Wild Thing (2000 issue RC Boat Modeller)

[Boben]

I have always like the slow moving tugboats. Built The Hercules from plans from the Boat Modeler. My ship has the autograph of the last captain on the skylight on top of the cabin. Really draws attention on the pond. With Capt Harold Sommers signature it makes this ship one of a kind.
The original plans didn't work too well when I started to plank the hull. So I scrapped it, went to the computer and redrew the bulkheads. This time it worked perfectly.

I also scratch built the Bunker Boat from the Winter 1987 issue

I scratch built the 32 inch "Wild Thing" from the October 2000 magazine, but put it on the back burner when I found the plans for Hercules.
Now I would like to get back to the Wild Thing, but instead of a nitro engine, I have a Grauppner 700BB Turbo, used very little.
ESC 50A for a brushed motor. At 80+ years old I don't think I could handle the speed with Brushless motors without wrecking the boat.
So I intend to use this ESC with the Grauppner engine with 2-3000 Nicad battery packs. 48 mm prop 3 blades.
My question is what size cooler is needed for this engine and do I need a cooler for the ESC. I measured the engine and my motor can it is 44-45 mm diameter. Where can I purchase a cooler to fit this engine?

Don't particularly care about speed, just want it to be quick. The brushless videos kind of scare me.

Is this a pipe dream, or can it be done?

[Fluid]

We used motors like that one in the old LSH race boats running on round cells. You will want to use 12 NiCd cells and I would start with an x440 prop with the potential to go up to an x645 - if things stay cool. The 48 mm prop is too large to start with. What do you mean by ?don?t particularly care about speed just want it to be quick?? How fast is ?quick??

We generally didn?t water-cool the motor or ESC. Standard coolers didn?t work very well on the motor due to its construction. You could try a coiled metal tubing cooler although those weren?t very efficient. The low amp draw of that setup could get by without cooling as long as run time wasn?t excessive and you didn?t go crazy with prop size.

BTW, just because you use a brushless motor doesn?t mean you have to be ultra fast. You could choose a mild BL setup and obtain cooler running, lower amp draw and longer component life compared to brushed power. Just a thought.


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[NativePaul]

Which 700bb turbo do you have 8.4v or 9.6v? I used to race these motors on 12 NiCad cells, in a mono we would use up to an X445 on the 8.4v or up to an X450 on the 9.6v, our boats back then were about 26-27" so likely lighter than yours, and thus I would probably chose a prop one size down from those. I think a 48mm 3 blade would be too much for it on 12 cells (if that is what you are using) unless it is of lower than 1.4 pitch or of a low blade area design.

I have a different viewpoint to Fluid on the watercooling, likely due to my experience being with 3 and 4 minute timed races and I believe Fluid was mainly sprint racing for a shorter duration. We found them to respond reasonably well to can cooling especially in monos with their longer 4 minute duration races (averaging about 30A with speeds in the mid 30s, than hydros that ran for 3 minutes averaging about 40A with speeds in the high 30s. The way to cool the cans was with a water cooling coil made from thin walled alloy tube, these are still available from CEM, but you could get better results making your own, as putting tension on the tube as you wrap it around the mandrel can with care result in deforming the round tube into a flat bottomed "D" section that has a LOT more surface area in contact with the can, and you then slather the inside of the can with thermal compound to fill what is left of the gaps before sliding it on the motor. The best method to wind a cooling coil is to wind it around an undersized mandrel so its own spring tension grips the motor can securely, but you can also form it around the motor, and put thick heat shrink around it, wind it up tight and then heat it up, the shrink once shrunk will hold it tight.
Whilst cooling coils did lower motor temperature, it did not significantly increase their lifespan when racing or stop us burning them up in SAWs, the weak spot of the 700BB turbo is the thin brass brush springs that have to carry all the current to the brushes, when these get hot they weaken and dont apply as much pressure to the brushes resulting in more arking and increased heat which weakens them further in a viscious cycle till they fail completely. We started soldering about an inch of copper tube to the brass motor terminals and that vastly improved the lifespan of the motors when racing, and increased the current we could put through them when running SAWs. While I would say a cooling coil while good is optional, cooling the terminals is mandatory.

I know you have the motor already, and maybe the ESC, but I agree with Fluid brushless doesn't have to be faster, a 3650 motor with 1350kv will spin the same prop as a 9.6v 700bb turbo at the same RPM, but with much better electrical efficiency and will weigh a lot less, giving you longer run time, and it will run cooler, and last forever.

[Norwest]

The posters are spot on all terms. Another thing would be go to YouTube and look up how to make a big rc boat. Now with balsa, weight will be less and i used ca and hardener and for seams, i used Gorilla glue. Mine came out great.

[Boben]

Thanks for your input. I'll knock down the prop size. Quick for me will be probably be in the 20 mph range. I would be happy with that speed. I have Nicad cells, 700BB Turbo and the charger, so I really want to use what I have. You know the saying, "a boat is a hole in the water where you throw money." Limited budget. So far I've been able to stay within the budget limit.
When I get started talking about boats, my wife sort of rolls her eyes and wants me to be quiet.
Been a passion since Cub Scouts.
Boben

[Boben]

Thanks guys, from Boben.

It is nice to be part of a hobby where people with more knowledge than I have are willing to share that KNOWLEDGE.
Thanks again. Will take your advice to heart.

Boben

[Norwest]

Rc boats are better than me in the pool hall soaking up the suds!!!!!!!!!!!!! The boss said so!!!!!!!!!!!

[Boben]

Rc boats are better than me in the pool hall soaking up the suds!!!!!!!!!!!!! The boss said so!!!!!!!!!!!

I agree.