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1186Re:: Underwater Sealant - and Thin Privateer Skegs

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  • g8jmb
    May 1, 2016

      Oliver

      thanks for the paper on reserve buoyancy; excellent. And very applicable to the Shipmate.  On which the lack of +ve buoyancy is a significant concer,n, despite SNBF approval.  I think there are some words somewhere on +ve buoyancy for the Shipmate - I'll see if I can find them.


      I would make the following suggestions:

      1 When calculating reserve buoyancy needed this may be reduced by the volume of the hull moulding below water {difficult to estimate, but if you ignore it that is a margin of safety]

      2.Similarly, allow for the volume of stores, etc EG, 100l of water + alcohol in plastic containers will effectively have neutral buoyancy and may be ignored.  Same goes for fuel

      3, A liferaft on deck will worsen stability

      4. Fit a downhaul on the cenreplate - but be careful, or build in some give, if you play touch and go.

      5 Access to the skeg - and keel void if it's like the Shipmate - cut a hole on the cockpit floor.  More easily closed and less worry than a hole below thw waterline.



      . In Poole YC we have a local racing class - the R19 - which has a cabin and heavy swing keel, 19ft x 8ft,weighs about 3/4 ton. Stability not probably dissimilar to the Privateer - can be capsized if you try hard enough - and people who should know better have done- and will then sink.. To sort this:

         a. keel lockdown with ~1ft movement possible [Poole is shallow]

         b.  approx. 1/2 m3 expanded polystyrene added at the aft end of the 1/4 berths

         c. very large inflatable buoyancy bag strapped in the bows. Later boats had foam under a V berth

      b and c coupled with hull skin buoyancy will ensure that she floats...the hull is grp/balsa sandwich, which helps

        d. positive fixing for the cabin hatch  - usually straps

       e self draining cockpit



      Cheers

      JohnB

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