Why foam?

the question on the acid bottles.....are they used? does the acid kill the bottle over time. I guess you just have to make a choice and hope it was right. can you use to much foam? up under the deck glued up. in the sides behind trim areas. I could use pink foam and bottles.....pink foam between the bottles so the don't make noise lol

 

Ive never understood why people are so negative toward pour foam.

If you use proper craftsmanship when building and fitting out you will have no water ingress and no problems with foam.

Most foam nightmare stories are caused by poor craftsmanship

 

You certainly wouldn't use pour foam in a metal boat, welding would set it aflame, but a lot of the prejudice against it is unwarranted. Lots of boat building concerns like to spread the horror stories, they don't want to price their products out of the market, because it isn't exactly cheap .

 

Ive never seen a metal boat foamed below the waterline...above the waterline all metal boats are foamed. Or insulated in some way and will always present a fire hazard that welders need to consider.

The last few fires on yachts at the shipyard were insulation fires started by welders...be alert, these type fires are slow burn and deadly.

You dont know your boat is on fire until the shipyard calls you to report your smoldering heap or you see in the newspaper the next morning at coffee time

 

Foam under the deck is OK. Foam below the waterline is OK if it is sealed cell.
Acid bags are collapsible, naturally they are not corroded by acid. you push them into place
and inflate them with the blow side of a vacuum cleaner and screw on the cap. If the compartment is ruptured the bag will not float out like bottles or ping pong balls and it will not puncture, cos the plastic is tough, as befits a container of ACID. The bags are new, not used, so are not contaminated with acid. And best of all they are Light. Find them in your Yellow Pages.

 

most foam damage is from neglect......its expensive that's why people want another idea

 

or inaccessible in some regions!

 

it seems expensive any way you go. the acid bottles seem like an idea im going to check into. but im a little ways away. not much the sole is next after the motor mounts. the ply is the next thing to save for then flotation. I like all the ideas
how doyou figure out the 2 litre pop bottles flotation?

 

You could do it the old-fashioned way and hang some weights from a bottle in a tank of water until it sinks. Or fill the bottle with water, weigh it, empty it, weigh again and the difference will be your pounds of floatation. For the most accurate measurement, be sure to fill with saltwater if you are going to be using the boat in saltwater. If you're too lazy to do any of that, the net fluid ounces on the bottle should get you a close approximation.

Obviously, the interstitial spaces among/between the bottles will not provide floatation if there is water infiltration into the hatch. That is why I suggested foaming in amongst the bottles. As well, the foam will keep the bottles in place so they are not rattling (or escaping during a hull breach), and jostling bottles will eventually rupture from (rubbing) friction fatigue (will take a long time, but it will happen).

There are various calculations for determining the volume of hatches using cylinders, rectangles (cubes), triangles (pyramids, cones), etc., all easy to find online. Once volume is determined, floatation is an easy calculation as roughly 64.2lbs per cubic foot of saltwater, or 62.4lbs per cubic foot of freshwater (it varies slightly due to specific gravity of water at various temperatures, but not enough to be concerned about it with your calculations).

 

There is another type of foam used in packaging. Similar to polystyrene but more plasticky and spongy in feel and not made up of lil balls. Usually sheets laminated and cut to fit home electronics. Has anyone tried this?

 

I think it is a form of polyethylene you are describing. Closed cell, but flexible. Would do the job, in fact is what is used in non-inflated boat collars, pool noodles etc.

 

Thats the stuff, pool noodle wife basher thingys I like it cos its a lot less messy then styrofoam. I have gone around all the home centre stores here asking them to keep it for me