Buoyancy retrofitting advice on Leo Blockley website
Stephen and Jane
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Jane and Stephen
Stephen and Jane
Kieran
Carl's guidelines are excellent, and very achievable by most handy folks
responsible for boat repairs around rowing clubs. So, what I'm about to
suggest is not meant to replace or supersede his retro-fitting suggestion.
I wonder if for clubs or boat owners who for whatever reason do not/can
not do the retro-fit for a boat, would inflatable bags be a viable, if
temporary stop-gap (no pun intended) solution?
In kayaking, swamping is almost a certainty. If you roll over and are
unable to successfully execute an Eskimo or similar roll to right
yourself, you must get out of the boat, which opens the cockpit to the
influx of water into the hull. To minimize the effects of this
flooding, kayakers stuff specially shaped inflatable bags into the bow
and stern portions of the hull, reducing the flood-able volume of the
boat buy around 60% (depending on the kayak).
Here are some examples of the types of bags used by kayakers:
http://nrsweb.resultspage.com/boating/Float%20Bags
So, it seems to me that it wouldn't be too hard to design some shaped
specially for the bow & stern hull volumes of a rowing shell, as well as
to fit under the seat decks of each rower.
Again, retro-fitting is probably better if you have the resources and
the time. But I can imagine that there might be some boat owners out
there, who do not have the skills, materials, etc., to do the retro-fit.
Wouldn't this be a viable 2nd option?
-Kieran
Carl
Thanks, Kieran -
Bags _could_ be a viable alternative, but first there are a number of
snags to be considered:
1. Sizing.
As the NRS website you quote does emphasise, bags need to be a
significant bit larger than the space to be filled. Only then will they
can easily creep into every crevice, which might cause problems with
bits of bag bulging out in inconvenient places. If under-sized, they
leave large unfilled voids & ample unfilled cross-section to allow water
to flow along the boat, which is not desirable since it allows pooling
at one end. Bags offered here in the UK for use under slide-beds have
been quoted at only ~7kgf/70newtons/15.5lb of buoyant support; you can
get 2 of these, side by side, under the slide-bed but that gives only
~1/3 of the buoyant capability you'd get from properly enclosing the
same void.
2. Over-inflation.
Rowing shells aren't designed or built to be internally pressurised.
Put more than minimal air pressure into a bag & you can destroy a boat.
0.1atm/0.1kgf per sq cm/1.5psi (which you can do by mouth) will
generate 350kgf/770lbf of upward force on one slide-bed of an eight.
That's ~1/3 of a ton or tonne on something meant to support no more than
1/3 of that load, & in the opposite direction too! So imagine the
effect of someone deciding to inflate bags quickly with an airline
delivering 4 atm/60psi air-line (& most compressors deliver ~7atm).
3. Slide bolts.
An inflated bag, however soft, will prevent access to slide-bolts
4. Maintenance.
This has 2 aspects which rowers are likely to disregard:
a) maintaining correct pressure - who wants or will bother to check
that all bags are correctly pressurised?
b) damage - will clubs bother to replace/repair damaged bags?
In either case, buoyancy will be compromised, & rowers who so easily
find excuses for not bothering with safety devices don't need to be
given burdensome safety jobs. Would we use seat belts or air-bags in
cars if we had to spend time checking they were fit to use before
driving off?
5. Weight.
Air bags do not come without a weight penalty. As soon as this is
noticed, folk will find reasons for removing the bags.
We come back to the old core argument: good safety is passive,
intrinsic safety. It is better, & cheaper too, if safety is built into
the boat.
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: ca...@carldouglas.co.uk Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)
nospa...@fsmail.net
Have you any experience of using Flexi-Ply? Is there anything
inherently troublesome that should shy me away from it?
I'm thinking that I could get the benefits of both the one piece quick
solution, but the neatness of the alternatives, by rolling the ply up
to get it through one of the holes in the bulkhead and then fixing to
the inside of the opening(s).
I'm assuming that what you call spiling and I call scribing on the
outside of the bulkhead will give a close enough shape match.
The follow-up question is what would be an appropriate adhesive? I'm
not clear if your saying Sikaflex is just good for mastic beads, or
also for the face to face join between the inside of the bulkhead and
the flexi-ply.
Peter
Carl
I think a good-quality flexible ply (bends easily to tight radius on one
axis) could be a good solution to the problem of fiddling bulkhead-sized
pieces in under the continuations of the slide-beds which brace the hull
& support the stretcher mounts. Do be sure to waterproof it's bonding
face before use (1-pack moisture-cure or 2-pack - not oil based -
polyurethane varnish, allowed to cure well, could be OK) but beware that
rolling up the ply may re-open the surface, so consider applying a film
of mastic all over the surface upon insertion.
Spiling is any process of scribing a line or series of points onto scrap
material at a set distance from the edge to which you want the finished
article to fit, & then scribing back by the same set distance from that
line or set of points to generate the required line on the material from
which the finished article is to be cut.
I think Sikaflex would, in my experience, be a good adhesive for a
full-face bond. Allow plenty of time for it to cure, do not be stingy
with the application & do not hang around applying the mastic as it will
start to skin over quite rapidly.
Your problem, whatever you do, if you are trying for a full face
covering of an existing structure, is to get adequate pressure across
the outward face of the new piece to achieve a reasonable level of
contact & squeezing-out of adhesive to minimise voids. One way might to
apply uniform pressure without distortion might be to cut a
roughly-fitting piece of polystyrene board (available at up to 4"/100mm
thickness from builders' merchants) and apply pressure to the outward
face & edges of that by inserting sticks, etc. which are jammed lightly
between that & the opposite bulkhead.
I hope that was helpful?
David Gillard
Just an idea... would it be possible to use an expanding foam (I was
imagining something like the spray insulation used in lofts of homes) to
fill underseat gaps? I did a quick check on Google and this company lists
one of the uses of their foam as "Marine Flotation"
http://www.rhhfoamsystems.com/apps_marine.php
I'm not sure what the density of the material is and therefore how much
weight it would add (for volume added), but, if it is a viable solution I
think it would be much quicker and easier than covering the holes.
DG
David Gillard
> Just an idea... would it be possible to use an expanding foam (I was
> imagining something like the spray insulation used in lofts of homes) to
> fill underseat gaps? I did a quick check on Google and this company lists
> one of the uses of their foam as "Marine Flotation"
> http://www.rhhfoamsystems.com/apps_marine.php
>
> I'm not sure what the density of the material is and therefore how much
> weight it would add (for volume added), but, if it is a viable solution I
> think it would be much quicker and easier than covering the holes.
>
> DG
>
Sorry, it does say on the Marine page to look at the Spec page
http://www.rhhfoamsystems.com/specifications.php for the Standard foam. This
has a density of 1.75 pounds per cubic foot, free rise (whatever that
means). For a retro fitting and given the benefits of this approach I would
have thought that this is an insignificant added weight. This is a DIY
system so you just buy the cans and apply yourself.
David Biddulph
news:45a4a8dc$0$22616$4d4e...@read.news.uk.uu.net...
Might make it difficult to get at slide adjustment?
--
David Biddulph
Rowing web pages at
http://www.biddulph.org.uk/
David Gillard
> Might make it difficult to get at slide adjustment?
> --
> David Biddulph
> Rowing web pages at
> http://www.biddulph.org.uk/
Good point! It is applied in layers though, so enough space could be left
(or cut free afterwards) to get at slide bolts.
kda...@kidare.com
Can also be used "to insulate ice chests, coolers, bait boxes and fish
holds".
Hmm, now that gives me an idea ...
Kit
Carl
At that specific gravity (0.028), foaming under the seats will add
~1.4kg at each position (taking an average 50-litre volume), or
11.2kg/24.6lb for an eight. This is not what most rowers want :( .
I've known of people reducing foam use & added mass by first filling
space with closed plastic bottles, but you may have trouble keeping them
where you want them & preventing formation of water-fillable voids.
You will have to consider how to avoid it generating locally high
pressure. PU foam in place materials cure by reaction, often with
atmospheric moisture. In a large volume, stuff in the interior might be
far from cured when stuff at the edges has already cured, & it might not
be too good to have your perfectly-fitting under-seat foam block still
trying to expand when it already fills the available space.
You will also have to consider how you are going to keep the stuff where
you need & want it. PU foam is incredibly sticky, & rather searching.
As it cures it oozes & since it generates internal pressure that oozing
can be fairly determined. So you'll need to contain it to prevent it
from extruding through all available holes & messing up the rest of the
boat, or mask everything off & be prepared to cut away the excess.
Meanwhile, the stickiness means you'll have the stuff welded to the boat
henceforth, with implications for future repair as well as the point
David Biddulph makes about access to slide bolts.
You could foam-in-a-bag, using very thin polyethylene tube (available
~2ft wide in massive rolls from Transatlantic Plastics). Insert a
length of the stuff through one bulkhead & out through the opposite
bulkhead, leaving it very loose. Then inject (or pour in 2-pack PU
foam) through one end & tie that end off, restricting extrusion at the
other end until you're sure the void is well-filled. Be sure to have
enough length of tube to handle any excess! At least the stuff won't be
stuck all over the inside of the boat (unless the tube has a hole in
it). But you'll still have trouble accessing the slide bolts.
A last point: if you foam inplace & water gets into any resulting
unfilled voids, you may have a long-term gunge & mildew problem in the
making as well as the trapped water.
So, foaming is a viable way of doing the job, but I'd hate anyone to
think it was the easy solution. You could really spoil a nice boat by
getting it wrong!
David Gillard
> So, foaming is a viable way of doing the job, but I'd hate anyone to think
> it was the easy solution. You could really spoil a nice boat by getting
> it wrong!
>
> Cheers -
> Carl
> --
Many thanks for your considered reality check!
Nick Suess
I had a "fun" experience with expanding foam on a DIY project last year.
Seemed a great idea, and with a few long squirts from the aerosol can, the
foam so neatly occupied the void we needed to fill, and everything seemed
hunky dory. You know, that clap your hands together, job well done feeling.
This lasted for at least 3 minutes. But the foam just kept on slowly and
inexorably expanding, curing internally as Carl has described, for about
another half hour. Thinks started to look a bit bloated. "Let's just clamp
it in place" I thought, but I was like King Canute (I see historians like to
spell him Cnut these days, but you have to be so damn careful with that one)
and the tide.
No, I wouldn't use expanding foam in a boat!
Phil
in uk.d-i-y):
"A friend of mine once built a canoe. He spent a long time on it and it
was a
work of
art.
Almost the final phase was to fill both ends with polyureathane
expanding
foam.
He duly ordered the bits from Mr Glasplies (an excellent purveyor of
all
things
fibreglass) and it arrived in two packs covered with appropriately dire
warnings about
expansion ratios and some very good notes on how to use it.
Unfortunately he had a degree, worse still two of them. One was in
Chemistry, so the
instructions got thrown away and the other in something mathematical
because
in a
few minutes he was merrily calculating the volume of his craft to many
decimal places
and the guidelines got binned as well.
He propped the canoe up on one end, got a huge tin, carefully measured
the
calculated
amounts of glop, mixed them and quickly poured the mixture in the end
of the
canoe
(The two pack expands very rapidly).
I arrived as he was completing this and I looked in to see the end
chamber
over half
full of something Cawdors Witches would have been proud of. Two thing
occurred to
me, one was the label which said in big letters "Caution - expansion
ration
50:1" (or
something similar) and the other that the now empty tins said
"approximately
enough
for 20 small craft"
Any comment was drowned out by a sea of yellow brown foam suddenly
pouring
out
of the middle of the canoe and the end of the canoe bursting open. My
friend
screamed and leapt at his pride and joy which was knocked to the ground
as
he started
trying to bale handfuls of this stuff out with his hands. Knocking the
craft over
allowed the still liquid and not yet fully expanded foam to flow to the
other end of the
canoe where it expanded and shattered that end as well.
A few seconds later and we had a canoe with two exploded ends, a
mountain of
solid
foam about 4ft high growing out of the middle, and a chemist firmly
embedded
up to
his armpits in it.
At this stage he discovered the reaction was exothermic and his hands
and
arms were
getting very hot indeed. Running about in small circles in a confined
space
while
glued to the remains of a fairly large canoe proved ineffective so he
resorted to
screaming a bit instead.
Fortunately a Kukri was to hand so I attacked the foam around his hands
with
some
enthusiasm. The process was hindered by the noise he was making and the
fact
he was
trying to escape while still attached to the canoe.
Eventually I managed to hack out a lump of foam still including most of
his
arms and
hands. Unfortunately my tears of laughter were not helping as they
accelerated the
foam setting. Seeking medical help was obviously out of the question,
the
embarrassment of having to explain his occupation (Chief Research
Chemist at
a
major petrochemical organisation) would simply never have been lived
down.
Several
hours and much acrimony later we had removed sufficient foam (and much
hair)
to
allow him to move again. However he still looked something like a
failed
audition for
Quasimodo with red burns on his arms and expanded blobs of foam
sticking
everywhere. My comment that the scalding simple made the hairs the foam
was
sticking to come out easier was not met with the enthusiasm I felt it
deserved.
I forgot to add that in retrospect rather unwisely he had set out to do
this
deed in the
hallway of his house (the only place he later explained with sufficient
headroom for
the canoe - achieved by poking it up the stairwell.
Having extricated him we now were faced with the problem of a canoe
construction
kit embedded in a still gurgling block of foam which was now
irrevocably
bonded to
the hall and stairs carpet as well as several banister rails and quite
a lot
of wallpaper.
At this point his wife and her mother came back from shopping......
Oh yes - and he had been wearing the pullover Mum in law had knitted
him for
his
birthday the week before. "
Carl
<snipped, but an absolute "must read"!>
ROTFLMAO!
Thanks Phil, but how do I get wet coffee stains out of a now soggy diary?
C
John Mulholland
news:1168520901....@i39g2000hsf.googlegroups.com...
>A now infamous usenet posting on expanding foam (google expanding foam
> in uk.d-i-y):
>
<snip the wonderful shaggy dog story; (btw the dog wasn't mentioned!)>
Please persuade your friend to do it again with a video camera!
--
John Mulholland