Solid foam buoyancy

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andrew
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Solid foam buoyancy

Post by andrew » Tue Jul 29, 2008 10:12 pm

Following my experiences at Netley.
Capsize and a drift to the beach fully submerged.
I want to add solid buoyancy to J26.
Does anyone have any experience of using polystyrene or foam encapsulated in grp ?

JimC
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Re: Solid foam buoyancy

Post by JimC » Tue Jul 29, 2008 10:35 pm

andrew wrote:Following my experiences at Netley.
Capsize and a drift to the beach fully submerged.
I want to add solid buoyancy to J26.
Does anyone have any experience of using polystyrene or foam encapsulated in grp ?
It tends to add weight, soak up water and so on... What's the situation, tanks, bags, not enough buoyancy, leaks, what?

andrew
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Re: Solid foam buoyancy

Post by andrew » Wed Jul 30, 2008 7:25 am

J26 is unusual among Jollyboats in having no tanks.
The bags are tied down.
When capsized the bags sit under the deck but there is insufficient buoyancy low down.
So the centrecase is fully submerged.
This makes bailing unrewarding !
I don't want to change the boat by adding tanks.
Solid buoyancy strapped low down is my plan.

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Re: Solid foam buoyancy

Post by Rupert » Wed Jul 30, 2008 8:05 am

Solid bouyancy is almost always a bad idea in the sort of quantities you would need to make much of a difference. Whenever I've owned a boat with it incorporated into tanks (so that if holed the boat doesn't sink) I have found it soggy and falling apart. Putting it into what is effectivly an open boat would be heavy, messy and cause damp to be held between it and the boat. That answer doesn't help much as I can't think of anything better to suggest, save not falling in...
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Re: Solid foam buoyancy

Post by JimC » Wed Jul 30, 2008 8:49 am

Well, I guess you could try blocks of styrofoam (Dow Floormate is one source) under the bags in order to give some buoyancy that will be down low and displace more water than bags when the boat is upright. Reckon to remove and dry out, maybe replace every winter. Try varnishing it to reduce water ingress. Looking at the net is probably in the very vague ballpark of £200 per cubic metre... Don't use ordinary white polystyrene foam : its soaks up water like a sponge!

Be prepared to throw the lot away if it doesn't work. In buoyancy tanks in ICs its not too bad, but free to be soaked in water, umm... not convinced.


A lot of improvement can probably be made by improving how well the bags are secured. I've noticed on some boats recently bags under laced down cloth which I reckon probably keeps them underwater far better than the traditional straps... If you try the foam blocks it would be good to have a way to remove them and dry them out that doesn't involve undoing the screws three times a year, so the laced down technique might be worth it fo that too...

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JB9
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Re: Solid foam buoyancy

Post by JB9 » Wed Jul 30, 2008 9:48 am

Is there any buoyancy under the rear deck? I find that with J9, which has side tanks, that the transom is very low following a capsize so I was thinking of putting in the largest bag I could fit in.
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Brookesy
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Re: Solid foam buoyancy

Post by Brookesy » Wed Jul 30, 2008 1:34 pm

Not sure what they're called but the long(2metre x 60mm) wand type things that are used in swimming pools for kids fun floats, can be cut to size, cable tied or stuck together to produce good bouyancy which does not soak up water in the same way as most foams. It comes in various colours and is available from places like Toys'rus.
I know of a few Finns that have shoved them in their bouyancy tanks as extra insurance against that sinking feeling.
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JB9
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Re: Solid foam buoyancy

Post by JB9 » Wed Jul 30, 2008 2:58 pm

Very good idea, thanks.
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jonathan
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Re: Solid foam buoyancy

Post by jonathan » Wed Jul 30, 2008 11:44 pm

Lacing down should do the trick and bags shouldn't squeeze up. Works like a well fitted sports bra - apparently!

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Ed
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Re: Solid foam buoyancy

Post by Ed » Thu Jul 31, 2008 9:58 am

There are a couple of Jollyboats with no tanks.....the other one 'Sweet Caroline' used to have lots of extra ones stuffed all over the place.

Personally, I don't think you will be able to easily use any form of 'hard' polystyrene type foam at a reasonable cost and ease of use. It is all pretty horrible stuff and is only really worth using when built into a structure....IMHO.


However, what I would do is this:

First, pull out the standard bow-bag. Even the Crewsaver Extra-Large is simply no where big enough. You will have to get one custom made that fits the 'whole' bow area. It has to blow up to expand and completely fill the bow. In the meantime, if you have to continue with the crewsaver bag, you have to pass a strap or rope across it from bow to mast foot that really holds it down. The problem is when you capsize, the bag floats up leaving a 1ft gap under it which the water swashes around in, providing little bouancy and making boat hard to balance, when water swishes to front. When the boat is flooded, the important thing is to keep the nose up, if you can't do this, you can't concentrate on bailing as you are continually having to jump around to change trim and stop diving. Look at Merlins which when flooded, often have their transoms under water, but their bow out of water and just hoist the kite, head down wind and empty the whole thing in 50m.

With the Jollyboat, the side tanks have much less bouancy in them than one tends to think. When you pulled off the decks, didn't you go "Gosh - not much in there!" The boat just is very thin and the tanks cut-back under the decks. If you use bags, they have to be bigger than those you have at moment, The middle bags need to bulge out from under decks by an inch or two. I can't give math off top of head (sure Michael can) but every inch of extra girth adds tons to the overall volume of the bags. The stern bags behind where the helm sits can afford to bulge out even more - 3-4 inches.

You can also with a little care, find room to fit two bags either side of mast under decks, which can be really quite big although they do get in way if you are using spinaker bags. But I don't think you will need them if you have the full-size bow bag.

Then finally, if you really think you need it, ( I don't think you will - if you enlarge all the others), there is room for a bag in the stern under the aft-decking. You can use this if you don't have transom flaps, but it seems a bit pointless if you do as it destroys the flow of water out the back. Mind you, with the transom flaps, you simply will never get them to work unless you either have a bow tank or the full-size bow bag.

Honestly if you do all this, you will be able to bring her up and it will be much easier. But you will still need a good sized bucket (I sometimes carry two if it is windy, and use them to keep kite in).

Will this keep water below the top of case. Yes, it should, but if not (didn't for me either till I got the big bow bag), then you have to grab a tee-shirt, cloth or even the kite and jam it in the slot, one of you stands in boat towards rear to keep the bow up and bails like fury with a BIG bucket, the other person swims off transom, putting no weight on it if low, but pulling themselves up as soon as the water rushes to bow. Two or three people in boat just makes it harder as your weight is pushing boat down, when you have got water level down to below the top of case, the other bods gets in and start bailing....or adjusting trim (or sails) to stop the nose-diving. Getting a boat going with low-bouancy is hard work, but by no means impossible and I fear it is a skill that we have largely lost, now that we are all used to boats with far higher float levels.

Hope this helps

cheers

eib
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Garry R

Re: Solid foam buoyancy

Post by Garry R » Thu Jul 31, 2008 11:31 am

Merlin 1728 was a real bugger when it capsized as the centreboard case top was always below the waterline no matter what I did. In the end I had a roll of bubblewrap I made up which as soon as the boat was upright I stuffed into the case and a few buckets worth of bailing got it above the waterline and off we went. (The bubblewrap is light and gave some more buoyancy I dare say!!)

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Ed
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Re: Solid foam buoyancy

Post by Ed » Thu Jul 31, 2008 11:39 am

Yes, I used to carry a chammy leather (fake one) for same purpose. Also useful to just to keep things spick and span - don't you know!

Once I was sailing at Cowes (Uffa Fox Centenary) and my sis Bella polished all the decks. Looked beaut, but I went out sailing on the one day that had any wind and every time we went over a wave, my bum would loose contact with the deck and I would end up slipping down till I was half off the transom, held in by my tow-tips. (Long way on a Jollyboat). At one stage my crew (Ben Whybrow) had to hold onto my buoyancy aid to stop me sliding down. We had to come in and remove all the polish.

Sorry....I digress

cheers

eib
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Michael Brigg
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Re: Solid foam buoyancy

Post by Michael Brigg » Thu Jul 31, 2008 12:56 pm

Ed said:
I can't give math off top of head (sure Michael can) but every inch of extra girth adds tons to the overall volume of the bags.
Linear to Cube ratio. Simple really, but it explains why a Sigma 38 feels so much bigger than a Sigma 31 (or for that matter why a 14ft boat is so much more of a handfull than a 12ft.)

Take a cube; 1cm sides; it contains 1x1x1=1cc (or 1gm) of water.

Double the linear measurements an you have a 2cm cube

It now contains 2x2x2 = 8cc or 8grams if its full of water of course.

3cm cube contains 3x3x3 = 27cc

And so on. The graph of linear size to cubic volume gives you a very steep parabolic curve.

If you move up to 10cm then a 10cm cube is 1000cc = 1kg of water.

100cm cubed, easily done in a Jollyboat is 1,000,000cc = 1ton!

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Ed
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Re: Solid foam buoyancy

Post by Ed » Thu Jul 31, 2008 1:34 pm

Yes, I remember doing the math when trying to work out the Kg of lift in my two stern bags in Firefly.

Now I can't remember if this was when I was trying to work out the lift in a couple of the tapered bags.....or a set of custom bags which I currently use to see if they were still in class (at time they changed volume requirements)

What amazed me was how much extra volume was given by simply extending the diameter an inch or two. It really made a very big difference.

Incidentally.....one source of bags that someone might like to follow up....

When you go to a trek/mountaineering shop that has lines of ruck-sacks, have a look inside them as Lowe and others make blow up bags for stuffing their ruck-sacks. They are pretty strong and have long tubes to blow them up from, which can be useful. When I worked as photographer on Snow&Rock catalogues, they gave me a few, two of which I still use in Firefly under covers.

The other thing I was going to mention to Andrew re Jollyboat bags was......Do make up bag covers. It keeps them secure, makes them last much longer and looks much much better. With the Jollyboat you can attach one side of the cover to inside edge of deck and then the cover totally holds the bag in place.

cheers

eib
Ed Bremner
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Pat
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Re: Solid foam buoyancy

Post by Pat » Thu Jul 31, 2008 1:57 pm

Half Cut is just the same and at Netley we carried a length of foam pipe insulation to stuff down the centreboard slot. It didn't do us any good as by the time I'd got back in the boat umpteen square metres of wet spinnaker was floating around and I couldn't get to it :D

We've decided we need more buoyancy but rather than changing the "not big enough" bow bag we are going to add two pillow bags above it to fill the gaps and lessen the risk of the only bow buoyancy puncturing. Also if I have to replace the rear bags it will be with two smaller for each one large, again to lessen the risk.

Another idea I've seen is under-inwhale buoyancy - maybe empty plastic lemonade bottles would work?

By the way we managed to sail on and empty the boat at Roadford (mainly due to lack of rescue cover) and found that when the boat is full the jib angle needs to be much less to give direction - back it completely to beat to windward and sheet in hard for a reach. This is due to the extra weight of water helping the mainsail force the bow around to windward.

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