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Okoume Joubert or Meranti plywood for new boat interior?

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10 hours ago, Guest said:

As Frank inferred; The hull thickness and designed floor structural grid work in concert with the type of keel fixing.


Hopefully you are using epoxy. 45/45 and one uni = good, csm not so good. Avoid use csm with epoxy. Csm is for rubbish bins and dog kennels.


Going to use 45/45 Biaxial, with CSM on one side.  
And you are saying uni-directional too?

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If there is any doubt in your mind of its current structural integrity I would glue in solid wood floors, centres at official Twister plans dimensions, with arrased  edges and coved  floor/hull junction to ease transitions. . Feather floor ends to hull so as not to create stress riser. Glass over floor side to side in one piece glass, overlap the ends to hull. Carefull to not entrap air. Say, 440gm db @+-45° and 220gm Uni @0° (parallel to floor.) min 4layers, staggering edges. Smallest last. Peelply. Don't use too heavier glass as wont go over floor easily. Vacuum will do a nice job. Cove and glass all in one operation. Use  slow/SS hardener and post cure with heater if necessary. You don't want to make the floors stiffer than hull as it needs to move together to distribute load evenly. That's why it pays to stick with designers scantlings.

If not, just replace with equivalent of what was there. 

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7 hours ago, Guest said:


If not, just replace with equivalent of what was there. 

All that was there previously was a glassed in bilge water tank, itself made of glass.
I am a neophyte when it comes to boat design, but with just a skimpy piece of construction tying that area together previously, I'd say the way the boat is built is already massively strong old school GRP boat building prior to the 1974 Oil Shock (mine is a '72 Twister built by John Tyler of Tyler boat works UK, who incidentally retired to NZ and is still alive, now in his 90's I would say) .

Here is some detail of how the GRP versions were built that I was able to obtain via the 'Twister Association':


The Hull

All hulls were moulded by Tylers. The specification for the lay-up was for a minimum hull thickness of 5/16” rising to at least 9/16” in way of the keel. These are minimum thicknesses and exclude the gelcoat thickness. For example, the after deck on an early glass hull has been found to be a ’12 mm ply core encapsulated between 12 mm glass fibre lay-ups.’ [12 mm is over 7/16”] Another Owner, when fitting cleats to the bow, has reported that the hull to deck lay-up is 1” thick in way of the deck.

Bilge fresh-water tank

A glass fibre tank could be built into the bilge. This was simply a capping, supported by interior baffles over the bilge with a deep sump at the aft end. The aft end was fitted with a small Henderson Hatch for access with the forward end, in some hulls, having a larger Henderson Hatch. This forward hatch is not shown on the original plans.  Tank capacity was around 18 gallons with steel ballast and some 33 gallons with lead ballast

Below is a picture of a neatly painted bilge after the tank top had been cut away. The stern, with its deep sump, is to the left.



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There’s your cue. And it has proof of service.Use  only enough glass and  ply to achieve support for what you have planned above.  Use your db /csm for tabbing if you already have it. Pay particular attention to end grain saturation of ply and apply on cooling cycle part of day. Thin or heat resin for first coat. Just repeating the mantra of others above.😉

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