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Old 08-14-2016, 12:17 PM   #1
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Upper Deck Capacity?

I have looked online and haven't been able to locate the answer to how many people I can safely have on the top deck of our 50' Ocean Alexander Mark 1 Pilothouse. It's the biggest outside area we have, and we have a teak table and chairs up there, so I'm expecting that to be the main 'gathering place,' but I want to restrict it to a safe number. We don't usually have a crowd, but will be taking a few out for a birthday cruise next week. Thanks in advance for any and all advice. We're new to all this, and so glad we ignored the naysayers. We have found the secret to happiness, and it's name is boat!
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Old 08-14-2016, 12:29 PM   #2
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I'd be concerned about weight. People come in a wide range of weights.

Perhaps the number of fixed seating positions would be a start.
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Old 08-14-2016, 12:44 PM   #3
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The concern is more about live load then dead weight. Unlike a table or dinghy people have a tendency to move about freely rather than remain strapped down in position. I've been aboard markpierce's 35'er with over a dozen people but that was tied to a dock and distributed equally about the boat.

I'd be leery of having that many folks aboard your boat away from the dock until you and your significant other has at least a year or more experience handling what sounds like a new to you boat. The real answer goes way beyond simple arithmetic and external conditions can radically change the answer.
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Old 08-14-2016, 02:01 PM   #4
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Quote:
Originally Posted by herbpeddler View Post
I have looked online and haven't been able to locate the answer to how many people I can safely have on the top deck of our 50' Ocean Alexander Mark 1 Pilothouse. It's the biggest outside area we have, and we have a teak table and chairs up there, so I'm expecting that to be the main 'gathering place,' but I want to restrict it to a safe number. We don't usually have a crowd, but will be taking a few out for a birthday cruise next week. Thanks in advance for any and all advice. We're new to all this, and so glad we ignored the naysayers. We have found the secret to happiness, and it's name is boat!

A few folks should not be a problem on the deck of a 50' boat. However, if you had a dozen folks on the deck and suddenly decided to go to on pe side to look at something, and that side happens to be on same side as the completely full fuel tank, and you just happens to catch a very large wake from a large cruiser on the other side that just decides to get up on a plane... you get the idea. It would take a lot of folks and a an unfortunate set of circumstances before it would be a problem.

Your biggest concern with folks on your upper deck will be making sure you have enough accessible PFDs for them all, making sure than the weather is calm enough to have gusts safely on the upper deck, and that no one drinks too much alcohol so they don't simply fall overboard.
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Old 08-14-2016, 02:15 PM   #5
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A friend has an OA Mark 1 50'. His upper deck is not large enough to accommodate more folks than a safe number. If you have reduced the available space my putting a big table up top, you will accommodate even fewer.
If you want to be sure of your load limit, add bodies one at a time, all on one side and observe how much the boat heels. If it gets so you are nervous about the degree of heeling, you have your limit.
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Old 08-14-2016, 02:36 PM   #6
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A naval architect could calculate it for you.

The ideas posited above saying, 'try a few more until...' and 'learn the boat to determine its stability', are problematical since I don't think the boat's behavior would give you much warning. Especially high off the water, and with a crowd's propensity to gather along one edge for a view.

A quick Google search brought me this: http://www.gerrmarine.com/Articles/P...tStability.pdf
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Old 08-14-2016, 03:33 PM   #7
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I worry about having a bit of extra weight up top on mine.
Then I saw her bigger sister and figured scaled back I have nothing to be to concerned about.


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Old 08-14-2016, 03:34 PM   #8
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My boat has a sticker at the top of the stairs that lead to the fly bridge that says the maximum safe load when underway is 1500lbs. There is seating on the bridge for 12 people.


FYI, my boat weighs about 60,000 with some fuel and water, and has a beam of 15' 6". We've been out on the river with much more weight than that but I make sure it stays evenly distributed side-to-side.
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Old 08-14-2016, 04:22 PM   #9
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At the dock, I'd be ok with up to 12. However, underway, my maximum would be 8, all seated, and fewer if I don't have seats for 8.
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Old 08-14-2016, 04:44 PM   #10
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Just get everyone to run back and forth from side to side. Start with 2 people and work your way up. When the boat gets to rocking you'll know your limit.
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Old 08-14-2016, 04:54 PM   #11
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Actually, when the roll terminates in a hang before promptly starting back upright is usually the limit.

Like most limits, know it and back off a safey margin.
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Old 08-14-2016, 06:33 PM   #12
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I believe that boat is set up for a cruising couple with occasional guests?

Having many people on board negates the value of/reason for the boat to me!
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Old 08-14-2016, 07:14 PM   #13
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Greetings,
Mr. h. Welcome aboard!
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Old 08-14-2016, 09:06 PM   #14
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The USCG has a method called the "Simplified Stability Test" for small vessels. "Simplified" may be a relative term. Google it. Here are two links to get you started:

http://www.uscg.mil/pvs/docs/Stabili...ity%20test.pdf

https://www.uscg.mil/forms/cg/CG_4006.pdf

Good Luck!
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Old 08-15-2016, 05:42 AM   #15
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The Krogen 42 has a design limit of 750 lbs on the top deck, people and equipment. Per Krogen Yachts in 2000. After this the stability is reduced. Don't know by how much or how fast.

Underway in any seas other than flat we limit the number of people to two. Flat seas four.

At anchor on a calm day we throw caution to the wind.
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Old 08-15-2016, 05:55 AM   #16
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While in the slip simply have the guests move to one side.

When 1/2 the free board is gone on that side , you are loaded .

Freeboard is from the WL to the first opening port, that doesnt have a secured metal shutter.

Sorta how the Coasties measure but quicker.

Coach roofs are built light so 20 folks at 200lbs each might be a structural problem , not a stability issue.
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Old 08-15-2016, 11:26 AM   #17
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Ship stability is an interesting, though sometimes confusing topic. Here is a link to a USCG booklet on fishing boat stability. Pretty much everything would apply to a pleasure power boat.

https://www.uscg.mil/hq/cgcvc/cvc3/r...ence_Guide.pdf

It may be more information than many are interested in, but it is good to have a basic understanding of the effects of design, loading, on board liquids, wind, and possible damage have on a boats ability to right itself.
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Old 08-15-2016, 04:09 PM   #18
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Many Thanks!

That's a lot of great information! I'm learning so much on these forums. My concern was really with the weight and structural issues as opposed to stability, but it's great to understand those issues as well. We are having a total of about 8 people on the boat that day, and since the table is up top and it is the nicest/biggest area to hang out once anchored, I was wondering how to restrict it so the roof didn't cave in. Thought there might be a simple formula, i.e., so many pounds per square feet or something.
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Old 08-15-2016, 04:59 PM   #19
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Quote:
Originally Posted by herbpeddler View Post
I was wondering how to restrict it so the roof didn't cave in. Thought there might be a simple formula, i.e., so many pounds per square feet or something.
I would guess structurally there would be little issue since the designers should have taken weight into consideration in the construction of the flybridge. The same with stability. But people are bigger now. A discrete way to limit the passengers up there would be to use some large tables or other items that would take up some square footage. And put the beer cooler on the main deck.
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Old 08-15-2016, 05:02 PM   #20
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Here's the formula to calculate what our state allows.

For boats fitted with flybridge the formula for total boat capacity is:

maximum capacity (adults) = 0.6L√B (nearest whole number)
where L = length of boat in metres and B = breadth of boat in metres.

For flybridge boats, no more than one-quarter of the maximum number of passengers allowed on board should be on the flybridge at any one time.



I wouldn't worry about it from a structural point of view, unless you have spongy decks damaged by water ingression. You will be at risk due to stability long before the deck collapses.
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