6 meter sailboat

by Fred

I have an old classic boat built in 1947.

This is a wooden boat and at some point someone covered the boat with fiberglass.

I am stripping the fiberglass because of moisture and replacing part of the stem.

As I have removed some of the planks I noticed there is no cotton caulking, only putty.

I do not plan to replace the fiberglass but rather paint and seal.

My question is, if there is no cotton between the planks is the putty alone going to keep the water out?

It seems either I have to remove the putty and caulk with cotton and putty or I have to replace the fiberglass?

Do I have to caulk only below the water line or the whole boat?


Comments for 6 meter sailboat

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6 meter 12/30/17
by: Ned L

Yes, cotton would be correct.

Oakum is for planking thicker than about 2" or so, and even then you start with cotton. (Start with cotton in the bottom of the caulking seam, then as the seam widens toward the surface you change to oakum for the big part of the seam.)

It is possible that this boat was built "tight seamed", and therefore would have nothing but a bit of seam compound.

Tight seam construction is typically more European and requires more care in fitting the planking.

I would suggest learning more about your boat’s construction before doing to much.

by: Anonymous

Thanks for your recommendations.

cotton caulking
by: Anonymous

Sorry Hugo, but you are way of the mark suggesting that he does not use cotton.

Hemp is only really useable in thicker planks.

On a smaller hull like this the only option is cotton.

If you have experienced discoloured cotton it is because of the cotton being contaminated some other way.

Currently working on a twenty four foot wooden yacht with seams which are definitely thirty plus years old and the cotton is pure white.

Anything thicker than a one eighth seam I would consider hemp, anything less absolutely not.

by: Anonymous

Thank you again for sharing your knowledge about the care of these boats


cotton caulking
by: Anonymous

The cotton serves another very important purpose other than keeping out water.

It serves to stiffen the planking and prevent sawing, the action where the planks move against one another when the boat heels.

Cotton and putty or sikkaflex and cotton, but either way don't be tempted to leave out the cotton.

A sheathe of fibreglass would have stiffened to an extent but doing such a thing shows a grave contempt for the boat and a lack of understanding of timber.

by: Anonymous

Thank you for your feedback . I will follow your advice .

by: Dr Hugo

Hi Fred,

Proper caulking below the waterline is essential.

It is much better to use hemp/jute/oakum than cotton that rots, turns black and stinks in time if there is seepage.

Hemp or jute is easier to work with, twisting and tightening and paying into the seams strongly with a caulking iron leaving an adequate groove for the sealant.

For sealant, marine Sikaflex is very good, the black one being easier to sand when dry than the white one.

Once applied, it can be smoothed while still soft by rubbing over gently with your finger with a little kerosene for an even finish with little or no sanding needed.

The 3M caulking compound, also in a tube to be used with a caulking gun is also good but more expensive.

Later when dry, just wipe down with thinners or acetone before painting with primer and top coat.

Caulking above the waterline is usually not necessary but clean all seams thoroughly by scraping, vacuuming and brushing with thinners or acetone to ensure good adhesion for the sealant.

Hope this helps.

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