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Itz a bird, itz a plane,..., itz, itz,...

Discussion in 'Chris Craft Roamer Yacht' started by alloyed2sea, Jan 10, 2013.

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  1. alloyed2sea

    alloyed2sea Moderator

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    ..., rather unconventional.
    The SS shark fins we bolted to the bottom of "Tin Tonic" yesterday that is. :eek:
    22 inches deep and 36 inches long, these babies promise to end the era of "busted props and bent shafts" on Potomac Rouge - river of dreams and deadheads - submerged logs that is; and whatever else "pops" up as we oh-so-innocently pass by. (New theme song: Janis Joplin - Me and Bobby Mc Gee - YouTube)
    Tired of the costs and aggravation ("Your season is now over sir, but please do head out again next year, my daughter's going to college.") I finally decided to do something (something dammit) about it. :mad:
    AND NO, I did not consult a naval architect or sum no-it-all from Boat USA, just me and my (well-paid) buddies Gary (welder) and Steve (boat mechanic/shoulder to cry on/daughter going to college) fijjured it ALL out by ourselves.
    You be the judge - award marks for:
    1. Appearance ("She's a looker");
    2. Enjineerin ("Gosh thatz neat");
    3. Likelihud of self-destruction ("Well, it worked in rehearsal mate").
    Will provide readouts come spring.
    Cheers!
    -Eric
    (ps-thenewhipo454isfinallyinplaceawaitingshaftalignmentandseatrial)

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    Last edited: Jan 25, 2013
  2. YachtForums

    YachtForums Administrator

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    So that's where you've been... bolting skegs to a steel surfboard. Good for wave ripping AND log jumping. A well enjineared piece for sure!
  3. alloyed2sea

    alloyed2sea Moderator

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    More, more,...

    Normally, I dont recommend drilling so many (20) holes in the bottom of your boat - but thatz what it took.
    Main issues in my (fine) mind:
    1. Aeration of water flow-by of the props.
    Cavitation kills, no? :confused:
    2. That, and having deadheads partially cut and getting "stuck" to fins (hence reverse gear, eh?).
    Thus, we mounted the fins just (barely) outboard of the props (all the better to protect them, no?) - welded at an 11 degree angle inboard (see third photo) commensurate with hull deadrise. This worked because of the open space just forward and abeam of the shaft logs inside the hull. Wanted to mount them centered around the stringer which was exactly there, but higher (better paid) powers said no.
    20 SS screws/lock nuts/hand-made washers, and 5200 down below - that otta werk!
    Stainless steel fabrication was no cinch but should not create any corrosion problems with aluminium hull, we'll see,...
    -E
    (realroamerswillnotethebarsofsealloy"wrapped"aroundthenewstrutsfrommarinetteyachts)

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    Last edited: Jan 25, 2013
  4. Capt J

    Capt J Senior Member

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    Why not make the fins out of aluminum and just weld them right to the hull rather than use dis-similar metals? You might want to put zincs on them.
  5. Laurence

    Laurence Senior Member

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    Fins

    I thought about doing the same on my steel Roamer but would just weld them on. I wonder how it will effect your slow speed turning. Please let us know.
  6. Capt Ralph

    Capt Ralph Senior Member

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    You may know better, but I would think, alloy hull would need more zinks. Even a steel hull would need more sinks if that was a stainless bilge keel ad on.

    Dawg, Thats a pretty ole boat.

    ,rc
  7. RT46

    RT46 Senior Member

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    I like it.

    I think it is a good idea.

    how about sharpen the knife edge?

    or a chain saw blade?
  8. alloyed2sea

    alloyed2sea Moderator

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    Dissimilar Metals/Marine Environment

    Always a concern.
    Normally, SS and aluminum get along pretty well - depending on the grade of each material;
    Anodizing World: Corrosion between anodized aluminum and steel
    so, choosing the "right" grades of each is important (see chart below). Still, much remains uncertain, even in the best metallurgists' minds.
    Consequently, we Tef-Gel'led (Ultra Tef Gel Fastener Lubricant the SS bolts inside and outside of the hull, and all along the fins' connection with the hull. Fins will also be coated with Interlux 2000E epoxy (Interlux Interprotect Epoxy Primer-Grey INT-2000E/01EG - Interlux Paint - JMSOnline.net Marine Supply and Boating Store) which adds an effective layer of protection (We be tef'gellin now. Would somebody pls call Dr. Scholls :p).
    NOTE: The larger the area of anode (Hull: 5086 AL) and smaller the area of cathode (Fins: grade 304 SS) and closer they are on the galvanic scale the better.
    May add Sea Alloy (low-grade AL, not MaG) strips from Marinette Yachts later, depending on what the fall pull-out reveals.
    No fears, just wait till you see my plans for her conversion into an ice breaker! :D
    Cheers,
    Eric

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    Last edited: Jan 25, 2013
  9. Beau

    Beau Senior Member

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    Redman

    Be interested to hear how those "log beaters" actually work out. BTW, with all that caulking, are you relying on the bolts for bonding or do you have them wired to the hull inside? Or is that not necessary?
  10. Innomare

    Innomare Senior Member

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    Redman,

    Did you align them straight fore-aft (parallel to the keel) or did you give them some "toe-in"?
    The streamlines on your bottom probably don't go straight, but somewhat from the keel to outboard. If you place the fins straight, they will add more drag than if they were aligned with the streamlines. Of course, this also depends on your speed.

    Another one to consider would be to make sure the fins (or their connection to the hull) have a weak spot, so in the event of impact, they would shear off rather than pull a piece of your hull out. In that respect, it could actually have been better to use fewer bolts.

    Looking forward to hear the results of the seatrials!
  11. alloyed2sea

    alloyed2sea Moderator

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    Naval Architecture

    Itz not for kids anymore. (Who remembers "Coco-Puffs"?)
    Answers:
    1. Thought that fins should go "straight" (in parallel to keel)- had no idea what streamlines were.
    2. Gave the idea of "breakaway"/weak connections to hull alot (alot) of thought: Finally decided that a strong connection to hull was the best way to go. The hull (AL 5086) is extremely strong (3/16" thick) and we were able to mount them on a 3" baseplate just below a major stringer inside.

    If we hit something that can bend that joint, can you imagine what it would have done to the running gear - yikes! (And yes we have done this - how many V-struts from Marinette do you think I've purchased?)

    Further thought:
    Might have gone with a curved fin design, but not sure Gary (the welder) could have accomplished that.
    Cheeers!
    -Eric

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  12. alloyed2sea

    alloyed2sea Moderator

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    Update

    We're all painted and ready to go - but have been pondering the anodic situation with the new skegs ("logbusters") all summer long.
    Think I really should have gone with mild steel instead of SS - just like the factory CC rudders which show little corrosion after 46 years. The two metals are much, much closer on the galvanic scale and so don't create as much of a battery when connected, especially underwater.
    Consequently, my conscience made me install yet another set of double-sided anodes to them - this in addition to the sealloy strips I "wrapped" around them where they meet the hull and tef-gelling the ss bolts that attach them to the hull.
    That, and a layer of 5200 between the two is enough, eh?
    Wish us luck.
    Cheers!
    -Eric

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    Last edited: Oct 28, 2013