I’m no physicist,but...

Soulshine

Soulshine

Well-Known Member
Sep 25, 2016
1,351
Seneca Lake, NY
Boat Info
'83 SRV 360 Express
Engines
Twin Merc. 454
I covered my boat today. Simple frame, good tarp laced up underneath like a big football.

We do this as a group of about six people who all think the expense of shrink wrapping is insane. It’s a well polished routine by now.

Unfortunately today there were only 4 of us and a 30 mph wind that made this a real blast.

We finish, go to another marina to do another before the rain starts when I get a call from the marina I just left.

The woman tells me that I have to come back immediately because I have some ropes tied to the jack stands.

The reason is that if the wind gets under the tarp it could lift the boat up and knock it off the stands.

Like I said, I’m no physicist, but a 17,000 pound boat is not blowing up in the air like the Wizard of Oz...tarp or no tarp.

A ploy to encourage me the shrink wrap next season or just plain foolishness?
 
Soulshine said:
I covered my boat today. Simple frame, good tarp laced up underneath like a big football.

We do this as a group of about six people who all think the expense of shrink wrapping is insane. It’s a well polished routine by now.

Unfortunately today there were only 4 of us and a 30 mph wind that made this a real blast.

We finish, go to another marina to do another before the rain starts when I get a call from the marina I just left.

The woman tells me that I have to come back immediately because I have some ropes tied to the jack stands.

The reason is that if the wind gets under the tarp it could lift the boat up and knock it off the stands.

Like I said, I’m no physicist, but a 17,000 pound boat is not blowing up in the air like the Wizard of Oz...tarp or no tarp.

A ploy to encourage me the shrink wrap next season or just plain foolishness?
Click to expand...

I'm with you, I can't see it lifting the boat. That being said, a guy around here said the wind did lift a tarp and get a boat moving enough to topple over. My immediate reaction was that boat was blocked incorrectly.
 
The tarp would disintegrate long before the boat moved.

Either way, it’s no more likely to move regardless of what the tarp is tied to.

We stopped in on the way home and fixed it. I feel much better about it now.

:confused:
 
lol gotta keep the marina managers happy I guess. I'm headed down towards your area tomorrow afternoon to look at a 02 340, its at Barrett Marina. Where do you slip yours?
 
I store at Watkins Glen, but slip in Montour Falls. Have for about 10 years.

Barrett’s is a great marina. Fran Barrett is probably the most trustworthy guy in the boat biz anywhere.

I work in Geneva and get most of my parts there.

Good luck. Tomorrow is supposed to be a pretty crappy day weather wise in this area.

3-4 inches of rain over the next two days and high winds out of the south. The north end of the lake is bound to be wild tomorrow.
 
When I store in the boat yard, the contracts state in all caps and boldface that NOTHING is to be attached to the stands. The yard owner told me that the tarp will act as a sail if it comes loose and can pull a stand or stands out from under the boat. The boat doesn't get lifted, the stand gets worked out from under the boat. He stated it has happened and that it causes a domino effect if one boat topples over.
 
That’s interesting when looked at from that perspective.

Always something new to learn.
 
I wouldn't tie anything to the stands. Have been putting winter covers on my boats since 2004 for the same reasons you do. Run the lines beneath the boat and tie off to the other side. Best way.

enhance
 
Agreed and that’s exactly what we do. In this case, the tag ends of 2 lines didn’t need to go back under so were tied off to the center stand on each side.

As I said a few posts above, I see the rationale, but that’s not the concern that was presented to me. The prospect of the boat being tossed up in the air by wind in the tarp was so immediately ridiculous that I didn’t think any further than that I guess.

Looking back I can see a wild 50’ tarp yanking on a stand for days maybe being a thing to avoid.

I went to have a look at it today after a few days of hard wind and rain and it was fine.
 
I like this lesson. I think the idea of the stand being weakened and moved over time is a good rationale. I plan to remember that if I ever need it. I also plan to move further south and avoid needing that knowledge.
 
What if someone walks (or drives a lift or whatever) by and trips on the line - tugging the back out? Either way, jacks are meant to load vertically and will be weak in a horizontal load. I don't blame the marina for being cautious, but doubt any of this is likely.
 
I too would initially think it’s a crazy possibility but...think of all that tarp catching the wind and a stand that might not have enough downforce on it. Better to be safe and keep the higher ups happy too!
 
If the stands were tied to each other under the boat they could not be pulled out from under the boat by the tarp. Ever notice the sailboats always connect the stands together under the boat. The issue is becomes more of problem if the yard is gravel or dirt.
 
I'm not a Gynecologist, but........
Never tie to a jack stand, never mind the physics involved. Too many other good places to tie to.
 
I have a degree in Physics (caveat... got it in 1984. a bit rusty these days)

To find out the force that could affect your jackstands:

Calculate the square footage of your tarp:

Ex 50 ft x 50 ft tarp would have 2500 sq ft of area if all were exposed directly to a lifting wind force (highly unlikely when used as a boat cover)

Calculate the wind pressure that could affect your tarp:

wind pressure (units of psf) is derived via the equation P = 0.00256 x V2, where V is the speed of the wind in miles per hour (mph) and the constant, 0.00256 corresponds to the mass density of air

Calculate the pressure per sq foot for your tarp assuming worst case winds of 50mph

p = 0.00256 * 50**2 = 0.00256 * 2,500 = 6.4 psf

To get the force of the wind pressure on the entire tarp:

multiply the tarp area times the calculated psf

2500 * 6.4 = 16,000

now multiply the tarp pressure of 16,000 lbs times the drag coefficient of fabric (estimate found via Google of 1.45, who knows how accurate it might be...)

16,000 * 1.45 = 23,200 lbs of force (pretty big number....)

now divide that 23,200 lbs of force by the number of grommets on the tarp

assume a grommet every 2 feet with 4 edges of 50 ft each 25 grommets x 4 sides for 100 grommets total

now divide the total force by the number of grommets to get the force on each grommet (ideal calculation, not real world)

The answer:

23,200 / 100 = 232 lbs force per grommet *

*refer to initial caveat... I haven't practiced much with Physics since my first job after college and as such might be way off. The real number will be probably be something smaller as the entire tarp wouldn't be exposed to the full force of the wind, each grommet wouldn't be evenly loaded, etc, etc... who knows?

HIGHLY unlikely to topple your boat

Given all this, I still wouldn't tie jack sh*t to the jackstands ;)
 
The reason is that the stands don't actually support the 17,000 lbs. The blocks under the keel do. The stands are just "snugged up" after the boat is blocked and keep it from tipping from side to side. With shifting soil under blocks and stands, they tighten and loosen over the winter. They can easily be shifted if tarps are tied to them. Never tie anything to the stands. And periodically check your boat over winter to see if any have loosened up from ground shifting.
 
This is a great post.

I visit my boat weekly over the winter since it’s so close by and have kept an eye on the attitude of the stands, their current position compared to the last time and have even snugged them up if they appeared to have sunken.

That said, I’ve only seen settlement that concerned me once when I wound up in a sandy part of the yard.

Some great points made here and I appreciate some of you putting a finer point on the issue.
 
I think "normally" there is more weight on the blocks than the stands so the keel will sink more than the stands, which firms them up. But those two brutally cold winters a few years ago caused soil to freeze swell and heave. I was on gravel that year and had to tighten up a couple stands mid winter.
 
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