LB26

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fallguy1000
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Re: LB26

Post by fallguy1000 »

Take a picture from the cuddy entry looking aft.

Here is a general idea of the places to foam. Hard to do because the picture not ideal. A fancier sketch is lots of work for me and been tired all day for some damn reason.

You want say 8 cuft of foam. A 2 gallon kit or a 2 and a 1 would be my plan. Up the sidewalls can be done on the back section somewhere. A 2 gallon pour kit of 2# or 8-10cuft of pink or blue extruded foam wpuld work. The extruded foam 2" thick is 5.3 cuft per board. Two of those boards is 10.6 cuft, offsets 600#.
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BarraMan
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Re: LB26

Post by BarraMan »

Why would you not put foam in similar positions in the more forward part of the cockpit. :doh:
Can you have too much foam? :doh:

les2021
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Re: LB26

Post by les2021 »

Afternoon guys

Cheers for the continued input.

Just a thought ( which is dangerous ) Can I use builders expanding foam or does that not have the same buoyancy values ?

Done a bit more work on the cabin top, just need to fill the overlaps and the corners and do some fillets and then I can tape.

Cheers

Les
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fallguy1000
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Re: LB26

Post by fallguy1000 »

BarraMan wrote: Tue Sep 13, 2022 11:29 pm Why would you not put foam in similar positions in the more forward part of the cockpit. :doh:
Can you have too much foam? :doh:
Yes, you can have too much foam. Too much foam in the bottom of the boat would cause it to flip in a water event. So sides and up the sides only. I do not profess more than a rudimentary understanding. To simplify the concept, in a water event, you want the tub to remain upright so as not to spill the people inside. Making the sides more buoyant and evenly buoyant is the general means.

Consider the engine as the offseting weight. Since the boat is already pos buoyant, but we do not know how much she is pos buoyant aft and the engine is aft, the valid concern is what would water do to the boat aft.

And, would the placement of foam in a water event result in a listing boat rolling over. Since boat weights are uncertain athwart and impossible to balance; the way to prevent a rollover is for even buoyancy foam and up the sides a bit.

Les-to your question, yes and no. Do not use latex foam. It will break down on you. Only use the horrible stuff that is petroleum based. I do not know the density of it. If you combine it with 2" extruded polystyrene, you can effectively glue the foam up on the sidewalls. If you do this on the aft hullsides; it would really make the boat much, much safer. It is already safe, but the concern that the engine would take you down to the cuddy is real and this would mean the boat could flip over or unknowns would occur. If the boat flipped; you'd be clinging to gear or skeg in unknown seastate versus staying in the cockpit with water sloshing to your feet or knees.

Get me a photo of the boat floor open looking toward the stern from the cuddy.

You can or I can also post it on boatdesign.net for advice there if you like.

Many of the naval architects there have passed examinations for vessels that must not flip. I have not.
Last edited by fallguy1000 on Wed Sep 14, 2022 8:07 am, edited 1 time in total.
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fallguy1000
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Re: LB26

Post by fallguy1000 »

I should mention, the boat already has a big ballast in the center; there is little reason to mess with foam in the middle of the boat where engine and gearing are. The foam effort is relatively simple work.

When you consider the ways a boat can take on water; this is why you may foam a foam boat more. The gearing or exhaust systems can leak. I do know Les gearing could someday leak. I do not know if the exhaust could. He has stated he will be in a slip or mooring ball, so foam also ensures the boat could take on a lot of even rain water and remain upright versus held up by the cuddy cabin...see?
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TomW1
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Re: LB26

Post by TomW1 »

Following up on what fallguy has said for foam above the deck place some under the side decks from stem to stern and this will keep the boat upright at level flotation. As long as you have your other foam properly distributed. Tom
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OrangeQuest
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Re: LB26

Post by OrangeQuest »

Any flotation above the water line only works when it is no longer above the water line. Flotation below the water line is there to keep the flotation above the water line, above it.
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fallguy1000
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Re: LB26

Post by fallguy1000 »

OrangeQuest wrote: Wed Sep 14, 2022 3:38 pm Any flotation above the water line only works when it is no longer above the water line. Flotation below the water line is there to keep the flotation above the water line, above it.
Yes. But important to remember, a boat that lists 5 degrees to starboard is then below her lines. Preventing it from listing further occurs when positive buoyancy is met. So only filling to dwl is not ideal, but foaming under the gunwhale is also not going to contribute. This is why I offered to take a picture to boatdesign; to get the best, most experienced advice.

So, in general, partway up the hullsides above dwl is still good.
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Re: LB26

Post by jacquesmm »

Foam does not affect stability unless the hull is flooded.
Stability becomes a problem with a flooded hull if it has all the foam low and a heavy superstructure. In that case, the hull will flip but float if enough foam.
A case can be made for having lots of foam just under the deck , the goal being to keep the boat afloat with just the deck awash. That is what we do for small boats that must have upright flotation but it is very difficult to plan for that on a bigger boat.

As always, safety is easier to attain by being proactive and not getting in to those catastrophic situations.
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BarraMan
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Re: LB26

Post by BarraMan »

I think the biggest danger to my boat is hitting something and putting a hole in the hull. Hence the reason I think it pays to put foam below the sole wherever possible as you can never be sure that in laying down the sole that you have created water tight compartments.

While I have great confidence in the strength of the hull, as Glossieblack recently illustrated its relatively to put a hole in a wooden/composite boat and have significant water ingress.
I have hit a pinnacle just under the surface with my boat. Travelling along nicely at 25 kts in 20' of water when "bang", 0' on the sounder then back to 20' by the time the boat stopped. In that case the prop wore the brunt of the collision but it could easily have been the hull.

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