Question for the Engineers here, regarding ballast weight

[Tomfoolery]

The only thing I disagree with in the above post, is about the daggerboard in the M being ballasted by the water that is inside when the daggerboard is lowerred. That water doesn’t become a ballast; while submerged, it is the same weight as the water around it. That submerged fin is what gives resistance to movement. The water in the actual ballast tank does not become a factor until it is higher than the water surface surrounding it.

On the other hand, if you plug the holes and there is air in there, you have negative ballast, i.e. the daggerboard actually works against your boat's stability as the CG of the boat is elevated slightly. That's why it has holes - so you can have a large fin with low mass that doesn't work against your stability against overturning.

[BOAT]

The only thing I disagree with in the above post, is about the daggerboard in the M being ballasted by the water that is inside when the daggerboard is lowerred. That water doesn’t become a ballast; while submerged, it is the same weight as the water around it. That submerged fin is what gives resistance to movement. The water in the actual ballast tank does not become a factor until it is higher than the water surface surrounding it.

On the other hand, if you plug the holes and there is air in there, you have negative ballast, i.e. the daggerboard actually works against your boat's stability as the CG of the boat is elevated slightly. That's why it has holes - so you can have a large fin with low mass that doesn't work against your stability against overturning.

Same goes for a wooden centerboard if it floats.

[NiceAft]

All very nice information if you're ever on a quiz show.

Let's see a raise of hands of who wants to plug the holes in their dagger board or center board

Not all at once now

I just remembered what Jimmy says,"Your boat, your rules".

[chipveres]

BOAT,

The only thing I disagree with in the above post, is about the daggerboard in the M being ballasted by the water that is inside when the daggerboard is lowerred. That water doesn’t become a ballast; while submerged, it is the same weight as the water around it. That submerged fin is what gives resistance to movement. The water in the actual ballast tank does not become a factor until it is higher than the water surface surrounding it.

Ray is right, I actually tried this with a bathtub and an empty plastic jar. Try it for yourself, but don't be surprised if your friends call you Archimedes, or something else that implies that you are an ancient Greek. Or in my case an ancient geek.
Chip V.

[Jimmyt]

...or something else that implies that you are an ancient Greek. Or in my case an ancient geek.
Chip V.

[OverEasy]

Hi Sheppie62!

Based on standard engineering methods one desires to place ballast as far directly below the center of buoyancy.
That concept applies side-to-side and fore-to-aft.
Moving/adding static weight to either side of the center of buoyancy tends to destabilize as heeling increases.
Moving/adding static weight in front of or behind the center of buoyancy tends to destabilize pitch stability as well as bow rise recovery.

From our own experience on our Mac26X when adding a second battery in the port(left) seat aft of the galley we found that there was an increase in list of about 3-5 degrees. Adding the A/C unit to the port(left) side increased list to about 6-8 degrees.
This is actual empirical results.
NOTE: The battery mod was accomplished on the hard then floated in SC
NOTE: The A/C mod was accomplished after the new bottom paint while on the hard then floated on Lake Champlain, VT.

We compensated with internal stores distribution to balance to Zero.

So with our experience we are going RE-evaluating our load/balance plan.
We are looking at:
—> adding static balance compensation with fresh water and grey water storage tanks on the starboard(right) side
—> moving the A/C unit to the starboard(right) side

The original design weight and balance work for the MacGregor boats was well thought out.
Rodger did a great job with allowing a reasonable amount of margin (forgiving) in the design of our boats.

We keep track of our additions and subtract what we add from the useful load to stay within design intent.

Our total modification weight (galley, electrical, battery, A/C, fuel tanks) increase is 250 lbs (which includes the 24 gallons of fuel).

Fortunately we are designing for an extended 2 + 2 person cruiser.

As a suggestion the more central to the widest beam location along the length, centered side-to-side and as low as possible to the hull is the target to aim for. As that is not directly possible look for way to compensate with static weights when/where possible.

Your boat, your rules.

Best Regards,
Over Easy

[Sheppie62]

[NiceAft]

Sheppie62,,

Just remember “left” and “port” both have four letters.

[OverEasy]

Hi Sheppie62!
Oopsies!!! My bad!!!
Sorry, didn’t mean to confuse anyone
Fixed it

Thanks!
Rather be a fool for a moment than forever