View Full Version : How do I make it float higher
08-29-2011, 04:49 PM
I have just finished making a Pooduck Skiff and sank it in a near by reservoir to test is ability to float and be bailed out. It failed and I need to add some flotation. Does anyone have advise as to what to use and how to use it?
08-29-2011, 05:14 PM
To address this same concern, and because I managed to bruise/break a rib or two, I have spent the summer adding flotation rear and aft. I figured I could put that left over plywood from the transom to good use, so I have retrofitted bulworks just aft of the front thwart and just forward of the rear thwart. They have inspection ports (ugly) so I can stow some stuff in them. Some other people have done the same. I can post pics if you would like. No sea trials yet, I am about ready to varnish and paint.
Several other members have built Pooducks and will doubtless be along; if they don't show up, I'll recommend you start a new thread with a different title, something like "Adding flotation to Pooduck Skiff?"
08-29-2011, 05:23 PM
What do mean it failed? Did it go to the bottom? Or did you try to bail it out when sitting in the boat when it was awash? If the latter you will often have to bail the boat from outside (swimming/standing alongside or from another boat) for a good bit before it can be boarded and you finish off clearing the bilge of water. Otherewise you will have trouble getting the sheer above water enough to make progress getting water out.
If it just went down you might need flotation bags, air filled rubber fenders or some kind of flotation strapped under the thwarts fore and aft. The thwart fastenings (epoxied fillets?) might need strengthening in that case.
08-29-2011, 08:14 PM
I don't know the boat, but one cheap and practical way to add flotation to small plywood dinghies is to add blocks of styrofoam under the seats.
Styrofoam is available in 2" planks at Home Depot and the like. With a bit of coarse scuffing, it bonds with epoxy. I'd bond it to a piece of 1/4" ply and screw the ply to the underside of the thwarts. Add ply facings if you want to protect it. Unscrew it for cleaning and maintenance.
08-29-2011, 08:18 PM
The closed cell foam board sold as house insulation glues well with PL Premium too. It was about $30/4x8x 2" sheet IIRC.
I used it for a sort of catamaran kayak exit / entry aid, gluing up two 1' x 8' by 8" thick floats. I can stand on one of them without getting my feet wet.
08-29-2011, 10:58 PM
I recently finished a Pooduck skiff and added flotation tanks at each end though i have not tested them by sinking the boat. Perhaps I should give that a try. Here is a link to my building blog in which you should find some pictures of the flotation i built. Best of luck!http://sailboatforme.blogspot.com/2011/01/new-project.html
08-29-2011, 11:22 PM
How much floatation did you put in? The boat's displacement is about two cubic feet of water. Which in some ways does not matter so much since the boat should stay near the surface, not sink to the bottom. Your problem is that you could not self-rescue. Everything above the water pushes the boat down and the mast is at the end that inevitably has the least floatation. So if you after a swamping can get the rig off and swim into the boat and mostly lay or sit on the bottom, not a seat, then you need enough floatation hold maybe half the boat and perhaps a bit more than half of you out of the water - three cubic feet should do it. Ideally, after you shake the boat swarm in you should end up with a little freeboard and any open top to the centerboard trunk above water. For a boat like that, shaking is depressing at the bow and shove the boat away to let water come out that way. But swarm in over the stern where you can have lots of floatation.
In terms of pushing the boat up, the lower the floatation the better. In terms of stability, the higher the better. Go low and use your dynamic balance for stability.
There have been many crackpot notions of cheap floatation on this Forum, ranking from ping pong balls to old soda bottles. These are incredibly inefficient. In regular areas you might be able to shape some foam pretty well to fill some space but it's hard to beat pour in place. You can combine them by putting regular shapes of block foam - just one per space as big as can fit, and then pour to fill the edges.
Poured foam is exothermic, sometimes rather spectacularly. Mix small batches - I use a paint stirrer on an electric drill in paper disposable buckets since there's always something left in the bucket that makes it unusable for a second pour - to get where you want to go. Give thought to pouring as much as possible before putting on the final bulkhead or covering and pouring through holes.
08-30-2011, 04:43 AM
No need to go overboard with this. I discovered the same thing after swamping this dory on purpose, and all
you need is a little bit of foam in each end so simply hanging onto the boat doesn't sink it further to the point where you can't bail it out after swamping it. I use existing compartments (or build them) and use poly construction foam.
First get a good coat of wax on the paint to serve as a release agent so the foam can be removed when the time comes.
Then I alternate layers of poly foam and styrofoam to fill the space. Be careful with the expanding foams as they expand with enough power to distort the wood...always allow them space to escape.
08-30-2011, 04:55 AM
It's not too late to install some buoyancy air chambers. Here's a couple of pics of the ones I put in Shellbacks
08-30-2011, 05:54 AM
Note the holes blogs68 covered with access lids. These allow enough room for the pour, nice and neat, are watertight so in use they don't cause trouble, and can be opened when the boat's stored. With age unvented foam compartments can be trouble which this heads off. I've some in my dink that are well over a decade of use. This approach is especially good where the pour-around blocks approach I mentioned and which Bob so wonderfully illustrated is not so suitable.
Foam is heavier than air so if you're building a composit wood/glass/resin boat, you might well go with air tanks.
Some small boats really need to be bailed almost dry from outside before you swarm in. That's generally over the stern. Even if you're strong and active, bailing after a bit of immersion in cold water can take it right out of you, so no matter how tough-guy you are, it's nice to have a line going from one upper corner of the transom to the other and enough slack that when dropped back over it hangs down enough to get a foot in. When not self-rescuing, this line's a great bridle for the stern line.
08-30-2011, 06:06 AM
Those tanks were air tanks only - no foam
08-30-2011, 08:16 AM
I put an inflatable seat from a zode under the thwart. Also, some of the soft blue foam is glued to the bottom. (some is not).
This is my dingy to my cruising boat,which stays mostly in the Caribbean, which makes it easy to "test" out the system. (AKA falling down drunk).
Whatever you do, test it.
08-30-2011, 02:46 PM
I'm game for a better idea if anybody has one. Those plastic airlocks look fine on contemporary designs but would be unsightly on a 1890 dory. I've even considered soldering up some fitted copper air tanks, but the condensation from those would be worse than foam.
Besides....floatation is a requirement in many states, and thousands upon thousands of plywood and traditional boats have had their bilges filled with 2-part polyurethane foam up to the sole since the 1960's. Yet if there has been a parade of owners showing up here with problems caused by that foam...I've missed it. The poly sticks to the wood and doesn't let water in, and doesn't cause a temperature differential precipitating condensation.
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