Building a rudder

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Re: Building a rudder

Postby GreenLake » Mon Feb 04, 2019 6:37 pm

Still using the same rudder.

The lamination between the two sheets of plywood in the blade was starved of glue and had to be reworked after the first season.

I refinished the blade once after repairing some minor dings from ground contact and also had to repair some cracks after the rudder was hit by another boat at the dock (hard enough to wrench out pintles and gudgeons).

Other than that, has worked fine for me.

I picked plywood because it has differently colored layers that make a pattern when you shape the blade. That was a great help in roughing out the foil shape. Also, plywood dimensions are in full / half inches, not some weird intermediate lumber sizes.

I used birch plywood with many more than the usual number of layers (5 or seven).

Did not use marine grade. You want some grade that has no voids, but once you seal in epoxy and encase in glass, there's really not the exposure that makes marine ply critical.

Since I have the factory rudder head and blade, I originally conceived of this as an experiment: can I create something with reasonable effort that is lighter and has better foil shape? I think I succeeded and find that it's standing up to some long-term use.

I use epoxy. Almost any epoxy (other than the H/W store stuff in the dual syringes) will work pretty well. I use SystemThree. Their "GelMagic" is the one formulated for gluing. You can get it in a caulk gun cartridge with self mixing tip -- makes it very convenient.

There's no point in gluing the nylon bushings other than to seal the drilled hole (the latter is important!). Doubt the glue will permanently bond with the Nylon.
~ green ~ lake ~ ~
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Re: Building a rudder

Postby tc53 » Mon Feb 04, 2019 7:12 pm

Thanks, Greenlake. As you could probably tell, I had not yet seen page two of this string when I posted my questions. For mounting the pintles, I think I may try your idea from that second page, cutting out "slots" for the brackets but applying layers of glass over these slots and an inch or two of the cheeks above and below them. From your drawing of that idea, it looks like your intention would be to taper down into these "slots" leaving a layer or two of the cheek ply in place, then applying glass across and beyond these tapered slots to maintain cheek strength. How would you suggest cutting or creating these slots?

Thanks again!
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Re: Building a rudder

Postby tc53 » Mon Feb 04, 2019 7:14 pm

Also, am I correct that you used 1/4" ply, sandwiched between layers of fiberglass, for the cheeks?

And looking at you photos from page two, it looks like the cheek portions begin approximately halfway between the two pintles and extend down from there, with the transition to the upper part of the head being fared to a gradual slope. Is that correct? I'm only asking because on my old rudder head, the cheeks extended almost all the way to the top of the head, only leaving room for the tiller attachment and rotation.
Last edited by tc53 on Mon Feb 04, 2019 8:20 pm, edited 1 time in total.
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Re: Building a rudder

Postby GreenLake » Mon Feb 04, 2019 8:20 pm

Yep, 1/4" ply.

You may find that the brackets for the pintles may not span more than 1". In which case you may have to use a coping saw to cut a slot into the cheeks, then use a router or chisel to take some material off the top of them main head; then do the glass thing to create a new continuous "skin" over the depression. If they span more, e.g. 1.25" of can be bent a bit to open, you can assemble first, then use your favorite tool to make a fairly wide depression about 1/8" deeper than needed for the bracket and fill that 1/8" with glass.
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Re: Building a rudder

Postby tomodda » Thu Feb 07, 2019 3:13 pm

GreenLake:

Two "curiosity killed the cat" questions:

-For your rudder cheeks, did you build a new set from scratch or saw down your existing cheeks? In other words, can I saw off the last 3 inches of the cheeks (below the bolt), seal it with some epoxy and paint it?

-Likewise, could I just take my existing rudder and round off the top 3 inches of the frontside using a router? Then seal and paint? This is a quick-and-dirty solution, not as elegant as making a new rudder with a much better foil shape.

What do you think?

Tom
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Re: Building a rudder

Postby GreenLake » Thu Feb 07, 2019 3:52 pm

Tom,

the "seal & paint" part, unless you do that very localized is the most labor intensive part of any project - the rudder is no exception.

You can certainly cut away part of the cheeks of an existing rudder head. I think most of the support for the rudder blade is provided from the pivot to the top edge of the blade portion. The outer end of the cheeks, being not supported will probably "give" a bit under load anyway and therefore not contribute much. But that's just my thinking on it. As it happened, I started with fresh 1/4" plywood with a sheath of fiberglass cloth to make the new cheeks.

Modifying the front end of the existing blade portion of your rudder is dicier - not sure what you will find (including mild-steel rebar) when you dig into it. (My factory rudder has rust stains).

But you are losing sight of the biggest advantage of building a new rudder: weight at the stern. I did an experiment recently (you can duplicate it if you have a GPS) of trying to measure the effect of boat balance at moderate speeds. I used my new ElectricPaddle for that, which drives the boat at 3.1 knots in calm flat water conditions. Shifting weight forward aggressively (by moving onto the cuddy top) I was able to increase the top speed to almost 3.5 knots.

Replacing a heavy factory rudder by one that has slight positive buoyancy - that is, it weighs "nothing" when deployed, reduces weight at the most critical point.

The improved foil shape should decrease drag, possibly even require slightly lower rudder deflection - if true, that would add another component of drag reduction (would be cool to see whether the effect is measurable under motor).

The added drag reduction from not exposing a bit of flat profile at the top and not dragging the cheeks through the water is unlikely the major component in all of this, so let's be charitable and say it makes up 1/3 of the improvement.

But because it involves "sealing & painting" it's not as quick as you might think compared to the full project. Roughing out the blank, cutting and assembling the pieces was at best 1/3 of the work I did. Another 1/3 went to fairing the blade - I should have used the notched spreader technique to speed this up - and the final 1/3 (and somehow the largest third :) ) was spent on final finishing and painting.
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Re: Building a rudder

Postby tc53 » Tue Apr 09, 2019 2:32 pm

Greenlake,

I've made progress on building a new rudder head. I was able to find (for free no less) a good piece of 1" thick Baltic Birch ply to use for what I call the "core" of the new head, and from the same source I got enough 1/4" BB ply for the "cheeks." Using my old rudder head as a starting point, I created stencils for both core and cheeks, then cut them out with a narrow blade on my band saw. Using a table top belt sander, I faired the edges of both cheeks and smoothed out the rough spots on the edges of the "core" (especially at the bottom along which the rounded top of my rudder blade will travel as the blade pivots to kick up.

With winter finally loosening its grip on our Northern California mountains, I'm ready to fiberglass, assemble and finish so I can get the boat out on the lake. I need some guidance, though, on the specifics of this part.

Specifically:

When you glassed the inside of each cheek before gluing them to the core, did you use one or two layers of fiberglass? You said you used one layer of mat and one of 6 oz cloth on the outside after gluing them to the core. I wondered if you used two layers on the inside. Also, did you sand this inner glassed surface before gluing to the core?

What resin and hardener did you use for the fiberglassing?

After gluing the cheeks on, when you added the two layers of glass to the outside, did you extend these layers onto the core at the tops and edges at all?

Did you sheath the core in fiberglass as well or simply seal it by painting it? It sounds like the Easypoxy you used had some issues. Do you have any other recommendations for sealing/painting the core?

Did you put a nylon bushing in the tiller bolt hole as well as the blade pivot holes in the cheeks?

I will probably go with a carriage bolt for the blade pivot as well, and I am wondering if I might find a washer with a square hole that matches the square “collar” of the bolt and glass that washer right into the cheek. What do you think?

As I do intend to use the “kick-up” function of the blade, I’d like to have a means to tighten and loosen the pivot bolt tension without tools and yet have enough leverage to get it tight enough, when needed, so it doesn’t kick back up under sail. Ideally, this would mean some sort of “handle nut” (I think that’s what they’re called). Any idea where I might find such a “handle nut?”

When you glassed in the nylon washer on the “nut side” cheek, did you notch out an area around the hole with a router or just position the washer on the outside surface of the cheek?

I've found a replacement for my lower pintle with a 1.5" spacing between the straps (from Annapolis Performance Sailing online), so I won't need to notch out the cheek for that.

I know that’s a lot of questions. My experience with fiberglassing is limited to surfboard repairs from way back when. I appreciate the help. Thanks!
Last edited by tc53 on Tue Apr 09, 2019 3:23 pm, edited 1 time in total.
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Re: Building a rudder

Postby tomodda » Tue Apr 09, 2019 2:43 pm

Just out of morbid curiosity, why not aluminum stock for the cheeks?
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Re: Building a rudder

Postby GreenLake » Tue Apr 09, 2019 4:00 pm

tc53 wrote:Greenlake,

I've made progress on building a new rudder head. I was able to find (for free no less) a good piece of 1" thick Baltic Birch ply to use for what I call the "core" of the new head, and from the same source I got enough 1/4" BB ply for the "cheeks." Using my old rudder head as a starting point, I created stencils for both core and cheeks, then cut them out with a narrow blade on my band saw. Using a table top belt sander, I fared the edges of both cheeks and smoothed out the rough spots on the edges of the "core" (especially at the bottom along which the rounded top of my rudder blade will travel as the blade pivots to kick up.

With winter finally loosening its grip on our Northern California mountains, I'm ready to fiberglass, assemble and finish so I can get the boat out on the lake. I need some guidance, though, on the specifics of this part.

Specifically:

When you glassed the inside of each cheek before gluing them to the core, did you use one or two layers of fiberglass? You said you used one layer of mat and one of 6 oz cloth on the outside after gluing them to the core. I wondered if you used two layers on the inside. Also, did you sand this inner glassed surface before gluing to the core?

I'm pretty sure I used only a single layer. However, you should use the same number of layers on both sides of the cheek. That is two. The cheeks can use the additional bit of strength. I use an epoxy system that is non-blushing and does not need to be sanded if it is glued promptly - with compatibly epoxy from the same line.

What resin and hardener did you use for the fiberglassing?

I exclusively use SystemThree. All my favorite stores stock it, and I like that it's non-blushing. Also, while epoxies are generally similar, by sticking to one line, I avoid running into any potential subtle differences. For laminating I would use their Silvertip range, for glueing the GelMagic - comes in a caulk gun cartridge with self-mixing tip. However, sometimes I glue pieces using the SilverTip and even laminate small sections using GelMagic. The latter, is intended to be non-sagging but still wets out laminate well enough.

After gluing the cheeks on, when you added the two layers of glass to the outside, did you extend these layers onto the core at the tops and edges at all?

You can see from this picture, that there is a 'bump' going from cheek to body, but is is "soft". Indication that I sanded the edges and let the laminate continue onto the "core", as you call it. Don't think I wrapped it over the edges.
943


Did you sheath the core in fiberglass as well or simply seal it by painting it? It sounds like the Easypoxy you used had some issues. Do you have any other recommendations for sealing/painting the core?

If memory serves, after shaping the blade, I sheathed both it and the core in the same operation, before sawing them apart. The main idea was that doing that in one go made it not more difficult and the process guarantees that the thickness of both match at the end. The shaped part of the rudder blade received additional fairing outside the glass layer. EasyPoxy is fine. You just need to let it dry for a good week. It's really durable once fully cured. Until then, it's a bit softish.

Did you put a nylon bushing in the tiller bolt hole as well as the blade pivot holes in the cheeks?

I think I did, but I would have to take the tiller off to know whether I did. It's definitely a good thing to do.

I will probably go with a carriage bolt for the blade pivot as well, and I am wondering if I might find a washer with a square hole that matches the square “collar” of the bolt and glass that washer right into the cheek. What do you think?

Nothing wrong with that as far as I can see. You simply make one yourself, get a round one that fits the shank of the bolt and file corners in it.

As I do intend to use the “kick-up” function of the blade, I’d like to have a means to tighten and loosen the pivot bolt tension without tools and yet have enough leverage to get it tight enough, when needed, so it doesn’t kick back up under sail. Ideally, this would mean some sort of “handle nut” (I think that’s what they’re called). Any idea where I might find such a “handle nut?”

I use a regular wing nut, but I've never seen a need to loosen it. I like to use the friction to "hold" the rudder down. That works marginally well. A better alternative, especially if you encounter flat water often, is to keep it a bit loose and use a nylock nut. Then use a downhaul line with a V cleat on the tiller that trips under overload. Some older post has a discussion of those.

When you glassed in the nylon washer on the “nut side” cheek, did you notch out an area around the hole with a router or just position the washer on the outside surface of the cheek?

As you can see from the picture, I'm using a SS washer for the wing nut.

2650

I've found a replacement for my lower pintle with a 1.5" spacing between the straps (from Annapolis Performance Sailing online), so I won't need to notch out the cheek for that.

That makes it easier, but the glass will add a bit of thickness, too, so you may find you end up needing a small depression or force the straps apart a bit.

I know that’s a lot of questions. My experience with fiberglassing is limited to surfboard repairs from way back when. I appreciate the help. Thanks!

No problem. Advice: mix the epoxy as if it was medication - as precisely and thoroughly as you can. Also, read the vendor's literature. All of it. When using mat, make sure it's epoxy compatible - the one for polyester uses some light adhesive that dissolves in styrene, but won't in epoxy. Or use two layers of cloth.

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Re: Building a rudder

Postby GreenLake » Tue Apr 09, 2019 4:11 pm

tomodda wrote:Just out of morbid curiosity, why not aluminum stock for the cheeks?


Tom, I see no reason that you couldn't use that material if you prefer it. I personally like to use wood.
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Re: Building a rudder

Postby jalmeida51 » Tue Apr 09, 2019 9:29 pm

I leave my pivot bolt loose and use a downhaul to keep my rudder down. The downhaul is secured to a quick release jam cleat. You can get an handle that is welded to the nut of the pivot bolt. The newer Rhodes19 uses this method. Call Stuart Marine up in Rockland Maine to buy one. They build the Rhodes19. You might have to buy a new pivot bolt to use on the handle nut.
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