Trimaran amas/floats buoyancy after a crash

[Ravenswing]

Starting a separate thread here, spurred by Buddy’s experience…

My question is, how should we proactively address potential post-crash buoyancy in trimaran amas/floats? I sail a sistership Farrier 39 to 2Flit’s boat, sharing the concerns he posted in the other thread.

The F36/39 has 3 compartments, segmented by the 2 bulkheads where the beams fit into the hulls. There’s a third, ring-frame bulkhead located mid-hull. This is open for storage convenience. Today I’m considering converting this ring frame to a sealable-underway full bulkhead (via a removable dogged or screwed in panel).

Farrier’s design places the forward bulkhead at least 8’ aft of the ama bow. Doesn’t that seem like too long a stretch, kind of an all-or-nothing forward crash zone? One could build another ring frame bulkhead out on the table, climb into that forward part of the hull, tab it in, then install a removable-but-sealable center panel. Don’t add anymore deck hatches to do this stuff.

What’s realistic for lightweight but truly waterproof access plates for internal bulkheads? I’ve already made Armstrong-knockoff discs with clamping bar 6” inspection hatches in the ama forward bulkheads to create ventilation at anchor/dock. But it was sobering to finish a long passage recently and found the starboard one jarred out of place by loose gear during rough upwind seas. I was probably sailing with no buoyancy protection for hundreds of miles. Ugh. Submarines have six(?) huge dogs on pass through hatches but obviously they weigh a ton. What really works for a pounding multihull?

And how about some detailed thoughts here on purposeful placement of floating gear? Empty fuel jugs? Large fenders? Partially inflated SUP or other water toys? These all seem to me only gimmicks, not engineering solutions. Is there any proof of intentional airbags having worked in a multihull crash scenario?

How many watertight compartments should we have on a 40-ish foot tri’s outer hulls? I heard the big ORMA race tris must have at least six.

If I just focus on adding one up front, how far back from the bow make sense? Seems such a trade off between protecting as far forward as possible, vs capturing more air volume by sliding it backwards…

How do we better address this for ocean catamaran hulls that push living spaces far forward?

I’m not posting this to solve just my F36/F39, but rather to continue the conversation for making ALL our multis more likely to continue navigating after a hull breach. What have you seen done proactively, what has worked, what is bs?
Thanks for debating or sharing your wins!

 

[Lykke]

I am close to getting 4 of these or similar buoys for the forward and aft compartments on the amas. Each is about 1 ton of buoyancy. More than enough.

Cylindrical Regatta Mark Buoy | West Marine

Check out our Cylindrical Regatta Mark Buoy and more from West Marine!

www.westmarine.com

 

[he b gb]

I’m surprised that the damage to Buddy seemed to be between the beams and not in the bow section?
Wondering if there was some pre existing issues that may have caused the damage considering none of the crew seemed to notice a collision. Would be interesting if they can salvage the boat and get some idea of what actually happened.
On my cat (whose forebeam is around 8'to10' aft of the bows) I've installed longitudinal bulkheads (like bunks) underneath which there is another bulkhead turning that section into two watertight areas.
This not only lessens the probability of major flooding of the hull but also greatly strengthens the forward hull sections from beam on wave impacts.

 

[Wess]

Hey Raven. Like you this event gives me great pause and reason to think about the how and what to do to mitigate an if…

Problem is there is so much unexpected in what happened. And I don’t mean I doubt it at all. Ryan’s experience speaks for itself and I have zero doubt it happened EXACTLY as he has said. That what he has said and described is almost 180 to what I thought would happen is irrelevant. It happened the way described so I am first trying to get my head around the why it happened like that before jumping to mitigation. Air bags of some sort seem obvious but equally I doubt they survive the abrasion of living in there long term or even the exact event that happened here. So I just don’t know…

Am road tripping this entire month. Will try to connect with you afterwards and we can brainstorm. Or maybe during a quiet moment while I am traveling if anything comes to mind.

Happy holidays!!

 

[boardhead]

That mid height floor in the bow is a really good way to go, particularly on a trimaran where it does double duty not only isolating likely bow collision damage but also reinforcing the hull to better resist the whole section shearing off foreword of the beam when struck by a breaking wave on the wind - has happened a number of times. That mid length partial bulkhead beneath - love it - small, light and effective, a second on longer bows would be good too.
My forty footer has bulkheads integrated into to beam attachments which extend down through the deck to the keel line. there is a sealed crash bulkhead midway from the stem to the bulkhead and another sealed bulkhead is required between the beams for OSTAR reg compliance which I never installed wanting to preserve the huge (light) storage volume those 300% plus buoyancy amas provided.
I use very light five gallon water containers for ferrying water in the dinghy - so light the are really glorified plastic bags. Good for 40+ pounds of float each they live, empty, in the hatch accessed bow compartments of my cruising cat - I guess the amas could be stuffed full of those on a tri!

 

[r.finn]

View attachment 558986

I like this "false floor-like" solution very much.

 

[Wess]

That mid height floor in the bow is a really good way to go, particularly on a trimaran where it does double duty not only isolating likely bow collision damage but also reinforcing the hull to better resist the whole section shearing off foreword of the beam when struck by a breaking wave on the wind - has happened a number of times. That mid length partial bulkhead beneath - love it - small, light and effective, a second on longer bows would be good too.
My forty footer has bulkheads integrated into to beam attachments which extend down through the deck to the keel line. there is a sealed crash bulkhead midway from the stem to the bulkhead and another sealed bulkhead is required between the beams for OSTAR reg compliance which I never installed wanting to preserve the huge (light) storage volume those 300% plus buoyancy amas provided.
I use very light five gallon water containers for ferrying water in the dinghy - so light the are really glorified plastic bags. Good for 40+ pounds of float each they live, empty, in the hatch accessed bow compartments of my cruising cat - I guess the amas could be stuffed full of those on a tri!

Board - no intent to be critical here. Your experience also speaks for itself. And maybe this is just a personal paranoia I need to get over… but does it concern you at all that with the mid height floor and bulkhead we have now created two critical spaces that are impossible to inspect? Again maybe it just my personal paranoia I need to get over and quite possibly the good outweighs the bad but I just hate having spaces that I can’t inspect. It sure does solve a lot of problems though. Just don’t know how I could retrofit that on existing boat without major surgery.

But both you and Ryan liking this idea speaks volumes…

 

[boardhead]

This is speculation and only inspection of the wreck would confirm or refute but for what its worth - - - I spoke to Buddy's owner on several occasions mostly regarding the rig and became aware that, like most boats of her type, she weighed a lot more than desired. The fractional rig although of generous dimensions, did not provide enough drive in moderate conditions so the masthead, light air screecher, became plain sail, with some rig stability issues.
So the weight - - the builder mentioned foam filled bow and stern sections in the amas - wooden amas AFAIK - I am wondering how much water that foam could have soaked up and what effect, if any, over the years that would have had on the structure. The fail was, as Ryan described, something of a disintegration.
I am offering this more as a reassurance to flit, wess and ravenswing all of whose boats are in good shape. I never had any concerns on not having installed that mid beam crash bulkhead on my trimaran being confident the impact resistance and reserve buoyancy of that light, strong structure would have provided an unsinkable haven for those aboard in the event of a severe collision.

 

[boardhead]

Wess - install a rigid PVC pipe from the front crash bulkhead through the second with a cap on it and another short one through the the second, again with a sealed cap or plug. Pull the plugs and both can drain, if necessary. Rigid PVC pipe is very tough and can be laminated in with polyester or vinyl ester resin

 

[Ovakus]

but does it concern you at all that with the mid height floor and bulkhead we have now created two critical spaces that are impossible to inspect?

I've worried about that too. I have similar false floors in my boat set up like in hebgb's diagram. But I've almost always tried to make sure that I have substantial access to any interior volumes. I can fit my head into most spots to look around. That means hatches -- a decent number of them. But it added weight and build complexity.

In addition, my boat is plywood/fiberglass/epoxy and I worry a lot about longevity. My sense is that for my construction method, a long lived boat needs substantial ventilation for all interior volumes. I think Jim Brown's writings make a big deal about that if I remember correctly. Meeting all those criteria (sealable watertight compartments while underway, inspectable so I can see in, open enough for ventilation for storage/not underway) seems to require largish sealable hatches. Weight, complexity and build time went up accordingly. Did I need all three criteria?

 

[SailingTips.Ca]

Like many of you the events surrounding the loss of Buddy have my mind buzzing.

At the same time, the catastrophic loss of an entire ama seems to be a relatively rare occurrence, and we are much more likely to find ourselves upside-down for a large variety of other reasons.

That said, if we are talking about complete ama failure, another perhaps more common occurrence seems to be the ama breaking clean off at the beams.

Given the variety of complete ama failure scenarios, I’m wondering if some discussion about the recommended seamanship / boat handling techniques in the event of losing an entire ama, regardless of the failure mechanism, might be a good complement to the discussion about adding floatation etc.?

For example, if your windward shroud begins to fail the first thing to do is tack. Can there be a simple set of recommendations for complete ama failure, or are the scenarios too varied for that?

 

[munt]

Not exactly on topic but the closet dehumidifiers that you can buy on Amazon are great for hanging inside your amas. I did it on my mostly wood L7 and even though the boat usually lived in the mast up storage those things really seemed to reduce the amount of dripping, steamy, wetness that would collect in there. Just gotta remember to empty them regularly. I hung em in my wife's closet in Charleston to protect her beloved purse collection and they would fill up very quickly, the air there being mostly water.

 

[Ravenswing]

I am close to getting 4 of these or similar buoys for the forward and aft compartments on the amas. Each is about 1 ton of buoyancy. More than enough.

Cylindrical Regatta Mark Buoy | West Marine

Check out our Cylindrical Regatta Mark Buoy and more from West Marine!

www.westmarine.com

lykke, will you show the math on how to calc the bouyancy number of those things? I doubt I could get them fully inflated in the given space. I can sling epoxy but I failed calculus . Thx!

 

[MultiThom]

Not calculus. 3ft diameter, 5 foot tall. volume is 1.5*1.5*5*pi. Then convert cubic feet of air times weight of water per cubic foot. But why would you put them in the float instead of tying them to the beams? That way if a great white eats the middle of your ama, you can pull the lanyard and inflate to keep upright.

 

[Ravenswing]

I like this "false floor-like" solution very much.

Agree.
Now let’s talk about how to build these. Farrier designed a large flush hatch ahead of the forward beam; that’s how you get to tab in the beam socket during build. That hatch is caulked and screwed down for rarely accessing. So at least 2Flit & I could crawl in there. Don’t know if Russ’ big Corsair or others have enough physical access forward of the beam.
The vertical half-bulkhead is easy to tab both sides. But for the new half-height floor, how about glassing to the hull foam block ‘stringers’ on each side that the new floor edges rest on. Floor gets underside glued around its edges to those stringers and the top of the new bulkhead, then normal glass tabbing all around the top to the hull. Not ideal for the underside but a good west 403 adhesive fibers bog glue on the stringers sounds pretty strong. Agree or no on that?
Materials? Thinking 1/2” pvc foam (corecell / dyvinicel, etc) with 12oz biax glass skins. Hmmm, What structural job is this floor really doing and thus does it’s lamination schedule need to match or can be less than the hull? We absolutely want to make this as light as possible - no more weight in outboard pointy ends!

As for adding access hatches, I don’t want to buy a bunch more bolt in circle ports that invariably leak, are heavy, need o-ring maintenance, etc. So how about: from a finished bulkhead or floor panel, jigsaw out the desired size access panel. Epoxy seal edges of cutout. Permanently embed a half dozen studs (316 SS bolts with heads cut off) around edges of hole. Add a glass bolting flange to the cutout part. Caulk and loctite-nut this occasional access plate in place. Seems about as much work but lighter and cheaper than buying deck plates? Or you got a better way?

Even with access plates, I’d still do Boardhead’s pvc drain pipe with screw cap at the bottom. I already embedded pvc fittings at the tops of our beam bulkheads years ago. We screw in / out pvc plugs to aid at-rest ventilation.

Thx to all willing to debate the construction methods here. Really appreciate the shared knowledge!

PS. Buddy’s story only adds to my negativity on spray foam-filled compartments. There seem to be too many examples of long term water saturation. Is there any proven best practice for using this stuff? Like Leaving drainage voids and access pipes at the bottom? Is anyone close enough to Mr. Patterson to learn what foam material was used in Buddy’s amas?

 

[MultiThom]

As for adding access hatches, I don’t want to buy a bunch more bolt in circle ports that invariably leak, are heavy, need o-ring maintenance, etc. So how about: from a finished bulkhead or floor panel, jigsaw out the desired size access panel. Epoxy seal edges of cutout. Permanently embed a half dozen studs (316 SS bolts with heads cut off) around edges of hole. Add a glass bolting flange to the cutout part. Caulk and loctite-nut this occasional access plate in place. Seems about as much work but lighter and cheaper than buying deck plates? Or you got a better way?

My amas are built that way but without studs. Basically there is a hole with a 1/2 inch flange slightly below the surface and a cover plate that rides on that flange. It is sikaflex'd into position (better bedding than 3M IMHO). However, if it leaks, it leaks a whole bunch if it is underwater. I've had to redo the ones done by the builder--so far so good on the ones I redid myself. You could add access hatches the same way but you would need to add the flange as a separate piece and use clamps plus epoxy to make the flange stick.

 

[Wess]

Raven - Agree re spray foam but I see a different problem and so am not even thinking about a fix yet.

However it happened and regardless of cause the float was breached, and eventually the deck and structure of it failed. No matter what we build or fill it with in a collision bad enough it could be any of us.

Here is the problem. I had always assumed that whatever was left would have some positive or maybe neutral buoyancy and not negative buoyancy pulling that side of the boat under. And even if whatever was left of a float and beam(s) was slightly negative buoyancy the boat would easily and by default rotate around that putting the damaged side to weather.

That ain’t what happened here. The boat sat broadside to the wind with the damaged side to lee and nothing they could do would turn it. At that point the damaged float to lee digs in, tripping the boat as she drifts downwind and the wind on the rig alone capsizes the boat.

I am still trapped in a box (thinking) stuck on that. How the boat sat afterwards and essentially doomed itself. Because I don’t care what we build I suspect if we hit a shipping container at 15 knots SOG with our lee float bow there ain’t gonna be much of that false floor (or any airbag) left.

That ain’t a solution I know but that is the (new) problem I never thought I could face.

 

[Lykke]

lykke, will you show the math on how to calc the bouyancy number of those things? I doubt I could get them fully inflated in the given space. I can sling epoxy but I failed calculus . Thx!

Not calculus. 3ft diameter, 5 foot tall. volume is 1.5*1.5*5*pi. Then convert cubic feet of air times weight of water per cubic foot. But why would you put them in the float instead of tying them to the beams? That way if a great white eats the middle of your ama, you can pull the lanyard and inflate to keep upright.

Yep. 1 cubic foot of water weighs 0.03ton.
I did it the other way: The beauty of the metric system is that 1 cubic meter weighs one ton (or tonne, which is about the same for this purpose). 1ft = 0.3m. So the area of the round part = pi x r^2 = 3.14 x 0.45 x 0.45 = 0.64sqm
Times the height of the cylinder of 1.5m = 0.95 cubic meter.

I would put them into the floats because of esthetics, windage, and protection from UV and the elements under normal operation. Assume you can’t inflate them in emergency, they need to be inflated.

If a great white bites a chunk of your ama, or a 40ft container hits, I think a soft buoy is more likely to stay airtight than a rigid bulkhead glassed in. But the issue of them having to be durable is nudging me towards these fenders:

https://a.co/d/bgQgF9P

They cost 25% more and are less than half the volume, though.

I think at least one of these (the aft one likely) would survive what happened to Buddy. At least long enough to manage a tack.

Air bags of some sort seem obvious but equally I doubt they survive the abrasion of living in there long term or even the exact event that happened here.

 

[boardhead]

That half floor can be depressed, longitudinally along centerline because it will be stiffer and present a domed surface to the hydraulic punishment if the bottom of the hull is holed and floods. No need for bi-axial, use uni transversely both side with a longitudinal band down the centerline if you want belt and braces - I wouldn't. Shape and fit the panel so the lower skin is snug against the inside skin of the hull with the perimeter square to the panel which creates a nice wedge to cement the floor in with a 1/4" fillet on top then tab it in with a bi-axial tape oriented 45 degrees so it lays in tight.Not a simple task but that's how I would do it.
Don't like inspection ports so on a composite boat I would cut out a piece of deck with a 45 degree cut and permanently glass it back in position to seal the compartment afterwards.

 

[boardhead]

62.4 pounds/cubic foot.