Small Day Boat Refurb Discussion Topic - Buoyancy

[Lakesailor]

I've been rained off from grinding out the superfluous grp edges from the old floor beams. (not an enjoyable task at the best of times).

Old mouldings in hull. (They don't look too bad in this shot, but are about 1/4" proud of the hull and some of the mat is not very well bonded.

Once I have it clean I will bond in some floor beams and knees for the thwarts down each side (actually I think they are properly called seats).

The question is, do I install buoyancy?

The original boat had a floor above the water level and the void was supposed to be watertight and provide a great deal of buoyancy. If I install the floor lower I will have removable panels to allow bilge access. There is a small buoyancy chamber in the bow (which I could extend up to the foredeck) and a locker in the stern which I could make watertight.

However the boat weighs nearly 500Kgs. That would need a hell of a lot of positive buoyancy to keep afloat. 500 plastic milk bottles?

I could make ply lockers along each side with the seat on top and seal them to provide bouyancy. But the original design was supposed to be watertight and seemingly they all failed. Trapped water is worse than no bouyancy.
How water tight would it need to be? A small hole at each bottom corner would allow it to drain into the bilge, but would retain enough air to keep the boat afloat in the event of a capsize. Plastic bottles stuffed in the boxes would prevent too much water rushing in.

But I fancy an open look with the seats on knees and a clear floor.
This would afford much less buoyancy.

However:-

Apart from recovering the boat, what benefit is buoyancy?

• It's a heavy old thing so righting it after a capsize is probably not an option.
• It'll be mainly sailed on a freshwater lake. Rescue is not far away
• It's a big dinghy, so a total loss is not a big deal.
  

I must admit I like the look of open boats rather than those with built-in flotation.

Open

Bouyancy

 

[Tranona]

The main advantage of the self draining cockpit in the original design is that you can leave it open when on the mooring. Not sure the buoyancy created by the supposedly sealed bilge is a great benefit on a ballasted day boat like this. Think I would go for grating on the new floors and a bilge pump, then have a cockpit cover for when the boat is not being used. You could then have a bonus of nice varnished seats and trim in the cockpit that would not be exposed to the weather.

 

[Lakesailor]

I will mainly be dry sailing the boat and it will be covered on the trailer. I may install a dinghy type bung in the hole the original cockpit drain occupied. There is a bilge pump already in the boat.
There is a slab of 200lbs of concrete and iron on the bottom of the hull (I will need to bond it in again as the plywood former has rotted away).

My query was really whether there is any advantage to having positive buoyancy on a boat which is unlikely to capsize in normal use. Manufacturers seem to make such a selling point of buoyancy these days. Is it purely so they can get a better category for the seaworthiness?

 

[Tranona]

Not sure there is any advantage in categorisation. On an unballasted dinghy buoyancy is essential but on your kind of boat I think it is more marketing speak rather than a practical feature. You can always add buoyancy bags under your side benches. Might also be worth doing a heeling test in the water to see how it behaves.

 

[Champagne Murphy]

In reality you don't need the full 500kg of buoyancy. If the boat is flooded it needs to be just better than negative and placed to upright it. After all, as you've said you're never going to upright it alone so if the combings can be kept a few inches above the water a few minutes baling from a rescue boat should restore happiness and let you get the boat back to dry land.
I'd have thought a bow tank and another as a watertight stern locker would do the job. Watertight plastic hatches a la Wayfarer type of thing maybe; for instance

http://www.ebay.co.uk/itm/MARINE-PL...E-OCEANS-/281285361280?_trksid=p2054897.l5672

 

[Croak]

I am probably being foolish here.

"However the boat weighs nearly 500Kgs. That would need a hell of a lot of positive buoyancy to keep afloat. 500 plastic milk bottles?"

Wouldn't that be needed to keep the whole boat above the water,

If my wooden boat weighed 100kg I wouldn't need any buoyancy, it would float enough to be recoverable.

Beaten too it

 

[Lakesailor]

Yes, although I'll probably make the hatches from ply and seal them down on rubber gasket material.

I wasn't wanting to go the whole hog and this seems a better half-way house. It'll let me move along the lines of this boat I found a pic of being fitted out.

 

[Lakesailor]

Next question. Do I encapsulate the floor bearers or leave them half open? If you encapsulate then and water gets in there'll be no change of them drying out.

 

[Croak]

Floor boards to keep your feet dry.

 

[blackbeard]

I would be reluctant to rely on sealed compartments to provide buoyancy - they are very prone to leak and, as you say, not a lot of use in that case - also the totally watertight hatch cover might not turn out to be all that watertight. Milk (or whatever) plastic bottles would certainly help, but there are air spaces between the bottles so that the amount of buoyancy you could rely on would be less than might be calculated from the volume of the buoyancy chamber. (OK, a 1 litre bottle would give you 1 kg (roughly) but that's a lot of bottles!)

Buoyancy bags (decent ones, not just a heat-sealed flimsy plastic bag) might be a good way to go, you would need some good big ones (plus, maybe, milk bottles as appropriate). Avoid sharp edges, obviously.

Of course, as already said, in the good old days, dayboats like that would not have bothered with buoyancy. As a matter of interest - any idea how many of them are at the bottom of the lake? Or did they not have ballast, relying on the weight of a wooden construction?

 

[AntarcticPilot]

Of course, as already said, in the good old days, dayboats like that would not have bothered with buoyancy. As a matter of interest - any idea how many of them are at the bottom of the lake? Or did they not have ballast, relying on the weight of a wooden construction?

Well, in "Swallowdale", Swallow sank when John hit the rock off Horseshoe Cove! And she was a "ballasted dayboat"; John had to dive to attach ropes to the pig-iron ballast blocks before she could be recovered.

Must read it again!

 

[Croak]

Another thing re buoyancy is to have a single buoy with a length of rope the same as the depth of the lake attached to the boat to assist recovery, You would just have to hope it uncoiled nicely as it went down.

I nearly lost my Merlin Rocket in Windermere when the buoyancy bags popped off and the buoyancy tank wasn't.

 

[Croak]

Well, in "Swallowdale", Swallow sank when John hit the rock off Horseshoe Cove! And she was a "ballasted dayboat"; John had to dive to attach ropes to the pig-iron ballast blocks before she could be recovered.

Must read it again!

But only one at a time....I read it last week.

 

[Lakesailor]

Another thing re buoyancy is to have a single buoy with a length of rope the same as the depth of the lake attached to the boat to assist recovery, You would just have to hope it uncoiled nicely as it went down.

I nearly lost my Merlin Rocket in Windermere when the buoyancy bags popped off and the buoyancy tank wasn't.

Hmm. That would be a 200ft line then. I guess that wouldn't get tangled
The Windermere Class yachts don't have buoyancy. Some have sunk but are usually recovered. The owners used to scuttle them when they had a better one built. Just so no-one would get their hands on a decent competitive boat!

 

[Iain C]

Nice looking little boat.

I'd also be looking at buoyancy, if just to protect from that one in a million freak gust at the same time as the Chinese gybe and mobo wash scenario. You might also find issues getting it insured or using it on certain lakes without bouyancy.

My old 15 has buoyancy bags...I'd be looking at strapping some in under the floorboards.

 

[DownWest]

I would go for the fore and aft sealed areas, with the bulkheads as close to the cockpit as possible. After a friend capsized his 15ft dayboat and could not bail it (partly because of the O/B well) we sealed the forward compartment and the space under the aft deck, complimented by Holt Allen bags under the side decks. Increased the ballast by 100kg and sealed the space under the floorboards and lastly, capped the centreboard case. The fore and aft spaces had waterproof hatches to store stuff. If they were not totally water tight, then the dribbles would not be enough to make a big difference before righting the boat. On test, we pulled the mast into the water, let go, and she came right up again ( plate was up) and the amount of water was easily bailed, one could have sailed off without bailing. The extra ballast has made her easier to handle solo too.
DW

 

[onesea]

Just a thought...

If she is not going to be self draining I would probably go with:
1) Good sized buoyancy forward,
2) U Shaped or split buoyancy aft and forward if possible,
3) Maximize buoyancy quite high up (under deck level),

You will still end up swamped, and probably/ possibly unable to bail yourself. At least it supplies big target to look for/ something to drift on.
i) If you are swamped and get towed it makes her less likely to nose dive,
ii) If the buoyancy is split you get more athwart-ship stability in the even you are swamped, I hated dinghys where it was a balancing act one they where up right.
iii) In the event of a broach/ capsize or swamping the high buoyancy and ballast should supply some positive stability. If the bouyancy and ballast are at the bottom of a swamped boat you have not got so much stability.

Then again for simplicity sake I would probably go with, not bothering at all open day boat sail conservatively. Less to maintain less to go wrong, more time sailing less time working on her. Just do not get it wrong out on the ogin

 

[prv]

Just do not get it wrong out on the ogin

He's not going out on the oggin, just paddling around a puddle

Pete

 

[Sniper]

We used to have a heavy old clinker day sailer (Thames Estuary One Design) which was sailed in lots of different conditions on a tidal river. It was stable enough never to even get the side decks near the water, let alone capsize. It had no buoyancy. Obviously there is a risk if the boat does take on water, but that is no greater than for any small keel boat, most of which don't have positive buoyancy. I think your boats more akin to,a keel boat than a dinghy.

 

[Lakesailor]

Yes. I don't quite see what Onesea is saying. Search and rescue on Windermere is not a difficult task.
My clinker dinghy had no bouyancy, other than the fact that the material was wood and probably had more intrinsic positive buoyancy.

I am leaning towards just the fore and aft buoyancy chambers as is.