Fiber Direction and Placement

50 mm thick!?!

 

He says 10mm thick to 50mm above the WL. And the glass without resin is about 1/2mm thick, but when you add resin, there is probably some increase.

Fortunately, there is core on the sides, so the WL is core all the way. It is just the very for'd section of the keel and bow where corecell work would have been extremely difficult. And I have beveled the edges of the core 1" for half inch core and plan to go up those sides 8" or so. None of the area is within any of the occupied areas of the hulls. Does the standard suggest I need to run my glass to above the WL even if the WL is core? I can do that as well, but it seems excessive, although not hard to meet, so maybe I should just do it.

I really think the 5 layers is a little light and I have no problem going with 10 layers. The area is 10" by 12' to the keel on each side. I am going to do an overlay of the entire section when the boat is flipped. The only thing I am wondering about it the tactical approach to laying all those layers of glass. If you overlap each piece within a singular layer; you'd end up with lots of ridges and might even have trouble with subsequent layers not laying down well. So, would you just side by side all the layers? Or is it going to be much stronger with 50mm overlaps within each layer and just deal with the ridges?

The interesting thing is this is where, if you were going to hit a shipping container, you would strike. I don't know if 10mm of hull would be spared super damage at 20knot speed. Cruise is going to be somewhere around 10 knots. I have a feeling if you hit a shipping container at 10 knots; you might just ride up on top of it, but I am guessing. The real likelihood is a floating log.

 

White area is hand laminating area ready for wax and pva once my panels are set, the panel on the right is not trimmed and the other panel is a bulkhead we did, and disregard the airhose, etc. We built the port side panel today and will trim and set both tomorrow.

I also need advice on how to join the panels at the bow. I was going to make epoxy, cotton fiber, balloons, and cabosil, but I really like ground corecell, too, so maybe I'll go 2 parts epoxy, one cotton, one balloons, one cabosil and one corecell by volume. Is there a Lloyd's standard for panel joins?

 

Go with overlap and deal with the ridges.
I would build for the sea containers awash and logs.
Nice photos.

 

No core then that makes sense, fall guy you can counteract the hitting the container/log scenario to a large extent with the "better than the titanic" approach. That is watertight compartments forward in both hulls that are watertight. My boat has a full height watertight bulkhead that is completely sealed 2ft from the bow, aft of this is a single bunk with two bulkheads underneath which form two more half height watertight compartments. A guy in the same design boat through some very negligent watch keeping sailed straight into a sheer rockface on a small outcrop near Prudhoe island on the great barrier reef. The very front section of both hulls was a six inch section of extruded polystyrene, with a proper structural bulkhead behind it that he stuck it to, and a very light laminate on it to act as a shock absorber of sorts. This area is completely sacrificial and very easily repaired and it worked a treat. The boat speed at the time was around 8.5 knots so it was a significant impact. I guess what I'm saying is there is two approaches here, build heavy like a tank and pray it doesn't break, or use the "airbag" approach and some sealed water tight compartments to contain the damage. With the foam core the boat may be "unsinkable" anyway if built lightly enough. There was another well publicised event in thailand some time ago where a bob oram cat "found" an uncharted reef and large sections of both hulls were completely destroyed. They motored the boat in a semi submerged state to the nearest haul out facility. http://www.mysailing.com.au/news/australian-cruising-catamaran-holed-on-unchartered-reef-in-thailand . Large areas of the hulls were completely destroyed, I'm not sure you can prevent this unless you build out of thick steel plate, I think it might be better to think about how to survive major damage rather than attempt to prevent it and use the watertight compartment approach and reserve buoyancy in the build. A lot of heavy laminate doesn't improve the reserve buoyancy situation so it's a catch 22 so to speak. The mini keel thing is a whole other issue, I hate them. They cause lots of problems for everyone I know that has them and that's a lot of cats after 14 years liveaboard and cruising. Just something else to tear a hole in your boat in my opinion and cause heaps of anchoring problems etc, but that's only my opinion there are lots of people who think they are good I'm not sure why. The only argument for them is beaching ability and as sacrificial depth sounders in reef country. The argument could be made that the cat in thailand may have escaped relatively unscathed if he had Mini keels depending on tides reef structure etc, the also could have trapped him on the reef who knows. It is a really big project you have undertaken and if I could give you one piece of advice, having been there done that, it's don't over think it. Just be confident in your abilities and go forward, focus on progress not the "what ifs". I found It's a psychological challenge more so than a physical and financial one, like the training for your navy seals it's about mental toughness and the what ifs can cause you to drop out. You've got a plan just stick to it and focus on progress and I'm sure you'll do a great job. From just a couple of pics that you've posted you appear to be right on the ball and going well, good luck.
Cheers

 

Thank you Sailhand. The boat has watertights between the bow and BH 0 and BH 1. The next bulkhead space is a bunk and you could opt for making the space under the bunk storage or make it watertight as well or perhaps a bit of both. The boat is a RW design and I hate to be so much a bother to Richard on all these nitty build questions. It has probably already driven him nuts. He has been a real champ thus far and no one ought say a word about the scantlings questions. I kidded with him a few times about this boat being built well enough to ram Orams. And further, he and I never said we were building to LR vs XR vs RR (a little fun).

I really want to be able to beach the boat. That is super cool to me n Mrs. I plan to put the beaching keel on with aramid over the top.

 

panel build today with my help, I couldn't see the picture I snapped because the door is right there, so my friend's heat is missing. I am probably going to move the vac lines to off the part after some advice from another builder. The wetout was well over 50% of fiberglass, so some bleed through is good.

 

If it is Richard you can trust him. His design is spot on.

Problem start when you start modifying. For example, if you want to minimize damage from hitting partially submerge objects, you cannot reduce the risk by adding more layers. Hard impact laminates usually transition from sandwich to single skin to increase shock absorption. Cored laminates are stiff whereas single skin is more pliant and can resist a higher magnitude of shock. Adding more layers will only make it stiff and heavy. Partially submerged objects floats slightly above water and 50 mm above waterline reinforcement makes sense.

Hitting a submerge container head on is just bad luck but you can prevent the boat from sinking by adding multiple watertight divisions and modifying the nose to absorb some of the shock. A solid foam sacrificial nose is the easiest way. A practice in Formula one car is to use honeycomb core. It is very stiff in the transverse direction but has little or no shear. When hit longitudinally, it disintegrates absorbing some of the shock. You can opt for a single skin laminate at the bow. That will solve minor collision problem.

The keel is the thickest part of the boat and there are several tackling the joint as shown.

 

Hi fall guy Mr woods knows what he is doing, he has the experience especially in the ply chine boats, possibly more than anyone else. I would never presume to question the designer of so many good boats he knows a million times more about it than i ever will. My boat is 44ft and i leave it on the beach for months at a time no dramas and no Mini keels. As per bobs plan we have a sacrificial layer of hardwood bracing ply stuck to the bottom of the hull and glassed over. We "rediscovered" a long charted reef some time ago in a big swell and i feared we may lose the boat, I kedged off in a decent swell and i will never forget the sound. I dived on the boat immediately and to my relief we had no damage at all. Bracing ply is made from hardwood in australia and is about quarter inch thick it is tough and it was a good idea of bobs and it worked. Boards are great and there is a lot of anecdotal evidence that they are safer at sea, don't need mini keels at all for beaching in fact they tend to point load on the boats I have seen. I have kick up rudders and they are great, wouldn't have anything else for safety and convenience and i have shaft drive diesels, but the shaft angle and rocker combine to keep them off the sand when i dry out. That bracing ply is stuck to the outside of the glassed hull by the way it is not part of the core. Obviously it can't stop everything but it worked for me, Mr woods may have something similar, he is the ply boat guru after all. I delivered a 39ft oram for a guy recently with boards kick ups and outboards. It went straight up on the beach next to mine when we got home and I stepped off into 300 mm of water that's almost as skinny as my dinghy runs, Oram's are beach bum boats and spent half there life on the hard, it's probably our favorite pass time, playing beachhouses with our boat. Just pick a nice beach in a sheltered area and hey presto instant beach shack, and by the way we can still open and close all the doors and hatches when we are on the beach, bobs boats are stiff and then some. With the boat on a concrete slab on chocks if you jack up one corner a quarter inch it rocks on the diagonals.

Cheers

 

Fallguy; 750gsm glass hand laminated is going to be just under 1mm, do not be concerned about the ridges at overlaps it will be hardly noticeable and it is on the inside. If you alternate the fabric longitudinal than transverse only the transverse will have the overlaps. you should be able to do the longitudinal in one piece, if not two pieces overlapped at the keel line. Also stager the transverse so the ridges will be only 1mm high.
Personally I would be more than comfortable with 5 x 750gsm glass in that area.
For the bow stem join I would pack the area with strips of foam offcuts set into something like a 4:1 spheres:silica mix so that you have a 50mm radius there to glass around.

 

Thanks all. I will stick to Richard's spec. I really appreciate the chatter on it. I can try to do the longitudinals in one piece, but it will be tricky; the wetout is going to be done on a table, and the area is not walkable once wetted. I think I'll do the bowjoin first and wait until the next day, then dryfit everything and wetout the transverse first layer and take it over to the vee in plastic and so on. I am also going to put a rebate along the edges to allow for an extra tape without fairing at the external long joins. It doesn't take anything away from the total strength to do it and adds a strength where there is loading from the bow.

The boat has two watertight compartments forward. The third bulkhead space is the bunk. That space did not have a watertight beneath it, but I could add one easily. It would be below the waterline though. But just enough to cover the keel area.

 

You can reach this area from the top, my preference is to place dry fabric in place as much as possible and then wet out.

 

I can reach it from the top, but the angles will make wetout extremely tough. The downside is wetted fabric can change shape and that might bother me as well.

 

Looking at your photo it does not look that difficult. Dry fit the first layer and see if you can get it flat, if not then dont use triax.
Do it with 450gsm Double bias and 450gsm UD or what ever the weights you have on hand. Or you could do it all from UD alone.

 

I have 180z double biax. The hardest part of the join will be the fiberglass staying down in the radius I made in the mold vee. I think I'll pack some sand into gallon ziplocks. As long as no one tells me to pound sand, I should be okay. It is really easy to have trouble with the glass pulling up from one side to the other when you are in a vee. I'll double bag the sand cuz who wants a sandbox in a boat?