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Nov 12, 2013, 05:27 AM
DONT TELL THE WIFE !!!
thren's Avatar
Build Log

Scratch build semi scale 1:35 PT boat


Hi all, I normally fly but due to a change in jobs, I have a very nice pond at work....
So, why not try my hand at boats. I originally thought of a cheap Chinese sailboat, but after reading reviews I started to think that I could build something that would be cheaper and more fun. (Im thinking of trying to catch a fish with the boat when finished)... yes Im also m.a.d.
Anyway's ..ike others, Ive always had a soft spot for PT's so started looking at what was available...Very expensive PT's or plastic PT's that can be converted to RC...mmmm ....why not just scratch build one me thinks.

I came across http://www.building-model-boats.com Great !! I love building stuff !! and payed for the 1/32 - 1/24 PT plans. Ive done a few searches here and on the interweb and cannot find much in the way on posts about this version. So I thought Ide post a build log.. I couldnt find a BOM, so I'll keep track of what I buy as I go and stick it here for anyone who follows. This is my first boat build so be nice to me lol

Heres the start.........
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Nov 12, 2013, 02:55 PM
Big Boats Rule!
boater_dave's Avatar
Why do the bulkheads look like they have flat bottoms? I followed the link but the thumbnail view of the plan sheet was the same.
Great subject, by the way. And welcome to the world of boats. There are so many build threads on RCG for PT's you should be able to find just about any detail you may need.

Dave
Nov 12, 2013, 06:03 PM
DONT TELL THE WIFE !!!
thren's Avatar
Quote:
Originally Posted by boater_dave
Why do the bulkheads look like they have flat bottoms? I followed the link but the thumbnail view of the plan sheet was the same.
Great subject, by the way. And welcome to the world of boats. There are so many build threads on RCG for PT's you should be able to find just about any detail you may need.

Dave
The templates are for the "top half " of the hull. The bulkheads for bottom "V" of the hull are made using the chine shelf and the kelson once in place. Hope that makes sence the pics I post in a couple of days will make it clearer.

cheers
Nov 12, 2013, 07:54 PM
Registered User
Tollytime's Avatar
I make the 1/32 hull. Might make things go a little faster.
Nov 13, 2013, 12:26 AM
DONT TELL THE WIFE !!!
thren's Avatar
I did see your hulls Tolly, but ... I couldn't tell my mates I made it if I bought a hull
Thats why Im scratch building instead of buying a hull or a plastic model and converting to RC, just not the same... but thats just me
But nice hulls you have.

This one is the smaller of the 2 plans I have, my plan is not to get too anal about scale, just get it looking and working so I can have fun and learn a few lessons along the way so when I build the 1:24 scale one I know what Im in for.

Question for someone into boats on running gear... plans call for a "Mabuchi RS-540" motor....Ive got lots of different outrunners from planes here...
any suggestion on the KV rating of an out runner that would push this thing ?
Specs from site say: "Finished, the RC PT boat will measure about 30 inches long and eight inches wide (760 by 200mm) and weigh about three pounds (1.5kg)."
Also I will, for this boat be using just a single motor and prop.

cheers
Nov 13, 2013, 11:45 PM
Registered User
Tollytime's Avatar
Quote:
Originally Posted by thren
I did see your hulls Tolly, but ... I couldn't tell my mates I made it if I bought a hull
Thats why Im scratch building instead of buying a hull or a plastic model and converting to RC, just not the same... but thats just me
But nice hulls you have.

This one is the smaller of the 2 plans I have, my plan is not to get too anal about scale, just get it looking and working so I can have fun and learn a few lessons along the way so when I build the 1:24 scale one I know what Im in for.

Question for someone into boats on running gear... plans call for a "Mabuchi RS-540" motor....Ive got lots of different outrunners from planes here...
any suggestion on the KV rating of an out runner that would push this thing ?
Specs from site say: "Finished, the RC PT boat will measure about 30 inches long and eight inches wide (760 by 200mm) and weigh about three pounds (1.5kg)."
Also I will, for this boat be using just a single motor and prop.

cheers
I would use a 540 sized (36mm) brushless motor with 2000Kv or less. I don't know much about using outrunners. I don't like them for planing boats.

The Turnigy XK3665-B-2100KV Brushless Inrunner looks like it would do the job with no problem.

My favorite is the Turnigy XK4042-2000KV Brushless Inrunner

There are no aluminum water jackets for the XK4042 made by anyone. You have to use a silicone jacket that fits up to 40mm or a coiled aluminum tube cooling apparatus.

There are similar motors with less KV like the XK3665-B-1200KV Brushless Inrunner

Take a look: http://www.hobbyking.com/hobbyking/s...at_Motors.html

Your gonna need at least a 100A ESC. Turnigy makes a couple of nice marine versions that will work fine.

http://www.hobbyking.com/hobbyking/s...ooled_ESC.html

I would defiantly us a 4mm Raboesch waterproof shaft and put that motor as low in the hull as you can.

A 34mm Traxxas speed prop will make it scoot.

I'm recommending 2s (7.4v) Lipo. 3s (11.1v) could be used with the 1200kv motor. 3s could be used on any of the motors, but it depends how much you blink your eyes when running your boat.

If you want to try twins, I've done all your homework.

https://www.rcgroups.com/forums/show...1588859&page=3
Nov 14, 2013, 01:55 AM
DONT TELL THE WIFE !!!
thren's Avatar
Thank you very much Tollytime.
I had a moment of clarity at work today Ive got and old tamiya hornet that has a 540 in-runner motor in it, then I though... hell, Ive got 3 hobbyking buggies with in-runners in them that do not get used specs from site...
"Motor: Brushless Inrunner 3300KV (3650 size)" ......to many KV's by the look of it ??

Thanks on the esc specs I need to get, as I am normally a fly boy I was not sure on esc spec needed. I take it that the high amp esc is needed because of the drag on the prop being in water?
I bought a shaft from a local ebay seller (Australia) as well as a prop..shaft is 4mm, prop is .........
Quote:
RC Boat CarbonFiber Reinforced Propeller D40*P1.4 66440
Material: carbon fiber Reinforced , Pitch: 1.4 , Diameter: 40mm , Aperture: 4mm
2mm bigger than the one on plan and alot bigger than your suggestion but cheap...

I think I will follow your suggestions on the running gear though again thank you very much.

Now for some more pics......deck stringers need to be curved so had to weigh the chime shelf down.. wishing I did not do a sinker pour last weekend as I had to resort to using beer...how long it sits there will depend on how thirsty I get

Warning for others ... the sheer stringer is wide... 100mm wide, just fits on the balsa I bought, I spose I could have scarf joind some balsa if needed, but if buying balsa for this model, be aware of that.
Nov 14, 2013, 08:06 AM
Registered User
Tollytime's Avatar
It should turn a 40mm no problem. You could try using that car motor at 2s.
Nov 15, 2013, 09:53 PM
DONT TELL THE WIFE !!!
thren's Avatar
Frame work on top half of hull done and sanded...
About to start sheeting the hull
Nov 15, 2013, 11:26 PM
Registered User
CaptCB's Avatar
You can build the hull and the house structure, BUT, getting the weapons needed, IS a major problem these days. I would have used the plastic kit, and the heck with what my buddies thought!!
Nov 16, 2013, 01:46 AM
DONT TELL THE WIFE !!!
thren's Avatar
Finished planking the top half of hull. Just rough sanded down atm..
@ CaptCB, yes Ive looked for an easy way of getting weapons, I figure I will hand make them..or perhaps use my 3d printer and lathe to make some parts and do rest by hand.
I cant start the keel till the shaft arrives in a couple of days, so its up to the shed to start on the torpedo tubes. And its not so much what others think, its the satisfaction I get
Nov 16, 2013, 06:02 AM
Boaters are nice people.
Quote:
Originally Posted by thren
till the shaft arrives in a couple of days
Hi Thren,

Your build is looking good!
Building in two parts is a bit out of the ordenary, but it'll work out fine, a lot of Glynn Guest's designs are built up the same way.

I took a look at the site where you purchased the plan and the propshaft angle doesn't look bad.
Hope you ordered one at least as long as indicated on the plan, to avoid having a too steep propshaft angle, resulting in 'running attitude issues', to put it mildly...

Rule of thumb for fast boats is not to exceed 7, steeper will start to lift the transom and bury the bow. No matter how much power you install, the boat will never run properly.

Regards, Jan.
Nov 16, 2013, 12:59 PM
Registered User
Quote:
Originally Posted by pompebled
.

Rule of thumb for fast boats is not to exceed 7, steeper will start to lift the transom and bury the bow. No matter how much power you install, the boat will never run properly.

Regards, Jan.
Jan

That is some good advise right there that I see ignored more than not.

Larry
Nov 16, 2013, 01:59 PM
Registered User
Tollytime's Avatar
Quote:
Originally Posted by pompebled
Hi Thren,

Your build is looking good!
Building in two parts is a bit out of the ordenary, but it'll work out fine, a lot of Glynn Guest's designs are built up the same way.

I took a look at the site where you purchased the plan and the propshaft angle doesn't look bad.
Hope you ordered one at least as long as indicated on the plan, to avoid having a too steep propshaft angle, resulting in 'running attitude issues', to put it mildly...

Rule of thumb for fast boats is not to exceed 7, steeper will start to lift the transom and bury the bow. No matter how much power you install, the boat will never run properly.

Regards, Jan.
That is some excellent research! You can't really argue with that rule and it sounds the most logical at the very least.
However, I do have to point out, having the motor too far forward will have the same effect. The angle of attack may be more ideal, but now you have a weight and balance issue. There is also the matter of clearance for the motor itself, especially if it has a water-cooling jacket. I've settled for 9 degrees and still have minimal transom lift. If this particular boat is light enough, it may be possible to use a single 28mm brushless in-runner. Using a motor with a smaller diameter will help reduce the shaft angle.
I recommend a 4mm Raboesch water-proof shaft, that will eliminate the need to keep the motor end of the shaft above the waterline and help reduce the angle even more. I must caution the use of the Raboesh waterproof shaft, it's only rated to 10,000 rpm's (in the water), so it may be a good idea to keep the rpm's below 13,000 out of the water. A 2000kv motor at 2s is roughly 15,000 rpm's.
Nov 16, 2013, 03:16 PM
Boaters are nice people.
Quote:
Originally Posted by bubbletop409
That is some good advise right there that I see ignored more than not.
Larry
Hi Larry,

One reason is ignorence from novice builders, another is working from 'ancient' plans; when those plans were draw, the motors available weren't nearly as powerful as those today, so a too steep angle would not affect the running attitude as severely as it would today...

Regards, Jan.


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