3d printing small props

Yes, the printed prop only has to last through one? trial so that measurements can be taken, and then cast or Mill it? In practice you may find that having and using a small selection of different props depending on the water conditions might be the way to go. The best prop might be different depending on the water conditions, for example low draft versus weedy Waters, or economy versus Power, Etc... At least that's what I've found with my selection of cheap RC props and aluminum mud props used with electric motors and at low power.

I've found that appendage drag may be at least as significant as propeller design, depending on where you want to be on speed and efficiency. Trailing shaft Motors similar to those used in Asia for racing as well as economy seem to be the way to go for me, compared to the lossy, and draggy conventional designs. Of course they may not work for everyone, and they have their disadvantages if precise steering or for extended use in reverse is needed.

 

Messabout, I'd be really interested to learn more about this hull you describe. Have you any photos? Especially of it at 13.5mph and of its wake at WOT? Is there any deadrise or is it totally flat aft? What does the rocker do aft of amidships?
Also with reference to the engine height on the transom, is the cavitation plate out when it is planing? You'll know if it is if it's the same engine as mine as the exhaust exits under the cavitation plate, so once you are planing things will get much noisier. My engine's water pickup is on the lower half of the gearbox so running it quite high shouldn't be an issue re cooling. Same for you if it's the same engine. Mine's a brown band so 1987 if memory serves me. I understand both Yamaha and Tohatsu made these Mercs, and the versions differed a bit. Only one of them has the slot washer restriction behind the carb (like mine), the other requires a carb change to get to 3.3 so not worth the hassle.

Mine's got a few days epoxy work left to do then I'll be heading out for first test with the first planing surface underneath. I'll get an exact all up weight for boat and driver before I go. I'm hoping I can actually pick the whole thing (incl engine) up over my head and get on the bathroom scales with it (in the garden, not in the bathroom), so I'll be interested to see where it comes out in the end, weight wise. I will need to brush up on my Spanish- my scales are speaking scales and are stuck on Spanish.

 

I'm with you on appendage drag, as I've said on here before, and posted the video to prove, I once attached two 6kg carbon windsurf boards together and put a two bladed RC air prop on it (about 9 inches diameter but I cant remember exactly now). It did over 9 knots with a 640W power drill connected through a flange bearing to about a metre and a half long flexible shaft of 10mm threaded rod. The prop self aligned to the flow as they do and as the HPB boys have known for years, so overall a pretty impressive system. The problem was the drain on the drill batteries- the thing went about 100feet at full throttle before the battery hit its thermal cutout. It did 7 knots for a full battery cycle though- which at that load was a few minutes. I was amazed though at what can be achieved with an efficient prop and minimised appendage drag.

 

Reiterating the earlier comment about using contract SLS nylon printing, if you're going to try it. I mostly use Xometry. Many times stronger than your garden variety FDM 3d printer (I have one of those too and love it, but it has its limitations). Should be strong enough for prototyping, at least.

But if you can't do the modeling/iteration yourself it's gonna be $$$. And outside of electric trolling motor type use I have a hard time imagining it would be durable in the long run- as skyak said, you can't use long fiber reinforcement with any commonly available printing technology. I guess you could vac bag it in carbon but that would be very difficult for a prop shaped object and good hydrodynamic result.

 

Just checked 3d printing prices for a speculative Prop candidate (2 parts, prop and hub), These were not modeled to actual spec with correct axle holes and clips for the hub but I assume those don't impact print pricing. 266mm diam so a hair over 10 inches. Prices are for extruder prints - not SLS.




Xometry ABS came out to 46 euros


And craft cloud to 33 euros


Both offer better materials like glass or carbon reinforced nylon.
Price goes up but not terribly, about 65 euros including shipping is not bad imo.




-
-

 

That's a level I'd be more than happy to pay. About twice a week I tell myself I really must learn a 3D package. When it becomes once a day, I'll do it. I'm guessing that's where the real saving is- being able to draw and design it yourself.

 

there is a learning curve for sure. I don't "really" CAD, but have done entertainment 3D (animation/visual effects) at a high level for quite a few years.
This prop was done by taking what Javaprop gives into a polygon modeling software.

I do have real CAD, on my iPad... Shapr3D it's great for what it is.