Composite floor, expanding foam question

This is my first post, so let me first say thanks to everyone for the awesome information in the forum, and a thanks in advance for any replies I may get to this question.

As a background to what I am trying to do, I have a Mastercraft Tristar 220 that I want to modify to have a self bailing deck. The hull is in good condition, and was originaly built with a 100% composite stringer system with all internal voids filled with flotation foam. The existing floor surface is solid fiberglass with no plywood core. (except access panels) The floor is in great condition, but is too low to add scupper valves for self bailing plus there is a structural crossmember at the transom that dams the water. I want to raise the whole floor about 3" to have positive drainage to the transom, and have the valves safely above the waterline.

My plan is to build a 3" high grid of PVC board on 12" centers fastened with epoxy to the existing floor. Then fill the grids with expandable foam level to the top of the grid boards, and then cap with ALUCOBOND panels as the new flooring surface.

My goal doing it this way is to use no wood as the hull is already all composite. I can buy the PVC board at the local home store. I already have plenty of the Alucobond panels, and have used them in many applications with good results. And I want to fill the voids with foam to increase the bouyancy (or counteract any moisture intrusion in the existing foam), and to provide a little extra support under the Alucobond panel.

So my questions are:

First... Is there any major flaws in this plan, or any alternate ideas?

Second, has anyone used this PVC board in a marine environment? I have used it on homes, and it seems to work as advertised. It is pretty weak compared to most types of wood, but my thinking is that the foam will add structural support, and should be fine. Any opinions?

Would 2# foam be strong enough, or should I go with 4#, or higher? Any real world experience is welcome. I tried a sample of the panel on a one foot square grid, and was barely able to deflect it with my body weight on one foot, so I am guessing with 100% of the void filled with the 2# foam would be fine, but I do worry about compression over time.

Probably my biggest concern is getting 100% of the void filled with the expanding foam. My plan to date is to drill 1.5" holes in the verticle boards that form the grid so I can foam each indvidual 12 inch square cavity, and cap if with wax paper, and a board. My plan is that any extra expansion will flow into the adjacent cavities, and leave a flat surface on top. The wax paper would then peel off without too much struggle, and I could then epoxy/screw the Alucobond to finish it off once I have filled each cavity.

The last one may be hard to visualize without an illustration? I hope I described it well enough.

Any tips, thoughts, etc. on the above is welcome. If it makes no sense the way I described it, feel free to tell me. I did my best, but I may have to draw a sketch, and post it to better describe what I have in mind.

Thanks!

 

Material links

My links did not come through in the original posts for the PVC boards, and Alucobond so I am trying again.

Alucobond
http://www.alucobondusa.com/alucobond_what_is.html

 

PVC board:
http://www.lowes.com/pd_238345-9989...ard&pl=1&currentURL=?Ntt=pvc+board&facetInfo=

 

I suggest you enjoy your boat as it is. What you are describing will eventually become a waterlogged sandwich between the original and new deck. It is a misconception that these foams do not absorb water.

I understand wanting a self bailing deck, but Mastercraft builds a fine boat and I would be reluctant to modify it as you describe with the only advantage being self bailing.

What you describe will not "increase buoyancy" but only add unnecessary weight. The only buoyancy you will enjoy is if you swamp her.

PVC Board works very well in the marine environment, but the products I am familiar with have no UV protection and so must be painted if used outside, otherwise I thinks it's pretty good stuff with a good price.

If you decide to do this I would fill the voids before putting on the new deck and then level the foam. Those foams can really get away from you once they start to expand and can be very destructive.

Steve

 

Be careful when raising the cockpit sole of a small craft. It may affect its stability. Also, its always best to use marine grade materials. Nidaplast is widely available , makes a good cockpit sole and is not too expensive . Google the boatdesign net forum

http://www.nidaplast.com/en/composites/sandwich-panels

 

Steve, Thanks for the advice, I believe it is sound, and I share your concerns.

I understand the bouyancy is only realized if the boat is swamped, but that was really my goal. I also know the foam will eventualy waterlog if subjected to constant exposure. In my mind, replacing it once this happens is part of an overall maint. schedule over time. The original foam seems dry with limited exploration, but I plan to do a few more core drills to confirm. In addition to a few cubic feet in this raised area, I plan to add some foam on the the gunwales to help it stay level it it should swamp.

I know this foam has a bad reputation for failing over time, but if it takes a few bucks, and some time replacing every it few years I feel that is a fair trade off for the piece of mind knowing if it ever takes on a lot of water it may just be a level swamp rather than just the bow bobbing in, and out of the water.

I am not sure what my other options are? I could try my best to seal the interior passages, and plumb them to drain into the bilge, but if I ever lose the bilge at dock I can see this failing as well. Any guidance is welcome, I reluctantly am still leaning towards the foam knowing it is not a permanent solution.

Is there a better type of foam? Perhaps epoxy encapsolated bocks to fit inside the grid I am proposing? I am here because I am looking for the best option, and the pour in expanding foam was my best guess when I started thinking about how to do this.

I am pretty determined to raise the sole to have it self bail. It may be a mistake in the end, and I probably just need another boat, but the low freeboard of the boat makes it very easy to take the occasional shot of water over the bow. Obviously you try to avoid this, but I just want a little more assurance that if this happens it does not lead to a game over situation. It is fine for a glassy morning, but in reality it gets used in conditions that are not always perfect. I am not looking to add a safety margin to go out in water I would not go out in before, just make it safer in the event I get in a situation I could not predict.

Truth be told, I want to use it every now, and then to do a little fishing off of in protected waters in the middle of the day.

Thanks again!

Chris

 

My main goal with this whole part of the project is for a little extra margin of safety so I am interested in how this may impact my overall stability. I realize I am raising the center of gravity for almost all of the loaded weight by about three inches, but considered this negligable. Is this realy enough to cause significant stability changes? The boat is 22' LOA, 96" beam, 2,700# unladen with a very flat bottom at the stern. I am not asking for some sort of calculation, just a practical impression. The extra structure as I envision it should be less than 100# added very low.

Was this just a word of caution, or do you get the impression from this information that this is going to lead to any appreciable instability.

I shudder when I see the amounts of lead ballast, water tanks, towers, etc. I see thrown on these boats by guys trying to modify their wakes. I just figured given the stuff done on a regular basis was way more than my plans.

I am not trying to justify a dumb decision with other dumb descisions, but to my way of thinking adding three inches in elevation to the sole is a fair trade off to have the deck self bail. If I am off base I would like to hear any opinions before I get started.

 

Hello Chris,

Happy to see you considered my post in the spirit it was written.

Michael makes a very good point and further expands my comment:

"Mastercraft builds a fine boat and I would be reluctant to modify it"

with: "It may affect its stability"

I can understand the sinking at the dock concern as I have seen this happen many a time and it is a real concern with any non self bailing (and even self bailing) boats.

Do you plan to leave it in the water for extended periods without checking on it? Is it going to be mostly trailered?

Why the concern regarding floatation after swamping? Where are you boating that this is even a real possibility?

Proper battery control and bilge pumpS in a clean bilge will keep her from sinking at the dock and you REALLY have to do something pretty extreme to swamp a 22ft boat in calm water, even here in So Florida boat swamping even offshore is pretty rare.

Steve

 

Steve,

I will trailer most of the time, but it will spend some time at a slip in the summer. The slip is on Chincoteague Island in Virginia. It may stay on the water for a week at a time, but there is no power, and it is not right by my friends house so it will not be closely watched. The slips are well protected, but there are frequent thunderstorms that time of year that not only fill them from the sky, but in a bad storm the waves may get bad enough that in conjunction with extra rain water make me a little nervous. Plus I never know where I may tie up overnight if I get out of my normal routine.

At the Island, I will stay in the bays, and only plan to go out on good days. I also want to use it a little in the Chesapeake Bay, again in good weather. The problem is, even a good day can turn rough if a storm sneaks up. In a perfect world, you see bad weather coming, but that is not always the case.

I was once swamped in a bass boat in a pretty large body of water, and while it was bad we managed to get back up, and running, but from that point on, I realized that having a plan, and a boat designed to deal with such an issue can really be a life saver. That day I was in a 20-22' Champion bass boat on the St. Lawerence river. It was a couple mile wide section with less than 2 foot waves from the wind, but it is also a seaway, and the wake from a tanker worked just right with the shore, and wind waves to really dunk us a few times in a row. That was the only time I ever had a scare like that, but this boat has about the same freeboard as that bass boat, and I am slightly paranoid. Especialy when some of the best bay fishing is not in the warm summer months.

After reading the feedback from earlier, I took a break at lunch, and made some more measurements. As best I can tell, the sole is about 1.5" above the waterline when empty. It is an option to plumb an inline scupper valve so that it would self bail all but about an inch of water above the sole, and what resides in the bilge. That may be the best compromise to keep it from really getting swamped, and trusting the bilge to handle the rest. The thing I cannot wrap my head around is if it takes on a lot of water over the sides, will it shed enough water through two 1.5" drains, or will it get loaded down enough that the drains are useless?

If I scrap the foam in the floor idea, I would then form a collar of foam around the perimeter of the floor just above the waterline. This would be easier to replace over time, and as I understand things would help maintain level even if the boat as a whole would sink a little lower.

At the end of the day, I am least worried about it going down in a shallow slip. What really concerns me is some freak chain of events that swamps it in the open water with others aboard. I guess I am getting old enough that my cowboy ways are losing out to the side of me that witnesses unexpected things happen every day.

I am spending the winter refurbishing the boat, and I want to do everything practical to make it as safe as possible.

Again, Thanks for your input! I am a pretty hands on guy, and have lots of mechanical experience, but boat flotation is not my specialty so I am reaching out for sound advice.

Chris

 

I know this is an old post but I had an idea: instead of using expanding foam, which has decent weight, I would put something like pingpong balls to add buoyancy without a lot of weight. The fill isn't structural if the rest of the framing is braced correctly, so the only purpose for it is emergency floatation. And the balls would be somewhat supportive of the framework too. I've even heard of using pool noodles to add emergency buoyancy to a boat.