Why are hull/deck joints built the way they are? - SailNet Community
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post #1 of 11 Old 10-08-2014 Thread Starter
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Why are hull/deck joints built the way they are?

I have noticed a few threads about perminently curing hull/deck leaks by either bonding the parts together, or glassing over the joint. Why are the joints not built this way from the start? Is it only a matter of cost? I assume some boats are built with the hull and deck glassed together?

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post #2 of 11 Old 10-08-2014
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Re: Why are hull/deck joints built the way they are?

I think it must be cost and ease of assembly. The hull and deck each come out of their own molds. The cheapest and fastest way to put them together is glue and screws. It would be very time consuming to laminate the two together along the seam. My boat (a custom Swedish Vindö), thankfully, was built as a monocoque- the hull and deck are entirely laminated together. There are no leaks and it makes for a much stronger boat.

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post #3 of 11 Old 10-08-2014
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Re: Why are hull/deck joints built the way they are?

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I assume some boats are built with the hull and deck glassed together?
There are some. But you don't hear of a lot hull/deck joints leaking, what you hear about is deck leaks from all the holes drilled into them.
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post #4 of 11 Old 10-08-2014
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Re: Why are hull/deck joints built the way they are?

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There are some. But you don't hear of a lot hull/deck joints leaking, what you hear about is deck leaks from all the holes drilled into them.
I don't know about that Don. I certainly know a few boats that have caused their owners a lot of strife trying to find leaks at the hull-deck seam. A friend had a leak that dripped in the cabin when underway about 2 meters from the source on the seam and it took him months to track it down. I think that many older boats develop leaks at the hull-deck joint when they are pushed into more challenging conditions (cruising) when the joint starts "working" and water is hitting the seam regularly. No doubt though, the holes in the deck are the principle cause of leaks.

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post #5 of 11 Old 10-08-2014
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Re: Why are hull/deck joints built the way they are?

Custom boats like my 63' CATARI and FRANCIS LEE have a bonded hull to deck joint. This is a labor intensive detail as the outer bonding layers have to be hand faired into the topsides and deck. Done well you end up with no "joint". This would not be feasible for high production models. Some of the newer boats like J boats and some Euro models have a glued joint with no fasteners.
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post #6 of 11 Old 10-08-2014
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Re: Why are hull/deck joints built the way they are?

Pearson - at least the older ones I have seen are bonded. They may have mechanical fasteners as well - I can't remember but they do have glass inside the joint.

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post #7 of 11 Old 10-08-2014
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Re: Why are hull/deck joints built the way they are?

Our Dencho-built Choate 40 had a inside-and-out glassed hull deck joint... but then they drilled upteen holes to attach the toerail. Fortunately we did not have any leaks despite this.

Our current boat (now 30 years old) had a hull deck joint bedded in Butyl - some of which continues to squeeze out in some small areas (?) which means it hasn't 'hardened'.. but is watertight to date.

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Re: Why are hull/deck joints built the way they are?

"Is it only a matter of cost? "
The phrase is "Built to a price." Every mass-market item is built to a price. There are several common ways of doing a hull-deck joint, each with different pros and cons and prices. But in the long run, it is "good enough" once price is factored in.
Now, if you have the wallet and want better, you could certainly have the boat built all in one piece. I wouldn't want to guess what that would cost though. Probably cheaper to buy a metal boat, where the deck has been welded in, making it integral to the hull.
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post #9 of 11 Old 10-08-2014
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Re: Why are hull/deck joints built the way they are?

I've noticed that "outside" hull deck joints have become more common - where the deck bolts through an outward turning hull flange. Supposedly this detail makes the joint more vulnerable to damage than an inward turned flange but I've always regarded that as a bit of a theoretical reach. Even if true, IMO the benefits far outweigh the potential downside - I suspect there have been a whole lot more leaky inward hull deck joints than outward ones damaged from hitting pilings and so forth.

That method means a single person can bolt the deck on - you don't need a "nut holder" inside the boat. It also means the bolt holes don't penetrate the deck inside the boat so potential leaking is greatly reduced - the adhesive/sealant in the joint can be continuous, not being holed by fasteners every few inches.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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Re: Why are hull/deck joints built the way they are?

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Originally Posted by SloopJonB View Post
I've noticed that "outside" hull deck joints have become more common - where the deck bolts through an outward turning hull flange. .......
That style of joint can make rafting up interesting depending on freeboard comparisons and the size of your fenders!!

Ron

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