flotation

[shipwrech]

flotationis has been covered a hundred times, but is xps pink board suitable for flotation in my chieftain? My other concern is if I can fit enough iny floor to make it stay afloat? Thanks

 

[Watermann]

Yeah II hear ya on the concern of there being enough room under the floor to float a Chief, there isn't much room for lots of foam. I would use the board though rather than the 2 part expanding. You can also put some behind the side panels too. I know I got more flotation into my Chief than the factory did, then there's the fuel tanks, wood, seats full of foam, extra PFDs and it all adds up to flotation too. Personally if things look bad I'm off the water and will wear my PFD when there's good waves or lots of other boat traffic around.

 

[Grandad]

Hi shipwrech. Yes, I believe the pink xps is suitable. It is an extruded foam as opposed to the expanded foam that white styrofoam is made of. I used the Dow equivalent which is blue in color as opposed to the pink that Corning makes. As to whether you can float your boat with insulation in the floor, you'd have to do some calculations that can very detailed. I would recommend that you be very efficient with how you shape your foam such that it completely fills the available space. If you put flotation only in the floor, you can anticipate it will cause your Chief to float inverted at the water's surface. Adding foam in some of the upper areas such as under the gunnels will encourage the boat to float upright. Remember though that flotation only helps when it becomes submerged, so don't expect foam under the gunnels will keep your feet from getting wet. - Grandad

 

[shipwrech]

thanks for the replys. so according to some of the flotation calculators that I have found I need roughly 20cu ft of flotation. If my math is correct I can only fit about 9 in the floor and 4 in the gunnels. 13 is a far cry from 20. do I even bother? May be my calculations are wrong I don't know. 18ft chieftain mk4 120 mercruiser. I figure I need to float 1250lbs. engine and outdrive = 700lbs, hull 1100lbs x .63 = 693 as per specific gravity, plywood 240lbs x -.81 = -194lbs cause it floats and 50lbs for battery. heres the calculator I used. http://newboatbuilders.com/pages/flotdiag.html Thanks again.

 

[laurentide]

Just fit it where you can. I figured that the amount of foam that I used on my Chieftain would at least keep it at the surface and allow it to be salvaged...plus something visible to hold on to. Lots of pfd's in the berth hatches, too.

 

[dozerII]

I totally agree with Chem put in what you can so long as it stays on the surface it Is better than going to the bottom

 

[Grandad]

Hi shipwrech. Here's a summary of the calculations that I made for my 21' Holiday. - Grandad
First column is water displacement in pounds. Second is cubic feet of foam. Third is location of foam.

177.19	2.95	Below 2 side pockets
702.00	11.70	Underfloor centre
192.50	3.21	Underfloor 2 sides
68.75	1.15	Behind 2 forward end side panels
75.00	1.25	(Second layer)
74.03	1.23	Behind 2 forward hull side panels
83.33	1.39	Behind 2 stern end side panels
130.56	2.18	Under 2 gunwales
125.00	2.08	Under foredeck
243.60	4.06	Nose wedge
200.00	3.33	Between hull ribs
123.00	2.05	Cork covered blocks (5)
2194.95	Lbs Total Displacement

 

[jigngrub]

When installed properly, you can fit more cubic feet of the 2 part urethane foam in a hull than the sheet foam. The expanding foam fills all voids, which means more cubic feet in the same area.

Just something to think about.