LB26

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jacquesmm
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Re: LB26

Post by jacquesmm »

Positive buoyancy is not required for boats that size but that does not mean that they will not float if damaged. In this case, the hull material with all bulkheads, frames, stringers and sole, will help her float. The same apply to all tanks.
Boats of that type and size are not designed to be unsinkable but thanks to the foam sandwich hull, she will be if not over loaded.
Builders often increase materials and add equipment. For that reason, I can not guarantee the weight and positive buoyancy.

At the time of the design, I ran hydrostatic calculations in Orca for different sinkage levels and loaded as designed, the LB26 had positive buoyancy fully immersed when the foam volumes were taken in account. That means, loaded at the designed displacement, she will float if holed. I don't have the figures anymore, I keep only the hydro files at DWL. All that was at the designed weight. A heavy boat with, for example a generator, AC and lots of gear, may not float if holed.
My calculations were based on the surfaces and thickness of foam not on the designed volumes of the panels. I used a surface model and extracted volumes from it. I used wide safety margins for those volumes.
I owned many large boats, still have a 15,000 lbs trawler today and never thought about positive buoyancy for them.

I can't run a redesigned model just for volumes. I am retired and don't have a subscription to Orca anymore but still have the surface model and, in storage, an old computer with Orca loaded.
It would take me more than a week to set up and I am not even certain that Orca will run. It is an expensive program protected by government regulations and I have not used it in years.
To repeat the calculations made 15 years ago, I would have to design model with all interior volumes and that would take another week. I always keep a copy of the hydrostatics at the DWL and you can have that as an Excel file but it will not help.

If you are still concerned, fill all unused volumes with 2 part foam. I don't think it is necessary and I don't like that it reduces access to some places but it may give you peace of mind.
Upright floatation is something to keep in mind. If all the extra buoyancy foam is in the bottom, a flooded boat will be unstable and flip over. That is why I mentioned foam sheets glued under the decks.
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fallguy1000
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Re: LB26

Post by fallguy1000 »

Sorry if my comments caused any trouble.

I am all about building the best boat! And the LB26 is a beautiful boat, why not make it best? Les has a lot of money in cores and epoxy now.

The Nanni diesel is 771#.

I would personally add 2# pour foam or xps foam at 4# to offset 500#. This is 60# per cubic foot of material, so 8 cuft is 480 pounds offset.

A single 2 gallon kit of pour foam would be my plan if this were my boat. I would probably fill the aft sole sections and aft sections of the sides, where possible to engine height to prevent a rollover if a water event. This would make a very, extremely safe boat. You do not need to use pour foam in all cases. If rectangular foam is desirable, just use extruded polystyrene 4#. This can be used, for example on the hullsides. It can be glued in with dow corning or a petro based foam i sulation in a can, then pour behind it. But xps cannot be laminated, so if laminating, use marine foam instead, etc.

But for a boat this small, it is not too difficult for the builder to square off sizes of panels and make good estimates and even check them against material usage.

Again, sorry if this causes any hard feelings; not the intent.
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jacquesmm
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Re: LB26

Post by jacquesmm »

One or two two gallon kits would provide more than enough extra volume. There is room in almost every compartment, you never use the full depth of the storage. A couple cm between stringers. some more along the chine and you will have a large safety margin.
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fallguy1000
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Re: LB26

Post by fallguy1000 »

I do apologize for being a bit late mentioning it. I saw the big inboard, then had some recall.
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rick berrey
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Re: LB26

Post by rick berrey »

Adding foam to the cabin top should be a given in all boats with a cabin , insulation and added flotation is a two fer .

fallguy1000
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Re: LB26

Post by fallguy1000 »

rick berrey wrote: Mon Sep 12, 2022 4:53 pm Adding foam to the cabin top should be a given in all boats with a cabin , insulation and added flotation is a two fer .
Yes.

My little cabin has a space of 1.5" and I will for sure be adding insulation between now and Texas summers.

Unfortunately, buoyancy foam calculations for the rooftop of the LB26 do not matter because Les would not want the boat to sink that far before holding..
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BarraMan
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Re: LB26

Post by BarraMan »

Most of my thoughts on the flotation issue that has emerged here have already been covered above, but its a topic that I think every builder needs to think about.

Here in Oz, there is no requirement for a boat 6M (20ft?) or bigger to have positive bouyancy - I assume something similar applies in the US as our standards are very similar.

My boat is 22' so its not a requirement. However, for the places I chose to fish, my boat is my 'life support system'. While I don't go far off-shore, lose your boat and you are in a world of hurt.

We had an incident here a few years ago where a new boat owner went out fishing on the Great Barrier Reef, got their anchor line fouled on the motor which caused the boat to get stern-on to the swell. It took a couple of waves over the stern and went straight to the bottom - leaving the owner and his fishing mates dog-paddling 40 miles from shore. Had another boat not been nearby, seen what happened and picked them up - they would have been lost.

I calculated what I thought my boat would weigh once completed (I was fairly close as it turned out!), ignored the inherent flotation of the wooden core, fuel tanks etc - and made sure that I incorporated sufficient closed-cell foam (Microlen) in the structure to 'float the boat'! To that I added 2-pack polyurethane pour foam to fill every available space under the sole. The end result is essentially a double hull below the waterline between the sole and the bottom of the boat. I also enclosed the sides where possible, particularly towards the stern, and filled them with foam to aid upright flotation.

I also have 4 x bilge pumps! 8O Two large capacity auto/manual electric pumps in the bilge, one smaller capacity manual electric pump at the very bottom of the bilge, and one large capacity manual pump that will pumps out the cockpit. I also carry a bucket! :lol: The cockpit drains into the bilge.

I am confident that if I hole the boat - it won't sink. If the worst happens :help: , I'll sit on the bottom of the upturned boat, fire the EPIRB, and wait patiently for the helicopter to come pick me up!

If I was going any distance offshore, I would carry a life raft - but probably overkill for where we currently fish.

PS: I think that Michael Glossie's recent adverture with holing Great Sandy on a reef and self recovery of the boat and crew illustrates how you have to be well prepared if you do what we choose to do. :D

rick berrey
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Re: LB26

Post by rick berrey »

Fallguy , you'll enjoy South Texas once you get there , just make sure you have made room for an ac .

fallguy1000
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Re: LB26

Post by fallguy1000 »

rick berrey wrote: Mon Sep 12, 2022 10:21 pm Fallguy , you'll enjoy South Texas once you get there , just make sure you have made room for an ac .
I do have a spot for it.
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les2021
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Re: LB26

Post by les2021 »

Evening All

Well where do I start....

Jacques I do not expect you to wade through old files, enjoy being retired. Live it and enjoy :D

To all those who have given input, thanks. No debate is a waste of time, all debate gives ideas and answers.

Regarding safety. Boring storey !!! when I was a teenager we were sailing back from France across the channel trying to beat an up and coming storm... we failed I spent the last 5-6 hours in a storm force 7-8 NOT A GREAT THING TO GO THROUGH I was aboard a Hurley 24 sailing boat !!!
I still thank the almighty for having a skipper who from the first minute took total control, safety first.

The first trip and all others aboard my boat will have the following, life jackets for all aboard, flairs, life raft and automatic distress device.

As I have mentioned before I have spent a reasonable time on the water BUT never built a boat. You have all come up with ideas which is helpful and greatly appreciated. What I would appreciate is sketches showing me exactly what is being proposed so I can plan plumbing and electric's.

When I had my construction company in the UK I relied on the structural engineer to provide all calc's with regard structure. In the UK structural engineers design a beam and then go 3x over the top, this is all to do with their indemnity insurance. I think what you are saying Jacques is that you have gone over the top with your calc's when designing LB26. I would still appreciate some sketches when you have time.

Cheers

Les

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