I ask this question because we plan to do structural work in the bilge area, rip up and lay back down the floor pan, and replace the bulkheads. We don't want to build this 'hump' into the repairs, then have them stressed when the boat is launched.
Hump in the floor
-
Bob McGovern
- Posts: 287
- Joined: Fri Oct 26, 2012 3:08 am
- Location: Wyoming, USA
Hump in the floor
Our Ballad exhibits a bit of a convex hump in the cabin sole as it sits on its keel on dry land. Has anyone else noticed this hump, and does the salon floor become flat or concave when the boat is in the water and the keel weight hangs down?
I ask this question because we plan to do structural work in the bilge area, rip up and lay back down the floor pan, and replace the bulkheads. We don't want to build this 'hump' into the repairs, then have them stressed when the boat is launched.
I ask this question because we plan to do structural work in the bilge area, rip up and lay back down the floor pan, and replace the bulkheads. We don't want to build this 'hump' into the repairs, then have them stressed when the boat is launched.
Re: Hump in the floor
When I reinforced Sanlens keel construction some 20 years ago she showed signs of the same hump, although not that much as on your ballad. My plan at the time was also to rip out the floor pan but since I wasn't able to remove the mast step I decided to do all the work through the existing openings. It did work out very well and wasn't that hard.
I made new bulkheads that reached all the way from the bottom of the bilge to the floor on each side of every opening. They were made of divinycell with 10 layers of fabric and polyester on each side - maybe overdoing it a little
The hardest part was to reach under the floor pan where it meets the hull on each side.
The best way is to let the boat hang in slings during the work. This wasn't an option for me so I slowly lifted her with jacks in front and aft of the keel to remove some of the load on the keel. Most important is to raise her in the stern since the hull is weaker behind the keel. I recall we raised her about 20cm here
We used a long board on the outside of the hull (on each side of the keel to the stern) to determine when she was raised properly (you probably have a concave bump in the hull aft of the keel - we did - that needs to be flattened before the repair). Now she is solid but we use a stand in the stern just in case.
I can take some pictures of the bilge and mast step this weekend.
Edit: We never noticed any humps in the flooring when she was in water, only when sitting on the hard. After the repair/reinforcement the flooring was flat even on the hard and still is.
I made new bulkheads that reached all the way from the bottom of the bilge to the floor on each side of every opening. They were made of divinycell with 10 layers of fabric and polyester on each side - maybe overdoing it a little
The hardest part was to reach under the floor pan where it meets the hull on each side. The best way is to let the boat hang in slings during the work. This wasn't an option for me so I slowly lifted her with jacks in front and aft of the keel to remove some of the load on the keel. Most important is to raise her in the stern since the hull is weaker behind the keel. I recall we raised her about 20cm here
We used a long board on the outside of the hull (on each side of the keel to the stern) to determine when she was raised properly (you probably have a concave bump in the hull aft of the keel - we did - that needs to be flattened before the repair). Now she is solid but we use a stand in the stern just in case.I can take some pictures of the bilge and mast step this weekend.
Edit: We never noticed any humps in the flooring when she was in water, only when sitting on the hard. After the repair/reinforcement the flooring was flat even on the hard and still is.
Best regards,
Jan
#547 Sanlen
Owner since 1993
Jan
#547 Sanlen
Owner since 1993
-
Bob McGovern
- Posts: 287
- Joined: Fri Oct 26, 2012 3:08 am
- Location: Wyoming, USA
Re: Hump in the floor
Thanks so much, Jan. Your post verifies what I believed was the issue: not strength of the keel/hull transition, but stiffness. All the layers of solid glass in the world won't supply stiffness unless there is core material between skins, or else some kind of dimensional member like a bulkhead or beam. I wouldn't bother with unweighting and stiffening except for all the repair work we have planned; as I mentioned, it would be sad if we built that distortion permanently into the hull, or if our new, carefully-fitted bulkheads pulled away when the boat was launched & the keel lowered down 3cm. 
The existing keel sump bulkheads ('floors'?) are adequate to stiffen the keel assembly side-to-side, but not up-and-down. We need stringers that tie those panels to the adjacent hull, as you describe doing on Sanlen. Looking forward to photos of your work, if and when you have the time. No hurry -- it will be too cold for outdoor epoxy here until May.
The existing keel sump bulkheads ('floors'?) are adequate to stiffen the keel assembly side-to-side, but not up-and-down. We need stringers that tie those panels to the adjacent hull, as you describe doing on Sanlen. Looking forward to photos of your work, if and when you have the time. No hurry -- it will be too cold for outdoor epoxy here until May.