Strip plank is stronger fore aft than foam, so foam needs additional stringers to make up for this, but strip is not significantly stronger across the grain. I am going about 30-50% thicker core than we probably need, and similarly for the skins, adding about 200kg to the total weight. I hope to get back some of this weight with slightly lighter reinforcing with the carbon, all composite rudders, composite hatches with wider edges and less clear areas, light weight batteries and possibly, (if the admiral wants to go extended cruising), electric motor, watermaker, solar cells, wind generator as well as losing about 30kg of blubber between the admiral and me.
Our 15m/10m Harry is basically a stretched Harry-extended, mainly in the bows with a reverse stem adding about a 500mm each end. I have added flares to the ww sides of both the ww hull and the lw hull to give extra accommodation. This probably adds a month or two to the build time. It is 200mm narrower in overall beam than the Harry as I wish to be able to telescope the boat into 4.2m. This probably adds another month or two to the build time. With a 3m wide ww hull and 1.2m lw hull, this allows 700mmm bury in the ww hull, and a full sailing beam of 6.5m. Theoretically, 400mm would have been enough bury but I am going cautious and reducing the point loads in the ww hull. I am going belts and braces by having the lifelines helping support the structure. I am using mainly PVC 20mm foam on the lw hull and in some of the bendy bits of the ww hull and polycore for the flat sheets elsewhere. For the lw hull there is 600g 0/90 glass and I will be adding +/-45 400g glass in the area between the rudders. There is also some 680g carbon twill around the crossbeams, rudders and hatches. I am going for twin masts through the crossbeams. There is a full bulkhead at the rudders, one full bulkhead and an almost full bulkhead (just a big enough hole for an inspection of the mast bearings) under the crossbeams. There is uni reinforcement under the masts. There are also bulkheads at 1/3 and 2/3 of the distance between the crossbeams with access hatches . There is also a horizontal bunk base 500mm up from the bottom of the hull between these bulkheads and the crossbeam bulkheads and the middle section extends this with stringers at this height which become shelves. These bunk bases aren't really necessary, but provide extra accommodation for guests in sheltered waters
The ww hull is to be mainly 15mm polycore with 400g +/- (though I may go up to 600g for an extra 65kg) with a bulkheads/ring frames where beams enter and a horizontal bulkhead above the beam going forward. Judicious use of 680 carbon twill around hatches and beam supports (I picked up some 680g carbon for the same price as tow, so I may as well use it) The enclosed volume above this becomes an external storage area for various bits of string needed.
Stiffness along the ww side of the ww hull is from a flare that increases internal room while keeping waterline skinny and hopefully reducing spray
--- In harryproa@yahoogrou
>
> Hello Rob,
>
> Have you added the bulkheads to the plans for the 12 M Harryproa ? Are there any 12 M currently under construction with foam core and how will this affect the construction and strength of hull as compared the the wood core ? I would think that the wood would be heavier but stronger than the foam core so I am surprized Arura had this type of problem. What measures are designed into a foam core to give it the needed strength ?
>
>
> Were the bulkheads on the original plans and the plans were not followed or are they a added addition that had not been installed yet ?
>
>
>
> Happy sailing,
> George Kuck
> Chestertown, Md.
> --- On Fri, 9/11/09, Rob Denney <harryproa@.
>
>
> From: Rob Denney <harryproa@.
> Subject: [harryproa] Aroha
> To: harryproa@yahoogrou
> Date: Friday, September 11, 2009, 11:15 PM
>
>
>
>
>
>
> G'day,
>
> This from another forum, posted by Mark Stephens, who helped build Aroha.
>
> The12m had some weather 8hrs east of Lord Howe and broke some gear, put
> out parachute for 36 hrs till it calmed down enough to do repairs. 250
> miles out from Lord Howe leeward hull started flexing a lot in a beam
> sea, solved the problem temporarly by using the jib halyard as shroud
> and tightened it with the winch and did the rest of the trip with the
> main with 1 and 2 reefs in, had to baby it. He's going to try solid
> bulkheads at beams and same at mast. end quote
>
> Before they left, Bain asked me about reinforcing the lee hull. I
> advised him to fit full bulkheads, which should have been in from the
> start for stiffness and watertightness reasons. As far as I know, he
> decided to just add more laminate to the hull. I have asked Mark for
> more details of the weather and the gear that broke, will let you know
> what I hear.
>
> regards,
>
> Rob
>
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