deck to hull joins

[jameshogan]

I recently went to a yard and asked about the way they connect the deck to hull pieces for a 50ft high speed (20+ knots) motor yacht. They told me "We just fiberglass it then screw it down." No glue or any other type of fastening. Just resin and screws. I think this is a cheap and quick way of doing things. Is this approach a "good enough" way of doing things?

[Ssor]

Pacific Seacraft used to use 3/8 inch ss through bolts, nuts and washers and 3M 5200 caulk. I never heard of any complaints about leaks or other failures in the joint. On the other hand my Islander has the deck glassed to the hull inside and outside and that doesn't leak either. I adhere to the principle that "nothing too strong ever broke". Now these boats that I speak of are sail boats, go-fast powerboats may be held together with majic in addition to screws and fiberglass.

[Thunderhead19]

Cheap and quick? Isn't adhesive cheaper and quicker? Not to mention stronger. Just squirt and stick the pieces together. ?? ?

[gonzo]

You said they fiberglass it. That is the best way. Yoy also said they only use resin. Which one is it?

[Thunderhead19]

Secondary fiberglass bonds and available adhesives like Plexus are completely interchangeable. Depending on how you do it, the adhesive could definitely be a better performer.

[War Whoop]

Since day one in the offshore race and high performance pleasure boat industry they have been completely bonded with fiberglass it is the only way...

[yokebutt]

Generally, bonding is preferable, since composites take poorly to concentrated point-loads, large flanges with lots of surface-area are ideal.

There are essentially three choices, flexible, like 5200, semi-flexible, (or semi-rigid) like methacrylimides (like plexus) or rigid, like epoxy or poly- or vinylester adhesives.

In the case of a flexible joint, if backed up with fasteners, the adhesive will not really carry any load until the fasteners have already failed, if the flexible joint is backed up by tabbing, it will yet again not carry any substantial loads until the tabbing has begun to fail, either in shear or in peel.

That brings us to the rigid adhesives, they seem like a better match for fasteners and tabbing, but, with rigidity also comes an increased susceptibility to peel-failure, so you can tab over the joint, it'll increase your bonding area and more gradually taper into the structures you're joining, and then you can also bolt through the flanges, that'll help arrest any peel-failure along the joint.

There are a lot of choices, and they're all dependent on how you intend to use the boat in question, chances are, if it's worked in the past, it'll work again.

Yokebutt.

[Thunderhead19]

Originally Posted by War Whoop

Since day one in the offshore race and high performance pleasure boat industry they have been completely bonded with fiberglass it is the only way...

Since day one ships have been built from heart of oak. This is also no longer the case.

[PowerTech]

I see boardes fasened to the deck clamp by beding them in epoxy and caridge bolting them through the clamp.then the deck is laid on top and glassed over and glassed to the side of the hull.seem to work like a champ.I don't build boat though but I have been in probly a thousand.I geuse there is more than one way to skin a cat.

[War Whoop]

Originally Posted by Thunderhead19

Since day one ships have been built from heart of oak. This is also no longer the case.

I myself like new processes much as the next guy But safety rules my material selection and systems What is so hard to see where in a fiberglass joint say a 1 ½” wide and you bet the entire game on that glued joint IE relying on the two adherends Peel strength that is a joke right? BTW in fiberglass SO no matter what the adhesive is or made out of the glass itself will fail.. That is the reason for the "Large Fiberglass" bonded areas in the first place.

And secondly at the speed my boats travel completly glassing the structure together is the only way to reliably join the major sections...

And third I when molding use a precision match system that eliminates the joint the deck mold is mated to the hull mold and is glassed together “seamless” and demolded.

Look I do not know what kind of little or hurry up and build boat you are gluing together if it works for you fine but I guarantee it will not survive in my world nor would I place my customers in danger!

[War Whoop]

Originally Posted by PowerTech

I see boardes fasened to the deck clamp by beding them in epoxy and caridge bolting them through the clamp.then the deck is laid on top and glassed over and glassed to the side of the hull.seem to work like a champ.I don't build boat though but I have been in probly a thousand.I geuse there is more than one way to skin a cat.

That would be fine if you chug around the harbor with birds sitting all over your boat in that speed mode anything will work!

Just when things like the Boats structure get highly stressed is where you need the finesse to keep things in one piece.

[PowerTech]

yea i geus.when I am doun in a yacht It is hard for me to see how they do it.the method I spoke of I see 0n 17-25 knot lobster boats.they cary around a hundered traps weighted with concreet out to there spots begining of the season ass fast as the seas and engines will let them.That is work boat stuff it ain't fancy but if it didn't work they would do something else.It is kind of redneck I know. It could be done lighter and stronger with high tech stuff on a fancy fast boat.I see that method on ballyhoo net boats and them over powerd things haul ass and cary 10,000+ pounds of ice boxes and net.This stuff I am talking about is just strong heavy comershial fishing stuff you won't see on a nice boat but they are fast.I am no athorety on the subject thats for sure.

[War Whoop]

PT in my arena I do not have the complete luxury of a lot of weight the boat would be vastly uncompetitive... So you see the dilemma here. It must be light and tough.