Is it a bird? Is it a plane? No, it’s…….a PT 109

[sihinch]

Yes folk, I'm sorry! I'm another TEMAC member building a boat!

A few years ago we went to a cottage and I bought a cheap 2S speed boat. I had way more fun with it than I ever imagined. So given I've run out of plane storage (especially after building all these novelty flying machines like Endeavour, Supermon and the Enterprise!) I decided to try a boat.

Frank kindly sold me a Dumas PT109 kit that someone had already started. So here goes my learning curve....

[sihinch]

So here is the hull, as received. First off I needed to try and remove the old epoxy that the previous builder had added. So lots of sanding.

And then I used the thinned epoxy trick to waterproof the inside of the hulll.

[GuyOReilly]

Nice!
Guy

[sihinch]

I've built a few balsa planes so I thought, how hard can a boat be? Well, lots of the skills and techniques are the same, but so much is different. Which is why I'm so glad Frank has been there to help...

So, after having sanded and waterproofed this gorgeous, wooden hull, Frank says you have to drill holes in it!

Apparently for a boat, you align the drivetrain based on the rudder position. So I drilled the hole for the rudder tube and stuffing box as per the plan. Now my boat has holes in it.

What's a stuffing box? This is allegedly the technical term for the tube that sticks out the bottom of the boat for the prop shaft to go through!

[Frank v B]

Simon,

Be prepared to be humbled on boating terms!!
I started seriously racing sailboats when I was 13 years old* and know every part, name and nickname of a boat.  There are probably 300 of them.  We carried 16 sails, each with a name and many parts (clew, head, leech, luff).  There were 27 adjustments (yes I counted them) we used to change the shape of the mainsail only...each with a name.

Then Paul Gray showed me the seamen's handbook of the British Navy before and during WW2.  It was his grandfather's book.  The 300 parts I knew represented probably only 5% of the terms in the book.  Yes I was humbled. "Pass me that thing" was not in there. 

Frank

* raced at the national and international level in high school and University.

[sihinch]

I had loads of questions for Frank about how to mount the motor. And although it makes sense now, it didn't a few weeks ago.

Frank said, as part of the power train, you mount the motor last! So apparently, to get effective rudder control you need to have the prop close to the rudder. And to make the rudder effective at low speeds it needs to be a balanced rudder. What's that, you ask? It's having a bit of the rudder ahead of the pivot point.

So in order to mount the motor, I need the prop on the prop shaft and the rudder positioned (not mounted yet.)

Frank very kindly donated a prop and rudder to me (he's really a nice Guy) but I had to work out how to attach the prop to the prop shaft (without any dogs! Yes that's a boating term!) And I had to build the rudder which involved soldering!

This is what I achieved - a balance rudder and a mounted prop on the 4mm shaft.

[sihinch]

OK, so this is where Frank & I agreed there were 2 alternate approaches!  Frank suggested to mount the stuffing box and motor and then do the fiberglassing but my hull doesn't really have a keel. So if I wanted to glass the hull with 1 piece of cloth, I decided it would be easier to glass first and then mount the stuffing box.

We agreed that neither approach was wrong and it was just whatever I was more comfortable doing.  So I did mount the prop on the shaft and get a rough position for the stuffing box, but decided I would glass.

I used the 50:50 mix of epoxy to alcohol, as per the video mentioned in other buid threads. I was using a 1oz-ish cloth and 3 coats of epoxy.

For the first 2 coats I used deluxe materials 60 minute epoxy and I wasn't really happy with the finish. It was kind of gloopy in places and stayed tacky for a long time. For the last coat I used Bob Smith industries 20 minute epoxy and the finish was amazing. Sanding with 100 grit sandpaper in between each coat.

My hull is now ready for the drive train and steering!

[sihinch]

Now that the hull is glassed and sanded, I can add the rudder block.

This is literally a block of wood that supports the brass tube that houses the rudder shaft.

Frank suggested that I deviate from plan and make the block touch the rear of the boat (transom) for extra support.

When mounting the rudder tube I copied Frank and had it 1/8" proud of the bottom of the hull to give the rudder clearance.

[sihinch]

Tonight I mounted the stuffing box. Again, not sure if this is how Frank would do it, but it's how I'm doing it.

I reckoned that, in order to get the straightest run to the motor, I want the stuffing box and prop shaft fixed in position. That way I can mount the motor perfectly inline with the prop shaft without things wiggling!

So I was working to get the shallowest angle on the prop shaft and the prop clear of the hull but close to the rudder.

I used a foam support and some tape to hold it in place while I tacked it in position with some 5 minute epoxy. Then I used Frank's magic putty!

[Frank v B]

Admiral Hinchcliffe,

You are doing well.  A neat trick to align the motor and prop shaft:
- figure out where the motor will be (fore and aft) for the coupling you have and pencil-mark the motor mount.
- cut a piece of brass tubing the diameter of the prop shaft and the motor's drive shaft.  Make it long enough so the motor can fit on the motor's fore/aft pencil mark.
- mount the motor with this brass tube instead of the coupling and it will solidly align the motor with the shaft.
- secure the motor.

It works like a charm.

Frank

[sihinch]

That's a great tip Frank, thank you! I'll be doing that for sure.

[sihinch]

So this is Frank's magic putty! Now I've got some I'm gonna use it for everything!

It's an epoxy putty I think with the consistency of old chewing gum. You mix it together (with gloves on) and then smoosh it on. It sets in about 10 mins but can be sculpted with a sharp knife after 5 mins and then sanded once hard.

I used it to set the stuffing box in place and then, to be cautious, added another coat of thinned epoxy to ensure it was waterproof.

Only thing I need to do with the stuffing box now is add the strut (at the end, near the prop.)

[sihinch]

Now that my drive shaft was fixed in place I could work on aligning and mounting the motor.

I'm using a brushed, geared motor that was kindly donated to the project by Frank. Because of the angle of my prop shaft my motor is going in upside down!

I didn't have any brass tubing to fit the prop shaft so I used a piece of  carbon tube, that is the same length as my universal coupling. This allows me to get my motor alignment virtually exact.

I fashioned a motor mount together from some hard balsa square stock and some ply support plates. Once in place I've reinforced it with the magic putty and will also add some more struts and braces later.

But I have a working propulsion system!

[sihinch]

So it's been a while...I had to make a trip to the UK but the time away gave me new enthusiasm for this build.

Today I built a custom foam stand since the prop and rudder kept getting dinged. And once it was elevated I started work on the electrical connections.

So now I have the ESC hooked up, the motor mount has been reinforced, the prop strut is in place and I also shaped the rudder a bit. The rudder isn't scale but I think it looks a bit nicer and more nautical now.

Later on this afternoon I might try to get the servo installed.

[sihinch]

Wow! This boat is something else. I'm hoping you can all forgive the nautical nature of this thread from now on because it's gonna get a whole lot more relevant to anyone that's built a scale model.

So the servo is in and I've tested the electronics with the ESC, so the hull is essentially done.

Unfortunately I'm missing the die cut parts for the cabin and pilot house. I was going to scratch build but Dumas sell the spare parts! It's 3 sheets of die cut wood for $5 each. As far as I'm concerned that's well worth it.

While I'm waiting for the parts for the main structure I've started to build the scale accessories - I need to build torpedoes, guns, depth charges etc.

Anyway, I'm learning loads! The kit comes with wooden dowels for the torpedoes and you need to add all the details. Straps, supports, end caps, mounting flanges. None of these parts (except the end caps) come with the kit. So you build them from styrene sheet and vinyl tape!

At the outset, I wanted a military looking boat that was semi scale but you get sucked in. "Oh I'll just add that detail" and "if I've done that I might as well add this bit." I guess this is what it means to build a scale model, whether plane or boat. And I now realize I've never done this before!

I'm not building a competition scale model here but I will invest some time to make the major parts somewhat detailed. So far I've spent 6hrs on the torpedoes and have finished one and nearly completed a second. I need 4!