I just learned about this little nasty little thing called "Crevice Corrosion".
In an oxygen free environment (like the gasket area in my pivot pin cover) this type of corrosion will attack and eventually destroy the metal in fairly short order. Since this part is below the water line, it seems prudent to replace it with something I won't have to worry about.
I checked into the "Passivation" process and various coatings to protect the Stainless, but there's no guarantee how long that might last. Not to mention the additional cost is unjustified since I can simply substitute that part with a threaded Glass Reinforced Polypropylene Flange.
Not to mention it'll likely be quite a bit lighter as well.
It's a real pity, I had put a lot of time and money into that piece.
Oh well, that's the cost of education (or lack thereof)!
The first of many mistakes along the way I suppose...
:(
Thursday, March 5, 2015
Monday, June 2, 2014
Centerboard Pivot Pin Cover
The Centerboard Pivot Pin Cover was delivered today!
I guess this little piece is really the first part of the boat to be made, although it won't be used for a long time.
Anyway, the original pieces of metal came in at 747g. At the time, I estimated a post machined weight at somewhere near 350g.
Good news is that it came in a bit lighter, even with the screws on the scale.
It's a solid chunk of 316 SS with matching screws, so corrosion shouldn't be an issue.
I plan to bury it in a layer or two of fiberglass to lock it in place.
Saturday, March 1, 2014
Stainless Blanks for Centerboard Pin Cover
The 316SS blanks came in today.
A bit heavier than I was expecting, but I'm "guesstimating" a final weigh in at somewhere near 350g after machining.
A bit heavier than I was expecting, but I'm "guesstimating" a final weigh in at somewhere near 350g after machining.
Friday, February 28, 2014
G10 Tubing for Centerboard(s)
A 2' (609mm) piece of G10 tubing for the Centerboard and Centerboard Case came in today.
I didn't need a piece this long, but it was a standard length and only $45 plus shipping.
On the plus side, it'll be more than enough for two Centerboards if I end up making or needing a spare.
The picture shows an igus bushing partially jammed into place by tapping it lightly on the floor. The igus bushings are oversized from the factory and reduce to specified dimensions after being press fit into the bore.
I didn't need a piece this long, but it was a standard length and only $45 plus shipping.
On the plus side, it'll be more than enough for two Centerboards if I end up making or needing a spare.
The picture shows an igus bushing partially jammed into place by tapping it lightly on the floor. The igus bushings are oversized from the factory and reduce to specified dimensions after being press fit into the bore.
Wednesday, February 26, 2014
Centerboard Pivot Pin Cover
The jury is still out on an Aft Cabin vs. Aft Cockpit boat - but my wife got a hold of the plans and pointed to the Aft Cabin configuration... So, it's looking more like that decision might already be made as well.
As for Daggerboard vs. Centerboard option... I have no issues with that decision.
For me it's a Centerboard all the way! I like the more open cabin plus the ability for the board to kick up and hopefully avoid damage. I realize there may be some loss of performance and more maintenance involved, but I'll take that over the big daggerboard trunk taking up a good portion of the cabin.
Anyway, last week or so I started thinking about a solution for the Centerboard Pivot Pin Cover. Maybe it had something to do with this note in the plans:
The recommended solutions didn't really appeal to me either:
So I started thinking of some better way to seal that pivot pin, especially since it shows to be about 12" (305mm) below the water line!
A simple 1/2" (12mm) plate of 316 Stainless Steel with an O-Ring groove and a 316 SS cover plate should do the trick. I chose 316 Stainless since I could get 316 SS screws to prevent issues with dissimilar metal corrosion.
As for the O-ring, you might think that something as simple as this would be a no-brainer. Just cut a groove in the metal, slap an O-ring in there and screw the lid down. Yeah, no chance! Over the course of six hours or so I learned more than I thought was possible about O-ring materials, diameters, clearances, squeeze tolerances, radial vs axial loads, failure modes, pressure directions, groove wall angles, round-overs and etc.
Anyway, to make a long story short. I drafted up a design and sent it over to the machine shop for review before committing it to the lathe.
**********************************************
This link will take you to a .PDF plan view of the part:
Centerboard Pivot Pin Base and Cover Details
(If you want the real .PDF or the CAD files, send me a PM)
**********************************************
The part was designed to be installed into the outer laminate of the Centerboard trunk using an additional layer or two of fiberglass cloth. The fiberglass will overlap the flange while the bored holes in the corners are there to reduce weight somewhat and allow for the overlapping fabric to bond with the material under the flange. This will "lock" the piece into place and provide a water tight mount.
The O-Ring will be:
Double Seal Buna-N O-Ring
AS568A Dash No. 320
McMaster Part #90025K402
The Stainless metal pieces are on order and should be delivered any day now. Then I'll have to get them over to the shop for processing. It's a LOW priority piece, so it may take a while to get it back depending on their backlog.
As for Daggerboard vs. Centerboard option... I have no issues with that decision.
For me it's a Centerboard all the way! I like the more open cabin plus the ability for the board to kick up and hopefully avoid damage. I realize there may be some loss of performance and more maintenance involved, but I'll take that over the big daggerboard trunk taking up a good portion of the cabin.
Anyway, last week or so I started thinking about a solution for the Centerboard Pivot Pin Cover. Maybe it had something to do with this note in the plans:
The recommended solutions didn't really appeal to me either:
So I started thinking of some better way to seal that pivot pin, especially since it shows to be about 12" (305mm) below the water line!
A simple 1/2" (12mm) plate of 316 Stainless Steel with an O-Ring groove and a 316 SS cover plate should do the trick. I chose 316 Stainless since I could get 316 SS screws to prevent issues with dissimilar metal corrosion.
As for the O-ring, you might think that something as simple as this would be a no-brainer. Just cut a groove in the metal, slap an O-ring in there and screw the lid down. Yeah, no chance! Over the course of six hours or so I learned more than I thought was possible about O-ring materials, diameters, clearances, squeeze tolerances, radial vs axial loads, failure modes, pressure directions, groove wall angles, round-overs and etc.
Anyway, to make a long story short. I drafted up a design and sent it over to the machine shop for review before committing it to the lathe.
**********************************************
This link will take you to a .PDF plan view of the part:
Centerboard Pivot Pin Base and Cover Details
(If you want the real .PDF or the CAD files, send me a PM)
**********************************************
The part was designed to be installed into the outer laminate of the Centerboard trunk using an additional layer or two of fiberglass cloth. The fiberglass will overlap the flange while the bored holes in the corners are there to reduce weight somewhat and allow for the overlapping fabric to bond with the material under the flange. This will "lock" the piece into place and provide a water tight mount.
The O-Ring will be:
Double Seal Buna-N O-Ring
AS568A Dash No. 320
McMaster Part #90025K402
The Stainless metal pieces are on order and should be delivered any day now. Then I'll have to get them over to the shop for processing. It's a LOW priority piece, so it may take a while to get it back depending on their backlog.
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