a little more offshore tug like.  Draft will be about 100mm.  displacement will be about 10kg. 

She'll have a single screw for simplicity, and here's where I have a couple of questions...

Does a kort nozzle make any difference to bollard pull force at model scale?  I was thinking of either a 60mm open prop, or 50mm kort nozzle.  I'll have an off-the-shelf rudder behind.  Speed is not important, slow is fine (and probably better if my 5yr old son starts driving...)

From the prop and hull dimensions, how do I decide which motor and speed controller to use?  From what I've read, a 540 motor should do the job with 6volt SLA batteries (ballast), but is there a more appropriate option?  And how do I then select a speed controller?

I'd like to buy the running gear before starting to build the hull just so I know where everything is going.  I'm planning to make it plank (or sheet) on frame, just to practice the methodology rather than out of structural need.  Frames / sides / bow / transom / deck will alll be 3.6mm ply doubled up to 7.2mm, then I was planning to use just 3.6mm ply for the bottom - but can I get a 100mm bend radius on that thickness of sheet or should I opt for a thinner / bendier bottom sheet?

Thanks in advance for the help.

Darren

[Darren81]

Profile view will look like this:

[Oops, pics don't work, do you normally post elsewhere and post links?]

[Tug-Kenny RIP]

Hi Darren and welcome to Mayhem.

Regarding posting of pictures you should be able to post direct from your computer as long as you keep the size to around 100K.

Also, I would not go for extreme thickness of your hull.  3.6mm plywood will be fine.  To achieve the bend, the good ol hairdryer works a treat. Clamp the piece in a vice and gently bend and heat.  Then lock it into position and leave overnight.

Happy sailing.

ken


 

[Darren81]

Hi Ken,

Thanks for the advice, much appreciated.  No hairdryer in this household so I'll have to dig out the wallpaper heat gun and use at a safe distance out in the garage...

I found the thread about posting pictures, lines plan sketch attached.

Any advice on the motor?  Is a 540 sufficient?

Darren

[Tug-Kenny RIP]

Any type of motor will do.  The 540 is a good choice.

Regarding the bending, any hot air machine will be OK.  I usually put the wood in the vice and apply the heat whilst bending it over a curved Former.  The bend is then held down with wire while it cools and the glue resets.

When  'set'  the operation is repeated for the second curve, the other way.

Watch your hands as the heat creeps up the sheet.     

Look forward to seeing the results

ken

[bill stafford]

be carefull w motor / prop choice , a 540 wont drive much bigger prop than 35/40 mm direct drive ,for a 50/60 mm prop  i would use a gear box of 3:1 ratio , much more battery friendly and longer duration
you can use RC car gears or tooth belts of MXL pitch , housing done in alum. sections

[Onetenor]

Another way to bend ply is to stand it in a pan of boiling water for a few minutes then bend and hold down in position over night. Make the bens just a bit more then you need as it will  spring back a little when released. A safer method is to soak it in household ammonia .Bend and secure as before and allow to dry out. Again bend it a little over what is needed. It is easier to push a bend flatter then force it further round if you get my meaning Please wear some stout gloves for the hot stuff.Welders gauntlets are ideal and can be used for gardening too.  Often to be found cheaply in Aldi and Lidl. Especially when they have welding machines on offer  Good luck.   P.S. Professional wood workers who do a lot of bending use a solid steel round bar that slips into a steel tube held in the vice. The bar is made red hot then slipped into the tube and the wood pressed  over the tube held for a little while then bent over it keeping it moving to avoid burning .Worth making up  a kit of this if you intend doing a lot of bending. Or even if just now and then. There you are you've got a choice now