Making a ballasted centreboard...any views on carbon fibre and molten lead?

Iain C said:
...the simple act of letting the kicker off is more likely to assist in getting the thing upright compared to the centre-keel (which incidentally would snap right off it was as thin as you propose!)
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Thanks Iain, I'll keep the kicker in mind. Actually I doubt my practical skills, re. carbon fibre, so if my centreboard ever gains weight, it may be by cheaper & less technical means.

But let's keep the point theoretical, it's more interesting for me and for respondents, than issuing instructions on what dinghy sailors are expected to do, which I know already...

...my outlook is not quite ordinary, so the possibilities are potentially more interesting than long-practiced actualities which mayn't have explored options outside class rules, etc.

I'm interested in the effect of ballast in small light boats & why it is that there are so few designs in the 'crossover' zone between 'heavy' keelboats and wholly unballasted dinghies.

I mentioned a boat I'd seen with a ballasted daggerboard. I Googled, found something similar...http://forum.woodenboat.com/showthr...-dayboat-from-BlueLightning-s-Keith-Callaghan

It's interesting (to me) that some of the voices on that thread seem so irritated by being asked to consider an idea which falls between historically established types of sailboat...

...and the unreadiness of certain posters there, to accept that a lifting ballast keel may offer as much benefit to certain users as it denies to others, sounds familiar! :rolleyes:

It's quite a long thread, but worth a read. The boat in question looks nice, though not quite what I'd want, and I never liked vertical-sliding boards.
 
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Dan,

One reason for dinghies being (usually) unballasted is that they spend much more time out of the water than on it. Therefore weight saved makes them easier to heave around ashore, or load onto a roof rack, as well as - theoretically at least - faster on the water.

In an unballasted dinghy the crew is the ballast. A one man dinghy is designed to be ballasted by one man, a two man dinghy… etc.

You're looking at ballasting a two man (or was it once upon a time three man?) dinghy with only one person's bodyweight. Hence, I suspect, your desire to glue the equivalent to a second crew member to the bottom of the board. Go ahead. Make sure you can remove the board/ballast when you beach the boat, to save on hernia treatments.

Also look at the structure. Second-crew ballast was designed (in the Ozzie) to be hanging from a trap wire, not three feet underwater. You might therefore want to add strength to the floor in the region of the slot, and some bracing between the top of the slot and the gunwales. Some Wayfarers and Wanderers were supplied with steel plates - might be worth checking out if/how the builders modded the structure to cope (or maybe they are over-engineered in the first place).
 
Wise words, thanks Ken.

The likely necessity for reinforcement of the pivot and centreboard case would deter me from adding ballast, more than any other reason. I mean, if the boat isn't structurally up to the job of bearing 50kg at the end of the centreboard, I can't be bothered to re-engineer her - even my weird fascination with the margins of boat-design, retreats at that prospect. :)
 
Twister_Ken said:
Dan,

One reason for dinghies being (usually) unballasted is that they spend much more time out of the water than on it. Therefore weight saved makes them easier to heave around ashore, or load onto a roof rack, as well as - theoretically at least - faster on the water.

In an unballasted dinghy the crew is the ballast. A one man dinghy is designed to be ballasted by one man, a two man dinghy… etc.

You're looking at ballasting a two man (or was it once upon a time three man?) dinghy with only one person's bodyweight. Hence, I suspect, your desire to glue the equivalent to a second crew member to the bottom of the board. Go ahead. Make sure you can remove the board/ballast when you beach the boat, to save on hernia treatments.

Also look at the structure. Second-crew ballast was designed (in the Ozzie) to be hanging from a trap wire, not three feet underwater. You might therefore want to add strength to the floor in the region of the slot, and some bracing between the top of the slot and the gunwales. Some Wayfarers and Wanderers were supplied with steel plates - might be worth checking out if/how the builders modded the structure to cope (or maybe they are over-engineered in the first place).
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I think the lateral loads from sailing with 3 sails powered up probably put the leverage of a bit of lead in the keel well in the shade?
 
dancrane said:
I'm interested in the effect of ballast in small light boats & why it is that there are so few designs in the 'crossover' zone between 'heavy' keelboats and wholly unballasted dinghies.
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Because sometimes when you cross two breeds of dog you get all the intelligence of a whippet with all the speed of a labrador.
(Guess how I know).
 
Mavanier said:
(Guess how I know).
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Did you try to breed dogs, or boats, Rob? ;)

I felt the 'crossover' is an interesting idea, particularly on big dinghies where addition of moderate ballast - a moderate proportion of the displacement - needn't destroy performance.
 
Definitely. But I'd rather struggle a bit with the boat on land, than out at sea! I can pull the Osp up the little hill in the dinghy park, running with very little steps...

...so it wouldn't be a total dead weight even with, eg, SWMBO's weight added. Don't tell her I said so though. :rolleyes:

How about this for an improvement on a lead keel...

...a big old inflatable lifejacket, filled with water instead of air...I just keep it on the centreboard case with a line going to each gunwale...

...and as I'm climbing over the gunwale to reach the board, I pull up the 15kg jacket & put it on, to accentuate my righting effect? :D Or...or, my corpse sinks and is never found. :nonchalance:
 
JumbleDuck said:
I misspent some of youth doing greensand casting of windmills, and greensand moulds are quite definitely damp when the metal goes in.
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I made many 3 -4 kg lead castings with plaster moulds in my mis-spent youth (for RC yacht keels). Sand moulds are a bit different, as they are porous, so the steam can get out without sending the metal before it.

Damp lead:

http://www.youtube.com/watch?v=Pe9wy9SjxjQ

Damp mould:

http://www.youtube.com/watch?v=gqiVd4rnbTU

Don't **** about with it.
 
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Another angle :) dinghies are designed to sail upright, at this angle to initiate planing the centre board with or without a lump of lead has no righting moment, unlike the crew hanging off a wire, to match the missing crew with under water lead you need greater mass than the crew at a similar angle (the buoyancy or support from the water works against you ) so what you need is a canting keel with a lump of lead ?
 
Iain C said:
Been done. But then you need a daggerboard to stop it going sideways.
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Blimey, £19K for a dinghy! Extra for a trolley & trailer.

SK2-GA-Oct127.jpg
 
Twister_Ken said:
Blimey, £19K for a dinghy! Extra for a trolley & trailer.

Interesting boat, I hadn't seen that before, about the same price as a new 14 Ken and you get a keel! a bit too complex for me and quite a weight to drag up a steep slipway though.

How about strapping a rib style inflatable tube around the boat? that might stop it going over and won't add as much weight
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Twister_Ken said:
How about strapping a rib style inflatable tube around the boat? that might stop it going over and won't add as much weight
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Elegant! I'll call it the Walker Bay 17. Ought to increase its value. :rolleyes:

Maybe I'll ditch the mast and sails too, then strap a couple of British Seagulls to the transom...awesome! I'll feel like Sonny Crockett.
 
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Personally I think you are better off selling the Osprey and getting another boat that was on your list when you were looking - an Albacore. Much better suited to sailing one up or two up. Just as spacious inside, more seaworthy than an Osprey, lighter by nearly 30kgs. Downside is that it isn't as fast (although only about 120 PY points), but then you don't have a trapeze or spinnaker to deal with. You can also pick them up pretty cheaply (ie. in the hundreds of pounds region).

That's what I have as my multi-purpose dinghy.
 
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