On DeckMovable Ballast

Stefan, I'm afraid it sounds like you use a "what if" question regarding the Backman 21 as a sort of indictment when, if you assume that the boat is designed and built right, the answer is simple: move the keel! That very thing happened to Pyewacket(or Glory?) in Antigua last year and the solution? They moved the keel. Not trying to be wise guy I'm just trying to point out that whether it is a canting keel or on-deck movable ballast system the boat SHOULD be designed to deal with the situations you describe.And as you point out any keelboat is subject to a knockdown. So if the boat is designed well , built right and sailed intelligently there should be no problem. But as you know there are always conditions that can get the best of any boat...
   I feel that while questions such as yours SHOULD be asked of every boat they should not be used as an indictment; a presumption of unsuitability unless you are familiar enough with the boat to know that it is NOT designed well or built right...
As to my concept of on deck movable ballast it allows for MUCH more RM than a normal canting keel while at the same time providing buoyancy greater than the weight in the wing and -in"safe mode" with a deep ballasted daggerboard is self righting. As I visualize this idea it could conceivably be sailed w/o the ballased board by an able bodied sailor and righted like any other dinghy-though even w/o the weighted board the thing would be almost self righting.
   The extreme situations you mentioned MUST be taken into account in the design of this boat or it won't work....
And just for the record most of my early, early racing was in a 20' gaff headed keelboat....

Another thing to think about is that you're trying to make a high performance dinghy/skiff - they work on the basis of combining very low hull weight and large sail area with a decent righting moment. The RS800 weighs about 10 stone, and presumably your ballast would be a similar weight. Add one crewman and either you're trying to single hand a 800 or double up in a 700 (Not sure if that's clear but I'm thinking of sail area to weight ratio), if you keep the sail area the same. You could increase the sail area, but then you'd be increasing sheet loads, and if this might be targeted at disabled sailors you could end up finding yourself needing winches, and suddenly you're building a sportsboat. This target market would also mean you wouldn't be able to use leg power to move or control the ballast. Just a thought.

Sorry old boy but it's not time to build yet. Good to know that Bethwaite and Bulloch are using ON DECK MOVABLE BALLAST on their Pterodactyl concept boat(about 65').
I would think that the likelyhood of the crew falling out of this boat would be much less than the crew falling out of a 2.4 meter which ,to my knowledge, has never happened.
I guess the model will have to serve as proof of concept for now-and believe me it 'twern't inexpensive to build and test:

And here is the url to the Bethwaite LAS(Lead Assisted Skiff):
Bethwaite Design // Latest News // NEW - UD 18 Skiff sailing for Sailors with disabilities
http://www.bethwaite.com/10837,02,2-0--new---ud-18-skiff-sai ling-for-sailors-with-disabilities.html

Edited by Doug Lord

The only(!) thing(s) Pteradactyl and the 17 have in common are on deck movable ballast, buoyancy pods and a ballasted appendage in the water. Interesting any way you look at it.
I've not learned how Bethwaite utilizes the ballast on his LAS but I have learned that apparently Herreshoff had a small boat using a brass ingot or so as on deck movable ballast; I was told it was one of his favorite boats.
The more I look into it the more I like the concept and not just for disabled sailors.
The boat seems like it could be configured from a high performance dinghy with numbers similar to a 505/FD to even more powerful. Since the ballast in the wing is adjustable and the ballasted board is removable there may be more than one level of performance/excitement achievable with the same basic hull+wing.