Boat purchase: Commercial Jon boat

M

Michael J.

Member
I am looking at buying a 22 foot commercial Jon boat, when I looked at the pictures the first thing thing I noticed was the wide open interior, then I thought, no flotation. The reason I am buying a bigger boat is safety, and in my mind flotation equates safety.

How does one determine the amount of flotation you need? Our current boat has split rear seat pods with flotation in them and flotation under the front deck, but with all the weight of the blind, heaters, stoves, propane, installed floor, shelves etc., I think if we took on water the boat would sink to the bottom.

Bigger boat, bigger blind, more stuff, how much flotation does a boat need?

Where are the critical spots for flotation? Does flotation under the floor do any good?

Thanks for any insight.

Mike
 
Any flotation you can add that doesn't get in the way of function is a do bee.

You may have enough already. Contact the Sea Ark folks and get the proper dope from them.

That 22 Sea Ark is a hoss of a boat and it'll need a lot of motor.

Do right by the boat and it'll do right by you.

best,
Harry
 
Flotation in the floor is better than none, but not the best place. If she is sunk it will act as a righting moment and try to flip the boat to get on the top. Not good. Best if you can fill the "corners" per se. The bow is easy with a closed in triangle that comes up to deck level. The stern needs more to carry the motor and its weight. A side setup like you described works well and is good if you can make it fit your use.
I think its Lee who has the bouyancy numbers. You need to take the boat and motor weight and then get out a scale and start to weigh your gear and crew.
If you are serious you weigh the worst case senario. The coast guard only makes the OEM meet the minimum for the Rating and loading.
A good eye opener is to take the boat and load her to the weight you think you will operate at using buckets of sand. In summer weather, with the motor off and then down flood in fresh water. It will open your eyes.
We get to salvage a number of boats in any given season and seeing how they handle in a bad situation separates the good from the not so good.
 
Sorry bout that chief . I've seen a number of the 22 SEA Arks used by gov't and road contractors. I'd add side flotation betwen the ribs and cerainly some under the floor.

If the boat has built in seats, I'd add some there too. With apologies to my Dad who was a coastie just prior to WWII,If you take it to the Coast Guard you may be asking for trouble.

In other words stuff it with flotation and tell the authorities nothing you absolutely don't have to.

Good luck with the project,
Harry
 
Found some information on the Coast guard page for homebulit boats and they had some equations to determine different levels of flotation and the placement of the flotation material in the boat.

Not having put a pencil to it yet, I would guess a metal fabricator could install some compartments in this boat and I could achieve the desired amount of flotation I would need.

Anybody know the name of the 2 part liquid that forms the floatation foam? Is it impervious to gas and oil?
 
If I am the "Lee" Bob was referring to...I don't have any numbers or fuzzy math equations. It looks like you found the stuff though. Just remember....foam floats, if it is in the bottom of the boat, then the bottom will float. Try to keep it as high as possible and in a 3 point configuration. The hull may be full of water but it's better than trying to hang onto the bottom waiting for rescue. A bucket tethered in the boat could be a lifesaver to empty it out in the event sinking does in the electric bilge...plus, bailing will keep you warm. You may think about foam around the gunnels, boxed in and bow and stern compartments filled with 2 part foam. The name of it to google is " two part foam" I bought mine from 2 different places, one in Florida was half the price and gave more yield but I can't remember the name of the company. Clark Craft and GlennL both sold it too. Different densities float differently.
 
Lee,
I thought it was you who had some simple math for volume vs weight flotation numbers. Hope whoever it was reads this and can add it.
 
Bob,

Maybe this line of thinking will help:

Water weighs roughly 8lb/gal (8.34 to be exact) , so we can assume that a (volume unit) gallon of foam will displace 8 lbs. Thats your flotation number and 1 gal = .134 cubic ft

So you can do this two ways.

1) Calculate how much flotation is NEEDED: i.e. 500 lbs of flotation would require 500lb / 8lb = 62.5 x .134 = 8.375 cu ft or a volume of foam roughly 1' x'2' x 4'

2) Calculate how much flotation is present: i.e. 10 cu ft / .134 = 74.63 gal (x8lb) = 597 lbs of flotation

This is all rough calculation and doesn't account for the volume of foam itself or the "level" of flotation of any boat involved. That means that a swamped boat "floats" but you still rather be in a dry one.

I am pretty sure that these numbers are reasonably correct but I may be wrong...hope it helps

Heres a couple of handy converters that you might want to use

http://www.unitconverters.net/volume-converter.html
http://grapevine.abe.msstate.edu/~fto/tools/vol/index.html
 
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