Will do. Thanks. I'm going to install surface drives for the cat and smaller 32 inch mono, but the 42 inch mono I'm going to try the existing drive line before doing a big swap. I have a bunch of props already that I can try, but they may all be too big.
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It was mentioned that the boats used submerged drive.
What size prop did you use for the 42 inch mono?
What size did you use for the cat?Comment
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The 42 inch still hasn't run on electric yet. I'll let you know when I get it up and running.Comment
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The twin cat rebuild has just started. Here are some reference pictures and details in case that helps narrow down what props I should be running and an estimated amp draw.
5kg (11.2lb) bare hull with cowl. I'm still doing some patch and filler work, but I took that into account.
43cm (17in) wide
15cm (6in) tall without cowl, 23cm (9in) with cowl
2.5kg (5lb) hardware. This includes rudder, stingers, shafts, stuffing, motors (two 40x94 1250kv), collets, servos, esc (two ZTW Seal 130A 6S), waterproof servo box (do I need this? Should I be working to waterproof the entire hull?), and some extra for some wires and tubing.
1.5kg (3.3lb) batteries this includes a 6S 5000 to each motor.
All up this should weigh about 9kg (20lb). Sounds porky, but I don't expect it to be a rocket, I just want it to run consistently and be able to handle some rough water.
I'm planning on using the existing holes in the bottom of the back of the hull to mount the shafts. I expect the center of the shafts to be about 13mm above the bottom of the hull. Does this sound right? Should I lower them?
The rudders will go below the bottom of the hull by about 8-10cm. Does that sound right?
Should I be mounting the motors as far back as I can? Granted I need to try to keep a gentle curve in the flex. This will allow me to mount the batteries last to balance the boat.
The existing stringers seem pretty big to me, Do you think I can safely cut them down to about half as tall? Or cut some holes in them to save some weight?
Thanks for your help!
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IMG_20190625_092258.jpgComment
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Jimmy, what is ahead of that bulkhead? Sometimes old foam can weigh a ton. I think you are good with your existing holes for stingers and rudder should have the depth. Mounting the blade closer to transom will tighten turns and farther back of course the opposite. Have you got the motor mounting system figured out? Dave at HRC and I designed a dual mount to fit in 5” rails.
ShawnComment
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I'm not sure what's in front of the bulkhead. I'll pull it and see. Do I need the bulkhead at all? It looks to be adding a bit of strength vertically, but might be Overkill.
The props will be on stingers so it sounds like it will have a larger turning radius which is fine.
I have a couple mounts in the mail right now, but thanks.Comment
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Maybe just drill a couple decent holes in that bulkhead. Perhaps if anything is up there you can dig it out. The bulkhead will add strength so try to keep it but cutting rounds will lighten it without sacrificing strength.
Lighter boat would help. FYI: a Boats weight doesnt matter much once up on plane. Getting it there mind you is where the energy goes. Just food for thought.Comment
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Yeah, that makes sense. I'll drill some holes with a hole saw.
I'm so used to worrying about weight since my main focus has been racing quadcopters. It's nice to be in an area of the hobby where other considerations are more important.Comment
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Yeah I still consider it because the old nicd days are so engrained into me. But have been realizing it doesn’t matter so much because of my last build. Built a lighter version of my BlownAway catamaran and still haven’t matched its runtime yet. The lighter one is 4lbs lighter.Comment
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Do you have details on that build? Just curious if it's close to this one.Comment
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The heavy one:
https://forums.offshoreelectrics.com...ast&highlight=
And the light version:
https://forums.offshoreelectrics.com...Cat&highlight=Comment
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Ok, a few more questions. I've done a bunch of searching for what I would think is common knowledge, but can't seem to come up with answers.
1. When mounting the stuffing tube to the transom, should I use epoxy or silicone to allow some movement? Something else like a rubber grommet? I don't expect to have to adjust the stinger much if any since this is not meant for racing.
2. How far into the stinger should the stuffing tube go? I read somewhere that the brass should stick out the back of the hull by 1/4 inch then the liner should go the rest of the way. Is that right?
3. Thrust bearings don't seem to be used any more. Just leave a 4mm gap from the stinger to the drive dog? My motors are on the cheap end. Do I need to worry about the bearings?
4. When bending the stuffing, just heat it up red hot and bend it with a screw driver in there? Do I need to fill it with salt or anything so it doesn't kink?
5. Do I need a servo box to keep the radio gear dry or should I focus on waterproofing the entire cavity of the boat?
6. When making a cowl, are there any good tutorials? Most of my boats never had a cowl and I will need to make a few.
Thanks for all of the help!Comment
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1) I use epoxy. Using a flexible sealant is not the solution to an adjustable stuffing tube height. Something called a flooded tube is.
2) It depends on the hull and hardware. I run the brass into struts just enough to get a good joint, but not too far so there's room for the prop shaft. On a stinger, the solid brass tube cant protrude too far into the assembly or you won't be able to adjust the stinger trim angle. I usually stop the stuffing tube flush with the rear of the hull and just extend my teflon liner into the stinger. Sometimes I'll install rubber O-rings over the liner between the hull and stinger to help keep the water out.
3) I don't run thrust bearings on my boats. Most people who do, run them between the collet and motor can. For basic sport boat setups, a gap at the drive dog will be sufficient.
4)I find the easiest method for bending brass stuffing tubes is to first anneal the brass with a stove or torch. Heat the area that needs to be bent to a cherry red, then quench in cold water. The annealed area will bend easily with finger pressure. To harden that part of the tube after you're done bending, heat it up again to cherry red, then allow it to cool on its own to room temperature. Clean, polish, or sand the black, oxidized area that will be in contact with epoxy to ensure a proper bond. The sand/salt method is cool, but I've never had to put such aggressive bends in a tube that required a filler to prevent kinking. The above method has worked well for me for basic bends.
5) No need for an electronics box. Use a waterproof servo, or, waterproof your non-waterproof servo. I conformal coat the circuit boards of my receivers with epoxy or liquid tape. Corrosion X spray also works well.
6) Can't help you with cowls. I've never had to make one.Vac-U-Tug Jr (13mph)Comment
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Thanks Fweasel! That's extremely helpful. The last thing I need to figure out is what size props to order. I'm thinking of starting with x440 or x442. Thoughts? This will be a dual motor setup with 6s to each 4094 1250kv motor. I don't need blistering performance. I'm hoping to keep the amps at or under 75 at each motor. Does that seem doable?Comment
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