Motor size etc

[Alan SmithParticipant @alansmith52971]

Hi, I’m building my second r/c boat. The first was from a plan in Model Boats of a WW2 destroyer. It looked great but its speed was too fast. Also, although it sailed on the correct waterline, it tended to tip to one side slightly as it went around corners and not come back to an even position. The boat I am building now is a Norwegian well boat, 600mm long and 123mm wide. Her name is Ronja Harvester and there are plenty of pictures of the real one on the web. I have drawn my own plans based on photos. How do I choose a suitable size electric motor and propeller for this size and type of boat? To overcome the tipping problem, I have given it a vee hull below the waterline. What is the best way of getting the side panels to fit the vee where it meets the bow? How do I shape the side panels to form the flared bow? What is the best material to conform to the curves and twists of the bow? I am thinking of either thin balsa or single ply plywood. Any help or suggestions would be much appreciated.

[JC Uknz 1Participant @jcuknz1]

You could use a block of balsa where the difficult curves are.  perhaps not a solid block but a built-up structure.  I would hate to use thin enough balsa to do curves becuase it gets very brittle when sealed. Better is to soak the planking* in warm water or amonia. For planking I make a former with brads on a plank of wood and let them dry before fixing to model.  

Your destroyer likely had a hull ratio of around 10 so not that stable without ballast in a model [ you probably could fix the problem by adding removeable ballast/keel when on the water], whereas the new boat at 4 shouldn’t have any troubles.  On this forum there is a shot of a paddle steamer fitted with a keel for stability.  To reduce its speed you could reduce the pitch of the propellor[s] so while they are spinning fast they don’t grab so much water.  That should also make the batteries last longer.  To get ‘scale’ speed I often simply move the trim tab to more forward without touching the speed lever.  this gives me a nice ‘good’ speed … but of course it depends on the boat   Also doing the same to the steering so that she goes around in nice circles on the pond and I can pay less attention to her if she is the only boat on the pond at exhibition pool once i get her set-up in the right position .

*likes of 2mm ply or thinner if available to you?

[Alan SmithParticipant @alansmith52971]

Thank you JC, I really appreciate your comments.

I have overcome the hull panel problem using 0.4mm plywood, held on with woodworking glue and then strengthened with fibreglass. It seems to be OK. I thought of the removable keel idea, but decided against further fiddling as the boat was limited anyway, in that it was struggling to accommodate the radio gear etc.

What do you think about a suitable motor size and should it be geared down? Is that the ideal solution or does it not matter, provided the result is what I want?

[JC Uknz 1Participant @jcuknz1]

I am afraid I know little about motors becuase I have a stock of 24v motors salvaged from photo copiers but for my Tyne offshore patrol boat I have bought a couple of 540 type motors but have no idea how they will work as yet .. not started on the build.

[Alan SmithParticipant @alansmith52971]

Thanks again. I’ll let you know how mine progresses. It looks like I can include a photo so I’ll try to add a couple. My boat is so plain and primative compared to the engineering masterpieces I see other people making, but still it looks OK, at least on the outside. On the inside you see what an amateur I am.

[Alan SmithParticipant @alansmith52971]

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