New Rudder for a West Wight Potter 19

Discussion in 'Boat Design' started by waterbear, Jun 24, 2022.

  1. waterbear
    Joined: Mar 2016
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    waterbear Junior Member

    I'm planning to make a rudder for my 19 foot West Wight Potter, which I have yet to sail. The finish on the existing rudder has failed, some of the glue joints are splitting, the cheeks are subtly bent and corroded, and there is slight bit of rot on the upper wooden portion. I could rebuild it, but I think it's time for a new rudder.

    From what I gather the existing design is reliable, however I do not like the looks of the kick-up hinge. There is not much overlap between the cheeks and the rudder blade and it looks to me like it would be prone to having slop. While I'm not sure this is the case, a couple of comments in the potter forum seem to confirm this.

    I've attached two images. First is the factory rudder next to Judy Blumhorst's one-piece performance rudder (image pilfered from Judy's website). Judy's rudder has about 30% more area and is partially balanced. She says it's superior and also mentioned it has the same area as the early potter 19 rudders, before cost cutting reduced the size in the early 1980s.

    The second image is a scale drawing of the original rudder, at left, and some proposed modifications, at right. The existing rudder has a 1.25 inch thick mahogany upper and lower (light blue and dark blue respectively) and 3/16 inch aluminum cheeks (in red). The drawing grid is 1 inch.

    Here's what I'd like to modify:

    -Increase radius of blade pivot from 2 inches to 4 inches, as shown on drawing.
    -Make cheeks taller as shown on drawing
    -Increase cheek thickness from 3/16 inch to 1/4 inch to reduce splaying seen on existing rudder
    -Possibly enlarge the rudder blade (green line) to improve balance and control

    Anyone see any issues with this? Anyone have any better ideas?
     

    Attached Files:

  2. wet feet
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    wet feet Senior Member

    The rudder on the right in the image does look pretty abysmal.I can understand why you would wish to improve on it and it seems that you have the kernel of the way to proceed.Two thoughts come to mind;where is the waterline of the boat relative to the cheek pieces?It would obviously be better if they weren't immersed as the drag would not help anything.Secondly,how would you lift or lower the rudder blade?
     
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  3. waterbear
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    waterbear Junior Member

    Wet feet,

    Here's the what the transom looks like. You can see the cheeks roughly line up with the bottom of the skeg.

    On the photograph of the two rudders you can see the lifting/lowering setup. The stainless arm I think is there to improve lifting leverage.

    Since I am proposing to move the pivot forward, the leverage lifting would be increased, and the pull down force (rope at left) would be decreased. I'm also now noticing these lines and their attachment points are below the skeg!

    Another alternative would be to build a ruddercraft style rudder. Potterers like their ruddercraft rudders, but they are expensive ($700?) and the hdpe blades tend to break. There is a place in Nevada that has cheap laser cutting of stainless and aluminum, so I think it would be economical to fabricate something like this. I can also tigweld stainless. The issue with this approach is I have no idea what to use for "scantlings" for the rudder.
     

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  4. wet feet
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    wet feet Senior Member

    No offence intended but nothing I have seen so far is particularly good.I wouldn't want a rudder as flexible as HDPE on anything I couldn't lift with my hands because I doubt it would be sufficiently rigid to reassure me that the boat would always and unfailingly respond.I have no idea if there are class rules to adhere to and if it is a factor then compliance is important.

    I have attached a very crude scheme that would work;you use 2 side plates of a material that you can work with and stainless might be a good choice.The side plates can extend from just above the waterline to just above the top of the transom.You can use a spacer of channel section to hold the top apart and if it forms a tapered recess with respect to the top of the plate,you can use a tapered wooden tiller.At the aft end you can use a pair of plastic sheaves:eek:ne for a downhaul and one for an uphaul.You can lead lines forward to cleats on the underside of the tiller.There ought to be no need for the rudder blade to lift any further than clear of the water and you are best advised never to tow with the rudder shipped.A couple of hours of drawing out the parts should make it ll clear.

    lifting rudder scheme.jpg
     
  5. waterbear
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    waterbear Junior Member

    No offense taken. Last time I built a rudder it was an overbuilt embarrassment, so I'd like to avoid that here .

    Your suggestion looks like the stock catalina 22 rudder to me, see attached. I believe that rudder has a 1 3/8ths thick blade and 1/4 inch cheeks, although I'm not sure of the other dimensions.

    If I were to build a rudder craft style rudder, I might use a stainless square tube post (say 1.25x1.25 0.100" wall) with 0.25" aluminum cheeks bolted on. These cheeks could be extended upward as in your design, but is that necessary? Again, these are just guesses on material dimensions, the devil is in the details...
     

    Attached Files:

  6. kapnD
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    kapnD Senior Member

    Stick with a simple one piece rudder, the kick up business is bringing far too much complication into the very important process of guiding the boats direction of travel.
    If you frequently sail in shallow waters, the aspect ratio of the rudder may need to be changed to wider and shallower.
    A WWPotter is not known as a high performance sailor, so I doubt that altering the rudders configuration would have huge performance consequences.
     
  7. waterbear
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    waterbear Junior Member

    KapnD,

    That's probably good advice, but one of the main reasons I bought the potter is for the fully retractable keel. I want to be able to cruise into shallow creeks and sloughs, and run the boat up on a beach. In that context it makes sense to me to put in a little more effort to make a kick up rudder.

    Improving the performance of the rudder is low on my list of priorities. I think Judy said having the performance rudder keeps the boat from rounding up in high winds, and gives the rudder a lot more authority. As far as I can tell that just means adding 30% more area to the leading edge, and taking some care when shaping the foil, which seems like a modest investment. I assume the added area adds more strain? Or maybe less because it's balanced? I'm not clear on whether there are drawbacks to more surface area, other than more wetted surface.
     
  8. Tops
    Joined: Aug 2021
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    Tops Senior Member

    It looks like there would be room to move the pivot down below the lower pintel/gudgeon (to keep that through bolted) before it would exceed the depth of the transom. If the dims are right you could have a 12" circle or 6" radius. On my boat the hinge point is so close to the bottom of the transom that there is 'no room at the inn' and my rudder cheeks drag underwater to facilitate a pivot. It could be solved on mine with some work but I am working on fixing other issues first...
    wwp19_judy_tip.jpg
    spot_s21_flam (1).jpg
     
  9. wet feet
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    wet feet Senior Member

    You should absolutely make every effort not to have the cheeks of the rudder stock extending below the waterline as they will do nothing good for the performance of the boat.It perhaps needs to be emphasised that the pivot bolt itself and the portion of the lower gudgeon will play a significant part in tieing the cheeks together.A one piece rudder is simpler and does give an unbeatable level of response but sadly, for most of us,there will be times when we need to remove a piece of seaweed or old line that has been picked up and the lifting rudder justifies it's installation.I don't see a huge amount of merit in having a rudder stock that permits lifting the rudder blade much above horizontal and clear of the water and would repeat my earlier comment about drawing the whole assembly out full size to see what improvements may be possible.
     
  10. kapnD
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    kapnD Senior Member

    Any additional rudder area will also increase strain on the fastenings.
    pointing the boat closer to the wind increases strains on everything!
    Tops remark about relocating the lower mount is wise.
     
  11. waterbear
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    waterbear Junior Member

    Thanks guys, I think maximum radius would be 5 inches, or a 10 inch circle, since 10 inches is the length of the blade. I will also move the cheeks upward just below the pintle, and they will just clear the bottom of the transom.

    One advantage of making the radius as large as possible is the added leverage when pulling the rudder up/down.

    I did a bit of digging and found some more information on the rudder craft rudder. Looks like ruddercraft have several standard rudders that are adapted to many different boats. For the potter 19 they use the "unifoil b" design, which has a 1.25inch square post (unknown wall thickness) and what I estimate to be 14 gauge cheeks. The cheeks are simply welded to the post.
     
  12. wet feet
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    wet feet Senior Member

    I have a strong feeling that the Ruddercraft design is a generic solution and not necessarily the best solution for any particular boat.For instance the notion of using a piece of box section so that the rudder blade is able to lift through a 180 degree arc is a dubious benefit and the lack of material in the upper portion of the piece that results from this design decision leads to poor seating of the tiller and this necessitates a spur that leads forward to provide support for the tiller.Similarly,I don't see any great benefit to the arc of material that has been removed,presumably so that a secondary bolt can follow it as the blade rotates.It would be a better solution to use the lower gudgeon as a strap to connect the two cheeks and to move the pivot bolt aft so that it prevents the cheeks separating.While we are at it,we might move the support for the tiller aft of the gudgeon axis and fill in the space to the tangent point of the lower cheek and we would have reduced the torsional loadings on the assembly .This is a less tall version of the concept https://dkutenx65dka0.cloudfront.net/product-media/38V/1000/1000/Seasure-Universal-Rudder-Stock.jpg .
     

  13. waterbear
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    waterbear Junior Member

    Ok, I had an unexpected solution to my rudder problem pop up today. I happened upon a $200 ruddercraft rudder in my local used marine chandlery, so I decided to buy that rather than build something. Thank you to everyone who took the time to make suggestions.

    I believe the rudder I purchased is sold as the "blue water" rudder for the potter 19 and is a bit thicker with heavier construction. The blade and post are 1.5" inches (vs 1.25) and the cheeks are 0.114 in (vs the standard ~0.080). Perhaps the extra thickness will keep the blade from snapping off? Only time will tell.
     
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