TOPIC: flotation foam or no flotation foam ?

Hi Everyone,

I'm working on a '61-'62 - 14' Lake N Sea Caribbean. The upper and lower halves are dismantled. There is a large foam ring attached to the underside of the upper half deck extending into the bow area and some additional foam attached in the underside of the fins and a little more in the ornamental transom pieces.

I'm not looking to start a debate on the type of foam or flotation product. I have done my research and if I add additional foam between the stringers, I'll use either the 2 part mix (2 or 4 lb, it is chemical resistant but if gas or oil were to get below the deck I think I would have bigger issues!)or ridged extruded (not expanded) polyurethane (home depot-lowes type, cheap easy to slice and my chambers are rectangular). There was no foam in the "bilge" between the 6 stringers, just open air. I am replacing the stinger cores and transom. I'll be left with 15 shallow void areas. I calculated these voids to equal approx. 9,834 cubic inches or 5.69 cubic feet which when filled with foam would yield approx 300 lbs of buoyancy force.

The new transom, stringers and deck will be composite no wood. All foam spec sheets allow for some small percentage of water absorption over time. Even in a composite bilge with 15 compartments there could be some condensation.

What is the consensus in the fiberglassic world regarding adding foam where it was not originally placed?

Put it in or leave it out?

If you put it in, has anyone had a bad experience in later years? My thought is that if I put it in and seal the deck down, I'll never deal with it again in my lifetime! I will use the boat, It won't be a trailer queen.

Thanks,
Eric

IMO, measure the CuFt of space you can get the foam below deck (floor) and multiply by 60lbs. See if you come up w enough flotation to keep the boat afloat.

A rough guess based on the pix you posted, is that you'll only have 1/3 - 1/2 enough, maybe even less depending on the outboard you mount.

So, if not beneath the deck, wheres the rest going to go?

Rigid and pour in both weigh about 2lbs per CuFt and float about 62lbs each (2lb pour in) so the net fain is about 60lbs per CuFt.

IMO pour in adds to the strength of the glass hull and makes for a quieter hull, which rigid doesnt quite do as well in either case.

I say foam it. Even if it's not enough to float the boat, it makes for a rock solid floor if you cut it even with the framing. Besides, it's a now or never proposition. A good glass job that runs about 4" up onto the bulkheads will ensure that it stays dry below.

thank you, yes calculated above at approx 300 lbs of buoyancy if foam is installed under the deck. Additional foam can be installed back in the bow where the original ring of foam is. It's still attached to the upper half. Will either leave it or replace with new 2 part foam.

original boat weight was between 450-500 lbs per sales sheet below plus maybe 175 lbs for the engine plus gas, gear and guests-

Just remember......

Interesting question. Part of my job with the USCG was testing boats for flotation and advising builders on how much to use and where to put the foam.

You run into a conundrum here. The point of the foam is to float the boat, but the point of where the foam goes is to make the boat float relatively level. On a 14 foot boat it doesn't take lot to achieve that. Putting it under the floor may result in the boat floating like a bobber, but upside down. That's why the foam was put under the deck. Foam does no good unless it is submerged. The idea was let the boat fill with water but when the water got up to the underside of the deck the foam would displace the water and keep the boat afloat, right side up.

Rather than go into a long discussion of how this is done and how the amount of flotation is calculated here's a link http://newboatbuilders.com/pages/flot2.html

HI Ike,

I took a look at the existing foam, pictures below. With a rough measurement and quick calculation as it is leaning against the wall, I estimate there to be approx 4 cf of foam under the deck, maybe less as there is an access hole to wire the bow light in the center and approx 1 cubic foot in each fin. So the manufacture put approx 350 lbs of buoyancy in a 450 lb hull at best. On the sales sheet I posted under the 1960 heading to the right it states "air cell". This is a '61-'62 vintage by Michigan Fiberglass Company. Perhaps the empty space under the deck was their "air cell"?

If I add the foam under the deck it would further offset the engine, gas, gear and guests weight. The 300 lbs of additional buoyancy would be very evenly distributed, bringing the total potential buoyancy up to approx 650 lbs. of buoyant force. Your "bobber" theory could happen but I think we are looking at even to 50 lbs more flotation in the top half.

The advantage of added support, sound and vibration insulation has me leaning towards adding it.

Have you or anyone else experienced an adverse performance effect from adding foam under the floor?

I've had a little carolina skiff J16 for years that I believe is foam filled and when it planes out on flat water you would think you are floating in the air (it depends on the number of riders).

If you distribute the flotation properly it should not be a problem. Generally boats with flotation under the floor have foam on either side and an empty space running down the middle. However, every boat is different and so you have to figure what is right for this boat.

Just a footnote. We tested a Boston whaler and it failed because it had too much flotation and rolled over too far. They actually had to take some out.

Actually you are fortunate that this boat had flotation. It was not required before 1972. Some builders did it voluntarily, but by no means all. I am not familiar with Michigan Fiberglass, but they must have been one of the good ones.

Hi Ike,

I appreciate your help both in the forum and via email. I'll be taking your advice and using the extruded poly board cut to size and wrapped in plastic. Your hands on experience in the USGC testing the various foams is invaluable.

So you had to throw another kink in this...foam all the compartments or leave the center 3 void!The center section is only 4" wide between the stringers and starts at 2.75" tall in the stern working towards 4" wide in the bow and averaging approx 3.75". I'll reach out to one more person that has done a restoration on this model boat, Andrew Gott, and see if he added foam and what the performance is like if he did.

Thank you,
Eric

Well, I'll hedge my bets here and say without actually seeing the boat, measuring it, weighing it, etc this is all an educated guess, but I would leave the center free. Actually these small boats need far less than people think because, when flooded (swamped) the boat, people and part of the engine that are under water weigh far less than they do when dry. If there is any wood in the boat, that also adds to the buoyancy. So you may not need as much as you think, especially for the hull weight and persons weight. Actually these small boats failed more often than not from not enough flotation to float the engine upright. They heeled too far over. 30 deg is the max allowed, and usually if they exceed that they rolled all the way over. That's why most outboard boats have large blocks of foam in the right and left rear corners of the boat. Usually the engine head is out of the water and if there is not enough flotation back there to balance the load, the boat rolls over.

Ike,
I've been out gett'in at it...per your research and experience; extruded NOT expanded board, sculpted and cut in, plastic wrapped and installed. I'll get a final calculation when I'm done regarding cubic inches and buoyancy force added. I'm just using the standard thickness boards available so it will be a bit less than I calculated above if I had used 2 part foam. Gota' love the harbor freight hot knife, $16 with the coupon!
Thanks,
Eric

Harbor Freight has hot knives?!?!?! I have not been spending near enough time there! So, what kind of plastic are you wrapping the foam in? And how are you sealing that? This will be some great insight when it comes time to do my Lake n Sea! Should be able to stuff a good amount of foam in the seat shells too.

most prob think i'm nuts but my 14'mantaray with the merc 700 weighs about 625lbs. the boat has no floatation. the hull is the floor. now a single pool noodle keeps me afloat and i'm 190lbs.
so i bought 8 pool noodles, taped them together, and attached em with t-rex tape to the underside of the deck. 8 x 190= 1,520 lbs. i think that should keep at least 1' of the bow above water for recovery. right or wrong???? ron

Except most of your 190lbs IS already water....... a typical pool noodle wont float a 12lb dead weight...

I tried standard tarp plastic. It's pretty thick for what I want it to do in this tight space.

The plastic in the pictures is a pallet or packing type shrink wrap, the thicker version. It conforms well to any shape and sticks to itself. Overlap and seam are on the back secured with a length of duct tape. Get a second pair of hands to help with the wrapping!

The possible absorption of water in this foam is less than 1 percent and grows slightly when immersed over time. There is a complete data sheet available on the owens corning web site for the formular 250 board commercial.owenscorning.com/assets/0/144/172/174/e45fe07d-5cc9-4e4b-866a-5e35d75090ec.pdf

Wrapping the board in the plastic per Ike's suggestion is just another precaution to keep water or condensation away from the foam.

I'll be adding something like foil tape around the perimeter prior to tabbing in the floor to ensure the resin does not seep through and attack the plastic or foam.

The boat will be approx 95% wood free. There will just be a small tab of wood left around the perimeter where the floor was cut out. Some of that has been removed as well. The transom, stringers and new floor are all composite materials.

I'll run a video compilation of the infrastructure build once the floor is installed.

soon as it warms up i'll attach 12 lbs. of bricks and try that. will let you know. ron

Foam done. I'll get some more in the gunnels when I get to the top half. Thanks again Ike. Headed to Carbon Core on Sat to get the new floor panels.

Looks like ya got as.much as ya possibly could stuffed in there.


For reference, whats the plastic wrap? Painters drop cloth?

It's the thick version of pallet or box wrap like saran wrap. It conforms nicely to the curved and sculpted sides & bottom on the sides. Sticks to itself. Seam on bottom sealed with a strip of duct tape. Use a helper for the large pieces to keep it from sticking on itself until you want it to!

Ike wrote:

Actually these small boats failed more often than not from not enough flotation to float the engine upright. They heeled too far over. 30 deg is the max allowed, and usually if they exceed that they rolled all the way over. That's why most outboard boats have large blocks of foam in the right and left rear corners of the boat. Usually the engine head is out of the water and if there is not enough flotation back there to balance the load, the boat rolls over.

Interesting. That would explain why my GW Invader 14 only had the 2 large blocks of foam, no foam anywhere else.

I'll leave the foam in the upper right and left wings as well as under the bow deck. There might be room under the wings for a bit more. Time to get the floor in-
thx

sorry I haven't been back here in a while, been busy. Looks like it's coming along well. By the way the boards these places sell are usually 2 inches thick, 2 feet wide by 8 feet which works out to about 2.5 cubic feet.

I used heavy tarp plastic. Polyvinyl plastic. The stuff is almost impervious to anything. Also nothing sticks to it. Epoxy sets up but just peels off. I used a really heavy packing tape to seal it up. It was the only thing I found that would stay stuck to the plastic sheet.