Ian McColgin
05-28-2005, 10:40 AM
We saw the clue yesterday morning at low tide. With only about a foot of water over the foredeck it was clear there was no chain. It had all stripped out.
I had a good chat with the professional crew of a large yacht that weathered Tuesday night not far from Grana. The wind never got above 50 kt but it was very strange with lots of up and down gusting and veering back and forth through about thirty degrees. There was a surprisingly large (about 3') very steep all whitecaps very closely spaced (less than 15' crest to crest) wind driven chop that also reflected back off the breakwater.
That boat had port and starboard bow anchors out on all chain and ran their engine to keep some strain off and stay pointed to the wind as it shifted. They chafed through three snubbers - two one side and one the other - in the course of the night. The wind was high enough and the water (about 20') shoal enough that the chain could not develop a very deep cantery. When a snubber was broken and the yacht lay on straight chain, they experienced very severe jolt impacts and the chain straightened in gusts and waves.
Grana had a 65# CQR and a 45# CQR in series - 45# to crown of 65# - on 150' all chain. The snubber was a husky 1" nylon double braid, thimbled eye for the chain hook. It ran through a block under the end of the bow sprit, over a roller fairlead with high well rounded stainless guides on each side on the port side of the bowsprit about half way back, and then to a stemhead cleat.
The chain led over a roller fairlead on the starboard side of the bowsprit past and under a vertically mounted stemhead cleat and back to the gypsy on the windlass. The purpose of passing the chain under this cleat was to limit its possible motion and keep the chain from hopping out of the gypsy. It's a tight fit getting the chain under there as the links have to be twisted just a bit, but once under the chain leads fairly straight back to the gypsy and can be trimmed or eased at will. The chain had just enough slack that a strain came on the windlass only when the snubber was at full stretch.
The snubber was chafed through about half way along the bowsprit where it passed over the fairlead on the port side. The block at the end of the bowsprit was gone.
It appears that the block broke first. This brought some chafe strain on the snubber as the boat veered back and forth. Some chafe would come from the bobstay as she veered on starboard tack and some on the side of the roller fairlead, both tacks. What's left of the snubber shows it failed at the roller fairlead.
At this point the direct strain of the chain would cause impact jolts, often a cause of an anchor breaking out and dragging. It seems the anchors held just fine but, with the shallow cantery, the impacts were sending waves of energy up the chain. If you lay a line along the deck and then rapidly raise and lower one end, you can make the same effect of a wave traveling along the line lifting up a little hump as it travels.
The vertically mounted cleat always in the past kept this wave from traveling to the gypsy.
It appears the fatal failure happened at the cleat. I'd never imagined it possible but it must be that Grana heeled way over on a port tack at a time when the chain went slack and the chain found a way to slip down and starboard under the cleat's lower ear.
Once the chain freed itself from under the cleat, it was unrestrained from hopping right out of the gypsy. It would then pay out to the bitter end, which was secured below with just enough line to get out the hawsehole. That restraining line then chafed through and Grana was free to drift onto the rocks.
Clearly, the restraint of the cleat was the key failure. A better rig would be a positive chain lock or shackle ahead of the gypsy that's strong enough to take the full strain. I had not arranged one because the cleat had worked so well to date in some very severe conditions and had the huge advantage of allowing anchor scope adjustment without complexities.
Should I have a future with an all chain rode, I will have some sort of bolt down postitive chain lock.
I had a good chat with the professional crew of a large yacht that weathered Tuesday night not far from Grana. The wind never got above 50 kt but it was very strange with lots of up and down gusting and veering back and forth through about thirty degrees. There was a surprisingly large (about 3') very steep all whitecaps very closely spaced (less than 15' crest to crest) wind driven chop that also reflected back off the breakwater.
That boat had port and starboard bow anchors out on all chain and ran their engine to keep some strain off and stay pointed to the wind as it shifted. They chafed through three snubbers - two one side and one the other - in the course of the night. The wind was high enough and the water (about 20') shoal enough that the chain could not develop a very deep cantery. When a snubber was broken and the yacht lay on straight chain, they experienced very severe jolt impacts and the chain straightened in gusts and waves.
Grana had a 65# CQR and a 45# CQR in series - 45# to crown of 65# - on 150' all chain. The snubber was a husky 1" nylon double braid, thimbled eye for the chain hook. It ran through a block under the end of the bow sprit, over a roller fairlead with high well rounded stainless guides on each side on the port side of the bowsprit about half way back, and then to a stemhead cleat.
The chain led over a roller fairlead on the starboard side of the bowsprit past and under a vertically mounted stemhead cleat and back to the gypsy on the windlass. The purpose of passing the chain under this cleat was to limit its possible motion and keep the chain from hopping out of the gypsy. It's a tight fit getting the chain under there as the links have to be twisted just a bit, but once under the chain leads fairly straight back to the gypsy and can be trimmed or eased at will. The chain had just enough slack that a strain came on the windlass only when the snubber was at full stretch.
The snubber was chafed through about half way along the bowsprit where it passed over the fairlead on the port side. The block at the end of the bowsprit was gone.
It appears that the block broke first. This brought some chafe strain on the snubber as the boat veered back and forth. Some chafe would come from the bobstay as she veered on starboard tack and some on the side of the roller fairlead, both tacks. What's left of the snubber shows it failed at the roller fairlead.
At this point the direct strain of the chain would cause impact jolts, often a cause of an anchor breaking out and dragging. It seems the anchors held just fine but, with the shallow cantery, the impacts were sending waves of energy up the chain. If you lay a line along the deck and then rapidly raise and lower one end, you can make the same effect of a wave traveling along the line lifting up a little hump as it travels.
The vertically mounted cleat always in the past kept this wave from traveling to the gypsy.
It appears the fatal failure happened at the cleat. I'd never imagined it possible but it must be that Grana heeled way over on a port tack at a time when the chain went slack and the chain found a way to slip down and starboard under the cleat's lower ear.
Once the chain freed itself from under the cleat, it was unrestrained from hopping right out of the gypsy. It would then pay out to the bitter end, which was secured below with just enough line to get out the hawsehole. That restraining line then chafed through and Grana was free to drift onto the rocks.
Clearly, the restraint of the cleat was the key failure. A better rig would be a positive chain lock or shackle ahead of the gypsy that's strong enough to take the full strain. I had not arranged one because the cleat had worked so well to date in some very severe conditions and had the huge advantage of allowing anchor scope adjustment without complexities.
Should I have a future with an all chain rode, I will have some sort of bolt down postitive chain lock.