To foam or not to foam..that is the question..

[tartuffe]

I believe you need to check your math. Try hooking 5 noodles to your motor and tossing it in the water and tell me what will happen. That 200 pounds is based on the difference of the weight of water and the weight of a person for the same volume of water. In reality, you are probably only looking at 15 pounds of buoncy (sp?) per noodle.

[Destroyer]

Originally Posted by tartuffe

I believe you need to check your math. Try hooking 5 noodles to your motor and tossing it in the water and tell me what will happen. That 200 pounds is based on the difference of the weight of water and the weight of a person for the same volume of water. In reality, you are probably only looking at 15 pounds of buoncy (sp?) per noodle.

Hmmmm...how to answer this?.... Ok, lets try this.. You have a 12 lb rock, and you lower it into water on a string and find it weighs 8 lbs. (roughly a 33% reduction in weight) Now you take a 4 lb block of lead and lower in into the same water and you find that it weighs 3.64 lbs (roughly a 9% reduction of weight) Why the difference? Lets look at the math.
4 lbs of lead X .4536kg/lb = 1.814kg x 1000g/kg=1814.4g. This is weight of the lead. So the density of lead is 11.3437g/cc
What is the volume of the 4lbs of lead? 1814.4g /11.3437 = 159.94 cc (That's the volume of water that the lead displaces.)
How much does this water weigh? It varies..the density of ocean water is 1.027 g/cc (fresh water is 1.0 g/cc) so 159.94cc ocean water X 1.027 g = 164.26g (That's the amount of positive buoyancy applied to the lead when it is submerged.)
Now, converting back to lbs, 164.26g = .16426kg /.4536 (kg/lb) = .3621 lbs
So the weight of the submerged lead is (4 - .3621) = 3.64lbs
The reason for the difference is the density of the two objects. Lead is much denser and so it displaces less water and is less buoyant than the rock. So too, the noodle will support an average 200 lb person in much the same way that a life jacket filled with foam will, because the human body is much less dense (and so has more positive buoyancy) than an outboard engine or a fiberglass boat. As to boats, a cubic foot of polyurethane (closed cell foam)will float about 60 pounds of "dead weight". The wood parts of a boat will probably float, as well as the gas tank(s), so you don't need flotation foam to offset that weight. The fiberglass parts of a boat will barely sink, so you really don't need much foam to offset the fiberglass- maybe one cubic foot of foam per two hundred pounds (or more) of fiberglass hull. The metal parts of the boat are what you really need to account for. A small (4-6hp) outboard may weigh 45-55 pounds. A 50hp outboard will weigh about 200 pounds. So a 16 foot fiberglass skiff with a 50 horse outboard will need about six cubic feet of urethane foam to keep it afloat. A 12 foot plastic kayak will only need about one cubic foot. Conversly, a 30 foot fiberglass sailing sloop with a diesel engine and lead keel would need about 150 cubic feet of foam. (Actually, very few 30 foot keelboats have positive foam flotation, but it's not out of the question, especially when you consider all of the air pockets that would exist, as well as all of the wood interior components that provide some positive flotation). As far as our V20's and V21's go, I really don't know exactly how much foam it will need in terms of cubic feet. But I figure that Wellcraft's engineers did know when they started adding foam into the boats. By law they had to put enough foam in place to support the boat, gear and engine. So I intend to mimic the amount they used as closely as possible in the compartments, and then add additional foam in the gunnels and other places to make up for any loss due to voids between the noodles. But as far as the original statement goes, 2 boxes (40 pcs) of noodles should support 8000 lbs of human density weight, since each noodle is rated for 200 lbs of floatation. (200 lbs x 40pcs = 8000lbs). I'm fully aware of the differences of density vs volume. Maybe I should have made it a little clearer but hopefully you understand what I meant in my original statement a little better now.

[RidgeRunner]

Originally Posted by tartuffe

I believe you need to check your math. Try hooking 5 noodles to your motor and tossing it in the water and tell me what will happen. That 200 pounds is based on the difference of the weight of water and the weight of a person for the same volume of water. In reality, you are probably only looking at 15 pounds of buoncy (sp?) per noodle.

I came up with 12.8 lbs based on the assumption that the noodle is solid 2 3/4" diameter x 5'long AND that seawater that the noodles will displace if submerged weights in at 64 lb/cu ft. I was going to post how he//a strong I must be when I can submerge one while swimming with my arm fully extended. LOL I know it will work, just funny math.
Destroyer, Ever consider making some limber holes to allow the water to drain from all compartments?

[Destroyer]

Originally Posted by RidgeRunner

I came up with 12.8 lbs based on the assumption that the noodle is solid 2 3/4" diameter x 5'long AND that seawater that the noodles will displace if submerged weights in at 64 lb/cu ft. I was going to post how he//a strong I must be when I can submerge one while swimming with my arm fully extended. LOL I know it will work, just funny math.
Destroyer, Ever consider making some limber holes to allow the water to drain from all compartments?

It is, indeed, funny math. You have to conceptualize that water is buoyant and is actually pushing up on the foam. I think it's Newtons 2nd law that gives us the equations.. I'll have to look it up.

In all cases, Spareparts made the comment that he:

Originally Posted by spareparts

put drain holes in each compartment that feeds to the bilge. if you get water in an area, it will drain to the bilge and not puddle in any compartment.

I liked the idea so much that in one of my followup posts I said that

Originally Posted by destroyer

I like the idea of having each chamber able to drain into the bilge and get pumped overboard...

Truthfully I never knew they were called limber holes, but your idea is sound and exactly what I was planning to do. I plan on drilling 3/4" holes at the very bottom of each compartment and then cementing PVC pipe into the holes to make drains into the bilge area. If anyone has a reason to use a different size for the pipe I'd be greatful if they would tell me.

[macojoe]

WOW!! you guy are thinking way to much!! I had a 1974 V20 cuddy with a gill bracket on back with a 175 rude on there, we got hit by a 10 foot wave that filled the boat to the gunnles!! The boat never went any deeper then the gunnles that day!! it was a rough water day, and after 1 guy drove slow the other (me) bailed the water out till it was down to the floor, we made it home.
1974 had NO foam or anything! So I would not worry about all this noodle crap, get her done and go fishing!!

[Destroyer]

Originally Posted by macojoe

Get her done and go fishing!!

Now THERE'S a man that has his priorities in order!!!

[tartuffe]

Gotcha Destroyer. You and I are on the same page. I'm going through the foam chronicles myself which is what drew me to your thread.

I'm kinda new around here so I'll just it.

[Destroyer]

Foaming complete.. after thinking about it and everything I just decided it was easier to foam, make it all watertight and (like MJ said) go fishing. Made a few improvements though... Foamed it completely up to the bottom of the deck , and, as shown in the last pic (sorry its a little dark) in the transom area we glassed from the splashwell to the transom to add a little extra strength to that area. (There's a gap of about an inch and a half on both sides of the splashwell that we filled with putty and then glassed over). Don't know why Wellcraft didn't do that when they made the boats... just seems like common sense. Oh well.....





Moving right along.... Next I have to add the hatch in the front area as previously discussed, get new rod boxes for the sides and install them and then start mounting things like the bimini, radar arch, antennas, engine, etc.