question about lateral rig placement
In a, say 10m Atlantic with cat schooner rig, It seems you could mount the masts along the centerline of the hull, or you could bring them to the windward gunwale, or on top of projections of the crossbeams, in which case the masts might be over the water to windward.
Does anyone have any comments on mounting the masts off-center, either to windward or to leeward?
thanks
Simon
It’s interesting to not be limited by putting masts on the vaka’s center line. Bolger and Michalak use off-center masts when it helps with cabin layout, or with slot-topped or ‘birdwatcher’ style boats. What are the forces at play? The ama to leeward (Atlantic mode) causes a drag force pulling the boat to leeward. The sails cause a force turning the proa to windward - more so when sailing off the wind, and the sails are sheeted out. If you can estimate those forces using hull design software for drag, and calculations for the sails, you can theoretically figure out the mast placement for a given sailplan so the forces are balanced.
Does anyone have any comments on mounting the masts off-center, either to windward or to leeward?
Simon,
The general consensus seems to be that in terms of heeling moment, it doesn’t matter where the rig is placed laterally.
However, it does seem to matter in terms of overall balance. As a broad generality, a rig placed further to windward will produce less weather helm / more lee helm than the same one placed further to leeward.
If you were to locate your schooner masts on the weather side of your vaka, there would be more weight to windward and less intrusion on accommodation down below. The possible downside would be getting the sails to sheet in hard enough, especially the aft sail. You might have to resort to Jzerro style sprits to get a decent sheeting angle, which on an atlantic configuration would make them pretty vulnerable when tying up alongside something.
Access around the masts for reefing and stowing of sails could also be an issue, especially if you are thinking of placing the masts outside the hull somewhere along the extended akas.
Rob
Rob
The general consensus seems to be that in terms of heeling moment, it doesn’t matter where the rig is placed laterally.
seems hard to believe, but the Tom Speer link is pretty emphatic
However, it does seem to matter in terms of overall balance. As a broad generality, a rig placed further to windward will produce less weather helm / more lee helm than the same one placed further to leeward.
nice, a two mast cat schooner rig is inclined to weather helm, as the CE is always aft, so getting the masts to windward, even if its only to the windward side of the vaka, will new an advantage, and as you say, probably open up space down below.
Crazy idea - if the windward side of the main hull was plumb, thou could drop a vertical bulkhead from the mast step to the keel.
The possible downside would be getting the sails to sheet in hard enough, especially the aft sail. You might have to resort to Jzerro style sprits to get a decent sheeting angle, which on an atlantic configuration would make them pretty vulnerable when tying up alongside something.
No, I think I’ve got that sussed. Rotating masts with mid boom fixed to semicircular track. With 8’ booms, that means a tack with a 48” radius, with a turning block and cleat at each end of each semicircle, dragging the car. If the booms are yoked, there is only two “sheets”.
Access around the masts for reefing and stowing of sails could also be an issue, especially if you are thinking of placing the masts outside the hull somewhere along the extended akas.
Yeah but, … with the boat positioned across the wind, booms will point to the ama, and reefing can be dome on the trampoline ?