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Cracking rudders and rounding up

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Sea Trac
Master Marine Consultant

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Vanuatu
1357 Posts

Initially Posted - 11/10/2003 : 16:22:17

The following just occurred to me and is probably all tripe, but...

When I pulled my rudder last weekend to bring it home and effect repairs, I was very surprised by its bouyancy. As a matter of fact, I was expecting it to be full of water and to weigh a ton. One test tug on the lifting line, and it literally popped up out of the gudgeons all by itself. After scrapping off the slime and while trying to dunk rinse it, I noticed that it was bouyant enough to hold itself 3/4 out of the water vertically (i.e., normal orientation), more longitudinally (i.e., on leading or trailing edge), and nearly 100% horizontally (i.e., lying flat).

Given those facts and the fact that the attitude of the rudder becomes more horizontal as the boat heels, isn't it possible that this extreme and increasing bouyancy is the cause of cracking rudders and a large contributor to the excessive weatherhelm that causes rounding up?

If so, why couldn't a replacement rudder be made of a less bouyant material? Any suggestions on what that material could or should be? I was thinking that a varnished wooden rudder to match the tiller handle and brightwork would look really cool.

J.B. Manley s/v Sea Trac Allied Seawind II #65
DPO s/v Antares Catalina 25 #4849
Association Treasurer 2002 - 2006
Association Bookkeeper 2002 - 2008
Association Quartermaster 2004 - 2008

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 11/10/2003 : 16:53:10

<blockquote id="quote">quote:<hr height="1" noshade id="quote">I was thinking that a varnished wooden rudder to match the tiller handle and brightwork would look really cool.<hr height="1" noshade id="quote"></blockquote id="quote">

Yes it would look cool, but would still probably be bouyant given it is made from wood.

Edited by - on

Sea Trac
Master Marine Consultant

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Vanuatu
1357 Posts

Response Posted - 11/10/2003 : 17:06:54

Wood laminate on steel?

BTW, I'm also toying with the idea of adding a traditional skeg that would match the rudder's width and depth. Ideas? Issues?

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 11/10/2003 : 17:27:20

<blockquote id="quote">quote:<hr height="1" noshade id="quote">BTW, I'm also toying with the idea of adding a traditional skeg that would match the rudder's width and depth. Ideas? Issues?<hr height="1" noshade id="quote"></blockquote id="quote">

Adding a skeg = more wetted surface = more drag = slower boat!

Additionally, it sounds like too much work.

Edited by - on

Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 11/10/2003 : 17:56:40

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Given those facts and the fact that the attitude of the rudder becomes more horizontal as the boat heels, isn't it possible that this extreme and increasing bouyancy is the cause of cracking rudders and a large contributor to the excessive weatherhelm that causes rounding up?<hr height="1" noshade id="quote"></blockquote id="quote">

Unless you were able to stand on the rudder as it was floating around, the buoyant force is probably neutral or slightly positive. (equal to, or slightly more than its own weight), and not of a magnitude that would affect the forces at play in a two ton rig doing 6 knots.

I suspect that a skeg should somehow be engineered into the "foundation..." If you just bolt/glue the skeg to the hull, and then hit something, it will take part of the skin with it on the way down.

Now you have a hole in your boat. (Bad

)

So you would have to provide some serious backing=lost space=more weight where you don't want it. You would also have to provide for a sheer point where the skeg would be intended to fail when subjected to destructive loads. This would require at least a little professional engineering.

I understand what you're after, and from a design viewpoint the idea is not bad, but it's sort of like turning a sedan into a convertible. If you do it right it might be as much money/effort as you'd spend on say, a fixer upper Pacific Seacraft.

Oscar
250WB#618 Lady Kay on the Chesapeake

Edited by - Oscar on 11/10/2003 18:02:33

Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 11/10/2003 : 19:37:02

Actually, I added a small skeg to my c250... it is made of foam... been there since '99. Glued on with 3M spray adhesive. I have about an hour invested in it... it looks as good as it did when I put it on (though my boat lives on the trailer).

The c250 3rd is evidently made similar to the replacement foam rudders for the C25 and uses a foam core. The 2nd is not foam but resin saturated filler which is what the center board is made of.

BTW... while you have the foam rudder subject open... remember not to leave a foam rudder with bottom paint on it lying in the sun. It can grow and split.

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 11/10/2003 : 20:53:05

JB: I have to assume you have the new balanced rudder (not the original on your boat)--the original rudder, in my experience, has nothing close to that boyancy, but the balanced rudder does. If you have an original that floats like that, it's in REALLY good shape! That said, the bouyancy forces you're talking about are not going to affect the heel and roundup problems discussed here; nor are the forces strong enough to cause breakage. (Most of the cracks reported here are in the seams around the original rudders, caused by swelling from moisture and in some cases freezing, and the clamshell construction of the original design.)

I have the new balanced rudder on our '85 fin, and my rig is balanced to the point that I have very moderate weather helm when virtually overpowered, and nearly neutral helm in 5-10 knots of air--maybe just a little too neutral. It has never rounded up on me. I use a stack of washers between the gudgeon and the cotter pin to keep the pintles from floating up on the gudgeons.

If something is going to break that rudder, I would guess that it would be some major pitching while the boat is heavily heeled, creating a vertical motion on the heeled blade, snapping it at the lower pintle. That would have nothing to do with boyancy and everything to do with the force of water against a surface that is being tossed around by a 5500 lb. boat. One preventative measure is to avoid fighting the rudder. If the boat is pounding, particularly at heel, give the tiller some "play" against the shock forces. By comparison, the boyancy forces are tiny and very constant.

Edited by - on

Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 11/10/2003 : 21:08:30

Arlyn.....JB wants to make a skeg that goes all the way to the bottom of the rudder......

JB, I did not realize you had the new balanced rudder. You don't want to put a skeg in front of that. It would mess up the balance.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">(Most of the cracks reported here are in the seams around the original rudders, caused by swelling from moisture and in some cases freezing, and the clamshell construction of the original design.)<hr height="1" noshade id="quote"></blockquote id="quote">

Dave, the 250 rudders that are cracking are new rudders, as in mine started after four days of sailing. From what it sounds like the current factory replacement for the 25 is now made the same way.

Oscar
250WB#618 Lady Kay on the Chesapeake

Edited by - Oscar on 11/10/2003 21:15:28

Sea Trac
Master Marine Consultant

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Vanuatu
1357 Posts

Response Posted - 11/10/2003 : 23:46:24

Hmmm...sorry, I was mixing thoughts...skeg for me...cracks on 250 rudders. I have the original '85 unbalanced C25 rudder. My thought regarding the bouyancy of the rudder was based upon the balance of the keel acting as the center point of a pivot and, therefore, the weight of the boat being immaterial to a force acting as a rotational agent. My thought regarding the cracks was based upon the downward directional force of the boat acting against the upward directional force of the bouyancy of the rudder. The rudder, of course, being the weakest link.

Mostly just rambling, but obviously I keep circling back to the same answer, as correctly identified by Don; different boat for different use -- Shannon 38.

Edited by - Sea Trac on 11/11/2003 14:17:48

Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 11/11/2003 : 09:55:57

I have a new balanced rudder for my 89 25. It has no visible seam. The original rudder did, was cracked, the reinforcement at the pintles was broken, and therefore I replaced it

Edited by - on

Sea Trac
Master Marine Consultant

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Vanuatu
1357 Posts

Response Posted - 11/11/2003 : 16:32:26

[url="http://www.paceship.net/how_to/rudder.htm#theory"]Interesting custom rudder building link with foil theory and references.[/url]
Makes for an interesting prospect when combined with the dimensional drawings for the new C25 balanced rudder in the Technical Tips section.

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Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 11/11/2003 : 17:28:12

<blockquote id="quote">quote:<hr height="1" noshade id="quote">It has no visible seam<hr height="1" noshade id="quote"></blockquote id="quote">

Not yet..

..and hopefully never...

JB I like your sign up sign off......good marketing.

Oscar

Lady Kay 250 WB #618
In the driveway in Behtlehem, PA ready to go anytime.

Edited by - on

tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 11/12/2003 : 08:56:36

All this talk of boyant rudders impressed me. So I weighed mine , it weighed 28.5 pounds. It's an original rudder from an'83 cat 25, clamshell, no cracks or swelling and definitly not a floater.
Has anyone weighed their rudders?

Val on the hard DAGNABIT

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 11/12/2003 : 09:24:46

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by tinob
 All this talk of boyant rudders impressed me. So I weighed mine , it weighed 28.5 pounds. It's an original rudder from an'83 cat 25, clamshell, no cracks or swelling and definitly not a floater.
Has anyone weighed their rudders?

Val on the hard DAGNABIT
<hr height="1" noshade id="quote"></blockquote id="quote">
I was carrying 1982 rudder around the boat yard yesterday. The weight changed dramatically during the morning. It had to be 50lb when I took it out of my Mountaineer. I sanded so many layers of paint off that I was simply stunned. The bottom several layers were copper paint that the sander simply polished with 60 grit, it looked really cool. Finally with 40 grit it yielded and came off. I would say it was around 30lb at the end of the morning.

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Sea Trac
Master Marine Consultant

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Vanuatu
1357 Posts

Response Posted - 11/13/2003 : 13:55:07

After much contemplation regarding weatherhelm, oscillating tiller and pending rudder repairs, I've decided that I'm firmly committed to building an all wood, balanced rudder for Antares. (Don't bother saying "buy one from CD", because there's absolutely no way that I can afford one for at least a couple of years.)

So, I would appreciate your experienced advice on woods and finishes. My very strong preference is for a natural, light wood finish that closely matches my varnished tiller. What wood are tillers generally made from? Would that work for the rudder? Would something work better? Does epoxy go on as a clear finish? Would epoxy be sufficiently waterproof, especially below the waterline? How's the durability of epoxy? We have the typical string algae (slime) growth problem in our lake, so would epoxy withstand regular scrubbing or scrapping? Thoughts?

Thanks, as always.

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Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 11/13/2003 : 14:14:14

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Antares
 After much contemplation regarding weatherhelm, oscillating tiller and pending rudder repairs, I've decided that I'm firmly committed to building an all wood, balanced rudder for Antares. (Don't bother saying "buy one from CD", because there's absolutely no way that I can afford one for at least a couple of years.)

So, I would appreciate your experienced advice on woods and finishes. My very strong preference is for a natural, light wood finish that closely matches my varnished tiller. What wood are tillers generally made from? Would that work for the rudder? Would something work better? Does epoxy go on as a clear finish? Would epoxy be sufficiently waterproof, especially below the waterline? How's the durability of epoxy? We have the typical string algae (slime) growth problem in our lake, so would epoxy withstand regular scrubbing or scrapping? Thoughts?

Thanks, as always.
<hr height="1" noshade id="quote"></blockquote id="quote">

How about using structural foam as a core and putting a wood veneer on it. I would think you could use "rebar" of your choosing, drive it through the foam after you shape it. Cover it with nice veneer of your choice and then encapsulate it in epoxy. Just a thought.

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Doug G.
1st Mate

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USA
49 Posts

Response Posted - 11/13/2003 : 17:33:02

JB, I had the rudder on my maybe list this winter. My rudder is '83 original, a visible center seam,no cracks. It weighed 32 lbs on my home bathroom scales after being out of the water for 5 days. My wife still thinks its more than odd that I brought 'that thing' into the house. There was a post that described making a balanced rudder out of plywood and epoxy. If you decide to do it, let me know. I'd love to see the process.

If you change the rudder and race, are you still legal, or rated differently?

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