I/O (Sterndrive) Conversion to Outboards

[tpenfield]

Ribs, gussets, and bolts. . . .

While away, I did some detailed drawings of the extension pod and support structure. Yellow is the boat's structure and gray is the extension pod and support structure.
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I am going to add a bunch of gussets to support many of the flange areas where the bolts will go. Some ribs to stiffen the long horizontal runs, . . . and lots of bolts, distributing the load.

In total there will be 74 gussets, 16 ribs, and 78 bolts. Since there are so many bolts planned, I am thinking 3/8" fine thread hardware (316 SS).

 

[alldodge]

Assuming flat washers and lock nuts?
Why fine thread, isn't it easier to over torque a bolt using fine?

 

[redneck joe]

And being a simpleton wood guy, more nails isn't better. 78 seems alot, but im not any kinda smart guy.

 

[tpenfield]

Fender washers and regular washers with nylock nuts.
I figure fine thread is better for both tightening and not loosening

 

[Pmt133]

I thought fine was more subject to loosening than coarse... but it's been a long time time since I did materials. Beyond that in the scope of pedestrian hardware I don't know there is much a difference between coarse and fine otherwise. I prefer fine as they nuts seem to thread on easier. No other reason lol.

 

[tphoyt]

I’ve always felt like there is more surface area being covered with fine threads and they are less likely to vibrate lose. Just my thoughts.

 

[redneck joe]

Don't you double nut and goop the threads?

 

[tpenfield]

Transom assembly is fine thread, outdrive to bell housing is fine thread.

Must be a reason.

 

[Pmt133]

Better clamping

 

[tpenfield]

I thought fine was more subject to loosening than coarse... but it's been a long time time since I did materials. Beyond that in the scope of pedestrian hardware I don't know there is much a difference between coarse and fine otherwise. I prefer fine as they nuts seem to thread on easier. No other reason lol.

According to AI . . .
"Coarse thread is more subject to loosening under vibration, while fine thread is less likely to loosen. This is because fine threads have a smaller helix angle, which makes them more resistant to self-loosening from vibration compared to the steeper angle of coarse threads."

 

[tpenfield]

One thing about working with SS bolts is 'galling' , which can ruin your day.

I had the issue with my extended swim platform build, so I'll have to be extra careful about the extension pod, considering the number of bolts.

 

[Scott Danforth]

Ted, look for 316-condition B hardware

It's a much harder 316 variant that is less likely to gall

 

[tphoyt]

I will have to look into that as well.
I use a lot of stainless for the marine environment on a seasonal basis and even though I know one more turn will be to much I usually do it and then I’m done and have to resort to cutting the bolts when the day comes.

 

[flashback]

I suspect once installed the bolts will never be removed similar to the hylocks used in aircraft of old. The head of the nut broke off at a predetermined torque..

 

[dingbat]

May want to look at tables 5 and 6 in the attachedm

https://nickelinstitute.org/media/8daa61d67a26b6e/10045_practicalguidetousingmarinefasteners.pdf

A write up on crevious corrosion

Pitting Corrosion vs. Crevice Corrosion in Stainless Steel

How to identify and prevent pitting corrosion and crevice corrosion in stainless steel tubing systems to avoid costly failures in offshore oil and gas operations.

www.swagelok.com