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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Converting the C25 fin keel into a bulb keel?

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Mel Parsons
Deckhand

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14 Posts

Initially Posted - 06/15/2008 : 13:28:00

I've read a lot about the different keels on the C25 on this forum and the advantages of each. I currently have a swing on a trailer, but would really like to have a shallow draft fixed keel for future Keys and Bahama trips. I'm aware that there is a retrofit wing for the swing, but it is expensive. One thing that I've never seen discussed here is converting the lead fin keel to a bulb keel. My question is, has anyone ever just cut a foot or so off their fin, melted down and recast the cut off portion into two half bulbs, thru bolted them back on, faired, sealed, epoxied and painted the whole thing to convert the fin to a 3' draft bulb keel. As an alternative to casting your own, maybe purchasing the two half bulbs and doing the same thing. Either way, it seems like it would be much easier and cheaper than doing the full wing conversion. What am I missing?

89 C25, #5876, SR/WK Diesel

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Steve Milby
Past Commodore

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USA
5902 Posts

Response Posted - 06/16/2008 : 08:18:38

You would destroy any value or marketability that the boat has. Nobody would want to buy a home designed, re-fabricated keel with workmanship of an undetermined quality, that has unknown sailing characteristics and is not class legal, not to mention the amount of work and materials involved. It would make more sense to sell this boat and buy one that better meets your needs.

Edited by - on

stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 06/16/2008 : 10:00:39

are you asking about making this conversion to a fin keel or to your swing keel?

I think a conversion of this type can be done. If a swing can be converted to a wing, why not a bulb!?
My understanding of this kind of experimentation is that you proceed with the expectation that your new creation may end up on the bottom and become a libility or simply a total loss.

Sounds like a big undertaking. How would you melt down a keel, or cut off part and melt it down?

Edited by - on

tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 06/16/2008 : 10:47:32

Mel,

I've converted my swing to a wing with the Catalina retrofit KIT. While it was expensive it solved all the headaches that the swing had going for me. Never regretted it for a moment.

The thought of doing as you are thinking of doing is mind boggling to me. Read all the other replies carefully. Steve Milby especially hit all the cognizant areas to be considered.

Val on Calista # 3936, Patchogue, N.Y.

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andy
Navigator

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USA
228 Posts

Response Posted - 06/16/2008 : 11:00:51

the fastest, best sailing C25 is the fin keel (TR) version. I can't imagine taking the chance of destroying it. The wing is the way to go if you need shoal draft. I love my wing.

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skrenz
Captain

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USA
351 Posts

Response Posted - 06/16/2008 : 11:04:28

Its not just weight that makes a keel do its thing. Its also square footage of the side face in the water and hopefully wing shape. The keel provides lateral resistance and its this resistance that allows you to tack into the wind. If the keel has a wing shape profile, that resistance is increased by lift just as an airplane wing provides lift enough to bear up the weight of the plane. If you were to do the modification your describe, you may maintain the weight aspect of a keel and gain a shallower draft. But you would really mess up the lateral resistance aspect that the keel provides.

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Stardog
Captain

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USA
319 Posts

Response Posted - 06/16/2008 : 12:09:32

I would mention also that the righting moment provided by the amount of lead relocated would change due to the length of the lever arm (read fin). To get the same righting moment you would need to increase the amount of lead. You would have to do some math to determine the amount of extra weight required. I've made bulb keels on a small scale, for 1-meter radio control yachts, I would not want to be doing it on a large scale, molten lead is poisonous and very dangerous, sort of like lava. It would take a lot of heat to make your bulb, you would probably want to get a foundry to do this part of the work. I'm not trying to be discouraging, just objective. I'm all for innovation and I want to see the results if you do it.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 06/16/2008 : 18:07:14

Also be aware that the lead fin keel is not solid lead, as the cast iron keel is solid iron. The lead version, because of the greater density of lead, has a thick casing over the lead casting--on the order of an inch thick where I've seen it damaged, and made of something that looks like asbestos furnace insulation. (Maybe somebody else knows what it is.) I presume that's to keep the same overall shape and weight as the earlier iron keel.

Also, wing keels are designed with a greater proportion of their weight lower in the keel than fins, to make up for the reduced lever arm. That's how the C-25 wing gets away with being lighter than the fin, without making the boat all that much more tender. Your plan would not accomplish that--it would just move some of the weight higher. The wing also compensates for the loss of lateral resistance of a shorter keel under heel by adding perpendicular surface that provides more lateral resistance the more the boat heels. As the keel trunk becomes more horizontal, the wing becomes more vertical. Bulbs don't help much that way.

Edited by - on

quilombo
Captain

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USA
301 Posts

Response Posted - 06/16/2008 : 20:11:57

I think It might be easier to buy a new boat, sounds like alot of trouble ,,
just a thought

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GaryB
Master Marine Consultant

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USA
4304 Posts

Response Posted - 06/16/2008 : 22:18:04

Can a wing keel be converted to a fin keel and vice versa? Just curious. If I ever have a chance to move to an area that has deeper water than I currently sail in I might be interested in switching to a fin keel. Would it just be a matter of unbolting the wing keel and bolting up the fin keel?

Edited by - GaryB on 06/16/2008 22:18:30

Stardog
Captain

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USA
319 Posts

Response Posted - 06/17/2008 : 11:55:13

Switching out the keels might be interesting, but you would have to do some fairing and painting each time you switched.

I've always thought it would be fun to put a bulb or wings on the bottom of the existing fin keel. That could create a much greater righting moment so the boat would stand more vertically and move faster. But then again, I don't know if the hull/keel joint would stand the increased loads. Sometimes fun ideas are not necessarily good ideas.

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millermg
Navigator

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159 Posts

Response Posted - 06/17/2008 : 18:10:57

<blockquote id="quote">quote:<hr height="1" noshade id="quote">I presume that's to keep the same overall shape and weight as the earlier iron keel.
<hr height="1" noshade id="quote"></blockquote id="quote">

I guess I was under the impression fin and wing C-25 keels had always been made of lead- were the early C-25 fins made of cast iron? If so, what year was the switch made?

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 06/17/2008 : 22:21:48

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by millermg
 <blockquote id="quote">quote:<hr height="1" noshade id="quote">I presume that's to keep the same overall shape and weight as the earlier iron keel.
<hr height="1" noshade id="quote"></blockquote id="quote">...what year was the switch made?<hr height="1" noshade id="quote"></blockquote id="quote">Maybe 1983.

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Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 06/18/2008 : 06:12:16

We had a guy in our club who couldn't get a slip with enough draught for his Pearson Flyer. He fixed the problem by taking a chainsaw to his keel. Yes, a chainsaw. After much work, he cut about a foot off the bottom of his keel.

The boat sailed terribly after the "mod". So much so that he went back a year later and bolted the foot of keel back on. This year his chainsaw came out again and he took a 3 foot section out of his hull for a real repair to some soggy fibreglass.

I think that if you alter your keel, two things will happen. You will lose pointing ability, and speed, and handling will change. I also think you will wish you hadn't done it. The bolt on retrofit compensated for loss of depth in the keel by going to a low aspect ratio, where the fin has a high aspect ratio. both give (more or less) enough lift to keep one design similar to the other. By slicing off a section of th ehigh aspect ratio keel, you will not get the chord length needed to get the proper low aspect ratio control (someone else chime in here to explain lift and aspect ratios, please!)

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Stardog
Captain

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USA
319 Posts

Response Posted - 06/18/2008 : 08:58:47

I'm not an expert in wings, so I hope this explanation will suffice. In simple terms a keel is a wing flying through the water. A low aspect wing, or keel, is shorter in length and has a greater distance from the leading edge to the trailing edge; it appears more stubby. It generates less lift, hence it gives more leeway. A high aspect wing is longer, it generates more lift therefore less leeway, so in sailing terms it points higher. A C25 fin keel is really not high aspect, it's somewhere between low and high. If you want to see a high aspect ration fin, look up America's Cup yachts.

I think it's important to mention righting moment also, though it is a separate component. It depends entirely on the weight of the keel and the distribution of the weight along its length. The more weight in the wing and especially toward the end of the wing, the more righting moment. Righting moment matters because it keeps the wing deeper in the water and the sails higher into the wind. The deeper your wing is in the water, the greater the lift and the same goes for your sails in the air.

Here is an in-depth analysis for those interested in fin design:
http://www.onemetre.net/Design/FinArea/FinArea.htm

Edited by - on

Patrice C25
1st Mate

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78 Posts

Response Posted - 06/18/2008 : 09:05:15

Hi,
you might want to check with a company named Marskeel, there in Burlington, Ontario. http://www.marskeel.com/
They do bulb casting, once you have cut the part you want, you ship it to them, they use it for the casting plusss some more material that they will need to add, as mentioned above, the bulb will require to be eavier than the part cut for momentum.
They have the expertise for that kind of project.
A good project in view....

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 06/18/2008 : 09:20:57

Remember that while a boat like the C-25 is "drawn" by a guy like Frank Butler, a naval architect will be involved in tuning the design to get the boat to (1) float right, (2) sail right, and (3) right (without filling with water and sinking). We can adjust the sails, but messing with the architecture is not for amateurs.

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Stardog
Captain

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USA
319 Posts

Response Posted - 06/18/2008 : 11:03:52

Something I failed to mention about changing the aspect ratio of your fin; you're going to lose significant performance up-wind, due to loss of the end of your wing. Most shoal-draft boats are designed with a keel that extends further forward and aft. These boats are generally referred to as "full keel" and have different characteristics; they don't have the lift of a fin keel, but they go in a very straight line and are easy to handle. On the down-side they turn very slowly and are hard to handle in close quarters.

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stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 06/19/2008 : 20:51:04

http://m244.ca/index.html

The new Martin 24' trailerable with bulb keel. Your $40,000 solution.

reviewed in Trailer Sailer and Pacific Northwest Sailor. This boat will be in charter fleets in the Pacific NW this summer.

this is taken from their web site - so if you want to make this mod, maybe these guys would be able to definitively answer the question.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Last time Forbes and Don collaborated, they produced the ultra-successful Catalina 27 under license by Catalina YachtsTM.
<hr height="1" noshade id="quote"></blockquote id="quote">

Edited by - stampeder on 06/19/2008 20:55:18

Mel Parsons
Deckhand

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14 Posts

Response Posted - 06/19/2008 : 21:39:08

You know, I haven't visited many other owner's forums, but this has got to be the best sailboat owner's forum out there. I really appreciate all of the input. I guess I got inspired by all of the boatbuilder magazines that I have laying around. I read an article awhile back about a guy with a larger boat that did just like the guy you mentioned - took a chainsaw to his keel and ordered the new bulb castings from Marskeel - apparently with pretty good results. I was bidding on C25 listed as a wing, but apparently was actually a fin - so I started thinking about my options - I didn't win the bid. The keel being encapsulated in at least an inch casing would have been a huge deterrent - good info. Not sure what I'll do yet, but reading about the Bahama's cruises in the Cruising Forum has given me the bug! I may go with the wing conversion. Actually, I'm going to look at a Bristol 26 tomorrow, but it's draft is 3'10", so I'd have to do some serious modifications to my trailer. If I had $40K to put into a boat, this wouldn't even be an issue! Actually, I think I would opt for the Hake/Seaward 26RK - http://www.seawardyachts.com/26rk.html?

Anyway, thanks again for all of the input - this is an incredible resource.

Mel

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