Hull flex question on 78 DSII

[fatire]

First, as a brand new owner of a 78 DSII, this site and those that contribute to it are an absolute godsend.
My first issue: I'm worried that I just bought a worn out or abused boat!
I read carefully the "what to inspect" sections of the forum but didn't see anything about hull flex, now I wish I HAD!

Background: My DSII is sitting on a small easyloader trailer and the bunks are 6ft 2X4s on the edge, 34" apart and the stern's hanging off about 3ft which positions the forward end of the bunks a bit forward of the CB trunk.
If I look down the bottom of the hull from the stern, I definitely see that the hull is flexing in the area's supported by the bunks.

I've read all I can reasonably find about hull flex but still don't know if what I'm seeing is normal or shouldn't happen at all?

Topics read:
SECTION: Repair and Improvement
Hull flex and soft fiberglass
Flex in the hull normal for a 50+ year old boat
Can hull damage from a trailer be fixed?
The Core Project

SECTION: DS1
Hull flexing on DS1
New old boat!
hull flexibility?

I thought I read in one of the above that in the water with equalized pressure the deformation would go away.

I also read that the trailer bunks should be positioned to align with the seat to floor interface but not sure that applies to a DSII and currently my bunks are 34" spread vs a 29-30" spread on that interface.

When I jack the stern up about 2 inches, starboard flex disappears while the port flex "almost" returns to normal (after about 2 mins.)

And if I wanted to stiffen, how the heck do you re-core a DSII with the permanent floorboard structure? I don't think it can be practically done without separating the deck assembly from the hull?

I'm just going to casually day sail but obviously want a safe boat should I encounter adverse conditions.

This belongs in the DSII forum I believe because the question of coring to me seems to be quite a different case from the DSI due to limited to no access.

Thanks very much in advance for your thougts.

[GreenLake]

Any advice from DS2 owners? All I can suggest at this point is that even if the bunks have created a soft spot, that doesn't necessarily mean that the boat is "unsafe" in its current condition.

[K.C. Walker]

Okay, because I'm sort of a loud mouth when it comes to boat stiffness, I'll jump in. I don't think that safety is the issue, unless we're talking extreme softness. It is performance that's more the issue. Thinking in terms of an extreme example, envision trying to catch waves with a surfboard versus an air mattress. You stay afloat with both and you can have fun with both but you go faster on a surfboard.

I think that you are correct that trying to stiffen up a DaySailer II is probably not practical. However, now you have a DaySailer to have fun with and you can always look for an upgrade over time. Every once in a while there is an outstanding deal on a DaySailer. Keep your eyes open! I think that is the best way to get a stiffer boat.

Do what you can to keep from softening the boat further by improving the trailer. I went to 2 x 10 bunks, laid flat, 12 feet long and contoured them to fit from the transom forward. I figured that I would try to distribute the load as much as possible. I've had people laugh at me for overkill, my trailer looks like I could haul a sport fishing boat. However, trailering does far more damage to a boat, as far as stiffness goes, than any other thing you can do. Just drive down the road and bounce the stiffness right out of them.

[fatire]

Thanks GreenLake and K.C., those were my initial thoughts but it's nice to have others confirm.

[talbot]

If you wanted to directly stiffen the hull, you could install additional inspection ports aft and lay up additional plies of fiberglass. I've done that near the mast step for supporting a battery well.

I put thwarts in our boat, along the same lines as a DS I. They don't address bottom flex, but it is my impression that the boat is a bit more responsive and points higher than it used to with the stiffened CB trunk. (I didn't set out to stiffen the hull; I just wanted a removable rowing seat. But we never take the thwarts out except for annual varnishing.)

[GreenLake]

Not being a DS2 owner, I'm a bit hazy on some details of the DS2 double hull. However...

Wouldn't the double hull allow you to create a "sandwich" by simple inserting suitable foam between the two layers - something like that would possibly support the outer hull in strategic locations so that it doesn't flex inward when the boat is on the water (or on the trailer).

The practicalities of that approach (types of foam, ports for access, internal drainage channels to the bilge, etc) aren't fully clear to me, but I wonder whether it's a useful direction for further thinking nevertheless.

[talbot]

Might work. I thought of doing that to support the floor of the cabin when it's loaded with camping gear. (I can get under there now through my battery well.)

I'm always a little concerned about unintended consequences, particularly as I have no engineering background to estimate those consequences. Would stuffing foam between the inner and outer hull create some stress elsewhere? No idea. That's why my first inclination is to reinforce the structure to return it to its original design, rather than introducing a new structural element.

[GreenLake]

First rule: don't overthink. However, there are some general considerations to keep in mind.

If you were to connect the inner and outer hull it would be useful to not make that connection with something that has a hard cutoff point (e.g. block or wood). That would introduce localized stresses. You should aim for some gradual transition.

Something with the characteristics of the firm insulation foam might be better - it's strong enough to support distributed weight but would yield a bit around the edges (if there is some flex in unsupported areas of the hull). So the load would transfer more gradually.

Or use even stiffer structural foam and do two thinner panels held apart by spacers that don't go the full width - again, to give the edge some give.

Another way to look at this would be to make sure that the supports cover all the areas resting on the trailer bunks. That would leave only those hull sections unsupported that aren't loaded when trailering. That would take care of the worst case scenario - the bouncing loads introduced by the trailer, which may well be more stressful to the boat than loads from water/waves.

Next issue (or perhaps primary one?)
Important to use material that can't get waterlogged, even over decades, and to make sure there are channels or voids for drainage of the bilge.

[fatire]

I was so annoyed by my hulls oil-canning out in moderate 1-2' seas yesterday that I have dreamed up a potential easy solution: using a 75cm dia fitness ball as an inflatable air bladder between the seats and the hull.
Who knows if it will work, but if it did what an elegant solution!