How much lead in the bottom =factory water Ballast

A forum for discussing boat or trailer repairs or modifications that you have made or are considering.
Post Reply
User avatar
Ixneigh
Admiral
Posts: 2225
Joined: Thu Sep 09, 2010 11:00 am
Sailboat: MacGregor 26M
Location: Key largo Florida

How much lead in the bottom =factory water Ballast

Post by Ixneigh »

I was pondering replacing that stub keel that I just installed with one made from poured lead and retiring the boats water ballast. It’s a long shot I’d ever do it. But I was wondering how much lead I’d need for at least equal or better stability. I could mold in a flaired out bottom on the aft part, bolt it through the bottom of the boat, and glass over the bolt heads. Thanks for any input.

Ix
"Shoal Idea"
2011 M, white
Etec 60
South Fl.
User avatar
pitchpolehobie
First Officer
Posts: 480
Joined: Wed Dec 18, 2019 8:46 pm
Sailboat: MacGregor 26X
Location: USA, OH

Re: How much lead in the bottom =factory water Bellast

Post by pitchpolehobie »

Ixneigh wrote: Fri Mar 03, 2023 12:10 pm I was pondering replacing that stub keel that I just installed with one made from poured lead and retiring the boats water ballast. It’s a long shot I’d ever do it. But I was wondering how much lead I’d need for at least equal or better stability. I could mold in a flaired out bottom on the aft part, bolt it through the bottom of the boat, and glass over the bolt heads. Thanks for any input.

Ix
Water = 1gm per cm3
Lead has a density of 11.34 g/cm3

So roughly same weight would take up 1/11 of the water balast volume.
2002 MacGregor 26X: Remedium
Tohatsu 25HP
Cruising Area: Inland Ohio, Lake Erie
User avatar
Ixneigh
Admiral
Posts: 2225
Joined: Thu Sep 09, 2010 11:00 am
Sailboat: MacGregor 26M
Location: Key largo Florida

Re: How much lead in the bottom =factory water Bellast

Post by Ixneigh »

Ok, but it’s actually lower than the water. My instinct is 800 pounds. I would also seal the water tank as bouyancy.
"Shoal Idea"
2011 M, white
Etec 60
South Fl.
User avatar
Stickinthemud57
Captain
Posts: 622
Joined: Thu Nov 12, 2020 7:50 am
Sailboat: MacGregor 26S
Location: Grapevine, Texas
Contact:

Re: How much lead in the bottom =factory water Bellast

Post by Stickinthemud57 »

26M, correct?

You may have crossed the Rubicon on the matter anyway, but...

I would be hesitant to make significant changes to the weight, nature, and positioning of ballast in a boat with a lightweight hull, which I consider the 26M to be. A boat must be properly designed to manage the inertia of its ballast, especially in the case of a weighted keel which will exert a good deal of perpendicular pressure to a not-especially-beefy fiberglass hull.

As always, YBYR.
The key to inner peace is to admit you have a problem and leave it at that.
OverEasy
Admiral
Posts: 2012
Joined: Mon Sep 28, 2020 11:16 am
Sailboat: MacGregor 26X
Location: NH & SC

Re: How much lead in the bottom =factory water Ballast

Post by OverEasy »

Hi Ixneigh
I’m with StickInTheMud57 on this.
It’s not a simple “swap out” of this for that….

The Mac26M has about 1500+ lbs of water ballast specifically distributed across and along the hull.
The concept of replacing that with a singular linear lump is fraught with concern.
The physical load distribution is a beginning…
The hull isn’t all that thick so a distributed bonded large area contact surface with fared edging is most likely required to avoid over stress of the fiberglass hull shell. That means stripping off the gelcoat to get a wide area footprint to bond to. That just the static weight distribution. There are also variable angular positional loads as the hull needs to lean to port and starboard which will also vary how the load is going to apply itself to the hull.

Then one comes to the fore/aft balance distribution.
The designed ballast is primarily in two different regions so the lead distribution should match that distribution.
To achieve that one would need kind of a dumb bell approach of two heavier sections connected by a lighter midsection.

Then comes the hydro dynamic loadings due to interaction with the water one is operating in.
There are drag forces as the boat move through the water trying to push the weighted structure aft.
There are also side loading aspects as well (think slip/skid movements) to resist.

Then comes the change to hull rigidity that are inevitable with this sort of modification.
Too much flex and the hull can cyclic fatigue …
Too rigid and the stress concentrates which could result in a fiberglass structure yield failure…..
Neither are nice options….

These are just the preliminary concerns… there are more but I think you get the general idea.

Best Regards
Over Easy 😎😎🐩🐈
User avatar
Ixneigh
Admiral
Posts: 2225
Joined: Thu Sep 09, 2010 11:00 am
Sailboat: MacGregor 26M
Location: Key largo Florida

Re: How much lead in the bottom =factory water Ballast

Post by Ixneigh »

All good points. I believe the odd shape of the ballast is to accommodate living space. My plan was to have most of the ballast just aft of the dagger boat trunk. That’s where the stub keel is now. It would be through bolted and my feeling is, the hull shell is thick enough there. I could always add like 10 layers of biax in the area inside it I thought it needed it. Im curious as to how much much lighter the ballast could be it it was a lead shoe on the bottom. The stub keel is 4 inches wide, 6 feet long and five inches deep, although it tapers towards the front.

Ix
"Shoal Idea"
2011 M, white
Etec 60
South Fl.
User avatar
Wyb2
Engineer
Posts: 143
Joined: Tue Jul 06, 2021 8:02 pm
Sailboat: MacGregor 25
Location: Northeast US

Re: How much lead in the bottom =factory water Ballast

Post by Wyb2 »

Some non-expert thoughts:

You will be lowering the ballast, but not by a ton of you are keeping a shallow stub keel configuration. The whole game is keeping the center of gravity (mass) of the boat close to the same. The CG of the water ballast is, what, maybe 8 inches below the waterline? So the CG of the new external ballast will be maybe 12 or 16 inches below the waterline? Say 16, so the ballast CG has dropped by 8 inches. But add in the rest of the boat, and if you used the same ballast weight, you’ve lowered the boat CG by maybe 4 inches? I think you’d want closer to 75% of the water weight in lead, so around 1,100 lbs.

My 25 only has 625 lbs of iron, but when down for sailing, the ballast CG is probably close to 3 ft below the waterline. To get the same stability with it up (ballast CG around 12 in below WL) I would expect to need 1200+ lbs, incidentally a pretty similar number.
OverEasy
Admiral
Posts: 2012
Joined: Mon Sep 28, 2020 11:16 am
Sailboat: MacGregor 26X
Location: NH & SC

Re: How much lead in the bottom =factory water Ballast

Post by OverEasy »

Hi Ixneigh

Given the amble room amidships between the existing water ballast main tanks the weight distribution was a designed function, not a convenience …
(Production Sailboats, much like airplanes, are designed for safety and stability, especially when sold commercially.
The manufacture liability insurers tend to make sure of it to minimize potential liability exposure.)
Not saying you can’t do something, just cautioning that you might be over simplifying how the existing design was arrived at.

Moving the center of gravity aft as you suggest would potentially adversely affect the stability of the vessel.
How much depends upon a variety of factors… aft loading a vessel will in general terms lead to a vessel more apt to porpoise ( pop up at the bow ) whereas the as designed would be less apt to behave that way. Combine this characteristic with wind and wave conditions one might have a vessel trying to tail stand if taken toward the extreme (not that you are doing that).

I’m curious as to why you’re interested in such a modification?
What operational characteristic of the existing design do you feel needs to be addressed?

Several years ago a Frenchman modified his Mac26 with a heavily weighted (several hundreds of pounds) swing keel.
After all his modification efforts there was little is any improvement but quite possibly the opposite.
I his case putting the weight in the keel was giving it the moment arm to lower the static Center of Gravity more effectively.
But in doing so required the use of a new method of raising the keel as it was now no longer just the pull of a line.
Not sure how well it worked out with the pivot structure for the keel…nor how it handled the angular moment loads when heeled.

So what specifically are you after?

Best Regards
Over Easy 😎😎🐩🐈
User avatar
Ixneigh
Admiral
Posts: 2225
Joined: Thu Sep 09, 2010 11:00 am
Sailboat: MacGregor 26M
Location: Key largo Florida

Re: How much lead in the bottom =factory water Ballast

Post by Ixneigh »

Re The CG calcs: cool. My rough guess of 800 was a bit shy.

Re why: a certainly legitimate question. The answer would be, to maximize performance under sail. Some will say thats just not too bright because the M will never be a stellar sailboat. But, anything substantially better is a-lot more money. Or a lot more work. I thought about getting a fin keel boat cheap somewhere like an old Catalina, drop the iron fin and put leeboards on it. Well, THAT outfit probably won’t be much better than my M is now. Maybe the Catalina is a little better built boat, however for the type of sailing I do, the Mac construction is fine.
England has some pretty boats (swallow yachts) but they are far away and unaffordable for me (right now)
And, I don’t mind messing around with my boat. I contemplate several off season projects each year. The existing stub keel was one, and it now allows useable windward sailing with no board at all. The rudder bushing mod was another, and now my brackets are much less prone to getting bent. I work through all these little issues with the goal of improving sailing where ever I can.
I have not had the boat out in really strong down wind conditions yet, but in lesser conditions the boat handled better. I’m sure the keel would work even better if it were lead. . Plus I never casted a lead keel before. It’s kind of like a bucket list item no? All those lead fumes, the molten metal, the furnace… :?

Ix
"Shoal Idea"
2011 M, white
Etec 60
South Fl.
OverEasy
Admiral
Posts: 2012
Joined: Mon Sep 28, 2020 11:16 am
Sailboat: MacGregor 26X
Location: NH & SC

Re: How much lead in the bottom =factory water Ballast

Post by OverEasy »

Hi Ixneigh
All those lead fumes, the molten metal, the furnace… :?
That too! :| :| :? :?

I toyed around with adding a pair of skeggs theoretically (thought experiments are less costly :D :D ) to our Mac early on when initially contemplating beaching or tiding out when traveling the ICW north and south to help keep the hull up off the bottom. What started off as a somewhat reasonable idea quickly became reasonably non viable without extensive hull reinforcements to de-concentrate the loadings to within the long term capabilities of the hull fiberglass. Better option was to make sure the bottom we’d be settling on to was smooth and soft or better yet avoid the issue altogether if possible and stay afloat.

On the wind side drift handling aspect in shallower waters that a skegg might afford I found that partially lowering our Mac26X swing keel to where the width of the blade was exposed below the hull was most beneficial in this regard at speeds below 6 knots (such as when docking). That would roughly equate to about 25-to-30 percent of the keel lift line travel. It does great 👍, didn’t require any modifications (other than operationally) and does swing up out of the way when moving forward and finding something hard in the way.

I did come across a while back pictures of a Mac26X with ‘Dutch Paddle” side mounted swing keels that appeared to possibly be bottom tip weighted. There wasn’t any description or commentary associated with it though. Just the photo. Maybe on Pinterest??

Anyway if yur happy experimenting with yur boat with wide open eyes I’m happy for you!👍😉😎 Tu feliz Yo feliz 😎😉👍
There is no absolute best single answer for most things (other than keeping the topside and bottom side in their relative defined relationship to each other on a sail boat. Swapping them gets messy🫣🙄)

Best Regards
Over Easy 😎😎🐩🐈
Post Reply