keel fin

Corrosion, Paint, Through Hulls, etc.
Butchel
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keel fin

Postby Butchel » Mon Dec 26, 2016 7:35 am

My 39' FB sedan has a thin, tapered fin stitch welded to the bottom of the hull on the center line. It is about 8' long and 8" deep at the stern. During transport from Maryland to Texas, some of the welds broke and it is hanging loose. The boatyard manager says it is an add-on and not factory original, thinks someone was trying to improve maneuverability and recommends removing it. Does anyone out there know its purpose, if it is necessary or desirable?

javalin390
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Re: keel fin

Postby javalin390 » Mon Dec 26, 2016 1:44 pm

Uh, that's part of the boat, not some useless add on. That is where your keel anodes bolt to. If I'm correct there should be a bunch of 1/4" bolt holes in it for the anodes. This will definitely need TIG weld back on before sticking it back in the water, AND put some new anodes back on it (especially if she is going into salt water) Can you post a picture of this?
Jim Elias
1974 37' SedanFlybridge
Twin 360 Chryslers.
Marblehead, Ohio

javalin390
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Re: keel fin

Postby javalin390 » Mon Dec 26, 2016 1:46 pm

By the way, glad you got her down there ok. Did you find a buyer for the flybridge top?
Jim Elias
1974 37' SedanFlybridge
Twin 360 Chryslers.
Marblehead, Ohio

jralbert
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Re: keel fin

Postby jralbert » Mon Dec 26, 2016 5:11 pm

Picture, please and we can clear this up in a flash. But from your desciption, it sounds like it sure is a part of the boat. I am attaching a photo of my former '32 showing the last few feet of the "fin" (a keel stabilizer integral to Marinettes) when I was having the bottom blasted and repainted. It has a piece of blue tape covering the zinc strip over on the left side
Attachments
IMG_3450.JPG
-joel-
former owner 1988 '32 FB Sedan
Chesapeake Bay
twin 318 / 240 hp
Potomac MD

Butchel
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Re: keel fin

Postby Butchel » Tue Dec 27, 2016 10:30 am

No pics at this time. Joels picture shows the fin that my boat has. I'm now convinced it is factory. Yes, the anodes are bolted to it. It is going into very warm salt water. But, the boatyard guy, who has restored a Marinette before, advocates deleting the fin, welding six aluminum plates to the bottom of the hull (two forward, two mid-ship, two low on the transom) and welding sacrificial aluminum anodes to these plate. He says that is the best electrolysis protection to be had.
What about the maneuverability question? Does the fin stabilize yaw? Does it reduce skidding in a fast turn? Why is it just stitch welded on? Would a skeg at mid-ships (under the center of gravity) provide better maneuverability? Am I playing with fire here?
No sale. I decided to keep the FB top but delete the enclosure. Boating is, after all, an outdoor activity. I hacked off the front, rear and side ("X") struts and left only the trussed posts at the rear corners. This was necessary for shipping (the top then sat on the bridge deck with the rear corner posts hanging down into the cockpit.) I am presently designing a radar arch that will support the top. (Wind loads will be much less without the enclosure.) And, it will mount a new, cool, Raymarine Quantum radar!

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Busia
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Re: keel fin

Postby Busia » Tue Dec 27, 2016 10:54 am

That is part of the keel, you need it. Factory installed. Clean it up and weld it back on. Easy job and will be done with MIG not TIG. The skin is not very thick so I would not weld plates to the skin to put anodes on. If you were to use the weld on anodes the thick keel would be the easiest place for them. The bolt on ones work well and are easy to do. ONLY use aluminum anodes. All the aluminum anodes are the same alloy. Best place I've found is boatzincs .com Just have the hull clean and bolt on with SS hardware.
BUSIA
located in Ketchikan, Alaska. Gods country
32 foot Marinette express. (no fly bridge)
twin 350 Crusader (Chev 350) engines
1:1 Borg Warner velvet drive transmissions
Closed cooling (antifreeze in the engine)
Proud to be retired IBEW

EWRice
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Re: keel fin

Postby EWRice » Tue Dec 27, 2016 8:44 pm

I would suspect that they stitch welded the outer keel to prevent it from warping bad.

Also, if that keel was not there, I bet that boat would be a bear to manuver at low speeds, and even a light wind would send you off course.
Muskegon Lake
1972 32' Express flybridge
"AL13"
Twin 318s
On board air & prime 920
1963 Thompson Super Sea Lancer
Graymarine 327
1961 Alumacraft 12'
'55 10hp Johnson

GB49
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Re: keel fin

Postby GB49 » Tue Dec 27, 2016 9:49 pm

The entire boat is stitch welded..... but I would be very concerned how much pressure was placed on the hull to break that skeg. Hopefully nothing else is damaged, ie shafts.

-Karl
1986 Sedan 32'. Twin Chrysler 360in^3, 275hp, with K&N flame arrestors

Butchel
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Re: keel fin

Postby Butchel » Wed Dec 28, 2016 7:28 am

Roger. Nuff said. The fin stays with aluminum anodes and SS bolts. Thanks guys.
Butch

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bill
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Re: keel fin

Postby bill » Sat Dec 31, 2016 11:09 am

BigM
Butch,
Great post so far. Lots of useful information on this site.
When you get a chance hows about adding a signature to your posts :?: . :D
bill
ALUMINATION
Grosse Ile MI
Located on LakeErie
37' F/B Sedan
1975
Twin 360 Chrysler Marine
Raw water cooled
Hydraulic steering both helms
USCG Master Lic. Retired

Third Owner bill