Ballast on keel

[CGN]

Hello everybody, I would like to ask for some help with this problem that I have, but I can't see how to approach it

I need to install ballast in a keel, I'm using 1/2" plate bolted to the keel, but I can't see how to calculate:

1 That the Keel (Wood) won't fail due to the weight of the ballast.
2 Make sure that the number of bolts that I'm using is right

I would like to ask for your help on how to calculate such failure of the timber and what formulas to use.

Thanks for your help

[Raggi_Thor]

Hi.
It seems like you are planning to bolt one plate on each side of a wooden keel?
If the wood has its grain orientated lengthwise, along the keel, which is normal for a shallow keel on a wooden boat, the wood will be subject to stress in it's wakest direction.
Why dont you put the ballast below the keel with vertical keel bolts opp through the floors? This will put the weihgt lower and the keel bolts will take the stress.

[Dutch Peter]

Why do you need to put on more ballast? Can't you ballast internally, is much easier.

[CGN]

I can't, the height of the cg of the ballast onboard still not good to meet the minimum stability requirement I will need some more ballast, and this also means more work inside the boat to accommodate the ballast, is not an oceangoing boat, with the actual condition of the vessel, the boat can sail with no problem, this is to meet stability standards.

the orientation of the grain is longitudinal.

Can you provide any information on how to calculate this?

Thanks for the help

[Tim B]

why don't you build on a small keel with a spruce I-I beam spar and then hang the load on that. Extend the spar into the hull and use two part-bulkheads (one forward, one aft) to hold it in place. The strength of the spars is determined by engineer's theory of bending. check out "DeckBeam" on my website (though I think DeckBeam only handles box-sections). you can build as many of these as you want, and they may (or may not) extend past the existing keel-line. E-mail me at Tim@MarineDesign.tk if you need further info, or want me to re-write deck-beam more generally (which would probably be a good idea.

Cheers,

Tim B.

[Dutch Peter]

Originally Posted by CGN

I can't, the height of the cg of the ballast onboard still not good to meet the minimum stability requirement I will need some more ballast, and this also means more work inside the boat to accommodate the ballast, is not an oceangoing boat, with the actual condition of the vessel, the boat can sail with no problem, this is to meet stability standards.

Sorry CNG,

I always want to know everything, what stability requirement?


Btw, possibly the wooden keel is already fixed to the keelson with larg bolts. Maybe you can replace the lowest piece of the keel with lead and thereby use the original keel bolts.
If the keelbolts can hold, calculate on tensile strenght and shear:

Tensile:

SF = 2 (safety factor)
Rx = tensile stress per bolt. (N/mm^2)
N = number of bolts.
A = area of keel bolt. (mm^2)
F = weight of complete keel. (Newtons)
R(0.2) = 0.2 % tensile stess or proof stress of the material of the bolts.(N/mm^2)

Rx = F/N*A, SF*Rx <= R(0.2)

Shear:

SF = 2
Tx = shear stress per bolt.
N = as above
A = a/b
F = a/b
R(0.2) = a/b

Tx(max) = F/N*A
Tx = 3/4*Tx(max) [circular sections]
Tx = 2/3*Tx(max) [rectangular sections]
{have to check these factors, I'm not completely sure}

SF*Tx <= R(0.2)

If the keel bolts are not in-line, you also have to calculate the bolts on tensile induced by the moment of the weight (90 degrees heel).

Hope this is clear!

[PAR]

How much weight are you adding to this craft? The percentage compared to the displacement and any ballast currently installed? You could end up with a stiffer boat with a bunch of undersized rig component issues glaring back at you.

Could you give the dimensions of the keel, top at the hull, vert. bow, bottom length, vert. stern. How thick on average the keel is. Do you intend to do this even if you have never done this before? We all need more to work with. Is there any chance of e mailing a picture of her?

[CGN]

Sorry guys for raising such interest, is just a small wood vessel is not a sailboat or some kind of super-ultra-specialized craft, is just a small boat that has been sailing for long time and now it has been asked to complied with this values(Dutch peter):

The area under the righting lever (GZ) curve should not be less than 0.055 metre-radians up to 30 degrees angle of heel, and not less than 0.09 metre-radians up to 40 degrees or the angle of downflooding if this angle is less than 40 degrees. Additionally, the area under the righting lever (GZ) curve between the angle of heel of 30 degrees and 40 degrees, or between 30 degrees and the angle of downflooding if this angle is less than 40 degrees, should be not less than 0.03 metre-radians.

-The righting lever GZ should be at least 0.20 metres at an angle of heel equal to or greater than 30 degrees.

-The maximum righting lever (GZ) should occur at an angle of heel preferably exceeding 30 degrees but not less than 25 degrees.

-The initial metacentric height (GM) should not be less than 0.15 metres

is pretty much what we all use

the reason why i asked is just that I wasn't too sure on how to approach the actual calculation of the bolts in wood, I mean there is other formulas from wood associations (awc.org, NDS, Wood handbook—Wood as an engineering material) etc...
but I wanted the opinion form the forum I knew that the forum will have answers that I can use and learn from, "steel good", "wood not so good" (joke)

I really appreciate your response and kindly attention.

[MikeJohns]

CGN
You would be far better off putting a single plate at the base of the keel. You end up making the vessel stronger rather than compromising its structural integrity.

Make up some steel "Floors" to sit on the existing wooden frames and bolt vertically from the floors to the base plate, that way the whole structure is strengthened
It is the garboard area where your existing frames are likely to be too weak.
Print this out take it to a local shipright and get him to eyeball the vessel out of the water. If you want further advice post all the scantlings. The condition of the vessel is a major player.

[CGN]

Thanks for the help mike, much appreciated