[Rhodes22-list] Hull strengthening

[Graham Stewart]

James:

Interesting. I am wondering whether 240 lbs of flotation would be adequate
given the weight of the boat - I have no idea what the weight would be when
submerged to the gunnels. I have not been able to see under the cockpit to
judge how much flotation there is there but I assume it cannot be very much.
If the original flotation is adequate to keep the boat from sinking
presumably if you replace the flotation with an equivalent volume of new
flotation, that should be adequate. I do think, however, that white bead
flotation would be questionable and I wonder whether what you found was
actually the work of a previous owner. I would want closed-cell flotation as
the white bead stuff can become waterlogged and if that were to occur, for
whatever reason,  would need to be replaced- or worse. I think that
high-density foam is closed-cell or close enough but I would want to check
that out. Is it the same as the pink flotation blocks that Home Depot sells?
If not, you might be better to cut up the flotation blocks to fill the space
or use foam-in-place.

I just found the following excellent article on the subject on the Glen-L
site that takes much of my guess work out f this discussion:
http://www.glen-l.com/weblettr/webletters-7/wl55-flotation.html 

Graham 


-----Original Message-----
From: rhodes22-list-bounces at rhodes22.org
[mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of James Nichols
Sent: December-20-13 11:02 PM
To: The Rhodes 22 Email List
Subject: Re: [Rhodes22-list] Hull strengthening

Graham,

Our boat is a '71 model.  The hull liner runs from bow to just before the
stern and was what formed pretty much all the structures inside the boat.
The only exception was the main cabin floor which was kind of a triangular
tub in the middle of the boat.

The blocks I pulled out of my boat simply looked like recycled shipping
foam.  My plan is to go back with some foam, but not as much as was there
previously.  I would like to recover most of that area for storage.

My plan for the foam replacement is the 1/2" sheets that Home Depot and
Lowes sell of high density foam insulation can be cut into strips and line
the hull. I plan on shoving it up under the hull liner as well to get foam
where there wasn't previously any.  When I lay in the framework for the new
v-berth, I'll add in the foam afterwards and then sheet over it with 1/4"
ply to provide a durable surface to push all those things we want when
cruising for the week.  My retired father-in-law plans on cruising Puget
Sound and beyond when we finish so we want as much storage space as we can
get.

By my calculations, I'll be using about 3 sheets of the foam which will get
me 4 cubic feet of foam lining the boat.  The foam weighs about 1.5 lbs per
cubic foot and water weighs a little over 62 lbs per cubic foot, so I'll
gain about 240 lbs of positive flotation in the cabin area, and I haven't
disturbed the positive floatation under the cockpit yet.

I'm thinking I'll leave that area alone.  The wood for the bulk head going
back that way only has a little mold growth on it and is fairly solid still.
The difficulty of removing the wood bulkhead and figuring out a method of
utilizing that area would be extremely difficult.  I can most likely just
kill the mold with a fungicide and finish drying it out so that it doesn't
continue to rot. The more I think about it the more I like the idea of
leaving it along.

As for strengthening the hull by adding more glass to the interior, on the
interior of my hull, the weave is very apparent so roughing up the surface
would be difficult unless I sanded the weave smooth to be sure I had abraded
all surfaces.  Doing this would remove a lot of material, at least 1/8",
from the hull.  My opinion is the hull would be better off left
undisturbed.  As you suspect, attaching the bulkheads and other interior
components that you plan to go back with to the hull thoroughly will help
with stiffening the hull.    James
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