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Dec 16, 2019, 04:34 AM
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Build Log

4BDN hull


Some progress on my new hull to test out my 35mm 4BDN stators.
Still doing cut-outs and I'll scale it hopefully to suit my max 2.5 kW brushless motor
Once I'm happy with cut-outs and I've added the jet intake foot then the plan is to CNC route the shape into some high density foam and manufacture a mould off it. Currently sitting around 320 beam x 734 long x 89 high.

The actual layup is partially iterative with OPENSCAD and partially manual(the bow).

I recess the jet outlet region because boats shouldn't be designed with lots of lift area in the stern region, it gives very bad behaviour at planning speeds.

Much of the handling comes from the tile orientations.

You can rotate it in 3D view here:
https://www.thingiverse.com/thing:4051537
Last edited by grael; Jan 08, 2020 at 03:29 AM.
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Jan 08, 2020, 03:26 AM
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Getting closer on my 4BDN hull.
I was inspired by rav3n87's printing of the thingiverse hull with the bad stator, his print progress looks awesome! Also his design went quite fast considering 3D printing isn't the lightest or strongest boat manufacture technique... I can always cast a mould off it later anyway.
So anyway, I don't much like ABS, I'll be printing this in PLA+ in 3 hull sections. I've included internal tubes to take 4x M3 SS threaded rod and nut pockets. This will give an end result vaguely like reinforced concrete but a lot lighter.
I should probably keep in mind fitting an intake grill too.
I've resized to 650x280x100mm to drop a bit of weight off the hull, I reckon it's still big enough for the size and length of the jetunit +motor.
Next big decision is whether to mod the FJD pump intake to be printed with the boat stern section, I really like built-in intakes, dead simple!
And at some stage I need to do a proper deck for it
Jan 08, 2020, 02:02 PM
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Kayaker's Avatar
I see similarity's between our steering systems and hull designs. Iím very interested in how this goes.
Jan 08, 2020, 11:44 PM
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Quote:
Originally Posted by Kayaker
I see similarity's between our steering systems and hull designs. Iím very interested in how this goes.
I think the biggest deterrent to porpoising is actually to reduce the lift area a bit further forward of those trim tabs but back from COG. But once the bow lifts well clear of the water, the reduced area of your ride plate and fixed tabs will definitely give a softer correction than a full width stern out that far.

My boat above is a bit different again. It can handle a lot of ride angle variation and still have lift over the entire contact area, this should correct a nose down landing a lot faster and my experience with one of my predecessor boats it that it's a lot more tolerant of COG change than a regular monohull.

It's intended to combine the best features of a hydroplane and a conventional monohull which it should do pretty well.
Jan 09, 2020, 07:27 AM
Jetdrives R Us
sundogz's Avatar
I was intrigued by the small file size of your model and found it was due to the low triangle count. Even the threaded rod bores are hex shaped to keep roundness (high triangle use) to a minimum. Very interesting indeed!

My thoughts on a 3D printed pump is that you'll never need to remove it from the hull. So if you're printing the hull, it is better to print the pump in place. Everything that can wear can be replaced/changed.

She (the boat) isn't well suited to go in reverse, is she? That (radical) hull resign may not catch on in the full size sector where reversing can be important. Keep her away from terra firma!
Jan 09, 2020, 12:26 PM
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Quote:
Originally Posted by sundogz
I was intrigued by the small file size of your model and found it was due to the low triangle count. Even the threaded rod bores are hex shaped to keep roundness (high triangle use) to a minimum. Very interesting indeed!

My thoughts on a 3D printed pump is that you'll never need to remove it from the hull. So if you're printing the hull, it is better to print the pump in place. Everything that can wear can be replaced/changed.

She (the boat) isn't well suited to go in reverse, is she? That (radical) hull resign may not catch on in the full size sector where reversing can be important. Keep her away from terra firma!
Openscad reduces automatic roundness for small sizes and I had no reason to fight it for the threaded rod inserts As for the hull, yes, I was rather surprised myself to see the extreme minimal size! Even the cone removed at the back significantly increases the file size! Would be quite easy to CNC aluminium panels to weld a full sized one over a frame.

Reversing? Who needs it! 99.9% ot the time we drive forwards.... and extreme low speed the steps increase resistance in both directions but I didn't design it for extreme low speed.
Jan 09, 2020, 06:25 PM
Jetdrives R Us
sundogz's Avatar
Quote:
Originally Posted by grael
.Reversing? Who needs it! 99.9% ot the time we drive forwards..
Ah yes, but that darn .1% of the time when we need it...
Jan 09, 2020, 07:35 PM
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Kayaker's Avatar
Grael’s steering system turns sharp enough to not need reverse very often. I’m finding that overlapping impeller blades work better than non-overlapping for reversing the motor to get reverse. A compression style steering nozzle like Grael’s helps control the direction of suction. My jet boats need a lot of battery weight so the nozzle is under water.
Last edited by Kayaker; Jan 09, 2020 at 07:41 PM.
Jan 09, 2020, 07:59 PM
Jetdrives R Us
sundogz's Avatar
Robin, I was just saying there are times reverse is helpful. Consider that most people don't need to turn so sharply or abruptly at slow speeds. You are of one of a kind when it comes to rapids/rocks, etc.! Most of us get by nicely with conventional steering (and don't reverse the motor to go backwards).
Jan 10, 2020, 12:55 AM
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Quote:
Originally Posted by Kayaker
Graelís steering system turns sharp enough to not need reverse very often. Iím finding that overlapping impeller blades work better than non-overlapping for reversing the motor to get reverse. A compression style steering nozzle like Graelís helps control the direction of suction. My jet boats need a lot of battery weight so the nozzle is under water.
I was surprised, the 4BDN7 vane pumps quite well in reverse. I bet it sucks a plug hole gurgle in normal boat mount position though. But nice to be able to back flush!

Why do you intentionally run your boats so low in the water kayaker? Or should I be calling them jetsubs?
Jan 11, 2020, 12:24 AM
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Finally!
Couldn't get sundogz and unusual_RCs 35mm intake to merge with my hull so I had to spin up my own intake and make that part of the hull. It really needs a bit of softening of the intake edges up front and sides but I couldn't do it easily with my preferred OPENSCAD so I've decided to use a file and sandpaper after.
Updates here: https://www.thingiverse.com/thing:4051537/files

Stoked that I can finally slice and print!
There are 3 printable sections that should print pretty well on my 260 x 260 heated bed. I like the way it's going to become 3 x sealed compartments for flotation.


Sunday 12/1/2020.
Found a few things I wanted to improve on so I did the mods and re-uploaded the split model to thingiverse.

The transom should now have improved stern side up printability, found a couple of weird sections at the sides of the jet intake that my print nozzle orifice is too wide to pretend aren't there, patched, thinned the shroud/spray deflector, corrected the motor flange attachment hole spacing, added a bottom fixing for the motor flange. My original stern design is 2/3 printed in Red PLA+. I might have to pause it when it gets to the transom and assist on the transom. as I'm printing pre-fixes.
Last edited by grael; Jan 11, 2020 at 06:15 PM.
Jan 14, 2020, 05:12 AM
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Added some progress pics of my prints
Jan 14, 2020, 09:57 AM
Jetdrives R Us
sundogz's Avatar
Coming along nicely. I like the red, white and blue color scheme and the integrated canopy.
Jan 15, 2020, 02:08 PM
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Kayaker's Avatar
Quote:
Originally Posted by sundogz
Consider that most people don't need to turn so sharply or abruptly at slow speeds. You are of one of a kind when it comes to rapids/rocks, etc.! Most of us get by nicely with conventional steering (and don't reverse the motor to go backwards).
Yesterdays session on the river my boat got wedged between rocks on the other side. I would have had a long walk and dangerous current to wade across in chest waders if I didn’t have reverse. My boat turns so well it doesn't get stuck often. The boat needs to be heavy enough so the nozzle is underwater for reverse to work.

Grail asked;
Quote:
Why do you intentionally run your boats so low in the water kayaker?
Jet boats stay hooked to the water better with some weight. I get better boat control when making maneuvers like racing through obstacles.

In aerated water (bubbles) the pump still finds some water to move. The three dimensional steering that I like works best when the boat is more engaged with the water. This allows the boat to dance with the power of the river.

Jet boats with a lot of thrust need bigger batteries so that ‘low voltage cutoff’ from voltage sag is less of a problem.

Heavy boats self-right faster and need less foam up top.

The down side is heavier boats need a stronger build because they hit things harder.
Jan 17, 2020, 04:38 AM
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Quote:
Originally Posted by Kayaker
Yesterdays session on the river my boat got wedged between rocks on the other side. I would have had a long walk and dangerous current to wade across in chest waders if I didnít have reverse. My boat turns so well it doesn't get stuck often. The boat needs to be heavy enough so the nozzle is underwater for reverse to work.

Grail asked;

Jet boats stay hooked to the water better with some weight. I get better boat control when making maneuvers like racing through obstacles.

In aerated water (bubbles) the pump still finds some water to move. The three dimensional steering that I like works best when the boat is more engaged with the water. This allows the boat to dance with the power of the river.

Jet boats with a lot of thrust need bigger batteries so that Ďlow voltage cutoffí from voltage sag is less of a problem.

Heavy boats self-right faster and need less foam up top.

The down side is heavier boats need a stronger build because they hit things harder.
It's going to be interesting anyway. I'm not far from having it in the water. Finished the bow about 10 minutes after I left for work this morning and tonight I have the threaded rods inserted and locking the 3 parts together, polyester over much of the hull in a couple of coats and some polyurethane resin over the top and inside of the bow section and as a final coat over the rest. It's probably around 3KG or triple weight of rav3n's one as I'm using 0.7 nozzle and I'm not just printing a shell, but a sparse filled hull with compartments and deck. Bow ended up glow-in-the-dark pink, middle is blue, stern is red with silver tips. Something for most people. Got everything almost ready do go except for locking the batteries in and sealing them. Maybe in the water in another day or two depending on how desperate I feel to test it....


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