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-   -   Deck to Hull fastening.... (http://www.sailnet.com/forums/boat-review-purchase-forum/8831-deck-hull-fastening.html)

john232 01-05-2004 10:28 PM

Deck to Hull fastening....
 
Some "production" type boat Companies try to save money and time by building a boat with a less than desireable mating of the deck to hull fastening system. Wouldn''t it be easy to just replace the sheet metel type screws with a nut and bolt replacement strenthening, or even just getting out the epoxy resin and some matt and biaxial cloth and roughing up the surface and applying some lay-ups in order to strenthen the hull to deck seam from the inside? I feel like if I really liked a Beneteau 40.7 of a Dufour 40 and found a used one at a great price, and liked the design and sailing characteristics then why not just do a little modifying to the boat to make it more sea worthy for Ocean passages? Has anyone ever done this? Thanks for any replys.

WHOOSH 01-05-2004 11:36 PM

Deck to Hull fastening....
 
John, the main reason many high volume, ''price-built'' production boats lack the kind of hull-deck layup you prefer is simply due to the sequence of construction. The boat''s hull is finished out after which the deck is fitted, so full access to the hull-deck joint from the interior of the boat is at that point impossible. Instead, a wide range of alternative attachment methods are used including mastic, bedding compound, or fiberglass slurry in combination with some form of mechanical fastening - from pop rivets to stainless screws being driven into an embedded aluminum strip (boat builders don''t often lie awake nights thinking about dissimilar metal issues like we boat owners...). Often, the mechanical fastening is done to insure the chemical bond or to supplement it, rather than being the primary source of strengthening as with thru-bolted deck systems.

This is why boats like Hallberg Rassy deserve praise for the method they use: place the deck onto the hull, totally fiberglass over the hull-deck joint on the inside, then grind and finally paint the entire inside of the boat...and only then transport it to the boatyard (from the molding factory) where the boat is actually built out. That provides not only for a totally dry joint but means everything going into the boat (tanks, engine, etc.) can fit thru the companionway opening - a real advantage some years later to its owner when things start needing replacement.

The one famous boat I can remember reading about that had its hull-deck joing glassed over was Hal Roth''s WHISPER. After a Pacific circle, during which they suffered endless joint leaks, Hal ground down the original joint on the outside (a mastic seal with thru-bolts, as I recall), and then glassed the outside of the joint with 1", 2", 4" and finally 8" glass strips, as memory serves. It was a lengthy, tiring process (imagine the grinding...!) that in the end produced a watertight and stronger joint. Acknowledging that he could criticize the builder for need ing to do this, he instead points out the financial balancing act any builder faces between doing things for ''power users'' like the Roths vs. producing something affordable, which the Roths also needed. He describes this in his _After 50,000 Miles_ book, a good read even today despite the dated nature of some topics discussed.

Jack

Jeff_H 01-06-2004 01:59 AM

Deck to Hull fastening....
 
I don''t know how the Dufour deck is joined but the 40.7 has a pretty wide inward facing deck flange that is glued and bolted. According to one of the Farr guys they are using a high strength adhesive (not 5200) and then thru-bolting. Many of the better modern adhesives develop an stronger bond than even the secondary bond when glassing. So if the flanges are wide enough, you effectively do end up with a monocoque joint. In the case of the 40.7 the thru bolt heads are concealed below the toe rail.

I sail aboard a 40.7 that has been raced quite hard and has roughly 10,000 sea miles and still feels as stiff, and is as leak free as a new boat.

Jeff

john232 01-06-2004 10:22 PM

Deck to Hull fastening....
 
Jeff: Thanks for the info on the 40.7, I really like that yacht. I was wondering if the 36.7 also has good integrity of construction?

Jeff_H 01-07-2004 02:09 AM

Deck to Hull fastening....
 
Both were engineered at by Farr and Associates rather than by the Beneteau in house design team, but I have very little time on the 36.7 so I don''t know if the 36.7 matches the techniques used on the 40.7.

Jeff

sailnaway 01-07-2004 08:34 PM

Deck to Hull fastening....
 
I have taken what would be a screwed on deck and bolted it where I could. first I removed the rub rail then pulled as many screws as I could reach from the inside. Bolted with as large of flat washers and locking nuts as I could bedding everything with 5200.I did the same when the rub went back on I must note the screws were loose in several areas not bad but in a bad blow it could be a problem.
If you do this make sure you mark with a piece of tape or some thing where the holes for the rub rail are or it can be a bummer having to take the rail back off to get a screw out.The boat was tight after that.

HeartofGold 01-23-2004 08:11 AM

Deck to Hull fastening....
 
Thank you Jeff H and WHOOSH if you are still following this thread.

I am in the midst of rebuilding my Ensenada 20. I decided to replace the rub rail and after removing it, I discovered that the hull and deck were joined with nothing more than 1/8" bolts spaced 2" apart. I was shocked!

As a result, I first decided to carefully seal the inside of the joint with 5200, and I am currently glassing the exterior with 2" followed by 4" cloth. I will be adding a mahogany rub rail which I will secure with 5200 and wood screws spaced approximately every 4". As this is only a trailered daysailor, I felt this would be sufficient. However your remarks back on January 6 explained why the joint was this way and justified to me the work on which I am currently involved. Again, thanks.

Doug


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