More on mast flotation

Moderator: GreenLake

More on mast flotation

Postby talbot » Sat Jun 18, 2016 1:24 am

Following recent discussion of mast flotation, I decided to insert a masthead pool noodle during a mid-season repair this week.

When I popped off the halyard sheaves, the absurdity of "waterproofing" mast rivets became apparent. At least on my Dwyer spar, the top of the mast is open to the air--or, if capsized, the water. The casting that contains the sheaves is not closed off from the mast extrusion.

Or it wasn't. I cut and shaped a thin layer of flat semi-rigid fibreglass board left over from another project and stuck it into the casting with silicone. Then I put new silicone into the rivet holes when I replaced the casting on top of the pool noodle. It occurred to me that if I had successfully sealed the spar, the noodle might be redundant extra weight at the top of the mast where I least want it. I guess I find out the next time the boat is on its side in the water.
talbot
 
Posts: 785
Joined: Mon Sep 03, 2007 3:37 pm
Location: Eugene, Oregon

Re: More on mast flotation

Postby GreenLake » Sat Jun 18, 2016 12:50 pm

From a safety point of view, a noodle beats a sealed mast (the former is not subject to as many possible points of failure).
~ green ~ lake ~ ~
GreenLake
 
Posts: 7136
Joined: Mon Jun 18, 2007 3:54 am

Re: More on mast flotation

Postby K.C. Walker » Sat Jun 18, 2016 3:27 pm

When I pulled the masthead from my old allspar mast it had the original plug in the top which was two thin aluminum plates with a closed cell foam gasket between them and a nut to tighten them together. The masthead itself has a rather large hole cast into it. It seems to me as if stopping the rush of in flowing water at the masthead would be a huge step in the right direction.

If sealed would a mast float? Something I've never tried…
KC Walker, DS 1 #7002
K.C. Walker
 
Posts: 1335
Joined: Sun Jul 06, 2008 10:50 pm
Location: North Stonington, Connecticut

Re: More on mast flotation

Postby talbot » Sat Jun 18, 2016 7:17 pm

Greenlake's probably right about foam being more secure than leaky rivets.

BTW -- anyone else have trouble getting the pool noodle into the spar? I was using the smaller of two sizes sold at our local Toys R Us, and I could only make it work by wrapping some vinyl tape around the noodle to compress it a bit. Even then, I could only get it in about 18" before it jammed. There was a question in a related discussion about how to keep the noodle from slipping down in the mast. Not a problem.
talbot
 
Posts: 785
Joined: Mon Sep 03, 2007 3:37 pm
Location: Eugene, Oregon

Re: More on mast flotation

Postby Alan » Sun Jun 19, 2016 12:03 am

Talbot,

My 1980 has square-section foam, looking to be factory original (in the bottom, anyway, because that's what I was able to look at when I replaced the hinge casting at the base of the mast that was involved in that unfortunate introduction to the powerline at Tahoe a couple of years ago). I'd say that at best it fills 3/4 of the mast.

Does the pool noodle have a hollow center? If so, would it make sense to split the noodle longitudinally, then split one of the split halves into two quarters, then slip one of the halves and one of the quarters into the mast? Just as a wild guess, you'd probably end up with a better foam-to-air ratio than I have.
Alan
 
Posts: 756
Joined: Wed Jun 17, 2009 4:39 pm

Re: More on mast flotation

Postby GreenLake » Sun Jun 19, 2016 7:28 am

It's not foam to air that matters most, but total buoyancy of the inserted foam. Someone with access to warm water might be able to test the required amount of flotation by capsizing the boat in shallow water and then resting the tip of the mast on various bits of foam to see how much is enough to prevent turtling. Doubling that would add some safety and also account for effects like the pool noodle not filing the mast fully or having its center of buoyancy somewhat below the mast tip.
~ green ~ lake ~ ~
GreenLake
 
Posts: 7136
Joined: Mon Jun 18, 2007 3:54 am

Re: More on mast flotation

Postby hsubman » Sun Jun 19, 2016 10:34 am

When I updated my standing rigging on my 83 DS II and drilled out the old rivets on the tangs on my original Dwyer mast, some foam dust fell out of the holes. It kind of ressembled spray insulating foam used around the home. Did O'day or Dwyer add mast floatation, or was this possibly done by a PO. Mine is a 3 owner boat. John
John
'83 DSII, 12279, MARY RUTH
hsubman
 
Posts: 30
Joined: Thu Aug 27, 2015 10:41 pm

Re: More on mast flotation

Postby K.C. Walker » Sun Jun 19, 2016 4:27 pm

Greenlake,

It seems to me, with the boat on its side and testing bits of foam under the mast tip, to see what it takes to keep the mast afloat, would be testing the amount of external flotation needed. :-) No amount of flotation added to the inside of the mast will make it more buoyant than a sealed mast. So, I think the question is, can you get enough flotation foam inside the mast to float a mast that is not sealed. And… I guess my next question would be if your mast is totally sealed is that enough flotation to keep the boat from going turtle?

This is got me thinking that I should seal my masthead, or at least check to see if it's sealed. It seems to me that if the masthead is sealed and the spreader rivets also, that water intrusion would be pretty unlikely, as long as the boat flotation keeps the lower part of the mast out of the water, as it does on my boat.
KC Walker, DS 1 #7002
K.C. Walker
 
Posts: 1335
Joined: Sun Jul 06, 2008 10:50 pm
Location: North Stonington, Connecticut

Re: More on mast flotation

Postby GreenLake » Sun Jun 19, 2016 10:01 pm

K.C. totally correct. What I was doing was a bit of "worst case" analysis. Adding foam to a perfectly sealed mast only does nothing other than reducing buoyancy a little. But my assumption was that the mast is flooded whether because it's not sealed or the seal failed. Testing (with the entire mast just barely out of the water) should yield a value for minimum buoyancy. If that value can be achieved with a reasonable amount of foam fitting somewhere in the top 3-4' of the mast, then external flotation would not be necessary and the foam would protect in case of mast-seal failure.

Now, I'm not sure we have a solid value for minimum mast-tip flotation needed to prevent turtling.
~ green ~ lake ~ ~
GreenLake
 
Posts: 7136
Joined: Mon Jun 18, 2007 3:54 am

Re: More on mast flotation

Postby K.C. Walker » Mon Jun 20, 2016 2:57 pm

Okay, I follow your thought train. So, would the experiment need to be with a mast full of water that is now sealed… Or submerge the mast and then put foam bits under? I have not done any of these experiments. It seems to me it would also matter where the flotation in the boat is. If the boat is on its side and floats above the midline it's going to put more downward pressure on the mast. Though, I don't know how much above midline it would take to make a significant difference.

The last time I swamped my boat it went right down to the midline before we righted it. But, that was with three of us on the upper rail, probably a total of 425 pounds. That was not really an experiment in mast flotation. Though, it was my older sealed mast and I don't think it took on any water, even the sails did not submerge as we got it up right away.
KC Walker, DS 1 #7002
K.C. Walker
 
Posts: 1335
Joined: Sun Jul 06, 2008 10:50 pm
Location: North Stonington, Connecticut

Re: More on mast flotation

Postby GreenLake » Tue Jun 21, 2016 2:58 am

Would be good to know what's needed to keep the mast tip from going under. Initially the mast would not be wet, because I assume when "level" the mast step on deck is a bit above the water, so it's actually pointing "down". In that position, initially, it would not be fully flooded, although eventually it would fill to the depth it's submerged (unless filled with noodles or perfectly sealed). If the DS sinks to the midline when capsized (CB flat on the water) that would be a different story.

Initial experiment is just to get an idea how much difference, say, a single pool noodle makes, given the lever arm of > 20'.

Refinement. If the noodle keeps the mast from dipping, try pulling the boat down from the gunwale, to see how sensitive this is to crew clinging to the boat...
~ green ~ lake ~ ~
GreenLake
 
Posts: 7136
Joined: Mon Jun 18, 2007 3:54 am

Re: More on mast flotation

Postby jeadstx » Wed Jun 22, 2016 1:12 pm

In my 2012 capsize the boat did sink to the point where the CB was level with the water, the mast head stayed on the surface with it's 2 feet of foam. The boat stopped settling when the CB was level with the water, despite the heavy cargo load.

John
1976 Day Sailer II, #8075 - Completed the 2011, 2012, and 2013 Texas 200
1952 Beetle Boat Swan Catboat
Early Rhodes 19
1973 Mariner 2+2, #2607 - Completed 2014, 2015 and 2016 Texas 200
1969 Day Sailer I, #3229
Fleet 135; Canyon Lake, Texas
jeadstx
 
Posts: 1216
Joined: Tue Jul 08, 2008 11:10 am
Location: Dripping Springs, Tx

Re: More on mast flotation

Postby K.C. Walker » Wed Jun 22, 2016 9:07 pm

Good info John, thanks. I do think that when the boat is settled down to the midline that there is less pressure on the mast tip.
KC Walker, DS 1 #7002
K.C. Walker
 
Posts: 1335
Joined: Sun Jul 06, 2008 10:50 pm
Location: North Stonington, Connecticut

Re: More on mast flotation

Postby talbot » Wed Jun 22, 2016 11:55 pm

Note that jeadstx is the Pool Noodle king. According to previous posts, his DS II is essentially a large pool toy with an accessory mast and sail. Do not expect the same results if your hull still depends on waterlogged 1970's era factory foam under the seats. I just installed additional pool noodles in my hull. Noodle envy.
talbot
 
Posts: 785
Joined: Mon Sep 03, 2007 3:37 pm
Location: Eugene, Oregon


Return to Rigging

Who is online

Users browsing this forum: No registered users and 20 guests