Floor re-build question

[frankk]

First post ? Floor / stringer rebuild..
My boat is a 1975 Hobo, manufactured in Canada. It is an 18' camper boat. See it here.. http://electronicinstrument.com/toocute.jpg In any event, the entire floor in the cabin is fiberglassed on the sides to the hull. There is no way for water to get under the floor except for the bow which is covered but raw fiberglass, as in no floor, but that first stringer (the bow one) is fiberglassed. So, any water that goes into the bow goes down a 11 foot or so sealed fiberglass 4? pipe to the back of the boat. There is no way for any water in the stringers to drain out through this pipe! I had spongy floor issues so I decided to remove the floor and uncover the stringers. In-between the stringers is some sort of foam. The foam was completely saturated. So here we are, about ready to rebuild the stringers and a new floor. My question for your experts is ?should this long 11 foot 4? dia pipe have water entry points to allow water in it from the stringers and drain out or should I seal it like before and seal the front by the bow like it was before? Also, should I use polystyrene sheet foam insulation sold at Home Depot or Lowes in-between the stringers or should I use some sort of pourable material in it like it was before. So, two questions.

 

[jigngrub]

Re: Floor re-build question

Your cutie-pie pic is... cute, I guess... if you're into that sort of thing.

But we need to see pics of the inside of your boat, what you're working on. Verbal descriptions get lost in the translation.

If your foam is wet, it doesn't sound like your 4" f'glass tube was doing any good. You may want to delete it entirely and opt for a working bilge.

Some people like to use the sheet foam in f'glass boats but I'm not a big fan of that application, your best build will be with 4 lb. density 2 part expanding urethane foam. IMO

 

[frankk]

Re: Floor re-build question

Yes the 4" tube had no slots in it to allow drainage into it. Here is what I have done in the last day. http://electronicinstrument.com/toocute_html_4dafa198.jpg

 

[jigngrub]

Re: Floor re-build question

If the foam was poured completely solid in that area drainage holes wouldn't have done any good. The foam would've had to become completely saturated for it to start draining and would never drain completely anyway.

Do you know how the water got into that area? Holes drilled in the deck and not sealed, then exposed to the elements?

What area drains into the pipe?

 

[frankk]

Re: Floor re-build question

Yes, it looks like it was poured completely as it is solid! My only idea is that this boat has an odd splash pattern, water goes over the deck all the time if you are on plane. The door needed to be sealed better, I can see now that it was never done! So my thought is to use PVC, some of the fiberglass is rotted out anyway (it is v-e-r-y thin) ... and seal the floor sides as was before. At least this way if any water comes in.. at least it can do out the back of the boat. So you are saying to use a 4 lb. density 2 part expanding urethane foam. When it expands how do you scrape it off then? Any manufacturer in mind for that? Does it absorb water (like the old stuff)?
Oh, the bow drains into this pipe (only as in when it was made), but now.. I am thinking some sort of slots or so so the stringers can drain also, rather then get trapped.

 

[shaw520]

Re: Floor re-build question

You dont want to cut the closed cell foam once it sets,.. that will break the water tight barrier,.. instead, complete your stringers/decking first, then drill 2" holes at strategic locations and pour foam in cavities,. allowing the foam to fill cavity and expand up to the deck, ads integrity while remaining water tight.
Im doing this now to a Searay 230, 2 part foam can be purchased on this site reasonable, (part #701800)

 

[frankk]

Re: Floor re-build question

Got it thanks! So what do you think about my idea on some sort of slots on that 11' tube for drainage on the stringer "boxes?"

 

[ondarvr]

Re: Floor re-build question

Use 2 lb foam, 4 lb is double the cost and weight with no real benefits. You can shave the foam if you pre-fill the space before putting the floor down. You are only breaking the cells at the surface, all the cells under it remain intact and watertight. If you want you can seal them with resin. You need to be careful when pouring the foam through holes in the floor, it expands a great deal and may push the floor up, it doesn't always happen, but can. The expansion rate varies a great deal with temperature and humidity.

A drain tube is a good idea, it just needs to be done correctly, more details can be supplied if you decide to go that route.

 

[frankk]

Re: Floor re-build question

Hmm did not post my comment.. retry.
Yes I am very interested in that. Especially now thinking about the expansion going into the slots, etc in the new pipe.
Friday I am going back in the boat, so YES, I need suggestions.

 

[jigngrub]

Re: Floor re-build question

There should not be any slots or holes in your drain pipe, your foam needs to be completely sealed off from exposure to water. Putting drain holes in the pipe will expose your foam to water that runs down the pipe, and that's the last thing you want.

4 lb. foam is twice as heavy as 2 lb., but I doubt the area in question will take more than 4 cubic feet and that only adds up to 8 extra pounds over the 2 lb. foam.

4 lb. foam is twice as expensive as 2 lb. foam, but it is also twice as water resistant as the 2 lb. ... you get what you pay for and there are real benefits for using a denser foam. Another benefit of 4 lb. foam will be better deck support because the foam is stronger and it will protect your drain pipe from future damage better. You didn't say if your drain pipe was already busted when you removed the decking and foam, but if it was... that's where all the water came from that soaked your foam and rotted your wood.

 

[ondarvr]

Re: Floor re-build question

4 lb starts out as twice as heavy, and will still absorb water, the time frame isn't much different once it begins to break down. typically new construction uses 2 lb or less.

When used as a structural component it fails rather quickly, the cells are somewhat ridged and weak, so when stressed it crumbles. You are much better off building up the laminate with more glass than relying on the foam for strength. Foam used as a core for strength is of much higher quality.

 

[jigngrub]

Re: Floor re-build question

4 lb. foam product description from USComposites:

4 LB Density Urethane Foam


Common Applications: This 4LB density foam is suited well for most flotation applications that require more support than the 2LB offers. This foam is recommended to be used when supporting gas tanks and some deck areas. Choose this density if you feel that the foam will be required to withstand minor to moderate loads. The 4LB density also works well in floating decoy or taxidermy applications as well as many other sculpting, casting, carving and other filling applications. More questions? [Try our Foam FAQ.]

This product doesn't break down any quicker than the 2 lb. density and is twice as strong and twice as water resistant.

 

[frankk]

Re: Floor re-build question

Hmm ok, I am getting it.
So, seal off the floor on all sides, use the pipe for taking the water from the bow of the boat as it was intended then, kinda makes sense then.
Do you think I should use schedule 40 or maybe some soft of 3" non-slotted drain tile (the black flexible stuff? I was thinking 3" to keep the stringer more rigid (more mass on the vertical side, thinking of what you said above.

 

[frankk]

Re: Floor re-build question

Here is a blog I am doing better pictures for you to view and comment on, http://www.electronicinstrument.com/toocute.html

 

[frankk]

Re: Floor re-build question

Not mine but here is what another fellow did. I note his drain line is not one piece. http://www.electronicinstrument.com/too.pdf

 

[jigngrub]

Re: Floor re-build question

Hmm ok, I am getting it.
So, seal off the floor on all sides, use the pipe for taking the water from the bow of the boat as it was intended then, kinda makes sense then.
Do you think I should use schedule 40 or maybe some soft of 3" non-slotted drain tile (the black flexible stuff? I was thinking 3" to keep the stringer more rigid (more mass on the vertical side, thinking of what you said above.

I'd use the rigid schedule 40 pvc for a couple of reasons:

1. It's very strong and it isn't going to get crushed below deck like the fiberglass, since it is strong/rigid it'll be less likely to be pushed from side to side when pouring the foam and will remain straight and true.

2. The smooth inside of the schd. 40 will let all the water drain out as opposed to the corrugated/ringed black drain pipe that will retain some water and never drain completely.

I wouldn't reduce the size of the pipe unless the 4" schd. 40 just won't fit below your deck, the 4" schd. 40 and 4lb. foam will be a very strong build and allow you the most drainage benefits.

 

[ondarvr]

Re: Floor re-build question

4 lb. foam product description from USComposites:



This product doesn't break down any quicker than the 2 lb. density and is twice as strong and twice as water resistant.

It is the same as 2 lb, only the expansion rate is different. I didn't say it broke down quicker.

There is a reason it's not used in the industry for this purpose. I only see it used in the DIY sector, sort of a "if 2 lb is good 4 lb must be better" line of thought. It isn't bad stuff, just not really needed.

This type of foam only really has one purpose, and that's to meet the requirement for the floatation spec in the build code. Because it may be used for decoys doesn't mean it's good for boats. Bedding gas tanks in foam is a bad idea, but done frequently.

 

[Woodonglass]

Re: Floor re-build question

JNG, I'd really appreciate it if you'd post your source for where it says specifically that the 4lb foam is twice as water resistant as the 2lb foam. I've not been able to find that posted in my research. All I've found is that Closed Cell foam is water resistant due to it's makeup but nothing about the density increasing the water resistance. Thanks.

 

[jigngrub]

Re: Floor re-build question

It is the same as 2 lb, only the expansion rate is different. I didn't say it broke down quicker.

There is a reason it's not used in the industry for this purpose. I only see it used in the DIY sector, sort of a "if 2 lb is good 4 lb must be better" line of thought. It isn't bad stuff, just not really needed.

This type of foam only really has one purpose, and that's to meet the requirement for the floatation spec in the build code. Because it may be used for decoys doesn't mean it's good for boats. Bedding gas tanks in foam is a bad idea, but done frequently.

So you missed this part of the product description??? VVVVV

4 LB Density Urethane Foam


Common Applications: This 4LB density foam is suited well for most flotation applications that require more support than the 2LB offers. This foam is recommended to be used when supporting gas tanks and some deck areas. Choose this density if you feel that the foam will be required to withstand minor to moderate loads.

JNG, I'd really appreciate it if you'd post your source for where it says specifically that the 4lb foam is twice as water resistant as the 2lb foam. I've not been able to find that posted in my research. All I've found is that Closed Cell foam is water resistant due to it's makeup but nothing about the density increasing the water resistance. Thanks.

Read here:
Flotation - Flotation Materials

It's not really that hard to figure out that a more dense material will repel water better.

 

[ondarvr]

Re: Floor re-build question

Theoretically in 4 lb there would be twice as many cells at half the size of what's in the 2 lb, so it could extend the time it takes to fully saturate the foam. But there are many ways for the foam to fail, and once the freeze and thaw cycle starts the cells rupture quickly.


Pour foam is a rather crude product and lowest cost is the driving factor for users and suppliers, it is also highly affect by temperature and humidity when expanding. So in the way it's used in this industry the final foam product can vary a good deal from one mix to the next.

I've seen extremely brittle foam, and somewhat flexible foam made from the same drum's, this is why it's actual physical properties aren't relied upon in construction. Sheet foam is used when the actual strength of the foam is factored in for strength.