building new skeg and rudder help

[vishnuleela]

ok so i have picked up a colvin 26 sailer (thick grp) today... the skeg has previously come off and the rudder was rebuilt by previous owner not to the best standard.

please if you have any tips on how i can attach a new skeg and build a rudder in a simple strong affordable way please share, im worried my replacement could fall of as well, would thick epoxy hold one on?

attached are the photos, i want to say in advance i really appreciate it guys!

[vishnuleela]

hi guys this is how it should look...

[UNCIVILIZED]

Note that in lieu of building a skeg, as well as a new rudder, it’ll be a lot less work, & most likely stronger & cheaper, to build the rudder as a stand alone fin, without a skeg. To include using a larger diameter rudder post, even though this’ll mean adding new bearings, etc. It’s worth pondering on anyway. And for more on this idea, read Steve & Linda Dashew’s thoughts on the subject in their Offshore Cruising Encyclopedia, vol. II which is available gratis at SetSail FPB » Search Results » free books

So, if you do decide to stick with a skeg configuration, then I’d do something much akin to the following:
~ Assuming that the stump of the skeg that's left is solid material, machine a rabbit/recess into both sides of the stump.
~ Grind off the coatings in the vicinity of the above (skeg stump & new recesses), & near the rudder.
~ Bond a layer of 3mm, epoxy saturated marine ply into both recesses, with a stiff core of high density structural foam (Divinycl, or CoreCell) bonded in between these pieces. So as to make an ultra-stiff fin-form.
~ Laminate multiple layers of axial fabric onto this fin form, & to hull bottom. Thus bonding everything together Into a tough, strong, stiff, monocoque structure.
~ Template & fair this new skeg as needed/is appropriate.
~ Seal it with epoxy (as a barrier coat).

It’s worth noting that stiffness of a structure, or rudder shaft, increases with the cube of it’s thickness. So that doubling it’s thickness results in an 8-fold increase in it’s stiffness. Thus, within reason, build the skeg, rudder shaft, & rudder blade itself, as thick as possible in order to resist bending loads. And or, in case you ground the boat. Which, the latter is another reason to upsize the rudder shaft when rebuilding things.

Rebuild the rudder around a new shaft & shaft structure, using slow curing resin mixed with micro-balloons as it’s core fill. See Nicholson58’s rudder rebuild pics & info for tips & an explanation on how to do this. And if you can’t find the info/instructions, LMK & I’ll dig up a copy.

Building it this way will utterly rule out the possibility of water intrusion into the rudder, which would thus result in the degradation of it’s core, along with the corrosion & eventual failure of it’s metal internal skeleton.


NOTE: When you build the rudder, build it strong enough with the idea in mind that it’ll be a stand alone fin rudder. Even though you may or may not attach it’s heel to the skeg. Should you choose to build a skeg that is.

Also, there are some excellent step by step instructions with pics of rebuilding rudder skeg hardware on the Tartan 37 Owner’s website. Many of the design features of which would be worth incorporating/copying into your setup.

Plus there are some good tips both on rudder foil shape selection, & rudder building on Sailing Anarchy Forums, here  Rudder stalling AOA....... - Fix It Anarchy - Sailing Anarchy Forums

That said, it’s worth your time to do some studying on what comprises a good overall shape for the combined skeg & rudder fin. One resource for which is www.BoatDesign.net/forums
And as is mentioned in the Dashew's book (above), fat foil shapes resist & recover from stalling better than do thin ones.


EDIT: Whether you go with a skeg or not, it's worth incorporating something of an eliptical shape into the rudder. Even if that means that the part of the rudder which hangs down below the lower skeg bearing doesn't have an internal shaft, & is only built out of structural core (epoxy & microballoons), with strong glass skins.

Plus which, a tip built thusly would be semi-sacrificial anyway, which could prove useful in a grounding situation, in that the tip being more fragile than the rest of the rudder blade might wind up protecting the shaft & bearings from damage due to the grounding. It's worth a "think".

[vishnuleela]

wow thanks a lot for that long reply definitely a lot to think about, i think ill go with the rudder as a stand alone fin then. its good to get some advice because im a real amateur.

something i can add is im taking out the inboard because its close to dead (free boat). maybe u can add to this. i was thinking about taking the prop off and epoxying the prop shaft bothe ends, then welding a steel rod onto the prop shaft ending just in front of the rudder. epoxying some hard wood with a hole drilled in it and a downward steel rod welded to the one coming out of the prope shaft. then adding that bit at the bottom that the rudder shaft sits in. does that make sense? what shortcomings can u see in that?

thanks a lot

[vishnuleela]

hi one more thing, can a 2.7 ton 26ft boat have a transom hung rudder? maybe even a giant dinghy style lift up rudder?

[vishnuleela]

how could you solidly fit a transom hung rudder on the back of the boat do u need to bolt ply in first or something to attach it to? i have access to teak that im thinkin about cutting in shape.

thanks for that answer uncivilized

[foufou]

Lots of transom hung rudders. Look at J boats. Be aware that early J24 rudders had failures and were upgraded

[Bluebeard]

Now you are thinking!
I'm familiar with the French ( Beneteau & Jeneau ) 26ft boats and they have transom hung rudders. Probably some of the bigger ones as well.
If you could find the right Rudder off one of those it would be a lot less work.

[KP44]

Originally Posted by vishnuleela

hi guys this is how it should look...

Lots of good advice and detail already given.
I have never replaced a rudder, but have some thoughts. I would be very hesitant to modify the hull design and wetted surface, so I would probably rebuild the skeg if I had good photos or line drawings.

If I ever replace or rebuild a rudder, I will increase the diameter of the rudder stock. Going larger gives a tremendous increase in strength.

I have done extensive epoxy work, replacing my teak decks with fiberglass/epoxy. I would probably use no wood or plywood, but airex-type close-cell foam sheets. The stuff they use for homebuilt airplane wings looks the best. Use that and heavy fiberglass cloth with epoxy to create the shape and size. I like the 17 oz bi-axial fiberglass cloth that you can buy 12" wide in a 50' roll. That is a manageable size and you will want several layers for strength.

The resin has little strength by itself. With fiberglass cloth and matt it is strong. You can also make a paste that has good strength but is better used for fairing the final product or filling where fiberglass cannot cover.

[KP44]

Originally Posted by vishnuleela

wow thanks a lot for that long reply definitely a lot to think about, i think ill go with the rudder as a stand alone fin then. its good to get some advice because im a real amateur.

something i can add is im taking out the inboard because its close to dead (free boat). maybe u can add to this. i was thinking about taking the prop off and epoxying the prop shaft bothe ends, then welding a steel rod onto the prop shaft ending just in front of the rudder. epoxying some hard wood with a hole drilled in it and a downward steel rod welded to the one coming out of the prope shaft. then adding that bit at the bottom that the rudder shaft sits in. does that make sense? what shortcomings can u see in that?

thanks a lot

Sounds like building a skeg, without building a skeg. Sounds like you realize the need for the support a skeg gives. Your boat might need extra structure to support the stresses of a dramatic change from skeg to no skeg.
If this is a free boat and you are just trying to "make do" so you can sail in protected waters, your changes are probably OK.

Keep in mind that sailors casually talk about "the occasional grounding". We ALL run aground on occasion when we are near land. That is when stresses on your transom, or wherever you attach a fin rudder, will be greatest. A skeg takes the brunt of groundings and protects your rudder and steering.

[captlloyd]

Originally Posted by vishnuleela

hi guys this is how it should look...

Although we do know how well the new rudder was built, we can see that it is quite a bit bigger. If it were me I would try to rebuild the skeg, making it look pretty much Like the picture. You might even try cutting the rudder back a bit, although this may not be necessary. Amazon has a number of books on fiberglassing. I really do not like the idea of tying into the prop shaft. I see a structure there which would be the root of the skeg. I would build on that or even expand it a bit. Being a welder I would fabricate a steel framework and glass around it.

[UNCIVILIZED]

Not to criticize, but rather to offer some pointers on the below...

Originally Posted by KP44

Lots of good advice and detail already given.
I have never replaced a rudder, but have some thoughts. I would be very hesitant to modify the hull design and wetted surface, so I would probably rebuild the skeg if I had good photos or line drawings.
More rudder tends to be better than less. Make sure that it's counterbalanced properly (study on this topic). And a spade (fin) rudder can be smaller than a skeg rudder due to it's much greater hydrodynamic efficency. And the boat will be more responsive, which also means that she'll need a bit more attention paid to helming her, but with a soft hand on the tiller due to the rudder's higher efficiency.

If I ever replace or rebuild a rudder, I will increase the diameter of the rudder stock. Going larger gives a tremendous increase in strength.
Yep, for certain.

I have done extensive epoxy work, replacing my teak decks with fiberglass/epoxy. I would probably use no wood or plywood, but airex-type close-cell foam sheets. The stuff they use for homebuilt airplane wings looks the best. Use that and heavy fiberglass cloth with epoxy to create the shape and size. I like the 17 oz bi-axial fiberglass cloth that you can buy 12" wide in a 50' roll. That is a manageable size and you will want several layers for strength.
Airex tends to be more flexible than some other types of boatbuilding foams. Which is good in most applications, however, in a rudder or skeg, rigidity is important.

When I mentioned epoxy saturated 3mm plywood, I meant exactly that. As with proper technique you can almost completely permeate such a thickness with epoxy resin. And there are some tricks to help ensure this. But that way rot's not much of a concern.
Also, the plywood as I described in the sequence of construction is there to act as a form over which to laminate your structural glass. Though it does contribute to the structure too.

Triaxial cloth may be better than biaxial, as it has a much greater percentage of it's structural fibers oriented in one direction. And it would thus be easier to align them with the primary stresses on a skeg or rudder when building it.
With the primary axis of the cloth being vertical, & the +/- 45 degree fibers oriented from 1:30 to 7:30 o'clock, & 10:30 to 4:30 o'clock, respectively

The resin has little strength by itself. With fiberglass cloth and matt it is strong. You can also make a paste that has good strength but is better used for fairing the final product or filling where fiberglass cannot cover.

Yes, "paste", AKA bog tends to be better as a structural filler, or for fairing, than for actually building stessed structures like rudders, or skegs.

Also, on transom hung rudders. There are RTW racing boats of significant size which have them, so they're totally viable when done correctly. The biggest issue with your boat would be finding one with the proper degree of counterbalance, so that the steering has the proper amount of helm. Specifically, a tiny bit of weather helm when the rig & sails are properly tuned & trimmed.

Fitting pintles & gudgeons is relatively easy, though yes, they tend to be somewhat highly loaded fittings, & thus require proper reinforcements in the vicinity of their mountings.

[spotfire]

I'm replacing my rudder on my 32. Couple of items worth considering that helped me that might be useful for you.

If your an engineer, or experienced boat builder, you can determine the best design and foil shape for your boat

If your not comfortable doing this, you will find that getting the designers blueprints very useful for specing out an equivelent design
In.my case the designer had specs for the existng skeg and spade ruďder design.

You also will find several companies here who fabricate new replacement blades for production boats like yours.
I have fiberglas experience, and after sizing up the project determined one well known company could build a new rudder cheaper than me. I hope to splash next week.

Either way, engineering is importtant .

Good luck