Yellowfin

Hi All and a Happy New Year!

I am new to RC boats and been and avid saltwater fisherman for many years and have been interested in bringing my bait a longer distance from shore with the help of a RC boat. I have spent many hours reading and searching the internet for information and have settled on a design that will be able to maneuver thru the waves to reach areas from shore that cannot reached by casting.

I would like some expert help in determining a good starting point for motor selection, prop size and other areas where I feel somewhat over whelmed with the selection of components on the market and my lack of knowledge.

I will try and be as descriptive as possible and I am sure there will be questions that I may not be able to answer.

The following is a description of the boat or sub as some might call it. I have attached an unfinished preliminary drawing for perspective.

Overall length 45”, width 12” height 11”, weight of shell 10 lbs., with electronics and ballast 24 -28 lbs. when complete. The hull is 31” from bow to stern. Like a deep v hull but wider for self righting as most of the weight will be in the bottom portion of the hull. Somewhat like a submarine with a deep vee hull. The compartment with be totally sealed to avoid water entry. A motor cooling system will be installed. Being in saltwater the need for marine tolerated electronics.

Performance considerations: 10-12 mph or more if possible, run-time average 7-8 mins, 40 to 50 mins of capacity to last all day about 5 - 6 trips out and back, voltage 11.1, batteries in parallel for amp capacity 35aH. Average distance 500 -1000 yards.


Would the Turnigy AquaStar T20 3T 730/1280 Water Cooled brushless motor be a good fit in the "Y" configuration? If not, a possible recommendation.

Also, what ESC would be compatible and battery selection in parallel, initial prop size to start off with.

Any help and recommendations would be greatly appreciated. If more information is need please ask away.

Thanks,

Scott

Yellowfin

At that distance I would never see the boat! It should be feet!

mfr02

The range wanted is rather more than most radio manufacturers claim with gear running at legal power levels, usual claim is 1000 meters for air, 500 for surface.
That is a lot of weight to shift at that kind of speed for the run time wanted. There will likely be a big difference in performance between going out loaded and returning light, along with changes in stability.
Most self righting designs involve a large enclosed air tight volume containing nothing but air above the waterline to ensure that the low weight will make it unstable when inverted.

Yellowfin

Hi mfr02,

Thank you for the response! I couldn’t agree with you more with on the information I posted earlier. I should have been a more descriptive. I did make a mistake in the distance of travel; it should have been feet instead of yards, 500 – 1000 feet or more if possible. You did bring up a good point about range. Would you have any suggestions on a brand of radio system that would meet my needs in feet not yards?

Here is some additional information that may be of help in determining the motor setup. I have included and addition pic that may be of help to better understand my approach.

The cavity in the hull is 4”wide by 11” tall by 24” long. At this point my target weight is 10 lbs for just the hull. All the heavy components will be in the first 4 – 5” in the bottom part of the hull (motor, batteries, ECS, receiver, motor mount, drive shaft etc. may have to use ballast to get the correct waterline in addition) thus giving the self righting ability. (The analogy of a balloon with a weight on it will spin so the heavy part is at the bottom). The top 5 - 6” will be air or in the case, foam. The top of the hull is rounded with a water tight double seal cover 10” long to access the components. Being round on top the hull will slip back to an upright position if tossed around. The entire hull is fiberglass, 3/16” thick on the top and ¼” on the hull. The front of the hull is tapered to a "V". If you notice on the bottom part of transom in the pic, it tapers to a "V" about two inches in on the inside. This allows the outside part to be tapered for a better flow of water behind the prop. Two inches inside it opens to 4" at the bottom.

As far as payload, there will be a line release on the deck or back of the boat that will release 1-2 lb bait (fish) at the target point. It is being towed behind the boat about an inch or two. There is no payload to dump.

I hope with the additional information and pic, this will add more information to ponder. I hope I will be able to get a few suggestions that will lead me in the right direction for motor setup.

Thank you!

Scott

mfr02

Any radio that is marked as "full range" will be fine as regards basic range. Some radios are marked "park flyer". Avoid them, they are intended as short range radios.
Modern 2.4GHz outfits are very convenient, but also very line-of-sight. At long range in lumpy water the waves might well block the signal path unless the receiver aerial is mounted very high. More traditional 40MHz or 27MHz with a vertical, much longer, aerial works better in these conditions.
The wanted speed might be rather high for a displacement hull with a 31" waterline length. It also needs a very good hydrodynamic shape to cut, rather than thump, its way through the water. There is a formula somewhere that gives the max speed for a given length beyond which a totally unreasonable amount of power is required, along with a loss of stability.