Albin 27 Skeg replacement

[PonusNick]

Would appreciate any counsel from fellow members on replacing the original skeg on my 1985 Sport. Thoughts on material? Drawings? Any help at all. Thanks, Nick

[motthediesel]

Funny you should post this today, I just glued up a new core for mine.



That's made from two pieces of 3/4" PVC lumber from Lowes. They were glued together with clear PVC plumbing cement. Now I will cover them with glass cloth in epoxy resin to bring the thickness up from 1-1/2" to 1-3/4" to match the old chunk of oak it will replace. The original SS lower rudder bearing bracket was made to accept a strut of that thickness.

You will note that I bullnosed all the edges with a router, that makes it much easier to get the cloth to adhere around the corners. I also used the old part as a drill guide to bore the holes, and then I counter-bored with a forstner bit to accept the new bolt heads and washers. I plan to glass them in when I cover it.

I'm also converting the rudder to a "Schilling" or "thistle" style while I'm at it, I'll start another thread about that when I get a little further along. I just can't leave well-enough alone

Tom

[Bob Noodat]

I don't want to be a harbinger of doom, or a wet rag, but I must say I would have some reservations about using PVC "lumber" in place of wood. If it is the same as the PVC from Home Depot that I have used on a number of projects, there is little structural strength in it, save for a degree of incompressibility.

Wood, and especially a structural hardwood like oak, has densely layered strands of cellulose running in the same direction, bound together by organic cements. This structure causes it to resist bending and to return elastically to its original shape if sufficient force is applied to bend it. On the other hand, PVC, which in this case I would call a decorative trim to be applied to a structural material, and not a structural material itself, is merely a, well, it is a plastic ! By definition a plastic is something that can be bent or deformed by steady pressure, or even pressed into a mould. It has no specific orientation of molecules to cause it to retain its shape or to resist pressure.

Unless your PVC lumber is sold as a structural, as opposed to a decorative, material, I would have strong reservations about using it to form a skeg.

I am always happy to be corrected if I am making unwarranted assumptions, since we all know what "ass-u-me" does.

The other assumption I am making is that we are talking about something very like this:

00Q0Q_gQjWznDYu21_1200x900.jpg

Which is going to have to resist lateral bending, torsion, and occasional violent impact from different directions. Quite a hard life in fact.

[motthediesel]

Don’t get me wrong, the PVC is just a core, and as such it’s way stronger than the foam which I might otherwise have used for the purpose. The strength will come from the biaxial cloth in epoxy resin layup all around the piece.

The advantage to using the PVC is that it has enough compressive strength to resist the through bolts. If I had used even dense structural foam I would have had to sleeve the bolt holes to prevent crushing.

[motthediesel]

Interesting picture by the way — that boat has a sheet metal rudder. Ours has the same oak strut as seen there, but our rudder is molded fiberglass.

Amazing how many variations there are in these boats!

[Bob Noodat]

Interesting picture by the way — that boat has a sheet metal rudder. Ours has the same oak strut as seen there, but our rudder is molded fiberglass.

Amazing how many variations there are in these boats!

Why not use oak? Cover it in cloth.


That picture is from an A27FC that is on Kreygslist in the Florida Keys right now.

[PonusNick]

Thanks for the feedback...

Like Motthediesel, my boat also has a fiberglass rudder.

Talk at my boat club (like most clubs, everyone is an expert) rings the same as this stream with some into engineered plastics and others pointing to oak.

One member has proposed steel...thinner than the original...probably 3/4...with a fabricated backing plate at each end to get it to the original thickness.

Nick

[nebulatech]

Nobody asked my opinion BUT...

PonusNick, you're going to add biaxial glass to change the thickness from 1.5" to 1.75" or .25" total. Things being equal, you would be adding fiberglass totaling .125" (1/8") to the top, bottom and sides. .125" isn't very thick, do you anticipate that being two layers of glass? I like the idea of using a polymer instead of oak, especially with the number of holes drilled in the work piece. Increasing the layers of glass would be ideal, especially if you will be sanding/fairing the outermost layer. If you were to plane down the side of your work piece which doesn't have the countersunk holes, say an extra .25", you would be able to add twice the amount of glass.

I would imagine the greatest concern would be a grounding, given this is the lowest point in the keel. A grounding will put exactly the type of stress Bob Noodat is concerned about on the skeg. Again, I like your plan. I wonder if some (stainless?) steel flat bar could be incorporated inside to reinforce it? The graphic below illustrates my thought, where the grey bits are .5" x .25" flat bar (although that's probably not a realistic size now that I think about it). A .25" wide channel can be cut using just two passes on the table saw as most blades are .125" thick, no need to set up a router guide or dado blade. That PVC cuts easily, the only danger is melting it if you go too slow. It will gum up the saw blade though. I have an old one I've kept just for PVC. Choosing where to run the flat bar to avoid lining up with your mounting holes would be another concern

a27-skeg.jpg

As an aside, one material not mentioned is starboard. I'm not sure it's density, bendability, etc. or how that compares to the PVC. I always thought of starboard as the same stuff cutting boards were made of. I'm sure I'm wrong on that. I got such a notion in my head long ago while I was still young and dumb.

[WillieC]

Bob Noodat,

The "C" word. Our founder here at AOG has respectfully asked us not to use that word. I do not know the backstory, nor do I feel a great need to, but out of respect for his wishes I try to honor that. Through interweb magic, use of that word results in the altered spelling.

You will not be given detention or have to give up your offspring, just reminded from time to time. He is pretty low key about it, which I also respect.

Carry on!

PS. I am not now nor have ever been a member of the AOG staff. Now about that skeg...

[tego]

The metal rudder is actually a cast bronze unit manufactured by" Edson", and was used on all the later model 27's. I think I'd use a piece of stainless channel if my shoe ever breaks. If you want to use fiberglass over plastic, I'd make sure your f'glass is at least 1/4" thick. You can shave your core down accordingly. Ben

[Bob Noodat]

Bob Noodat,

The "C" word. Our founder here at AOG has respectfully asked us not to use that word. I do not know the backstory, nor do I feel a great need to, but out of respect for his wishes I try to honor that. Through interweb magic, use of that word results in the altered spelling.

You will not be given detention or have to give up your offspring, just reminded from time to time. He is pretty low key about it, which I also respect.

Carry on!

PS. I am not now nor have ever been a member of the AOG staff. Now about that skeg...

Thanks Willie. The British have a saying: "Nod's as good as a wink". No, never understood it myself, but it means Message Understood.

[Bob Noodat]

I just do not think that plastic without high fibre content will last past its first real stress or impact. If you want to get a really strong structure, why not line a suitable size and shape mould with your cloth, get a stack of old fishing rods and/or whip antennae, cut to length and remove metal hardware, pack them into the mould adding resin as you place them, top up with resin to fill the mould within 0.25" of the surface and use cloth to finish it. Now THAT ain't gonna break, and it'll go back to shape if bent.

I have just remembered. In our sheep farming days we would use fibreglass fence posts, round, white, about 40" long and diameter of blackboard chalk, for supporting temporary electric fence. They were dense fibreglass, and inexpensive, available from feed stores in farm country. They would be ideal.

[motthediesel]

Well, jeepers, I think I have a pretty good understanding of composite sandwich structures. The whole point is that the strength comes from separating the stressed skins with the core. Just as the strength of an I beam comes from the separation of the top and bottom plates by the web.

Adding steel or fiberglass rods into center of the core would add little to the stiffness of the beam. Stiffness comes from the balance of the compression/tension forces of opposing skins. It’s all about the skins.

Two 1/8” skins of good MAS bi-axial cloth, well rolled and saturated with epoxy resin separated by 1-1/2” solid core will be very strong. In fact, maybe I’ll see if I can come up with some kind of fixture to test for stiffness compared to the oak original. A true test would be to destruction, but I don’t think I want to go quite that far.

[Bob Noodat]

Well, jeepers, I think I have a pretty good understanding of composite sandwich structures. The whole point is that the strength comes from separating the stressed skins with the core. Just as the strength of an I beam comes from the separation of the top and bottom plates by the web.

Adding steel or fiberglass rods into center of the core would add little to the stiffness of the beam. Stiffness comes from the balance of the compression/tension forces of opposing skins. It’s all about the skins.

Two 1/8” skins of good MAS bi-axial cloth, well rolled and saturated with epoxy resin separated by 1-1/2” solid core will be very strong. In fact, maybe I’ll see if I can come up with some kind of fixture to test for stiffness compared to the oak original. A true test would be to destruction, but I don’t think I want to go quite that far.

If you had enough of a thickness of fiberglass. But.

If you have a choice for your core of, on the one hand a material of limited incompressibility and no resistance to torsion or flexure (the PVC) and on the other hand a fibrous material with similar incompressibility plus the added resistance (a straight grained hardwood or oriented glass fibres for instance) why would you use anything but the latter?

I can break a PVC plank over my knee. No I couldn't if it were sheathed in 1/8" fibreglass. But English oak at least would break my knee sheathed or not. Of course maybe American oak is not up to snuff.....

I doubt that we shall alter each other's mind. And, it is after all your skeg. I look forward to your report on its progress. The greatest success an innovator can have is to prove the poo-pooers wrong!

Test: I think a simple deflection test would be instructive. I enjoy materials tests!

[Bob Noodat]

Two links:

https://www.jlconline.com/how-to/framin ... pvc-trim_o
https://www.builderonline.com/design/in ... problems_o
( sorry, I messed up that 2nd link)

I am assuming that we are talking about this product, varieties of which I have used (even on a boat, as spacers and stops). I see I was wrong about PVC and wood being similarly incompressible.