Hull flex and soft fiberglass

[telimon]

I am resustating a 1973. It had been sitting on a trailer for 15 years I think. I have repaiered with fiberglass, a couple of cracks but the hull on either side midway of the centerboard and to the stern does flex a fair amount.
Someone had suggested injecting the hull with foam as a possible reinforcement. Does this make sense at all.
Anyone ever do this?

[priceless9192]

i previously owned a 1963 day sailor and was so "flexy" that it was not fun to sail anymore. if i went up to the side of it on the beach and tried to push it off the sand it would almost fold in half.

[K.C. Walker]

I think theoretically putting foam between the hulls would stiffen it up. This is the exact method that Sunfish uses (with block foam and then expanding foam). However, doing this as a retrofit would be problematic. To get the foam to adhere properly to both sides would be unlikely unless it were thoroughly cleaned and dry. Also, getting just the right amount of foam in their so that it doesn't distort the hull would be pretty tricky.

When expanding foam is used between the hulls it needs to be adhered and without voids. I live near the Mystic Seaport which uses the JY 15 in their sailing program. When the hulls get soft from the foam de-laminating they just cut the hulls up and send them to the dump.

[telimon]

thanks for the replies. I actually don't think it is that far gone but would like to try the expandible foam injection idea. I think it wuld work. I've seen how rigid that stuff gets once dried. One concern i do have is that is that if there remained any space in there and water got in some how, I'd never be able to get it out again.

I'm going to sail her first to understand how bad it affects performance.
Is there any flex at all normally in the hull of a good condition boat?

[GreenLake]

As designed, the DS has some areas that will flex under load. This concerns the flat sections of the hull, especially in the rear, but also the CB trunk walls. Localized loads from waves would have flexed even a new hull in those areas.

Because of the properties of polyester resin in comparison to glass, this flexing is not benign and will lead to softening of the laminate - at which point you see more flexing. (Substantially more).

I have '63 DS 1, but I think what I am seeing is something closer to the original flex, rather than widespread softening. Many sailing venues in the area have little or no chop and wind speeds tend more often to be on the low end of the range. Consequently, it's possible my boat hasn't been sailed enough to see noticeable softening in the laminate.

I suspect that the foam cored boats are now actually stiffer than the original hulls were, but short of time travel, I don't know how I could verify that assumption.

For foam to stiffen your hull, it needs to bond to the skins, so it can transmit shear forces. That's what turns a double skin into a sandwich (of multiple times the strength of either skin). With foaming between the hull skins, you will run into some limitations on what you can do in terms of surface preparation. Not to mention the issues of potentially trapping water. There must be other boat classes with double hulls out there - I would definitely recommend a thorough search on the net to see what experience is out there.

[ctenidae]

I'm going to sail her first to understand how bad it affects performance.
Is there any flex at all normally in the hull of a good condition boat?

My '62 flexes a bit overall- if I've got my feet up on the seat across, I can feel the hull twist when rolling over waves. Other than that, the only time I notice flex in particular hull sections is of the boats on the trailer- the deck behind the CB trunk bends if the cloarboards aren't in, and the wide spots in front of the trunk flex as well. Neither is surprising, considering the span in both areas. Both are quite stable in the water, though.