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

..., rather unconventional.
The SS shark fins we bolted to the bottom of "Tin Tonic" yesterday that is.
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.
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)

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?
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)

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 ).
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!
Cheers,
Eric

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

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