New IRCWCC Rudder Rules

Discussion in 'Construction' started by Anvil_x, Dec 12, 2020.

  1. Anvil_x

    Anvil_x Well-Known Member

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    Hey,
    Has anybody built rudders to the new specs and tested them? I figure this is a great time to ask, since the rule change just came, it's building season, and it might be a good reason to hold onto old rudders to do a side-by-side comparison when possible.

    Me, I just walked out on a lake and drilled a hole in it looking for food this afternoon, so I'm limited til spring.
     
  2. Commodore

    Commodore Well-Known Member

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    I'm thinking of being lazy and not making new rudders this year. :p
     
  3. Anvil_x

    Anvil_x Well-Known Member

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    lolololololol @Beaver mind posting your video links up in here?

    So.... it might be a good idea to do so for the following video-documented reasons.... I'll let Beaver take it from there.

    I cane here to post pics of my rudder test articles.
    So after drafting up some rudder shapes, I decided that with the new rudder rule, I would make a few test articles for each boat in order to gauge performance. Why not. two weeks ago it was -42 and the ice fishing has been terrible with all the cold.

    I've managed to generate two test articles for each boat. I'm thinking of designing a third for each.
    Since I am in the caterpillar stage of working with CAD, thanks to @SnipeHunter , I handmade these articles in my shop using 1/8" ply and basswood. Once I sanded them to shape, I gave them a silicone bath and then cast them using featherlite, which I find to be a delightful product for the purpose.

    My prior rudders were wood with filler and basswood, which was then fiberglassed over. Unfortunately, these rudders sucked, and I never had a spare available if they got damaged. Now I can have several identical rudders on standby.

    All of the rudders are new-rules legal.

    Idaho's two test articles are actually the same rudder. After I showed @Bob the original (this one)
    IMG_20210108_101716.jpg
    I heard the *facepalm* from 300 miles away. it has good thrust cone coverage with the 1.625 props I have. not 100%, but good. if I went back to 1.5" props, it would be 100* coverage because the rudder's vertical centerline is in-line with the shaft. my shafts run a little deep to fit bigger props, as I'm sure everyone else does.

    So, that led to me modding a second casting of the rudder to meet Bob's advice to follow the contour of the hull.
    IMG_20210205_225556.jpg

    yeah I lose maybe 1/4 sq in. of material, but if it's the best performing rudder, I will take this test article and make a new, better casting and add area to the rudder elsewhere, like on the back end of it. simple fix. the change in spacing brought the rudder up by about 3/8", and I may try to make another version of this rudder which gets the contour gap even tighter.


    So for Texas, I was fortunate because the rudder rule was changed right as I was re-doing my prop shafts. so I laid my shafts to fit a 5.5 square inch rudder

    the first article is this....... billboard that follows the contour of the hull.
    IMG_20210116_133520.jpg

    it's absurd. huge. clown-shoes big. can't wait to test it. it has 95% thrust cone coverage in a full turn with 1.5" props, and 100% with 1.25" props.

    The second test article is the Idaho's rudder, but with a different pivot point.

    IMG_20210103_212614.jpg IMG_20210103_212629.jpg

    look at how stupid this is. but I figure why not giver a try. I have high-durability high torque servos.

    Again, this places the maximum amount of area in front of the props and ignores the contour of the hull. As you can see, pulling my props back and re-laying the shafts has put my rudder post in a weird spot now. If it's a problem, I may address it by moving the rudder post. but at this time, I just finished a huge refit on this boat, and will settle for whatever performance I get, as long as it's reliable.
    I have a Derfflinger and a Warspite to build.

    So. with regard to testing.
    I kept both of the original 4.5 sqin rudders. I am going to set up measurement tools to evaluate the combat radius of each boat and each test article. I will do five tests for each rudder for confidence, and if I can get an accurate measurement set up, I'll run some minor statistical analysis using an ANOVA.

    If it's blatantly obvious which is better, I'll use the measurements to evaluate by how much.

    I'm really interested in whether following hull contour, or putting the most surface area in front of the props is more important. I may be trained as a research scientist, but I didn't spend much time on fluid dynamics and other such tomfoolery--I was worrying over stable isotope biogeochemistry.
    So if you're an engineer, don't spoil the surprise!

    The third test article for each will be to test rudder depth. I am still brainstorming the design, but it would be weird-looking for sure. More to follow.

    until then. Anybody have some side-by-sides of the new rudders, or reports on performance?
     
  4. Commodore

    Commodore Well-Known Member

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    Your TX billboard that follows the hull is probably the best.
    Your latter pictures - you don't want to do that. You want the pivot slightly ahead of center, about 1/8" or 40% or something like that.
    I haven't done the science. But I may have built a boat or two. :)
     
  5. Anvil_x

    Anvil_x Well-Known Member

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    oh for sure, I'm pretty sure that super-forward goofy thing isn't going to work. *guess which rudder I've already painted on each boat* lololol.

    We'll see how it goes. It'll at least be mildly amusing to get data on precisely how bad it fails!
     
  6. Caractacus Patt

    Caractacus Patt Member

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    Yes, I agree completely! Sure, people say that something is a bad idea, but it is important and valuable research to empirically quantify exactly how bad of an idea it is. I plan on committing my share of rookie mistakes, if nothing else to satisfy my curiosity. Who knows, maybe a bad idea is simply a good idea used in the wrong circumstances...
     
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  7. Devasen

    Devasen Member

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    Why do you use a horizontal flat piece at the top and bottom of your rudders? The rudder that conforms to your hull looks like it would drag your stern down in forward movement and push it up in reverse kind of like a hydrofoil. I don't see anything against it in the irc rules, but does the horizontal bit count as "rudder area"? This is certainly a modifier for a ship's performance characteristics so I want the old hands to clarify.
     
  8. bsgkid117

    bsgkid117 Well-Known Member

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    The top and bottom plates catch prop wash that would otherwise hit the rudder and divert up/down. This helps trap some of that and direct it in the desired direction.
     
  9. Anvil_x

    Anvil_x Well-Known Member

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    The forward downforce effect is minimal, and somewhat desired in reverse because Texas will basically submerge itself all the way to C turret if I go for more than 20 ft in full reverse.

    I've got like three shaft squirrelpower cranking out of that boat, it's a miracle my deck seals well enough!

    the area is measured in profile, so the thickness, and variation in thickness isn't a consideration as long as the rudder is no thicker than 7/8"
     
  10. Devasen

    Devasen Member

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    That makes sense. I would like to see the best rudder design that keeps the stern from plowing under the water in full reverse as you stated above. I never thought of this before but I can now imagine some of the funky rudder designs are to this purpose.
     
  11. Beaver

    Beaver 2020 Rookie of the Year Admiral (Supporter)

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    Shaft angle has more effect on submarining in reverse than the rudder. Try to get the shafts and level as possible to keep from sucking the stern under.
     
  12. Anvil_x

    Anvil_x Well-Known Member

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    lolol so to Beaver's note, my shafts, prior to the reconstruction on Texas, were 100% flat. 0 degrees.

    I relaid the shafts with about eight degrees of down angle and super close together for the biggest props with the tightest thrust cone possible and...... the results are going to be comical.