Rebalancing the keel of a CD31

[Cathy Monaghan]

You shouldn't have to add lead shot to the bilge. All Cape Dorys like to heel between 15 and 20 degrees. If that's too much for you, I think it would be easier to control heel by balancing the sail plan rather than making structural changes to the boat. And all that takes is shortening sail.

By the way, on our CD32 we enlarged the opening in the cabin sole at the base of the companionway ladder and added a second one farther forward. There is ALOT of space down there. We now use that space as our "basement". We keep a 5 gallon bucket down in the deep bilge which we keep filled with cans and bottles of beverages and we keep bottled water in crates on the slope of the bilge. So I guess that's one way to add weight in the bilge.

I think the CD31 has a pedestal mounted table forward, so you may not be able to add the second hatch.

Hope this helps,
Cathy
CD32 Realization, #3
Rahway, NJ
Raritan Bay

[Frenchy]

That's a great idea, Kathy. You've got me thinking how I can copy that. I'm imagining you created a template
possibly attached with double sided tape and followed it around with a router, then squared off the corners with a chisel.
Making the hatch with a glue-on teak and holly veneer would be comparatively easier.
The project, including the finishing, came out beautifully. - Jean

[John Stone]

Very nice Cathy.

[fmueller]

Boat looks great Kathy ... interesting thread ... Just a general observation - messing around with the amount, type, and position of ballast is pretty common (isn't it) in the production runs of boats ?

Somewhat related - I'm doing a lot of work on my CD 27 and one thing we have done is move my two group 27 AGMs to the space just above the encapsulated ballast under the cabin sole. We cut a second hatch in the sole. The batteries will live in a glass tray (ABYC compliant) on blocks with retaining brackets. They fit nicely and AGMs don't need periodic watering - so they are ok down there where flooded batteries would be difficult.

I wanted to get them out of the starboard locker because Jerezana has had a slight list to starboard since I bought her, which I have ascribed two the two batteries sitting in that position.

Anyway I figure it can't hurt to get 120 pounds down lower and centered in the boat. It will be interesting to see if my little boat looses her slight limp.


Fred

31 Jerezana refit @ Carbon Ocean Yachts.jpg

46 Jerezana refit @ Carbon Ocean Yachts.jpg

[CruiseAlong]

Folks,
My CD31, #45, does have the additional ballast as described, covered with epoxy. From my memory, at that time, it was the owner's choice. Of course it sails points and sails well. Besides normal sailing, it would affect the capsize/knock down stability.
Dana

[Jim Walsh]

Folks,
My CD31, #45, does have the additional ballast as described, covered with epoxy. From my memory, at that time, it was the owner's choice. Of course it sails points and sails well. Besides normal sailing, it would affect the capsize/knock down stability.
Dana

Are you the original owner?

[Frenchy]

I wonder: Does anyone know if there were other Cape Dory models that went through a ballast re-thinking?

[Steve Laume]

While there may be some merit to adding additional ballast to a particular boat to correct a design flaw I can't really say if that is the best way to go. Raven was always a bit heavy in the stern. I chose to move the batteries and water heater as far forward as possible. I also keep my, heavy, tool box on the sole of the V berth, along with a 5 Gal jug dof emergency water. Then there is the 90' of 5/16" chain I added to the anchor rode in the bow. Redistributing movable ballast seems like the first step in correcting any issues. My boat is already heavy enough when I have all my cruising gear and supplies on board. If you planned to strip her down for racing and eliminate all extra weight, then I could see where adding fixed ballast might be the best option.

I never liked the idea of filling the bilge with anything. It might be great to get the battery weight, low and centered in the boat. The down side is what happens to those batteries if you should start to take on water. At a time when you most need your electrical system and the bilge pump, you are now going to have flooded batteries. Anything you store down there is going to take away from the bilges capacity to buy you time before the flooding reaches a higher level.

I had one incident where I first noticed a flooded bilge when a trickle of water started to leak from the inspection hatch. If I had had any less volume in the bilge, the floor boards would have been awash by the time I noticed the problem. I look at the bilge as sort of an insurance plan against flooding the cabin, Steve.

[jen1722terry]

Sounds like our kind friend Dave Perry was correct: adding ballast was a factory option for the 31s. I wonder why.

The 31 is a bit of an odd duck among the larger CDs models (30-36) in that her beam is nine inches wider than the 30C, a big jump in beam and a jump that is not repeated as you go up thru the larger boats (32, 33, 36). This additional beam is carried well aft to allow for the large aft head. The 31 is just not as pointy at the ends as the other larger models, and one would think this additional beam and hull shape would increase stability. However, the 31 also has a significant increase in sail area over the 30C (15.3 %), but only an 8.7% increase in ballast (350 lbs). Note I'm comparing cutters to cutters here.

The CD 32 on has a.009 more sail area than the 31, though she carries 8% more ballast and has 2 more inches of beam

The CD 33 has 6.4% more sail area than the 31, 26% more ballast and about 5 more inches of beam.

The above data seems to indicate that the CD 31 could be considered under-ballasted for her length and sail area as compared to the CD 30C, 32 and 33, a fact that may have prompted new owners to order more ballast at the factory or install it later. But the significant increase in sail area may be canceled out by the additional beam and hull shape and thus may have prompted some other owners to stay with the stock ballast of 4350 lbs. after they had sailed this unusual CD for a season.

I note again that our 31, #33, was extensively raced on the Chesapeake for 15 years with an expensive suit of racing sails. Spring and fall racing down there can be frisky and, if she was tender close-hauled with the large genoa flying, one would think the owner would have added more lead.

The above are just musings on a sunny Tuesday morning here in Mahone Bay, Nova Scotia while I continue to recover from shingles. Hope you all enjoy
them as a part of the continuing, sometimes rhetorical, but always enjoyable discussion of these fine old yachts that we all love so much.

Terry

Bonus points question: I have heard from another old Cape Dory hand that the 31 was not entirely or even mostly designed by Carl Alberg. I can't recall the name of this other designer (Clive Dent, possibly?). Does anyone know the name? This could explain why the 31 is so different from the other Alberg-designed CDs.

[Jim Walsh]

As per Dave Perry, as noted at the Annapolis Annual Meeting a couple years ago, the CD31 was an Alberg design. He noted that the in-house designers often made the final decisions as to the interior accommodations only. There's no better authority than the man who was there as an eyewitness and an active participant in the manufacturing operation.

[Frenchy]

[quote][/quote]
The CD 32 on has a.009 more sail area than the 31, though she carries 8% more ballast and has 2 more inches of beam

The CD 33 has 6.4% more sail area than the 31, 26% more ballast and about 5 more inches of beam

One thing to keep in mind is that these two boats are sloops and have higher aspect ratio rigs than the cutters. The
mast of the 33, in fact, is the same as the 36. The higher rigs would require more ballast. - Jean

[John Stone]

This is an interesting thread. But, I don’t know what to make of it. All the comments seem accurate and reasonable to me. Sure, a boat with a taller rig will heel more and sooner as the wind rises in than same boat with a shorter rig. But if it’s a different boat with more beam or firmer bilges then not necessarily so. And while the 33 may have a taller rig I’m sure Carl Alberg knew exactly how to compensate for such changes.

So the question in my mind remains, why would Cape Dory recommend adding 400-700 lbs of ballast to the bilge? Why was this an option? Was it an option on any other CDs? And I’m confused by some of the comments that span from correcting fore and aft trim to lateral trim to making the boat stiffer.... it sure doesn’t take 500 lbs of added ballast to correct a lateral trim issue.

I can’t belive Carl Alberg made a mistake like that. So I am left wondering if the ballast is additive to the ballast Alberg called for or was there a mistake made by CD and the recommended additive ballast brings the total ballast up to the amount originally called for by Alberg. Or is this some other issue that eludes our interesting discussion?

I’m with Steve L. on this one. Sure, ballast makes a boat stiffer. But our boats are cruising boats and designed to be sailed with a lot of stuff on board. Thousands of pounds of of stuff. At some point extra weight begins to have negative consequences, even for crusing boats. So, if you start with too much ballast by the time you get all your gear and supplies on board you are unnecessarily overloaded. As was pointed out, boats that are raced often benefit from added ballast because they are sailed with very little additional stuff on them. Minimal equipment. Hard core racers will even remove water tanks etc. but who ever bought a CD primarily to race?

I have worked with the finest intelligence organizations in the world. And we still get ourselves confused from time to time and sometimes seem at a loss to figure out where a piece of information originated or how it got into the decision making process. This usually occurs after something bad happened and we are back tracking to figure out how we did something dumb. So, I’m not convinced the left and right hand at Cape Dory were talking to each other. Hmmmmm...

Very strange indeed.

Happy sailing.

[fmueller]

Steve,

AGMs are sealed batteries ... saltwater has about 60-70 ohms resistance per inch. Terminals are about 10 inches apart ... so the resistive load between terminals is about 700 ohms submerged in salt water. amps = volts divided by resistance. 12/700 = .017 amp. Would take many many days to kill an AGM by flooding it in the bilge. I think I've got this right.

I think part of the reason to spring for AGMs is that they can be put in places where you would not ordinarily put a flooded battery. They don't even need to be upright for instance.

cheers

Fred

[Steve Laume]

Thanks Fred, it seems you should be fine with AGMs. I might even have to re think the location of my AGM start battery as it is low in the cockpit locker and it makes it more difficult to remove the access panel to the engine and the servicing of the seacock. It would move that weight a bit further forward and the start battery would only displace a couple of gallons at best.

You wouldn't want to do this with flooded batteries, Steve.

[wsonntag]

Weighing in on re-ballasting (sorry!) (re-balancing). Interesting thread but it does not make for a compelling rationale for adding ballast as described. There were exchanges on this Board a few years ago starting with an observation that the CD31 was tender, especially initial stability. I agree but it is exactly what you expect for a boat with the type of wine glass hull sections she has at and below the waterline. I have never felt the boat lacked stability while sailing in any kind of weather or sail trim. It seems intrinsic to these Cape Dory designs that they heel over, harden up and go. To avoid heeling or have her stand up shorten sail, sometimes earlier than you might expect. Could it be that this initial tenderness was the reason for the option of additional ballast? Also, I've never found the boat to be off her lines fore and aft. Well except of course when me and all of my substantial middle-aged crew are ke-bobbling in the cockpit!

One other matter that has also been discussed on the Board is resting lateral stability. With the stock equipment set up you have starting from aft on port side, the water heater, the batteries, the fuel tank and the head. Especially when the starboard water tank is empty my boat sits abit heeled to port. You have to look for it but I can see it of course. There were posts a few years back where about 250 lbs of lead (I think that's how much though that seems like allot as I write this) was glassed in under the bunk, just outboard of the starboard water tank to compensate. That sounds like "re-balancing" of some merit.

All this said, it would be great to hear about changes in sailing characteristics from someone who has the extra weight in the bilge.

I too am particularly looking forward to spring commissioning and sailing this year. SURPRISE was stored inside for the last year and a half due to my absence for an overseas work assignment. I'll be re-stepping the mast and getting her ready to go in the next two weeks. I have to collect all the interior stuff that's been in storage, cushions and equipment etc so it will be a bit bigger job than usual. But worth it, I have really missed my SURPRISE boat.

Cheers!

Bill Sonntag