Installing a Chain Stopper

A while back I installed a Lewmar chain stopper on the foredeck to make anchoring a bit easier. It was a simple job to fashion a mounting block out of teak, make a backing plate out of apitong and bolt it all together. The job was done in a day. Then I went out and anchored and discovered that if I left it as is, the stopper would soon knock all the galvanizing off the chain. This is a standard flapper type chain stopper, rated at 5,000 lb SWL and sized for 5/16 chain. I had used this unit on my last boat, which had 1/4" chain and a vertical capstan windlass, and it worked well. The problem is that there is barely enough clearance in the stopper for the chain to pass through, and only if it is perfectly aligned and set at an angle that matches the angle of the chain as it passes from the windlass to the roller. On top of that, the deck in that area is only about half an inch thick. It is made of a fairly heavy fiberglass laminate and a bit of wood core.  This isnt really enough structure to simply throughbolt the stopper to, so I added a carbon fiber top plate and a larger wood backing plate to bring it up to snuff. The photos below outline the process.

Mold. 

First I measured the amount of crown in the deck forward of the anchor locker. Its nearly flat but I wanted the edges of the top plate to fit tightly to the deck so I created a bit of extra curvature in the mold, which is made of a piece of old 1/4" Starboard.

Paper pattern with pre-cut carbon fiber

I took a template off the deck and drew the shape in AutoCad. I wanted the top plate to be fairly large so I could attach it to the deck with several widely spaced fasteners to spread the loads out as much as possible. The rectangular shape is the outline of the teak mounting block.

Laminating the carbon fiber

I used four layers of Vectorply C-LT2200 carbon fiber cloth for the laminate. This fabric is made of carbon fiber bundles aligned along the 0 degree and 90 degree axes of the roll and stitched together. This architecture is stronger than traditional woven fabric. The four layers amounted to about 88 ounces/sq yd of material for a total thickness of about 3/16" when it was finished.

Second layer is rotated 45 degrees 

I oriented the first and fourth layers so the fibers run at 0 and 90 degrees to the centerline of the boat and rotated the second and third 45 degrees to provide strength in all directions. I used WEST systems resin which works really well for hand laminating projects.

Finishing the top plate

After the plate was laminated and cured, I glued another copy of the paper pattern to it so I could precisely locate all the holes. It was a simple matter to drill and countersink them exactly where they need to be.

Top plate ready for finish sanding and paint

Check fitting the hardware

Finished part installed

I made a backing plate out of 1" thick apitong that extends out to the bulwarks to help spread the loads as much as possible. The 10" cleat allows for a snubber to be run out over the port bow roller. I found that if I take a turn around the roller with the snubber, it wont jump off if it when the boat swings at anchor.

Chain and snubber geometry works

It took a couple of tries to get the alignment and angle of the stopper to match up perfectly with the chain. It would have been nice to have a larger stopper, but there was just enough clearance between the shank of the anchor and the hatch for this smaller unit.

55 LB Rocna just fits

Continue

Americas Cup Lessons Learned

Apologies for the long hiatus from this blog. Its been a very busy six weeks since my last post, with several projects completed on Finisterra. But first we need to consider the AC regatta and lessons we can take from the racing and the boats themselves, and what this incredible event might mean for the future of the competition.

The boats:

1. It appears that Team Oracle really did have the better boat. I had thought that the bows might be too fine, lacking sufficient buoyancy to support the wing mast. But the designers and crew were able to keep the boat on its feet throughout the event. The Kiwis chose another route with fuller, more buoyant bows. Perhaps in a bit more swell that would have paid off, but it is clear that the Yanks had the faster boat for the conditions they encountered. This is an indication that Team Oracles designers had a better feel for the expected conditions on the bay and did a better job of targeting their boat for them, while the Kiwis opted for perhaps more of a safety margin in their bows and paid the price with more weight and windage up forward. This would cost them speed especially on the upwind legs.

2. Deck layouts for both boats showed significant differences. The most striking of which were the airfoils mounted on the aft cross beam of ENZ. There was a price to pay for them in terms of weight and drag and I think its doubtful that they did enough to smooth out the wind vortices swirling off the boat to offset the negative factors. The Kiwis seemed to have a more efficient winch layout, but I noticed in the later races there were times when grinders werent in the cockpit but grinding from a position on the trampoline instead. This was an indication to me that the crew was getting a bit rattled as they racked up loss after loss.

3. Much has been said about the fact that the tactician aboard Oracle had to grind winches on each tack or jibe while his counterpart on ENZ was able to keep his head out of the boat more and focus exclusively on tactics and strategy. This was more than offset by the addition of a strategist aboard Oracle. The early races showed that communication between tactician, strategist and helmsman would be crucial and it looked like ENZ had the better operational arrangement. However, once Ben Ainsley replaced John Kostecki those lines of communication improved drastically and it was beautiful to see how well Oracles afterguard worked together, and this was a key factor in Oracles string of victories.

4. There were other design features in the boats that probably made a difference. For example the helms on Oracle were angled inward a few degrees. This probably resulted in better ergonomics for the helmsman than the directly forward facing helms aboard ENZ.

5. As far as I could tell, the daggerboards were roughly the same but of course I dont know what the actual foil sections were. Another area of vital importance is the board control systems. We dont really know what the differences were and which worked best at raising and lowering them. Nor do we know which system worked best for adjusting cant and rake of the boards. Of course we can infer that Oracles worked better since they won but it would be fascinating to see side-by-side comparisons of these systems.

Ill write more about the actual racing in a later post.

Continue

Americas Cup The Plot Thickens

Just when we thought the Kiwis owned this regatta, the Yanks stepped up. As I mentioned previously, team Oracle is still on the steep part of the learning curve. They apparently took a giant stride forward over the last few days and the race results show it. Of course they still have a very steep hill to climb if they want to keep the Cup, but they are definitely improving their boatspeed, tactics and boat handling.

In race 8 team Oracle showed improved upwind boatspeed, but more important than that, they tacked much more efficiently than before. In previous races Oracle lost out to the Kiwis on nearly every tack but this time they held onto them on leg three. Near the top of that leg ETNZ, on port tack could not cross the starboard tack Oracle and attempted to tack under them, nearly capsizing in  the process. This rare boathandling mistake cost them the race and came near taking them out of the regatta altogether. No one knows if they would have won this race if not for the blown tack but the key point of this race is that Oracle managed to up their game and breathe some life into their chances.

With the next race canceled due to high winds, both teams retired to their respective corners, one to review what went wrong, the other to continue their climb up the learning curve. When race 9 got underway the next day, the Yanks showed that 8 was not a fluke. They won the start and led ETNZ at every mark.

Race 10 was a spectacular display of yacht racing. The American boat won the start but couldnt quite slam the door on the Kiwis at mark one and trailed on the run. It was on the next beat that we were treated to a tacking duel that no one prior to the event would have predicted. It was an awesome spectacle of high speed sailing, split second timing and superb boathandling. Rounding opposite marks at the windward gate the two boats split to opposite sides of the course and jibed back toward each other with ETNZ on starboard. This was a situation that has never happened before, two boats hurtling down the course at 40 knots, approaching each other on a collision course. Oracle opted to slow down and take the stern of the Kiwi boat. At this speed, the result was a 200 meter advantage for ETNZ and that was all they needed to take the race. Was the slowdown the right choice? I think that, given the situation, it was probably a better option than gybing on top of the Kiwis and getting pinned outside at the leeward mark. The question is how far ahead does the tactician have to think in order to make this the right decision. At 40 knots, the Kiwis were a long way off thirty seconds before the cross, but thats about when the decision to take their stern needed to be executed. This is sailing on a whole new level, the ultimate high speed chess game where the stakes include putting the lives of the crew on the line. Intense!

Continue