Engineering Question - flexion of hull

[VChild]

Originally Posted by Pete7

Hmm, I was wondering that too.

Pete

After 39 years, probably crevice corrosion at imperfect welds.

[MicHughV]

It's typically not the stainless plate that corrodes, but the welded seams. During the welding process, impurities in the welding rod can transfer to the tank and initiate rust.

[boatpoker]

Originally Posted by VChild

After 39 years, probably crevice corrosion at imperfect welds.

Yup, seen it many times.

[Dockhead]

Originally Posted by boatpoker

Yup, seen it many times.

39 years is a good long life for a metal tank.



My tanks are all welded high density polyester, by Tek Tanks, EXCEPT -- the fuel tank. Which is aluminium. A ticking time bomb. Good news is it doesn't sit in the bilge, and there's never water in my fuel, so maybe I'll get a few more years out of it.

[MicHughV]

this is likely a thread drift....
but...
my first boat was home built....my fuel tank was fabricated from plywood and slathered in WEST system....never had a lick of problems with it...
That tank was eventually replaced with an aluminum tank, when a bigger engine was installed...as with the plywood tank....functioned flawlessly...
next boat had bladder tanks.....while the bladder tanks never gave me a problem, the hose connections to the bladder tanks did...
next boat had stainless steel tanks...never had it long enuff to determine if it was a problem...these were custom built for the boat...
next boat had plastic tanks....no problem with the tanks, but problems with the fittings..
my fishing boat has galvanized steel tanks....not diesel, but gas, but trouble free to date...
not sure, at this point, what material is best suited for a diesel fuel tank..
I did inspect an older boat one time, that had some type of black steel tanks, but had leaking issues, not sure what the cause was....
Seems like welded aluminum is a good bet for a diesel fuel tank...I'd add WEST/plywood to this mix, but bound to find a lot of resistance to this line of thought..

[VChild]

Interesting.
My fuel tanks are supposedly "black iron".
I've heard these types of tanks have had issues. Mine are completely encapsulated in fiberglass. I don't know if that was standard for the Lord Nelsons or if it was done by a previous owner. When I opened the inspection ports I was pleasantly surprised. The interior of the tanks are still like new. Clean looking metal with no evidence of corrosion. I don't know if the exterior coating had anything to do with their longevity.

I just put together 2 sets of expansion bars using 3/4" square head bolts, nuts, washers and iron pipes. I'll try them tomorrow on the sole supports while removing the H frame.

[boatpoker]

Originally Posted by Dockhead

39 years is a good long life for a metal tank.



My tanks are all welded high density polyester, by Tek Tanks, EXCEPT -- the fuel tank. Which is aluminium. A ticking time bomb. Good news is it doesn't sit in the bilge, and there's never water in my fuel, so maybe I'll get a few more years out of it.

I believe aluminum is a terrific fuel tank material ... if properly installed.
i.e. no contact with porous materials and no place on top or inside for water to sit..

I had new aluminum fuel tanks (to replace improperly installed steel) built two yrs. ago. Tank tops are sloped so no water sits on top, tanks are isolated from any absorbent material and fuel supply comes from the bottom of the tank so any water in there never sits but goes directly to the separators.

[boatpoker]

Originally Posted by VChild

Interesting.
My fuel tanks are supposedly "black iron".
I've heard these types of tanks have had issues. Mine are completely encapsulated in fiberglass. I don't know if that was standard for the Lord Nelsons or if it was done by a previous owner. When I opened the inspection ports I was pleasantly surprised. The interior of the tanks are still like new. Clean looking metal with no evidence of corrosion. I don't know if the exterior coating had anything to do with their longevity.

I just put together 2 sets of expansion bars using 3/4" square head bolts, nuts, washers and iron pipes. I'll try them tomorrow on the sole supports while removing the H frame.

No pleasure craft was ever built with iron tanks. Thats an old slang plumbing term to diferentiate between steel and galvanized steel. They are actually common mild steel tanks.

[boatpoker]

Originally Posted by MicHughV

my fishing boat has galvanized steel tanks....not diesel, but gas, but trouble free to date...

Just FYI ... under ABYC Standards galvanized steel tanks are acceptable only if they are galvanized inside and out.

[VChild]

Originally Posted by boatpoker

No pleasure craft was ever built with iron tanks. Thats an old slang plumbing term to diferentiate between steel and galvanized steel. They are actually common mild steel tanks.

Yeah, I was aware that it was not actual iron but some type of sheet steel. That’s why I had it in quotes. However, the term was very commonly used especially in Taiwanese built boats of the era. I actually have the original Lord Nelson sales brochure listing all standard specifications. Under tankage, even the official brochure called them black iron fuel tanks. I guess it was just the common term back then for some grade of mild steel.

[MicHughV]

When I pulled out my original plywood and WEST system tank, after about 10 years of service, on a whim I decided to open the inspection covers and peek inside and was surprised to find the bottom and lower sides covered in a black gooey substance.....maybe 1/8-1/4" thick. I've since learned that diesel fuel can promote bacterial growth. The how's and why's are complicated to explain.
Having good fuel filters goes a long way to protect your engine in this regard.

That Lord Nelson 41 is a beautiful looking boat. I have a thing for those classic boats, couldn't explain why, but I do.

[VChild]

Originally Posted by MicHughV

That Lord Nelson 41 is a beautiful looking boat. I have a thing for those classic boats, couldn't explain why, but I do.

Thanks!
She was a “diamond in the rough” when we first purchased her but we saw her potential. It was a long journey bringing her back properly and modernizing her systems. But no regrets. We hope to be cruising on her full time very soon.

[Cheechako]

SS tanks under the floor are a pretty bad idea, but those lasted a long time!

The boat in my avatar had one under there, It was an '85 boat, the center tank had multiple holes by '92. Not in a weld but right where the tank rested on a crossmember. The dampness down there gets into the closed resting area and SS corrodes fast in that situation.

[Cheechako]

Originally Posted by boatpoker

I believe aluminum is a terrific fuel tank material ... if properly installed.
i.e. no contact with porous materials and no place on top or inside for water to sit..

I had new aluminum fuel tanks (to replace improperly installed steel) built two yrs. ago. Tank tops are sloped so no water sits on top, tanks are isolated from any absorbent material and fuel supply comes from the bottom of the tank so any water in there never sits but goes directly to the separators.

I can attest to Aluminum being a terrible tank material if it's down under a damp floor. I've replaced two in that situation after filling a bilge with diesel.

[Cheechako]

Originally Posted by VChild

Yeah, I was aware that it was not actual iron but some type of sheet steel. That’s why I had it in quotes. However, the term was very commonly used especially in Taiwanese built boats of the era. I actually have the original Lord Nelson sales brochure listing all standard specifications. Under tankage, even the official brochure called them black iron fuel tanks. I guess it was just the common term back then for some grade of mild steel.

Yes, glassed in 'black iron' was used in some Hans Christian? or Passport? boats too. It seems to have held up better than I expected it would. One used glassed over SS though. I cant remember which.