Modifying a Maxwell Chain Gypsy

[Sailing Amok]

As has been discussed in the past, for some reason I can't fathom (cost?) Catalina installed Maxwell 500 windlasses on our boats. These only accept a 1/4" chain gypsy, which by most accounts is undersized for these vessels, in storm conditions, with a modern high holding anchor. I'm wondering if anyone has ever compared a Maxwell 5/16" gypsy from one of their larger windlasses to the 1/4 gypsy from the 500? I'm thinking a modification could be made, a bushing machined, etc. The cost of a new windlass is wild, and I know wire wheeling the chrome off the capstan, and wrapping the chain around that is an option, but if a simple mod can be made to an appropriate gypsy, it could be a great option.
Aaron

[Noah]

Call Maxwell US office (on Atlantic coast) and ask their advice. I talked to them once regarding a parts order and they were helpful.

[Sailing Amok]

I sent them an email a while back, and basically got "we can't recommend using 5/16 chain with this windlass"

[waughoo]

This would likely require someone to fabricate a whole new gypsy and machine it with the appropriate taper/keyway/ shaft to match the windlass you have.  It is certainly doable, but it is a rather signifocant project to sort out.  If you could manage to get an engineering drawing in a cad format for a 5/16 chain already, you would be light years ahead.

[Mick Laver]

Hi Aaron
I'm curious why you think 1/4" chain is undersized for the 34. The breaking strength for 1/4" G43 is the same as 5/16" BBB. Maybe just upgrade your chain? Besides, you can carry a heck of a lot more 1/4" than 5/16". More chain to let out if needed.

-Mick

[Stu Jackson]

Hi Aaron
I'm curious why you think 1/4" chain is undersized for the 34.
>>>>>>>>>>>>>>>>>>>>>>>

I agree with Mick.  The question you have to ask is for what wind strength are you designing the ANCHORING SYSTEM.

Anchor System Sizing Tables (Reply #6) & Swivels http://c34.org/bbs/index.php/topic,4990.msg30400.html#msg30400

[Sailing Amok]

We're actually already running G43. My issue isn't with the strength of the chain, it's with the strength of the shackle which will fit the chain. Using the 2,400# load estimates 1/4 G43 is fine, with a WLL of 2,600#. Unfortunately the largest shackle which will fit 1/4 chain is a 5/16, with has a WLL of 1,500#. There are Grade B shackles, with twice the WLL if grade A but they seem next to impossible to find in 5/16, and are mostly available larger. It seems Peerless makes one, but I have not been able to find them.
Also, with the smaller chain, and smaller shackle, I need to use a larger shackle in the anchor, and then the smaller shackle in the chain. The shackle to shackle connection seems to me like point loading, though it does seem to be a common way to do things.

EDIT:
I did just find this, from Crosby

"The popular Crosby forged chain and anchor shackles (3/16" – 3") can be point to point loaded to the Working Load Limit without bending of the pin/bolt. Connecting bow to bow, or bow to pin is the preferred method. Connecting pin to pin is also acceptable if there is not interference between the diameter of the shackle ears.

No matter which method is used, caution should be given to maintain the load at the center of the span, by spacers on the shackle pin if necessary, to prevent the load or attaching shackle from sliding over to one side and concentrating loading near the shackle ear.
Keeping the load reasonably centered is key."

[Stu Jackson]

Aaron,  In my previous post I provided a link to the anchor system sizing tables from Calder's Cruising Handbook.  I also wrote in Item #4 in that link:

I have been suggesting that handy reference sources be used, like Calder's Cruising Handbook.  The photos below are the three important tables from that book for sizing anchoring SYSTEMS.  You can wander on down to your local WM store or any handy nautical book chandlery and read the rest of the two pages on how to use the tables, but they're pretty self explanatory.  You've already mentioned "The Gotcha" about this whole exercise:  some chain won't allow a fit of certain sized shackles.  So, it becomes important to plan ahead.  In many cases, windlasses dictate the size and type of chain, with the the rest of the bundle to follow along.

In the pages following those tables in Calder's book is a very detailed discussion of shackles.  I won't reproduce it here, but you could do as I suggest and find it, and also realize this whole chain/shackle strength thing has been around since they invented chain and shackles.

[Ron Hill]

Aaron : The breaking strength of 1/4" HT chain is 9450 lbs. As Stu mentioned - I believe that something else in your anchoring system will probably fail before that 1/4" HT chain will break!! Where as 5/16" BBB (for windlasses) has only a breaking strength of 7600 lbs.!!!

I have 1/4" HT chain and am well satisfied with it!!

A few thoughts

[Sailing Amok]

Thanks for the replies. I don't have a copy of Calder's cruising handbook, probably the only one of his I don't own! I know that shackles use a higher safety factor than chain, which in theory  makes shackles with a lower WLL than chain actually suitable. But, it's not great practice to use anything other than WLL for calculations, sure wouldn't do it in overhead lifting, so why with our boats? One of the reasons shackles use a 5:1 or 6:1 safety factor, is because of the massive reduction in strength in the event of a side pull. A 5/16 Crosby shackle, suitable for 1/4 chain only has a WLL of 800# when side loaded (4,800# ultimate strength). The ABYC table gives us 4,800# in 60 knots, so it is possible, but that's a whole lot of bad luck to end up with a 90 degree pull on the shackle, and 60 knots of wind. A more likely scenario would be a 45 degree pull, which would give us a WLL of 1,050# or an ultimate strength of 6,300#. Shackles distort well before breaking, so I could definitely see bending a shackle being a realistic occurrence in a summer storm. That would probably require cutting the shackle off the chain to replace it. It also probably means we should make a habit of inspecting our 5/16 shackles after sitting out big weather.
All this is to say that while our 5/16 shackles are most likely completely sufficient, 3/8 shackles would likely live longer, have a lower risk of the pin binding, and give a little more safety factor. So, if running a 5/16 chainwheel turns out to be a simple affair, why wouldn't we (other than chain weight)? That being said, if it turns out to not be an option, I'm certainly not about to throw more than a handful of boat bucks at it, because 1/4 chain and a 5/16 shackle will be fine 99% of the time.

[Jon W]

Are you planning to use a swivel to connect the chain to the anchor or a shackle?

[Sailing Amok]

Are you planning to use a swivel to connect the chain to the anchor or a shackle?

Shackle. Swivels tend to be the failure point. I have been considering something like an omni link. I am curious to do some pull testing to compare Grade A American made shackles, to Grade B Chinese shackles (which are available in smaller sizes). I may buy a few, and bring them by my local rigging shop, for science. Will report back if I do.

[Ron Hill]

Aaron : The only way I can figure out that a shackle would ever receive close to a 90 degree pull is if you double anchored with one on the bow and one off the stern!!  What a crazy ride that would be in a blow!!

A thought