Arne Kverneland wrote:

Lighter deck or shorter mast?

Frankly, as for loss of stability due to making SibLim top-heavy, I am at least as concerned by the tall mast, which seems to be planned for her. Two-three kilos, ten meters up, robs just as much stability as 20-30 kilos only one metre up.

It is a general rule to give shoal draught sailboats a fairly low rig compared to boats with really deep-set ballast. I regard SibLim to be mid between shoal- and deep-draught, but I think she would benefit from a rig with a shorter mast, if possible. Compromises...

Arne

Bryan Tuffnell wrote:

Time for an experienced NZ flier to step forward with an indoor drone. Bryan?

Boat under construction has become victim of aircraft crash. Boat builder 'disappointed', say friends...

I've already said that I'm using lighter plywood and long ago decided that the 12mm suggested for the cockpit was heavier than I need, so I don't think I'm adding a little more here and a little more there.  Moreover, unlike the vast majority of people who live on their boats, my lockers won't be overflowing with stuff that I never use and never will use.  So I am very confident that if the designer did his sums correctly, this boat will not be overweight.

Look guys, would you object to my putting my dinghy on deck?  Well, I'm adding about the same weight as my 5ft pram and the mass of the dinghy would be higher.  And if I use lighter plywood, I will be adding hardly any additional weight.   Moreover, you won't see a single 25l jerrican on deck - which would weigh more.  Nor will I have a wind generator 8 ft above deck, nor an outboard motor on the stern rail.  I think you're getting a tad carried away, in all honesty.

The deck beam approach I think makes more sense, since looking at the spans and trying to work out how to secure the decks.  From fitting the hull panels, I have found that it helps having fastening points at pretty regular intervals. 

David, on Badger, some of the teak had worn away almost completely after 20 years, but that which hadn't stayed stuck down.  The epoxy in the gaps between the teak became more and more prominent (and improved the non-skid as it did so).  To replace a plank, all that was necessary was to chisel out the worn teak and fit a new length.  Where we had been able to use quarter sawn, it lasted quite a lot longer.  However, in 20 years time, if the teak has worn right down, I can always replace it with something else, or put some layers of glass on instead. 

Annie Hill wrote:

David Tyler wrote:

David has found out. What will the finished thickness be? 4mm? If so, use 9mm ply for the deck. I don't want this boat to turn out to be cranky.

Why not: her designer and owner both are?!

I'd already thought about putting on lighter decks, David.  The side decks are going to need beams - they'll be too flexible even with stringers, but I'll make those out of laminated (treated) Kahikatea, of which I have a good pile.  The centre deck can most certainly be 9mm, with its pronounced camber.   However, in 20 years, the teak will be well worn and I wonder if 9mm will be strong enough for the side decks by then.  The extra weight of wood will be about 10 kilos at the very maximum.  The alternative of glass, epoxy, primer, polyurethane and deck paint would also add a not inconsiderable weight.  Are we worrying, in fact, about 5 kg?

The side decks are flat. So neither stringers nor transverse beams alone are going to make them stiff, if the total thickness of the deck structure is kept down to 48mm, as designed.

The design relies entirely on the inner skin of the deck, the headlining, for stiffness. That is, 5mm ply, glued to the underside of either stringers or transverse beams, and either 9mm ply + 4mm teak, or 12mm ply + glass glued to the top, forming an I-beam structure. Either will be satisfactory. If 12mm ply is used, then either deck beams or longitudinal stringers (but not both) can be used. However, in the case of 9mm ply + 4mm teak running fore and aft, only transverse deck beams should be considered. Forget deck stringers, and laminate full-width deck beams, 30mm deep. 

I don't buy the argument about the teak being so worn after 20 years that 9mm ply won't be strong enough. If it were that worn, it would have to be replaced, or the deck would be a dangerous and unsightly mess. 

I emphasise: the deck is the very worst place to add extra weight to a boat. Even more so on a shoal draught boat. Don't do it. I'm finding it difficult to resist editing this paragraph to be in 72pt bold red text, but so far, I'm succeeding...