Hull Flex ?

[abl1111]

I was wondering - I have 23' Tsunami (1975). Recently, I hit a 2-3' chop wave, 'funny'/hard on a chine ( my teak door to the cabin was closed ) and the teak door cracked in several places from the hit.

It got me thinking. Could it have been that my hull flexed and the teak door got sandwiched between the door framing ?

I re-did the door with epoxy, and w/ a router, countersunk some teak biscuits set w/ epoxy in all the back-facing joints - she looks great and is solid as a rock.

Yesterday, I was cruising around, w/ the door closed again and I put my finger in the space between the edge of the door and the frame; 'the gap ' was definitely moving around a lot - note: the door is mounted solid via a piano hinge on one side.

Is this an indicator for hull flex ? And, is it a problem, or is it a common thing ?

My hull is very solid with absolutely no stress cracks anywhere except the normal toe rail ones.

What'cha think ?

PS: I have on my "to-do" list to remove the rub rail, remove the old SS screws that hold the topside to the hull and replace with ss bolts.

[FELLOW-SHIP]

All hulls will flex some that is the nature of boats in general. Just his week I saw a TV program that talked about building larger ships out of steel and some were welded together and some were riveted together anyway in the show they said that the riveted ships could flex some which was better because if they didn’t then they would crack like the welded ships can. What I like about SeaCrafts is that they have the two large port and starboard stringers and then you have the center line stringer on your Potters. In addition to that you also have the 4 longitudinal steps in the hull and the hull lamination schedule is much better / thicker then many of the boats build today. It seams that most companies want to build light weight boats now a days by either using a foam lamination with in the hull or by not using as much glass in the boats, usually that adds to the potential of damaging flex in the final product. There are times I hit 2-4 footers running at approx 30 mph waves coming either from the port or starboard bow lets say at 30 degrees on either side that I get some shutter effect as well. I would say that if not all most boats well do that some depending of boat and sea conditions. As for you doors you might check for a wobble in that section of your boat or stress cracks around that area or you might need to shave down ¼” around the doors to prevent your problem.
FellowShip [img]/images/graemlins/cool.gif[/img]

[BigMike8o9]

My boat was over flexing. Because of some damage before I bought my walkaround. I checked the bulkhead and found it crushed and rotted.
My experience has showed that even exceleration can flex a boat. I beefed up and replaced the bulkhead. Also filled in most of the screw holes for the screws that hold the deck to the hull and made the sides of the deck thicker by grinding out some of the core and making the glass several layers thicker. I know I have way to much free time. But when the deck screws went back in tight the boat became very stiff with only a very minamal flex. Even the transom is much stiffer.
The bulkhead helps keep the boat from flexing outwards because I glassed and screwed it tight at the gunnels and the space between the bottom of the hull and deck are supported by the stronger bulkhead. if it is supported the boat cant flex out ward because the cabin and deck would need to compress for this to happen. The movement caused the srews to become loose and worked the holes so that the screws could not be made tight. I also put fibrglass tape behind the srew holes after filling them. to strenthen the hold. I can tighten them almost to brake if I try to hard.

[abl1111]

Big Mike,

Did you re-screw screws back in where you filled those screw holes or thru bolt them ?

I plan on thru-bolting.

[BigMike8o9]

I sorry I thought I replied to this. It's most likely in the wrong thread. Yes on the large screws that the factory used to hold the deck to the hull I used ss fender type washers and Nyloc nuts.Where I could get to it. In a walkaround it's hard to reach all of them. But int the srews for the rubrail, I wasn't concirned as much. With the holes filled with glass and apoxy I just used the same screws that were good and bought some to replace the bad ones. The large screws were about every six or eight inches and would keep the deck from working on the hull.
The main point is the beefed up bulkhead.