1/20 scale Aluminum WW2 ELCO PT Boat

[kenb]

Hello folks,

New member here. I was referred to you guys by a member from another boating website, for some advice on the best way to outfit my scratch built boat project with electric power. This is a project I've been working on since 2003, and it's looking like the springtime of 2010 will be when this boat will hit the water for the first time.

The original plan up until now has been to power the boat with a G26M Zenoah two stroke engine, and at this point I have the internals pretty much completely roughed in for gas power. For various reasons, I am having second thoughts about running gas in this boat, so I've decided to start educating myself on the possibilities that an electric drivetrain can provide. I should add that I'm a complete noob when it comes to electric power, so it might take me a little while to get my head wrapped around the finer details.

The most pressing reason for the change is the fact that I'd like to enter this boat into some scale model regattas next year, and most clubs I've found so far have a strict "no-gas" policy for entries. Other reasons include excessive vibration (bad for rivets), gas & oil spills, heat from exhaust systems, and lastly, the possibility of an aluminum mangling accident caused by going a bit too fast for my own good. I've probably got 1000+ hours into designing and building this boat, so the thought of cracking it up on a reef somewhere literally sends shivers up my spine.

Here's a few pictures of my boat. This is an aluminum 1/20 scale replica of a WW2 ELCO PT Boat, scratch built from 3003 aluminum sheet and secured together with aviation style rivets. The hull is 45" long, and weighs 12 lbs empty as seen in these pictures. I'm expecting the finished boat to weigh in at 20-23 lbs or so.
















I'll upload some more pictures of the drivetrain layout soon.

Ken

[CornelP]

All I can say is... WOW!!
Well, to do this hull justice, you should go for twins... as most PTs are.
It all depends if you want shear speed or scale speed... and the budget. Set these targets and it will be easy to help.

BTW... your workshop is WAAAY too clean... :)

[Gerwin Brommer]

Wow ! a true T.L.C boat !
Very impressive , outstanding job !

[kenb]

All I can say is... WOW!!
Well, to do this hull justice, you should go for twins... as most PTs are.
It all depends if you want shear speed or scale speed... and the budget. Set these targets and it will be easy to help.

Yep, it's going to be a twin drive as shown in the pictures below. The real 80' ELCO's actually had three prop shafts, each powered by a 1300 HP Packard V-12, but the engineering nightmares brought about by the third center shaft coaxed me into settling for two props.

BTW... your workshop is WAAAY too clean... :)

To be honest with you, the shop's a pretty messy place most of the time, and lots of things tend to get moved around when the camera comes out!


Here's a look at the drivetrain layout:

This is the inside of the engine bay looking aft. If I decide to use the gearbox pictured at the front, I'll use one large electric motor at the back of the engine bay driving the power forward to the center top area of this gearbox, where it will be split between the twin shafts that exit through the bottom of the hull. I can do pretty much anything I want with the gearbox, as it's a home built unit I designed myself using plastic gears for the Traxxas line of 4x4 R/C trucks, so I can fine tune it to any drive ratio I desire.

Alternately, I suppose I could delete the gearbox entirely and go with two separate electric motors, each driving one shaft directly if that's the better way to go.





Here's a look at the propeller shafts where they pass through the bottom of the hull. I used delrin sleeves to keep the stainless tubes isolated from the aluminum to prevent any nasty reactions between the dissimilar metals.






Here's where the prop shafts come out the other end. I intend to add support struts for the prop shafts just ahead of the propellers.





So there's the drivetrain layout, now I just have to figure out the best way to make electrical power turn those props.

As for expectations, I'm looking for a drive system capable of slow to medium speeds, with the emphasis being directed to long battery life to get me through long days at the scale model regattas. Going fast once in while would be nice too, but it ain't the main priority at this point!

Ken

[detox]

Checkout this Proboat site. You may get ideas from there.

http://www.proboatmodels.com/Products/ProductGallery.aspx?ProdID=PRB3600

...

[Gerwin Brommer]

strutt supports are a MUST.

[westbeach]

Ken,

Very impressive sheet metal skills you have. Can't wait to see the rest of this build.

[tth]

Welcome to Offshore Electrics Forum. Very nice hull you are doing. It looks like you have the skills to machine what you want..........keep up the good work!

[KillerDave]

Holy moly man! That thing is un-real! I can't wait to see it finnished and on the water!
Wow!!!!!

[CornelP]

On the water? It should be framed as it is now....
Two suggestions to start with: keep it as it is, do not use any filler/paint and keep the gearbox, it is a thing of beauty itself.
For a motor, you will need something in the 1500W area to properly move that thing.
My opinion is to go for 12V lead battery for regattas, plenty of time and decent speed, with a big Lipo every now and then for fun (like 6S2P or bigger)
For a scale speed, you should be looking at 15-20000 rpm, so any big beast around 1500kv would be fine.
Maybe a 10L
http://www.offshoreelectrics.com/pro...prod=fei-580-L
or a 1521 1Y
http://www.offshoreelectrics.com/pro...?prod=neu-1521

[KillerDave]

I absolutely agree!!! It is an amazing piece of engineering let alone model boat....
I would guess that you are either in aircraft or auto restoration?????

Either way, It is beautiful and you should NEVER put paint on it!!!!! NEVER!!!!!
If it was me, I would maybe lead the seams buff the skin,only to get rid of any mark and scratches and then laqure it for protection.... But that's just me....

Having said that, Painting it might not be such a bad idea as long as you could still show off the craftsmanship on the inside!
This thing could be a show stopper!!!!

Awsome job Ken! Keep it up! The work that is!!!! Lol!!!!

[kenb]

Thanks for all the kind words guys. It's been a tremendous learning experience that's for sure, and I'm not quite finished yet. The basic hull design began with a set of drawings for a balsa wood boat to be outfitted with electric power, which I modifed in autocad to produce a set of plans more suited to aluminum construction. Once I get the drivetrain finalized and installed, I'll move on to the scale modelling challenges above decks, such as the cabins, two pairs of 50 cal machine guns, torpedo's, depth charges, and a couple of big anti-aircraft guns that will fit in the round holes on the aft and fore decks.

keep it as it is, do not use any filler/paint

I made the final decision on the outer finish about a year ago, and I've decided that she's going to remain bare aluminum with various degrees of shine depending on the location. I originally intended to match it up with period color schemes for the South Pacific during the early to mid 1940's, and I even went as far as to research the dozens of different color combinations used by the US Navy at the time. Then one day I suddenly realized that painting the hull would make it indistinguishable from any other PT-109 plastic model kit out there, so I made the decision to preserve the beauty of the polished aluminum, both inside and out.

I might have to wear my welding goggles to see it on the water on a sunny day, but I'll deal with that when the time comes!

For a motor, you will need something in the 1500W area to properly move that thing. My opinion is to go for 12V lead battery for regattas, plenty of time and decent speed, with a big Lipo every now and then for fun (like 6S2P or bigger) For a scale speed, you should be looking at 15-20000 rpm, so any big beast around 1500kv would be fine.

Is that 15-20000 rpm at the props, or is that the rpm I want the motor to be running at? I'm just beginning to try to figure out what I'll need to be doing with the power as it goes through the gearbox, such as whether I'll be gearing the power up or down, or simply passing through it 1:1.

Thanks for the links to those motors.

Ken

[kenb]

I absolutely agree!!! It is an amazing piece of engineering let alone model boat....
I would guess that you are either in aircraft or auto restoration?????

I'm actually a DSL technician, I'm the guy people freak out at on the phone when their internet doesn't work!

In my spare time, I'd call myself a "metalshaper", we're the guys who use english wheels and planishing hammers and things to make motorcycle gas tanks and other compound shapes from sheetmetal. The PT Boat was actually the very project that lured me into the craft back in 2004, and it's taken me this long to figure out how to build what I had designed! Click on the link in my sig to see some of the other metalshaping projects I've done.

Either way, It is beautiful and you should NEVER put paint on it!!!!! NEVER!!!!!

Not a chance! I'm going to do a bit of experimenting with different effects on the finish, such as sanding different areas with coarser and finer grades of emery cloth, wet sanding vs dry, etc, just to see what kind of finish contrast I can achieve. I've seen pictures of reproduction aluminum bodied AC Cobras, where a 1 foot wide stripe down the middle of the hood and trunk lid was created by simply finish sanding it with a slightly coarser grade of emery than the rest of the surrounding body.

Ken

[CornelP]

The rpm's are at the prop. The only problem I can see here is if the gears will hold to 30000 rpms (with he big batteries). If you are confident with it, it should be ok.

PS Looking at prices, you could go for the Feigao as a start...

[Doby]

Not entirely sure that brushless motors would be the best choice for this boat. Some big brushed Graupner 800's might be more suitable....remember, brushless motors/controllers like full speed for heat reasons. For scale regattas , I'd go with brushed motors.