fixing screws through the hull

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john burke
Posts: 17
Joined: Sat August 4th, 2007, 11:41 pm

fixing screws through the hull

Postby john burke » Wed May 7th, 2008, 8:10 pm

I am in the process of installing a bulkhead on my three tonner. I am intending to fix some shaped blocks of timber through the hull in front of the bulkhead and then fix the bulkhead to the shaped timber blocks. Should I use cotten grommets/ washers on the screws and if so, where can I obtain them? Any advice welcome.
John

Wooden Boat Fittings

Postby Wooden Boat Fittings » Thu May 8th, 2008, 11:17 am

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John, as a general proposition I wouldn't advocate putting holes (not even screw-holes) through the hull unless it's absolutely necessary. With that as background, can you explain where you intend the new bulkhead to go, and what it's to do? Maybe we can come up with a solution that doesn't require through-hull fastenings.

Mike

john burke
Posts: 17
Joined: Sat August 4th, 2007, 11:41 pm

Postby john burke » Thu May 8th, 2008, 7:37 pm

Thanks Mike, the bulkhead is underneath the fore deck and has an eliptical shaped hole in it as on the drawings. unfortunately, the boat has been built with a different deck beam arrangement to the drawings and the bulkhead is positioned just infront of the fore hatch in the fore deck. I assume the bulkhead will provide some ridgity to the hull, but as you can tell, i'm no expert!
many thanks again,
John.

Wooden Boat Fittings

Postby Wooden Boat Fittings » Fri May 9th, 2008, 1:19 am

John, in this photo the clock and barometer are on the front face of the cabin -- the point where, on deck, the deckhouse steps down to become the foredeck. The bulkhead with the elliptical opening in it is forward of that point by about 9" or so.

Image

But from your description, the bulkhead on your vessel has been placed against that vertical face where my barometer is, is that right? In that case I can certainly see why you'd want to move it. Apart from making use of the forehatch difficult, it would do the same with the head.

OR -- is the existing bulkhead where it shows here, but the builder put the forehatch forward of it instead where you can see it here, in the cabin itself above the head? That would put the hatch either partly or fully in the forepeak, (where my spurling pipe is as you can tell by the anchor warp hanging down,) and make it almost impossible to use.

(Don't worry, we're getting there...)

Mike

john burke
Posts: 17
Joined: Sat August 4th, 2007, 11:41 pm

Postby john burke » Sat May 10th, 2008, 4:41 pm

Thanks Mike, The hull on my boat has been built as on the drawings but the deckhouse arrangement is somewhat different and looks a little amateurish. There was no existing bulkhead in the boat when I bought it and the boat was never properly completed. It has never seen water! The bulkhead I am attempting to fit is completely new. The forehatch on the boat is situated immediately in front of the deckhousing, where the deckhouse steps down. I have therfore had to situate the bulkhead a little further forward under the foredeck on the foreside of the forehatch. I'm sorry if this sounds confusing. I am attempting to insert a photo. Thanks Mike, your time and help is much appreciated.

Wooden Boat Fittings

Postby Wooden Boat Fittings » Sun May 11th, 2008, 3:50 am

Here's a photo of John's forehatch as he emailed it to me --

Image

John says, "As you can see my son's head is peeking out of the forehatch which has been situated on the foredeck. This makes the siting of the bulkhead difficult.If I site it aft of the hatch, it would be some 9 inches too much in the cabin area. I have thrfore had to site it in front of the hatch further under the foredeck."

It's good having the picture, as not only does it show the hatch too far forward, it also shows that the hull is clinker. The only good thing to be said about the hatch is that the hinges are on the right side.

So my next question is, are there the right number of frames interspersed along the inside of the hull to support a clinker skin? This depends on the thickness of the planks of course, but it might be that the frames should be at about 9" centres or so.

Assuming the existence of sufficient frames to properly support the planking, then I don't think the bulkhead (which, as we now know, is presently missing altogether from John's boat) is a structural necessity. While no doubt it provides some marginal additional stiffness, the deckhouse structure, deck beams, and frames should, between them, provide quite sufficient resistance to hull stresses. (From memory the bulkhead is only 5/8" ply, and anyway has that large elliptical hole cut in it.)

I think the real purpose of the bulkhead is simply to separate the forepeak from the main cabin. But because there's such low headroom under the foredeck it was never intended that one should actually enter the forepeak through the bulhkead as you might on a larger vessel -- rather, there's only that elliptical opening there to allow head, shoulders, and an arm through to retrieve warps from the shelf just visible in Sanderling's photo, or to attach an anchor warp to a ringbolt on the keelson.

By kneeling on the cushion covering the head (aft of the bulkhead and just below the bottom border of Sanderling's photo,) one can reach right to the stem to do these tasks. (I might add that the paler-coloured piece of ply across the lower part of the elliptical opening is not part of the original design. I placed it there, with turnbuckles for easy removal, to better retain wet muddy warps in the forepeak where they belong.)

So, summing everything up, I think the best answer is to build a new forehatch in the deckhouse where it was supposed to be in the first place, and to deck over the original hatch-opening altogether. Then the new bulkhead can go where it was always supposed to.

Failing that, I wouldn't bother installing the bulkhead at all, although you might consider building a very high floor forward of the existing hatch in order to retain warps stored in the forepeak. The hatch will still be very difficult to use because of the low headroom, and the forepeak will be considerably smaller than it was designed (and in my view requires) to be.

Failing that again, if a bulkhead is still considered necessary it could be held in place by epoxy-gluing butt-blocks to the planking forward of the bulkhead's location and against the after-side of the nearest frame, and then fastening the bulkhead to the blocks. In this case you would need to spile a new bulkhead shape to fit the narrower hull dimensions at the new location.

I hope all this helps.

Mike

john burke
Posts: 17
Joined: Sat August 4th, 2007, 11:41 pm

Postby john burke » Sun May 11th, 2008, 6:11 pm

Mike, Thank you for putting the photo on the forum. The hull is constructed out of larch planking, approx 1 inch thick, built on oak frames.I shall check the frame centres this week and get back to you. With regard to the hatch and bulkhead siting, if I build another hatch on top of the deckhouse, it may well interfere with the siting of the mast tabernacle as my deckhouse is a little shorter than it should be. A solution might be to leave the hatch where it is and instead of having a full bulkhead, I could install two half bulkheads with a throughway between them. the size of the throughway could match the size of the hatch or indeed be slightly larger. In front of this, as you suggested I could build a higher floor to retain warps. I will, ofcourse take your advice on using glued butt-blocks to fix any new bulkheads in place. Once again, kind regards for all your help and time.


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