Composite replacement of a edge glued strip planker

[Roly]

We have not owned Pukka long; just long enough to fall in love with her
and sailing.
She is an edge glued strip planker (1969) that we bought knowing it would probably only be a couple of years before some major work.
The two years was actually less than a year, when we discovered she was taking on water after some heavy windward work in 30knts.
We hurriedly pulled her from the water to rectify a leak from failed glue lines at the front of a poorly constructed mast step. The boat had been sailed hard and stopped taking on water when sailed sedately, but had enough signs to warrant a refurb.
Definitely not a blue water boat in this condition , and not fit to race.

http://www.boatdesign.net/forums/sho...3830#post53830

After a complete stripdown and not knowing what is worth rebuilding we consulted a respected boat builder/surveyor to advise.

"Scrap her" were words we had joked about; but when they came from an expert they have a completely different meaning. Somewhat final!

The postive side is we have the plans, the rig, 6 good
sails, electronics,keel, rudder,Yanmar 3gm30,and loads of gear.

The embryonic dream at this stage is to make a new hull out of modern materials, divinyl cell foam core, epoxy and triaxial outer, polyester and triaxial
inner hull. Cost is an issue as we have already spent 10k on a shed, cradles, drying facilities,stripping. But we would end up with something lighter(read faster)that we could add weight for class racing but lighten for free sailing & out of class. Something we could have confidence in . Never really had that in pukka, bless her!

Does anyone out there have a hull lay up schedule fitting the above for the
approx. the following specs.
LOA 34'3"
WL 29'
Bm 10' 2"
Drft 5' 6"
Displ 3.56tonnes
Ballast 1527kg
Main luff 37.5' foot 16.5'
#1 luff 42' foot 21'
Sym spin luff 43.5' 1/2width 15'

Any advice, site references,similar personal experiences, would be most welcome. I am trying to cost this up for feasibility at this stage.

Cheers,
Roly

[nero]

You might save yourself a lot of time by using the existing hull as a mold or as a plug to make a mold from.

[Roly]

What about the boat being 2x hullthickness bigger? I guess I would have to measure her vitals to see how close to plan she is built.
That is a good idea, though, in principle. I guess the divinyl cell will smooth any irregularities out. What would be the best way to fix the foam to the hull?
Screws from the inside or staples from the outside and have them pull thru when pulling off the plug? Dismantling her from underneath would be a B#gg#r
of a job. Taking the sodden planks off the bottom required sawing parallel with the frames and chiseling of sections.

Hmmmmm...good possibilities to save time. I guess I should check with the president of club to make sure they agree or she might end up being an "outcast".
Also I wonder how much liberty is taken in the lofting process from boat to boat? Thanks!

[nero]

Was thinking that you could wax the hull (as a release agent) then coat it with resin and a layer of glass cloth. Then you could bond extruded polystyrene to that. Add another layer of glass and supports as needed. This would give you a female mold to do any sort of layup you wanted to. Might even be able to reuse the bulkheads and interior parts.

All this since you seem to be satisfied with the boat.

If you were going at it your way, perhaps screws thru the hull from the inside. There might be too much force to overcome if you try to pull thru staples.

[Raggi_Thor]

If you are making just one hull it makes sens to use teh old one as a male plug, without making a female plug first. You can make the new sandwiched core twice as thick as the original. Staples is hard to pull through, but regular nails with small heads can be used to fasten one layer of foam to the old hull. Then glass and epoxy (my choice over polyester because of smell and water absorption), then pull the new hull off the old one, add another layer of foam on the inside and then glass everything before you fit the old bulkheads (if they are fine).

[FAST FRED]

LOA 34'3"
WL 29'
Bm 10' 2"
Drft 5' 6"
Displ 3.56tonnes
Ballast 1527kg


WE built a similar , but considerably heavier boat to USCH Sub chapter T specs.

33X27X10.5 16250 lbs , 7000 ballast ,737 working sail 1200 light weather.

The hull sides to the turn of the bilge were 3 layers of 3/4 oz matt with 2 layers of 28 oz roving between.

M-R-M-R-M Airex M-R-M-R-M all hand laid up "Frans Mass " Style over a plug.

This was done inside & out , normally a last layer of 3/4 mat is not used inside to save weight , but with this design the interior skin was simply painted and was fine inside.

Foam was 3/4 Airex , which is hugely expensive today.

The USCG demands a 400% safty factor , this layup gave 425% after structural & burn tests. IT NEVER EVER flexes .

Hetron FR resin was required for this Inspected Vessel.

HIGH flame thrower std resin which basically can not be extinguished and is not allowed if the vessel carries over 6 passengers.


At only a cent or two a pound over std resin , I have no idea why it is not used on EVERY vessel.
FAST FRED

[Roly]

Thanks, Nero, Raggi, Fred! All thought provoking stuff.
I have access to the original female mould as well, just to complicate things further. The steel work is shot but the tooling gelcoat is ok. It is miles away and the logistics of stablising with steel again and trucking to my workshop
are just not on.
I like the idea of Pukka as a male plug rather than lofting new x-sections frames.
The decision hinges on wether boat "measurers tolerance" will deal with the
the addition of 2x composite hull thicknesses to the x-section.
Pulling it off with only one layer of thinner foam is a good idea! (may fall within % tolerance)
There is evidence the plans were not strictly adhered to on Pukka so
I better go measure the old girl and see what I am dealing with.
I have the layup for poly/balsa but would like to use PVC epoxy/poly or all epoxy and take the hit on resin cost. My layup would have to be either USCG
approved or our MOT, which may be expensive?
Phew!----------- Maybe my thinking is unrealistic but surely with the inclusion of epoxy and axial cloths I can lose alot of weight.

BTW Fred, what is Frans Maas style? Searched but could find no ref.

112oz to turn of bilge and to sheer in chain plate area I presume? Hell thats an ice breaker!
What oz above bilge? Many Thx!

[Roly]

Seems this layup utilises a lot of chopstrand matt an relatively thin core thickness. Is it not possible to increase the core thickness an decrease the
skin thicknesses by using triaxial and epoxy?

[Karsten]

That looks like a typical cheap polyestyer layup. If you use polyester you need all the CSM to enure propper bonding between the plies. If you use epoxy you don't need CSM except for the outermost layer to reduce print through of the fibres. If you want to build up thickness quickly and cheaply I would use stitched quadraxial materials. They have fibres running in the 0, 90, +45 and -45 degree direction. For a boat this size about 1500g of glass on the outer skin and about 1000g on the inside skin should be fine. Guess 15mm of core would be a first guess but that depends a bit on the frame / bulkhead spacing and shear strength of the core.

[Raggi_Thor]

For maximum stiffness in a sandwich you want glass fibres that are straight and not woven, as Karsten said, use a stitched material. Devold AMT in Norway has a very fine biaxial 450g. Actual weight is a little more than the nominal weight because the stitching material is not regarded as a strengthening member.

[FAST FRED]

"BTW Fred, what is Frans Maas style? Searched but could find no ref."

If you contact Airex they have a good construction book.

Frans Mass would create a plug out of wood that was really a shaped basket , and sew the airex on to create the shape of the hull.
The outside would be laminated and faired while still upsidedown.

Then a set of supports would hold the hull shape as it was rolled (crained) over and the interior layup installed.

The superbly faired hull would be used as the plug to create a std boatbuilding female mold.Then the boat would be outfitrted for racing.

As the Airex hull was stiffer & lighter than the later solid glass hulls , he would win lots of races , & the free publicity from winning.

Worked till the GRP art advanced , and the customers started demanding cored hulls.

While Epoxy is a fantastic material for one of racers and other places where Super Light is demanded , for cruising where docking and pilings are a fact of life there is a huge need for tha abrasion resistance and shock loading of above minimal scantlings. On a cost basis an Epoxy cruising boat wold be hard to justify in realistic scantlings.

The USCG does it best , NOTHING EVER FLEXES, and the hulls go on for decades , at a low cost.

FAST FRED

[Roly]

I crunched the numbers all wrong. Actually Fred, the boat you mention is slightly more lightly built than the layup I quoted.

"3 layers of 3/4 oz matt with 2 layers of 28 oz roving between each side"
equals total sq. ft. wt of .........................6*3/4 + 2*28/9
= 10.72oz/sq ft.
As opposed 12oz layup quoted in table.
(CSM, I assume, quoted per sq ft, W/roving per sq yd.) Why do they do that
I cannot find any reference to 28oz woven roving. Possibly 24oz converted to /m2 rate (x1.2)


Karsten: Table quoted; Total bilge glass = 12oz/ft2
= 12*9*28.6
= 3088gm/m2

"1500g of glass on the outer skin and about 1000g on the inside skin "
= 2500gm/m2 (20% reduction on above but possibly stronger in tension and
shear as no csm. Although considerably thinner skin.)


I wonder on the relative strengths of the two? Abrasion and shock resistance? The frame dimensions of the polyester layup I haven't an inkling of; And, even less idea of the dimensions and configuration of a frame system for the latter.
I am seriously considering going back to plan A, removing planks to above waterline,replanking, glassing,flip over,remove old internal frames,glass to chainplates,relaminate in new basic frames.
Thanks to all for your input, the curve is steep.

[nero]

About plan A

What style of planking was used. Perhaps using strip planking sheathed with uni fiber could reduce the number of internal frames (and the work to install them)

[Roly]

"What style of planking was used"

Resorcinol edge glued strip 40x20mm bead and cove. Edge nailed with galv.
65mmx2.8mm jolt heads and it doesnt come apart easy either.
I bought 650m of heart old growth kauri to replace it but when I was given
the verdict decided to change the program.(I still have it)
Difficult to know which is more work. Plan A or B. Of plan B, epoxy and multi-axial cloth seems less work than polyester. I am faxing the poly layup off to be costed today.

[nero]

let us know what decision you make. ... good luck