Redecking composite Heron

I am replacing the wooden deck on a FRP Heron hull.

The owner requested the work because the mast was showing imminent signs of pushing through the deck. The step had been installed partially in front of the king post and as a result, the king plank had fractured.

Dismantling the deck showed the following defects:

1. Broken King Plank not glued to deck beams.
2. Soft timber in King Post - no maintenance on concealed surface and water penetration via various screw holes. (See picture)
3. Main deck beam joint to gunwale (port) broken - also next beam forward
4. Soft timber in gunwale at point where chain plate passes through plywood deck.
5. Out of six knees supporting the side decks, four were losely attached to the hull where the bond to the hull had fractured when the boat was lifted. (See picture)
6. Large parts on the inwale appear to be bare wood or the finish has long ago vanished.

Should be a fun project. I am now at the point where I can begin planning the reconstruction.

I will keep posting and will ask advice from time to time.

 

Side deck knees

The picture in post 1 showing the knees suggests that they were of insufficient dimensions to transfer the lifting force applied at the carlins to the hull without damage.

Further examination suggests that the knees were part of the original construction and were built in during the moulding process. There is very little glass left in the hull at these locations, possibly only gelcoat.

I would appreciate input on the following points:

1. If I make the knees longer - down to the top of the bouyancy tanks, will I create a concentration of forces at the top of the tanks which could crack the hull and make things worse?
   
2. The moulding was polyester, with a flowcoat which has then been overpainted. I plan to remove the paint, abrade the flowcoat and soften with acetone before applying glass, probably several layers. Better to use Epoxy resin?
   
3. Finally I will attach wooden pads to the new surface - 30 mm in width and slot the new knees into these before glassing over these pads.
   

Is this overkill?

 

Nice little project WhiteDwarf.

I'm just ripping the gunwhales off an Otter at the moment, just love finding 3/16th clenched copper rovings about 150mm long...

Remove as much as you need to so you can actually work on the thing. As long as all bond surfaces are down to the polyester/glass layup you will get a solid bond. I would use epoxy for most of the work, with the exception of if you have to do a bit of glass and gelcoat it. Good abrasion will give you a good enough key. Acetone will not do much except remove any remaining contaminents. Hell this stuff has been cured long enough.

Pre saturate all the timber bond faces with epoxy ie give it a coat and let it go off prior to applying bond coat. This ensures the grain is much better filled and water cannot seep in so easily. Very common fault in even current production builds, the timber is not pre saturated. I've replaced timber cores on six year old boats....

Replace the king plank, and king post. King plank should be I beam like so change the shape if you need to. A lot of older boats had a wide shallow king plank, utterly wrong for the loads. Spruce is fine for the plank, WR cedar a little light. Looking at your boat it suffers from that fault. If you re notch the deck beams on the c/l you could create a T shape king plank. Use a stiff q/sawn vertical with two light packers each side. This is my own personal preference as max strength and bond area for the foredeck.

King post, well anything with decent compressive strength should be fine. I tend to use Douglas Fir but only because I have some. Minimum repair is to core all old holes and fill with cross grain cut plugs. New one prefered. Done a lot of replacement ones for glass and wooden Enterprises.

The shroud plate area needs to be as strong a practicable. Maybe a knee onto a pad spread to the carlin. Might require a local reinforcement of the carlin. Just spread the load. It is not really high stress, no sail area to generate that but it should be pretty secure. I personally like a ply pad down to the stringer! but you cannot get to that on this boat. However you just need to get the shroud plate to be held by the inwhale and gunwhale and partly supported by the carlin. Not too fussed about using screws either instead of bolts. Both work fine as long as in shear. Ideally the block/knee that takes the screws is something like mahogany ie fine grain and fair strength. Khaya (African mahogany) is a decent substitute. Screws must be put into cross grain NOT end grain.

Rest of the knees will be fine if you bond back cleanly and use a nice fillet around them. I would not be too keen to take the knees onto the buoyancy tanks. If it has not cracked in this part you may well over stiffen it. Bleed the knee out close to it, perhaps a greater taper. If your knees are say 15 -18mm + wide, I would not be too bothered about a ply pad, if they are 6-10mm then use the pad.

Might be better off looking at the glass. What type? CSM or roving? If CSM you may be better off locally flatting it out and adding a couple of layers of 200gsm roving. Resin type does not matter too much for this. I'd probably use polyester as it goes off fast and you can get a lot of work done quite quickly. A lot cheaper too. You may use polyester pigments to colour the resin to get a reasonable match. Try and use no more than 2% pigment in resin - up to 5% in gelcoat. It also works in epoxy but may affect the ultimate bond strength. I've not actually had any problems but have not put stuff in a tensile tester etc. So instead of a ply pad a little extra glass may be an easier solution. Looks like CSM from you shots, woven roving is quite a bit neater to use and finishes better on the whole. I would rebuild the 'damaged' upon removal areas and fractionally reinforce if I had to deal with that problem you have.

Scarf in new wood where appropriate, as lonfg as you can get say a 1:4 you should not have a problem. The ideal is 1:7 but is often hard to achieve in repair work. Not had one fail - yet and some have held for 30+ years.

 

Progress report 1

First of all SukiSolo, thank you for your consider and extensive reply. I have excised the rot from the inwales and will make the replacements tomorrow.

The removal of the rot showed damage to the moulding from a former fitting and I envisage encapsulating that area with epoxy. On the outside of the moulding there is also water penetration where the chainplates pass through the gunwale.

I envisage the early steps towards reconstruction being:

1. Repair gunwale
2. Reinforce hull where removal of the knees has reduced the moulding to mere gelcoat.
3. Install the new king post.
4. Replace deck beam 2
5. Replace deck beams 1A and 1B
6. Install new king plank
7. Pause and think!!!

Pictures are of port chainplate area with rot excised and starboard chainplate area seen from outside and below.

 

Nice stuff. Below is how I would suggest approaching the new king plank. Do not weaken the cross beams unduly though so a little 'feel' is required but should give a much stronger result overall.

 

Thank you for image

SukiSolo,

Thank you for that. I agree, the 15mm Western Red Cedar deck beam was barely sufficient as a gluing surface for the two halves of the foredeck. Structurally it proved totally inadequate. Your scheme is far more satisfactory.

By the way, that picture is very clear. May I ask what software you used to make it?

W D

 

Be careful to splice in a little harder timber at the bow end where the King plank joins to the apron. This is to take the stem fitting. Exactly how you do this will vary depending on the type of fitting employed. One of the common ones has two screws on the stem and four from above, deck side. The primary jib load should be as far forward as possible putting the two stem screws in shear. A lot of people make the mistake of using the rear clevis pin (if a two pin fitting) and then pull the fitting from the deck!

Although it is a little more work, it is good practice to engineer a decent screw holding timber in the area taking the mounting screws. Even drilling out locally and putting large cross grain plugs in say Ø10 or Ø12mm is a lot better than expecting WR cedar to take the load. Personally I tend to scarf in a short length of something suitable.

The little section was only a minute or two to create in Rhino, crude render using Flamingo plug in.

 

Reply to SukiSolo re bow.

Thanks for that.

I was introduced to Rhino at TAFE (Technical And Further Education) powerful program but I would get too little use out of it to become competent.

With all the Australian Herons that I have seen, the forestay is connected to the bow by a tang or tangs on the bow structure. In this case, two bolts have been passed through a block of timber which is positioned under the sheer clamps and bresthook, they pass through the moulding at which point the fitting is bolted in place. Reasonably substantial, but I will treat all the wood with epoxy.

I have finished scarfing in the new timber on the sheer clamps, by the way.

Next task will be to create a former for the main deck beam, but I have computer training this week, so that will happen next weekend.

Again, thank you for your interest.

W D

 

Deck beams and knees in place - reinforce?

The more I examined the hull, the more deterioration I found. In the end I removed all the timber except the transom dressing, the sheer clamps and the original gunwales.

In the last month, I have constructed and installed all the beams and knees. I used templates to develop all the shapes of the various joints, knees etc. A friendly neighbouring builder generously provided shuttering timber which proved perfect - perfect includes free!

The original knees - plywood covered with polyester and chopped strand mat had detached from the hull (four out of six), probably due to "enthusiastic" help bringing the boat up the beach. The owner wants wider side decks, which means the moment arm when lifting on the carlin, will be increased.

To gain greater strength in the attachment of the knees to the hull, I have:

1. Reinforced the attachment area for each knee with 3 layers 225 gm/sq metre of chopped strand mat in polyester resin.
2. Increased the knees from 8mm to 12mm section
3. Glued on each side of the knee a triangular piece of Western red cedar
4. Glue used throughout is epoxy

The gluing surface is therefore 19 + 12 + 19 mm ie 50 mm or 2".

Question, should I further reinforce the knees by linking them to the hull with chopped strand mat and polyester?

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I envisage finishing the interior of the hull (up to the undersides of the sheer clamps) with polyester flowcoat, apart from any uncovered wood which will be treated with International Everdure penetrating epoxy and then varnished. The interior faces of the sheer clamps which are now largely untreated! will also be treated with Everdure.