Skegs and structural integrity

[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/f47/duncanson-37-yachts-76328.html

Any and all opinions appreciated.

Thanks, B

[neilpride]

I would first investigate if it is add on skeg or a molded one.

[neilpride]

https://www.cruisersforum.com/forums...ir-175344.html

[RaymondR]

The function of a skeg is to protect and support the rudder and if you can flex it by hand it's probably not going to do a very good job of doing so.

[JPA Cate]

The Duncanson's have a known vulnerability to the boat pox. Maybe the skeg is weakened?

Fwiw, we've had 3 boats with skeg hung rudders, and none of them flexed at all to human pressure on them.


Ann

[Surfshack]

Wow, stellar work by Minaret there.

Very concerning then, the flex. Thanks everyone for your input.

I've used fibreglass a little and am pretty happy doing my homework. Would it be realistic to aim to sandblast then add layers over the skeg/surrounding hull as reinforcement?

[neilpride]

Without knowing the cause, it is difficult to give an opinion, it could be a factory defect, moisture, lack of fg laminate, poor workmanship, osmosis, etc...the skeg should be rock solid, no flex at all, if you can get rid of antifouling, gelcoat or anything else that prevents you from seeing the entire laminate, do a moisture test, look for cracks or anything suspicious and then take a decision to strengthen it.

[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.

[RaymondR]

Originally Posted by Surfshack

Wow, stellar work by Minaret there.

Very concerning then, the flex. Thanks everyone for your input.

I've used fibreglass a little and am pretty happy doing my homework. Would it be realistic to aim to sandblast then add layers over the skeg/surrounding hull as reinforcement?

The successful solution would appear to be dependent upon where the flwxing is occurring.

If the flexing is occurring because the skeg is bending then increasing the wall thickness by applying more glass fibre to stiffen it could fix the problem.

However, it the skeg is flexing because the stresses are not being resisted sufficiently where the skeg is attached to the hull then this would need to be remedied by increasing the structure which distributes the bending loads into the hull.

[Sailor Sailor]

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.
Any and all opinions appreciated.

Thanks, B

No such boat is shown on SailboatData.com. Why don't you buy a known brand and model from a reputable builder and respected designer?

[wholybee]

My boat (Morgan 382) the skeg flexes quite a bit and isn't considered a problem. I don't think it is accurate to say flex is a problem, but I think it depends on the boat. Robert Perry has written about skegs quite a bit. His opinion is that they are very difficult to engineer, and in most cases the rudder is supporting the skeg.

So, while it might be worth investigating, I don't know what is "normal" on the OP's boat. IMO, there might not be any issue at all.

[wrwakefield]

All of my larger boats (40-50ft) over the years have had skeg hung rudders. [2 Perry and 1 S&S hulls...]

All rudder skegs were very rigid (I would say as rigid as the solid lead keels) and all served as the lower pivot point for the rudder shaft.

I would be extremely concerned if I was able to flex the skeg by any means.

Flexing while steering underway would exert enormous leverage on the rudder's upper bearing and waterproof seal- I suspect leading to premature failure of those through-hull rudder components, if not diminished rudder travel speed or angle (due to increased friction) or even seizing of the steering system due to excess friction or a bent rudder shaft (if the shaft is too small for the displacement...)


This is just how I would approach your question if it were my vessel; everyone has their own risk tolerance.

FWIW

Cheers! Bill

PS: If you can move the skeg by hand, I would be suspicious that a grounding incident has occurred that involved the rudder and/or skeg.

PPS: I found this image of the skeg and rudder from a Duncanson 37 (in case your's is different...)

[Searles]

Believe it or not sailboatdata is not the beall and endall,Duncanson yachts were in there day one of the largest yacht and boat builders in the Southern Hemisphere,after the firm folded the moulds were hired around to amateur builders ,as usual some good some not so good,but no the rudder skeg should not flex, not the slightest bit ,the 37 was a split mould joined down the middle including the keel stub and the rudder skeg the lead keel with j bolts bolted on ,normally overbuilt by modern standards ⛵️⚓️

[rslifkin]

Originally Posted by Sailor Sailor

No such boat is shown on SailboatData.com. Why don't you buy a known brand and model from a reputable builder and respected designer?

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.

[GILow]

Originally Posted by Sailor Sailor

No such boat is shown on SailboatData.com. Why don't you buy a known brand and model from a reputable builder and respected designer?

Dear god, what a stupid remark.

There are literally thousands of boats not on Sailboatdata, and many of them are are of a pedigree that far exceeds some of the crap boats on that database.

Stop treating some arbitrary free web site as gospel.

(And, frankly, much of the data on that site is incorrect anyway.)