Why do Keels fall off and rudders fail?

[Cruiser2B]

Originally Posted by downunder

Plenty of other threads have debunked your ideas of a bluewater vessel. There are plenty of modern design expedition passagemakers (a better term developed on another similar thread) being built that aren't built the same as your BWB.

You have no need to try an justify your own preferences. Its OK. We are all different. No doubt you would make an argument that my choice of a catamaran is crazy.

Seems there are plenty of builders still selling these dangerous designs so it a matter of buyer beware but in the end it comes back to personal preferences and everyone is different.

Seems also plenty of evidence that crews break before vessels. Preparation is the other factor.

cheers

Not trying to justify anything. Never had a keel or rudder fall off. Seems as some posters have. I was wondering why it happened, was it design, material or operator error. thanks to all those who shared.

I haven't mentioned catamarans in any post because I don't like anything about them, nothing. They are eye sores, take up too much space, crazy expensive. I wouldn't take one out of the site of land personally. They are fast, luxurious, state of art and spacious...all great things for living aboard. They make for great looking ads in SAIL magazine. They are always at anchor ....with land in the background and many women in bikinis...good stuff. I am concerned about other things when going offshore.

[roland stockham]

I haven't mentioned catamarans in any post because I don't like anything about them, nothing. They are eye sores, take up too much space, crazy expensive. I wouldn't take one out of the site of land personally. They are fast, luxurious, state of art and spacious...all great things for living aboard. They make for great looking ads in SAIL magazine. They are always at anchor ....with land in the background and many women in bikinis...good stuff. I am concerned about other things when going offshore.[/QUOTE]

I am now going to unsubscribe from this thread as I don't want to witness the outrage and flaming that will follow this. Opinions are fine but does this show respect for the choices and opinions of others?

[jeepbluetj]

This is always such a fun subject.

Is there any accurate data as to the failure rate of rudders? Of Keels? No doubt it happens (there's photos of some) but at what rate? It's all just chatting at the bar unless we can find out that the overall failure rate of rudders is x%.


I've searched and I've never found a single account of a keel actually falling off a C30. Lots of horrific problems, catalina smile, crushed compression posts, corroded keel bolts, etc... But never one falling off. Out of 7500+ hulls made there should have been a few. (And nobody will ever say a C30 is a super-overbuilt boat...)

[Island Time O25]

Originally Posted by roland stockham

I am now going to unsubscribe from this thread as I don't want to witness the outrage and flaming that will follow this. Opinions are fine but does this show respect for the choices and opinions of others?

I don't see how voicing one's honest opinion (unless it is a deliberate flame) shows any disrespect? But then again in these PC times one must not call spade a spade but an agricultural manual implement.

BTW the racial understanding of the phrase in US came about in 1920s, 400 years after it was first recorded in the English language as a Renaissance mistranslation of Plutarch.

[Cadence]

Originally Posted by roland stockham

I haven't mentioned catamarans in any post because I don't like anything about them, nothing. They are eye sores, take up too much space, crazy expensive. I wouldn't take one out of the site of land personally. They are fast, luxurious, state of art and spacious...all great things for living aboard. They make for great looking ads in SAIL magazine. They are always at anchor ....with land in the background and many women in bikinis...good stuff. I am concerned about other things when going offshore.

I am now going to unsubscribe from this thread as I don't want to witness the outrage and flaming that will follow this. Opinions are fine but does this show respect for the choices and opinions of others?[/QUOTE]

Don't go away mad. I like tris. I could probably catch more **** for that. Everyone has an opinion. If I can't learn or discard an opinion I'll never learn squat

[Cruiser2B]

I am now going to unsubscribe from this thread as I don't want to witness the outrage and flaming that will follow this. Opinions are fine but does this show respect for the choices and opinions of others?

Don't leave, not necessary. honestly it's cold and snowy outside and we are just having a discussion. It's the internet, take everything you hear from me and just about everyone with a grain of salt. Sail whatever makes you happy. I look at this like a discussion around a bar or campfire...just having good time Shooting the bull. We are all not going to agree and thank goodness for that...our else we'd have almost no choice or variety in anything.

[Don C L]

Originally Posted by jeepbluetj

This is always such a fun subject.

Is there any accurate data as to the failure rate of rudders? Of Keels? No doubt it happens (there's photos of some) but at what rate? It's all just chatting at the bar unless we can find out that the overall failure rate of rudders is x%.


I've searched and I've never found a single account of a keel actually falling off a C30. Lots of horrific problems, catalina smile, crushed compression posts, corroded keel bolts, etc... But never one falling off. Out of 7500+ hulls made there should have been a few. (And nobody will ever say a C30 is a super-overbuilt boat...)

Naturally certain designs will have 0% failure rates for keel and rudder failures. Boats that are maximized for speed and lightness will be pushing their luck, and racers accept that. Often it seems it is not the whale or lost container but years and miles of relentless wobbling that will wear at the weak points, even if they were built pretty strong to begin with. I have not heard of Catalinas losing keels either, but I have heard of slow leaks from some bolt-on keels. Spade rudder failures happen at a much higher rate than skeg and keel hung rudders, that is a safe bet. The length of the spade rudder has a lot to do with it, and how often it is inspected. My long molded keel and keel-hung rudder have a lot of years behind them (50) and they pretty much look the same as the day they were made. Those are two fewer things I have to worry about, and my boat is fast enough for me.

[sardinebreath]

Originally Posted by Don C L

Naturally certain designs will have 0% failure rates for keel and rudder failures. Boats that are maximized for speed and lightness will be pushing their luck, and racers accept that. Often it seems it is not the whale or lost container but years and miles of relentless wobbling that will wear at the weak points, even if they were built pretty strong to begin with. I have not heard of Catalinas losing keels either, but I have heard of slow leaks from some bolt-on keels. Spade rudder failures happen at a much higher rate than skeg and keel hung rudders, that is a safe bet. The length of the spade rudder has a lot to do with it, and how often it is inspected. My long molded keel and keel-hung rudder have a lot of years behind them (50) and they pretty much look the same as the day they were made. Those are two fewer things I have to worry about, and my boat is fast enough for me.

Sometimes bad design isn't about pushing the performance envelope. The bolt-on keels where there really is no tenable way to replace the bolts when they corrode (and they will corrode), to me is an example of disposable boat design. I would put embedded chainplates in that category as well.

[Cadence]

Originally Posted by sardinebreath

Sometimes bad design isn't about pushing the performance envelope. The bolt-on keels where there really is no tenable way to replace the bolts when they corrode (and they will corrode), to me is an example of disposable boat design. I would put embedded chainplates in that category as well.

I believe you have it correct. Bolt on keels is new to me, Thank God.

[robert sailor]

Originally Posted by Cadence

I believe you have it correct. Bolt on keels is new to me, Thank God.

Bolt on keels have been around for the last 40-50 years and very few have failed. The way the better ones were built was with a substantial keel stub which was part of the hull. That also meant that you got a bilge that could hold more than a cup of water. Now a days on many boats they just bolt on the keel to a little flat spot, it works but lacks a real bilge and is not as strong although in almost all cases good enough. Some of the newer boats have to be watched very carefully, especially if it has been grounded, no matter how lightly.

[Cadence]

Originally Posted by robert sailor

Bolt on keels have been around for the last 40-50 years and very few have failed. The way the better ones were built was with a substantial keel stub which was part of the hull. That also meant that you got a bilge that could hold more than a cup of water. Now a days on many boats they just bolt on the keel to a little flat spot, it works but lacks a real bilge and is not as strong although in almost all cases good enough. Some of the newer boats have to be watched very carefully, especially if it has been grounded, no matter how lightly.

Got you. Bolt on keels where prominent with wood boats. Seems they where an economic factor with glass hulls.

[robert sailor]

Originally Posted by Cadence

Got you. Bolt on keels where prominent with wood boats. Seems they where an economic factor with glass hulls.

I don't think it was economics back n the day. With a full keel boat you have a lot of wetted surface and drag so when the designers tried to get more speed and higher pointing out of racing sailboats they knew they needed a deep draft and thinner profile on the keel. The thinner you can make the interface between the keel and hull the higher and faster you will go, its called end plate effect. So now we have really thin/narrow keels that are bolted to a flat section of the hull. Because the area is very narrow where the keel bolts on there is a very high force on this joint. So far the boats seem to hang together but unlike the old days where you could bounce off rocks with a fin keel boat and not worry about it because they were very strong...these days even a very light grounding is reason for concern because they are engineered so tightly that there may not be room to bounce off anything without a very careful check after pulling the boat. Todays boats do have better performance than yesterdays boats and are often more fun to sail but some of them do not have the tolerance when bouncing off bottoms.

[builder dan]

Wooden yacht sunk in our marina last year keel bolts rusted off and lead fell off.Lucky the owner never took her out.

[Cadence]

Originally Posted by robert sailor

I don't think it was economics back n the day. With a full keel boat you have a lot of wetted surface and drag so when the designers tried to get more speed and higher pointing out of racing sailboats they knew they needed a deep draft and thinner profile on the keel. The thinner you can make the interface between the keel and hull the higher and faster you will go, its called end plate effect. So now we have really thin/narrow keels that are bolted to a flat section of the hull. Because the area is very narrow where the keel bolts on there is a very high force on this joint. So far the boats seem to hang together but unlike the old days where you could bounce off rocks with a fin keel boat and not worry about it because they were very strong...these days even a very light grounding is reason for concern because they are engineered so tightly that there may not be room to bounce off anything without a very careful check after pulling the boat. Todays boats do have better performance than yesterdays boats and are often more fun to sail but some of them do not have the tolerance when bouncing off bottoms.

Got it, good point. I don't seem to think in high performance monos. I think of sailing as a pleasure not a contest but to each his own.

[Ericson38]

Originally Posted by Hydra

The analogy with a ground vehicle is valid: a "normal" car should be able to cross a bad patch of road. But you don't expect it to go full speed off-road, which is equivalent to sailing in a storm.

It is very difficult for a naval architect to estimate the forces acting on a keel or a rudder in *very* bad weather. Then, the normal solution is to include a *big* margin (for example 500%). But this is costly and heavy. The real market for these sturdy, heavy and expensive yachts is narrow.

The other phenomenon is the meeting of a slight design error, a small manufacturing error, a lapse in quality control and severe conditions.

Alain

Here is a site with a good seat of the pants spade rudder force calculation-

OYRA EMERGENCY EQUIPMENT AND PROCEDURES SEMINAR

Based on this, and consistent with-

http://www.theijes.com/papers/v3-i1/.../A03130109.pdf

if you assume a worse case 10 knot condition, with a higher than normal C lift of 3.0, with a rudder of 4 foot length and 2 foot span, with a total rudder working area of 8 sq feet, the rudder side force is 6800 lbs, and the bending moment at the lower rudder bearing is 13,600 lbs.

Back it off to a 5 knot condition with a rudder CLift of 1.0 (normal), the loads are 567 side force and 1367 total bending moment at the lower bearing.

Falling off a wave or surfing to 12 kts, with a momentary surge lift of 3.0 (more like a design margin) and temporary loads can reach 10,000 lbs side force and 20,000 lbs bending moment at the lower bearing, which is being applied to the post as it enters the lower bearing.