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Old 14-12-2012, 02:36   #1
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Fin Keel Strength ?

Hi all,
Relatively new sailor here, don't beat me up too bad , have been looking at getting a boat, both my wife and I and our son have been taking lessons, and loving it!
One of the boats we looked at (34') had a lead fin keel bolted to the cold molded hull. Just seems to me that provides a long "arm" for flexing, leading to problems with leaking, and bolt stressing, as opposed to a full keel with lead poured in for ballast.
Or am I just looking for problems that don't exist?

Thanx, Paul
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Old 14-12-2012, 02:57   #2
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Re: Fin keel strength?

Paul hi and welcome. Tens of thousands of yachts sailing around Europe with fin keels and very few have problems. Indeed if you visit any of the big us and European boat shows I think you will struggle to find a long keeled yacht, they just aren't made anymore. I didn't see a single long keeled yacht at the Southampton Boat Show this year.

There is a You tube video of a nordic manufacturered yacht (whose name escapes me at the moment) being repeatedly driven into a rock at about 4 knots. It survives with some minor scratches, quite impressive for an ordinary 30 ft yacht.

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Old 14-12-2012, 03:10   #3
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Re: Fin keel strength?

Some of us have two keels btw, so that is twice the risk at sea but damned useful when you want to dry out without needing a crane and a boat yard.

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Old 14-12-2012, 03:15   #4
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pirate Re: Fin keel strength?

Hi Gypsy... Welcome to CF
Don't stress to much about the keels... though I must confess the encapsulated keel does hold my affections quite strongly...
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Old 14-12-2012, 03:37   #5
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Re: Fin keel strength?







All standard production boats

then some dont even need the keel !!

CHARTER BOAT LOSES KEEL: And No One Noticed
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Old 14-12-2012, 05:13   #6
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Re: Fin keel strength?

Greetings and welcome aboard the CF, Paul.
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Old 14-12-2012, 06:08   #7
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Re: Fin Keel Strength ?

Quote:
Originally Posted by Gypsynurse View Post
Hi all,
Relatively new sailor here, don't beat me up too bad ,

almost like you know us already


Or am I just looking for problems that don't exist?

It exists, but isn't something to prevent you from getting a fin keel boat. Most sailboats out there are bolted on keels.
enjoy your learning curve
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Old 14-12-2012, 06:36   #8
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Re: Fin Keel Strength ?

In the case of fin keels with bolts my preference is for a heavy fiberglass stub molded into the hull to wich the keel bolts can be bolted, but lots of boats this days have full lenght keels bolted flush to a much smaller stub or none at all .

In this case you have this large lateral plane surface and only a relative small surface to bolt on, this is going to generate plenty of stress even without being subjected to a collision or grounding, there is 2 methods mostly to attaching keels with bolts, one is to place the bolts in line and generally the bolts are pretty hefty and the other is to bolt side by side with smaller diameter bolts, in any case look inside and see if the bolts are flush with the hull or bolts are attached to any frame or vertical bilge suport, the later is better to spreads loads evenly...


The other scenario is a heavy fiberglass hull filled with lead or cement , here no worrys about bolts or joints, both types are fine if are designed and build it to last....
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Old 14-12-2012, 07:15   #9
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Re: Fin Keel Strength ?

An excellent article by Jeremy R. Hood
ITS HOW WELL ITS DONE THAT REALLY COUNTS

It's how well it's done that really counts

Another from Richard Jordan
Keel Construction External Bolt-on, Internal Encapsulated Ballast, Fiberglass Stub

Keel Construction – External Bolt-on, Internal Encapsulated Ballast, Fiberglass Stub - Waves Jordan Yacht Brokerage
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Old 14-12-2012, 07:45   #10
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Re: Fin Keel Strength ?

Good articles, but i doubt is more easy to fix a fin bolted keel than a integral keel, if the keel is attached to a stub there is more chances in case of a tough collision to leave the hull intact, without the stub the hull take a big load , and by chance this particular impact is normally at the aft trail edge , keel pushing the hull upwards and breaking the interior suport members , here the repair is a expensive one, surgery inside , outside, lift the mast out, block the boat hig , drop keel, lots of grinding , epoxy , bolts, sometimes destroying cabin sole and furniture around, no doubt that lead can absorb the impact in a grounding very well , but just in case of a sweet grounding, tough collisions end in a more complex way to repair the damage.

In a internal ballast keel the repair is a $$$ to, but here you are dealing with glass and grinding work, no bolts , or droping keels, or droping mast to ground..

My keel is made of 2 inch solid fiberglass laminated filled with 3000 pounds of concret in the bottom of the keel at the 4,11 draft level, the concrete is later covered with one inch of fiberglass resulting in a fiberglass second bottom, after two lead castings with a weight of 8900 pounds shall then fiberglassed in top of the second concrete bottom and hull appendages, looks like a hell of a keel, hard to break....

I like the way Nauticats bolt their keels , big heavy and strong stub, or swans as a example , other older designs with full keels also have the ballast bolted to the long stub, in my opinion the deal is the stub....

Cheers...
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Old 14-12-2012, 10:03   #11
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Re: Fin Keel Strength ?

If I was a boat designer I would bolt the keel on, but just putting bolts through the layup creates pretty high localized stresses. I would put a metal flange between the hull and the keel and a larger metal backing plate inside the hull.
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Old 14-12-2012, 23:31   #12
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Re: Fin Keel Strength ?

Paul,

As you can see the conventional wisdom is that fin keels aren't a problem. Like everything in boat design keel type is a trade off between different important characteristics. In this case, a fin keel trades a little maximum safety for a whole lot of sailing performance.

In reality keels and the attachment systems are very well understood, and unless you are looking at a truly radical boat the likelihood of sustaining any damage, even from a hard grounding at speed is very slim. These systems are engineered to take the expected loads, even from a grounding.
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Old 15-12-2012, 02:00   #13
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Re: Fin Keel Strength ?

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Originally Posted by Stumble View Post
Paul,

As you can see the conventional wisdom is that fin keels aren't a problem. Like everything in boat design keel type is a trade off between different important characteristics. In this case, a fin keel trades a little maximum safety for a whole lot of sailing performance.

In reality keels and the attachment systems are very well understood, and unless you are looking at a truly radical boat the likelihood of sustaining any damage, even from a hard grounding at speed is very slim. These systems are engineered to take the expected loads, even from a grounding.
I felt so much safer after I read your post. Then I read this...

Keel failures prompt call for oversight
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Old 15-12-2012, 02:18   #14
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Re: Fin Keel Strength ?

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Originally Posted by Gypsynurse View Post
(...) a lead fin keel bolted to the cold molded hull. Just seems to me that provides a long "arm" for flexing, leading to problems with leaking, and bolt stressing, as opposed to a full keel with lead poured in for ballast.(...)
The problem is real and whether or not it exists in this specific boat is up to her design and build.

If in doubt, steer towards designs that give you peace of mind.

b.
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Old 15-12-2012, 03:27   #15
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Re: Fin keel strength?

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Some of us have two keels btw, so that is twice the risk at sea but damned useful when you want to dry out without needing a crane and a boat yard.
And some of those boats "ground" twice a day. So the keels must be up to it...
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