Re: [bolger] Shifting Ballast
>...The minimum wetted surface for a square boat is achieved when beam is exactly half the canoe-body draft...Only very bad math would give you that result, try canoe-body draft exactly half the beam. Much better :)
In order to accomodate Bolger's 'equal curvature' concerns for flat bottom boats (side and bottom curvature should be matched to reduce eddymaking and poor
handling), this Square Boat would have to be a double-ender with the base of her stem and sternpost exactly at the waterline.
Also, if she was as tall as she is wide, she would put the center of her deckline in the water at 90 degrees, it doesn't seem like a particularly good idea. Sponsons might
fix that, or, perhaps we shouldn't go for minimum wetted surface in a square boat...
Pax,
Chris B
Has anyone else thought about using movable lead ballast in a square boat? It seems to me that the AS-*9 boats, Whalewatcher, the Breakdown Schooner, etc. might
be very easy to rig with an athwartships lead-sled :) and benefit from the increased control over the righting moment. None of these vessels carry outside ballast, so the
VCG could remain the same or even be lowered (especially in the case of the water ballasted models).
Points to consider:
1. Shifting a substantial hunk of lead to windward (below the waterline no less) could allow more/higer sail to be carried on modest beam (less drag).
2. Shifting the CG to leeward in light air will allow sails to lay out and fill.
3. Heeling the vessel slightly to windward when hove-to or running off in bad weather reduces the vunerability to knockdown and broach, respectively.
4. At 90 degrees the ballast offers the same contribution to the righting moment, regardless of it's athwartships position.
5. The vessel could be have any undesirable list wrung out when at anchor or mooring.
6. Alternately, if the inhabitants could accomodate it, a flat bottomed vessel could be heeled down when at anchor to reduce pounding.
7. No complicated plumbing is required, simple mechanics suffice (a horizontal scissor jack?).
8. Provisions would have to be made to keep the ballast from getting loose or knocking the hull sides off the chine logs.
9. There might be conflicts with accomodations or with centerboard installations.
Shifting lead ballast could enable the development of even more radical box-like vessels. The minimum wetted surface for a square boat is achieved when beam is
exactly half the canoe-body draft (proof is left to the reader, hint/warning: it requires basic differential calculus). If such a vessel can meet it's stability requirements with
shifting ballast it would be a model of efficiency. If it is then made as tall as it is wide (literally square in section), it's freeboard will equal the draft... it's sounding a bit like
an English cutter [ 6' beam x 3' draft x 28' lwl x 0.56 prismatic coeff. = > 18,036 lbs or about 8 long tons displacement and a D/L of 367]. It certainly would be easy to
manage proper headroom.
I've probably already lost most of you good folks already so I will rap up.
Pax,
Chris B
be very easy to rig with an athwartships lead-sled :) and benefit from the increased control over the righting moment. None of these vessels carry outside ballast, so the
VCG could remain the same or even be lowered (especially in the case of the water ballasted models).
Points to consider:
1. Shifting a substantial hunk of lead to windward (below the waterline no less) could allow more/higer sail to be carried on modest beam (less drag).
2. Shifting the CG to leeward in light air will allow sails to lay out and fill.
3. Heeling the vessel slightly to windward when hove-to or running off in bad weather reduces the vunerability to knockdown and broach, respectively.
4. At 90 degrees the ballast offers the same contribution to the righting moment, regardless of it's athwartships position.
5. The vessel could be have any undesirable list wrung out when at anchor or mooring.
6. Alternately, if the inhabitants could accomodate it, a flat bottomed vessel could be heeled down when at anchor to reduce pounding.
7. No complicated plumbing is required, simple mechanics suffice (a horizontal scissor jack?).
8. Provisions would have to be made to keep the ballast from getting loose or knocking the hull sides off the chine logs.
9. There might be conflicts with accomodations or with centerboard installations.
Shifting lead ballast could enable the development of even more radical box-like vessels. The minimum wetted surface for a square boat is achieved when beam is
exactly half the canoe-body draft (proof is left to the reader, hint/warning: it requires basic differential calculus). If such a vessel can meet it's stability requirements with
shifting ballast it would be a model of efficiency. If it is then made as tall as it is wide (literally square in section), it's freeboard will equal the draft... it's sounding a bit like
an English cutter [ 6' beam x 3' draft x 28' lwl x 0.56 prismatic coeff. = > 18,036 lbs or about 8 long tons displacement and a D/L of 367]. It certainly would be easy to
manage proper headroom.
I've probably already lost most of you good folks already so I will rap up.
Pax,
Chris B