Hull/deck Joint Debate

Tunnels, thank you. I'll look into the triaxle cloth.

 

Just remember 100% 0f the glass needs to go across the join if it doesn't go across the joint its doing nothing at all ,just soaking up resin and going along for the ride . Some of these glasses are available in a pre-cut roll form almost any width to make life even easier !!,also some have a very light chopped strand matt attached on one side its a good thing not bad as you will get told here by a few people !!. The csm is good to have outermost and peel ply over the whole lot 20mm wider each side over the edges of the glass !!It also is available in a pre-cut roll form !!

 

What about stainless fasteners? How far apart? Or do I need them with a strong glassing like you suggest?

 

how wide is the glued join of the deck onto the hull??and how good has it been glued ?? squeeze out every where inside and out or just in places ??


For racing boats the glued surface would need to be in excess of 60 mm at a absolute minimum and the inside and outside glass would need to be 100 mm wide minimum as well ! with all that I would say why use any fasteners at all!!
The holes even filled are a weakness but using epoxy and two good layers of glass both sides over the join should not we a worry .
As for the twisting or flexing its more beneficial than you might think !! things that move absorb shock loading's without getting damaged but if they are ridged they break and part company much easier than you would like !!

 

this is actually not always true, and a much more complex problem than you might think. Controlled and limited flex can be beneficial for reducing impact loads, but too much will make control difficult and lead to structural failures where assemblies are mounted.

It would be true if the whole assembly was designed to accommodate the flex, including the fastening and the joints, as well as the mounting of any sub assemblies. If you have a fairly rigid structure mated to a flexible one, more than likely you will get localized stress concentrations at the fasteners between the two. there is almost no way to evenly distribute the load between a flexible member or surface joined to a rigid one, the softer side has to be reinforced at the point of fastening, or you have to have a flexible mount. and you still have to watch out how you mount sub-assemblies and fixtures, they could pull out or damage structure if they are not allowed to flex with the main structure.

Usually the stronger and less flexible you make a complex assembly the better, less relative movement between the adjoining parts.

For example a light and flexible skin-on-frame kayak has lashed joints that distribute the flex of the hull and allows movement at the joints, it is also usually more comfortable and a better controlled ride in rough water than a hard shell kayak. all of the members are made of similar wood and fit loosely together to allow the movement. but on a large complex assembly conventional fasteners will create stress concentrations and usually fail at the fastener. Many upset rivets in aircraft fuselages work loose and have to be routinely replaced due to fatigue and flex of the lightweight airframe.

And I know from my previous employment in the aircraft industry, they have to limit the flex of an aircraft fuselage to maintain control of the flight surfaces and prevent damage to the mounting of internal systems. Seismic design of buildings requires deflection limits to prevent damage to wiring and plumbing as well as risk damage to the attachment of structural members.

I also once had a large one-ton Ford van (same chassis as the pick-up truck), I was using it to back-up and park a trailer on my uneven driveway. the darn frame had so much flex in torsion that the cooling fan on the engine struck the radiator (which was mounted on the body, the engine was mounted on the frame). This was a very bad design. A similar thing can happen on a boat hull, the larger the more severe the problem could be.

 

Excessive amounts of twist in older boats yes can be a problem but in Yachts the depth of the hull to the deck is far greater than is in a normal power boat so twist is something that is quite minimal plus with side stays same bow and stern stays its even less
Yachts we manufactures 30 odd years ago apart from a main bulkhead inside usually close to where the side stays were attached there was very little else but bunk fronts were a really important structural part running fore and aft so twist really is pretty much impossible in a yacht !!

Power boats is a completely different scenario !

 

The width of the glued surface is about 3". I'd have to double check. It's a very solid seal still after all these years. The twisting and flexing have hurt performance in these boats in the past. ULDB.

 

that is too bad, it looks like a very attractive and functional sailboat, with some strategic strengthening/stiffening it would be a better sailor too.

 

Oh, they still are great! But yes you are right! Strategic stiffening is what it's all about.