RickK's 170 rebuild

[RickK]

That's what I could hope for too.

[dirtwheelsfl]

Guess in theory the corners could expand....but seems the expansion should occur in the areas of least resistance, that is, the centers of each run.

Exactly what my thinking is. As long as the corners and top are held snug, let the rest expand how it wants.

I actually just filled it with water for test fit then pumped it out. Fuel would still be in there if i did that haha.

[gran398]

That's what I could hope for too.

 

That to me makes good sense. Equal pressure is the "control" here...the corners are the most rigid portion physically....then back them up with a corner stanchion in the same four spots as you have....I'd be good with that. Set it and forget it. Wouldn't hurt though to have a thin bit of rubber per each corner as a chafe guard for vibration, etc.

And to take it a step further...2% max expansion...which should occur on the "saggy" portion (middle portion). If we do the math, what does that equate to per side? 3/8ths max in the middle?

Feel free to input here guys....I'm wrong a plenty...every day at home

Rick, getting back to you're build...you're smoking it bud

[CLM65]

I think a test is a great idea, but I'm not sure that water is a valid test medium.  The instructions talk about expansion after being exposed to fuel, and someone previously mentioned a chemical reaction.  IMO, you would be better off using gas.  Is your boat on a trailer?  If so, take it to the gas station and fill it up.  Let it sit for a day or two so that it has time to undergo whatever reaction occurs.  Then siphon the gas out and put it into your vehicle.

[gran398]

Great pic regarding 2% expansion.

The idea is to leave room in the center of the longitudinal run on each side to prevent tank expansion from exerting enough lateral pressure to "break" the stringers.

2% expansion...translates to 1% per side...but actually less given the other two short "sides" of the rectangle..... bow and stern tank walls.

1% per side max...looks to be 3/16ths or less. Most likely 1/8th.

Per this install...a non-issue IMHO.

[CLM65]

Hate to disagree Scott, but 2% is 2%, no matter how you slice it.  I think Rick's tank is 28"wide, so it will theoretically expand 0.56" in width, or a little over 1/4" per side.

If you look at it halves, each half is 14".  2% of that is 0.28".  So each side may grow a little over 1/4"   .

If his tank is 50" long, each end will grow 1/2" (theoretically).

[CLM65]

Also, as robust as those stringers are, I would be more worried about busting that tank

[gran398]

Hate to disagree Scott, but 2% is 2%, no matter how you slice it.  I think Rick's tank is 28"wide, so it will theoretically expand 0.56" in width, or a little over 1/4" per side.

If you look at it halves, each half is 14".  2% of that is 0.28".  So each side may grow a little over 1/4"   .

If his tank is 50" long, each end will grow 1/2" (theoretically).

Good deal Craig

No disagreement....it's all about the math, you've calculated it, so each sides grows by 1/4 inch max. in theory.

Given the pic...he's still safe there.

But the ends befuddle me...why would they grow larger than the sides by 1/4 inch?

This is going to be a function of calculus and physics...of which my knowledge is freshman level...

[CLM65]

But the ends befuddle me...why would they grow larger than the sides by 1/4 inch?

The growth is a percentage of the original dimension, in this case 2%.  So multiply the dimension of concern (in this case the length, 50") by 0.02, and your result is 1".  Assume the midpoint is fixed, so each end grows 1/2".

I hope my input is not construed as stirring up trouble - hopefully Rick's build has enough room for the expansion.  But I only found that document today.  And I would rather bring up any issues before the deck is on....

[Blue Agave]

Also, as robust as those stringers are, I would be more worried about busting that tank

X2 - the tank will crack before the stringers break.

[Blue Agave]

I think a test is a great idea, but I'm not sure that water is a valid test medium.  The instructions talk about expansion after being exposed to fuel, and someone previously mentioned a chemical reaction.  IMO, you would be better off using gas.  Is your boat on a trailer?  If so, take it to the gas station and fill it up.  Let it sit for a day or two so that it has time to undergo whatever reaction occurs.  Then siphon the gas out and put it into your vehicle.

Agreed

[gran398]

But the ends befuddle me...why would they grow larger than the sides by 1/4 inch?

The growth is a percentage of the original dimension, in this case 2%.  So multiply the dimension of concern (in this case the length, 50") by 0.02, and your result is 1".  Assume the midpoint is fixed, so each end grows 1/2".

I hope my input is not construed as stirring up trouble - hopefully Rick's build has enough room for the expansion.  But I only found that document today.  And I would rather bring up any issues before the deck is on....

Gotcha.

Makes good sense

Stirring up trouble, heck no...we're a team here. You're math is right, and based upon your explanation...I failed to do the math in a planar manner.

 I stand corrected. But given the smaller dimension on the ends it is still difficult to analyze. We may need to bring physics to the equation with regard to ease of direction/expansion.

 As far as Rick's install....these numbers represent a worst-case expansion scenario...yet if diminished by just a tad...he's golden.

The 2% maximum expansion is based upon a full tank of petrol.

Let's analyze this further.

[gran398]

Just took another look at the pic posted.

The tank could expand by 2% max...in the easiest direction.

The easiest direction of expansion is across the top...largest area without encumberance. Given the tank design...and the narrow dimensions/angles on the bottom portion and corners...appears they have engineered the expansion to occur/puff on the aft top.

[RickK]

I have plenty of expansion room 'cept the corners. Guess after the CR trip I'll fill it up and see what is going to happen - I'll need some gas in my truck for sure after that trip.

If you look at the tank it is not the typical rectangle - side shot:


End shot:


I was hoping any growth would be in the big areas and that would be in the top and bottom (bow up and sag) - can't see how it could grow much in the sides and ends. We'll see I guess.

[CLM65]

I agree that the test is your best bet.  And I suspect, as in pretty much any instance where there may be some liability involved, that the vendor's 2% expansion value is very conservative.  See you in Crystal River, Rick.