Modifying rudder contour :: Catamaran Sailboats at TheBeachcats.com

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Modifying rudder contour

catdan

Rank: Lubber

Registered: Jul 25, 2008

Last visit: Aug 10, 2010

Posts: 91
Posted: Sep 24, 2009 - 06:04 AM

I'll soon have to do a polyester job on both hulls and rudders/centerboards as they are in bad shape. Centerboards are about to split in half.

While you're at it, would you do this?

Of course I'd also change the cross section contour, not just cut off that part.

Btw, just noticed, someone marked the rudders L and R, but I do not think there is a starboard and portside. Or is there?

Thanks,
Dan
HULLFLYER

Rank: Mate

Registered: Aug 06, 2004

Last visit: Oct 20, 2024

Posts: 878
Posted: Sep 24, 2009 - 06:41 AM

I would not change the shape of the rudders, what is there to gain? There is not a difference in the rudders, but there is a difference in the rudder castings. Make sure that the logo (P) is on the outboard side when you put them on.
MN3

Rank: Master Chief

Registered: Jun 20, 2006

Last visit: Dec 04, 2024

Posts: 7090
Posted: Sep 24, 2009 - 09:57 AM

perhaps purchase a second set of rudders for R&D.. but i wouldn't change my primary set.
TileMan5309

Rank: Lubber

Registered: Aug 12, 2009

Last visit: Sep 22, 2011

Posts: 36
Posted: Sep 24, 2009 - 10:43 AM

Hullflyer is correct, I have a P18 and accidentally put the rudders on the wrong sides and saw that I had a bit of "tow-in" to say the least! (or tow-out...I forget!)

While we are on the subject. I have a P-18 and am wanting to install H-16 style tiller assymbly. (I am trying to get away from the string thing which does not work well for me...) I have an H16 I can take a set of tillers, rudders, etc off of and was thinking of installing them on my P18.
The H16 rudders are about 3" shorter, but are a bit deeper (front to back) so as far as surface area for control, I think I am ok.

My question for you more experienced guys is:
Can I mount H 16 grudgeons on the back of my P18 hulls? Is there like plywood behind the layer of fiberglass that I am looking at so I drill and then screw in the bolts into the back of the hulls to mount the H16 grudgeons? Or, is there some kind of blind nut inside the hulls these bolts go into?

Thanks!

edited by: TileMan5309, Sep 24, 2009 - 07:44 AM
HULLFLYER

Rank: Mate

Registered: Aug 06, 2004

Last visit: Oct 20, 2024

Posts: 878
Posted: Sep 24, 2009 - 12:11 PM

The rudder gudgeons bolts are screwed into a metal plate (SS). The plate has been tapped to size to accept the bolts.
TileMan5309

Rank: Lubber

Registered: Aug 12, 2009

Last visit: Sep 22, 2011

Posts: 36
Posted: Sep 24, 2009 - 12:28 PM

Uhhmmm....ok, so it really sounds like my idea would be close to impossible. Is that correct?

Thank you,
catdan

Rank: Lubber

Registered: Jul 25, 2008

Last visit: Aug 10, 2010

Posts: 91
Posted: Sep 24, 2009 - 07:10 PM

As for the shape, this would come close to the new rudder style.

As for left and right; the rudder blades are symmetric. The castings are a different matter! I'm just talking about the blades. Sorry about not being clear on that.

Thanks,
Dan
pbegle

Rank: Mate

Registered: Mar 12, 2003

Last visit: Feb 19, 2021

Posts: 879
Posted: Sep 24, 2009 - 10:19 PM

The aluminum plate on the inside of transom is not glassed into place. If you remove both bolts from gudgeon, plate will fall to hull bottom in most cases. You can remove one bolt at time & change gudgeons---but I don't recommend it. Put hull on milk crate & get to understand the system. Take springs off and put in vice very tightly. Adjust bolt so that two hands can reasonably easily pull rudder from casting. Hobie rudders have no skin & break fairly easily. Prindle rudders are much stronger, though need some upkeep. And be sure you have good 3/16 strings/line. Pete
catdan

Rank: Lubber

Registered: Jul 25, 2008

Last visit: Aug 10, 2010

Posts: 91
Posted: Sep 25, 2009 - 05:37 AM

Thanks for the info about the gudgeons, appreciated.

This might be debatable, but this limited access to the inside of the hulls just does not sound like a very good system to me.

Why not screws with 2 inches spacing instead of gluing the decks, and silicone in between to seal it. Sure it would be adding perhaps a pound of weight and 30$ production cost.

Dan
mma600psi

Rank: Mate

Registered: Mar 08, 2008

Last visit: Feb 05, 2017

Posts: 247
Posted: Sep 25, 2009 - 05:11 PM

HULLFLYERI would not change the shape of the rudders, what is there to gain? There is not a difference in the rudders, but there is a difference in the rudder castings. Make sure that the logo (P) is on the outboard side when you put them on.

Also I learned the hard way...an older boat is going to wear a certain way. After a few years the parts may not be interchangeable because of the wearing.
HULLFLYER

Rank: Mate

Registered: Aug 06, 2004

Last visit: Oct 20, 2024

Posts: 878
Posted: Sep 26, 2009 - 07:03 AM

I have owned Prindles since the mid 70's and have removed numerous rudder gudgens, most cases all the bolts at once and have never had the plate fall. I firmly believe that it is glassed in place. I could not imagine the factory doing that. How would the initially get the bolts in the first time.
pbegleThe aluminum plate on the inside of transom is not glassed into place. If you remove both bolts from gudgeon, plate will fall to hull bottom in most cases. You can remove one bolt at time & change gudgeons---but I don't recommend it. Put hull on milk crate & get to understand the system. Take springs off and put in vice very tightly. Adjust bolt so that two hands can reasonably easily pull rudder from casting. Hobie rudders have no skin & break fairly easily. Prindle rudders are much stronger, though need some upkeep. And be sure you have good 3/16 strings/line. Pete
catdan

Rank: Lubber

Registered: Jul 25, 2008

Last visit: Aug 10, 2010

Posts: 91
Posted: Nov 14, 2009 - 08:51 PM

Since no one really suggested I should do this, we only changed the contour a little.

I haven't had a chance to test the cat in a high wind yet, but there does not seem to be any change in feel or behavior.

Dan
yurdle

Rank: Mate

Registered: Aug 22, 2007

Last visit: Jan 07, 2015

Posts: 742
Posted: Nov 14, 2009 - 09:42 PM

I'd imagine that you'd be hard pressed to notice any difference in that change.

I've gotta agree with Hullflyer. In my limited experience of one prindle the gudgeons were definitely glassed or in, or attached with some sort of adhesive or something. I've taken the bolts out numerous times with no issue.

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Rob
OKC
Pile of Nacra parts..
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