Waterwitch

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tomfindlay
Posts: 3
Joined: Sun September 24th, 2006, 4:33 am
Location: Edinburgh
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Waterwitch

Postby tomfindlay » Fri May 15th, 2009, 9:48 am

I've been researching self building Maurice Griffiths' Waterwitch Mk ll which he designed around 1963. Its a 30 foot single chine hull in two versions. The Mk ll has steel leeboards and what Griffiths calls an iron barge keel, drawing only two feet of water.

The hog is about 20 feet long by 1 foot wide and by 2 inches deep, followed by a keel 8 inches wide and 2 deep, and below that is the bolted on iron keel of about 16 feet by 8 inches by 3 inches.

David Gerr in his book The Elements of Boat Strength declares that heavy keel timbers add little strength, and it's best to avoid using massive lumps of wood. Of course Mr Buehler in his book is all for great big heavy duty lumber.

I'm taking Glen L. Witts advice and changing the chine log from a batten to a butt joint. He also suggests in his book Boatbuilding with Ply that the keel should also if possible be butt jointed.

I'd like to butt joint the lower ply panels at the keel, as he suggests, and shed the large hog and keel for a much lighter structure.

On the plans he calculates the weight of the ballast keel at 1200lbs, with internal ballast to trim at 800lbs.

If I make the keel a simple butt joint, how can I bolt on the wide and bulky ballast keel? I would really prefer to keep all the ballast internal. As Atkins, way back, designed Topsy. And many traditional 30ft to 50ft fishing boats built here in Scotland have been using concrete and pig iron as internal ballast for almost a century...

Keping all the ballast internal would make construction a lot easier, and cheaper. Obviously scantlings, hydrostatics and stability, would have to be recalculated, but is it that simple...

The most important part of this design for me, is the very shallow draft of just 2 feet. This is needed to allow me to navigate the Union Canal from the sea locks on the West and East sides of my little country right to the centre of Edinburgh.

Any suggestions or solutions would be welcome...

Tom in Edinburgh, Scotland

JamesH
Posts: 35
Joined: Mon October 13th, 2008, 11:22 am
Location: Bradford UK

Re: Waterwitch

Postby JamesH » Tue June 23rd, 2009, 8:41 am

Hi I have been contemplating a ww build for simalar reasons ie a sailing boat suitable of the UK canals.
I shouldthink that you can reduce the keel depth somewhat, however the ww hull shape has very little shape to it either for or aft or accross wise, so that to reduce the keel section too much may cause hogging. Are you keeping to all other dimensions? 30ft x8? I was thinking of going to 33ft by 10 which MG allowed.
My keel is to be 6 x 6" with 8" wide at top.
4 x2 frames - soft wood.
Please keep me informed
yours James
Hi looking to build an WW!
any thoughts.
Have many of the materials for keel and frame.
Yours James


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