Foam in mast

[zeehag]

Originally Posted by anjou

Fit an airbag system from a scrap yard car, triggered by a water soluble switch

now THAT is a good idea....but water soluble-- would dissolve in water-----mebbe water activated?????

[capngeo]

Not to mention automotive airbags are designed to DEFLATE almost as fast as they inflate!

[Cormorant]

Just thinking out loud here for a flotation solution that won't add much weight, or gain weight over time -- can you fit plastic soda bottles in there? Or maybe the air-filled bags used for packaging (not bubble wrap, but the bigger things that seem impossible to pop without a knife).

[Abaco]

If you are in serious storm conditions which cause you to lose the rig, wouldn't you want to be able to cut it away and have it sink? I can imagine a scenario where you cut away a floating rig that would then pound into your hull potentially sinking your boat.

[MaggieJ]

Ted Brewer told me that in event of a knowckdown, a mast full of water vs a mast full of air may be the difference between coming back up and sinking.

Accordingly, I sealed the mast with a couple feet of expanding foam. Don't ever expect to test this, but it seemed like a good idea

[Talbot]

Originally Posted by Mark Johnson

On mine, I put in 4' of crumpled up aluminum foil, about 3/4 of the way up, for additional RADAR reflection.
Mark

ROFLMAO

you really need to learn a bit more about your subject before pontificating about things. This would have had zero effect on your radar reflection.

the best return is caused by 90 degree reflectors or a focussed luneberg lens. The number and size of these controls the size of the return.

The alternative is an electronic system that transmits a return pulse mimicing the radar return.

IMHO using the foam to provide quiet does have some merit. Although you will get more quiet by hiding your halyards inside the mast and then making sure that they are secured. Using foam to make the mast buoyant works for a dinghy or small racing cat that might fall over. On a large boat, if the mast falls over the side, you are more worried about it pounding a hole in the side of the boat, than in the recovery. Therefore a mast that sinks at that moment is a distinct advantage.

[FloridaWriter]

Originally Posted by smurphny

Was thinking about foaming at least some sections of my mast to make it float if it should ever go over the side. Has anyone had experience doing this? Best kind of foam? Negatives. I have no internal halyards so it would be straight forward other than putting in a couple of conduits for wiring.

I'm assuming you have external halyards. If you don't have an open sheave box then you would be better off sealing any openings in the mast. That will let it float without adding weight aloft. You can plug the butt of the mast with a Styrofoam plug and epoxy it in place.

Good luck

[smurphny]

The mast has a center sheave, open below and yes, I moved the shrouds outboard last year. The best idea I've heard so far is to insert some air filled packaging/bottles of some sort- light, no absorbtion, easily replaced, 0 cost and as far as I can see, completely effective to keep a mast afloat long enough to get it back on the boat. From what I've been able to find, knockdowns that cause a complete roll usually result in the mast being broken when a swage/swageless gives from the extreme forces generated by the weight of the hull opposed to the drag of mast through the water. In an old full keel boat like mine with a safe capsize ratio, the likelihood of demasting in a roll is almost 100% because of the leverage produced by 6000# of lead coming up and going back down quickly. Whether it would be less dangerous floating or hanging down on the remaining wire is a good question but having something to jury rig is certainly a plus. I'd rather have the option to sail back from such an episode than flick the switch of the EPIRB.

[SkiprJohn]

Remember that if you seal the mast and it sweats or ever does get a little seawater in it for some reason it has no way of escaping. Moisture from seawater combined with aluminum means corrosion.

Putting plugs or styrofoam or anything against the aluminum just traps moisture where it can corrode.

kind regards,

[Jim Cate]

Before getting too tied up in that project you might do a bit of arithmetic. Measure your mast cross sectional area, multiply by length to get total volume, assume zero water intrusion and calculate total buoyancy.

Then calculate the total weight that you will be hoping to float. Besides the weight of the spar, don't forget the boom, standing rigging, sails that might well be hoisted/furled, running rigging, winches, blocks... all the stuff that will be there in the water along with that aluminium extrusion. In most cases I expect that it will still sink like a stone, even with no water in the mast.

When we were dismasted (1996, western Tasman sea) we got rid of the wreckage ASAP as it was grinding away at the topsides. In the extant conditions there was no hope of Ann and I recovering anything (dark as the inside of a cow, seas still breaking although diminishing in size, us fatigued from 4 days of storm force winds and a knockdown, etc), but it still hurt to cut the final bit of main sheet and see it snake over the side. Other pundits, from their perch on the bar stool, have derided us for giving it up too easily. I know that in a similar position today I'd do the same thing.

We were only about 75 miles offshore at the time, and I was confident that we could motor in. Had we been mid-ocean the idea of leaving the mess on a long tether after cutting it away (thus MAYBE being able to salvage stuff later for a jury rig) might have merit. I hope to never have to make that decision again, but I doubt strongly if having a sealed mast would have changed anything.

Incidentally, we were "self insured" so there was a strong financial stimulus to save as much as possible. Didn't slow us down in getting rid of the battering ram!

Cheers,

[four winds]

Originally Posted by Talbot

ROFLMAO

you really need to learn a bit more about your subject before pontificating about things. This would have had zero effect on your radar reflection.

the best return is caused by 90 degree reflectors or a focussed luneberg lens. The number and size of these controls the size of the return.

The alternative is an electronic system that transmits a return pulse mimicing the radar return.

IMHO using the foam to provide quiet does have some merit. Although you will get more quiet by hiding your halyards inside the mast and then making sure that they are secured. Using foam to make the mast buoyant works for a dinghy or small racing cat that might fall over. On a large boat, if the mast falls over the side, you are more worried about it pounding a hole in the side of the boat, than in the recovery. Therefore a mast that sinks at that moment is a distinct advantage.

Talbot, you might consider reading a bit about Electronic Countermeasures. In particular the physical characteristics of chaff. The earliest versions were shredded foil hand tossed out the window of aircraft.

Chaff (countermeasure) - Wikipedia, the free encyclopedia

Back when cars actually had hubcaps, a crumpled up piece of foil behind them worked quite well in confusing radar guns of the day. The velocity of the spinning foil would give speed readings off the scale. It didn't take long for law enforcement to catch on though.

Of course it's true a right angle reflector is a much better radar image than a fiberglass boat.

A crumpled piece of foil would have hundreds of right angles in all directions.

[Jim Cate]

Originally Posted by four winds

Talbot, you might consider reading a bit about Electronic Countermeasures. In particular the physical characteristics of chaff. The earliest versions were shredded foil hand tossed out the window of aircraft.

Did you ever see the ECM guys toss their chaff out enclosed in an aluminium mast?

Talbot is correct.

Cheers,

[Cormorant]

They say you need at least a few full radar wavelengths in length per side of a corner cube retroreflector to get a good reflection. With S-band at 10 cm wavelength and X-band at 3.2 cm, you would need a cubic corner at least 20-40 cm per side. In theory.

But we do hear anecdotal evidence of things like crumpled tin foil giving an improved radar return, or even DOT or SOLAS retroreflective tape. Which makes me wonder if in cases like that there is some sort of aggregate reflection going on -- the sum of all the facets facing a particular direction adding up to one face of the cube, etc. Doesn't really seem like a strong possibility, but I've often wondered about those anecdotal bits of evidence. . . .

[smurphny]

Originally Posted by Jim Cate

Before getting too tied up in that project you might do a bit of arithmetic. Measure your mast cross sectional area, multiply by length to get total volume, assume zero water intrusion and calculate total buoyancy.

Then calculate the total weight that you will be hoping to float. Besides the weight of the spar, don't forget the boom, standing rigging, sails that might well be hoisted/furled, running rigging, winches, blocks... all the stuff that will be there in the water along with that aluminium extrusion. In most cases I expect that it will still sink like a stone, even with no water in the mast.

When we were dismasted (1996, western Tasman sea) we got rid of the wreckage ASAP as it was grinding away at the topsides. In the extant conditions there was no hope of Ann and I recovering anything (dark as the inside of a cow, seas still breaking although diminishing in size, us fatigued from 4 days of storm force winds and a knockdown, etc), but it still hurt to cut the final bit of main sheet and see it snake over the side. Other pundits, from their perch on the bar stool, have derided us for giving it up too easily. I know that in a similar position today I'd do the same thing.

We were only about 75 miles offshore at the time, and I was confident that we could motor in. Had we been mid-ocean the idea of leaving the mess on a long tether after cutting it away (thus MAYBE being able to salvage stuff later for a jury rig) might have merit. I hope to never have to make that decision again, but I doubt strongly if having a sealed mast would have changed anything.

Incidentally, we were "self insured" so there was a strong financial stimulus to save as much as possible. Didn't slow us down in getting rid of the battering ram!

Cheers,

Wow. Thanks for sharing that harrowing story Jim Cate. It surely depends on the particular situation. Only so much can be predicted. Sounds like you made the only logical decision.

Last year, as mentioned above, I made a whisker pole from 2 1/2 x 1/4" wall aluminum, welded up some pretty heavy spring-loaded ends-certainly heavier than a store-bought pole. I stuffed it with closed cell polyisocyanurate insulation foam and figured it would probably sink. To my surprise, it floats incredibly high. If I had a scale, it would be interesting to know the exact weight of the mast and all the attached rigging. Could be done when raising or lowering the mast. Boning up on the "flute music" to accurately calculate the cross section of the mast is another matter. Where's that slide rule?

[four winds]

Originally Posted by Jim Cate

Did you ever see the ECM guys toss their chaff out enclosed in an aluminium mast?

Talbot is correct.

Cheers,

Well, no, actually I haven't. And I did wonder what effect being shrouded in a curved aluminum housing would have in terms of shielding the foil inside. My training in the Air Force didn't address that scenario.

I merely was attempting to point out that crumpled foil makes a fine radar reflection under some circumstances. But admittedly I'm unsure of the efficacy in this installation. I'm not as sure as you, however, that it would have "no effect" on the radar signature.

I have seen a fumble fingered F4 pilot unload all his flares and chaff over a runway on approach once. Burned some nice holes in the tarmac for the battle damage guys to practice there craft on.

Part of my job was keeping the chaff and flare dispensers working. It was the most outdated ECM hardware I worked on. The Wild Weasels were much more fun to work on.