Skegs and structural integrity

[GILow]

Originally Posted by rslifkin

Just because a boat is uncommon or not well known doesn't make it a bad boat. It just requires a bit more due diligence to determine if it's worth buying.

For the record, Duncansons are a dime a dozen around here. Damn good boats. Fast, well finished.

A bit squeezy for my tastes but I’d be nervous of one behind me on an upwind leg, that’s for sure. They cut through chop like the proverbial knife through hot butter.

[GILow]

Originally Posted by Surfshack

Hi All,



Should a skeg be entirely rigid?



A Duncanson 37 I'm looking at is on the hard and has minor flex when pushing the base of the skeg laterally by hand, perhaps 5mm each way. Hard to tell if it is flexing down the length of the skeg or if the hull is flexing.



I've read an old thread on this forum discussing this issue, which prompted my testing the skeg in the first place.



https://www.cruisersforum.com/forums...hts-76328.html



Any and all opinions appreciated.



Thanks, B

Searles is the guy to listen to on this one.

I’ve worked on a handful, all different models. I’m currently helping a mate replace the standing rigging on his Duncanson 37. (Searles, Bliss is a 37, right?)

My limited experience of them tells me the flex is NOT normal and IS a reason to be worried.

That being said, the 37 is a nice little rocket to windward and the interior is superb. If you can find and fix the problem you’ll be rewarded with a very nice boat indeed.

[Surfshack]

Originally Posted by knot smart

Yes. The prop strut should be solid. Our boat beat on the dock and submerged in the slip. When the boatyard picked the boat up, the boat was apparently lifted with the strap under the prop shaft. When I pushed and pulled on the strut it flexed about 1/16in .. very slight.. but it bothered me. I consulted the boatyard and was advised to dismantle the aft cabinets and bed to see what's going on under there. Sure enough the fiberglass around the humb the strut is embedded in was damaged and delaminated. The solution was to drill many holes around the strut . The objective is to drill down to the void and not through the bottom of the boat. Then use the west marine two part epoxy in a caulk tube. Place the tip of the tube in each hole and keep pumping until the epoxy fills the voids and squirts out of the other holes.. when it cured it was solid as a rock


https://www.walmart.com/ip/610-Resin...tems/938095065

Then grind and glass over the cracks around the hump and you're good.

That seems like a reasonable approach for the skeg, maybe in addition to exterior glassing (after excluding other causes). There didn't seem to be any damage/cracks visible so may just be insufficient layup as originally advised.




Great to hear everyone's experiences and thoughts.

The to-do list is long and the issues, of unknown size... but I'm not too surprised at that part

All this talk of the two halves, there is a visible join line crack (~1mm open at worst part) down the aft centreline above-water section of the skeg (quite far separated from the long flexing part of the skeg). It's the same arrangement as the photo posted earlier (thanks for finding that ). So that may be a big part of this too. If that is a crack separating two halves of the skeg apparatus, what are the options? Would I need to start studying Minaret's work?

[Nicholson58]

Originally Posted by Surfshack

Hi All,

Should a skeg be entirely rigid?

A Duncanson 37 I'm looking at is on the hard and has minor flex when pushing the base of the skeg laterally by hand, perhaps 5mm each way. Hard to tell if it is flexing down the length of the skeg or if the hull is flexing.

I've read an old thread on this forum discussing this issue, which prompted my testing the skeg in the first place.

https://www.cruisersforum.com/forums...hts-76328.html



Any and all opinions appreciated.

Thanks, B

I highly recommend you find a competent surveyor to get an opinion.

Our 1984 ketch, modified full keel and skeg settles on the keel enough to be noticeable in the floors and cabinets fit. We are 58 feet, 40 tons.

My skeg is very solid. I would be concerned about a skeg you can move by hand. Possibilities include delamination in the hull.

[nofacey]

Skegs flex, just a question of how much. My wife couldn’t flex the skeg on our old boat….she weighs 100#. I could….

They are typically narrow blades widened with some sort of base fillet into the hull structure. It isn’t typically the blade portion that flexes, it’s the hull where it ties in.
5mm by hand is a tad high (are you using your hand or your shoulder?) I’d go inside the boat where the skeg ties in and look for interior structural reinforcing - frames & longitudinals in that immediate zone. Then have someone big bounce on the skeg while you’re inside and look/feel for hull flexing. There could be missing frames, broken bonds….or simply a weakness in the design that needs a bit of reinforcement. It would really help if you could check out 3 different boats of same model.

Everything flexes (ever watch the wing tips on jumbo jet as it takes off?) , it’s not the end of the world, just need to understand why.

[Cheechako]

Skegs vary a lot. If yours is a thin type as opposed to the broad one shown in post #12 then yes it will flex. Many skegs are hollow like the hull, fairly thin, others are filled with "stuff".

Fiberglass is a VERY flexible material and it gets rigidity from the shape, not the material. So a narrow thin skeg will flex for sure. It's a rudder support among other things and some rudders have no support at all, so I wouldn't fret, but would analyze what you think by looking at the rudder also, shaft size etc.

As mentioned, The Boeing 747 test wing was bent 34 feet when it broke in 1969. The wing test goes on for months flexing the wing in an apparatus 100's of thousands of times!